Despite being crucial to the conservation of batoids (skates and rays), assessments of fine-scale movements and habitat use of these taxa are lacking in the scientific literature. Here we used active acoustic telemetry to characterize habitat use and movement behavior of the state-protected whitespotted eagle ray Aetobatus narinari in the Indian River Lagoon, Florida, USA. Seven mature individuals (6 males and 1 female) were individually tracked for a total of 119.6 h. Brownian bridge movement models of ray distribution showed the importance of habitats with high anthropogenic activity (i.e. boat traffic) such as inlets and channels, as well as clam aquaculture lease sites close to shore. This was supported by the significantly lower rates of movement in these habitats relative to other regions (offshore, open lagoon). Rate of movement significantly increased with temperature, suggesting that rays are more active during warmer periods. No tidal patterns in ray habitat use or distribution were evident. On average, rays used the deeper portions of the lagoon during the day and shallower portions during the night. While more extensive tracking is required to elucidate long-term movement patterns, this study is the first to characterize fine-scale habitat use by the whitespotted eagle ray in Florida while also identifying areas of potential interactions between this species and multiple anthropogenic threats.
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 (15.2‐ versus 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.
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