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Seasonal occurrence of larval fishes in the nearshore Southern California Bight off San Onofre, California
Estuarine,
Coastal
and Shelf
Science ( 1987) 25,9 l-l 09
Seasonal Occurrence of Larval Nearshore Southern California San Onofre, California
H. J. Walker
Jr,’ William
Watson
Marine Ecological Consultants of Southern Suite 110, Encinitas, CA 92024, U.S.A. Received
18 September
Keywords: upwelling;
1985
fish larvae; California
and in revisedform
seasonal;
Fishes in the Bight off
and Arthur
Chlifornia,
1 OJuly
temperature;
M. Barnett
531 Encinitas
Boulevard,
1986
spawning;
zoogeography;
Larval fishes were sampled from the nearshore region of the Southern California Bight off San Onofre for 29 months and analyzed with a Curtis-Bray Cluster Analysis to determine temporal assemblages and species associations. Two major assemblages of larvae were found: members of the winter-spring (DecemberMay) assemblage were most abundant from January to May; members of the summer-fall (June-November) assemblage were most abundant from July to September. The winter-spring assemblage was composed primarily of Engraulis mordax, Genyonemus lineatus, Sebastes spp. and Paralichthys californicus; some abundant taxa in the summer-fall assemblage were Seriphus politus, Paralabrax spp., and Hypsoblennius spp., although E. mordax again predominated. Demersal spawners tended to have spawning seasons of longer duration than pelagic spawners; winter-spring spawners generally had longer spawning seasons than summer-fall spawners. We suggest that temperature is an important determinant in the seasonal pattern of larval fish occurrence. The annual ocean temperature cycle near San Onofre was a good indicator of the seasonal occurrence of fish larvae in this area. Larvae found in the cooler months were generally offspring of adults whose northern ranges extend to Canada. Warm-water larvae were offspring of adults whose northern ranges extend to Point Conception or northern California. Introduction This paper describes the seasonal abundance patterns of nearshore (within 7 km of shore) larval fishes off San Onofre, California (Figure l), and the relationship of those patterns to water temperature, adult zoogeography and coastal upwelling. This study, based on 29
months of sampling of the entire water column, is one of the first long-term, intensive studies of coastal ichthyoplankton made in the Southern California Bight. Previous larval fish studies in California waters have been predominantly in the oceanic realm (> 200 m depths) e.g. Ahlstrom, 1959, 1965; Loeb et al., 1983) or in bays and estuaries (e.g. Eldridge & Bryan, 1972; Leithiser, 1981). Most studies of coastal “Present address: Marine Vertebrates Collection, Scripps Institution of Oceanography, University
of California,
San Diego
AOOB, La Jolla, CA 92093,
U.S.A.
91 0272-7714/87/010091+
19 $03.00/O
0 1987 Academic
Press Inc. (London)
Limited
92
H. J. Walker Jr
et al.
San Onofre Nuclear Generating Station
E Cu
I&
D
37 ‘m-------,, 55 imp-
E 74 lm
\ 117”33’
20”
I
L
t
San Onofre
7
0
33’22’
30”
\
I km Pacific
Ocean
1 Figure
1. Map
of the study
area showing
its position
in the Southern
California
Bight.
ichthyoplankton have either concentrated on a few species (e.g. Brewer & Smith, 1982), on spatial patterns (e.g. Barnett et al., 1984), or have sampled too infrequently or over too short a time span to define seasonal patterns (e.g. Brewer et al., 1981; Gruber et al., 1982). Icanberry et al. (1978) sampled monthly for more than a year, but did not sample the entire water column. Thus, a gap exists in the knowledge of the ecology of the ichthyoplankton in California coastal waters; namely, the seasonal assemblages of larval fishes have not been well defined or documented. The primary purpose of this paper is to identify the seasonal assemblages of larval fishes which occur in the nearshore Southern California Bight. Materials
and methods
Sampling The study was conducted off San Onofre, California, located in the Southern California Bight about half way between Los Angeles and San Diego (Figure 1). The coastline is fairly uniform, with a regularly sloping shelf ending about 7 km from shore at a depth of 70 m. The Gulf of Catalina, a broad area characterized by depths of 1 km, lies beyond the shelf.
Seasonality ofnearshore larvalfish
93
All sampling was done along an offshore transect located approximately 1 km south of San Onofre Nuclear Generating Station (SONGS) (Figure 1). The 500-MW unit operating at that time was shown to have only localized effects which did not influence our results (Marine Review Committee, 1979). Because this was a multipurpose study, the spatial scale of sampling was finer than necessary, and the temporal scale of sampling deviated somewhat from the scalesthat would be required for a seasonalstudy alone. Field procedures and their rationale (for sampling gear, depth strata, offshore sampling blocks and sampling frequency) are described in detail by Barnett et al. (1984). A stratified random-sampling design (Snedecor & Cochran, 1967) was used wherein the neustonic, mid-water and epibenthic layers of the water column were sampledat a randomly chosen isobath in each of five blocks defined by depth contours: (A) 6-9 m; (B) 9-12 m; (C) 12-22 m; (D) 22-45 m; and (E) 45-75 m. Three different types of gear, all equipped with 0.333 mm mesh Nitex nets, were required to sample the three strata in shallow water adequately: a Brown Manta net, 88 cm wide x 16 cm deep, for the neuston (Brown & Cheng, 1981); a Brown-McGowan opening-closing Bongo net, 71 cm diameter, for midwater; and an Auriga net (Marine Biological Consultants, Inc., 947 Newhall Street, Costa Mesa, CA 92627, U.S.A.), 2 m wide x 0.5 m high for the epibenthic stratum. On five occasionswhen a vesselcapable of handling the Auriga was not available, a smaller epibenthic sled (mouth 1 m wide x O-3m high) was used to sample the epibenthos (Clutter, 1977). Two-tailed Mann-Whitney U-tests of comparative samplesshowed no differences (p>O.lO) in catch per unit area (number per 100 m’) between the two epibenthic samplers. In order to assessrelative catch efficiencies, additional comparative tows were made between an Auriga (modified to samplethe midwater) and a bongo, and between a bongo fitted with wheels (to sample the epibenthos) and an Auriga. In midwater, Wilcoxon’s signed-ranks tests showed no difference @> 0.05) between the samplersin catch per unit area, while in the epibenthic stratum the Auriga caught more (p < 0.05) of most taxa per unit area. The Manta was not compared with the other samplers. However, because neither the bongo nor the Auriga is appropriate for sampling the neuston when towed in a conventional manner (i.e., astern) it was felt that this specialized sampler was required. All samples were taken at night, parallel to shore. Each sampler was fitted with a flowmeter and towed at ca. 1 m s-l for a fixed time in order to filter a target volume of 400 m3. This volume was determined, during a preliminary investigation, to be the optimal sample size’ for the study area (Barnett et al., 1984). Samples were preserved in the field in IO”,, Formalin-seawater, The transect was sampled monthly in January and February 1978, fortnightly from March through August 1978, monthly through September 1979, and then weekly from March through October, 1980. Each sampling episode in 1978 and 1979 consisted of sampling all blocks on 1-3 successivenights; each episode in 1980 consisted of a single night. The 29-month study thus comprised 86 sampling dates. “Although an argument could be made for sampling the water column with equal intensity per unit depth rather than sampling an equivalent volume from each stratum, the latter approach was both adequate and logistically preferable because equalintensity sampling would require that offshore midwater samples be extremely large (or that neustonic and epibenthic samples be extremely small). Alternatively, an argument based on the scale of patchiness could be made for using tow length (400m) rather than volume (400 m’) as the sampling unit. Most of our tows were at least 400 m long.
