Standardized CPUE of blue shark in the Portuguese pelagic longline fleet operating in the north Atlantic

Coelho, Rui; Santos, Miguel; Lino, Pedro

http://hdl.handle.net/10400.1/14883

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Authors

Coelho, Rui

Santos, Miguel

Lino, Pedro

Abstract(s)

This working document analyzes the catch, effort and standardized CPUE trends for the north Atlantic blue shark captured by the Portuguese pelagic longline fleet. Nominal annual CPUE were calculated as kg/1000 hooks and were standardized with Generalized Linear Models (GLM) and Generalized Linear Mixed Models (GLMM) using year, quarter, area, gear type, targeting effects and area:quarter interactions as fixed factors, and year:area as random effects. Sensitivity analyzes were carried out for the model type (lognormal, tweedie, gamma or delta lognormal), the definition of targeting effects (based on ratios or cluster analysis), and definition of areas. Model goodness-of-fit and comparison was carried out with AIC and the pseudo coefficient of determination (R2 ), and model validation with a residual analysis. The final standardized CPUE trend shows a general increase over the studied period, between 1997 and 2014, with some inter-annual oscillations. This paper presents the first index of abundance for the blue shark estimated from captures from the Portuguese pelagic longline fleet in the North Atlantic, and can be used in future stock assessments models.

Keywords

Blue shark Prionace glauca CPUE standardization North Atlantic Catch/effort Longline fisheries Fishery indicators Generalized linear models Generalized linear mixed models