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Fishery Bulletin 88(4), 1990 



examined and measured. Delayed survival (DSURV) 

 or mortality (DMORT) is that portion alive or dead 

 after crabs were held in seavi^ater for a specified time 

 period. 



Sampling technique 



An experiment was conducted during the period 12 

 August— 12 September 1987 to compare catch rates 

 between standard Bering Sea joint venture commer- 

 cial sole trawls and two experimental nets designed to 

 reduce the bycatch of crabs (Highliners Association 

 1988). Although the results of that experiment are not 

 discussed in this report, the experimental design will 

 be briefly described in order to facilitate understanding 

 of the survival experiment. During the study, five Ber- 

 ing Sea combination trawlers made 307 tows within an 

 area of the EBS between lat. 57° and 58°N, and be- 

 tween long. 162° and 163°W. Tows ranged from 1 to 

 6.4 hours in length and averaged 20 metric tons (t) of 

 fish. Target species were yellowfin sole Limandn 

 aspera, rock sole Lepidopsctta bilineatti. and Pacific 

 cod Gadus macrocephalus. One vessel fished continu- 

 ously with a previously used 'Standard' trawl (STD). 

 The four other vessels rotated four trawls between 

 them including two new and unused standard trawls, 

 referred to as 'Control 1' (Cl) and 'Control 2' (C2), and 

 two experimental trawls. One of the experimental 

 trawls, referred to as the 'Panel' (PAN) trawl, had the 

 front portion of the bottom panel removed and replaced 

 with longitudinal lines, such that crabs could fall out 

 the bottom of the net after passing over the footrope. 

 The second experimental trawl, referred to as the 

 'Chute' (CHU) trawl, had a webbed funnel-shaped chute 

 sewn into the lower half of the net at the junction be- 

 tween the belly and intermediate section, such that 

 anything entering the mouth of the chute would exit 

 the bottom of the net. During the experiment, codends 

 from each trawl were delivered to the USSR MV Sidak 

 at 2-3 hour intervals, where they were sampled by 

 biologists before processing. 



Once onboard the Sulak, codends were dumped, and 

 all crabs were recovered by sorting through the entire 

 catch. The first 21 tows were dumped on deck and 

 crabs sorted there. The remainder of the tows were 

 dumped directly into storage bunkers, and crabs were 

 recovered from the processing line conveyor in the fac- 

 tory, as the fish were processed. All crabs were sorted 

 by species (and usually by sex), placed into plastic 

 baskets (~25 kg capacity), and weighed. Because of 

 logistic constraints, higher priority was assigned to col- 

 lecting data on king crabs than on Tanner crabs. Total 

 numbers were determined either by direct counting, 

 or by counting and weighing a subsample. When sub- 

 sampling occurred, each crab was assigned a sampling 



factor equal to the proportion of the total number of 

 crabs in the tow represented by the subsample. Crabs 

 were then treated in one of four ways: 



(A) IVIeasured crabs Up to 150-200 crabs of each 

 species from each haul were measured to the nearest 

 1.0 mm with steel vernier calipers. Subsampling oc- 

 curred when >200 of either species were captured. 

 King crabs were measured from the rear of the right 

 eyesocket to the midpoint of the rear margin of the 

 carapace (carapace length, CL). Tanner crabs were 

 measured across the widest portion of the carapace, 

 including spines (carapace width, CW). Shell conditions 

 were coded as 1 = molting, or recently molted with a 

 soft or flexible shell; 2 = hard shelled but molted within 

 recent year, without epifauna or scratches; 3 = oldshell 

 or skipmolt, with scratches, epifauna, scars, or dam- 

 aged dactyls. 



(B) Vitality coding For most liauls, all measured 

 crabs were also given a vitality code on a 3-point scale: 

 (1) alive and active, i.e., exhibiting spontaneous vigor- 

 ous movement of appendages and attempting to escape 

 or pinch the examiner; (2) moribund (alive but inactive), 

 i.e., exhibiting only slow weak movements, or only in 

 response to prodding; and (3) dead. In practice, death 

 was not easy to determine, as some crabs which initially 

 appeared dead would exhibit spontaneous movements 

 after examination. After the first few tows, a criterion 

 was developed which consisted of (a) looking for spon- 

 taneous movement of ai)pendages, (b) lacking that, at- 

 tempting to stimulate movement by moving and bend- 

 ing appendages, followed by (c) flicking the mouthparts 

 with a finger three times at 5-10 second intervals. The 

 minimum requirement for a vitality code of 2 was any 

 spontaneous movement of the antennules or any other 

 appendage. These criteria were tested by placing 30 

 crabs which were classified as dead into the live tanks; 

 none recovered. Presence or absence of injuries was 

 not a criterion used in this coding procedure. 



(C) Injury assessment Approximately 30-40 king 

 crabs per tow (usually the first basket examined of each 

 sex) and occasional Tanner crab were examined for in- 

 juries. Since there was considerable shuffling and 

 repositioning of crabs and baskets during the weighing 

 and subsampling process, this was assumed to be a ran- 

 dom sample, and represents a subset of the crabs ex- 

 amined for vitality in step B above. Examination en- 

 tailed a visual scan of the carapace, sternum, abdomen, 

 and each leg in turn. Bodily injuries were recorded as 

 present or absent. Leg injuries were categorized as 

 being distal to the autotomy or breakage plane, prox- 

 imal to the breakage plane, or recent autotomy, dis- 

 tinguished by the presence of a clear membrane with 