94
H. J. Walker Jr et al.
Temperature data were obtained from continuous monitors and other recorders positioned between the 12- and 15-m isobaths. These measurements were not taken during the ichthyoplankton sampling, but were part of other studies conducted at the samelocation (Barnett & Jahn, 1987; Barnett et al., 1980, Southern California Edison Company, 1979, 1980, 1981). Additional temperature data was obtained from Scripps Institution of Oceanography, La Jolla, California (60 km south-east of San Onofre). Surface temperature was measured daily at the end of Scripps pier, located at the 6-m isobath. Laboratory
procedures
Ichthyoplankton samples were cleaned of debris and most were subsampled with a Folsum plankton splitter prior to being sorted for fish larvae. The subsamplesize, which averaged one-fourth of the original and was rarely less than one-eighth (range l/32-1), was set to include at least 100 non-engraulid larvae. Sampleswere sorted under 6-10 x magnification and checked by a second sorter to ensure that at least900,, of the larvae were removed. Larval fish were identified to the lowest taxonomic level possible. Analytical
techniques
A cluster analysis was used to determine taxon associations (defined here as species groups) and temporal assemblages(defined here asmonth groups). A large number of rare taxa were found in the study which carried little classification information (Boesch, 1977) but which could maskmuch of the information available from the more frequently occurring species.To ensurethat this did not happen, two criteria were applied before accepting a speciesfor analysis: (1) a taxon had to be among the top 25 in abundance on at least one survey of the 86 taken; and (2) a taxon had to occur in at least six of the 29 months. These criteria reduced the number of available taxa from approximately 140 to 63. However, these 63 taxa cornprized about 969; of the total larval abundance; unidentified yolk sacand unidentifiable damaged specimenscomprised 3?,, of the total. As the principal aim of the study was to identify seasonalassemblagesof fish larvae, the analysis was based on monthly mean abundances of larvae in the entire cross-shelf transect. Specifically, for a given taxon a one-dimensional abundance wascalculated based on the estimated number of larvae, Dijr, in each of fifteen (3 depth strata x 5 cross-shelf blocks), 100-m wide (alongshore dimension) strata on each sampling date:
where i indicates depth (1 = neuston, 2 = midwater, 3 = epibenthos); j indicates cross-shelf block (1 = block A, . . . 5 = block E); r is the replicate number (r = I, 2, . . . R); Aij, is the number of individuals at depth i, in block j, of replicate r; rij, is the vertical thickness (m) of depth i, block j, replicate r; Vij, is the volume (m3) sampled from depth i, block j, replicate r; and Lj is the cross-shelf length of block j. The Dij, were summed over the 15 strata to give a transect total for each sampling date: D, =
;
;
I=1
1=1
Dij,
and the D, within each month were averaged to give a monthly mean:
Seasonality of nearshote larvalfish
95
Variances were calculated from the transect totals: s = E @-@Z/(&l) Both normal (months classified by the species’abundancesoccurring within them) and inverse (speciesclassified by their monthly abundances) classifications were performed. The monthly mean transect abundances were square-root transformed. Following the recommendation of Smith (1976), the transformed abundances for each species were standardized by division with that species’mean transformed abundance before performing the normal classification, whilst for the inverse classification the transformed abundances were standardized by dividing the maximum transformed abundance for each speciesbefore clustering. The species’mean standardization tends to give more weight in the calculation of the distance matrix to taxa with more leptokurtic abundance distributions; thus temporally wide-spread taxa do not dominate the classification ofmonths. On the other hand, the speciesmaximum standardization tends to give equal weights to all taxa and to prevent the overinfluence of abundant speciesin the speciesanalysis (Smith, 1976). The sorting strategy was an agglomerative hierarchical technique with flexible sorting of Bray-Curtis distance index values using a cluster intensity coefficient cc> set at - 0.25. Using p= - 0.25 with flexible sorting produces distinct groups and is considered conventional (Boesch, 1977). The level of resemblancedeemed sufficient to identify a group was set subjectively and differed for the speciesand temporal classifications. A certain degree of subjectivity is inherent in the interpretation of numerical classifications and, ashasbeen pointed out by Boesch (1977), use of a fixed stopping rule is inappropriate when flexible sorting with negative b is used. Results Fish larvae
Approximately 140 types (sensuRichardson & Pearcy, 1977) of larval fishesrepresenting 43 families were collected during this study. Northern anchovy (Engraulis mordax) and the sciaenids (Genyonemus lineatus and Seriphus politus) ranked first, second and third in abundance.’ The following were amongst the 10 most abundant taxa: Sebastes spp., Paralabrax spp., Paralichthys californicus, Hypsoblennius spp., Citharichthys spp., Stenobrachius leucopsarus, and Atherinidae. Two principal month groups (I, II), separated by a distance of greater than 1.1, were identified from the temporal dendrogram; each was further split into subgroups (I,.?, II l _3) separated by distances of greater than 0.5 (Figure 2). The principal separation clearly divided the year into winter-spring (December-May) and summer-fall (JuneNovember) groups. Within each of these, the subgroups formed cohesive units on a calendar basis. Months in groups Ii and I, fit ‘ winter-early spring ’ and ‘ spring ’ designations, respectively, whilst months in groups II, _ 3 consistently fit the terms ‘ early summer ‘, ‘ fall ‘, and ‘ late summer-early fall ‘, respectively. Two major groups of taxa (A, B) were separatedin the speciesdendrogram at adistance of greater than 2.3. A distinct, homogeneoussubgroup (B,) wasthen split from the remainder ‘The rankings pertain only to the years 1978 and 1979 because a large portion of the winter was not sampled in 1980. Data, in the form of a table of monthly mean abundance with two standard deviations for each species, are available upon request from the authors.
96
H. J. WulkerJr
I12 LIL--3
093
et al.
075
DISTANCE 0 56
0 37
019
0
--
-~ ----~
Figure 2. Temporal Onofre, California. within them.
JAN 70 FE9 78 MAR 78 JAN 79 FEE79 MAR 79 DEC 78 APR 78 MAY 78 MAY 80 APR 79 APRBO MAR80 JUN 78 JUN 79
~
t _
or ‘ normal ’ dendogram based on larval fish abundance off San Months are classified by the abundances of the species occurring
of B (distance > 1.5). Group A and the remainder of B were further partitioned into relatively homogeneous subgroups (A,.,, B, _ 4) separated by distances greater than I.1 (Figure 3). Species in subgroups A, (dominated by Chromispunctipinnis) and A, (dominated by Paralabrax spp.) generally were most abundant in summer (July-September), with subgroup A, speciesoccurring more frequently in early summer (seeFigure 4 and Table 1). Group B, species (dominated by Seriphus politus) were also abundant from JulySeptember, but with highest abundances occurring in early summer and a tendency to occur in spring and winter as well (Figure 4). All three groups were rare or absent in October and November. Species in group B, (dominant taxon Genyonemus lineatus) were most abundant in winter and spring (seeFigure 5 and Table 1). Likewise, group B, taxa (dominant taxon Engraulis mordax) also were most abundant in winter and spring but also appeared in the remainder of the year at least in moderate abundance (see Figure 5), except for a small group of three taxa (containing two cottids and Girella nigricans) which apparently should have been classified with the summer-fall groups. Group B, speciesalso tended to be moderately abundant in summer, but with lower abundance from July-October (month groups II, and II,). Temperature
The temperatures and seasonaltemperature changesrecorded off San Onofre in 1978-80 were characteristic of recent decadesin the Southern California Bight (Radovich, 1961;
27
24
Seasonality
of nearshore
2.1
9’5STANfiE 09 06
18
larvalfish
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Semtcossypbus p&her Oxyphs cal~forn~co Chromis punchpmnis Hokhoeres semwnctus Symphurus otrlcoudo Sphyroeno orgenteo Amsotremus dovfdsom ttermosftto azure0 Xenistius cotiformensls Poro/obrox spp Menhcirrhus undulotus Ophtdlon scrlppsoe Chettotremo soturnum tfippoglossmo stomoto Lythrypnus dolh Atroctoscion nob//is
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Siomber jopomcus Sertphus pohtus Hypsypops rubicund0 Girelfo mgr,cons Artedtus creaser1 Cotttdae type 9 Pleuromchthys rttteri Porohchthys coftfornicus tfypsopsetto guttutoto Cithorichthys spp. Ilypnus gIlbert/ Sebostes spp Gobtesox rhessodon Gtbbons/o sp A Clevetondfo ios Ilypnus/Clevetondlo Pteuromchthys verhcohs Leptdogobtus lepldus Quletulo y-couda Engrouhs mordox Heteroshchus rostrotus Sordmops sogox Goblesacldae type A Lomponyctus spp. Zontolepfs spp
,’
Zcehnus quad /Chltonotus ;ryphtogobtus coftformensls Porophrys vet&s Dtophus theta Peprilus sim/fhmus Argentmo slobs -~ -- Protomyciophum crockerl Bothylogus ochotensis
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Stenobrochfus leucopsorus Genyonemus hneotus Neochnus sp A Lz Cotttdoe type 14 Agontdae Leurogtossus st//bws - Merluccws productus ------ Scorpoemchthys mormorotus-
Figure 3. Species or ‘ inverse ’ dendogram California. Species are classified by their
of 63 larval fish taxa occurring monthly abundances.
I I_ 83
off San Onofre,
iAN
I;E!
JUL’B
“UL79
JAN80
UNDULATUS
ARGENTEA
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JAN80
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JAN81
A,, A2 and B, the 6- and 75-m
J”LB0
SPP.
MEXICANUS
JAN80
POLITUS
Figure 4. One-dimensional monthly mean abundances of selected fish larvae belonging to summer subgroups Abundances represent numbers (in millions) in a 100-m wide (longshore direction) segment of ocean between isobarhs.
JAN79
MENTICIRRHUS
SPHYRAENA
ANISOTREMUS
Seasonality
of nearshore
99
larvaljish
Lynn, 1967; Mearns, 1979); temperatures tended to be somewhat warmer than average through much of 1978 (Figure 6). Consistently cool temperatures near the annual minimum occurred in December-April followed by warming to an annual maximum in August-September, and then followed by cooling in October and November. Approximately 12 cooling episodes of variable duration in the spring and summer interrupted the general warming trend. Examination of the Scripps pier temperature record showed that these cooling episodes occurred over a longshore distance of at least 60 km. Five of these cooling episodes (shown by arrows on Figure 6) represent upwelling episodes‘ which occurred as shallow as the 15-m station in the years 1978-80 (the method used for identifying upwelling is given in Appendix I).
