Hoff: Biology and ecology of Gymnocanthus pistilliger m the eastern Bering Sea 



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peratures and salinities; thus, during winter the entire 

 area may be covered in thick ice sheets. Gymnocanthus 

 pistilliger may move in and out of the shallow local bays 

 seasonally to sustain a suitable habitat. However the 

 nearshore distribution was difficult to assess for G. pistil- 

 liger from the present study owing to limited sampling in 

 very shallow coastal waters and single season collections. 

 The timing of spawning movements, however, may signif- 

 icantly affect population estimates if the species moves 

 between depths seasonally and may help to explain a 50'^'f 

 decline in fish from 1997 to 1998. Although water temper- 

 ature is often associated with fish movements, there was 

 no significant difference between the means (/-testP=0.18) 

 in bottom water temperatures in the survey area <.50 

 m in depth for the two years sampled (1997, f=4.22°C, 

 SD=1.88; 1998, .v=4.48°C, SD=0.87). 



Vdovin et al. ( 1994) suggested that G. pistilliger remains 

 within shallow water and except for spawning, probably 

 remains in the nearshore area most of the year. Spawn- 

 ing migrations in winter resulted in both sexes aggregat- 

 ing in deeper bay areas of Peter the Great Bay (Vdovin 

 et al., 1994); however, the proportion of females increased 

 with increasing depth (a depth range of 80 to 110 m was 

 maintained during spawning) (Tokranov, 1987; Vdovin et 

 al. 19941. 



If Bristol Bay populations are similar to Peter the Great 

 Bay populations, then at the time of capture (June) G. pis- 

 tilliger has already spawned and dispersed in the near- 

 shore areas. Females probably migi-ate to join the males 

 in the deeper part of Bristol Bay (around 50 m depth) 

 during late winter to early spring to spawn, although it 

 is unlikely that Bristol Bay populations reach the spawn- 

 ing depths of populations in Peter the Great Bay. Dis- 

 tributional data from Alaska indicate that G. pistilliger 

 are rarely found deeper than 50 m, except occasionally in 

 coastal areas of the Gulf of Alaska (Hoff, unpubl. data). 



Age and growth 



Age data gathered from otoliths suggest that G. pistil- 

 liger is short lived (to 10 years), the females exhibit faster 

 growth, and that this species reaches a maximum size of 

 205 mm for females and 160 mm for males. The age struc- 

 ture of western Bering Sea populations has shown older 

 populations than those for Bristol Bay (a strong mode 

 from 7 to 9 years (range 3-13 years) and a larger maxi- 

 mum size of 270 mm TL for females and 220 mm TL for 

 males (Tokranov, 1987). Length-at-age data for fish col- 

 lected off Kamchatka (Tokranov, 1987) were similar to 

 those reported in the present study, suggesting that simi- 

 lar aging techniques were used and similar growth rate 

 estimates were calculated for the two populations of G. 

 pistilliger. Therefore, different size composition and age 

 groups for eastern Bering Sea and western Pacific popula- 

 tions appear real. 



The ovaries from females collected in June from Bristol 

 Bay were deflated and a few large females contained resid- 

 ual eggs from a previous spawn. Wilson ( 1973) stated that 

 G. pistilliger spawn in spring but provided no evidence for 

 this. Ovaries collected from eastern Bering Sea popula- 



240 



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80 



40 







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160 



120 



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Males 



n=395 



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Females 



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Females 



Males 



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Age (years) 



Figure 5 



Von BertalanfTy growth curves and individual data for 

 male and female Gymnocanthus pistilliger collected during 

 1997 and 1998, combined with curves plotted together for 

 comparison. Length-at-age data were gathered from sagit- 

 tal otoliths by the break-and-burn method. 



tions in June of 1997 suggest that G. pistilliger is a late 

 winter to early spring spawner. Tokranov (1987) reported 

 that G. pistilliger spawn in winter, are single batch spawn- 

 ers in shallow waters, and produce adhesive eggs. 



