- Email: [email protected]
Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions
Estuarine,
Coastal
and Shelf
Science
(1985) 21,365-378
Abundance and Distribution of Ichthyoplankton in the Upwelling Zone off Oregon During Anomalous El Niiio Conditions
Richard Pearcy’, “College Newport, Corvallis,
D. Brodeur”, Dena M. Gadomski”,‘, Harold P. Batchelde@ and Charles of Oceanography, Marine OR 97365, and bGollege OR 97331, U.S.A.
Received
23 May
Keywords: conditions;
1984
Science Center, of Oceanography,
and in revisedform
Oregon State University, Oregon State University,
30 October
ichthyoplankton; distribution; upwelling; Oregon Coast
William G. B. Millerb
1984
abundance;
environmental
The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engrazdis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Nifio could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.
Introduction
Much information has been gathered on the abundance and distribution patterns of ichthyoplankton during spring and summer in the upwelling zone off Oregon (Waldron, 1972; Richardson, 1973; Pearcy & Myers, 1974; Richardson & Pearcy, 1977; Richardson et al., 1980; Kendall & Clark, 1982a,b; Mundy, 1984; Boehlert et al., in press). These studies were conducted during years when upwelling predominated in the nearshore zone in summer, with nutrient-rich deep water of low temperature and high salinity replacing surface water advected offshore (Huyer, 1983). During the fall of 1982 through late summer of 1983, anomalous oceanographic conditions associated with a strong El Nirio-Southern Oscillation (ENSO) event were ‘Present address: Section 900 Exposition Boulevard,
of Fishes, Los Angeles County Los Angeles, CA 90007, U.S.A.
Natural
History
Museum,
365 0272-7714/85/090365
+ 14 $03.00/O
0 1985 Academic
Press Inc. fT.ondnn~
1 imiwrl
366
R. D. Brodeur et al.
Newpor9. /
I .
VA
Yaquino Bay
44’
>_
43
0
42
.a-
I270
126”
Newport
:
.‘:-,-
125”
124O
Figure 1. Location of stations occupied off the designators are distances in km from the coast.
123O
central
coast
of Oregon.
Station
witnessed throughout the entire Pacific Ocean (Cane, 1983). A surface layer of high temperature, low salinity offshore water was advected onshore along the western coast of North America resulting in extremely high sealevels, enhanced poleward transport and a substantial depression of the thermocline (Simpson, 1983, 1984~; McLain, 1984). Upwelling and southward transport of cold water and the normal ensuing plant production were reduced relative to more typical years (Fiedler, 1984). This study was initiated to investigate the effects of El Nifio on the zooplankton and ichthyoplankton off Oregon and was basedon sampling along one transect off the central Oregon Coast from April through September of 1983. Inshore-offshore and temporal patterns of distribution and abundance of fish larvae during these atypical oceanographic conditions are compared to those of previous years at the same locations to evaluate the possible effects of ENS0 conditions on the speciescomposition and abundance of larval fishes. A companion paper (Miller et al., in press) discussesthe results of the zooplankton study conducted simultaneously. Materials
and methods
Larval fishes were collected along the Newport Hydroline transect (44”39.1’N) off Yaquina Bay, Oregon at stations 2,6,9 and 18 km from the coast (Fig. 1) aboard the R V Sacajawea. Ten cruises were conducted between April and September, although not
Ichthyoplankton
during
anomalous
El Nirio
conditions
367
TABLE 1. Station occupancies and hydrographic data recorded at each station along the Newport Hydroline from April through September, 1983
Date 4 Apr 13 Apr
27 Apr
12 May
Station (km from coast)
Surface temperature (“0
6 9
11.5
6 9
11.9 10.7
18
11.0
2 6 9 18
13.2 13.3 12.5 12.1 13.4 13.2 13.3 12.7 -
2 6 9
18 23
May
-
9
June
2 6 9 18
7 July
2 6 9 18
21 July
6 9 18
Aug
2 6 9 18
19 Aug
2 6 9 18
13 Sep
2 6 9 18
4
Bottom salinity (S)
28.16 28.49 31.87 31.10 28.57
32.59 32.72 33.20
31.24 31.18 31.79 31.31
32.58 33.18
31.61 31.25 31.01 31.51
32.39 32.76 32.63 32.50
-
18 20
Surface salinity CM
14.9 15.1 14.8 14.5 14.4 15.0 15.4 14.6 16.7 17.1 17.2 14.6 15.4 14.5 14.4 10.0 10.0 10.2 10.2 14.8 15.3 14.9 15.9
31.44 31.44 31.36 31.09
32.55 33.34 33.69 33.24
31.96 31.75 31.58 31.37
33.02 33.41 33.59 33.69
31.47 30.61 32.13
33.37 33.59 33.63
32.20 32.17 31.92 31.74
32.96 33.57 33.59 33.66
33.37 33.32 33.12 32.96
33.53 33.57 33.57 33.56
32.14 31.98 31.71 32.08
33.08 33.19 33.16 33.43
every station was occupied on each cruise due to rough seaconditions (Table 1). Collections were made with a gimballed, bridleless 70-cm frame, fitted with a 0.333-mm Nitex cylindrical-conical net. In addition, the 9- and 18-km stations were sampled on one date (23 May) aboard the R V Wecoma using 70-cm bongo frames with one side containing an
identical 0.333-mm mesh net. All tows were oblique from near bottom to surface, interrupted during retrieval by 4-6 stepsof 1-min duration each. These tows were generally made parallel to depth contours
368
R. D. Brodeur er al.
at speedsof 2-3 knots for 8-20min (depending on depth). A calibrated flowmeter was mounted off-center in all nets to measure water volume filtered on each tow. A time-depth recorder was usedto determine depth and path of tow. Oceanographic measurements,made at all stations except those of the Wecoma cruise, included surface temperatures, surface salinities and bottom salinities. On most dates, a self-contained Applied Microsystems CTD-12 was used to obtain salinity and temperature profiles of the entire water column. The CTD was lowered approximately lOmmin-’ and had a responsetime of 2 s. Plankton sampleswere preserved at seain a loo, buffered-formalin seawatersolution. Sorting and identification procedures were similar to those described by Richardson (1977) and Richardson and Pearcy (1977). Many of the taxonomic problems discussed by these authors remain unresolved, although Washington (1982) was able to assign specific names to many of the unidentified cottid larval types. Standard lengths (SL) of larvae were measured with an ocular micrometer. Larval abundanceswere standardized to number under 10 m2 sea surface area following calculations given in Richardson (1977).
Results and discussion Larval
occurrence,
seasonality
and abundance
The 1220 larvae collected in the 38 tows belonged to 17 families and 39 larval types, of which 32 were identified species(Table 2). Northern anchovy (Engraulis mordax) larvae were collected on each sampling date and occurred in 86.8O0 of the tows. The only other taxa collected on all sampling dates were larvae of the genus Sebastes, presumably of several species,which were found in 68.4O, of the samples.All other taxa were found in lessthan half the collections and 16 were found only once. Over 90Y0 of the total standardized abundance was composed of larvae from five families: Engraulidae (51.29,); Pleuronectidae (17.7O,); Scorpaenidae (10.7”,,); Myctophidae (7.2?;); and Cottidae (4.30,“). One species, Engraulis mordax, accounted for over half the larvae collected (Table 2). Lyopsetta exilis, Psettichthys melanostictus and Isopsetta isolepis larvae were the most abundant pleuronectids taken; however, high abundances seldom occurred at any one station. In contrast, Stenobrachius leucopsarus, the dominant myctophid collected, had a more uneven distribution with 89O, of the larvae of this species taken at the 18-km station on 23 May. The cottids collected included several common species, most of which were taken in the early part of the study, except for a relatively high catch on 19 August. Richardson and Pearcy (1977) examined the inshore-offshore distribution of fish larvae from the Newport transect and classified most of the speciesthey found as either coastaltypes (80% of all larvae collected 2-28 km from the coast) or offshore types (80”,, of all larvae collected 37-l 11 km from the coast). Using this classification system, five of our ten most abundant species(including the four specieswith the highest standardized abundances)were considered offshore types (Table 2). Offshore larvae were numerically dominant in almost every tow with the exception of a few collections from the 2-km stations and also the 6- and 9-km stations on 19 August. The most abundant species collected in this study, Engraulis mordax, has been generally collected offshore in previous years. Larvae of this speciesoccurred at almost every station in each month (Fig. 2), and small larvae (3-4mm SL) were taken at the inshore stations in substantial numbers suggesting that adult anchovy spawned nearby.