Discussion
Spawning times, as inferred from the data, generally confirmed the findings of other workers: for example, Lasker (1978), and Smith and Lasker (1978) for Engraulis mordax; Goldberg (1976) for GenyonemusZineatus and Seriphus politus; Kramer (1960) and MacGregor (1976) for Scomber japonicus; Ahlstrom (1969) for Trachurus symmetricus; Ahlstrom (1972) for Bathylagus ochotensis, Leuroglossus stilbius, Stenobrachius leucopsarus and Triphoturus mexicanus; Ahlstrom and Counts (1955) for Merluccius productus; Ahlstrom et al. (1978) for Sebastes spp.; Quast (1968) for Paralabrax clathratus; and Ahlstrom and Moser (1975) for Paralichthys calijornicus. The spawning times based on larval occurrence do indeed coincide with actual spawning: otolith (Walker et al., 1980), and mortality (Barnett et al., 1983) studies on Genyonemus lineatus and Seriphus politus suggestthat most of the larval taxa reported herein are within two weeks of spawning. Relationship
of larval
temporal
distribution
with temperature
Seasonalreproductive cycles in teleosteanfishesare probably controlled by an endogenous rhythm (Harrington, 1959; Bye, 1984; Stacey, 1984) synchronized with the environment in response to predictable (recurring) exogenous factors (Bye, 1984). Photoperiod and temperature are the exogenous factors most commonly evaluated for the timing of reproduction (see, for example, Schwassman,1971; de Vlaming, 1972; Billard & Breton, 1978; Hubbs, 1985). However, although regularly recurring environmental events regulate the timing of cycles, the role that they play in the complex of activities called spawning is far from clear (Scott, 1979). In many teleost groups spawning (ovulation) is not simply a consequenceof completed ovarian development (Stacy, 1984), but is connected with an abrupt change in the environment or to the attainment of an annual maximum or minimum of somephysical variable (Orton, 1920; Gunter, 1957; Nikolsky, 1963; Breton, 1978). Spawning of the summer-fall speciesoccurs predominantly from July-September, the period of maximum water temperature. The autumn drop in water temperature may curtail or end spawning for these species.The winter-spring speciesapparently spawn most heavily either in January-May when temperatures are near the annual minimum, or spawn all year long. The role of the photoperiod/temperature interaction hypothesized by many authors for spawning initiation is not discounted. The summer-fall spawners could indeed be using the summer solstice as a cue, as could the winter-spring spawners be using the winter ‘We consider upwelling events in the sense of ‘ meso-scale associated with cooling episodes of one or two weeks duration.
’ (Haury,
et al.,
19781,
100
H. J. Wulker
Jr et al.
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Searonality
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VERTICALIS
to subgroups Bz and B, with highest in a 100-m wide ilongshore direction’
CITHARICHTHYS
STENOBRACHIUS
PLEURONICHTHYS
of selected fish larvae belonging represent numbers (in millions‘i
LEPIDUS
JAN00
SPP.
JAN00
CALfFORNlCUS
J”L78
J"L79
Figure 5. One-dimensional monthly mean abundances average abundance m uinter and spring. Abundances segment of ocean between the 6- and 75-m isobaths.
ATHERINIDAE
Figure 6. Temperature j above! and nitrate-nitrite (belowj records 6%year mean surface temperature recorded at the 6-m isobath off California. ---, (temperature) represents Scripps pier surface temperature recorded off San Onofre at the 12-15-m isobaths. identical to Scripps data and are not shown). The 10 nmol isopleth each year. Arrows indicate upwelling episodes.
for the three-year study period off San Onofre, California. ., the end of Scripps Institution of Oceanography pier, La Jolla, temperature for the particular year. p, yearly mid-depth (Surface temperatures off San Onofre, 1978-80, were nearly of nitrate-tnitrite, measured at the 30-m isobath, is shown for
104
H. J. Walker
Jr et
al.
--
solstice. This would agree in part with Hubbs (1985) and Marsh (1980) (both worked with the freshwater family Percidae) who believed that photoperiod was the dominant factor for the initiation of the spawning season and that temperature was the dominant factor for its termination. With regard to environmental influences on the timing of reproduction, Bye (1984) believed that habitat and ‘ lifestyle ’ are more important considerations than phylogenetic relationships. Kendall and Dunn (1985) also support part of this idea: they found that the species with demersal eggs spawned in late summer-fall, whilst spring-summer spawners had pelagic eggs. This is consistent with the species groups of this work, which are taxonomically heterogeneous but relatively homogeneous in terms of reproductive mode and spawning temperature. The year-round spawning of many demersal-spawning species may result from a combination of broad temperature tolerance and of low batch fecundity which may necessitate periodic spawning of egg clutches over a long time span to ensure reproductive success. Lambert and Ware (1984) also found reproductive seasons to be longer for demersal than for pelagic spawners. Although the annual temperature cycle, by its direct influence on reproduction and larval survival, may potentially account for the seasonal occurrence and abundance of temperate fish larvae, other environmental factors probably modify larval abundance during the spawning season.d For example, a lower abundance of larvae might be expected in the nearshore zone during upwelling periods (De Martini, pers. comm.; Lasker, 1978; Smith & Lasker, 1978). However, comparison of larval abundance with upwelling dates (see Appendix I) gave inconclusive results: abundance fluctuations during the spawning seasons were at least as great during non-upwelling periods as between upwelling and non-upwelling periods. Thus it is unclear whether upwelling is important in determining the abundance of fish larvae on the spatial and temporal scale of our sampling. Relationship of larval temporal distribution to adult zoogeography Briggs (1975) characterized the San Diego Warm-Temperate Province asa zone of mixing where speciesof northern and southern origin are brought into contact. Qasim (1955) stated that neritic speciesnearer the warmer limits of their range breed during the colder months of the year and speciesnearer the colder limits of their range breed during the warmer months of the year. Our data confirm this observation not only for neritic species, but also for epipelagic and mesopelagic species.The winter-spring larvae are primarily (69%) offspring of adults whosenorthern rangesgenerally extend to Canada (or rarely, to Oregon) (Miller & Lea, 1972). Among the mesopelagicspecieswhose adult ranges could be ascertained, five are northern forms (Bathylagus ochotensis, Leuroglossus stilbius, Diaphus theta, Protomyctophum crockeri and Stenobrachius leucopsarus) and their larvae were found in the colder months. Summer-fall larvae are principally (91 00) offspring of adults whose northern range limits or centers of distribution extend mainly to Point Conception or to Monterey, California; 99, range to Oregon (Miller & Lea, 1972). The species with centers of distribution in warm waters, but northern range endpoints extending beyond Monterey in warm years (Hubbs, 1948; Radovich, 1961; Miller & dFood is not considered a limiting factor in the Bight, with the possible exception of the fall period (Smith & Lasker, 1978). Although no critical evidence exists to discount starvation, nearly all larvae examined appeared robust, and rarely emaciated. Similarly, predation could not be evaluated. We observed little evidence of predation by zooplankters collected in the 1300 samples analyzed, but cannot assess the impact of predation by juvenile and adult fishes.
Seasonality of neat-shore larvaljish
105
Lea, 1972), are the neritic speciesSphyraena argentea, Seriola lalandi and Atractoscion nobilis, and the epipelagic species Scomber japonicus and Trachurus symmetricus. The remaining mesopelagic specieswhose adult range could be ascertained was Triphoturus mexicanus. Triphoturus mexicanus hasa southern distribution (Miller & Lea, 1972) and the larvae were found predominantly in the summer months. There were few exceptions to the relationship between the geographic distributions of the adults of neritic speciesand the temporal distributions of their larvae. Exceptions among the pelagic spawners were the pleuronectids Pleuronichthys ritteri, P. verticalis and Hypsopsetta guttulata. Although distributed northward only to central California or further south, they usually occurred in the winter and spring samples.These three species were the only pelagic spawners of the entire analysis that unexplainedly violated this relationship. Among the 10 winter-spring demersal spawners (whose larvae afforded enough taxonomic precision for geographic information) five were exceptions, reflecting the occurrence of these larvae throughout the year. Temperature frequently has been cited as the most important factor determining the world-wide distribution of poikilotherms (see,for example, Ekman, 1953; Gunter, 1957; Briggs, 1975), and this is true for California fishes(Horn 81Allen, 1978; Horn, 1980). The high degree of similarity within the winter-spring and summer-fall speciesgroups and their respective zoogeographic ranges indicates that temperature is the variable most influencing spawning in the Southern California Bight. This is also evident in shifts in spawning seasonover the geographic rangesof somewidely-ranging species.For example, in contrast to Southern California, the spawning seasonof Engraulis mordax is summer off the Oregon coast (Richardson & Pearcy, 1977) where this speciesnears its northern range limit (British Columbia: Miller 81Lea, 1972). Love et al. (1984) believe that the colder water off Monterey may account for the more extended spawning seasonof Genyonemus lineatus there than in the Southern California Bight. The distribution of Seriphuspolitus, the only species in the summer-fall assemblagewith consistently high abundance in spring, extends northward to Oregon. On the other hand, the spawning season for Parophrys vet&s is winter in both Southern California and Oregon waters (Pearcy & Myers, 1974); its distribution extends to north-west Alaska (Miller & Lea, 1972). Johannes (1978) used the term ‘ collective spawning peaks ’ to refer to certain times of the year when unusually large numbers of speciesand individuals within speciesreproduce. The data from this work support this concept, but the time frame for thesecollective spawning peaks appears to be broader in the Southern California Bight than in tropical waters. Our data suggestthat such periods of simultaneously increased spawning by large numbers of specieshave a duration of three to five months in the Southern California Bight, whereas in tropical waters these periods tend to have a duration of two to three months (Johannes, 1978). Basedon larval abundance, corroborated by adult zoogeography and recurring temperature patterns, we believe that January-May and July-September can be considered ‘ collective spawning periods ’ for fishes of the Southern California Bight.
Acknowledgements This paper is a result of research funded by the Marine Review Committee (MRC), Encinitas, California. The MRC does not necessarily accept the results, findings or conclusions stated herein.
106
H. J. WalkerJr
et al.
The authors wish to thank cruise leaders Kevin George, James Hare and Gloria Hoff who directed many nightly cruises, Capt. Robert Hundt, skipper of the R. V. LoAn, and numerous technicians who processed the samples. Raymond Davis, Vivian McCoy and Peter Steinkirchner assisted with figures and calculations. Rita Dave and David Williams were kindred spirits. Jeffrey Leis, Michael Marika and Patti Schmitt reviewed earlier versions of the manuscript. We thank Michelle Armstrong, Kathleen Pangborn and Judy Sabins for typing the manuscript in its many forms and Susan Watts who diligently addressed our statistical analysis. References Ahlstrom, U.S.
