The effect of fishing on fish movement, trophic cascades and species interactions

Fishing is a major driving force in marine systems. The behavioral and evolutionary changes associated with fishing are expected to be relaxed within MPAs, but it remains unclear under what conditions this occurs. We show here, using three different examples, how behavioral changes may impact MPA function and the interaction with surrounding fished areas. First, we examine whether fish home ranges differ between MPA and surrounding areas. Home range size will define the probability of remaining safe within that MPA or crossing its boundaries and being exposed to mortality. We find evidence that home range size is reduced close to MPA borders, but only in large MPAs. Second, we find that while MPAs contain the same biomass of invasive species as fished areas, invasive impact is reduced inside MPA. We attribute this to behavioral changes associated with the presence of large predatory grouper within MPA which induce fear in the invasive prey which reduces feeding rates. Third, we examine how interactions among species within guilds, estimated from co-occurrence patterns, differ between MPA and fished area. Surprisingly, we do not find major differences in interactions patterns between MPA and fished area. Taken together, it seems that fishing-induced changes in fish behavior are the strongest for individuals directly exposed to fishing, followed by indirect top-down interactions, while the impact of fishing on interactions within the same guild seem to be minimal. This has strong implications for understanding how fishing modifies fish behaviors and impacts MPA function.