Ichthyoplankton
TABLE 2. distributional September,
during
anomalous
Species composition, patterns of fish 1983
Taxa Engraulidae Engraulis
mordax
Osmeridae Undetermined Bathylagidae Bathylagus
spp.
conditions
369
frequency of occurrence, total abundance and larvae collected at all stations from April through
Number of occurrences (total = 38)
Total standardized abundance’
Total abundance (%)
33
794.56
51.16
0
Coastal/ offshore type’
1
1.32
0.08
c
2
4.79
0.31
0
Myctophidae Lampanyctus ritteri Protomyctophum crockeri Stenobrachius leucopsarus Tarletonbeania crenularis
1 1 7 2
0.48 1.45 96.59 12.98
0.03 0.09 6.22 0.84
(o:l
Gadidae Microgadus
9
35.05
2.26
C
1
1.35
0.09
0
26 4
153.93 11.92
9.91 0.77
0
Hexagrammidae Ophiodon elongatus
1
1.55
0.10
c
Cottidae Artediusfenestralis Artedius harringtoni Artedius meanyi Chitonows pugerensis Clinocotcus embryum Cottus asper Leptocottus armatus Radulinus asprellus Scorpaenichthys marmoratus
3 9 4 1 1 1 4 2 1
3.99 26.67 19.19 1.35 0.62 1.46 8.72 3.35 1.46
0.26 1.72 1.24 0.09 0.04 0.09 0.56 0.22 0.09
2
Agonidae Odontopyxis Undetermined
1 1
2.62 1.49
0.17 0.10
CC!
Cyclopteridae Liparis spp.
9
15.43
0.99
ic)
Bathymasteridae Ronquilus jordani
3
11.62
0.75
C
Stichaeidae Anoplarchus
spp.
1
1.46
0.09
C
Gobiidae Clevelandia
ios
4
9.20
059
C
2
2.85
0.18
0
1 1 I1
1.44 0.96 48.24
0.09 0.06 3.11
0
Bythitidae Brosmophycis
ochotensis
El Nifio
proximus marginata
Scorpaenidae Sebastes spp. Sebastolobus spp.
trispinosa spp.
Centrolophidae Icichthys lockingtoni Bothidae Citharichthys Citharichthys Citharichlhys
sordidus srigmaeus sp~.~
0 0 0
0
C4 cs C Cb C C-O C C
C
C 0
370
R. D. Brodeur
et
al.
TABLE 2. (Continued)
Taxa
Number of occurrences (total = 38)
Pleuronectidae Glyptocephalus zachirus Isopsetta isolepis Lyopsetta exilis Microstomus pacificus Parophrys vet&s Platichthys stellatus Pleuronichth_ys coenosus Psettichthys melanostictus
7 10 14 1 7 3 1 15
Z no. larvae under 10 m2 sea surface: Mean no. larvae under 10 m2 sea surface:
Total standardized abundance’
14.41 57.20 105.88 1.47 24.02 5.69 0.62 65.76
Total abundance (I’,,)
0.93 3.68 6.82 0.09 1.55 0.37 0.04 4.23
Coastal. offshore type*
0 C 0 0 C C CC) C
1553.14 40.87
‘Expressed as the sum of the standardized number of larvae below 10 mz of sea surface. *Distribution patterns assigned by Richardson and Pearcy (1977): c = coastal type ( > 80° o of larvae taken 2-28 km from coast); o = offshore type ( > 80° U of larvae taken 37-l 11 km from coast). Distribution patterns in parentheses represent species not collected by Richardson and Pearcy (1977) but were based on larval distributions found for that species in other studies. 31dentified as Artedius sp. 2 by Richardson and Pearcy. “Identified as Artedius sp. 1 by Richardson and Pearcy. SIdentified as Icelinus sp. 1 by Richardson and Pearcy. ‘Identified as Cottidae sp. 20 by Richardson and Pearcy. ‘Specimens too small to identify to species.
Richardson (1977) rarely caught E. mordux larvae at the 2- to 18-km stations. Moreover, she generally found the highest abundances of E. mordax farther than 46 km offshore. Mundy (1984) also found low abundances and occurrences of this speciesat the same stations from 1969 to 1972. Richardson (1980), drawing on extensive collections along the Oregon-Washington coast, concluded that E. mordax larvae were associatedwith Columbia River plume waters, which generally occur well offshore at the latitude of Newport during normal upwelling years. Pearcy and Myers (1974) collected some E. mordax at the inshore stations aswell asfar inside Yaquina Bay, but these were probably late larvae or juveniles which are known to inhabit estuaries and are often captured in plankton nets. In addition to unusually high abundance of E. mordax larvae inshore, the larvae of this speciesappeared much earlier in 1983 than in most previous years. A broad size range of E. mordux larvae were taken during April, the first month of sampling (Fig. 2). Larvae over 12 mm were found on the first sampling date (4 April), indicating that spawning must have occurred somewhat earlier. The appearanceof small larvae late in the summer (Fig. 2) and the occurrence of eggs as late as 20 June further suggests prolonged spawning of this species. Richardson (1973), analyzing samplescollected in 1969 with several different types of sampling gear from many different locations off Oregon and Washington, found no anchovy larvae in May and very low abundances in June, although abundances were very high later in the summer. Similarly, Richardson (1977) did not find larval E. mordax along the Newport transect until 28 June in either 1971 or 1972 despite intensive sampling previous to that date. Richardson et al. (1980), on the
Ichthyoplankton
during
anomalous
El Ninlo
37 I.
conditions
STATION 2krn
9 km
6 km
18 km
35 -
5. . 10
. 20
30
. . . 10 20 STANDARD
Figure 2. Length 1983. Abundances for each station.
30 LENGTH
SEPT
.I. (0
20
30
10
20
30
(mm)
frequency distributions for Engraulis mordax are mean values for each month standardized
larvae collected during (no. larvae per 10 m’)
other hand, showed that E. mordax larvae occurred in low numbers in March and April of 1973, but not during the spring of 1972,1974 and 1975. The seasurface temperatures in early 1973 were above normal due to a mild winter (Laroche & Richardson, 1979). Therefore, this early occurrence of anchovy larvae in 1983 is unusual, but not unprecedented. Other taxa designated as offshore types by Richardson and Pearcy (1977) include the myctophid species Stenobrachius leucopsarus and Tarletonbeania crenularis, the scorpaenid genus Sebastes, and the pleuronectid species Glyptocephalus zachirus and Lyopsetta jordani. Although these taxa have been previously found inshore of 18 km (Richardson, 1977; Mundy, 1984), their abundances were substantially higher in 1983 than in prior years. Three taxa that occurred at least twice in our collections, Sebastolobus spp., Bathylagus ochotensis and Zcichthys lockingtoni, were never found inside of 46 km by Richardson (1977), and the latter two were only rarely found inshore of 18 km in four years of sampling by Mundy (1984). We collected other larvae which have rarely been taken inshore including Lampanyctus ritteri, Protomyctophum crockeri, Brosmophycis marginata and Microstomus pacificus. Increases in the occurrence and abundance of offshore larvae in 1983 were accompanied by decreasesin the abundance of inshore taxa commonly found at these stations. Osmerid larvae were the most abundant taxa collected by Pearcy and Myers (1974), Richardson (1977) and Mundy (1984), especially during the period from April to June. We collected only one osmerid larva at the 6-km station on 13 September, which places this group among our rarest taxa. Other inshore specieswhich were found less commonly in 1983 than in previous years include Microgadus proximus, Artedius meanyi, Artedius harringtoni, Zsopsetta isolepis and Platichthys stellatus.
