Permit Spawning Aggregation Dynamics

Leadership

Kirk Gastrich MSc, Research Specialist at Florida International University

Benjamin Binder PhD, Postdoctoral Researcher at the Boswell Lab for Marine Ecology and Acoustics at FIU

Jessica Robichaud, MSc

Expedition Summary

From April 3rd - 15th, 2023, The International SeaKeepers Society assisted researchers from Florida International University, supported by Bonefish & Tarpon Trust, in conducting research on permit (Trachinotus falcatus) spawning aggregations in the Lower and Middle Florida Keys. Permit aggregate on natural and artificial reefs in the Keys surrounding the full moons from March through June each year. Catch-and-release angling for permit during their spawning season has become a popular sport fishery for many anglers, and, although not inherently detrimental to the fishery since permit harvest is prohibited between April 1 and July 31 throughout the Florida Keys, depredation (i.e., the removal of hooked fish by a predator) has produced a high level of concern regarding the sustainability of this practice.

As a result, Florida Fish and Wildlife Conservation Commission implemented a seasonal fishing closure from April 1 – July 31 each year at Western Dry Rocks, where depredation mortality has been historically high, to protect permit and other species that aggregate here. To evaluate the efficacy of this closure and monitor other fished aggregation sites throughout the Florida Keys, we used a combination of active acoustics (multi-beam imaging sonar), video (360° and line-cameras), and hook-and-line fishing surveys to collect data on permit school size and individual size. Observational data on fishing pressure (i.e., number of fishing boats, time spent fishing) and depredation rates (i.e., number of angled permit lost to sharks) at openly fished sites were also collected.

Lastly, as an added method for researching the movements of permit throughout different geographic areas, acoustic tags were implanted in each fish caught. These tags emit a unique frequency which is then heard by acoustic receiver arrays. These receivers which log the data, are then retrieved and downloaded.

Highlights from data collected on this trip:

Fishing pressure in the Middle Keys consisted of 1-5 boats spending 0.1-1.5 hrs fishing for permit. At sites in the Lower Keys, we did not observe any boats targeting permit, including WDR where the closure went into effect on April 1st.

We observed sharks across most sites, including bull (Carcharhinus leucas), Caribbean reef (C. perezi), and great hammerhead (Sphyrna mokarran) sharks, as well as depredation events, which occurred at the surface, were communicated by charter captains, or were recorded by line camera footage.

Our initial results from the combined acoustic and video data suggest that abundance ranged from 1-400 individuals at all sites where permit aggregations were observed. School size at WDR was larger than what was observed at Middle Keys sites in April and at WDR in March 2023.

We surgically implanted 32 acoustic transmitters in fish across sites in the Lower and Middle Keys, building upon Carleton University’s multiyear tagging efforts.

The range of permit sizes captured was consistent with site-specific data from previous years, where Middle Keys fish were noticeably smaller than those in the Lower Keys.