Ahlstrom, surveys.
Ahlstrom,
E. H. 1959 Vertical Fish
and
Wildlife
E. H. 1965 Kinds California
E. H.
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wesethi, No. 17.
E. H. &Counts, Service,
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based on egg and larval
Report
Triphoturus ochotensis,
of the California mexicanus,
region: California
jack mackerel, Cooperative
1955-1960.
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six common
Stenobrachius leucopsarus, Leuroglossus California Cooperative Oceanic Fisheries
E. C. 1955 Eggs and larvae of the Pacific hake, Merlucciusproductus.
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1 I.
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lucetia, Bathylagus
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Ahlstrom, E. H. 1972 Distributional mesopelagic fishes-Vinciguerria
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Ahlstrom, E. H. & Moser, H. G. 1975 Distributional atlas of fish larvae in the California Current region: flatfishes, 1955-1960. California Cooperative Oceanic Fisheries Investigations Atlas No. 23. Ahlstrom, E. H., Moser, H. G. & Sandknop, E. M. 1978 Distributional atlas of fish larvae in the California Current region: rockfishes, Sebastes spp., 1950-1975. California Cooperative Oceanic Fisheries Investigations
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Barnett, A. M. & Jahn, southern California. Barnett, A. M., Hartwig,
and persistence of a nearshore planktonic ecosystem in 7, l-25. E. O., Jahn, A. E., Sertic, I’. D. &Watts, S. D. 1980a Long-term Average Spatial Patterns, Temporal Patterns, and Inter-relationships of Physical-Chemical Measures off SONGS. Marine Ecological Consultants of Southern California, 531 Encinitas Boulevard, Suite 110, Encinitas, CA 92024, U.S.A. Barnetr, A. M., DeMartini, E. E., Goodman, D., Larsen, R., Sertic, I’. D. & Watson, W. 19806 Predicted larval fish losses to SONGS Units 1,2 and 3 and preliminary estimates of the losses in terms of equivalent forage fish. In Report of the Marine Review Committee to the California Coastal Commission: Predictions of the Effects of San Onofre Nuclear Generating Station and Recommendations. Fish Appendix 4. Marine Review Committee Document 80-04(l). Marine Review Committee of the California Coastal Commission, 631 Howard Street, San Francisco, CA 94105, U.S.A. Barnett, A. M., Jahn, A. E., Sertic, I’. D. &Watson, W. 1984 Distribution of ichthyoplankton off San Onofre, California, and methods for sampling very shallow coastal waters. Fisher-v Bulletin, United States 82, 97-111. Billard, R. & Breton, B. 1978 Rhythms of reproduction in teleost fish. In Rhythmic Activity of Fishes (Thorpe, J. E. ed.) pp. 31-53. Academic Press, London. Boesch, D. E. 1977 Application of Numerical Classi’cation in Ecological Investigations of Water Pollution U.S. Environmental Protection Agency, Special Scientific Report No. 77. Brewer, G. D. & Smith, P. E. 1982 Northern anchovy and Pacific sardine spawning off southern California during 1978-1980: preliminary observations on the importance of the nearshore coastal region. California
Cooperative
Brewer, G. D., Lavenberg, larvae in the Southern
A. E. 1987 Maintenance Continental
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G. E. 1981 Abundance and vertical distribution of fish eggs and June and October 1978. In Symposium on the early life history of fish. Introduction and background, Woods Hole, April 1979 (Lasker, R. & Sherman, K. eds) Vol. 178, pp. 165-167. Rapp. P.-v. Reun. Cons. int. Explor. Mer. Briggs, J. E. 1975 Marine Zoogeography. McGraw-Hill, New York. Brown, D. M. & Cheng, L. 1981 New net for sampling the ocean surface. Marine Ecology Progress Series 5, 225-227. Bye, V. J. 1984 The role of environmental factors in the timing of reproductive cycles. In Fish Reproducrion: Strategy and Tactics (Potts, G. W. & Wootton, R. J. eds). pp. 187-205. Academc Press, London.
of nearshore
Seasonality
Clutter,
R. I. 1977 Estimated
larval
Station Unit 1 on mysids. In Annual 1977. Appendix. Estimated effects of SONGS Unit 1 on marine organisms: technical analysis and results. MRC Document 77-09, No. 2, pp. 3-l-3-45. Marine Review Committee of the California Coastal Commission, 631 Howard Street, San Francisco, CA 94105, U.S.A. de Vlaming, V. L. 1972 Environmental control of teleost reproductive cycles: a brief review. Journal of Fish Biol0g.v 4, 131-140. Ekman, S. 1953 Zoogeography of the Sea. Sidgwick and Jackson, London. Eldridge, M. B. & Bryan, C. F. 1972 Larval Fish Survey of Humbolt Bay, California. NOAA Tech. Rep. NMFS SSRF 665. Goldberg, S. R. 1976 Seasonal spawning cycles ofthe sciaenid fishes Genyonemus lineatus and Seriphuspolitus. Report
effects of San Onofre
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Bulletin,
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United
States
Commission,
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74,183-184.
Gruber, D., Ahlstrom, E. H. & Mullin, M. M. 1982 Distribution of ichthyoplankton in the Southern California Bight. California Cooperative Oceanic Fisheries Investigations Report 23,172-179. Gunter, G. 1957 Temperature. In Treatise on Marine Ecology and Paleoecology, Vol. 1, Ecology (Hedgpeth, J. W. ed.), pp. 159-184. Geological Society ofAmerica, Memorandum 67. Harrington Jr, R. W. 1959 Photoperiodism in fishes in relation to the annual seasonal cycle. In Photoperiodism and Related Phenomena in Plants and Animals Publ. No. 55, pp. 651-667. American Association of Advances in Science, Washington DC. Haury, L. R., McGowan, J. A. & Wiebe, I’. H. 1978 Patterns and processes in the time-space of plankton distributions. InSpatialPatternand PlanktonicCommunities (Steele, J.H., ed.) PlenumPress,New York. Horn, M. H. 1980 Diversity and ecological roles of non-commercial fishes in California marine habitats. California
Horn,
M.
Cooperative
H. & Allen,
Biogeography
Oceanic
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L. G. 1978 A distributional
Report
analysis
21,37-47.
of California
coastal
marine
fishes. Journal
of
$23-42.
Hubbs, C. 1985 Darter reproductive seasons. Copeia 1985(l), 5668. Hubbs, C. L. 1948 Changes in the fish fauna of western North America correlated with changes in ocean temperature. Journal of Marine Research 7,459-482. Icanberry, J. W., Warrick, J. W. &Rice Jr, D. W. 1978 Seasonal larval fish abundance in waters off Diablo Canyon, California. Transactions of the American Fisheries Society 107,225-233. Johannes, R. E. 1978 Reproductive strategies of coastal marine fishes in the tropics. Environmental Biology of. Fisheries
3,65-84.
Kendall, A. NOAA Kramer, D. larvae, Lambert, T.
W. & Dunn, J. R. 1985 Ichth-voplankton of the Continental Shelf Near Kodiak Island. Alaska. Tech. Rep. NMFS 20. 1960 Development of eggs and larvae of Pacific mackerel and distribution and abundance of 1952-1956. U.S. Fish and Wildlife Service, Fishery Bulletin 60,393-438. C. &Ware, D. M. 1984 Reproductive strategies ofdemersal and pelagic spawning fish. Canadiatl Journal ofFisheries and Aquatic Science 41, 1565-1569. Lasker. R. 1978 The relation between oceanographic conditions and larval anchovy food in the California Current: identification of factors contributing to recruitment failure. Rapport et proces-verbartx des Reunions
Conseil
permanent
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173,212-230.
Leithiser, 1~. M. 1981 Distribution and seasonal abundance of larval fishes in a pristine southern California salt marsh. Rapport et pro&s-verbaux des Reunions Conseilpermanent internationalpour 1’Exploration de la Msr 178, 17+175. Loeb, V. J., Smith, I’. E. & Moser, H. G. 1983 Geographical and seasonal patterns of larval fish species structure in the California Current area, 1975. California Cooperative Oceanic Fisheries lnvestigatzons R~ort 24, 132-151. Love, M. S., McGowen, G. E., Westphal, W., Lavenberg, R. J. &Martin, L. 1984 Aspects ofthe life history and fishery of the white croaker, Genvonemus lineatus (Sciaenidae), off California. Fisher-y Bulletin. United States 82, 179-198. L*ynn, R. 1967 Seasonal variation of temperature and salinity at 10 meters in the California Current. C&forma Cooperative Oceanic Fisheries Investigations Report 11, 157-186. MacGregor, J. L. 1976 Ovarian development and fecundity of five species of California Current fishes. California Cooperative Oceanic Fisheries Investigations Report 18, 181-188. Marine Review Committee 1979 Interim report of the Marine Review Committee to the California Coastal Commission. Part 1: general summary of findings, predictions, and recommendations concerning the cooling system of the San Onofre Nuclear Generating Station. In Marine Review Committees Document 79-02, pp. l-20. Marine Review Committee of the California Coastal Commission, 631 Howard Street, San Francisco, CA 94105, U.S.A. Marsh, E. 1980 The effects of temperature and photoperiod on the termination of spawning in the orangethroat darter (Etheostoma spectabile) in central Texas. TexasJournal of Science 32, 129-142. Mearns, A. B. 1979 Variations in coastal physical and biological conditions, 1969-1978. In Coastal Water Research Projecr Annual Reportfor the Year 1978 (Bascom, W., ed.), pp. 147-156. Southern California Coastal Water Research Project, El Segundo, CA.
