Quantifying the impact of environmental variables upon catch per unit effort of the blue shark Prionace glauca in the western English Channel

Abstract

The effect of environmental variables on blue shark Prionace glauca catch per unit effort ( CPUE ) in a recreational fishery in the western English Channel, between June and September 1998–2011, was quantified using generalized additive models ( GAMs ). Sea surface temperature ( SST ) explained 1·4% of GAM deviance, and highest CPUE occurred at 16·7° C, reflecting the optimal thermal preferences of this species. Surface chlorophyll a concentration ( CHL ) significantly affected CPUE and caused 27·5% of GAM deviance. Additionally, increasing CHL led to rising CPUE , probably due to higher productivity supporting greater prey biomass. The density of shelf‐sea tidal mixing fronts explained 5% of GAM deviance, but was non‐significant, with increasing front density negatively affecting CPUE. Time‐lagged frontal density significantly affected CPUE, however, causing 12·6% of the deviance in a second GAM and displayed a positive correlation. This outcome suggested a delay between the evolution of frontal features and the subsequent accumulation of productivity and attraction of higher trophic level predators, such as P. glauca .