Uncovering causal interaction networks between target species in a multispecies recreational fishery.

In fisheries that opportunistically target multiple species, hierarchies in angler preferences, sea state, and any number of other biological or environmental factors may influence species-specific catch. In this study we use a uniquely long time series of landings from a multispecies fishery to investigate whether dependencies exist between species, and to what extent such dependencies vary through time as a result of external drivers (e.g. changes in fisheries regulations). We used convergent cross mapping (CCM) to identify causal relationships between species targeted by the San Diego commercial passenger fishing vessel fleet. CCM analyses uncovered complex interaction networks between species that varied across different time periods, suggesting that target species landings do causally influence each other in this fishery. We demonstrate that ecological, regulatory, and fisher preference changes that influence landings of individual species can have cascading effects throughout the portfolio of target species in this multispecies fishery. For instance, we found evidence that changes in the legal size and bag limit of one popular group of recreational fishes (Paralabrax spp.) had causal effects on catch in another complex of targeted fishes (Sebastes spp.). Our findings suggest that single species management rules are likely to have multispecies impacts. The identification of interaction networks, such as those introduced here may provide insight regarding the nature and extent of such multispecies impacts prior to management implementation.