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Miller,
D. J. &Lea, R. N. 1972 Guide to the coastal marine fishes of California. California Department of f”ish & Game, Fish Bulletin 151. Nikolski, G. V. 1963 The Ecology of Fishes. Aademic Press, London. Orton, J. H. 1920 Sea temperature, breeding and distribution of marine animals. Journal of the Biological Association of the United Kingdom 12,339-366. Pearcy, W. G. &Myers, S. S. 1974 Larval fishes ofYaquina Bay, Oregon: a nursery ground for marine fishes? Fishery Bulletin, United States 12,201-213. Qasim, S. Z. 1955 Time and duration of spawning season of teleosts in relation to their distribution.Journaldu Cons&l Permanent International pour I’Exploration de la Mer 21,144-155. Quast, J. C. 1968 Observations on the food and biology of the kelp bass, Paralabrax clathratus with notes on its sportfishery at San Diego, California. California Department of Fish Q Game, Fish Bulletin 139, 81-108. Radovich, J. 1961 Relationships of some marine organisms of the northeast Pacific to water temperatures. California Department of Fish & Game, Fish Bulletin 112. Richardson, S. L. & Pearcy, W. G. 1977 Coastal and oceanic fish larvae in an area of upwelling off Yaquina Bay, Oregon. Fishery Bulletin, United States 75, 125-146. Schwassmann, H. 0. 1971 Biological rhythms. In Fish Physiology, Vol. 6. Environmental Relations and Behavior (Hoar, W. S. &Randall, D. J., eds), pp. 371-428. Academic Press, New York. Scott, D. B. C. 1979 Environmental timing and the control of reproduction in teleost fish. In Fish Phenology: Anabolic Adaptiveness in Teleosts (Miller, P. J., ed.) Symposium of the Zoological Society London 44, 105-132. Smith, R. W. 1976 Numerical analysis of ecological survey data. Ph.D. Thesis, University of Southern California, Los Angeles. Smith, I’. E. & Lasker, R. 1978 Position of larval fish in an ecosystem. Rapport et pro&-verbauxdes Reunions Conseil permanent international pour I’Exploration de la Mer 173,77-84. Snedecor, G. W. & Cochran, W. G. 1967 Statistical Methods, 6th edition. Iowa State University Press, Ames, Iowa. Southern California Edison Company 1979 Annual Operating Report, San Onofre Nuclear Generating Station. Vol. 1. Oceanographic Data 1978. Report No. 79-RD-9, pp. 3-14-6. Southern California Edison Company 1980 1979 Annual Operating Report, San Onofre Nuclear Generating Station. Vol. 1. Oceanographic Data Report. Report No. 80-RD-10, pp. 3-l-3-95. Southern California Edison Company 1981 1980 Annual Operating Report, San Onofre Nuclear Generating Station. Vol. II. Comprehensive Data Supplement, Part 1 of 2, Oceanographic. Report No. 81-RD-8, pp. 2A-l-2A-105. Stacey, N. E. 1984 Control of the timing of ovulation by exogenous and endogenous factors. In Fish Reproduction: Strategy and Tactics (Potts, G. W. & Wootton, R. J. eds), pp. 187-205. AcademicPress, London. Strickland, J. D. H. & Parsons, T. 1972 A Practical Handbook of Seawater Analysis. Fisheries Research Board of Canada, Bulletin 167 (2nd edition). Walker Jr, H. J., Schmitt, I’. D., Davis, R. L. & Barnett, A. M. 1980 Age and Growth of Larval Queenfish (Seriphus politus) and White Croaker (Genyonemus lineatus) 08 San Onofre, California. Marine Ecological Consultants of Southern California, 531 Encinitas Boulevard, Suite 110, Encinitas, CA 92024, U.S.A.
Appendix
I
In order to confirm upwelling episodes inferred from the temperature record, profiles of dissolved nitrate and nitrite were examined. Water samples for nutrient analyses were not available at the 12-15-m stations, but were collected at a nearby 30-m station. Samples were collected with a cleaned and purged submersible pump (Little Giant), filtered first through 0.202~mm mesh Nitex and then through glass-fibre filters (Gelman Type AE) into acid-washed plastic bottles, and quick frozen in dry ice. These water samples were maintained in the laboratory at - 20°C until analyzed following the method of Strickland & Parsons (1972). The laboratory analyses indicated that (based on the 10 Fmol isopleth of nitrate-nitrite from the 30-m station) nutrient-rich water intruded into shallow depths (10 to -20-m) in the third week of April and last week of July, 1978, with a relatively high level maintained between these dates at deeper depths. Other episodes of shallow intrusion of nutrient-rich water included: a fairly long period beginning approximately 20 April and lasting until the
Seasonality of nearshore larvalfish
109
secondweek of May, 1979; the secondand third weeks of July, 1979; the last week of June to the first week of July, 1980. The coincidence of these shallow intrusions of nutrient-rich water with temperature depressionswere interpreted asupwelling episodes.From the combined temperature and nitrate-nitrite data we conclude that five upwelling episodesoccurred as shallow as the 15-m station in the years 1978-80. These were: the third week of April, 1978; the last week of July, 1978; the secondweek of May, 1979; the secondand third weeks of July, 1979; the second and third weeksof July, 1980. Near-shore upwelling might be expected to affect the distribution of fish larvae in shallow coastal waters. For example, upwelling hasbeen shown to disrupt aggregations of suitable food organisms for larval fish in the Bight and thus initially to be potentially detrimental to larval fish survival (Lasker, 1978). Upwelling also transports nearshore, planktonic organisms offshore where conditions are less favorable (Smith & Lasker, 1978). Adults of some inshore speciesof fish apparently move offshore to avoid areasof lowered temperatures resulting from upwelling (DeMartini, pers. comm.). Consequently, their spawning products would not be expected inshore during upwelling periods. To determine whether our data were suitable for addressing the question of potential upwelling effects on the nearshore distribution and abundance of fish larvae, we qualitatively compared abundances of Engraulis mordax, and of all other larvae combined, with the upwelling episodesidentified above. The abundance of E. mordax larvae substantially decreased on the sampling date during or following only two of the five upwelling episodes.The non-engraulid abundance decreasedduring or following three of the episodes. However, someabundance fluctuations during the spawning seasonswere at leastasgreat during non-upwelling periods. Thus we cannot evaluate the effect of upwelling using this data set.
Coastal
and Shelf
Science ( 1987) 25,9 l-l 09
Seasonal Occurrence of Larval Nearshore Southern California San Onofre, California
H. J. Walker
Jr,’ William
Watson
Marine Ecological Consultants of Southern Suite 110, Encinitas, CA 92024, U.S.A. Received
18 September
Keywords: upwelling;
1985
fish larvae; California
and in revisedform
seasonal;
Fishes in the Bight off
and Arthur
Chlifornia,
1 OJuly
temperature;
M. Barnett
531 Encinitas
Boulevard,
1986
spawning;
zoogeography;
Larval fishes were sampled from the nearshore region of the Southern California Bight off San Onofre for 29 months and analyzed with a Curtis-Bray Cluster Analysis to determine temporal assemblages and species associations. Two major assemblages of larvae were found: members of the winter-spring (DecemberMay) assemblage were most abundant from January to May; members of the summer-fall (June-November) assemblage were most abundant from July to September. The winter-spring assemblage was composed primarily of Engraulis mordax, Genyonemus lineatus, Sebastes spp. and Paralichthys californicus; some abundant taxa in the summer-fall assemblage were Seriphus politus, Paralabrax spp., and Hypsoblennius spp., although E. mordax again predominated. Demersal spawners tended to have spawning seasons of longer duration than pelagic spawners; winter-spring spawners generally had longer spawning seasons than summer-fall spawners. We suggest that temperature is an important determinant in the seasonal pattern of larval fish occurrence. The annual ocean temperature cycle near San Onofre was a good indicator of the seasonal occurrence of fish larvae in this area. Larvae found in the cooler months were generally offspring of adults whose northern ranges extend to Canada. Warm-water larvae were offspring of adults whose northern ranges extend to Point Conception or northern California. Introduction This paper describes the seasonal abundance patterns of nearshore (within 7 km of shore) larval fishes off San Onofre, California (Figure l), and the relationship of those patterns to water temperature, adult zoogeography and coastal upwelling. This study, based on 29
months of sampling of the entire water column, is one of the first long-term, intensive studies of coastal ichthyoplankton made in the Southern California Bight. Previous larval fish studies in California waters have been predominantly in the oceanic realm (> 200 m depths) e.g. Ahlstrom, 1959, 1965; Loeb et al., 1983) or in bays and estuaries (e.g. Eldridge & Bryan, 1972; Leithiser, 1981). Most studies of coastal “Present address: Marine Vertebrates Collection, Scripps Institution of Oceanography, University
of California,
San Diego
AOOB, La Jolla, CA 92093,
U.S.A.
91 0272-7714/87/010091+
19 $03.00/O
0 1987 Academic
Press Inc. (London)
Limited
92
H. J. Walker Jr
et al.
