ARMETTA and STEVENS: BIOLOGY OK 11 IK IIAIK CKAB 



RESULTS 



Distribution and Abundance 



In the EBS, hair crab range from Bristol Bay 

 west to about long. 174°00'W and north to St. 

 Matthew Island at lat. 60"30'N (Fig. 7). Because 

 so few juvenile and female hair crab were caught 

 in NMFS surveys, the following information on 

 distribution and abundance primarily concerns 

 large males. Since fishery landings consist pri- 

 marily of male crabs >89 mm CL, these are called 

 "large", whereas "small" refers to male crabs <90 

 mm CL. 



Within the survey area, the crabs are divided 

 into eastern and western centers of abundance. 

 The western group occurs primarily in the Pri- 

 bilof District (Alaska Department of Fish and 

 Game [ADF&G] statistical district; south of 

 58°39'N, and west of 168°00'W) and is most dense 

 (>10 crabs/nmi trawled) immediately adjacent to 

 the Pribilof Islands. Moderately dense concentra- 

 tions (1-10 crabs/nmi trawled) surround the Pri- 

 bilof high-density region, especially to the north- 

 east and south. The eastern gi'oup occurs in the 

 Bristol Bay District (south of 58°39'N and east of 

 168°00'W) and is centered along the northern 

 shore of the Alaska Peninsula from western Uni- 

 mak Island to about 160°00'W. This group is mod- 

 erately dense, with areas of high density (10-100 

 crabs/nmi trawled) located near the western end 

 of the Alaska Peninsula in 1979, and offshore of 

 Unimak Island in 1981. Hair crab are scattered 

 across the continental shelf between these two 

 major population centers and in the Northern 

 District (north of 58°39'N) in low densities 

 (<1 crab/nmi trawled). As with large males, 

 small males and females displayed distinct east- 

 ern and western concentrations, but very few 

 were scattered between these two regions. Be- 

 cause of the more-or-less continuous distribution 



of hair crab across the EBS, we subsequently 

 treat them as belonging to a single widespread 

 population. 



Population estimates have been made for hair 

 crab only since 1979 (Table 2), and as previously 

 mentioned, these reflect primarily the abundance 

 of large males. From 1979 to 1981, the estimated 

 population of EBS hair crab remained fairly sta- 

 ble between 22 and 24 million crabs. The popula- 

 tion dropped 607( between 1981 and 1982, 35'7r 

 from 1982 to 1983, and 307f more from 1983 to 

 1984, to a low of only 4.4 million crabs. {Note 

 added in proof: Hair crab abundance has contin- 

 ued to decline to a total of 2.5 million crabs in 

 1986.) From 1979 to 1984, an average of 67Vr of 

 the EBS hair crab occurred in the Pribilof Dis- 

 trict, 279^ in the Bristol Bay District, and 67( in 

 the Northern District. Although the total popula- 

 tion size did not vary greatly from 1979 to 1981, 

 the proportion of the population in the Pribilof 

 District increased from 51 to 81'7( , while it de- 

 creased from 40 to 18% in the Bristol Bay District, 

 and from 9 to 1% in the Northern District. By 

 1984, the population distribution was again simi- 

 lar to that of 1979. The population was very 

 densely concentrated around the Pribilofs in 

 1981; however, since that time, the densities and 

 range of hair crab in the EBS have declined 

 greatly. 



Females comprised only 8% (248) of the total 

 catch of about 3,091 hair crab during the 1979-84 

 NMFS summer surveys. In contrast, females ac- 

 counted for 40% (48) of the 120 hair crabs >40 mm 

 CL caught during the survey conducted in the 

 Pribilof Islands in May 1983, when fishing was 

 conducted both day and night around the Pribilof 

 Islands, with dredge, try-net and beam trawl. 



Habitat 



Male E. isenbeckii collected during the summer 



Table 2. — Population estimates for Erimacrus isenbeckii. in the eastern Bering Sea, and proportions of the total population present in each 

 statistical district. See text and Figure 7 for description of districts. Numbers are millions of crabs', M = Male, F = Female. 



1 Numbers represent only crabs within the survey area and those large enough to be retained by the trawl, i e mostly large males 

 2Two standard errors expressed as a percentage of the mean 



■89 mm CL) 



531 