R. D. Brodeur et al.
373
TABLE 3. The ten taxa ranked most abundant abundant taxa collected from 2 to 18 km offshore 1972. All abundances are standardized to number
1983”
in 1983 compared to the ten most from April to September of 1971 and per 10 mz sea surface area
1971b
Engraulis mordax Sebastes spp. Lyopsetta exilis Stenobrachius leucopsarus Psettichthys melanostictus Isopsetta isolepis Citharichthys spp. Microgadus proximus Artedius harringtoni Parophrys vet&s
0
1972b
Osmeridae
c31-----@ o-
0
Osmeridae I. isolepis
L1 Artedius Spearman
rank correlation
meanyi
analysis
rs= -0.307
r,=0.839 I rr=
“Data
from present
study
-0.382
and bfrom
Richardson
(1977).
The ten most abundant taxa ranked by standardized abundance collected in 1983 are compared in Table 3 with the ten most abundant taxa collected from 2 to 18km off Newport from April to September of 1971 and 1972 by Richardson (1977). There is a strong coherence between the rankings of 1971 and 1972 (Spearman rank correlation, r =0.839), despite the fact that these two years were quite different hydrographically (Peterson & Miller, 1975). Many of the dominant taxa were different in 1983 and the rank order of abundance was negatively correlated with both 1971(r = -0.307) and 1972 (r = - 0.382).
The overall standardized abundance patterns seen in our study (Fig. 3) were somewhat different than those found by Richardson and Pearcy (1977) for 1971. They found a peak in abundance for the inshore larval fish assemblageoccurring from May through July with the modal abundance occurring in mid-June. Our peak abundances occurred in the middle to late part of April and again in late July (Fig. 3). These seasonal patterns, however, are strongly influenced by the dominant taxa. Osmerids comprised 717; of the larvae collected by Richardson and Pearcy during their summer upwelling peak. Anchovy larvae madeup almost 53% of the larvae we collected from 13 April to 21 July and contributed substantially to our major peaks. Our overall abundances were also much lower than those found by Richardson and Pearcy (1977) by a factor of 2-3. Part of this difference may be attributed to the useof slightly different gear and sampling on different dates within the sameseason.This difference, however, is probably conservative becauseof the decreasedretention of small larvae by the 0.571-mm mesh nets used in 1971vs. the 0.333-mm mesh nets we used in 1983 (Lenarz, 1972). Relation
of larval
catches to oceanographic
conditions
Sea surface temperatures were unusually warm early in April and continued to increase at most stations until the 21 July sampling date (Table 1). A moderate drop in
Ichthyoplankton
during
anomalous
El NiZo
373
conditions
/ -
I -
, -
I-
J
,-
M
A
M
J
A
J
0
S
MONTHS
Figure
3. Mean
standardized
I M
abundance
I A
I M
(no. larvae
I
I
I J
J
per 10 m’) for each cruise in 1983.
A
I S
0
MONTHS
Figure 4. Comparison of sea surface those of 1969-1972 [data from Mundy
temperatures (1984)].
at the 9-km
station
for
1983 with
temperature occurred on the next sampling date followed by a precipitous decrease on 19 August and a substantial rise on the last sampling date. For comparison, the surface temperature data for the 9-km station from 1983 are shown with similar measurements from the years 1969-1972 [data from Mundy (1984)] in Fig. 4. In all the previous years, surface temperatures either remained low throughout the summer, or fluctuated about a
374
R. D. Brodeur et al.
Distance
offshore
Dlstonce
(km)
offshore
(km)
18
9
6
2
18
9
6
2
18
9
6
2
18
9
6
2
Figure 5. Vertical temperature sections derived from CTD casts made at the indicated stations off Newport in 1983. All isotherms are in “C. The 10-l 1°C isotherms are stippled for comparative purposes.
much lower mean level than in 1983. High seasurface temperatures alsooccurred during June and August of 1971 and were associatedwith weak upwelling (Peterson 81Miller, 1975). The CTD vertical temperature sections (Fig. 5) indicate a persistent but gradually shallowing thermocline through 4 August 1983. On the next sampling date (19 August) conditions were relatively isothermal, probably resulting from an upwelling event that was evident in the daily upwelling indices during a five day period immediately preceding this date (A. Bakun, Pacific Environmental Group, personal communication). The stratified water column and the surface temperatures returned to conditions similar to those found in mid-summer by 13 September. The salinity data show similar trends (Table 1). The surface salinities were below 32.5% for much of the summer, indicating the probable nearshore presenceof Columbia River plume water (Barnes et al., 1972). The vertical salinity structure (Fig. 6) again suggeststhat the water column was stratified through much of the summer. The exceptional profile of 19 August, when the isohalines slant sharply upwards toward the coast, is indicative of upwelling. Upwelling indices based on wind stress calculations at 45”N and 125”W (Andrew Bakun, Pacific Environmental Group, personal communication) were similar to the long-term average during April and May but were substantially lower than the longterm advantage from June through early August of 1983 (Table 4). This weak upwelling, in conjunction with a deep thermocline associatedwith the 1982-1983 El Nifio, resulted in reduced entrainment of cool, nutrient-enriched water into the euphotic zone off Oregon through most of the usual upwelling season.As a result, surface chlorophyll concentrations were below normal for most of the 1983 suIlltner months and subsurface
Ichthyoplankton
Dlstonce
during
offshore
18
9
anomalous
El Niiio
(km) 6
Dlstonce 2
18
conditions
375
offshore 9
(km) 6
2
.3 D L . : ..&.~z” ’ 0 .&?&$s; y ‘.‘.... m n
IR
r
I
?
18
9
6
2
18
9
6
2
31.5
52Q ,.:.:.: :,,~;:.:.:.,
20 30 40 50 60
-33.0 -33.5
20 June
,. 20 30 40 50 60 70
Figure stations stippled
6. Vertical salinity sections derived off Newport in 1983. All isohalines for comparative purposes.
TABLE 4. Mean monthly upwelling Bakun, personal communication) upwelling indices at 45”N, 125”W Month
8
May June July Aw Sep
35
19 19 41 28
at the indicated %O isohalines are
indices from April through September of 1983 (A. and anomalies from the 1948-1967 overall mean (Bakun, 1973)
1983 Index
Apr
from CTD casts made are in %. The 32.0-325
Anomaly -1 +1 -29
-55 -9 f12
chlorophyll maxima, typical of non-upwelling conditions, were often observed (Miller et al., in press). The unusual larval fish catches in 1983 were correlated with these hydrographic conditions. Species from the offshore assemblage dominated the catches at most stations until 19 August, when many inshore taxa were apparently transported offshore and were collected in substantial numbers at the 2-, 6- and 9-km stations. Abundances of typical offshore taxa such as Engraulis mordax and Sebastes spp. were very low on this same date but showed a moderate resurgence in September. Weak coastal upwelling was probably unfavourable to the survival of fish larvae that normally are abundant inshore. In addition, onshore transport of oceanic or Columbia
