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Life history characteristics of the deep-sea crab Chaceon affinis population off Tenerife (Canary Islands)
Fisheries Research 58 (2002) 231–239
Short communication
Life history characteristics of the deep-sea crab Chaceon affinis population off Tenerife (Canary Islands) L.J. Lo´pez Abella´n*, E. Balguerı´as, V. Ferna´ndez-Vergaz Centro Oceanogra´fico de Canarias, Instituto Espan˜ol de Oceanografı´a, Carretera de San Andre´s, s/n, 38120 Santa Cruz de Tenerife, Spain Received 17 January 2001; received in revised form 25 July 2001; accepted 12 August 2001
Abstract Although Chaceon affinis is largely unknown to Canarian fishermen, relatively abundant quantities of deep-sea red crab have been found over the last 10 years, in all trap surveys conducted around the Islands. Waters deeper than 550 m have been surveyed. From July 1994 to May 1996, monthly samples were taken from north-eastern waters of Tenerife using traps. Crabs were caught at depths ranging from 550 to 1200 m on muddy–rocky bottoms. Recruitment takes place in deeper waters, but individuals migrate to the upper slope as they grow. Other migrations are related to females and reproduction. Gonadosomatic indices and ovarian stages suggest an extensive spawning period, starting in October and ending in May. There is a moderately high level of infection by Sacculina affecting small individuals. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Population structure; Biology; Chaceon affinis; Geryonidae; Canary Islands
1. Introduction Several species of red crabs Geryonidae are exploited commercially in different parts of the world. Of the 15 species of genus Chaceon, (Manning and Holthuis, 1989), three are spread throughout the Atlantic Ocean and support relatively important fisheries. The red crab Chaceon affinis is the largest epibenthic brachyuran of the family Geryonidae (Manning and Holthuis, 1989), inhabiting oceanic seamounts throughout the eastern Atlantic Ocean, Iceland to Senegal, and around all the Macaronesian Islands (Milne Edwards and Bouvier, 1894; Kjenerud, 1967; Samuelsen, 1975; *
Corresponding author. Tel.: þ34-922-54-9400; fax: þ34-922-54-9554. E-mail address: [email protected] (L.J. Lo´pez Abella´n).
Manning and Holthuis, 1981; Sanchez and Olaso, 1985; Lozano et al., 1992; Lo´pez Abella´n et al., 1994). Although there are some local fisheries based on this species in north-western Spain (Galicia Bank) (Pe´rez Ga´ndaras, in Sanchez and Olaso (1985)), it was first collected in the Canary Islands, July 1985, during a scientific survey (Lozano et al., 1992), since then and has been fished in all trap surveys conducted around the Canaries at depths greater than 550 m. Unlike other Geryonidae species, knowledge about the biology of C. affinis is scarce (Pinho et al., 1998; Ferna´ndezVergaz et al., 2000). The objective of this work is to describe the spatial structure of the deep-sea red crab C. affinis population inhabiting a small area north-east of Tenerife, as well as other life history characteristics, spawning season and parasitism by the Rhizocephala.
0165-7836/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 7 8 3 6 ( 0 1 ) 0 0 3 8 4 - 8
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L.J. Lo´ pez Abella´ n et al. / Fisheries Research 58 (2002) 231–239
2. Materials and methods Between July 1994 and May 1996, monthly samples of C. affinis were taken in waters to the north-east of Tenerife waters (Fig. 1), setting traps on rocky and muddy bottoms at depths ranging from 500 to 1200 m. A systematic sampling scheme was applied in which the area was divided into seven strata of 100 m depth each. Operations were conducted aboard a fishing boat operated by the Instituto Espan˜ ol de Oceanografı´a. Traps were baited with sardine or mackerel and the time between setting and hauling ranged from 24 to 48 h. A total of 631 crabs was collected, 362 males and 269 females. At the laboratory, carapace width (CW, the distance between the 5th lateral spine tips), sex, total wet weight and gonad weight (0.1 g), were measured for each specimen. Differences in size frequency distributions of C. affinis by depth were analysed using a two-tailed Kolmogorov–Smirnov test for large samples, performed for all strata combinations. Critical values were
obtained at the 0.05 level of significance using the Siegel and Castellar (1988) method. Sex ratios were estimated by size, depth strata and annual quarters. Results were tested using the chisquare analysis. The spawning season was primarily determined by ovarian development stages as described by Ferna´ ndez-Vergaz et al. (2000) and corroborated by reference to the gonadosomatic index ðGSI ¼ ðgonad weight=total weightÞ 100Þ and the occurrence of ovigerous females or those showing egg remnants. Finally, the level of parasitism by Rhizocephala in relation to size and depth strata was recorded.
