Research Document - 2012/048
Temperature-corrected abundance index of sub-legal lobsters in LFA 33 – 1999-2000 to 2008-2009
By J. Allard, R.R. Claytor, and M.J. Tremblay
Abundance indices, temperature-catchability relationships, spatial abundance variation, and low-effort sampling schemes are of interest in the management of several crustacean fisheries. A low-effort sampling scheme and a mathematical model that simultaneously produces an estimate of the temperature-catchability relationship, a temperature-corrected catch-per-unit-effort (CPUE) based abundance index (TCAI), and a spatial abundance index for a non-exploited class of a population of crustaceans are presented. The sampling scheme is based on standardized traps monitored continuously through the fishery and water temperature recorders retrieved at the end of each season. The TCAI is obtained from a probabilistic model of the catch from a single sampling event as a function of the number of crustaceans available at the sampling location, the current temperature, and the catchability-temperature relationship. The parameters of the model, including the TCAI, are estimated by maximum likelihood and standard errors are obtained using Wald’s method. Model diagnostic procedures are proposed. The model is applied to data from Nova Scotia (Canada) Lobster Fishing Area (LFA) management zone LFA 33. In LFA 33, there is a strong association between catchability and water temperature, suggesting that the TCAI improves on CPUE. The TCAI indicates that the abundance of prerecruit lobsters in LFA 33 increased substantially (approximately 1.9 fold) from 1999 to 2009.
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