ARMETTA and STEVENS: BIOLOGY OF THK HAIR CRAB 



surveys occurred at a mean temperature 

 (weighted by crab abundance) of 3.4°C and depth 

 of 65.6 m, although they ranged from -0.9° to 

 10.1°C and from 22 to 249 m depth. One male hair 

 crab was found outside this range, at 401 m. The 

 mean values for females were 2.4''C (range -C.9°- 

 7.3°C ) and 63.8 m depth (range 26-243 m). Results 

 of a 2-sample ^-test with unequal variances 

 (Minitab "Twosample T" test; Ryan et al. 1976) 

 indicated there was no significant difference 

 (^ = 1.52, df=213, P=0.13) between mean 

 depths at which male and female hair crab were 

 found; however, there was a significant difference 

 it = 5.82, df = 219, P < 0.01) between mean tem- 

 peratures. 



Data from the Pribilof Island study of May 1983 

 indicate that hair crab appear to prefer a het- 

 erogenous substrate as early juveniles, switching 

 to sandy bottoms with increasing age. Among 120 

 juveniles <20 mm CL, 41% were on a substrate of 

 gi-avel (less than about 1 cm diameter), poly- 

 chaete tubes, and shell fragments, and small 

 numbers were found in areas of large rocks, mud, 

 or large shells. A substrate of medium or fine 

 sand (usually containing shell fragments) was oc- 

 cupied by 589f of crabs in the size range <20 mm 

 CL, 70% of 10 crabs in the range 20-40 mm CL, 

 94% of 73 males >40 mm CL, and all 48 females 

 >40 mm CL. 



Reproduction 



The scarcity of juvenile and female hair crabs 

 in NMFS collections prevented a thorough study 

 of reproductive characteristics of the EBS popula- 

 tion; only eight ovigerous females were caught 

 from 1979 to 1985. The size at maturity of these 

 crabs in the EBS is unknown, however, the 

 smallest mature female caught by NMFS was 38 



mm CL and had spermathecae filled with a vis- 

 cous liquid, indicating it had been mated. The 

 smallest female with empty egg cases caught by 

 NMFS was a 42 mm CL old hard-shell crab. We 

 follow Abe ( 1977) in assuming that the mean size 

 at maturity for female hair crab is above 55 mm 

 RL (50 mm CL). 



Some female hair crabs collected during NMFS 

 summer surveys were found with hard, proteina- 

 ceous plugs in the gonopores. The plugs were root- 

 like in appearance and formed a large, whitish, 

 irregular-shaped protuberance outside the aper- 

 ture (Fig. 8a). Each plug had a white, tapered 

 stem that extended inward to the spermatheca 

 (Fig. 8b). Some gonopores without plugs were 

 closed by a flexible, swollen membrane (Fig. 8c) 

 similar to the arthrodial membrane and continu- 

 ous with the lining of the canal leading to the 

 spermatheca. Some gonopores were open (Fig. 

 8d), owing to the flexible membrane having be- 

 come flaccid. 



Although the presence of closed pores was not 

 associated with any particular shell condition of 

 the female, plugs and open pores were. Plugs 

 were present only in recently molted soft-shell 

 crabs, while most females with open pores (28 of 

 30, or 93%) were new or old hard-shell crabs. 

 Some females had only one plug, and 96'7( of these 

 also had the other pore closed. During the May 

 1983 OCSEAP cruise, 40% (19) of the 48 large 

 females O40 mm CL) caught had plugged 

 gonopores, 1 had new uneyed embryos, 4 carried 

 eyed embryos that were in the process of hatch- 

 ing, and 11 carried empty egg cases. Of the 19 

 females with plugged gonopores, 89'}^ (17) were 

 new hard-shell crabs and 2 were newly molted 

 soft-shell crabs. 



Most female hair crabs caught carried no exter- 

 nal embryos (Table 3A). Although few crabs with 



Table 3. — Seasonality of egg bearing and molting in Erimacrus isenbeckii Uom the eastern Bering 

 Sea. A) Percent of female crabs (actual number in parentheses) with embryos in each of 4 

 developmental stages. B) Percent of molting or soft-shelled crabs for each sex (total number of 

 males or females caught shown in parentheses). 



February surveys 

 1983 1985 



Summer surveys, 1979-1984, years combined 



A. Condition of external embryos 

 None 86(26) 93(14) 

 Uneyed 7(1) 

 Eyed 7(2) 

 Hatched 7(2) 



B. Frequency of molting or soft-shell crab 

 Male 20.0(136) 0.0(56) 

 Female 30.0(30) 6.7(15) 



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