3. Results 3.1. Catch per unit effort (CPUE) Maximum CPUE (kg/trap) was found between 600 and 900 m depth (Fig. 2), with a peak at 700–800 m (4.66 kg/trap). Graph of CPUE (crab/trap) is similar, showing a progressive increase from 500 m depth and reaching a maximum of around 8 crabs/trap in the 800–900 m strata. However, after a sharp decrease in deeper waters, a new peak of 6 specimens/trap appears at 1100–1200 m that it is not found in CPUE (kg/trap) records. Both CPUE (crab/trap) peaks indicate the presence of smaller crabs in this deeper strata because no increase in CPUE (kg/trap) occurs. However, data from 500–600 to 700–800 m show the presence of individuals with similar large size. 3.2. Size structure
Fig. 1. Location of study area. Shaded area to northeast of Tenerife showing depths surveyed; dots: deployment position.
Males ranged from 5.2 to 18.9 cm in CW and females ranged from 6.1 to 16.5 cm. Mean sizes for males and females were 13.0 ðS:D: ¼ 2:52Þ and 12.07 cm ðS:D: ¼ 1:7Þ, respectively. Length frequency distribution for males is bimodal and for females unimodal (Fig. 3). The two-tailed Kolmogorov–Smirnov tests, performed for all possible combinations of strata and all individuals, show significant differences between size frequency distributions at various strata (Fig. 4), i.e. shallower (500–800 m), intermediate (800–900 m) and deepest (deeper than 900 m). The first stratum is characterised by a greater presence of males (68%)
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233
Fig. 2. C. affinis. CPUE in weight and numbers by depth.
and greater mean size for both males (14.16 cm, S:D: ¼ 1:91) and females (13.13 cm, S:D: ¼ 1:31). The second stratum contains smaller crabs of a similar mean size for both sexes (12.76 cm males, S:D: ¼ 2:48; 12.26 cm females, S:D: ¼ 1:5). The deepest stratum contains the smallest individuals with a mean size of 11.19 cm ðS:D: ¼ 2:37Þ for males and 11.17 cm ðS:D: ¼ 1:8Þ for females. A similar pattern is observed for sizes by sex, although significant differences are not observed in females between the strata of 800–900 and 1100– 1200 m. Males show an intermediate wider stratum (800–1000 m), with a smooth transition (900–1000 m) towards the deepest strata (1000–1200 m).
3.3. Sex structure Differences in sex ratios become statistically significant as size increases, which is expected in species with differential growth rates between sexes. This is characterised by a 1:1 ratio with smaller sizes (less than 7 cm CW), an intermediate sharp part between 7 and 14 cm CW and continuous increase in the proportion of males which reach 100% at sizes of more than 17 cm CW. A sex-structure analysis was carried out on the various size strata (Tables 1 and 2). The total sex ratio (1:0.74) shows a statistically significant predominance of males. This predominance is based on
Fig. 3. C. affinis. Length frequency distribution by sex for all individuals analysed.
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Fig. 4. C. affinis. Results of two-tailed Kolmogorov–Smirnov test showing spatial structure of the population in relation to size: (A) females; (B) males; (C) all individuals. Shaded areas represent different depth strata obtained after size analysis.
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Table 1 C. affinis: sex ratio by length, depth and total by 10 mm size class (M: males; F: females; sex ratio; w2-analysis)a Size class (mm)
<800 m M
50 60 70 80 90 100 110 120 130 140 150 160 170 180
1 6 8 6 18 28 53 26 20 9 2
Total a
800–900 m 2
Sex ratio w
F
M
F
>900 m Sex ratio
2
w
M
F
Sex ratio
w
M
F
Sex ratio
w2
1 2 14 16 22 16 25 10 6 1
1:1 1:0.50 1:1.55 1:0.76 1:0.96 1:0.89 1:6.25 1:1.43 1:2 1:0.17
0.00 0.67 1.09 0.68 0.02 0.12 15.21 0.53 1.00 3.57
1 4 11 38 44 40 26 46 63 39 34 13 3
2 2 17 18 34 38 69 57 27 2 3
1:2 1:05 1:1.55 1:0.74 1:0.77 1:0.95 1:2.65 1:1.24 1:0.43 1:0.05 1:0.09
0.33 0.67 1.29 7.14 1.28 0.05 19.46 1.17 14.40 33.39 25.97
0.56
362 269 1:0.74
13.71
1
1 2 3 28 33 12
1:0.17 1:0.25 1:0.50 1:1.55 1:1.18 1:0.23
3.57 3.60 1.00 2.17 0.41 25.86
3
1:0.15
12.57
177 83
1:0.47
33.98
Total
1 11 13 16 4 11 7 7 9 3 1
3 1 10 19 16 14 9 1
1:3 1:0.09 1:0.77 1:1.91 1:4 1:1.27 1:1.29 1:0.14
1.00 8.33 0.39 0.26 7.20 0.36 0.25 4.50
1 4 9 21 23 18 4 7 3 6 5 1
83
73
1:0.88
0.64
102 113 1:1.11
2
w2 > w2t1;0:05 ¼ 3:841.
800 m strata (upper slope) where the number of males is significantly greater than females (w2-test, p<0.05). Deeper strata have more females, most abundant at 900 m strata (1:1.11) although neither relationship differs statistically from 1:1. Analysing data by season, statistical differences are localised in 800 m strata with the only exception
being the July–September quarter, during which a marked increase of females occurs at depths 900 m. Fig. 5 shows different combinations of male and female percentages by depth and quarter.
