Performance of Two Survey Gears Targeting Elasmobranchs in a Shallow, Subtropical Estuary

Fishery-independent surveys have become increasingly prevalent in recent decades for monitoring the population trends of highly mobile species like elasmobranchs (sharks and rays). Despite the utility of gear evaluations for streamlining costs and increasing the efficiency of fishery-independent surveys, these assessments are sparse for elasmobranch-specific surveys. Catch data were examined from a fishery-independent longline and gill-net survey that targeted elasmobranchs in Florida's southern Indian River Lagoon from July 2016 to September 2018. The goal of the study was to assess the effects of the type of longline bait that is used (Striped Mullet Mugil cephalus versus Atlantic Mackerel Scomber scombrus) and the size of gill-net mesh (15.2versus 20.3-cm stretch mesh) on the species composition, catch per unit effort (CPUE), and size distribution of captured elasmobranchs. Elasmobranchs were caught more often in the gill net than on the longline. Striped Mullet yielded a significantly higher CPUE of elasmobranchs than Atlantic Mackerel did. Although Striped Mullet caught more sharks than Atlantic Mackerel did, the mean length of the sharks did not differ between groups that were captured with the two bait types. Species composition differed with respect to bait type; significantly more Bull Sharks Carcharhinus leucas and Atlantic Sharpnose Sharks Rhizoprionodon terraenovae were caught with Striped Mullet. Elasmobranch abundances were similar between the two sizes of gill-net mesh. However, species composition differed, with a greater abundance of both Atlantic Stingrays Hypanus sabinus and Bull Sharks caught in the 15.2-cm mesh. Elasmobranchs that were caught in the 20.3-cm mesh were significantly larger than those caught in the 15.2-cm mesh. The length distributions for the common species (Bull Sharks, Atlantic Stingrays, and Bluntnose Stingrays H. say) differed significantly with respect to the two mesh sizes. This study is the first assessment of a standardized elasmobranch-specific survey in this nationally significant estuary and increases our understanding of the performance of complementary gear types for targeting sharks and rays in a shallow lagoonal system. Elasmobranchs (sharks and rays) are essential components of marine food webs as both predators and prey (Navia et al. 2017). Additionally, these species are an important food source in some countries (Davidson et al. 2016) and support valuable ecotourism industries around the world (Gallagher and Hammerschlag 2011; Corcoran et al. 2013). Unfortunately, the life history strategies of many elasmobranchs (including their long lifespans, slow growth rates, late sexual maturity, and small number of offspring) make these fishes highly susceptible to population declines due to overfishing (Stevens et al. 2000) and habitat loss (Knip et al. 2010). These declines have elicited fisheries management and conservation measures in recent decades, such as the development of the first fishery Subject editor: Patrick Sullivan, Cornell University, Ithaca, New York *Corresponding author: aroskar2017@fau.edu Received July 31, 2019; accepted November 1, 2019 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science 12:50–63, 2020 © 2020 The Authors. Marine and Coastal Fisheries published by Wiley Periodicals, Inc. on behalf of American Fisheries Society. ISSN: 1942-5120 online DOI: 10.1002/mcf2.10101