Ajemian, Matthew

Shellfish aquaculture “grow-out” sites for Northern Quahog (Mercenaria mercenaria) clams have substantially higher densities than the surrounding ambient environment and thus can attract local molluscivores to these areas. I used acoustic telemetry to examine potential interactions of two highly mobile ray species (cownose ray, whitespotted eagle ray) with two clam grow-out sites in the Indian River Lagoon near Sebastian, FL, where clammers have reported damaged grow-out gear. Visitation patterns of telemetered rays to these sites were compared to other reference sites in the region and modeled using local environmental data. While both species spent greater time elsewhere, I found many instances in which rays remained within range of clam grow-out sites for extended periods (>60 minutes). Mesocosm experiments with whitespotted eagle rays confirmed they were capable of interacting with and damaging clams housed within antipredator materials, although mortality was significantly reduced compared to controls and in particular by multi-layer netting.

Recent research confirmed white shark (Carcharodon carcharias) nursery habitat off Long Island, New York; however, additional research is required to determine the habitat use and fine-scale movements of young-of-the-year and juvenile white sharks within this nursery. Between 2016 and 2019, twenty-five white sharks were fitted with satellite and acoustic tags to better define habitat use. Individuals exhibited horizontal movements parallel to Long Island’s southern shoreline and coastal New Jersey. Log-likelihood chi-square analyses determined preference for water column depth, SSTs, sea surface salinities, and chlorophyll a concentration. Vertical analysis of diving behavior revealed swimming behavior primarily in the upper 20 m of the water column, in temperatures between 18°C and 20°C. Generalized additive mixed modeling suggested SSTs above 20.5°C affected dive depth. These results can help improve characterization of essential fish habitat for young white sharks and provide data to determine the species’ susceptibility to anthropogenic activities.

Florida’s Indian River Lagoon (IRL) has experienced myriad anthropogenic impacts and knowledge on elasmobranchs (sharks and rays) in the southern IRL is lacking. A fishery independent survey (longline/gillnet) was implemented to 1) assess the effects of bait type [striped mullet (Mugil cephalus) versus Atlantic mackerel (Scomber scombrus)] and mesh size (15.2 cm versus 20.3 cm stretch mesh) on elasmobranch species composition, catch-per-unit effort, and size distributions and 2) characterize elasmobranch abundance and distribution. From 2016 - 2018, 630 individuals (16 species) were captured, more often in the gillnet than the longline. Catch-per-unit-effort was significantly higher with mullet than mackerel. Species composition differed among gears. Although dependent on gear, there was evidence of seasonal and spatial patterns in abundance and species composition. This study provides the first baseline abundance indices for many elasmobranchs in the IRL and develops the capacity to understand how elasmobranchs may respond to changes in this highly modified estuary.

Elasmobranchs play ecologically important roles in coastal environments.
Unfortunately, the basic distribution and movement patterns of these species, particularly
rays, remain relatively unknown. This is especially true for the Whitespotted Eagle Ray
(Aetobatus narinari), a protected species in Florida with poorly described migratory and
habitat use patterns. I employed a combination of acoustic telemetry techniques to reveal
multi-scale spatial patterns of A. narinari around Florida. Movement patterns between the
east and west coast individuals were distinct; a majority of west coast tagged A. narinari
exhibited migratory or transient behavior while most east coast tagged individuals
remained resident in the Indian River Lagoon. Fine-scale tracking of A. narinari revealed
individuals spent a large percentage of time in the inlets and channels and frequently
reused habitats parallel to the shore. This study fills a knowledge gap on the species
ecology which may be used for adaptive management strategies throughout A. narinari’s
range.