Table 2 C. affinis: sex-ratio by quarter and strata (M: males; F: females; sex ratio; w2-analysis)a Quarter
Strata (m) M
F
Sex ratio
w2
January–March
800 53 800–900 21 900 33
15 18 29
1:0.28 1:0.86 1:0.88
21.24 0.23 0.26
April–June
800 45 800–900 27 900 21
19 18 24
1:0.42 1:0.67 1:1.14
10.56 1.80 0.20
July–September
800 31 800–900 24 900 26
33 32 41
1:1.06 1:1.33 1:1.58
0.06 1.14 3.36
October–December
800 48 800–900 11 900 22
16 5 19
1:0.33 1:0.45 1:0.86
16.00 2.25 0.22
a
w2 > w2t1;0:05 ¼ 3:841.
Fig. 5. C. affinis. Sex ratio by strata and quarter.
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236
Fig. 6. C. affinis. Monthly evolution of the proportion of females in each ovarian stage: (I) immature; (II) early; (III) intermediate; (IV) advanced; (V) mature; (VI) redeveloping.
3.4. Reproduction Monthly records of ovarian development stages (Fig. 6) show an increase in the Stage V (mature) from April to August, whereas Stage I (Immature) follows an inverse trend. Ovigerous females (Stage VI, spent) were found only on March and April. Some females carrying egg remnants were observed in subsequent months (Fig. 7). These specimens ranged from 11.5 to 16.5 cm of CW (13.16 cm of mean width, S:D: ¼ 1:13) and were found mainly at 650–800 m depth (756 m of mean depth). Otherwise, the GSI for females (Fig. 7) increases from early in the year to October, suggesting a wide
spawning period that may start in October and end in May. 3.5. Rhizocephala parasitism Ten percent of crabs caught were infected by Sacculina sp. (10.4% females and 9.9% males), representing a moderately high level of infection (prevalence). This parasitism largely affected smaller individuals inhabiting the deepest waters (Fig. 8); 26% of the individuals between 5 and 11.5 cm CW were infected, as well as the 16% of crabs between 800 and 1200 m depth, although the highest prevalence occurs in 1000–1100 m strata (19% females and 27% males).
Fig. 7. C. affinis. GSI and percentage of ovigerous females or with eggs remnants by month and depth.
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237
Fig. 8. C. affinis. Length frequency distribution and parasite presence by host size and depth. Unfilled bars represent percentage of crabs infected in relation to carapace width and all individuals caught within each depth strata.
4. Discussion CPUE (crab/trap) by strata and size distribution suggests that recruitment occurs in the deepest stratum and an ontogenetic migration towards shallower waters from deeper strata takes place. The presence of some large females in the 800–900 and 1100– 1200 m strata, which corresponds with the two peaks of abundance could, however, be a consequence of a migratory behaviour related to reproduction. MelvilleSmith (1987) described how patterns of migration affected the size structure of the population of Chaceon maritae. These species have a contagious behaviour and tend to aggregate in areas close to canyons and other bottom features.
Our results agree with Pinho et al. (1998), who reported similar changes of mean size by depth for C. affinis in the Azores. It seems likely that C. quinquedens inhabiting the north-east American coast show the same size segregation by depth as C. affinis (Wigley et al., 1975). Although some authors (Intes and Le Loeuff, 1976; Beyers and Wilke, 1980) have reported similar size structure by depth for other Chaceon species (e.g. C. maritae), probably based on observations affected by seasonal movements of individuals, size segregation in this species seems to be inverse to the C. affinis structure (Cayre and Bouchereau, 1977; Lo´ pez Abella´ n and Garcı´aTalavera, 1992), with larger individuals located at deeper bottoms. However, most of them agree on
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the size structure of the population by sex which is the same for several species in a typical pattern characterised by a bimodal structure in males and unimodal in females. According to Melville-Smith’s (1989) moult description on C. maritae, differences between size frequency distributions by sex could be caused by differences in moulting of males and females. Thus, the unimodal structure of females could be the result of shorter intermoult periods for immature individuals, larger intermoult periods after maturity. The size at first maturity (113 mm CW) (Ferna´ ndezVergaz et al., 2000), is seen to be is smaller (10%) and closer to the modal size (125 mm). Depth distributions of C. affinis might also be related to the presence of Cancer bellianus at a shallower distribution, creating a border of competition at around 500–600 m depth, where larger males of C. affinis exist maintaining the area of distribution and isolating reproduction and recruitment zones. Segregation by sex related to depth is a characteristic of geryonid crabs and the dominance of C. affinis males at depths 800 m is reported in the Canary Islands and the Azores (Pinho et al., 1998). This is not so for other geryonid crabs (e.g. C. maritae) (Intes and Le Loeuff, 1976; Beyers and Wilke, 1980; Lo´ pez Abella´ n and Garcı´a-Talavera, 1992), where females are predominant on upper slopes, males in deeper waters, with an intermediate zone of transition between both extremes of depth distribution. However, this structure seems to be dynamic as Hastie (1995) suggests and could change during the annual cycle, as a consequence of female migration to shallow water for copulation and spawning. The presence of ovigerous females in shallower areas confirms the possibility that later another migration occurs towards deeper waters. Data also confirm a long period of reproduction from October to April or May, which agrees with Pinho et al. (1998). However, their results suggest that females do not spawn annually and that this event probably takes place for every 2 years. The moderately high level of infection by Sacculina sp. is typical of relatively closed systems, canyons (Sloan, 1984), which would be the case of C. affinis presenting a very contagious spatial distribution. Males parasitized by Sacculina are morphologically and behaviourally feminised (Kuris and Lafferty, 1992), whereas females are castrated (Hoggart, 1990); growth in both males and females is reduced
or stopped. Taking the size at maturity of this species into account (Ferna´ ndez-Vergaz et al., 2000), most individuals are parasited prior to becoming sexually mature and probably suffer a higher level of natural mortality than uninfected crabs.
