Use of passive acoustic monitoring to estimate fishing effort on artificial reefs in Alabama during the recreational red snapper fishing season

Estimating fishing effort is an important aspect of effective fisheries management for populations such as red snapper (Lutjanus campechanus) in the Gulf of Mexico. Monitoring effort, however, can be limited by where and when anglers can be easily observed, such as boat launches or aerial surveys. Passive acoustic monitoring (PAM) can be used to detect boat presence spatially and temporally, which can be used to infer fishing effort. In this study, we deployed PAM devices at multiple artificial reef sites (up to three at a time) in federal waters of the Alabama Reef Permit Zone during the recreational red snapper fishery in 2017 and 2018. Reefs at our deployment sites included multiple structure types (concrete and steel pyramid modules, bridge rubble reefs, chicken coops, and M1 tanks). Reef sites included a mix of publicly available reef coordinates (published reefs) and unpublished sites. To improve reliability of estimates of site-specific fishing activity from captured boat noise, we developed a method to automatically detect sounds indicative of idling vessels maintaining station (live-boating) near an artificial reef. Detections of boat gearshift sounds were consistent with our prediction that fishing effort would be reduced on unpublished sites, decrease as the season progressed, and show a strongly diurnal pattern. Counter to our prediction, fishing effort as measured by boat detections did not appear to differ between open and closed recreational fishing days at our sites, which may be partially explained by commercial fishers that operate on an individual quota system that allows for fishing on days closed to recreational fishers. Our results indicate that PAM in conjunction with this novel method could be an effective way to monitor daily and longer term patterns of live-boating fishing vessel presence at specific artificial sites for the red snapper fishery in the Gulf of Mexico.