758 



Fishery Bulletin 102(4) 



Results 



The sampled rays belonged to eight species (Table 1). Of 

 the 66 sampled rays, a total of 21 were dead at sampling, 

 four recovered breathing but then died, and 39 survived. 

 Two rays recorded as category DD in the "stamina 

 index" were released before full recovery after being held 

 for 4 to 9 hours in running water. Even though these 

 individuals were still breathing, both were considered 

 dead because they still had stiffened bodies and curved 

 wings. If they had been in such a state for a long time 

 in their natural habitat, they almost certainly would 

 have been consumed by scavengers or caught again by 

 another trawler. The overall survival rate was 59.1%, 

 female survival rate was 66.7%, and male survival rate 

 was 56.4%. 



All five rays assigned to the "stamina index" category 

 A were sampled between 5 and 30 min (mean 20 min) 

 after the catch was poured into the fish bin. All five 

 individuals began immediately to breathe normally and 

 recovered within 5 to 20 minutes. 



Of a total of 18 rays assigned to the "stamina index" 

 category I, which were sampled between 15 and 145 min 

 (mean 55.7 min) after haul, 88.9% (n=16) survived. The 

 breathing of these specimens at the time of sampling 

 was usually slow, although occasionally normal. Spira- 

 cle contraction rates gradually increased from an initial 



rate of 5-15 bit/min to 25-28 bit/min for B.brachiurops 

 specimens and to 35-38 bit/min for individuals of B. 

 albomaculata and Bathyraja sp. Upon attaining normal 

 breathing, they remained immobile, but fully recovered 

 between 15 minutes and 3 hours. 



The survival rate of 28 rays that were assigned to 

 the "stamina index" category D was 39.3% («=11). Of 

 the remaining individuals, two rays died after 15 and 

 45 minutes after being placed in running seawater and 

 15 rays were dead at the time of sampling. The skates 

 were sampled between 30 and 200 min (mean 84.2 min) 

 after the haul. Those that survived took 5-80 minutes 

 to recover normal breathing and between 15 and 315 

 minutes to attain full recovery. 



A total of 15 rays were assigned the "stamina index" 

 category DD. However seven of them (46.7%) survived. 

 These individuals were sampled between 20 and 115 

 minutes (mean 63.9 min.) after the haul and fully re- 

 covered within 40 to 150 minutes. 



Survival rate varied substantially among the eight 

 species sampled (Table 1). In general, ray survival dras- 

 tically decreased and recovery time increased with the 

 time spent in the fish bin (Table 2). The critical dura- 

 tion in the fish bin appeared to be between one and two 

 hours; only one Psammobathis sp. survived more than 

 two hours in the fish bin and exhibited a surprisingly 

 fast recovery. 