Acknowledgements We thank our colleagues from the Centro Oceanogra´ fico de Canarias: Jose´ A. Dı´az, Ma Teresa Garcı´a, Ubaldo Garcı´a-Talavera, Jose´ F. Gonza´ lez, C. Perales and Ma Eugenia Quintero, for support in the sampling process and also the master and crew of M/P Lahera for assistance. References Beyers, B.C.J., Wilke, C.G., 1980. Quantitative stock survey and some biological and morphometric characteristics of the deepsea red crab Geryon quinquedens off south-west Africa. Fish. Bull. S. Afr. 13, 9–19. Cayre, P., Bouchereau, J.L., 1977. Biologie et re´ sultats des peˆ ches expe´ rimentales du crabe Geryon quinquedens Smith, 1879 au large de la re´ publique populaire du Congo. Doc. Sci. Cent. Pointe-Noire (ORSTOM) NS 51, 1–30. Ferna´ ndez-Vergaz, V., Lo´ pez Abella´ n, L.J., Balguerı´as, E., 2000. Morphometric, functional and sexual maturity of the deep-sea red crab Chaceon affinis inhabiting Canary Island waters: chronology of maturation. Mar. Ecol. Prog. Ser. 204, 169– 178. Hastie, L.C., 1995. Deep-water Geryonid crabs: a continental slope resource. Oceanogr. Marine Biol. 33, 561–584. Hoggart, D.D., 1990. The effects of parasitism by the rhizocephalan, Briarosaccus callosus, Boschma on lithodid crab, Paralomis grannulosa (Jaquinot) in the Falkland Islands. Crustaceana 59, 156–170. Intes, A., Le Loeuff, P., E´ tude du crabe rouge profond Geryon quinquedens en Coˆ te d’Ivoire. 1. Prospection le long du talus continental re´ sultats des peˆ ches. Doc. Scient. Centre Rech. Oce´ anogr. Abidjan 7, 101–112. Kjenerud, J., 1967. A find of Geryon affinis Milne-Edwuards y Bouvier, 1984 (Crustacea Decapoda) off the coast of Norway. Sarsia 29, 193–198. Kuris, A.M., Lafferty, K.D., 1992. Modelling crustacean fisheries: effects of parasites on management strategies. Can. J. Fish. Aquat. Sci. 49, 327–336. Lo´ pez Abella´ n, L.J., Garcı´a-Talavera, U., 1992. Resultados de la campan˜ a de prospeccio´ n pesquera de los stocks de crusta´ ceos profundos en aguas de la Repu´ blica de Angola Angola 9011. Inf. Te´ c. Inst. Esp. Oceanogr. 119, 1–73. Lo´ pez Abella´ n, L.J., Santamarı´a, M.T.G., Balguerı´as, E., 1994. Resultados de la campan˜ a experimental de pesca, realizada en
L.J. Lo´ pez Abella´ n et al. / Fisheries Research 58 (2002) 231–239 aguas del suroeste de la isla de Tenerife, Canarias 9206. Inf. Te´ c. Inst. Esp. Oceanogr. 147, 62. Lozano, I.J., Caldentey, M.A., Santana, J.L., Gonza´ lez, J.A., 1992. Crusta´ ceos y peces capturados en una campan˜ a de prospeccio´ n en aguas profundas de Canarias. Actas V Simp. Ibe´ r. Estud. Bentos Mar. 2, 203–208. Manning, R.B., Holthuis, L.B., 1981. West African brachyuran crabs (Crustacea: Decapoda). Smithsonian Contrib. Zool. 306, 379. Manning, R.B., Holthuis, L.B., 1989. Two new genera and nine new species of geryonid crabs (Crustacea, Decapoda, Geryonidae). Proc. Biol. Soc. Wash. 102 (1), 50–77. Melville-Smith, R., 1987. Tagging study reveals interesting red crab (Geryon maritae) movements off Namibia (Southwest Africa). J. Cons. Int. Explor. Mer. 43, 194–295. Melville-Smith, R., 1989. A growth model for the deep-sea red crab (Geryon maritae) off Southwest Africa/Namibia (Decapoda, Brachyura). Crustaceana 56 (3), 279–291. Milne Edwards, A., Bouvier, E.L., 1894. Crustace´ s de´ capodes provenant des campagnes du yacht l’Hirondelle (1886, 1887, 1888). Brachyures et anomoures. Re´ sult. Camp. Sci. Monaco 7, 1–112.
