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 hasbecome a key area of research in support of management and conservationdecision-making processes. This includes the optimal design of networksof marine reserves, as movements of fish are a major determinant for thereserve effect (increase in size and number inside reserves) andspillover effect (emigration from reserves). The increasing use ofacoustic telemetry techniques, particularly passive acoustic arrays, isproviding much of that information, but studies have typically used onespecific approach at a specific spatial-temporal scale. We studiedmovement patterns, habitat use and dispersal in the red porgy, Pagruspagrus (a commercially important species) in the Azores islands,mid-north Atlantic, with the aim of supporting the design of marinereserves that would protect local populations while enhancing fisheries.Movements were quantified using: (1) short-term active acoustictracking; (2) multi-year passive acoustic monitoring; and (3) standardtag-release experiments in the Faial Channel. We found the short-termhome ranges of red porgy to be quite large for a reef fish - up to 50ha. Further-more, frequent short-term displacements of up to 9 km andperiodic absences from main core activity areas indicate that HR variesconsiderably in size and location throughout the year. Home rangeexpansion occurred mostly during the protracted period of spawningactivity, but we saw no evidence for spawning aggregations. We foundevidence that individuals of smaller size utilize larger home ranges andare less site-specific, supporting the hypothesis that dispersal in thered porgy is largely determined by ontogenic changes. Large individualvariability in both short-term and long-term movement patterns accountedfor some emigrations from tagging sites and for one documentedrelocation. These findings indicate that adequate protection ofsubpopulations of red porgy will not be achieved using small, isolatedreserves (1 to 5 km(2)), but reserves of size in the order of tens ofkm(2) and spaced a few kilometers apart should provide protection whilepromoting emigration (spillover) of red porgy from reserves toneighboring grounds. This study shows that the combination of spatialand temporal scales and approaches is needed to capture a realisticpicture of the full suite of spatial behaviors used throughout aspecies' life history.