Using acoustic monitoring to evaluate MPAs for shark nursery areas: the importance of long-term data

Abstract

The presence and movements of a population of young blacktip sharks (Carcharhinus limbatus) was monitored via a series of acoustic hydrophones over a period of three years to examine their use of a coastal nursery area. Data from this project were used to investigate the efficacy of hypothetical marine protected areas for this population. Small and large reserve designs were used to determine which would provide better protection for this population. The small reserve provided consistent levels of protection across years with sharks receiving good protection early in the summer season, but with declining protection thereafter. The large reserve provided less consistent levels of protection across years, but provided protection for a greater portion of time than the small reserve. Excursions from the small reserve were high early in the season and declined as sharks used this region less through the later portion of the summer. Excursions from the large reserve did not show any consistent pattern, but were also high early in the season and decreased through time as sharks used less of the reserve area. These results, coupled with previously calculated mortality estimates, revealed that the large reserve provided better protection for young sharks during their most vulnerable period within the nursery. We suggest that time-area closures for nursery populations of highly mobile shark species may be of value. Results of this study also show that long-term data may be critical to effective reserve design and placement, and assessment of reserve efficacy.