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Pinho, M.R., Gonc¸alves, J.M., Martins, H.R., Meneses, G.M., 1998. Some aspects of the biology of deep-water crab Chaceon affinis (Milne Edwards and Boubier, 1894) off the Azores. ICES CM 1998/O:34, 13 pp. Samuelsen, T.J., 1975. The third record of Geryon affinis, A. Milne-Edwards and Bouvier (Crustacea, Decapoda) from western Norway. Sarsia 59, 47–48. Sanchez, F., Olaso, I., 1985. Presencia de Geryon affinis MilneEdwards y Bouvir, 1894, en el golfo de Vizcaya (Decapoda, Brachyura). Bol. Inst. Esp. Oceanogr. 2 (1), 155–157. Siegel, S., Castellar, N.J., 1988. Nonparametric Statistics for Behavioral Sciences. McGraw-Hill, New York. Sloan, N.A., 1984. Incidence and effects of parasitism by the rhizocephalan barnacle, Briarosaccus callosus Boschma, in the golden king crab, Lithodes aequispina Benedict, from deep fjords in the northern British Columbia, Canada. J. Exp. Mar. Biol. Ecol. 84, 111–113. Wigley, R.L., Theroux, R.B., Murray, H.E., 1975. Deep-sea red crab, Geryon quinquedens, survey off northeastern United States. Mar. Fish. Rev. 37, 1–21.
Short communication
Life history characteristics of the deep-sea crab Chaceon affinis population off Tenerife (Canary Islands) L.J. Lo´pez Abella´n*, E. Balguerı´as, V. Ferna´ndez-Vergaz Centro Oceanogra´fico de Canarias, Instituto Espan˜ol de Oceanografı´a, Carretera de San Andre´s, s/n, 38120 Santa Cruz de Tenerife, Spain Received 17 January 2001; received in revised form 25 July 2001; accepted 12 August 2001
Abstract Although Chaceon affinis is largely unknown to Canarian fishermen, relatively abundant quantities of deep-sea red crab have been found over the last 10 years, in all trap surveys conducted around the Islands. Waters deeper than 550 m have been surveyed. From July 1994 to May 1996, monthly samples were taken from north-eastern waters of Tenerife using traps. Crabs were caught at depths ranging from 550 to 1200 m on muddy–rocky bottoms. Recruitment takes place in deeper waters, but individuals migrate to the upper slope as they grow. Other migrations are related to females and reproduction. Gonadosomatic indices and ovarian stages suggest an extensive spawning period, starting in October and ending in May. There is a moderately high level of infection by Sacculina affecting small individuals. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Population structure; Biology; Chaceon affinis; Geryonidae; Canary Islands
1. Introduction Several species of red crabs Geryonidae are exploited commercially in different parts of the world. Of the 15 species of genus Chaceon, (Manning and Holthuis, 1989), three are spread throughout the Atlantic Ocean and support relatively important fisheries. The red crab Chaceon affinis is the largest epibenthic brachyuran of the family Geryonidae (Manning and Holthuis, 1989), inhabiting oceanic seamounts throughout the eastern Atlantic Ocean, Iceland to Senegal, and around all the Macaronesian Islands (Milne Edwards and Bouvier, 1894; Kjenerud, 1967; Samuelsen, 1975; *
Corresponding author. Tel.: þ34-922-54-9400; fax: þ34-922-54-9554. E-mail address: [email protected] (L.J. Lo´pez Abella´n).
Manning and Holthuis, 1981; Sanchez and Olaso, 1985; Lozano et al., 1992; Lo´pez Abella´n et al., 1994). Although there are some local fisheries based on this species in north-western Spain (Galicia Bank) (Pe´rez Ga´ndaras, in Sanchez and Olaso (1985)), it was first collected in the Canary Islands, July 1985, during a scientific survey (Lozano et al., 1992), since then and has been fished in all trap surveys conducted around the Canaries at depths greater than 550 m. Unlike other Geryonidae species, knowledge about the biology of C. affinis is scarce (Pinho et al., 1998; Ferna´ndezVergaz et al., 2000). The objective of this work is to describe the spatial structure of the deep-sea red crab C. affinis population inhabiting a small area north-east of Tenerife, as well as other life history characteristics, spawning season and parasitism by the Rhizocephala.
