Spatial dynamics of female snow crab (Chionoecetes opilio) in the eastern Bering Sea

Abstract

Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Based on preliminary information, we hypothesized that females undergo an extensive ontogenetic migration, tracking down environmental gradients. We analyzed a 25-year time series of survey data and defined ontogenetic stages in terms of a "shell condition index" calibrated with radiochemical methods. "Pseudo-cohorts" of mature females (groups of females that undergo puberty molt in a given year) "recruit" to the mature female pool in the Middle Domain (50–100 m) of the intermediate shelf. Females undergo puberty molt and primiparous mating in winter. Over the next year, they migrate an average net distance of 73.5 nautical miles towards the shelf edge following a predominantly northeast–southwest direction. Maximum post-terminal molt life span is 6–7 years. Results support the hypothesis that the variable tracked is near-bottom temperature. Although near-bottom temperature fields vary from year to year, the corresponding vector field is a conservative template, which explains the consistency observed in the pattern of migration. Elucidation of the life history schedule of mature female snow crabs in the eastern Bering Sea revealed that it is very similar to that reported for eastern Canada, although patterns of migration may differ substantially between the two systems.

Size-frequency distribution, growth, and mortality of snow crab (Chionoecetes opilio) and arctic lyre crab (Hyas coarctatus) in the chukchi sea from 2009 to 2013

“…Migrations of adolescent and mature crabs could play a role in explaining this unconventional finding of large C. opilio in the Beaufort Sea, and the observed latitudinal cline in this study. Ontogenetic migrations tend to follow an "upstream" pattern regarding local currents (Ernst et al, 2005). This seems contrary to the observed pattern as larger crabs were found in the southern regions of the study area; however, large C. opilio have also been found in the Beaufort Sea, and southwestward migrations of females were also observed in the Bering Sea (Ernst et al, 2005;Rand and Logerwell, 2011).…”

“…Bering Sea water usually replaces the cold, dense winter water that forms on Hanna Shoal in the early summer but slower flushing times could result in the colder bottom water temperatures observed in 2012 and 2013 (Day et al, 2013;Weingartner et al, 2005). The reduced productivity of brachyuran crabs in sub-zero temperatures may be causing ontogenetic migrations to deeper waters (Ernst et al, 2005;Orensanz et al, 2007;Sainte-Marie and Gilbert, 1998). Sub-zero temperatures limit or even inhibit crab growth and lead to smaller sizeat-maturity (Ernst et al, 2005;Kolts et al, 2015).…”

“…The reduced productivity of brachyuran crabs in sub-zero temperatures may be causing ontogenetic migrations to deeper waters (Ernst et al, 2005;Orensanz et al, 2007;Sainte-Marie and Gilbert, 1998). Sub-zero temperatures limit or even inhibit crab growth and lead to smaller sizeat-maturity (Ernst et al, 2005;Kolts et al, 2015). Ontogenetic migration of adult C. opilio females out of extremely cold temperatures results in increased reproductive potential because size-at-maturity is limited at cold temperatures and this decreases their reproductive potential.…”

“…However, explanations for this extreme recruitment variability remain not well known (Émond et al, 2015). Along with temporal variability, spatial variability has been observed along a latitudinal cline in the Bering Sea and the Gulf of St. Lawrence, with C. opilio size decreasing with increasing latitude (Ernst et al, 2005;Sainte-Marie and Gilbert, 1998). This finding seems to be directly related to lower bottom water temperatures or an environmental covariate (Burmeister and Sainte-Marie, 2010;Somerton, 1981).…”

“…They are found over a wide depth range, with C. opilio occurring between 30-1400 m water depth at year round bottom water temperatures of −1.5 to 4°C (Dawe and Colbourne, 2002), and H. coarctatus occurring between 2 and 457 m water depth and a similar temperature range as C. opilio (Bryant, 1991). Both species are found on muddy or sandy grounds, and are carnivorous, cannibalistic and opportunistic feeders, preying on gastropods, ophiuroids, crustaceans, bivalves and polychaetes with polychaetes, bivalves and amphipods being the more frequently consumed prey items by C. opilio in the Chukchi Sea (Bryant, 1991;Dawe and Colbourne, 2002;Divine et al, 2015;Ernst et al, 2005;Kolts et al, 2013;Wieczorek and Hooper, 1995a). …”