On-going Studies Links
For conservation purposes, we must understand the foraging ecology of dolphins and their role as predators in the ecosystem.
This research is a first attempt to quantify prey selection for Sarasota dolphins. The analysis combines our published research on stomach contents of known Sarasota Bay dolphins, with a robust assessment of the structure of the Sarasota fish community.
Our dolphin surveys over 40 years suggest that Sarasota dolphins most often feed on single fish, rather than on schooling fish.
Dolphins hunt prey fish in different ways.
It has long been hypothesized that dolphins use passive listening to locate noise-producing or “soniferous” fish (e.g., pigfish and toadfish). Our studies of Sarasota Bay dolphins have provided opportunities to test this theory.
Since 2004, more than 475 purse-seine sets have collected more than 210,000 individual fishes, comprising 56 families and 120 species. While comprising only 6.3% of the total available prey, soniferous fishes accounted for 51.9% of the total prey consumed by dolphins.
Sarasota dolphins use passive listening to locate noise-producing or “soniferous” fish
These results, along with stomach content data, and fish sound playback experiments from Sarasota Bay,
support the hypothesis that Sarasota dolphins use passive listening to locate sound-producing fishes.
We also were able to demonstrate that the dolphin select some prey items disproportionately as compared to the availability of those prey fish species in Sarasota Bay.
Some common dolphin prey, such as pinfish, are also among the most common prey-sized fish collected in purse seines. Stomach contents analysis, however, show snook or other species are found more commonly than would be expected based on their relative abundance in the bay. This evidence supports the idea that Sarasota dolphins feed selectively, rather than just forage on what is most commonly available.
The same may be true in other areas with similar habitats and fish communities (i.e., soniferous fishes).
Threats to dolphin foraging are many. They include habitat degradation, overfishing, and harmful algal blooms (i.e., red tide), which may deplete the abundance of soniferous fishes. Noise, such as that caused by power boats and marine construction may mask soniferous fish calls. These threats potentially can limit the ability of dolphins to locate their prey through passive listening.
This work would not be possible without the help of many dedicated interns and volunteers who have donated their time and effort to this project. NOAA’s Fisheries Service provided primary funding for this project. Harbor Branch Oceanographic Institution’s Protect Wild Dolphins Program and Florida’s State Wildlife Grants Program provided additional funding. Chicago Zoological Society provided programmatic support.
All photos © Sarasota Dolphin Research Program under NMFS permit #522-1785