San Onofre Nuclear Generating Station
E Cu
I&
D
37 ‘m-------,, 55 imp-
E 74 lm
\ 117”33’
20”
I
L
t
San Onofre
7
0
33’22’
30”
\
I km Pacific
Ocean
1 Figure
1. Map
of the study
area showing
its position
in the Southern
California
Bight.
ichthyoplankton have either concentrated on a few species (e.g. Brewer & Smith, 1982), on spatial patterns (e.g. Barnett et al., 1984), or have sampled too infrequently or over too short a time span to define seasonal patterns (e.g. Brewer et al., 1981; Gruber et al., 1982). Icanberry et al. (1978) sampled monthly for more than a year, but did not sample the entire water column. Thus, a gap exists in the knowledge of the ecology of the ichthyoplankton in California coastal waters; namely, the seasonal assemblages of larval fishes have not been well defined or documented. The primary purpose of this paper is to identify the seasonal assemblages of larval fishes which occur in the nearshore Southern California Bight. Materials
and methods
Sampling The study was conducted off San Onofre, California, located in the Southern California Bight about half way between Los Angeles and San Diego (Figure 1). The coastline is fairly uniform, with a regularly sloping shelf ending about 7 km from shore at a depth of 70 m. The Gulf of Catalina, a broad area characterized by depths of 1 km, lies beyond the shelf.
Seasonality ofnearshore larvalfish
93
All sampling was done along an offshore transect located approximately 1 km south of San Onofre Nuclear Generating Station (SONGS) (Figure 1). The 500-MW unit operating at that time was shown to have only localized effects which did not influence our results (Marine Review Committee, 1979). Because this was a multipurpose study, the spatial scale of sampling was finer than necessary, and the temporal scale of sampling deviated somewhat from the scalesthat would be required for a seasonalstudy alone. Field procedures and their rationale (for sampling gear, depth strata, offshore sampling blocks and sampling frequency) are described in detail by Barnett et al. (1984). A stratified random-sampling design (Snedecor & Cochran, 1967) was used wherein the neustonic, mid-water and epibenthic layers of the water column were sampledat a randomly chosen isobath in each of five blocks defined by depth contours: (A) 6-9 m; (B) 9-12 m; (C) 12-22 m; (D) 22-45 m; and (E) 45-75 m. Three different types of gear, all equipped with 0.333 mm mesh Nitex nets, were required to sample the three strata in shallow water adequately: a Brown Manta net, 88 cm wide x 16 cm deep, for the neuston (Brown & Cheng, 1981); a Brown-McGowan opening-closing Bongo net, 71 cm diameter, for midwater; and an Auriga net (Marine Biological Consultants, Inc., 947 Newhall Street, Costa Mesa, CA 92627, U.S.A.), 2 m wide x 0.5 m high for the epibenthic stratum. On five occasionswhen a vesselcapable of handling the Auriga was not available, a smaller epibenthic sled (mouth 1 m wide x O-3m high) was used to sample the epibenthos (Clutter, 1977). Two-tailed Mann-Whitney U-tests of comparative samplesshowed no differences (p>O.lO) in catch per unit area (number per 100 m’) between the two epibenthic samplers. In order to assessrelative catch efficiencies, additional comparative tows were made between an Auriga (modified to samplethe midwater) and a bongo, and between a bongo fitted with wheels (to sample the epibenthos) and an Auriga. In midwater, Wilcoxon’s signed-ranks tests showed no difference @> 0.05) between the samplersin catch per unit area, while in the epibenthic stratum the Auriga caught more (p < 0.05) of most taxa per unit area. The Manta was not compared with the other samplers. However, because neither the bongo nor the Auriga is appropriate for sampling the neuston when towed in a conventional manner (i.e., astern) it was felt that this specialized sampler was required. All samples were taken at night, parallel to shore. Each sampler was fitted with a flowmeter and towed at ca. 1 m s-l for a fixed time in order to filter a target volume of 400 m3. This volume was determined, during a preliminary investigation, to be the optimal sample size’ for the study area (Barnett et al., 1984). Samples were preserved in the field in IO”,, Formalin-seawater, The transect was sampled monthly in January and February 1978, fortnightly from March through August 1978, monthly through September 1979, and then weekly from March through October, 1980. Each sampling episode in 1978 and 1979 consisted of sampling all blocks on 1-3 successivenights; each episode in 1980 consisted of a single night. The 29-month study thus comprised 86 sampling dates. “Although an argument could be made for sampling the water column with equal intensity per unit depth rather than sampling an equivalent volume from each stratum, the latter approach was both adequate and logistically preferable because equalintensity sampling would require that offshore midwater samples be extremely large (or that neustonic and epibenthic samples be extremely small). Alternatively, an argument based on the scale of patchiness could be made for using tow length (400m) rather than volume (400 m’) as the sampling unit. Most of our tows were at least 400 m long.
94
H. J. Walker Jr et al.
Temperature data were obtained from continuous monitors and other recorders positioned between the 12- and 15-m isobaths. These measurements were not taken during the ichthyoplankton sampling, but were part of other studies conducted at the samelocation (Barnett & Jahn, 1987; Barnett et al., 1980, Southern California Edison Company, 1979, 1980, 1981). Additional temperature data was obtained from Scripps Institution of Oceanography, La Jolla, California (60 km south-east of San Onofre). Surface temperature was measured daily at the end of Scripps pier, located at the 6-m isobath. Laboratory
procedures
Ichthyoplankton samples were cleaned of debris and most were subsampled with a Folsum plankton splitter prior to being sorted for fish larvae. The subsamplesize, which averaged one-fourth of the original and was rarely less than one-eighth (range l/32-1), was set to include at least 100 non-engraulid larvae. Sampleswere sorted under 6-10 x magnification and checked by a second sorter to ensure that at least900,, of the larvae were removed. Larval fish were identified to the lowest taxonomic level possible. Analytical
techniques
A cluster analysis was used to determine taxon associations (defined here as species groups) and temporal assemblages(defined here asmonth groups). A large number of rare taxa were found in the study which carried little classification information (Boesch, 1977) but which could maskmuch of the information available from the more frequently occurring species.To ensurethat this did not happen, two criteria were applied before accepting a speciesfor analysis: (1) a taxon had to be among the top 25 in abundance on at least one survey of the 86 taken; and (2) a taxon had to occur in at least six of the 29 months. These criteria reduced the number of available taxa from approximately 140 to 63. However, these 63 taxa cornprized about 969; of the total larval abundance; unidentified yolk sacand unidentifiable damaged specimenscomprised 3?,, of the total. As the principal aim of the study was to identify seasonalassemblagesof fish larvae, the analysis was based on monthly mean abundances of larvae in the entire cross-shelf transect. Specifically, for a given taxon a one-dimensional abundance wascalculated based on the estimated number of larvae, Dijr, in each of fifteen (3 depth strata x 5 cross-shelf blocks), 100-m wide (alongshore dimension) strata on each sampling date:
where i indicates depth (1 = neuston, 2 = midwater, 3 = epibenthos); j indicates cross-shelf block (1 = block A, . . . 5 = block E); r is the replicate number (r = I, 2, . . . R); Aij, is the number of individuals at depth i, in block j, of replicate r; rij, is the vertical thickness (m) of depth i, block j, replicate r; Vij, is the volume (m3) sampled from depth i, block j, replicate r; and Lj is the cross-shelf length of block j. The Dij, were summed over the 15 strata to give a transect total for each sampling date: D, =
;
;
I=1
1=1
Dij,
and the D, within each month were averaged to give a monthly mean:
Seasonality of nearshote larvalfish
95
Variances were calculated from the transect totals: s = E @-@Z/(&l) Both normal (months classified by the species’abundancesoccurring within them) and inverse (speciesclassified by their monthly abundances) classifications were performed. The monthly mean transect abundances were square-root transformed. Following the recommendation of Smith (1976), the transformed abundances for each species were standardized by division with that species’mean transformed abundance before performing the normal classification, whilst for the inverse classification the transformed abundances were standardized by dividing the maximum transformed abundance for each speciesbefore clustering. The species’mean standardization tends to give more weight in the calculation of the distance matrix to taxa with more leptokurtic abundance distributions; thus temporally wide-spread taxa do not dominate the classification ofmonths. On the other hand, the speciesmaximum standardization tends to give equal weights to all taxa and to prevent the overinfluence of abundant speciesin the speciesanalysis (Smith, 1976). The sorting strategy was an agglomerative hierarchical technique with flexible sorting of Bray-Curtis distance index values using a cluster intensity coefficient cc> set at - 0.25. Using p= - 0.25 with flexible sorting produces distinct groups and is considered conventional (Boesch, 1977). The level of resemblancedeemed sufficient to identify a group was set subjectively and differed for the speciesand temporal classifications. A certain degree of subjectivity is inherent in the interpretation of numerical classifications and, ashasbeen pointed out by Boesch (1977), use of a fixed stopping rule is inappropriate when flexible sorting with negative b is used. Results Fish larvae
Approximately 140 types (sensuRichardson & Pearcy, 1977) of larval fishesrepresenting 43 families were collected during this study. Northern anchovy (Engraulis mordax) and the sciaenids (Genyonemus lineatus and Seriphus politus) ranked first, second and third in abundance.’ The following were amongst the 10 most abundant taxa: Sebastes spp., Paralabrax spp., Paralichthys californicus, Hypsoblennius spp., Citharichthys spp., Stenobrachius leucopsarus, and Atherinidae. Two principal month groups (I, II), separated by a distance of greater than 1.1, were identified from the temporal dendrogram; each was further split into subgroups (I,.?, II l _3) separated by distances of greater than 0.5 (Figure 2). The principal separation clearly divided the year into winter-spring (December-May) and summer-fall (JuneNovember) groups. Within each of these, the subgroups formed cohesive units on a calendar basis. Months in groups Ii and I, fit ‘ winter-early spring ’ and ‘ spring ’ designations, respectively, whilst months in groups II, _ 3 consistently fit the terms ‘ early summer ‘, ‘ fall ‘, and ‘ late summer-early fall ‘, respectively. Two major groups of taxa (A, B) were separatedin the speciesdendrogram at adistance of greater than 2.3. A distinct, homogeneoussubgroup (B,) wasthen split from the remainder ‘The rankings pertain only to the years 1978 and 1979 because a large portion of the winter was not sampled in 1980. Data, in the form of a table of monthly mean abundance with two standard deviations for each species, are available upon request from the authors.