0165-7836/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 7 8 3 6 ( 0 1 ) 0 0 3 8 4 - 8
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L.J. Lo´ pez Abella´ n et al. / Fisheries Research 58 (2002) 231–239
2. Materials and methods Between July 1994 and May 1996, monthly samples of C. affinis were taken in waters to the north-east of Tenerife waters (Fig. 1), setting traps on rocky and muddy bottoms at depths ranging from 500 to 1200 m. A systematic sampling scheme was applied in which the area was divided into seven strata of 100 m depth each. Operations were conducted aboard a fishing boat operated by the Instituto Espan˜ ol de Oceanografı´a. Traps were baited with sardine or mackerel and the time between setting and hauling ranged from 24 to 48 h. A total of 631 crabs was collected, 362 males and 269 females. At the laboratory, carapace width (CW, the distance between the 5th lateral spine tips), sex, total wet weight and gonad weight (0.1 g), were measured for each specimen. Differences in size frequency distributions of C. affinis by depth were analysed using a two-tailed Kolmogorov–Smirnov test for large samples, performed for all strata combinations. Critical values were
obtained at the 0.05 level of significance using the Siegel and Castellar (1988) method. Sex ratios were estimated by size, depth strata and annual quarters. Results were tested using the chisquare analysis. The spawning season was primarily determined by ovarian development stages as described by Ferna´ ndez-Vergaz et al. (2000) and corroborated by reference to the gonadosomatic index ðGSI ¼ ðgonad weight=total weightÞ 100Þ and the occurrence of ovigerous females or those showing egg remnants. Finally, the level of parasitism by Rhizocephala in relation to size and depth strata was recorded.
3. Results 3.1. Catch per unit effort (CPUE) Maximum CPUE (kg/trap) was found between 600 and 900 m depth (Fig. 2), with a peak at 700–800 m (4.66 kg/trap). Graph of CPUE (crab/trap) is similar, showing a progressive increase from 500 m depth and reaching a maximum of around 8 crabs/trap in the 800–900 m strata. However, after a sharp decrease in deeper waters, a new peak of 6 specimens/trap appears at 1100–1200 m that it is not found in CPUE (kg/trap) records. Both CPUE (crab/trap) peaks indicate the presence of smaller crabs in this deeper strata because no increase in CPUE (kg/trap) occurs. However, data from 500–600 to 700–800 m show the presence of individuals with similar large size. 3.2. Size structure
Fig. 1. Location of study area. Shaded area to northeast of Tenerife showing depths surveyed; dots: deployment position.
Males ranged from 5.2 to 18.9 cm in CW and females ranged from 6.1 to 16.5 cm. Mean sizes for males and females were 13.0 ðS:D: ¼ 2:52Þ and 12.07 cm ðS:D: ¼ 1:7Þ, respectively. Length frequency distribution for males is bimodal and for females unimodal (Fig. 3). The two-tailed Kolmogorov–Smirnov tests, performed for all possible combinations of strata and all individuals, show significant differences between size frequency distributions at various strata (Fig. 4), i.e. shallower (500–800 m), intermediate (800–900 m) and deepest (deeper than 900 m). The first stratum is characterised by a greater presence of males (68%)
L.J. Lo´ pez Abella´ n et al. / Fisheries Research 58 (2002) 231–239
233
Fig. 2. C. affinis. CPUE in weight and numbers by depth.
and greater mean size for both males (14.16 cm, S:D: ¼ 1:91) and females (13.13 cm, S:D: ¼ 1:31). The second stratum contains smaller crabs of a similar mean size for both sexes (12.76 cm males, S:D: ¼ 2:48; 12.26 cm females, S:D: ¼ 1:5). The deepest stratum contains the smallest individuals with a mean size of 11.19 cm ðS:D: ¼ 2:37Þ for males and 11.17 cm ðS:D: ¼ 1:8Þ for females. A similar pattern is observed for sizes by sex, although significant differences are not observed in females between the strata of 800–900 and 1100– 1200 m. Males show an intermediate wider stratum (800–1000 m), with a smooth transition (900–1000 m) towards the deepest strata (1000–1200 m).
3.3. Sex structure Differences in sex ratios become statistically significant as size increases, which is expected in species with differential growth rates between sexes. This is characterised by a 1:1 ratio with smaller sizes (less than 7 cm CW), an intermediate sharp part between 7 and 14 cm CW and continuous increase in the proportion of males which reach 100% at sizes of more than 17 cm CW. A sex-structure analysis was carried out on the various size strata (Tables 1 and 2). The total sex ratio (1:0.74) shows a statistically significant predominance of males. This predominance is based on
Fig. 3. C. affinis. Length frequency distribution by sex for all individuals analysed.
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Fig. 4. C. affinis. Results of two-tailed Kolmogorov–Smirnov test showing spatial structure of the population in relation to size: (A) females; (B) males; (C) all individuals. Shaded areas represent different depth strata obtained after size analysis.
