711 



Abstract— The threaded sculpin (Gvm- 

 nucanthus pistilliger) is distributed in 

 the North Pacific from Norton Sound 

 south to Southeast Alaska and west 

 to Russia and Japan. It reaches its 

 greatest abundance in the eastern 

 Bering Sea in Bristol Bay where it 

 is typically found in waters less than 

 50 m deep. Alaska Fisheries Science 

 Center groundfish surveys in the east- 

 ern Bering Sea have estimated densi- 

 ties of up to 102 fish per hectare (catch 

 per unit of effort, CPUE) for 1997 and 

 1998. Population estimates for 1997 

 were 111.20 million and for 1998 were 

 51.70 million. The population estimate 

 drop is reflected in length-frequency 

 data that suggest a complete lack of 

 2-year-old fish for 1998. Gymnocanthus 

 pistilliger is a short-lived species (age 

 estimates from otoliths range up to 10 

 years for males and up to 9 years for 

 females), and the maximum size is 161 

 mm and 201 mm total length for males 

 and females, respectively. During June, 

 when specimen collections were made, 

 ovaries are in the resting stage and con- 

 tain some residual eggs from a previ- 

 ous spawning. The diet of G. pistilliger 

 changes from predominantly gammarid 

 amphipods and polychaetes to cran- 

 gonid shrimp and fish with increased 

 total length. Comparisons with studies 

 from the western North Pacific on G. 

 pistilliger suggest biological differences 

 between populations, which may reflect 

 adaptation to different habitats. 



Biology and ecology of threaded sculpin, 

 Gymnocanthus pistilliger, in the eastern Bering Sea 



Gerald R. Hoff 



National Marine Fisheries Service 

 Alaska Fisheries Science Center 

 7600 Sand Point Way NE 

 Seattle, Washington 98115 

 E-mail address jerry hoffuj'noaa gov 



Manuscript accepted 2 June 2000. 

 Fish. Bull. 98:711-722 (20001. 



Gymnocanthus pistilliger (Pallas), the 

 threaded sculpin, is a small marine 

 cottid that inhabits waters from South- 

 east Alaska north to Norton Sound 

 and west to Russia and Japan (Wilson, 

 1973). It is found in shallow waters 

 (<50 m) over soft sandy to muddy bot- 

 toms and is the most abundant cottid 

 in the Bristol Bay region (>15 m) of 

 the eastern Bering Sea. Gymnocanthus 

 pistilliger may compete for resources 

 with juvenile stages of commercially 

 important flatfish in the shallow bays 

 and nearshore areas used as nursery 

 grounds (Grigorev and Fadeev, 199.5). 

 Although G. pistilliger is an abundant 

 species, little life history information is 

 available on Bristol Bay populations. 

 The present study reports on the ecol- 

 ogy and biology of G. pistilliger from 

 Bristol Bay, Alaska, and compares it to 

 ecology studies conducted on western 

 North Pacific populations. 



Methods 



Specimens of G. pistilliger were col- 

 lected in June of 1997 and 1998 during 

 the National Marine Fisheries Service, 

 Alaska Fisheries Science Center (AFSC ), 

 eastern Bering Sea survey. The survey 

 area extended from the Alaska Penin- 

 sula north to Nunivak and St. Matthew 

 Islands, and west to the 200-m shelf 

 break (Fig. 1). Trawls were conducted 

 on a grid of 356 fixed stations (20 nmi 

 X 20 nmi) fished during daylight hours 

 throughout the Bering Sea sui-vey area. 

 Thirty-minute trawls towed at 3.0 knots 

 were conducted at each station. The 

 shallowest depth surveyed was 15 m 

 in Bristol Bay and the deepest was 

 178 m near the shelf edge. Trawling was 

 conducted with the AFSC 83-112 east- 



ern trawl, which is a low-opening two- 

 seam trawl with a 26.5-m headrope and 

 34.1-m cable footrope (Rose and Wal- 

 ters, 1990) wrapped with rubber strip- 

 ping and chain hangings that contact 

 the bottom while the trawl is towed. 

 Height and width measurements of the 

 net were recorded with an acoustic 

 SCANMAR net mensuration system. 

 Global positioning system was used to 

 record latitude and longitude data at 

 the start and end of the trawl in order 

 to determine distance fished. 



The entire catch was sorted to spe- 

 cies, enumerated and weighed, or a 

 weighed subsample was used if there 

 was a very large catch. Catch per unit 

 of effort (CPUE) was calculated as 

 number offish per hectare (no./ha) by 

 dividing the number of fish caught for 

 each haul by the estimate of the area 

 swept (net width x distance fished). 

 Gymnocanthus pistilliger occurred m 

 the survey area only at stations less 

 than 50 m in depth (Fig. 1); therefore 

 only this area was used for calculating 

 population estimates. A population esti- 

 mate was calculated by first deter- 

 mining a mean CPUE from all hauls 

 combined (<50 m) and then expanded 

 to the area. The biomass estimates 

 were calculated in a similar manner by 

 using weight in metric tons. The popula- 

 tion and biomass estimates were made 

 under the assumption that all fish in 

 the path of the trawl were caught and 

 were a representative sample for each 

 station grid. However, given that there 

 may be gear selectivity for fish size and 

 given the patchy nature of fish distri- 

 butions, the populations and biomass 

 stated in this study are best estimates. 

 In May of 1995 and June of 1988-91 

 exploratory trawling was conducted in 

 the shallow bays (<30 m) within Bristol 