96
H. J. WulkerJr
I12 LIL--3
093
et al.
075
DISTANCE 0 56
0 37
019
0
--
-~ ----~
Figure 2. Temporal Onofre, California. within them.
JAN 70 FE9 78 MAR 78 JAN 79 FEE79 MAR 79 DEC 78 APR 78 MAY 78 MAY 80 APR 79 APRBO MAR80 JUN 78 JUN 79
~
t _
or ‘ normal ’ dendogram based on larval fish abundance off San Months are classified by the abundances of the species occurring
of B (distance > 1.5). Group A and the remainder of B were further partitioned into relatively homogeneous subgroups (A,.,, B, _ 4) separated by distances greater than I.1 (Figure 3). Species in subgroups A, (dominated by Chromispunctipinnis) and A, (dominated by Paralabrax spp.) generally were most abundant in summer (July-September), with subgroup A, speciesoccurring more frequently in early summer (seeFigure 4 and Table 1). Group B, species (dominated by Seriphus politus) were also abundant from JulySeptember, but with highest abundances occurring in early summer and a tendency to occur in spring and winter as well (Figure 4). All three groups were rare or absent in October and November. Species in group B, (dominant taxon Genyonemus lineatus) were most abundant in winter and spring (seeFigure 5 and Table 1). Likewise, group B, taxa (dominant taxon Engraulis mordax) also were most abundant in winter and spring but also appeared in the remainder of the year at least in moderate abundance (see Figure 5), except for a small group of three taxa (containing two cottids and Girella nigricans) which apparently should have been classified with the summer-fall groups. Group B, speciesalso tended to be moderately abundant in summer, but with lower abundance from July-October (month groups II, and II,). Temperature
The temperatures and seasonaltemperature changesrecorded off San Onofre in 1978-80 were characteristic of recent decadesin the Southern California Bight (Radovich, 1961;
27
24
Seasonality
of nearshore
2.1
9’5STANfiE 09 06
18
larvalfish
0.3
0
-4
Semtcossypbus p&her Oxyphs cal~forn~co Chromis punchpmnis Hokhoeres semwnctus Symphurus otrlcoudo Sphyroeno orgenteo Amsotremus dovfdsom ttermosftto azure0 Xenistius cotiformensls Poro/obrox spp Menhcirrhus undulotus Ophtdlon scrlppsoe Chettotremo soturnum tfippoglossmo stomoto Lythrypnus dolh Atroctoscion nob//is
L-
7
-
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--
-1
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Siomber jopomcus Sertphus pohtus Hypsypops rubicund0 Girelfo mgr,cons Artedtus creaser1 Cotttdae type 9 Pleuromchthys rttteri Porohchthys coftfornicus tfypsopsetto guttutoto Cithorichthys spp. Ilypnus gIlbert/ Sebostes spp Gobtesox rhessodon Gtbbons/o sp A Clevetondfo ios Ilypnus/Clevetondlo Pteuromchthys verhcohs Leptdogobtus lepldus Quletulo y-couda Engrouhs mordox Heteroshchus rostrotus Sordmops sogox Goblesacldae type A Lomponyctus spp. Zontolepfs spp
,’
Zcehnus quad /Chltonotus ;ryphtogobtus coftformensls Porophrys vet&s Dtophus theta Peprilus sim/fhmus Argentmo slobs -~ -- Protomyciophum crockerl Bothylogus ochotensis
pug
~
L
L-
Stenobrochfus leucopsorus Genyonemus hneotus Neochnus sp A Lz Cotttdoe type 14 Agontdae Leurogtossus st//bws - Merluccws productus ------ Scorpoemchthys mormorotus-
Figure 3. Species or ‘ inverse ’ dendogram California. Species are classified by their
of 63 larval fish taxa occurring monthly abundances.
I I_ 83
off San Onofre,
iAN
I;E!
JUL’B
“UL79
JAN80
UNDULATUS
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ii\,,,
-1
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A,, A2 and B, the 6- and 75-m
J”LB0
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MEXICANUS
JAN80
POLITUS
Figure 4. One-dimensional monthly mean abundances of selected fish larvae belonging to summer subgroups Abundances represent numbers (in millions) in a 100-m wide (longshore direction) segment of ocean between isobarhs.
JAN79
MENTICIRRHUS
SPHYRAENA
ANISOTREMUS
Seasonality
of nearshore
99
larvaljish
Lynn, 1967; Mearns, 1979); temperatures tended to be somewhat warmer than average through much of 1978 (Figure 6). Consistently cool temperatures near the annual minimum occurred in December-April followed by warming to an annual maximum in August-September, and then followed by cooling in October and November. Approximately 12 cooling episodes of variable duration in the spring and summer interrupted the general warming trend. Examination of the Scripps pier temperature record showed that these cooling episodes occurred over a longshore distance of at least 60 km. Five of these cooling episodes (shown by arrows on Figure 6) represent upwelling episodes‘ which occurred as shallow as the 15-m station in the years 1978-80 (the method used for identifying upwelling is given in Appendix I).
Discussion
Spawning times, as inferred from the data, generally confirmed the findings of other workers: for example, Lasker (1978), and Smith and Lasker (1978) for Engraulis mordax; Goldberg (1976) for GenyonemusZineatus and Seriphus politus; Kramer (1960) and MacGregor (1976) for Scomber japonicus; Ahlstrom (1969) for Trachurus symmetricus; Ahlstrom (1972) for Bathylagus ochotensis, Leuroglossus stilbius, Stenobrachius leucopsarus and Triphoturus mexicanus; Ahlstrom and Counts (1955) for Merluccius productus; Ahlstrom et al. (1978) for Sebastes spp.; Quast (1968) for Paralabrax clathratus; and Ahlstrom and Moser (1975) for Paralichthys calijornicus. The spawning times based on larval occurrence do indeed coincide with actual spawning: otolith (Walker et al., 1980), and mortality (Barnett et al., 1983) studies on Genyonemus lineatus and Seriphus politus suggestthat most of the larval taxa reported herein are within two weeks of spawning. Relationship
of larval
temporal
distribution
with temperature
Seasonalreproductive cycles in teleosteanfishesare probably controlled by an endogenous rhythm (Harrington, 1959; Bye, 1984; Stacey, 1984) synchronized with the environment in response to predictable (recurring) exogenous factors (Bye, 1984). Photoperiod and temperature are the exogenous factors most commonly evaluated for the timing of reproduction (see, for example, Schwassman,1971; de Vlaming, 1972; Billard & Breton, 1978; Hubbs, 1985). However, although regularly recurring environmental events regulate the timing of cycles, the role that they play in the complex of activities called spawning is far from clear (Scott, 1979). In many teleost groups spawning (ovulation) is not simply a consequenceof completed ovarian development (Stacy, 1984), but is connected with an abrupt change in the environment or to the attainment of an annual maximum or minimum of somephysical variable (Orton, 1920; Gunter, 1957; Nikolsky, 1963; Breton, 1978). Spawning of the summer-fall speciesoccurs predominantly from July-September, the period of maximum water temperature. The autumn drop in water temperature may curtail or end spawning for these species.The winter-spring speciesapparently spawn most heavily either in January-May when temperatures are near the annual minimum, or spawn all year long. The role of the photoperiod/temperature interaction hypothesized by many authors for spawning initiation is not discounted. The summer-fall spawners could indeed be using the summer solstice as a cue, as could the winter-spring spawners be using the winter ‘We consider upwelling events in the sense of ‘ meso-scale associated with cooling episodes of one or two weeks duration.
’ (Haury,
et al.,
19781,
100
H. J. Wulker
Jr et al.
c
* t-
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Searonality
ofnearshore
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larvalfish
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++
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GENYONEMUS
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7
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;-JJj--J
JAN70
JAN78
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JAN79
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JUL78
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JULBO
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JANB,
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LEUCOPSARIJS
VERTICALIS
to subgroups Bz and B, with highest in a 100-m wide ilongshore direction’
CITHARICHTHYS
STENOBRACHIUS
PLEURONICHTHYS
of selected fish larvae belonging represent numbers (in millions‘i
LEPIDUS
JAN00
SPP.
JAN00
CALfFORNlCUS
J”L78
J"L79
Figure 5. One-dimensional monthly mean abundances average abundance m uinter and spring. Abundances segment of ocean between the 6- and 75-m isobaths.
ATHERINIDAE
Figure 6. Temperature j above! and nitrate-nitrite (belowj records 6%year mean surface temperature recorded at the 6-m isobath off California. ---, (temperature) represents Scripps pier surface temperature recorded off San Onofre at the 12-15-m isobaths. identical to Scripps data and are not shown). The 10 nmol isopleth each year. Arrows indicate upwelling episodes.
for the three-year study period off San Onofre, California. ., the end of Scripps Institution of Oceanography pier, La Jolla, temperature for the particular year. p, yearly mid-depth (Surface temperatures off San Onofre, 1978-80, were nearly of nitrate-tnitrite, measured at the 30-m isobath, is shown for
104
H. J. Walker
Jr et
al.
