CURRENT RESEARCH

I am interested in feeding and foraging behavior in marine mammals, and how it varies with demographics (e.g., age, sex, maternal lineage), prey behavior, geographic location, environmental conditions, and short- and long-term disturbances (e.g. harmful algal blooms, human development, changes in climate).

My study species is the bottlenose dolphin, Tursiops truncatus, and much of my work involves a community of free-ranging dolphins that lives year-round in Sarasota Bay, Florida and has been studied since the 1970s by the Sarasota Dolphin Research Program.

Diet and disturbance vulnerability in bottlenose dolphins (Tursiops truncatus)

Cetaceans increasingly face diminished fitness and mortality due to natural and anthropogenic disturbances that disrupt access to prey, and understanding diet variation under undisturbed conditions and how disturbances impact diet is key to evaluating cetacean vulnerability and mitigating disturbance effects. 

Most cetaceans are cryptic underwater predators, however, so how can we figure out their diet? There are many methods, from hard part analyses and molecular prey detection using stomach contents, fecal matter, or regurgitates to stable isotope and fatty acid analyses. Each method has its own strengths and weaknesses, and is effective in different conditions (Rosen and Tollit, 2012; Rossman et al., 2015). My Ph.D. dissertation focuses on validating and applying quantitative fatty acid signature analysis (QFASA), which has been applied in many marine mammal species but not, to my knowledge, in cetaceans.

What are fatty acids? Essentially, they’re chains of carbon, hydrogen, and oxygen atoms that are the building blocks of fat in an animal’s body (including in humans!). Since fatty acids from prey are deposited in bottlenose dolphin blubber with little structural change, we can compare the proportions of different fatty acids found in dolphins and their potential prey items to estimate the predator's diet over the previous several months (Iverson et al., 2004; Budge et al., 2006)

I start by collecting minimally invasive dolphin blubber samples and a representative sample of potential dolphin prey. Then, I extract the lipids (fats) from the samples, turn the fatty acids in those lipids into fatty acid methyl esters (FAMEs), and run those through a gas chromatographer with flame ionization detection. This yields a fatty acid signature, the relative proportions of different fatty acids, for each sample. Finally, I create model diets from the "library" of prey fatty acid signatures and compare them to the actual fatty acid signatures of each predator's blubber; the model diet with the signature that is most similar to the predator's represents a close approximation of that predator's diet. 

Once I have a close approximation of a predator's diet from the previous several months, I can investigate all sorts of interesting questions. For instance, how does diet vary between different sexes or ages of dolphins? Do moms and calves feed on the same prey, and does that go along with any kind of learned foraging behaviors? How does diet change following a harmful algal bloom that decimates prey fish populations, or when recreational or commercial fishing changes the kinds of prey fish available?  These are the kinds of questions that diet, determined using QFASA, can help us answer. 

More broadly, with QFASA’s detailed, long-term information, researchers can determine diet and disturbance vulnerability in cetaceans worldwide, including endangered species that rarely strand or cannot be captured. Knowing key prey species and how disturbances affect diet also helps wildlife managers create targeted and justified responses, such as limiting certain fisheries or nutrient run-offs, with a greater chance of public compliance and success.

References: 

1. Rosen D and D Tollit. 2012. Effects of phylogeny and prey type on fatty acid calibration coefficients in three pinniped species: implications for the QFASA dietary quantification technique. Marine Ecology Progress Series. 467: 263-276. DOI: 10.3354/meps09934

2. Rossman S, et al. 2015. Foraging habits in a generalist predator: Sex and age influence habitat selection and resource use among bottlenose dolphins (Tursiops truncatus). Marine Mammal Science. 31(1): 155-168. DOI: 10.1111/mms.12143

3. Iverson SJ, et al. 2004. Quantitative fatty acid signature analysis: A new method for estimating predator diets. Ecological Monographs. 74(2): 211-235. 2)

4. Budge S, et al. 2006. Studying trophic ecology in marine ecosystems using fatty acids: a primer on analysis and interpretation. Marine Mammal Science. 22(4): 579 – 801. DOI: 10.1111/j.1748-7692.2006.00079.x