376
R. D. Brodeur et al.
River plume waters apparently provided a mechanism to increasethe abundance of offshore ichthyoplankton speciesin waters near the coast during spring and early summer. The limited vertical distribution data that exist for ichthyoplankton off Oregon (Richardson & Pearcy, 1977; Boehlert et al., in press) show that many of the speciesof the offshore assemblagewhich were common inshore in 1983 (e.g. E. mordax, Sebastes spp., Lyopsetta exilis, Stenobrachius leucopsarus and Glyptocephalus zachirus) are abundant in shallow waters at some time during the day and are often collected within 5 m of the surface. Residenceat this depth would render these speciessusceptible to offshore transport of surface layers during normal upwelling conditions and to onshore transport when winds are from the south or west. Although both Richardson and Pearcy (1977) and Mundy (1984) document interannual variability in larval fish species abundance patterns off Oregon, they did not document so great a shift in the dominant taxa aswe found in 1983. Long-term fluctuations in the physical and biological characteristics of the California Current are known to occur (Chelton et al., 1982; Simpson, 1984b). However, the unusually strong mid-latitude El Niiio of 1982-1983 may have substantially altered biological conditions off Oregon, thus limiting the survival potential of many specieswhich have spawning seasonskeyed to the normal upwelling cycle. Richardson (1980) suggeststhat the relatively stable and productive Columbia River plume provides a suitable spawning area for the northern subpopulation of anchovy centered off Oregon. Sexually immature northern anchovy are found in nearshore waters during spring and ripening adults normally move offshore of 65 km to spawn (Laroche & Richardson, 1980). Richardson (1980) further suggeststhat adult anchovy only spawn in waters warmer than 13°C found mainly in the Columbia River plume during the typical upwelling season.The relatively warm, stratified conditions that persisted throughout much of the area for most of the spring and summer of 1983 apparently provided northern anchovy an inshore spawning ground off Oregon over an expanded spawning season. In a comparison of three hydrographically different years, Lasker (1981) found that survival of E. mordax off southern California, asmeasured by subsequentyear-class contributions to the fishery, was greatest in years of reduced upwelling and increased water column stability. Survival was reduced during years of substantial upwelling or strong turbulence causedby storms. Although northern anchovy larvae had broad spatial and temporal distributions off Oregon in 1983, prospects for the eventual survival of the 1983 year-class of northern anchovy as well asother spring and summer spawning fish species off Oregon are uncertain because of the low levels of production associated with the much reduced upwelling.
Acknowledgements We thank the following from Oregon State University for their assistancein this study: R. Barrell, A. Chung, J. Fisher, J. Kalish, R. Merrick and M. Willis for their help at sea; B. Mundy for assistancein identifying fish larvae and for suggesting improvements on the manuscript; R. Smith and A. Huyer for useful discussions on the physical oceanography off Oregon. We also thank A. Bakun from the NOAA Pacific Environmental Group for allowing us to use some of his unpublished data. Special thanks to J. A. McGowan of Scripps Institution of Oceanography for suggestingthat the
Ichthyoplankton
during
anomalous
El Nirio
conditions
study be done. This study was funded by the Oregon State University Program and National Science Foundation Grant No. OCE-8201899.
377
Sea Grant
References Bakun, A. 1973 Coastal upwelling indices, west coast of North America, 1946-71. U.S. Department of Commerce, NOAA Technical Report NMFS SSRF 671.103 pp. Barnes, C. A., Duxbury, A. C. & Morse, B. A. 1972 Circulation and selected properties of the Columbia River effluent at sea. In The Columbia River Estuary and Adjacent Ocean Waters; Bioenvironmental Studies (Pruter, A. T. 81 Alverson, D. L., eds). University of Washington Press, Seattle. pp. 41-80. Boehlert, G. W., Gadomski, D. M. & Mundy, B. C. (in press) Vertical distribution of ichthyoplankton off the Oregon coast in spring and summer months. Fishery Bullerin, 83(4). Cane, M. A. 1983 Oceanographic events during El Nirio. Science, 222,1189-1195. Chelton, D. B., Bernal, I’. B. & McGowan, J. A. 1982 Large-scale interannual physical and biological interaction in the California Current.Journal ofMarine Research, 40, 1095-l 125. Fiedler, I’. C. 1984 Satellite observations of the 1982-1983 El Nina along the U.S. Pacific Coast. Science, 224,1251-1254. Huyer, A. 1983 Coastal upwelling in the California Current System. Progress in Oceanography, 12,259-284. Kendall, A. W., Jr. St Clark, J. R. 1982a Ichthyoplankton off Washington, Oregon, and Northern California, April-May 1980. U.S. Department of Commerce, NMFS NWAFC Processed Report 82-l 1.44 pp. Kendall, A. W., Jr & Clark, J. R. 19826 Ichthyoplankton off Washington, Oregon, and Northern California, August 1980. U.S. Department of Commerce, NMFS NWAFC Processed Report 82-12.43 pp. Laroche, J. L. & Richardson, S. L. 1979 Winter-spring abundance of larval English sole, F’arophrys vetulus, between the Columbia River and Cape Blanco, Oregon during 1972-1975 with notes on occurrences of three other pleuronectids. Estuarine and Coastal Marine Science, 8,455-476. Laroche, J. L. & Richardson, S. L. 1980 Reproduction of northern anchovy, Engraulis mordax, off Oregon and Washington. Fishery Bulletin, 78,603-618. Lasker, R. 1981 Factors contributing to variable recruitment of the northern anchovy (Engraulis mordax) in the California Current: contrasting years, 1975 through 1978. Rapports et Proces-verbaux des Reunions du Conseil International pour I’Exploration de la Mer, 178.375-388. Lenarz, W. H. 1972 Mesh retention of larvae of Sardinops caerula and Engraulis mordax by plankton nets. Fisherv Bulletin. 70.839-848. McLain, D. R. 1984 Coastal ocean warming in the Northeast Pacific, 1976-83. In The Znfluence of Ocean Conditions on the Production of Salmonids in the North Pacific (Pearcv, W. G.. ed.). Oreeon State ’ University Sea Grant College Program Publication ORESU-W-83-001.?27 pp. ’ Miller, C. B., Batchelder, H. I’., Brodeur, R. B. & Pearcy, W. G. (in press) Response of the zooplankton and ichthyoplankton off Oregon to the El Nifio event of 1983. El Nifio North: Nifio effects in the Subarctic Pacific Ocean (W. S. Wooster & Fluharty, D. L., eds). University of Washington Sea Grant Publication. Mundy, B. C. 1984 Yearly variation in the abundance and distribution of fish larvae in the coastal upwelling zone off Yaquina Head, Oregon from June 1969 to August 1972. M. S. Thesis, Oregon State University, Corvallis. 158 pp. Pearcy, W. G. & Myers, S. S. 1974 Larval fishes of Yaquina Bay, Oregon: a nursery ground for marine fishes? Fishery Bulletin, 72,201-213. Peterson, W. T. & Miller, C. B. 1975 Year-to-year variations in the planktology of the Oregon upwelling zone. Fishery Bulletin, ?3,642-653. Richardson, S. L. 1973 Abundance and distribution of larval fishes in waters off Oregon, May-October 1969, with special emphasis on the northern anchovy, Engraulis mordax. Fishery Bulletin, 71,697-711. Richardson, S. L. 1977 Larval fishes in ocean waters off Yaquina Bay, Oregon: abundance, distribution and seasonality, January 1971 to August 1972. Oregon State University Sea Grant College Program Publication ORESUT-77-003. 73 pp. Richardson, S. L. 1980 Spawning biomass and early life of northern anchovy, Engraulis mordax, in the northern subpopulation off Oregon and Washington. Fishery Bulletin, 78,855-876. Richardson, S. L. & Pearcy, W. G. 1977 Coastal and oceanic fish larvae in an area of upwelling off Yaquina Bay, Oregon. Fishery Bulletin, 75, 125-145. Richardson, S. L., Laroche, J. L. & Richardson, M. D. 1980 Larval fish assemblages in the northeast Pacific Ocean along the Oregon coast, winter-spring 1972-1975. Estuarine and Coastal Marine Science, 11, 671-699. Simpson, J. J. 1983 Large-scale thermal anomalies in the California Current during the 1982-1983 El Niiio. Geophysical Research Letters, 10,937-940. ,
I
378
R. D. Brodeur
et al.
Simpson, J. J. 1984a El Nifio-induced onshore transport in the California Current during 1982-1983. Geophysical Research Letters, 11,233-236. Simpson, J. J. 19846 A simple model of the 1982-83 Californian ‘ El-Niiio ‘. Geophysical Research Letters, 11,237-240. Waldron, K. D. 1972 Fish larvae collected from the northeastern Pacific Ocean and Puget Sound during April and May 1967. U.S. Department of Commerce, NOAA Technical Report NMFS SSRF-663. 16 PP. Washington, B. B. 1982 Identification and Systematics of larvae of Artedius, Clinocottus, and Oligocottus (Scorpaeniformes: Cottidae). M.S. Thesis, Oregon State University, Corvallis. 192 pp.
