Shark captures near west-central Florida by Coastal Marine Education and Research Academy

Identifying critical habitat for highly mobile species such as
sharks is difficult, but
essential for effective management and
conservation. In regions where baseline data are lacking,
non-traditional data sources have the potential to increase
observational capacity for species distribution and habitat
studies. In this study, a research and
education organization conducted a five
year (2013-2018) survey of shark
populations in the coastal waters
of west-central Florida, an area where
a diverse shark assemblage has been observed but no
formal population analyses have been conducted. The objectives of
this study were to use Boosted Regression
Tree (BRT) modeling to quantify environmental
factors impacting the distribution
of the shark assemblage, create species
distribution maps from the model outputs, and identify
spatially explicit hot spots of high
shark abundance. A total of 1,036 sharks were
captured, encompassing eleven species. Abundance hot spots
for four species and for immature
sharks (collectively) were most often located
in areas designated as “No Internal Combustion
Engine” zones and seagrass bottom cover,
suggesting these environments may be fostering
more diverse and abundant populations. The BRT models were fitted for
immature sharks and five species where
n>100: the nurse shark (Ginglymostoma
cirratum), blacktip shark (Carcharhinus limbatus), blacknose
shark (C. acronotus), Atlantic sharpnose shark (Rhizoprionodon
terraenovae), and bonnethead (Sphyrna
tiburo). Capture data were paired
with environmental variables: depth (m), sea surface
temperature (ºC), surface, middle, and bottom salinity
(psu), dissolved oxygen (mg/l), and bottom type (seagrass, artificial
reef, or sand). Depth, temperature, and bottom type were
most frequently identified as predictors with the
greatest marginal effect on shark distribution, underscoring the
importance of nearshore seagrass and barrier island habitats
to the shark assemblage in this
region. This approach demonstrates the
potential contribution of unconventional science to effective management and conservation of coastal sharks.