Sharks--Ecology

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.

Sharks possess an electrosensory system which allows the detection of
electric fields . How this system varies among related taxa and among species
inhabiting different environments remains unexplored. Electroreceptor number
was quantified for representative species of related taxa (genera, families, orders)
from different environments (pelagic, coastal, deepwater) and taxa from similar
environments to determine potential phylogenetic constraint or evolutionary
convergence. Coastal open water sharks possess the greatest number of
electroreceptors; deepwater sharks the least. Pelagic and coastal benthic sharks
retain comparable electrosensory pore numbers despite inhabiting vastly different
environments. Electrosensory pores were primarily located in ventral
distributions, except among coastal open water sharks which possess roughly
even distributions around the head. Among related species and genera, pore
numbers and distribution are comparable, with greater variation among higher
taxa. Results implicate evolutionary convergence as the primary influence in
electroreceptor development, while phylogenetic constraint establishes similar
base values for number and distribution.