Coastal
and Shelf
Science
(1985) 21,365-378
Abundance and Distribution of Ichthyoplankton in the Upwelling Zone off Oregon During Anomalous El Niiio Conditions
Richard Pearcy’, “College Newport, Corvallis,
D. Brodeur”, Dena M. Gadomski”,‘, Harold P. Batchelde@ and Charles of Oceanography, Marine OR 97365, and bGollege OR 97331, U.S.A.
Received
23 May
Keywords: conditions;
1984
Science Center, of Oceanography,
and in revisedform
Oregon State University, Oregon State University,
30 October
ichthyoplankton; distribution; upwelling; Oregon Coast
William G. B. Millerb
1984
abundance;
environmental
The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engrazdis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Nifio could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.
Introduction
Much information has been gathered on the abundance and distribution patterns of ichthyoplankton during spring and summer in the upwelling zone off Oregon (Waldron, 1972; Richardson, 1973; Pearcy & Myers, 1974; Richardson & Pearcy, 1977; Richardson et al., 1980; Kendall & Clark, 1982a,b; Mundy, 1984; Boehlert et al., in press). These studies were conducted during years when upwelling predominated in the nearshore zone in summer, with nutrient-rich deep water of low temperature and high salinity replacing surface water advected offshore (Huyer, 1983). During the fall of 1982 through late summer of 1983, anomalous oceanographic conditions associated with a strong El Nirio-Southern Oscillation (ENSO) event were ‘Present address: Section 900 Exposition Boulevard,
of Fishes, Los Angeles County Los Angeles, CA 90007, U.S.A.
Natural
History
Museum,
365 0272-7714/85/090365
+ 14 $03.00/O
0 1985 Academic
Press Inc. fT.ondnn~
1 imiwrl
366
R. D. Brodeur et al.
Newpor9. /
I .
VA
Yaquino Bay
44’
>_
43
0
42
.a-
I270
126”
Newport
:
.‘:-,-
125”
124O
Figure 1. Location of stations occupied off the designators are distances in km from the coast.
123O
central
coast
of Oregon.
Station
witnessed throughout the entire Pacific Ocean (Cane, 1983). A surface layer of high temperature, low salinity offshore water was advected onshore along the western coast of North America resulting in extremely high sealevels, enhanced poleward transport and a substantial depression of the thermocline (Simpson, 1983, 1984~; McLain, 1984). Upwelling and southward transport of cold water and the normal ensuing plant production were reduced relative to more typical years (Fiedler, 1984). This study was initiated to investigate the effects of El Nifio on the zooplankton and ichthyoplankton off Oregon and was basedon sampling along one transect off the central Oregon Coast from April through September of 1983. Inshore-offshore and temporal patterns of distribution and abundance of fish larvae during these atypical oceanographic conditions are compared to those of previous years at the same locations to evaluate the possible effects of ENS0 conditions on the speciescomposition and abundance of larval fishes. A companion paper (Miller et al., in press) discussesthe results of the zooplankton study conducted simultaneously. Materials
and methods
Larval fishes were collected along the Newport Hydroline transect (44”39.1’N) off Yaquina Bay, Oregon at stations 2,6,9 and 18 km from the coast (Fig. 1) aboard the R V Sacajawea. Ten cruises were conducted between April and September, although not
Ichthyoplankton
during
anomalous
El Nirio
conditions
367
TABLE 1. Station occupancies and hydrographic data recorded at each station along the Newport Hydroline from April through September, 1983
Date 4 Apr 13 Apr
27 Apr
12 May
Station (km from coast)
Surface temperature (“0
6 9
11.5
6 9
11.9 10.7
18
11.0
2 6 9 18
13.2 13.3 12.5 12.1 13.4 13.2 13.3 12.7 -
2 6 9
18 23
May
-
9
June
2 6 9 18
7 July
2 6 9 18
21 July
6 9 18
Aug
2 6 9 18
19 Aug
2 6 9 18
13 Sep
2 6 9 18
4
Bottom salinity (S)
28.16 28.49 31.87 31.10 28.57
32.59 32.72 33.20
31.24 31.18 31.79 31.31
32.58 33.18
31.61 31.25 31.01 31.51
32.39 32.76 32.63 32.50
-
18 20
Surface salinity CM
14.9 15.1 14.8 14.5 14.4 15.0 15.4 14.6 16.7 17.1 17.2 14.6 15.4 14.5 14.4 10.0 10.0 10.2 10.2 14.8 15.3 14.9 15.9
31.44 31.44 31.36 31.09
32.55 33.34 33.69 33.24
31.96 31.75 31.58 31.37
33.02 33.41 33.59 33.69
31.47 30.61 32.13
33.37 33.59 33.63
32.20 32.17 31.92 31.74
32.96 33.57 33.59 33.66
33.37 33.32 33.12 32.96
33.53 33.57 33.57 33.56
32.14 31.98 31.71 32.08
33.08 33.19 33.16 33.43
every station was occupied on each cruise due to rough seaconditions (Table 1). Collections were made with a gimballed, bridleless 70-cm frame, fitted with a 0.333-mm Nitex cylindrical-conical net. In addition, the 9- and 18-km stations were sampled on one date (23 May) aboard the R V Wecoma using 70-cm bongo frames with one side containing an
identical 0.333-mm mesh net. All tows were oblique from near bottom to surface, interrupted during retrieval by 4-6 stepsof 1-min duration each. These tows were generally made parallel to depth contours
368
R. D. Brodeur er al.
at speedsof 2-3 knots for 8-20min (depending on depth). A calibrated flowmeter was mounted off-center in all nets to measure water volume filtered on each tow. A time-depth recorder was usedto determine depth and path of tow. Oceanographic measurements,made at all stations except those of the Wecoma cruise, included surface temperatures, surface salinities and bottom salinities. On most dates, a self-contained Applied Microsystems CTD-12 was used to obtain salinity and temperature profiles of the entire water column. The CTD was lowered approximately lOmmin-’ and had a responsetime of 2 s. Plankton sampleswere preserved at seain a loo, buffered-formalin seawatersolution. Sorting and identification procedures were similar to those described by Richardson (1977) and Richardson and Pearcy (1977). Many of the taxonomic problems discussed by these authors remain unresolved, although Washington (1982) was able to assign specific names to many of the unidentified cottid larval types. Standard lengths (SL) of larvae were measured with an ocular micrometer. Larval abundanceswere standardized to number under 10 m2 sea surface area following calculations given in Richardson (1977).
Results and discussion Larval
occurrence,
seasonality
and abundance
The 1220 larvae collected in the 38 tows belonged to 17 families and 39 larval types, of which 32 were identified species(Table 2). Northern anchovy (Engraulis mordax) larvae were collected on each sampling date and occurred in 86.8O0 of the tows. The only other taxa collected on all sampling dates were larvae of the genus Sebastes, presumably of several species,which were found in 68.4O, of the samples.All other taxa were found in lessthan half the collections and 16 were found only once. Over 90Y0 of the total standardized abundance was composed of larvae from five families: Engraulidae (51.29,); Pleuronectidae (17.7O,); Scorpaenidae (10.7”,,); Myctophidae (7.2?;); and Cottidae (4.30,“). One species, Engraulis mordax, accounted for over half the larvae collected (Table 2). Lyopsetta exilis, Psettichthys melanostictus and Isopsetta isolepis larvae were the most abundant pleuronectids taken; however, high abundances seldom occurred at any one station. In contrast, Stenobrachius leucopsarus, the dominant myctophid collected, had a more uneven distribution with 89O, of the larvae of this species taken at the 18-km station on 23 May. The cottids collected included several common species, most of which were taken in the early part of the study, except for a relatively high catch on 19 August. Richardson and Pearcy (1977) examined the inshore-offshore distribution of fish larvae from the Newport transect and classified most of the speciesthey found as either coastaltypes (80% of all larvae collected 2-28 km from the coast) or offshore types (80”,, of all larvae collected 37-l 11 km from the coast). Using this classification system, five of our ten most abundant species(including the four specieswith the highest standardized abundances)were considered offshore types (Table 2). Offshore larvae were numerically dominant in almost every tow with the exception of a few collections from the 2-km stations and also the 6- and 9-km stations on 19 August. The most abundant species collected in this study, Engraulis mordax, has been generally collected offshore in previous years. Larvae of this speciesoccurred at almost every station in each month (Fig. 2), and small larvae (3-4mm SL) were taken at the inshore stations in substantial numbers suggesting that adult anchovy spawned nearby.