--
solstice. This would agree in part with Hubbs (1985) and Marsh (1980) (both worked with the freshwater family Percidae) who believed that photoperiod was the dominant factor for the initiation of the spawning season and that temperature was the dominant factor for its termination. With regard to environmental influences on the timing of reproduction, Bye (1984) believed that habitat and ‘ lifestyle ’ are more important considerations than phylogenetic relationships. Kendall and Dunn (1985) also support part of this idea: they found that the species with demersal eggs spawned in late summer-fall, whilst spring-summer spawners had pelagic eggs. This is consistent with the species groups of this work, which are taxonomically heterogeneous but relatively homogeneous in terms of reproductive mode and spawning temperature. The year-round spawning of many demersal-spawning species may result from a combination of broad temperature tolerance and of low batch fecundity which may necessitate periodic spawning of egg clutches over a long time span to ensure reproductive success. Lambert and Ware (1984) also found reproductive seasons to be longer for demersal than for pelagic spawners. Although the annual temperature cycle, by its direct influence on reproduction and larval survival, may potentially account for the seasonal occurrence and abundance of temperate fish larvae, other environmental factors probably modify larval abundance during the spawning season.d For example, a lower abundance of larvae might be expected in the nearshore zone during upwelling periods (De Martini, pers. comm.; Lasker, 1978; Smith & Lasker, 1978). However, comparison of larval abundance with upwelling dates (see Appendix I) gave inconclusive results: abundance fluctuations during the spawning seasons were at least as great during non-upwelling periods as between upwelling and non-upwelling periods. Thus it is unclear whether upwelling is important in determining the abundance of fish larvae on the spatial and temporal scale of our sampling. Relationship of larval temporal distribution to adult zoogeography Briggs (1975) characterized the San Diego Warm-Temperate Province asa zone of mixing where speciesof northern and southern origin are brought into contact. Qasim (1955) stated that neritic speciesnearer the warmer limits of their range breed during the colder months of the year and speciesnearer the colder limits of their range breed during the warmer months of the year. Our data confirm this observation not only for neritic species, but also for epipelagic and mesopelagic species.The winter-spring larvae are primarily (69%) offspring of adults whosenorthern rangesgenerally extend to Canada (or rarely, to Oregon) (Miller & Lea, 1972). Among the mesopelagicspecieswhose adult ranges could be ascertained, five are northern forms (Bathylagus ochotensis, Leuroglossus stilbius, Diaphus theta, Protomyctophum crockeri and Stenobrachius leucopsarus) and their larvae were found in the colder months. Summer-fall larvae are principally (91 00) offspring of adults whose northern range limits or centers of distribution extend mainly to Point Conception or to Monterey, California; 99, range to Oregon (Miller & Lea, 1972). The species with centers of distribution in warm waters, but northern range endpoints extending beyond Monterey in warm years (Hubbs, 1948; Radovich, 1961; Miller & dFood is not considered a limiting factor in the Bight, with the possible exception of the fall period (Smith & Lasker, 1978). Although no critical evidence exists to discount starvation, nearly all larvae examined appeared robust, and rarely emaciated. Similarly, predation could not be evaluated. We observed little evidence of predation by zooplankters collected in the 1300 samples analyzed, but cannot assess the impact of predation by juvenile and adult fishes.
Seasonality of neat-shore larvaljish
105
Lea, 1972), are the neritic speciesSphyraena argentea, Seriola lalandi and Atractoscion nobilis, and the epipelagic species Scomber japonicus and Trachurus symmetricus. The remaining mesopelagic specieswhose adult range could be ascertained was Triphoturus mexicanus. Triphoturus mexicanus hasa southern distribution (Miller & Lea, 1972) and the larvae were found predominantly in the summer months. There were few exceptions to the relationship between the geographic distributions of the adults of neritic speciesand the temporal distributions of their larvae. Exceptions among the pelagic spawners were the pleuronectids Pleuronichthys ritteri, P. verticalis and Hypsopsetta guttulata. Although distributed northward only to central California or further south, they usually occurred in the winter and spring samples.These three species were the only pelagic spawners of the entire analysis that unexplainedly violated this relationship. Among the 10 winter-spring demersal spawners (whose larvae afforded enough taxonomic precision for geographic information) five were exceptions, reflecting the occurrence of these larvae throughout the year. Temperature frequently has been cited as the most important factor determining the world-wide distribution of poikilotherms (see,for example, Ekman, 1953; Gunter, 1957; Briggs, 1975), and this is true for California fishes(Horn 81Allen, 1978; Horn, 1980). The high degree of similarity within the winter-spring and summer-fall speciesgroups and their respective zoogeographic ranges indicates that temperature is the variable most influencing spawning in the Southern California Bight. This is also evident in shifts in spawning seasonover the geographic rangesof somewidely-ranging species.For example, in contrast to Southern California, the spawning seasonof Engraulis mordax is summer off the Oregon coast (Richardson & Pearcy, 1977) where this speciesnears its northern range limit (British Columbia: Miller 81Lea, 1972). Love et al. (1984) believe that the colder water off Monterey may account for the more extended spawning seasonof Genyonemus lineatus there than in the Southern California Bight. The distribution of Seriphuspolitus, the only species in the summer-fall assemblagewith consistently high abundance in spring, extends northward to Oregon. On the other hand, the spawning season for Parophrys vet&s is winter in both Southern California and Oregon waters (Pearcy & Myers, 1974); its distribution extends to north-west Alaska (Miller & Lea, 1972). Johannes (1978) used the term ‘ collective spawning peaks ’ to refer to certain times of the year when unusually large numbers of speciesand individuals within speciesreproduce. The data from this work support this concept, but the time frame for thesecollective spawning peaks appears to be broader in the Southern California Bight than in tropical waters. Our data suggestthat such periods of simultaneously increased spawning by large numbers of specieshave a duration of three to five months in the Southern California Bight, whereas in tropical waters these periods tend to have a duration of two to three months (Johannes, 1978). Basedon larval abundance, corroborated by adult zoogeography and recurring temperature patterns, we believe that January-May and July-September can be considered ‘ collective spawning periods ’ for fishes of the Southern California Bight.
Acknowledgements This paper is a result of research funded by the Marine Review Committee (MRC), Encinitas, California. The MRC does not necessarily accept the results, findings or conclusions stated herein.
106
H. J. WalkerJr
et al.
The authors wish to thank cruise leaders Kevin George, James Hare and Gloria Hoff who directed many nightly cruises, Capt. Robert Hundt, skipper of the R. V. LoAn, and numerous technicians who processed the samples. Raymond Davis, Vivian McCoy and Peter Steinkirchner assisted with figures and calculations. Rita Dave and David Williams were kindred spirits. Jeffrey Leis, Michael Marika and Patti Schmitt reviewed earlier versions of the manuscript. We thank Michelle Armstrong, Kathleen Pangborn and Judy Sabins for typing the manuscript in its many forms and Susan Watts who diligently addressed our statistical analysis. References Ahlstrom, U.S.
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Appendix
I
In order to confirm upwelling episodes inferred from the temperature record, profiles of dissolved nitrate and nitrite were examined. Water samples for nutrient analyses were not available at the 12-15-m stations, but were collected at a nearby 30-m station. Samples were collected with a cleaned and purged submersible pump (Little Giant), filtered first through 0.202~mm mesh Nitex and then through glass-fibre filters (Gelman Type AE) into acid-washed plastic bottles, and quick frozen in dry ice. These water samples were maintained in the laboratory at - 20°C until analyzed following the method of Strickland & Parsons (1972). The laboratory analyses indicated that (based on the 10 Fmol isopleth of nitrate-nitrite from the 30-m station) nutrient-rich water intruded into shallow depths (10 to -20-m) in the third week of April and last week of July, 1978, with a relatively high level maintained between these dates at deeper depths. Other episodes of shallow intrusion of nutrient-rich water included: a fairly long period beginning approximately 20 April and lasting until the
Seasonality of nearshore larvalfish
109
secondweek of May, 1979; the secondand third weeks of July, 1979; the last week of June to the first week of July, 1980. The coincidence of these shallow intrusions of nutrient-rich water with temperature depressionswere interpreted asupwelling episodes.From the combined temperature and nitrate-nitrite data we conclude that five upwelling episodesoccurred as shallow as the 15-m station in the years 1978-80. These were: the third week of April, 1978; the last week of July, 1978; the secondweek of May, 1979; the secondand third weeks of July, 1979; the second and third weeksof July, 1980. Near-shore upwelling might be expected to affect the distribution of fish larvae in shallow coastal waters. For example, upwelling hasbeen shown to disrupt aggregations of suitable food organisms for larval fish in the Bight and thus initially to be potentially detrimental to larval fish survival (Lasker, 1978). Upwelling also transports nearshore, planktonic organisms offshore where conditions are less favorable (Smith & Lasker, 1978). Adults of some inshore speciesof fish apparently move offshore to avoid areasof lowered temperatures resulting from upwelling (DeMartini, pers. comm.). Consequently, their spawning products would not be expected inshore during upwelling periods. To determine whether our data were suitable for addressing the question of potential upwelling effects on the nearshore distribution and abundance of fish larvae, we qualitatively compared abundances of Engraulis mordax, and of all other larvae combined, with the upwelling episodesidentified above. The abundance of E. mordax larvae substantially decreased on the sampling date during or following only two of the five upwelling episodes.The non-engraulid abundance decreasedduring or following three of the episodes. However, someabundance fluctuations during the spawning seasonswere at leastasgreat during non-upwelling periods. Thus we cannot evaluate the effect of upwelling using this data set.