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Table 1 C. affinis: sex ratio by length, depth and total by 10 mm size class (M: males; F: females; sex ratio; w2-analysis)a Size class (mm)
<800 m M
50 60 70 80 90 100 110 120 130 140 150 160 170 180
1 6 8 6 18 28 53 26 20 9 2
Total a
800–900 m 2
Sex ratio w
F
M
F
>900 m Sex ratio
2
w
M
F
Sex ratio
w
M
F
Sex ratio
w2
1 2 14 16 22 16 25 10 6 1
1:1 1:0.50 1:1.55 1:0.76 1:0.96 1:0.89 1:6.25 1:1.43 1:2 1:0.17
0.00 0.67 1.09 0.68 0.02 0.12 15.21 0.53 1.00 3.57
1 4 11 38 44 40 26 46 63 39 34 13 3
2 2 17 18 34 38 69 57 27 2 3
1:2 1:05 1:1.55 1:0.74 1:0.77 1:0.95 1:2.65 1:1.24 1:0.43 1:0.05 1:0.09
0.33 0.67 1.29 7.14 1.28 0.05 19.46 1.17 14.40 33.39 25.97
0.56
362 269 1:0.74
13.71
1
1 2 3 28 33 12
1:0.17 1:0.25 1:0.50 1:1.55 1:1.18 1:0.23
3.57 3.60 1.00 2.17 0.41 25.86
3
1:0.15
12.57
177 83
1:0.47
33.98
Total
1 11 13 16 4 11 7 7 9 3 1
3 1 10 19 16 14 9 1
1:3 1:0.09 1:0.77 1:1.91 1:4 1:1.27 1:1.29 1:0.14
1.00 8.33 0.39 0.26 7.20 0.36 0.25 4.50
1 4 9 21 23 18 4 7 3 6 5 1
83
73
1:0.88
0.64
102 113 1:1.11
2
w2 > w2t1;0:05 ¼ 3:841.
800 m strata (upper slope) where the number of males is significantly greater than females (w2-test, p<0.05). Deeper strata have more females, most abundant at 900 m strata (1:1.11) although neither relationship differs statistically from 1:1. Analysing data by season, statistical differences are localised in 800 m strata with the only exception
being the July–September quarter, during which a marked increase of females occurs at depths 900 m. Fig. 5 shows different combinations of male and female percentages by depth and quarter.
Table 2 C. affinis: sex-ratio by quarter and strata (M: males; F: females; sex ratio; w2-analysis)a Quarter
Strata (m) M
F
Sex ratio
w2
January–March
800 53 800–900 21 900 33
15 18 29
1:0.28 1:0.86 1:0.88
21.24 0.23 0.26
April–June
800 45 800–900 27 900 21
19 18 24
1:0.42 1:0.67 1:1.14
10.56 1.80 0.20
July–September
800 31 800–900 24 900 26
33 32 41
1:1.06 1:1.33 1:1.58
0.06 1.14 3.36
October–December
800 48 800–900 11 900 22
16 5 19
1:0.33 1:0.45 1:0.86
16.00 2.25 0.22
a
w2 > w2t1;0:05 ¼ 3:841.
Fig. 5. C. affinis. Sex ratio by strata and quarter.
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Fig. 6. C. affinis. Monthly evolution of the proportion of females in each ovarian stage: (I) immature; (II) early; (III) intermediate; (IV) advanced; (V) mature; (VI) redeveloping.
3.4. Reproduction Monthly records of ovarian development stages (Fig. 6) show an increase in the Stage V (mature) from April to August, whereas Stage I (Immature) follows an inverse trend. Ovigerous females (Stage VI, spent) were found only on March and April. Some females carrying egg remnants were observed in subsequent months (Fig. 7). These specimens ranged from 11.5 to 16.5 cm of CW (13.16 cm of mean width, S:D: ¼ 1:13) and were found mainly at 650–800 m depth (756 m of mean depth). Otherwise, the GSI for females (Fig. 7) increases from early in the year to October, suggesting a wide
spawning period that may start in October and end in May. 3.5. Rhizocephala parasitism Ten percent of crabs caught were infected by Sacculina sp. (10.4% females and 9.9% males), representing a moderately high level of infection (prevalence). This parasitism largely affected smaller individuals inhabiting the deepest waters (Fig. 8); 26% of the individuals between 5 and 11.5 cm CW were infected, as well as the 16% of crabs between 800 and 1200 m depth, although the highest prevalence occurs in 1000–1100 m strata (19% females and 27% males).
Fig. 7. C. affinis. GSI and percentage of ovigerous females or with eggs remnants by month and depth.
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Fig. 8. C. affinis. Length frequency distribution and parasite presence by host size and depth. Unfilled bars represent percentage of crabs infected in relation to carapace width and all individuals caught within each depth strata.
4. Discussion CPUE (crab/trap) by strata and size distribution suggests that recruitment occurs in the deepest stratum and an ontogenetic migration towards shallower waters from deeper strata takes place. The presence of some large females in the 800–900 and 1100– 1200 m strata, which corresponds with the two peaks of abundance could, however, be a consequence of a migratory behaviour related to reproduction. MelvilleSmith (1987) described how patterns of migration affected the size structure of the population of Chaceon maritae. These species have a contagious behaviour and tend to aggregate in areas close to canyons and other bottom features.
