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Pattern and causes of a temperature-dependent gradient of size at terminal moult in snow crab (Chionoecetes opilio) along West Greenland
Authors:AnnDorte Burmeister  Bernard Sainte-Marie
Institution:1. Greenland Institute of Natural Resources, P.O. Box 570, 3900, Nuuk, Greenland
2. Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, Rimouski, QC, G5L 3A1, Canada
3. Department of Fisheries and Oceans, Maurice Lamontagne Institute, 850 route de la Mer, CP 1000, Mont-Joli, QC, G5H 3Z4, Canada
Abstract:Geographic variation in size of male and female snow crabs (Chionoecetes opilio) was investigated along the west coast of Greenland to test the hypothesis that size at terminal molt (=adulthood) is temperature dependent. A total of 81,490 snow crabs were collected in small-mesh traps in Disko Bay (68–69°N) and six sites near Sisimiut (66–67°N) in May and June from 2000 to 2005. Average bottom temperature over the study period ranged from −0.8 to 3.2°C across the sampling sites. Mean carapace width was positively correlated with temperature in both sexes, a pattern often described as a converse Jame’s cline. We infer that temperature per se is the causative factor and discount season length, food availability or density as ultimate causes of the cline. Temperature effects on body size of crabs apparently result from a change in the number of instars before terminal molt. This interpretation is supported by size frequency analysis showing that in general crabs were larger at instar in a colder than in a warmer site. We briefly discuss the implications of our findings for population reproductive potential and the effectiveness of a fixed legal size limit in protecting some adult males from exploitation at different temperature regimes.
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