Abstract
Soft-shelled lobsters pose economic challenges to the lobster industry due to low meat yields and survivability during holding and transportation. Our objectives were to describe spatio-temporal patterns of soft-shelled lobsters in southwestern Nova Scotia, and identify environmental and lobster-related factors associated with shell quality. We analyzed data obtained from a broad-scale, intensive monitoring project and remotely sensed water temperatures. Mixed-effect logistic regression and linear regression methods analyzed more than 130 000 samples collected between 2004 and 2014. The annual overall prevalence of soft-shelled lobsters ranged from 9% to 38% and varied significantly among fishing areas. Shell quality was influenced by sex and size, and in the 2 months before the fishing season, lower water temperatures (4–6 weeks prior to sampling) were associated with reduced prevalence of soft-shells. High annual variability of soft-shell prevalence, that water temperature alone could not explain, suggests that adjusting fishing seasons, arbitrarily, in two fishing areas will not improve the overall shell quality of landed lobsters. Further research is needed to evaluate the effects of long-term temperature and ecosystem changes on lobster health in eastern Canada.
Highlights
The Atlantic lobster (Homarus americanus), fished across 40 managed lobster fishing areas (LFAs) in the Atlantic provinces and Québec, is one of the most important iconic seafood exports of Canada and is worth more than $1 billion (CAD) annually (Department of Fisheries and Oceans (DFO) 2014) with sustained increases in market demands.Since the early 2000s, there has been a significant increase in the proportion of soft-shelled lobsters landed in southwest Nova Scotia (SWNS) (ASHS 2014)
We evaluated the effect of making the fishing season dynamic, depending upon water temperature profiles in preceding weeks, by choosing the week for the start of the fishing season in each study year based on a cutoff temperature, and estimated the corresponding changes in probability of soft-shelled lobsters three weeks before and three weeks after that week
The longer-term trend of increasing water temperatures in the North Atlantic together with the recent observed increases in both the abundance and size of lobsters in Canadian fishing areas make it difficult to identify a single risk factor associated with soft-shelled lobsters
Summary
The Atlantic lobster (Homarus americanus), fished across 40 managed lobster fishing areas (LFAs) in the Atlantic provinces and Québec, is one of the most important iconic seafood exports of Canada and is worth more than $1 billion (CAD) annually (Department of Fisheries and Oceans (DFO) 2014) with sustained increases in market demands.Since the early 2000s, there has been a significant increase (from historically 5–10% to over 30–40% in recent years) in the proportion of soft-shelled lobsters landed in southwest Nova Scotia (SWNS) (ASHS 2014). Lobster shell hardness is directly related to the timing of their molting stages, a natural process whereby they shed their exoskeleton, allowing them to grow (Cobb and Phillips 2012; Howell 2012). While they molt, a new, soft shell is formed, and lobsters actively take in water to expand and stretch this soft exoskeleton (Glenn and Pugh 2006; Laufer et al 2013). Recently molted lobsters have reduced meat yield and excess water content, which is sometimes undesirable to consumers (Wang and Mcgaw 2014). In the days to weeks following molting, excess water is replaced with new tissue growth and re-mineralization of the newly formed exoskeleton, producing harder shells (Howell 2012)
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