Somerton and Donaldson: Biology of Chionoecetes tannen and C. angulatus 



349 



63 00N 



tribution (Hughes, 1981; Alton, 1986) has 

 been reported for Alaskan waters. Further- 

 more, nothing about the biology of C. 

 angulatus has ever been reported. We collected 

 information on both species on a 1982 Japan- 

 U.S. cooperative trawl survey of the continen- 

 tal slope of the eastern Bering Sea. Here we 

 summarize these data, focusing on the depth 

 and size distributions, sizes at maturity, 

 weight-size relationships, and various aspects 

 of the reproductive biology of both species. 



Materials and methods 



Sampling of C. tanneri and C. angulatus was 

 conducted from the Japanese stern-trawler, 

 Ryujin Maru No. 8, on the continental slope 

 of the eastern Bering Sea between 58.3"N and 

 60.9°N latitude (Fig. 1). Crabs were captured 

 with a bottom trawl that measured 23 m be- 

 tween the wings, had a codend consisting of 

 three layers of 90-mm mesh, and had a 

 footrope equipped with 55-cm diameter steel 

 bobbins. The study was divided into two 

 parts: from 11 July to 4 August 1982, scien- 

 tists from the Alaska Fisheries Science Cen- 

 ter collected data on all of the biological pa- 

 rameters described below; from 8 August to 25 Au- 

 gust, Japanese scientists collected only carapace 

 width data. For both parts, species identification was 

 based on characteristics provided in Garth ( 1958). 



Maximum carapace width of all crabs was mea- 

 sured with vernier calipers to the nearest 1.0 mm, 

 excluding lateral spines. In the first part of the study, 

 both sexes were evaluated for shell condition and 

 females were additionally evaluated for reproductive 

 condition. Shell condition was rated on a 4-point 

 scale, based on hardness, color, and wear of the ex- 

 oskeleton (see Somerton, 1982), which represents the 

 approximate time interval since the last molt. Briefly, 

 the characteristics of each shell-condition category and 

 its assumed postmolt interval (PMI) are as follows: 



1 carapace pliable (PMI <2 wk); 



2 carapace hard, little wear on tips of dactyli, few 

 scratches (2 wk <PMI <1 yr); 



3 carapace hard, conspicuous wear on tips of dac- 

 tyli, abundant scratches (1 yr <PMI <2 yr); 



4 same as condition 3, except that wear on dactyli 

 is more pronounced (PMI >2 yr). 



Reproductive condition was rated on a 5-point scale. 

 Characteristics of each reproductive condition cat- 

 egory are as follows: 







- 



Alaska 



Figure 1 



Area surveyed during the Japan-U.S. cooperative survey of the slope 

 of the eastern Bering Sea. The 100-m (dotted line), 200-m (dashed 

 line), and the 1,000-m (solid line) isobaths are shown for the east- 

 ern Bering Sea. 



1 immature — narrow flattened abdomen; 



2 nonovigerous — no embryos or empty egg cases 

 attached to the pleopod setae; 



3 uneyed embryos — embryos without conspicuous 

 dark eyes; 



4 eyed embryos — embryos with clearly visible dark 

 eyes; 



5 empty egg cases — empty egg cases and funiculi 

 attached to the pleopod setae. 



Whenever possible, one or more of the following types 

 of data were also collected: 



• height of the right chela of males (excluding males 

 with partially regenerated right-hand chela) mea- 

 sured to the nearest 0.1 mm according to the defi- 

 nition in Jamieson et al. ( 1990); 



• total wet body weight of intact males measured to 

 the nearest gram on a triple-beam balance; 



• uneyed egg masses from ovigerous females ( stored 

 in formalin diluted to 10% with seawater). 



Egg masses were processed as follows: mean egg 

 diameter was estimated by randomly selecting 10 

 eggs from each of 10 randomly selected egg masses 

 and measuring the diameters to the nearest 0.1 mm 

 with an ocular micrometer. Fecundity was estimated 



