Where there's a fin, there's a way: Fishery-dependent shark fishery monitoring in Puerto Rico using fisher-submitted secondary fins

Abstract

Small-scale shark fisheries in the Caribbean are subject to growing concerns regarding their sustainability. In Puerto Rico, a small-scale targeted shark fishery is driven by local demand for inexpensive shark meat. The complex jurisdictional framework involving disparate territory and U.S. federal regulations, coupled with lack of species-specific landings information, are obstacles to effective management. This study evaluates a new fisher-dependent monitoring approach to obtain species-specific landings data for Puerto Rico's shark fishery, and compares results to a previous characterization based on traditional, resource exhaustive surveys of landings sites. From November 2022 to May 2024, a monitoring program in which shark fishers submitted anal fins from landed sharks was implemented at two major landings sites. Morphology-based anal fin identification supplemented with DNA barcoding allowed species-specific enumeration of the landings. Regression of total length from anal fin size provided information on size structure of landings. These analyses revealed nine species in the fishery, with adult-sized Caribbean sharpnose (Rhizoprionodon porosus), which are federally prohibited, and juvenile-sized scalloped hammerhead (Sphyrna lewini), which are federally prohibited and listed as ‘Threatened’ under the U.S. Endangered Species Act (ESA), numerically dominating the catch. Over three-quarters of landed sharks are federally prohibited species, yet, they are landed legally in territory waters. These findings align with results from previous landings site surveys, suggesting this type of monitoring can be a useful supplement. Further genetic analysis of scalloped hammerhead fin samples support their designation under the Endangered Species Act. Achieving shark conservation within this small-scale shark fishery may be possible through continued cross-sector engagement to develop nuanced alignment between species-specific management at territorial and federal levels.