Scientists catalogue shark and ray distribution in Florida lagoon

Date:
August 25, 2020
Source:
Florida Atlantic University
Summary:
A study is the first long-term, in-depth analysis of the
elasmobranch community in Florida's Indian River Lagoon and develops
capacity to understand how these species may respond to further
environmental changes. From 2016 to 2018, researchers caught 630
individuals of 16 species, including two critically endangered
smalltooth sawfish. Results showed that many elasmobranchs use the
southern Indian River Lagoon throughout their life histories and the
area may serve as an important nursery habitat for multiple species.



FULL STORY ==========================================================================
Many elasmobranch species, which include sharks, skates, and rays, use estuaries as nurseries, for birthing, and as foraging grounds. Florida's
Indian River Lagoon is one of 28 estuaries designated as an "estuary of national significance" by the Environmental Protection Agency's National Estuary Program. In recent decades, this estuary has experienced many environmental impacts, such as habitat degradation and harmful algal
blooms resulting in degraded water quality and fish kills. Currently,
there is a substantial data gap surrounding the status of elasmobranchs
in this estuary system.


========================================================================== Researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute conducted a fishery-independent survey to characterize the elasmobranch community and understand distribution patterns and habitat
use in the Indian River Lagoon from Sebastian to St. Lucie Inlet. This
study provides the first long-term, in-depth analysis of the elasmobranch community in the southern Indian River Lagoon and develops capacity to understand how these species may respond to further environmental changes.

Results of the study, published in Estuaries and Coasts, the journal
of the Coastal and Estuarine Research Foundation, showed that many elasmobranchs use the southern Indian River Lagoon throughout their
life histories and the area may serve as an important nursery habitat
for multiple species.

From 2016 to 2018, researchers caught 630 individuals of 16 species,
including two critically endangered smalltooth sawfish (Pristis
pectinata). They characterized the species composition and distribution
of elasmobranchs, examined spatial and temporal variability in the
elasmobranch community, and assessed how temperature, salinity, dissolved oxygen, depth, water clarity, distance to an inlet, and distance to a freshwater source affect elasmobranch community composition. The two
most commonly caught species were bull sharks and Atlantic stingrays,
the only two species to each comprise greater than 20 percent of the
catch. The remaining 14 species comprised 53 percent of the catch.

Researchers also observed size and compositional differences by region
and season; for example, bull sharks were most abundant in Vero Beach
and the St.

Lucie River, and both bull sharks and Atlantic stingrays were more
abundant in the fall than in the spring and summer. Clearer, relatively
deeper, and higher salinity waters farther from freshwater sources and
closer to inlets resulted in a more diverse community; while bull sharks
and Atlantic stingrays dominated shallower, less clear waters closer to freshwater sources and further from inlets.

"As global human populations increase and environmental pressures on
estuaries become more widespread, it is essential to continue to monitor changes in elasmobranch communities in order to effectively manage
and conserve these populations," said Grace Roskar, M.S., lead author,
current Knauss Fellow with NOAA Fisheries and former graduate student
working with Matt Ajemian, Ph.D., co-author and an assistant research
professor at FAU's Harbor Branch.

"Establishing updated records of the diversity and distribution of elasmobranchs in the Indian River Lagoon is a critical first step to
understand how varying environmental and pollution impacts may affect
these species, which are integral to the fish community of the lagoon and surrounding habitats." The interconnected nature of abiotic parameters
such as distance to freshwater sources or inlets and salinity that
influenced elasmobranch distributions suggest important implications
for future hydrological changes in the Indian River Lagoon.

"If freshwater discharges into the Indian River Lagoon increase in
duration and/or volume, the elasmobranch community could shift even
further to bull shark and Atlantic stingray dominance. Less tolerant
species may be driven closer to the inlets or even out of the estuary to nearshore ocean habitats," said Ajemian. "These community shifts could
result in both decreased elasmobranch diversity and biodiversity of the
estuary as a whole, possibly altering the dynamics of prey populations as
well. Moreover, displaced species may face increased risks of predation or competition as well as declines in habitat quality or prey availability."
The researchers emphasize the importance of continuing the survey
for additional years to yield greater sample sizes and allow for the formulation of standardized relative abundance indices that will be
useful in the stock assessment process, which is essential to fisheries management.


========================================================================== Story Source: Materials provided by Florida_Atlantic_University. Original written by Gisele Galoustian. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Grace Roskar, Michael P. McCallister, Adam M. Schaefer, Matthew J.

Ajemian. Elasmobranch Community Dynamics in Florida's
Southern Indian River Lagoon. Estuaries and Coasts, 2020; DOI:
10.1007/s12237-020-00804-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825110750.htm

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