Ichthyoplankton
TABLE 2. distributional September,
during
anomalous
Species composition, patterns of fish 1983
Taxa Engraulidae Engraulis
mordax
Osmeridae Undetermined Bathylagidae Bathylagus
spp.
conditions
369
frequency of occurrence, total abundance and larvae collected at all stations from April through
Number of occurrences (total = 38)
Total standardized abundance’
Total abundance (%)
33
794.56
51.16
0
Coastal/ offshore type’
1
1.32
0.08
c
2
4.79
0.31
0
Myctophidae Lampanyctus ritteri Protomyctophum crockeri Stenobrachius leucopsarus Tarletonbeania crenularis
1 1 7 2
0.48 1.45 96.59 12.98
0.03 0.09 6.22 0.84
(o:l
Gadidae Microgadus
9
35.05
2.26
C
1
1.35
0.09
0
26 4
153.93 11.92
9.91 0.77
0
Hexagrammidae Ophiodon elongatus
1
1.55
0.10
c
Cottidae Artediusfenestralis Artedius harringtoni Artedius meanyi Chitonows pugerensis Clinocotcus embryum Cottus asper Leptocottus armatus Radulinus asprellus Scorpaenichthys marmoratus
3 9 4 1 1 1 4 2 1
3.99 26.67 19.19 1.35 0.62 1.46 8.72 3.35 1.46
0.26 1.72 1.24 0.09 0.04 0.09 0.56 0.22 0.09
2
Agonidae Odontopyxis Undetermined
1 1
2.62 1.49
0.17 0.10
CC!
Cyclopteridae Liparis spp.
9
15.43
0.99
ic)
Bathymasteridae Ronquilus jordani
3
11.62
0.75
C
Stichaeidae Anoplarchus
spp.
1
1.46
0.09
C
Gobiidae Clevelandia
ios
4
9.20
059
C
2
2.85
0.18
0
1 1 I1
1.44 0.96 48.24
0.09 0.06 3.11
0
Bythitidae Brosmophycis
ochotensis
El Nifio
proximus marginata
Scorpaenidae Sebastes spp. Sebastolobus spp.
trispinosa spp.
Centrolophidae Icichthys lockingtoni Bothidae Citharichthys Citharichthys Citharichlhys
sordidus srigmaeus sp~.~
0 0 0
0
C4 cs C Cb C C-O C C
C
C 0
370
R. D. Brodeur
et
al.
TABLE 2. (Continued)
Taxa
Number of occurrences (total = 38)
Pleuronectidae Glyptocephalus zachirus Isopsetta isolepis Lyopsetta exilis Microstomus pacificus Parophrys vet&s Platichthys stellatus Pleuronichth_ys coenosus Psettichthys melanostictus
7 10 14 1 7 3 1 15
Z no. larvae under 10 m2 sea surface: Mean no. larvae under 10 m2 sea surface:
Total standardized abundance’
14.41 57.20 105.88 1.47 24.02 5.69 0.62 65.76
Total abundance (I’,,)
0.93 3.68 6.82 0.09 1.55 0.37 0.04 4.23
Coastal. offshore type*
0 C 0 0 C C CC) C
1553.14 40.87
‘Expressed as the sum of the standardized number of larvae below 10 mz of sea surface. *Distribution patterns assigned by Richardson and Pearcy (1977): c = coastal type ( > 80° o of larvae taken 2-28 km from coast); o = offshore type ( > 80° U of larvae taken 37-l 11 km from coast). Distribution patterns in parentheses represent species not collected by Richardson and Pearcy (1977) but were based on larval distributions found for that species in other studies. 31dentified as Artedius sp. 2 by Richardson and Pearcy. “Identified as Artedius sp. 1 by Richardson and Pearcy. SIdentified as Icelinus sp. 1 by Richardson and Pearcy. ‘Identified as Cottidae sp. 20 by Richardson and Pearcy. ‘Specimens too small to identify to species.
Richardson (1977) rarely caught E. mordux larvae at the 2- to 18-km stations. Moreover, she generally found the highest abundances of E. mordax farther than 46 km offshore. Mundy (1984) also found low abundances and occurrences of this speciesat the same stations from 1969 to 1972. Richardson (1980), drawing on extensive collections along the Oregon-Washington coast, concluded that E. mordax larvae were associatedwith Columbia River plume waters, which generally occur well offshore at the latitude of Newport during normal upwelling years. Pearcy and Myers (1974) collected some E. mordax at the inshore stations aswell asfar inside Yaquina Bay, but these were probably late larvae or juveniles which are known to inhabit estuaries and are often captured in plankton nets. In addition to unusually high abundance of E. mordax larvae inshore, the larvae of this speciesappeared much earlier in 1983 than in most previous years. A broad size range of E. mordux larvae were taken during April, the first month of sampling (Fig. 2). Larvae over 12 mm were found on the first sampling date (4 April), indicating that spawning must have occurred somewhat earlier. The appearanceof small larvae late in the summer (Fig. 2) and the occurrence of eggs as late as 20 June further suggests prolonged spawning of this species. Richardson (1973), analyzing samplescollected in 1969 with several different types of sampling gear from many different locations off Oregon and Washington, found no anchovy larvae in May and very low abundances in June, although abundances were very high later in the summer. Similarly, Richardson (1977) did not find larval E. mordax along the Newport transect until 28 June in either 1971 or 1972 despite intensive sampling previous to that date. Richardson et al. (1980), on the
Ichthyoplankton
during
anomalous
El Ninlo
37 I.
conditions
STATION 2krn
9 km
6 km
18 km
35 -
5. . 10
. 20
30
. . . 10 20 STANDARD
Figure 2. Length 1983. Abundances for each station.
30 LENGTH
SEPT
.I. (0
20
30
10
20
30
(mm)
frequency distributions for Engraulis mordax are mean values for each month standardized
larvae collected during (no. larvae per 10 m’)
other hand, showed that E. mordax larvae occurred in low numbers in March and April of 1973, but not during the spring of 1972,1974 and 1975. The seasurface temperatures in early 1973 were above normal due to a mild winter (Laroche & Richardson, 1979). Therefore, this early occurrence of anchovy larvae in 1983 is unusual, but not unprecedented. Other taxa designated as offshore types by Richardson and Pearcy (1977) include the myctophid species Stenobrachius leucopsarus and Tarletonbeania crenularis, the scorpaenid genus Sebastes, and the pleuronectid species Glyptocephalus zachirus and Lyopsetta jordani. Although these taxa have been previously found inshore of 18 km (Richardson, 1977; Mundy, 1984), their abundances were substantially higher in 1983 than in prior years. Three taxa that occurred at least twice in our collections, Sebastolobus spp., Bathylagus ochotensis and Zcichthys lockingtoni, were never found inside of 46 km by Richardson (1977), and the latter two were only rarely found inshore of 18 km in four years of sampling by Mundy (1984). We collected other larvae which have rarely been taken inshore including Lampanyctus ritteri, Protomyctophum crockeri, Brosmophycis marginata and Microstomus pacificus. Increases in the occurrence and abundance of offshore larvae in 1983 were accompanied by decreasesin the abundance of inshore taxa commonly found at these stations. Osmerid larvae were the most abundant taxa collected by Pearcy and Myers (1974), Richardson (1977) and Mundy (1984), especially during the period from April to June. We collected only one osmerid larva at the 6-km station on 13 September, which places this group among our rarest taxa. Other inshore specieswhich were found less commonly in 1983 than in previous years include Microgadus proximus, Artedius meanyi, Artedius harringtoni, Zsopsetta isolepis and Platichthys stellatus.
