Everglades Pilot Whale Standing

As a student in the MPS marine mammal science track, I was fortunate enough to be one of the volunteers to respond to the recent mass stranding of pilot whales in Everglades National Park. I was a little apprehensive, as this was my first stranding experience. No one knew what to expect. After the early morning drive out to the Everglades, as well as an hour and a half boat ride, we arrived to the stranding site where we found about 50 pilot whales in barely three feet of water. All of the volunteers, law enforcement, NOAA officials, scientists, and even some concerned patrons huddled to generate an effective rescue strategy. It was truly inspiring to see so many people utilizing their precious time and resources in order to create the best possible outcome for the distressed whales.

Pilot Whales 2

Throughout the day, I was assigned various tasks to assist with the collection of samples acquired from live whales, as well as a necropsy of an expired whale. I was fascinated by the way the veterinarian and her team effectively tagged the animals and collected important blood and tissue samples, all while hanging off of the side of a flat bottom boat! I helped record the relevant data, which was a great first-hand experience in the amount of diligence that is put into collecting the samples, as well as keeping them all organized. Observing the necropsy also opened my eyes to the complexity and importance of these operations; various tissue samples from each organ must be obtained to send out to the appropriate laboratories for examination. This way, scientists are able to maximize the number of test results generated from a single sample, which will hopefully aid in discovering the reason for the stranding event.

Pilot Whales 1(1)

After this experience, I am looking forward to being a regular member of the volunteers who respond to marine mammal strandings in southern Florida. I have a newfound respect for the scientists and veterinarians who organize these response efforts, especially after witnessing the amount of valuable scientific data that can be garnered just from one stranding incident. Our efforts to herd the group offshore on Wednesday proved to be successful, as the whales were recently spotted offshore, in deeper water, and swimming freely.

— MPS student Samantha Tufano

Photo credits: RSMAS/MPS student Maureen Duffy

The Florida Everglades: Lair of the Bull Shark

It’s always fascinating to watch different species of fish arrive seasonally at the spots you frequent. Last weekend, while tagging sharks for research in the Everglades, it became clear to me that this very phenomenon was occurring, with blacktip sharks beginning to trickle back into the habitats, being followed around by even bigger local predators.

The Everglades is a fascinating spot to work because there are lots of predators – and those predators vary in size, number, and relative power over each other. At the apex – literally the top of the food chain – are the bull sharks. The Everglades is their lair. Blacktip and lemon sharks are also predatory sharks, but the blacktips are potential prey for the bulls, making them the proverbial “middle man on the totem pole.” The blacktips are usually the largest in number, and are often smaller than both the lemons and the bulls. Indeed, parts of the Everglades and Florida Bay give sub-adult blacktip sharks refuge from the risky, open water of the Gulf where they risk being consumed by larger predators. However, in nature, there is no free lunch, so by trading off open ocean habitats for the Everglades ecosystem, blacktip sharks gain some refuge and feeding opportunities, but subject themselves to a smaller number of large predators – the bulls – which are cruising the river mouths, coastlines, and estuarine areas for small prey. In fact, a recent study published in PLoS ONE by R.J. Dunlap Director Dr. Hammerschlag and colleauges found that bull sharks in the Everglades cause other prey species (such as tarpon) to alter their behavior when swimming through areas of high bull shark abundance. These “risk effects” are especially difficult to detect with large predatory fishes, and this study is the one of the first of its kind to detect these often overlooked measures of predator-prey relationships in marine settings. Another reason for this change in the shark presences is due to the prevailing water conditions– strong oxygen content, slightly cooler temperatures that we see from July – September, and stable salinity.

Most visits to Everglades National Park usually produce a large bull shark for our research. It is critical to establish estimates of how many bull sharks in the area, what they are eating, and if/how they can tolerate human-induced changes in the ecosystem. I encourage all of the readers to visit the Everglades and explore – the ecosystem is starting to ignite, and it is awesome to watch the predator-prey interactions between different coastal shark species. If you plan on fishing, I urge you to practice catch and release, as the seasonal blacktip aggregation already gets enough pressure from the bull sharks in the area, and the bull sharks themselves are in smaller numbers because they are the top predator. Release is a great option for these species, because both bulls and blacktips do relatively well with responsible catch and release.

-Austin Gallagher
PhD Student, Research Assistant
RJ Dunlap Marine Conservation Program
Abess Center for Ecosystem Science and Policy