416 



Fishery Bulletin 92(2). 1994 



These CPUE values were derived from only four 

 fishing sets that were placed on the commercial 

 fishing grounds opportunistically. 



On the commercial fishing grounds off the 

 Avalon Peninsula, CPUE's derived from research 

 cruises were nearly identical to those of commer- 

 cial enterprises at approximately 19.5 kg/trap 

 haul in 1979 (spring). However, CPUEs diverged 

 over the years primarily because commercial 

 vessels had a greater fishing range than the re- 

 search vessels. Nevertheless, the sharp drop in 

 CPUE between 1982 and 1983 was reflected in 

 both the commercial and research cruise data. 

 In the commercial fishery, CPUE dropped from 

 13.8 kg/trap haul in the spring of 1982 to 8.0 kg/ 

 trap haul in the spring of 1983 (Fig. 3). This de- 

 cline in crab abundance was mirrored in research 

 cruise data, which indicate a decline from 9.3 kg/ 

 trap haul to 2.9 kg/trap haul over the same pe- 

 riod (Fig. 4). 



Research cruise data for this period in 

 Bonavista Bay are not available. Logbook data, 

 however, indicate that CPUE dropped by only 0.2 

 kg/trap haul (Fig. 4). 



Data on shell conditions of legal-sized and pre- 

 recruit crabs from research cruises conducted off 

 the Avalon Peninsula demonstrate that the drop 

 in CPUE coincided with a decline in the propor- 

 tion of new-shelled crabs from 52.4% to 18.6% 

 (Fig. 5). In Bonavista Bay, the percentage of new- 

 shelled animals dropped to 68.4% in the fall of 

 1983 from 97.7% in the spring of 1982. However, 

 the proportion of new-shelled animals quickly 

 rebounded to 97%> in 1984 as opposed to 40.6% 

 off the Avalon Peninsula during the same year. 



Temperature data 



From the spring of 1978 through the first half of 

 1982, mean bottom temperature ranged from -0.3° C 

 to -0.8°C off the Avalon Peninsula (Fig. 5). During 

 the second half of 1982, the beginning of a trend to- 

 wards colder bottom temperatures was evident. Bot- 

 tom temperatures during this period dropped as low 

 as —1.6 C and rarely rose above — 1.0°C the entire pe- 

 riod of mid 1982 to 1986. Two brief periods of warm- 

 ing occurred in both 1983 and 1984 but these peri- 

 ods were short-lived and weak. In 1986 a general 

 warming trend began with an increase from the 1985 

 low of -1.6°C to around -1.1°C, a trend that has con- 

 tinued to the present. 



The drop in temperature and the decrease in the 

 proportion of new-shelled crabs appeared to coincide 

 with bottom temperatures declining during April- 

 May of 1982 whereas the percentage of new-shelled 



crabs dropped from 52.4% in April to 17.0% in Sep- 

 tember. Figure 5 illustrates that between 1982 and 

 1986 there were two brief periods (1983 and 1984) 

 when mean bottom temperature at Station 27 in- 

 creased slightly and coincidental increases in the 

 proportion of new-shelled animals followed in 1984 

 and 1985. This delay between increase in water tem- 

 peratures and appearance of new-shelled crabs is 

 consistent with our current understanding of snow 

 crab molting mechanisms (Moriyasu 5 ). 



The warming trend in July 1984 was short-lived 

 (Fig. 5). During 1985 water temperatures dropped 

 to the lowest level of all the years examined. Shell 



5 Moriyasu, M. Dept. Fisheries And Oceans, Gulf Fisheries 

 Centre, Box 5030, Moncton. N.B. E1C 9B6. Personal commun. 

 April, 1987. 



