A Multi-Scale Study of Red Porgy Movements and Habitat Use, and Its Application to the Design of Marine Reserve Networks

Abstract

Understanding the movements of marine organisms in space and time has become a key area of research in support of management and conservation decision-making processes. This includes the optimal design of networks of marine reserves, as movements of fish are a major determinant for the reserve effect (increase in size and number inside reserves) and spillover effect (emigration from reserves). The increasing use of acoustic telemetry techniques, particularly passive acoustic arrays, is providing much of that information, but studies have typically used one specific approach at a specific spatial-temporal scale. We studied movement patterns, habitat use and dispersal in the red porgy, Pagrus pagrus (a commercially important species) in the Azores islands, mid-north Atlantic, with the aim of supporting the design of marine reserves that would protect local populations while enhancing fisheries. Movements were quantified using: (1) short-term active acoustic tracking; (2) multi-year passive acoustic monitoring; and (3) standard tag-release experiments in the Faial Channel. We found the short-term home ranges of red porgy to be quite large for a reef fish – up to 50 ha. Furthermore, frequent short-term displacements of up to 9 km and periodic absences from main core activity areas indicate that HR varies considerably in size and location throughout the year. Home range expansion occurred mostly during the protracted period of spawning activity, but we saw no evidence for spawning aggregations. We found evidence that individuals of smaller size utilize larger home ranges and are less site-specific, supporting the hypothesis that dispersal in the red porgy is largely determined by ontogenic changes. Large individual variability in both short-term and long-term movement patterns accounted for some emigrations from tagging sites and for one documented relocation. These findings indicate that adequate protection of subpopulations of red porgy will not be achieved using small, isolated reserves (1 to 5 km²), but reserves of size in the order of tens of km² and spaced a few kilometers apart should provide protection while promoting emigration (spillover) of red porgy from reserves to neighboring grounds. This study shows that the combination of spatial and temporal scales and approaches is needed to capture a realistic picture of the full suite of spatial behaviors used throughout a species’ life history.