Diet determination of Sarasota Bay bottlenose dolphins, using DNA-based identification of prey remains in scat samples

Jan 12, 2008 No comments By , , , , and

 

This work is part of larger on-going studies being conducted by the Australian Antarctic Division, developing and applying methods to determine the diet of free ranging cetaceans, non-invasively. We are using the simple concept that if prey is eaten, then prey remains will be present in fecal matter (‘scat’) and the prey can be identified by unique DNA sequences that are present in all different species. Put simply; ‘prey goes in, prey DNA comes out’. Generally in cetaceans, diet can only be specifically examined either by observation (which is rare and inevitably biased towards surface activity) or by examining prey remains in the stomachs of stranded or incidentally killed individuals. These data may not be representative of healthy free-ranging individuals so the advantage of DNA techniques is they can examine the diet of free ranging animals in a minimally biased, non-invasive fashion. These data can then be used not only to further understand the ecology of the focal species and ecosystem processes but also to examine whether the assumptions of more traditional diet analysis techniques are valid for estimating the diet of healthy, free ranging individuals.

The basic way these techniques work involves collecting feces from free-ranging animals, extracting DNA from the scat sample in the laboratory and analyzing the scat derived DNA for prey DNA sequences. When prey sequences are found, they can be compared to large on-line databases that can match a specific sequence to a specific prey species or groups. How do we collect scat from a live free-ranging marine mammal you may ask? Well, there are a number of different (rather glamorous) ways, however in the case of Sarasota dolphins scat is collected opportunistically during the capture-release process for health assessment. When scat is collected it is preserved in buffer for the long trip back to Tasmania where the sample analysis takes place. So far we have results back for scats from 15 different Sarasota dolphins and we have discovered 19 different prey items in their scats. Two species, pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus), were found in most scats (71% and 57% respectively) indicating that they are important prey items in the time of year when the samples were collected. These results fit in well with Dr. Nélio Barros’s work on prey consumption in this population.

These results are important as they demonstrate for the first time the ability to gain unbiased specific prey information from multiple live free-ranging individual cetaceans. This proves the utility of DNA methods as a viable alternative, as well as being able to further complement, stomach contents analyses. These methods can also help us to understand the prey range and foraging ecology of top level predators such as bottlenose dolphins, which can inform us as to possible adverse effects human actions might have on ecosystems. For example, we can better understand the direct and indirect effects of fisheries and environmental catastrophes that result in large scale mortalities of focal species if we know where they fit in food webs. I wish to acknowledge the financial support of the Australian Antarctic Division and the Ian Holsworth Wildlife Research Trust Fund. Dolphin Quest provided support for the health assessment operations. I am also especially grateful to the staff at Mote Marine Laboratory and the Chicago Zoological Society, who have made the field component of this work possible (and a pleasure).

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Australian Antarctic Division

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Australian Antarctic Division

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University of Tasmania

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Randall Wells, PhD, is the Director of the Chicago Zoological Society’s Sarasota Dolphin Research Program (SDRP). He began studying bottlenose dolphins in Sarasota as a high school volunteer at Mote Marine Laboratory in 1970. He received his BA in Zoology from the University of South Florida in 1975, a Master’s in Zoology from the University of Florida in 1978, a PhD in Biology from the University of California, Santa Cruz in 1986, and a Post-doctoral Fellowship in Biology from the Woods Hole Oceanographic Institution in 1987. Employed by the Chicago Zoological Society since 1989, he is a Senior Conservation Scientist, and in this capacity he also manages Mote Marine Laboratory’s Dolphin Research Program. As a Professor of Ocean Sciences (adjunct) at the University of California, Santa Cruz, he serves as major advisor for MS and PhD students, and he is an adjunct Professor with the University of North Carolina, Wilmington, Duke University, and the University of Florida’s College of Veterinary Medicine. Wells was President of the Society for Marine Mammalogy (2010-2012).
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