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Fishery Bulletin 92(2). 1994 



Aiken (1980) demonstrated that molting is inhib- 

 ited in American lobsters, Homarus americanus, at 

 5° C if active premolt is not achieved before water 

 temperature drops to that level. A similar physiologi- 

 cal response to declining temperature may have con- 

 tributed to the apparent reduction in molting in the 

 snow crab population off the Avalon Peninsula after 

 temperature dropped in 1982. 



Molting in Newfoundland snow crab in this area 

 generally occurs during May-August. The sharp de- 

 cline in abundance of new-shelled crab in Septem- 

 ber indicated that many animals that would normally 

 molt during this period apparently failed to do so, 

 possibly as a result of extremely cold water tempera- 

 tures. 



Both Bonavista Bay and the offshore Avalon are 

 affected by the Labrador Current. In 1982 the cur- 

 rent became wider and deeper than in previous years 

 causing a cooling effect throughout the water column 

 (Akenhead 7 ). Whereas this phenomenon affected the 

 entire east coast of Newfoundland, it was most se- 

 vere near the Avalon Peninsula primarily because of 

 its comparative shallowness ( 174-200 m). Bonavista 

 Bay is 220-486 m deep on the crab grounds and its 

 depth may reduce the cooling effect of the Labrador 

 Current (Akenhead 8 ). This may explain why snow 

 crab molting activity here was not as adversely af- 

 fected as it was on the Avalon crab fishing grounds 

 (Fig. 5). 



The lack of recruitment into the fishery, between 

 1982 and 1986, meant that the snow crab resource 

 off the Avalon Peninsula had been in effect "mined" 

 rather than harvested as a renewable resource. The 

 impact of the decline in snow crab abundance was 

 dramatic. This marked decline in landings, from the 

 Avalon Peninsula area, resulted in a substantial drop 

 in employment and earnings from the snow crab fish- 

 ery (Collins 9 ). 



Evidence of a link between temperature and molt- 

 ing is circumstantial. However, the drop in water 

 temperature followed by a rapid decline in molting 

 activity (Fig. 5), and subsequently CPUE (Fig. 4), 

 makes a compelling argument that the yearly pro- 

 portion of snow crab molting in an area is largely 

 dependent on environmental conditions in the par- 

 ticular case where temperatures are very low and 

 variable. The argument is supported by the observa- 



tion that twice between 1984 and 1988 water tem- 

 peratures rose and fell, affecting subsequent changes 

 in the proportions of crabs molting off the Avalon 

 Peninsula (Fig. 5). If molting of pre-recruit snow 

 crabs and consequent recruitment into the fishery 

 are affected by changes in water temperature, the 

 impact of these changes should be included in re- 

 source management programs. The existing policy 

 of allowing yearly exploitation rates of 50-60% should 

 be re-examined. As the effects of these environmen- 

 tal changes may be long term, recommended exploi- 

 tation rates could be reduced to prolong a fishery in 

 which recruitment has been interrupted. Assess- 

 ments of the fishery off the Avalon Peninsula (Tay- 

 lor and O'Keefe 4 ) indicate that exploitation rates 

 were <65% between 1979 and 1981. However, owing 

 to the failure of undersized males to molt into the 

 fishery beginning in 1982, each successive year's 

 standing stock was reduced until fishing was no 

 longer economically viable. In contrast, although 

 exploitation rates in Bonavista Bay consistently ex- 

 ceeded 75% (Taylor and O'Keefe 10 , 1983 11 , 1984b 12 , 

 and 1987 4 ), molting within the population continued 

 to provide sufficient recruitment for a viable fishery 

 even though catch rates declined. With the excep- 

 tion of 1983 when the incidence of new-shelled ani- 

 mals (shell condition 1 and 2) in research cruise 

 catches fell to 68% (Fig. 5), new-shelled animals com- 

 posed in excess of 85% of the catch of legal-sized and 

 immediate pre-recruits. This high level of molting 

 appears to have prevented the precipitous decline in 

 catches experienced in the offshore Avalon Peninsula 

 area. 



To prevent future declines of such proportions it 

 may be advisable to monitor temperature, catch 

 rates, and crab shell condition more closely on a sea- 

 sonal basis. Efforts should also be made to determine 

 thermal requirements for molting in snow crab. The 

 implications for resource management strategy are 

 simply that, regardless of exploitation levels, changes 

 in temperature likely affect molting and hence re- 

 cruitment to the standing stock to such an extent 

 that assumptions regarding long-term sustainability 

 of annual landings are not justified. 



' Akenhead, S. A. 1986. The decline of summer subsurface 

 temperatures on the Grand Bank, at 47°N, 1978-1985. NAFO 

 SCR Doc. 86/25, 8 p. 



8 Akenhead. S. A. Institute of Ocean Sciences, Box 6000, Saanick 

 Rd. Sydney, B.C. V81 4B2. Personal commun., April 1987. 



9 Collins, J. F. Chief, Economic Analysis Division, Program 

 Coordination & Economics Branch, Northwest Atlantic 

 Fisheries Centre, P.O. Box 5667, St. John's, Newfoundland A1C 

 5X1. Personal commun. September 1993. 



10 Taylor, D. M., and P. G. O'Keefe. 1981. Assessment of snow 

 crab (Chionoecetes opilio) stocks in Newfoundland, 1979. Can. 

 Atl. Fish. Sci. Advis. Comm. CAFSAC Res. Doc. 81/57, 

 Dartmouth, Nova Scotia, 34 p. 



11 Taylor, D. M., and P. G. O'Keefe. 1983. Assessment of snow 

 crab (Chionoecetes opilio) stocks, in Newfoundland in 1980. 

 Can. Atl. Fish. Sci. Advis. Comm. CAFSAC Res. Doc. 83/3, 

 Dartmouth, Nova Scotia, 40 p. 



12 Taylor, D. M., and P. G. O'Keefe. 1984b. Assessment of 

 Newfoundland snow crab (Chionoecetes opilio) stocks in 

 Newfoundland for 1982. Can. Atl. Fish. Sci. Advis. Comm. 

 CAFSAC Res. Doc. 84/3, Dartmouth, Nova Scotia, 30 p. 



