To explore the relationship between wild dolphins and their prey, the SDRP monitors seasonal fish abundance, distribution, and body condition in Sarasota Bay, Florida. Data from this multispecies fish survey have allowed us to investigate fine-scale habitat and prey selection in wild dolphins, and to explore the effects of Karenia brevis red tides on different fish species and community structure.
This ongoing project has facilitated a variety of novel research, including studies on the diet of wild dolphins (Sam Rossman, Michigan State Univ.), mercury content in dolphin prey (Yongseok Hong, Johns Hopkins Univ.), modeling work involving human interactions with dolphins (Katie McHugh, Sarasota Dolphin Research Program), dolphin population modeling (Bob Lacy, Chicago Zoological Society), and comparisons between iron (Melissa Zabojnik, Chicago Zoological Society) and nutrient content (Amanda Ardente, Univ. of Florida) of fish consumed by wild dolphins versus dolphins under human care.
Our standardized multi-species fish survey consists of a winter and summer fishing season (January-March, June-September, respectively), during which we catch, measure, count and release fish from the R/V Flip using a 183 m purse seine. This summer we completed 40 seine sets in seagrass habitat. Preliminary data indicate that we had a very good year! We caught a total of 34,110 individuals of 60 different species through September 2015. Our 30 seine sets this past winter yielded a total of 4,805 fish and 56 different species. After limiting for the influence of small schooling fishes on the mean number of fish caught per seine set (CPUE, or catch-per-unit-effort) by excluding clupeids, our preliminary 2015 summer CPUE was 620. Our final winter CPUE was 109.
After severe red tides in 2003, 2005 and 2006 and subsequent spikes in summer fish abundance, CPUEs remained fairly steady since 2009. However this year fish abundance spiked to our third highest CPUE on record. Pinfish, scaled sardine, Atlantic threadfin herring, silver perch, mojarra, and mangrove snapper were particularly abundant compared to past years. For the second year in a row, summer mullet abundance was negligible. Last year we caught two individuals, while this year we did not catch a single mullet. Despite our findings in Sarasota Bay, the Florida Fish and Wildlife Conservation Commission reports that commercial landings on the west coast of Florida have remained stable since 2008 and the mullet stock is neither overfished nor undergoing overfishing. Winter fish abundance has varied little since our survey began (range=81-211), despite sampling through three distinct red tide periods (2004-2005, 2006-2007, and 2012-2013). Additional analyses are needed to determine trends in species-specific abundances and body condition.
We thank the many interns and dedicated volunteers who have worked on this project over the years since its inception in 2004. This work would not be possible without them! The Batchelor Foundation, Disney Worldwide Conservation Fund, NOAA’s Fisheries Service, Harbor Branch Oceanographic Institution’s Protect Wild Dolphins Program, and Florida’s Fish and Wildlife Research Institute have provided funding for this work. This research was authorized by the Florida Fish and Wildlife Conservation Commission (13-0809-SR, current Special Activity License).
This article appeared on page 25-26 in the December 2015 issue of Nicks n Notches.