Movement and spawning migration patterns suggest small marine reserves can offer adequate protection for exploited emperorfishes

Abstract

A critical feature of effective marine reserves is to be large enough to encompass home ranges of target species, thereby allowing a significant portion of the population to persist without the threat of exploitation. In this study, patterns of movement and home range for Lethrinus harak and Lethrinus obsoletus were quantified using an array of 33 acoustic receivers that covered approximately three quarters of Piti Marine Reserve in the Pacific island of Guam. This array was designed to ensure extensive overlap of receiver ranges throughout the study area. Eighteen individuals (12 L. harak and 6 L. obsoletus) were surgically implanted with ultrasonic transmitters and passively tracked for 4 months. Both species displayed high site fidelity and had relatively small home ranges. The home ranges of L. harak expanded with increasing body size. Feeding of fish by humans, which was common but restricted to a small area within the study site, had little effect on the distribution of the resident populations. L. harak made nightly spawning migrations within the reserve between full moon and last quarter moon of each lunar cycle, coinciding with a strong ebbing tide. Results indicate that even small reserves can include many individual home ranges of these emperorfishes and can protect spawning sites for L. harak. These species are heavily targeted in Guam, and there are major demographic differences between fished and protected sites. This study shows the potential for protected areas to sustain reproductive viability in exploited populations.