R. D. Brodeur et al.
373
TABLE 3. The ten taxa ranked most abundant abundant taxa collected from 2 to 18 km offshore 1972. All abundances are standardized to number
1983”
in 1983 compared to the ten most from April to September of 1971 and per 10 mz sea surface area
1971b
Engraulis mordax Sebastes spp. Lyopsetta exilis Stenobrachius leucopsarus Psettichthys melanostictus Isopsetta isolepis Citharichthys spp. Microgadus proximus Artedius harringtoni Parophrys vet&s
0
1972b
Osmeridae
c31-----@ o-
0
Osmeridae I. isolepis
L1 Artedius Spearman
rank correlation
meanyi
analysis
rs= -0.307
r,=0.839 I rr=
“Data
from present
study
-0.382
and bfrom
Richardson
(1977).
The ten most abundant taxa ranked by standardized abundance collected in 1983 are compared in Table 3 with the ten most abundant taxa collected from 2 to 18km off Newport from April to September of 1971 and 1972 by Richardson (1977). There is a strong coherence between the rankings of 1971 and 1972 (Spearman rank correlation, r =0.839), despite the fact that these two years were quite different hydrographically (Peterson & Miller, 1975). Many of the dominant taxa were different in 1983 and the rank order of abundance was negatively correlated with both 1971(r = -0.307) and 1972 (r = - 0.382).
The overall standardized abundance patterns seen in our study (Fig. 3) were somewhat different than those found by Richardson and Pearcy (1977) for 1971. They found a peak in abundance for the inshore larval fish assemblageoccurring from May through July with the modal abundance occurring in mid-June. Our peak abundances occurred in the middle to late part of April and again in late July (Fig. 3). These seasonal patterns, however, are strongly influenced by the dominant taxa. Osmerids comprised 717; of the larvae collected by Richardson and Pearcy during their summer upwelling peak. Anchovy larvae madeup almost 53% of the larvae we collected from 13 April to 21 July and contributed substantially to our major peaks. Our overall abundances were also much lower than those found by Richardson and Pearcy (1977) by a factor of 2-3. Part of this difference may be attributed to the useof slightly different gear and sampling on different dates within the sameseason.This difference, however, is probably conservative becauseof the decreasedretention of small larvae by the 0.571-mm mesh nets used in 1971vs. the 0.333-mm mesh nets we used in 1983 (Lenarz, 1972). Relation
of larval
catches to oceanographic
conditions
Sea surface temperatures were unusually warm early in April and continued to increase at most stations until the 21 July sampling date (Table 1). A moderate drop in
Ichthyoplankton
during
anomalous
El NiZo
373
conditions
/ -
I -
, -
I-
J
,-
M
A
M
J
A
J
0
S
MONTHS
Figure
3. Mean
standardized
I M
abundance
I A
I M
(no. larvae
I
I
I J
J
per 10 m’) for each cruise in 1983.
A
I S
0
MONTHS
Figure 4. Comparison of sea surface those of 1969-1972 [data from Mundy
temperatures (1984)].
at the 9-km
station
for
1983 with
temperature occurred on the next sampling date followed by a precipitous decrease on 19 August and a substantial rise on the last sampling date. For comparison, the surface temperature data for the 9-km station from 1983 are shown with similar measurements from the years 1969-1972 [data from Mundy (1984)] in Fig. 4. In all the previous years, surface temperatures either remained low throughout the summer, or fluctuated about a
374
R. D. Brodeur et al.
Distance
offshore
Dlstonce
(km)
offshore
(km)
18
9
6
2
18
9
6
2
18
9
6
2
18
9
6
2
Figure 5. Vertical temperature sections derived from CTD casts made at the indicated stations off Newport in 1983. All isotherms are in “C. The 10-l 1°C isotherms are stippled for comparative purposes.
much lower mean level than in 1983. High seasurface temperatures alsooccurred during June and August of 1971 and were associatedwith weak upwelling (Peterson 81Miller, 1975). The CTD vertical temperature sections (Fig. 5) indicate a persistent but gradually shallowing thermocline through 4 August 1983. On the next sampling date (19 August) conditions were relatively isothermal, probably resulting from an upwelling event that was evident in the daily upwelling indices during a five day period immediately preceding this date (A. Bakun, Pacific Environmental Group, personal communication). The stratified water column and the surface temperatures returned to conditions similar to those found in mid-summer by 13 September. The salinity data show similar trends (Table 1). The surface salinities were below 32.5% for much of the summer, indicating the probable nearshore presenceof Columbia River plume water (Barnes et al., 1972). The vertical salinity structure (Fig. 6) again suggeststhat the water column was stratified through much of the summer. The exceptional profile of 19 August, when the isohalines slant sharply upwards toward the coast, is indicative of upwelling. Upwelling indices based on wind stress calculations at 45”N and 125”W (Andrew Bakun, Pacific Environmental Group, personal communication) were similar to the long-term average during April and May but were substantially lower than the longterm advantage from June through early August of 1983 (Table 4). This weak upwelling, in conjunction with a deep thermocline associatedwith the 1982-1983 El Nifio, resulted in reduced entrainment of cool, nutrient-enriched water into the euphotic zone off Oregon through most of the usual upwelling season.As a result, surface chlorophyll concentrations were below normal for most of the 1983 suIlltner months and subsurface
Ichthyoplankton
Dlstonce
during
offshore
18
9
anomalous
El Niiio
(km) 6
Dlstonce 2
18
conditions
375
offshore 9
(km) 6
2
.3 D L . : ..&.~z” ’ 0 .&?&$s; y ‘.‘.... m n
IR
r
I
?
18
9
6
2
18
9
6
2
31.5
52Q ,.:.:.: :,,~;:.:.:.,
20 30 40 50 60
-33.0 -33.5
20 June
,. 20 30 40 50 60 70
Figure stations stippled
6. Vertical salinity sections derived off Newport in 1983. All isohalines for comparative purposes.
TABLE 4. Mean monthly upwelling Bakun, personal communication) upwelling indices at 45”N, 125”W Month
8
May June July Aw Sep
35
19 19 41 28
at the indicated %O isohalines are
indices from April through September of 1983 (A. and anomalies from the 1948-1967 overall mean (Bakun, 1973)
1983 Index
Apr
from CTD casts made are in %. The 32.0-325
Anomaly -1 +1 -29
-55 -9 f12
chlorophyll maxima, typical of non-upwelling conditions, were often observed (Miller et al., in press). The unusual larval fish catches in 1983 were correlated with these hydrographic conditions. Species from the offshore assemblage dominated the catches at most stations until 19 August, when many inshore taxa were apparently transported offshore and were collected in substantial numbers at the 2-, 6- and 9-km stations. Abundances of typical offshore taxa such as Engraulis mordax and Sebastes spp. were very low on this same date but showed a moderate resurgence in September. Weak coastal upwelling was probably unfavourable to the survival of fish larvae that normally are abundant inshore. In addition, onshore transport of oceanic or Columbia
