Prey fish availability is one of the most important drivers of dolphin behavior, survival, and reproductive success. Since 2004, the Sarasota Dolphin Research Program has explored relationships between the long-term resident dolphins of Sarasota Bay and their prey by conducting seasonal multi-species fish surveys. These surveys allow us to monitor seasonal abundance, distribution, and body condition of the fishes in Sarasota Bay, Florida. Data from this project enable us to investigate fine-scale habitat and prey selection in wild dolphins, and to explore the effects of Karenia brevis red tides and other environmental events on different fish species and community structure. This project has facilitated a variety of novel research, including modelling work involving the consequences of disturbance on a dolphin population.
Our standardized multi-species fish survey consists of a winter and summer fishing season (10 sets per month; Jan-Mar; Jun-Sep), during which we catch, measure, count and release fish from the R/V Flip using a 183 m purse seine in seagrass habitats. Our 2016 data indicated healthy fish abundances in Sarasota Bay (at least prior to the red tide that began after we completed our fish surveys). In the winter we caught a total of 3,172 fish of 43 different species. This summer yielded 31,681 individuals of 59 different species. After controlling for the influence of small schooling fishes on the mean number of fish caught per seine set (CPUE, or catch-per-unit-effort), winter CPUE was 105.7 and summer CPUE was 792.0.
After severe red tides in 2003, 2005 and 2006 and subsequent increases in summer fish abundance, CPUEs remained fairly steady from 2009-2014. Then, in 2015, summer fish abundance jumped to our third highest overall CPUE since this study began in 2004. This summer fish abundances remained high again, giving us our 6th highest overall CPUE ever. Pinfish, pigfish, mojarra, scaled sardine, Atlantic threadfin herring, and silver perch ranked highest, respectively, in abundance by species. Mullet abundance, which was negligible the past two summers, jumped up to our 7th highest CPUE! Other notable species abundances this summer included hardhead catfish, which ranked eighth highest, compared to the past two years in which they were ranked 16th and 18th. We also caught our first gafftopsail catfish since 2012 and our first snook since 2013. In contrast, winter fish abundance has varied little since our survey began in 2004 (range = 81.2-211.3), despite having sampled through four distinct winter red tide periods as well as cold events. Additional analyses are needed to determine trends in species-specific abundances and body condition.
We thank the many interns and dedicated local volunteers who have worked on this project. The work would not be possible without you! Funding for this work during 2016 was provided by the Batchelor Foundation. This research was authorized by the Florida Fish and Wildlife Conservation Commission (13-0809-SR, Special Activity License) and by Mote Marine Laboratory’s Institutional Animal Care and Use Committee (15-6-RW2).
This article appeared on pages 24-25 of the 2017 SDRP Annual Report, Nicks n Notches.