“It’s difficult to imagine how these shallow water environments will continue to sustain many
top predators in the future — not with many more storms at that intensity,” said Diane Claridge,
Ph.D., executive director of Bahamas Marine Mammal Organization (BMMO).

With sprawling seagrass meadows, meandering mangroves that hug the shoreline, and gin-clear
water, the Bahamas is home to dozens of iconic species, from great hammerheads and tiger
sharks to loggerhead sea turtles, and of course, the world-famous, curious and playful Atlantic
spotted dolphins. Yet, changing environmental conditions — and human activity — threaten
their very survival.

Scientists predict that one result of climate change is more frequent and intense hurricanes,
which can impact dolphins’ social structure, when animals die or move from the storm.

In 2004, Hurricanes Jeanne and Frances were two very strong Cat 2/3 hurricanes that hit the
Bahamas. Just like Hurricane Dorian of 2019, Frances hovered over the Bahamas for days before
heading toward Florida. Additionally, both Frances and Jeanne hit within a few weeks of each
other.

When WDP returned the following summer for our normal field season, about 30% of both the
spotted and bottlenose dolphin communities were gone. Most likely, they died, because those
dolphins were never seen again in any neighboring islands despite attempts to find matches
among catalogs of the different research groups.

As mammals, dolphins must surface every few minutes to breathe. It could be difficult and
exhausting for these animals to swim and breathe in the middle of large and continuous waves,
rain, and wind, particularly the new calves, often born in the fall and need to learn to swim,
breathe and nurse, said Elliser.

In addition to the losses, the animals’ behavior changed. They spent far less time socializing and
spent more time traveling. My first summer in the field with WDP in 2010, was the first time
interspecies interactions between the spotted and bottlenose were observed in five years, since
the hurricanes.

For Herzing, what was most shocking after the 2013 immigration event was the splitting up of
families. Usually mothers and offspring tend to stay in the same area, especially females. It
would be normal to see a grandmother with a mother and her offspring — three generations, she
Herzing. These relationships are important for learning. For instance, younger females gain
valuable practice by babysitting their nieces and nephews, and younger siblings.

A WDP researcher takes video and photo data underwater in the Bahamas to document individuals.

“Think about it in terms of humans. It is not just about our ability to physically survive, but our
ability to survive as a community. They survive together, as we do, working together,” said
Elliser. “How the individuals work together and what they can contribute to the society, are
critical for how successful they are moving forward. Dolphin societies rely on social connections
and when those are impacted in small or large ways, they can have significant effects on the
population — and ultimately their ability to survive.”

Another possibility is that the storms change food availability or some aspect of the food web.
Hurricanes kick up dirt and sand in shallow water, and this kills fish that essentially suffocate
when their gills get clogged and the water is devoid of oxygen. Coral reefs and seagrasses die
when sunlight gets blocked by the stirred up water. And storms can destroy habitat directly too.
According to Bonefish and Tarpon Trust (BTT), a Florida-based organization, its initial surveys
suggested 73% of mangrove forests in Grand Bahama and 40% in Abaco were damaged or
destroyed due to Hurricane Dorian in 2019.

“It’s difficult to imagine how these shallow water environments will continue to sustain many
top predators in the future — not with many more storms at that intensity,” said Diane Claridge,
Ph.D., executive director of Bahamas Marine Mammal Organization (BMMO).

In a recent study in Mammalian Biology, Claridge and other marine mammal scientists with
BMMO explored whether hurricanes may have influenced the survival rates of calves, juveniles
or adults in the South Abaco bottlenose dolphin population.

They found evidence that survival was indeed linked to hurricane activity, and it led to increased
deaths or emigration (it’s impossible to know which completely). But estimated survival
declined by 9% in adults, 5% in juveniles and 36% in calves.

Even in the most optimistic scenarios, the team of scientists predict based on their models that
South Abaco dolphins will go extinct within decades. However, they note that future work
should figure out if the South Abaco population is a source or sink for the entire Little Bahama
Bank dolphin community. “Coastal bottlenose dolphins are at great risk from climate change.
Local populations are in decline and these declines have been linked to intense and more
frequent climate events,” she said. Claridge is grateful Abaco has not had a severe storm since
the study, giving the vulnerable calves a chance to grow up.

It’s likely that the location and resilience of a population and ecosystem, as well as the severity
of a storm will impact how dolphins fare after catastrophic events like hurricanes. “While they
have a lot of behavioral flexibility, which is key to their survival, as they are able to adapt (by
moving, changing behavior and relationships, there is a limit where that will be enough,” Elliser
said. “At some point the changes may be too much, too close together, too fast and/or remove too
many in the population for them to be able to adapt effectively. The increasing stresses put on a
population will affect its ability to survive, even for relatively flexible species like dolphins.”

A mixed group of spotted dolphins, including the Bimini residents and immigrants.

Change could be coming, too. Herzing has been keeping tabs on the ocean conditions, and has
begun to see another drop in chlorophyll levels, this time off Bimini. “I am worried. I don’t know
where they would go,” she said. “They might expand their search area, which could be
energetically expensive. It may be that another food crash would reduce the community size and
some would be displaced completely. The dolphins are lucky in the sense that they are pretty
opportunistic feeders, so they have a varied diet. But, there may be better fish to eat if you are a
nursing mother for example, or a pregnant female. It’s complicated.”

It’s not just climate change that’s an issue either. Habitat destruction causing the loss of vital habitats like seagrasses and mangroves is an issue too. 

Read the full story in the latest issue of Oceanographic Magazine.