376
R. D. Brodeur et al.
River plume waters apparently provided a mechanism to increasethe abundance of offshore ichthyoplankton speciesin waters near the coast during spring and early summer. The limited vertical distribution data that exist for ichthyoplankton off Oregon (Richardson & Pearcy, 1977; Boehlert et al., in press) show that many of the speciesof the offshore assemblagewhich were common inshore in 1983 (e.g. E. mordax, Sebastes spp., Lyopsetta exilis, Stenobrachius leucopsarus and Glyptocephalus zachirus) are abundant in shallow waters at some time during the day and are often collected within 5 m of the surface. Residenceat this depth would render these speciessusceptible to offshore transport of surface layers during normal upwelling conditions and to onshore transport when winds are from the south or west. Although both Richardson and Pearcy (1977) and Mundy (1984) document interannual variability in larval fish species abundance patterns off Oregon, they did not document so great a shift in the dominant taxa aswe found in 1983. Long-term fluctuations in the physical and biological characteristics of the California Current are known to occur (Chelton et al., 1982; Simpson, 1984b). However, the unusually strong mid-latitude El Niiio of 1982-1983 may have substantially altered biological conditions off Oregon, thus limiting the survival potential of many specieswhich have spawning seasonskeyed to the normal upwelling cycle. Richardson (1980) suggeststhat the relatively stable and productive Columbia River plume provides a suitable spawning area for the northern subpopulation of anchovy centered off Oregon. Sexually immature northern anchovy are found in nearshore waters during spring and ripening adults normally move offshore of 65 km to spawn (Laroche & Richardson, 1980). Richardson (1980) further suggeststhat adult anchovy only spawn in waters warmer than 13°C found mainly in the Columbia River plume during the typical upwelling season.The relatively warm, stratified conditions that persisted throughout much of the area for most of the spring and summer of 1983 apparently provided northern anchovy an inshore spawning ground off Oregon over an expanded spawning season. In a comparison of three hydrographically different years, Lasker (1981) found that survival of E. mordax off southern California, asmeasured by subsequentyear-class contributions to the fishery, was greatest in years of reduced upwelling and increased water column stability. Survival was reduced during years of substantial upwelling or strong turbulence causedby storms. Although northern anchovy larvae had broad spatial and temporal distributions off Oregon in 1983, prospects for the eventual survival of the 1983 year-class of northern anchovy as well asother spring and summer spawning fish species off Oregon are uncertain because of the low levels of production associated with the much reduced upwelling.
Acknowledgements We thank the following from Oregon State University for their assistancein this study: R. Barrell, A. Chung, J. Fisher, J. Kalish, R. Merrick and M. Willis for their help at sea; B. Mundy for assistancein identifying fish larvae and for suggesting improvements on the manuscript; R. Smith and A. Huyer for useful discussions on the physical oceanography off Oregon. We also thank A. Bakun from the NOAA Pacific Environmental Group for allowing us to use some of his unpublished data. Special thanks to J. A. McGowan of Scripps Institution of Oceanography for suggestingthat the
Ichthyoplankton
during
anomalous
El Nirio
conditions
study be done. This study was funded by the Oregon State University Program and National Science Foundation Grant No. OCE-8201899.
377
Sea Grant
References Bakun, A. 1973 Coastal upwelling indices, west coast of North America, 1946-71. U.S. Department of Commerce, NOAA Technical Report NMFS SSRF 671.103 pp. Barnes, C. A., Duxbury, A. C. & Morse, B. A. 1972 Circulation and selected properties of the Columbia River effluent at sea. In The Columbia River Estuary and Adjacent Ocean Waters; Bioenvironmental Studies (Pruter, A. T. 81 Alverson, D. L., eds). University of Washington Press, Seattle. pp. 41-80. Boehlert, G. W., Gadomski, D. M. & Mundy, B. C. (in press) Vertical distribution of ichthyoplankton off the Oregon coast in spring and summer months. Fishery Bullerin, 83(4). Cane, M. A. 1983 Oceanographic events during El Nirio. Science, 222,1189-1195. Chelton, D. B., Bernal, I’. B. & McGowan, J. A. 1982 Large-scale interannual physical and biological interaction in the California Current.Journal ofMarine Research, 40, 1095-l 125. Fiedler, I’. C. 1984 Satellite observations of the 1982-1983 El Nina along the U.S. Pacific Coast. Science, 224,1251-1254. Huyer, A. 1983 Coastal upwelling in the California Current System. Progress in Oceanography, 12,259-284. Kendall, A. W., Jr. St Clark, J. R. 1982a Ichthyoplankton off Washington, Oregon, and Northern California, April-May 1980. U.S. Department of Commerce, NMFS NWAFC Processed Report 82-l 1.44 pp. Kendall, A. W., Jr & Clark, J. R. 19826 Ichthyoplankton off Washington, Oregon, and Northern California, August 1980. U.S. Department of Commerce, NMFS NWAFC Processed Report 82-12.43 pp. Laroche, J. L. & Richardson, S. L. 1979 Winter-spring abundance of larval English sole, F’arophrys vetulus, between the Columbia River and Cape Blanco, Oregon during 1972-1975 with notes on occurrences of three other pleuronectids. Estuarine and Coastal Marine Science, 8,455-476. Laroche, J. L. & Richardson, S. L. 1980 Reproduction of northern anchovy, Engraulis mordax, off Oregon and Washington. Fishery Bulletin, 78,603-618. Lasker, R. 1981 Factors contributing to variable recruitment of the northern anchovy (Engraulis mordax) in the California Current: contrasting years, 1975 through 1978. Rapports et Proces-verbaux des Reunions du Conseil International pour I’Exploration de la Mer, 178.375-388. Lenarz, W. H. 1972 Mesh retention of larvae of Sardinops caerula and Engraulis mordax by plankton nets. Fisherv Bulletin. 70.839-848. McLain, D. R. 1984 Coastal ocean warming in the Northeast Pacific, 1976-83. In The Znfluence of Ocean Conditions on the Production of Salmonids in the North Pacific (Pearcv, W. G.. ed.). Oreeon State ’ University Sea Grant College Program Publication ORESU-W-83-001.?27 pp. ’ Miller, C. B., Batchelder, H. I’., Brodeur, R. B. & Pearcy, W. G. (in press) Response of the zooplankton and ichthyoplankton off Oregon to the El Nifio event of 1983. El Nifio North: Nifio effects in the Subarctic Pacific Ocean (W. S. Wooster & Fluharty, D. L., eds). University of Washington Sea Grant Publication. Mundy, B. C. 1984 Yearly variation in the abundance and distribution of fish larvae in the coastal upwelling zone off Yaquina Head, Oregon from June 1969 to August 1972. M. S. Thesis, Oregon State University, Corvallis. 158 pp. Pearcy, W. G. & Myers, S. S. 1974 Larval fishes of Yaquina Bay, Oregon: a nursery ground for marine fishes? Fishery Bulletin, 72,201-213. Peterson, W. T. & Miller, C. B. 1975 Year-to-year variations in the planktology of the Oregon upwelling zone. Fishery Bulletin, ?3,642-653. Richardson, S. L. 1973 Abundance and distribution of larval fishes in waters off Oregon, May-October 1969, with special emphasis on the northern anchovy, Engraulis mordax. Fishery Bulletin, 71,697-711. Richardson, S. L. 1977 Larval fishes in ocean waters off Yaquina Bay, Oregon: abundance, distribution and seasonality, January 1971 to August 1972. Oregon State University Sea Grant College Program Publication ORESUT-77-003. 73 pp. Richardson, S. L. 1980 Spawning biomass and early life of northern anchovy, Engraulis mordax, in the northern subpopulation off Oregon and Washington. Fishery Bulletin, 78,855-876. Richardson, S. L. & Pearcy, W. G. 1977 Coastal and oceanic fish larvae in an area of upwelling off Yaquina Bay, Oregon. Fishery Bulletin, 75, 125-145. Richardson, S. L., Laroche, J. L. & Richardson, M. D. 1980 Larval fish assemblages in the northeast Pacific Ocean along the Oregon coast, winter-spring 1972-1975. Estuarine and Coastal Marine Science, 11, 671-699. Simpson, J. J. 1983 Large-scale thermal anomalies in the California Current during the 1982-1983 El Niiio. Geophysical Research Letters, 10,937-940. ,
I
378
R. D. Brodeur
et al.
Simpson, J. J. 1984a El Nifio-induced onshore transport in the California Current during 1982-1983. Geophysical Research Letters, 11,233-236. Simpson, J. J. 19846 A simple model of the 1982-83 Californian ‘ El-Niiio ‘. Geophysical Research Letters, 11,237-240. Waldron, K. D. 1972 Fish larvae collected from the northeastern Pacific Ocean and Puget Sound during April and May 1967. U.S. Department of Commerce, NOAA Technical Report NMFS SSRF-663. 16 PP. Washington, B. B. 1982 Identification and Systematics of larvae of Artedius, Clinocottus, and Oligocottus (Scorpaeniformes: Cottidae). M.S. Thesis, Oregon State University, Corvallis. 192 pp.