AES Gruber I2021-07-21 09:30 - 10:15 |
| Moderator: Kady Lyons |
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1. 09:30 IN-PERSON The Influence of Environmental and Social Factors on Aggregation Behavior of the Leopard Shark (Triakis semifasciata). Jack May*, CSULB; Chris Lowe, CSULB jackmay3rd@gmail.com
Mature female leopard sharks commonly aggregate during summer months in warm shallow water, specifically during daytime hours. They are thought to be utilizing relatively warm water temperatures in a thermally heterogenous environment to shorten gestation, but it is not known what specific water temperatures they occupy in an aggregation. It is also unknown to what extent social behaviors may play a role in forming an aggregation or if high density of individuals can create competition for limited desirable habitat. I flew 345 survey flights during the summers of 2018 and 2019 at known aggregation sites on Santa Catalina Island using an Unmanned Aerial Vehicle (UAV). Only images taken after 12:00 were used in analysis to survey shark abundance and density where solar radiation had an opportunity to create a thermally heterogenous environment. Images collected from the UAV were georeferenced in ArcMap 10.7 to spatially enable them. This allows for the coordinates of each visible shark to be determined. Seafloor temperature prediction surfaces were created from interpolated temperature data collected hourly at each site from an array of HOBO temperature loggers. Georeferenced images containing the spatial distribution of sharks were overlaid on the temperature prediction surfaces to record the estimated temperatures the sharks were occupying. Preliminary results indicate that thermal habitats may not be as limited as previously expected and that social factors also drive aggregation formation. |
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2. 09:45 IN-PERSON Temporal community structure and seasonal climatic migration of coastal sharks and large teleost fishes in the northeast Gulf of Mexico. Cheston Peterson*, Florida State University; Dean Grubbs, FSU Coastal and Marine Laboratory cpeterson@bio.fsu.edu
We conducted monthly, year-round fishery-independent sampling using scientific gillnets and longlines at two seagrass shoals and the surrounding soft-bottom habitat in the northeast Gulf of Mexico. We conducted 214 paired sets from April 2011 to December 2020, capturing representatives from 33 families of fishes encompassing 19 species of elasmobranchs and 50 species of teleosts. We used non-metric multidimensional scaling (NMDS) with environmental fitting to explore the effects of abiotic variables on temporal patterns of community structure, compared temporal community structure using permutational multivariate analysis of variance (PERMANOVA) of monthly catch rates in both gear types, and tested for cyclicity in community structure using RELATE. Additionally, we used generalized additive models (GAMs) to explore the effects of environmental variables (e.g. temperature and photoperiod) on immigration and emigration phases of dominant taxa. We found strong seasonality and cyclicity in assemblages captured by both gear types, with depauperate winter communities and diverse assemblages in warmer months - especially late summer and fall. Species richness and diversity generally declined during the warmest months. Our results suggest temperature may determine the timing of immigration and duration of the residency period of dominant taxa, including the juvenile life stages of some coastal sharks, but photoperiod may cue immigration and emigration in adults when the purpose of those migrations includes predicable reproductive functions (e.g. parturition). We found evidence of partial migration in juvenile life stages of some coastal sharks, and hypothesize that rising temperatures due to climate change may have variable effects on residency patterns over ontogeny. |
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3. 10:00 IN-PERSON Assessing mesopredator residency around clam leases in Eastern Florida. Brianna V. Cahill*, Harbor Branch Oceanographic Institute, Florida Atlantic University; Charles W. Bangley, Fisheries Conservation Laboratory, Smithsonian Environmental Research Center; Matthew B. Ogburn, Fisheries Conservation Laboratory, Smithsonian Environmental Research Center; Michael McCallister, Harbor Branch Oceanographic Institute, Florida Atlantic University; Matthew J. Ajemian, Harbor Branch Oceanographic Institute, Florida Atlantic University bcahill2019@fau.edu
The Indian River Lagoon (IRL) is a primary location for field-based “grow-out” of bivalves like the Northern Quahog (Mercenaria mercenaria) for shellfish aquaculture along Florida’s Atlantic coast. These grow-out locations have substantially higher clam densities than surrounding ambient sediment, potentially attracting mollusk predators to the area. Inspired by clammer reports of damaged grow-out gear, our objective was to examine the potential interactions between two highly mobile mollusk predators—whitespotted eagle rays (Aetobatus narinari) and cownose rays (Rhinoptera bonasus)—and two clam lease sites near Sebastian Inlet using passive acoustic telemetry. In addition, use of these habitats was compared to other reference sites in the vicinity (Saint Sebastian River mouth, Sebastian inlet) to provide context.Overall, the inlet sites logged the highest proportion of detections for whitespotted eagle rays (>95%), while cownose rays (<5%) did not use the inlet region extensively. All species exhibited long-duration visits (>60 minutes) to clam lease sites. These visits did not vary substantially between species, although there was individual variability. Considerably higher numbers of detections were recorded at inlet sites during daytime hours, whereas the two clam lease sites were more frequently used during nighttime. This information suggests that observed interactions with the clam leases potentially underestimate the use of these areas by predators, given most clamming operations occur during daytime. These results justify the need for continued monitoring of mobile mollusk predators in the region, including additional experimentation to assess the behaviors (e.g., foraging) being exhibited at the clam lease sites. |