Taylor et al.: Snow crab, Chionoecetes opilio, fishery collapse 



417 



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YEAR 



Figure 5 



Changes in the percentages of new-shelled Avalon Peninsula and 

 Bonavista Bay Chionoecetes opilio males > 70 mm CW in relation to 

 changes in bottom water temperatures on snow crab commercial fish- 

 ing grounds, 1979-88. Solid circles connected by solid lines represent 

 the proportion of new-shelled crabs and the triangles connected by a 

 broken line represent bottom water temperature. 



Although there was a significant 

 decline in the proportion of new- 

 shelled crab in 1983 after the water 

 temperature declined (68.4% vs. 

 97.7%) in the spring of 1982 this value 

 quickly rebounds in 1984 to 97.0% de- 

 spite only a marginal warming of the 

 water (Fig. 5). 



Discussion 



condition sampling in February 1986 indicated no 

 molting activity during the summer and fall of 1985 

 (Fig. 5). 



A further indication that the impact of these in- 

 creases in new-shelled animals was minimal is il- 

 lustrated by continuing low CPUE's (Figs. 3 and 4). 

 Large proportions of new-shelled animals and higher 

 CPUEs were not observed until the warming trend 

 of 1986 was firmly established. While the decline in 

 temperature between 1982 and 1983 is mirrored in 

 data collected during Bonavista Bay research cruises 

 (Fig. 5), the lowest temperatures encountered in 

 Bonavista Bay are roughly equivalent to normal tem- 

 peratures at Station 27 off Avalon Peninsula. 



The tight confidence intervals for the 

 Avalon Peninsula research cruise 

 CPUE's (Fig. 4) for 1982-1987 (except 

 February 1986) are indicative of just 

 how severe, widespread, and enduring 

 the resource depletion was in this 

 area. Each research survey fished sta- 

 tions randomly selected and stratified 

 by depth and covered virtually all the 

 approximately 3600 sq. km. of com- 

 mercial snow crab fishing grounds 

 (Taylor et al. 6 ). Had a sustained recov- 

 ery been made by the crab population 

 in any section of the commercial fish- 

 ing grounds, it would have almost cer- 

 tainly been detected, either by our re- 

 search cruises or by commercial crab 

 fishermen. 



Little is known about environmen- 

 tal factors that affect snow crab molt- 

 ing physiology. Low water tempera- 

 tures may inhibit molting in crabs 

 (Hiatt, 1948; Adelung, 1971; Leffler, 

 1972; Warner, 1977) and other deca- 

 pods (Travis, 1954; Aiken, 1980;Ennis, 

 1983). 



Foyle (1987) determined that snow 

 crab from Cape Breton Island are able 

 to maintain normal physiological func- 

 tions at temperatures much higher 

 than their normal temperature range. At high tem- 

 peratures however and at temperatures below 1°C, 

 reproductive growth and net energy consumption 

 become slightly negative. Snow crab on the north- 

 east coast of Newfoundland live at much lower wa- 

 ter temperatures (<-0.75°C) than do those off the 

 Cape Breton Island and a drop in temperature may 

 result in such a "deficit" in their energy budget that 

 molting physiology is impaired. 



Taylor, D. M., W. R. Squires,and P. G. O'Keefe. 1983. An alternate 

 methodology for estimating snow crab (Chionoecetes opilio) 

 populations in commercially fished areas. Can.Atl. Fish. Sci.Advis. 

 Comm. CAFSAC Res. Doc. 83/1. Dartmouth, Nova Scotia, 10 p. 



