FISHERY BULLETIN: VOL. 85, NO. 3 



ner) crab iChionoecetes bairdi and C. opilio) also 

 occurred in the EBS (Stevens and Macintosh 

 1985^). These events may be responses to common 

 causes such as changes in the oceanogi'aphic envi- 

 ronment of the Bering Sea, increased predation, 

 or increased incidence of disease. A. K. Sparks^*^' 

 indicated that a presumptive viral infection was 

 present in 13 of 20 hair crabs collected oppor- 

 tunistically in 1983, and in 2 of 3 examined from 

 1984 collections in the EBS. Although damage to 

 the antennal gland in these infections suggest 

 that the disease is fatal, this has not been proven. 

 Fishery removals have ranged from <1% (before 

 1980) to a high of 11% (1983) of the estimated 

 population of large males, which is probably 

 underestimated (see Tables 1 and 2). Thus fishing 

 pressure does not seem to have played a signifi- 

 cant role in the population decline. A more plausi- 

 ble explanation of the decline in the hair crab 

 population (and perhaps other EBS crab species 

 as well) is that very large year classes may have 

 been produced in the EBS in the late 1960's or 

 early 1970's, recruited to the fisheries in the pe- 

 riod 1977-80, and then declined to lower levels as 

 these crabs succumbed to mortality. Historical 

 data support this hypothesis for red king crab, 

 and it may be applicable to hair crab as well as 

 other species of crab. 



Changes in the proportions of the hair crab pop- 

 ulation in various districts of the EBS (Table 2) 

 may indicate that many crabs shifted from the 

 Bristol Bay and Northern Districts into the Pri- 

 bilof District and back again over the 6 survey 

 years, or more likely, that the eastern and north- 

 ern segments of the population began to decline 

 several years before the Pribilof population, 

 which may have been increasing until 1982. Bot- 

 tom temperature did not seem to be an important 

 factor in determining distribution of hair crab 

 since there was no narrow range of tempera- 

 ture consistently associated with high catch 

 rates. 



The low percentage of female hair crab caught 

 in the annual NMFS summer trawl surveys, com- 



yStevens, B. G., and R. A. Macintosh. 1985. Report to in- 

 dustry on the 1985 eastern Bering Sea crab survey. NWAFC 

 Processed Rep. 85-20, 48 p. Kodiak Facility, Northwest and 

 Alaska Fisheries Center, National Marine Fisheries Service, 

 NOAA, P.O. Box 1638, Kodiak, AK 99615. 



1" A. K. Sparks, Fisheries Research Biologist, Northwest and 

 Alaska Fi.sheries Center, National Marine Fisheries Service, 

 NOAA, 7600 Sand Point Way N.E., Seattle, WA 98115, pers. 

 commun. May 1985. 



pared with the relatively high percentage caught 

 in the May 1983 survey, might be a result of gear 

 selectivity, and possibly indicates that females 

 were more abundant in shallow (<25 m) water or 

 nearshore habitats that were not heavily sampled 

 during the summer surveys. Low proportions of 

 female hair crabs have also been captured during 

 surveys around Hokkaido, where females 

 comprised only 1-12% of the total catch 

 (Kawakami 1934; Hirano 1935; Matui 1970). 

 Hirano (1935) felt that the low numbers could be 

 attributed to the small size of females in relation 

 to mesh size of the net used for sampling, a prefer- 

 ence by females for different habitats, or perhaps 

 frequent burrowing. In a laboratory experiment, 

 Hirano noted that females burrowed as deep as 

 13-15 cm for up to 4 days, whereas males 

 burrowed for relatively short periods of time and 

 usually so shallowly that the carapace protruded 

 at the surface. Most (90%) of the adult females 

 collected in the May 1983 survey were caught by 

 trawl or try-net between the hours of 1900 and 

 0600. Abe (1973), however, found very little 

 difference in the trawl catches of females between 

 night (two 1-h tows at 2100 and 0330; 11 caught) 

 and day (two 1-h tows at 0900 and 1500; 9 

 caught), although he did find that females were 

 significantly more vulnerable to crab pots during 

 the day (281 crabs/118 pots) than at night (46 

 crabs/115 pots). It is possible that increased activ- 

 ity of females during the day resulted in the 

 higher pot-catch. During Abe's survey, females 

 comprised 35% (347) of the total catch of 996 hair 

 crab. 



Depth, temperature, and substrate preferences 

 appear to be similar for EBS and Japanese popu- 

 lations of hair crab, although maximum annual 

 bottom temperatures in the EBS rarely exceed 

 12°C. 



Compared with the distribution of juvenile and 

 adult hair crab in the EBS, hair crab larvae were 

 distributed primarily north and northwest of Uni- 

 mak Island (Fig. 10) and concentrated in the 

 upper 40 m of the water column, during surveys 

 in the spring and summer of 1976-81 (Armstrong 

 et al. fn. 4). Highest concentrations (over 5,000 

 larvae/100 m") occurred from Unimak Island 

 north to about 55°30'N, mostly along the 50 m 

 isobath. Low numbers (1-1,000/100 m^) were scat- 

 tered broadly over shelf and slope areas, but were 

 more abundant along the 100 and 200 m isobaths. 

 Sparse sampling occurred in the Pribilof Islands 

 area during those surveys, but extensive sam- 

 pling was conducted there in May 1983 (Arm- 



540 