Our results agree with Pinho et al. (1998), who reported similar changes of mean size by depth for C. affinis in the Azores. It seems likely that C. quinquedens inhabiting the north-east American coast show the same size segregation by depth as C. affinis (Wigley et al., 1975). Although some authors (Intes and Le Loeuff, 1976; Beyers and Wilke, 1980) have reported similar size structure by depth for other Chaceon species (e.g. C. maritae), probably based on observations affected by seasonal movements of individuals, size segregation in this species seems to be inverse to the C. affinis structure (Cayre and Bouchereau, 1977; Lo´ pez Abella´ n and Garcı´aTalavera, 1992), with larger individuals located at deeper bottoms. However, most of them agree on
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the size structure of the population by sex which is the same for several species in a typical pattern characterised by a bimodal structure in males and unimodal in females. According to Melville-Smith’s (1989) moult description on C. maritae, differences between size frequency distributions by sex could be caused by differences in moulting of males and females. Thus, the unimodal structure of females could be the result of shorter intermoult periods for immature individuals, larger intermoult periods after maturity. The size at first maturity (113 mm CW) (Ferna´ ndezVergaz et al., 2000), is seen to be is smaller (10%) and closer to the modal size (125 mm). Depth distributions of C. affinis might also be related to the presence of Cancer bellianus at a shallower distribution, creating a border of competition at around 500–600 m depth, where larger males of C. affinis exist maintaining the area of distribution and isolating reproduction and recruitment zones. Segregation by sex related to depth is a characteristic of geryonid crabs and the dominance of C. affinis males at depths 800 m is reported in the Canary Islands and the Azores (Pinho et al., 1998). This is not so for other geryonid crabs (e.g. C. maritae) (Intes and Le Loeuff, 1976; Beyers and Wilke, 1980; Lo´ pez Abella´ n and Garcı´a-Talavera, 1992), where females are predominant on upper slopes, males in deeper waters, with an intermediate zone of transition between both extremes of depth distribution. However, this structure seems to be dynamic as Hastie (1995) suggests and could change during the annual cycle, as a consequence of female migration to shallow water for copulation and spawning. The presence of ovigerous females in shallower areas confirms the possibility that later another migration occurs towards deeper waters. Data also confirm a long period of reproduction from October to April or May, which agrees with Pinho et al. (1998). However, their results suggest that females do not spawn annually and that this event probably takes place for every 2 years. The moderately high level of infection by Sacculina sp. is typical of relatively closed systems, canyons (Sloan, 1984), which would be the case of C. affinis presenting a very contagious spatial distribution. Males parasitized by Sacculina are morphologically and behaviourally feminised (Kuris and Lafferty, 1992), whereas females are castrated (Hoggart, 1990); growth in both males and females is reduced
or stopped. Taking the size at maturity of this species into account (Ferna´ ndez-Vergaz et al., 2000), most individuals are parasited prior to becoming sexually mature and probably suffer a higher level of natural mortality than uninfected crabs.
Acknowledgements We thank our colleagues from the Centro Oceanogra´ fico de Canarias: Jose´ A. Dı´az, Ma Teresa Garcı´a, Ubaldo Garcı´a-Talavera, Jose´ F. Gonza´ lez, C. Perales and Ma Eugenia Quintero, for support in the sampling process and also the master and crew of M/P Lahera for assistance. References Beyers, B.C.J., Wilke, C.G., 1980. Quantitative stock survey and some biological and morphometric characteristics of the deepsea red crab Geryon quinquedens off south-west Africa. Fish. Bull. S. Afr. 13, 9–19. Cayre, P., Bouchereau, J.L., 1977. Biologie et re´ sultats des peˆ ches expe´ rimentales du crabe Geryon quinquedens Smith, 1879 au large de la re´ publique populaire du Congo. Doc. Sci. Cent. Pointe-Noire (ORSTOM) NS 51, 1–30. Ferna´ ndez-Vergaz, V., Lo´ pez Abella´ n, L.J., Balguerı´as, E., 2000. Morphometric, functional and sexual maturity of the deep-sea red crab Chaceon affinis inhabiting Canary Island waters: chronology of maturation. Mar. Ecol. Prog. Ser. 204, 169– 178. Hastie, L.C., 1995. Deep-water Geryonid crabs: a continental slope resource. Oceanogr. Marine Biol. 33, 561–584. Hoggart, D.D., 1990. The effects of parasitism by the rhizocephalan, Briarosaccus callosus, Boschma on lithodid crab, Paralomis grannulosa (Jaquinot) in the Falkland Islands. Crustaceana 59, 156–170. Intes, A., Le Loeuff, P., E´ tude du crabe rouge profond Geryon quinquedens en Coˆ te d’Ivoire. 1. Prospection le long du talus continental re´ sultats des peˆ ches. Doc. Scient. Centre Rech. Oce´ anogr. Abidjan 7, 101–112. Kjenerud, J., 1967. A find of Geryon affinis Milne-Edwuards y Bouvier, 1984 (Crustacea Decapoda) off the coast of Norway. Sarsia 29, 193–198. Kuris, A.M., Lafferty, K.D., 1992. Modelling crustacean fisheries: effects of parasites on management strategies. Can. J. Fish. Aquat. Sci. 49, 327–336. Lo´ pez Abella´ n, L.J., Garcı´a-Talavera, U., 1992. Resultados de la campan˜ a de prospeccio´ n pesquera de los stocks de crusta´ ceos profundos en aguas de la Repu´ blica de Angola Angola 9011. Inf. Te´ c. Inst. Esp. Oceanogr. 119, 1–73. Lo´ pez Abella´ n, L.J., Santamarı´a, M.T.G., Balguerı´as, E., 1994. Resultados de la campan˜ a experimental de pesca, realizada en
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