Times of the Islands Summer 2017

green pages newsletter of the department of environment & coastal resources
Juvenile lemon sharks are reliant on shallow inshore waters during
the early stages of life.
The end result of this “trophic cascade” might be a
radically altered ecosystem—dead coral skeletons overgrown
by algae where once there were healthy coral reefs,
for example. Shark populations have already experienced
massive declines on a global scale, due mainly to a combination
of commercial fishing pressure and habitat loss.
So it is extremely important that further serious declines
are prevented, not just for the sake of the sharks, but
also for the populations of other species that they are
connected to, both directly and indirectly.
The School for Field Studies Center for Marine
Resource Studies on South Caicos has been studying the
ecology of local shark populations since 2005, with a view
to determining their status and conservation needs. The
longest running of these studies has been an investigation
into habitat use by juvenile lemon sharks, a species
that is classified as “Near Threatened” by the International
Union for the Conservation of Nature (IUCN). Its distribution
ranges from New Jersey to Brazil, and throughout this
range it has experienced heavy fishing pressure, causing
a considerable reduction in population size. However, the
biggest threat that this species currently faces is habitat
loss, as lemon sharks are reliant on shallow inshore
waters during the early stages of life.
In late spring and early summer, pregnant females
move into extremely shallow waters close to mangroves,
where they give birth to between 4 and 17 pups, each
measuring around 60 cm in length. Having given birth,
the females then move straight back out into deeper
waters, but the newborn shark pups remain in these shallow
areas for the first few years of life. As mangroves
support large populations of fish and invertebrates, the
shark pups have access to plenty of food as well as being
protected from larger predators.
Our research on this species has been mainly concerned
with identifying areas of particular importance for
the shark pups. What we have found is that almost everywhere
that you find mangroves, you will find lemon shark
pups. But, some areas do seem to be more important
than others. As we have recently reported in an article
for the scientific journal Aquatic Conservation, the most
important area for these pups around South Caicos is the
Bell Sound Nature Reserve.
Not only is there a greater concentration of the
sharks within Bell Sound, relative to other areas around
South Caicos, but Bell Sound is also home to the smallest
pups. In other words, Bell Sound appears to be an
important birthing ground for the pregnant sharks, and
the young sharks prefer the sheltered, shallow waters
that Bell Sound provides. While our research is ongoing,
it seems highly likely that the shark’s main food source is
the fish that live around the mangroves in the northeastern
corner of the reserve around Iguana Cay, as well as in
the western part of the reserve around Man-O-War Bush.
Unfortunately, Bell Sound faces an uncertain future,
as there have been calls to redraw the boundary of the
Nature Reserve and to downgrade it to a National Park.
While these proposals would facilitate greater waterbased
recreational use of Bell Sound for South Caicos’
growing tourism industry, there can be no denying that
any such change will negatively impact the resident
lemon shark pups—particularly as there are also plans to
remove some of the mangroves from around Iguana Cay.
And it’s not just the lemon sharks that rely on these
mangroves; most of the fish that live among the mangrove
roots are juveniles of species that live out on the
reef as adults. The mangroves are an essential nursery
habitat for these species, without which populations of
reef fish are also likely to decline.
More recently, we have started to investigate the ecology
of other shark species that live out on the reef and
in the deeper sand flats of the Caicos Bank. Our first goal
was to determine which species occur locally, in addition
to the lemon sharks, and then to assess their movement
patterns and habitat preferences. The main techniques
that we use for this research are tag and release, and
baited remote underwater video stations (BRUVS).
Tag and release, as the name suggests, involves
capturing, tagging, and releasing the sharks. Captured
Times of the Islands Summer 2017 33