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Investigating Bonefish Spawning Aggregations


The Fisheries Conservation Foundation has partnered with several organizations in The Bahamas to identify bonefish spawning aggregation sites. We are currently focusing our efforts on the island of Eleuthera. Working out of the Cape Eleuthera Institute, Georgiana Burruss (a graduate student at Michigan State University) is leading the study to track bonefish populations across Eleuthera to identify these aggregation sites and critical spawning habitat for this economically important species.

Map of five regions dividing Eleuthera into bonefish tagging areas.

The team first identified a number of potential bonefish spawning migration corridors using an array of 62 VEMCO acoustic receivers to record the movements of 39 tagged bonefish as they migrated away from known foraging grounds and tidal creeks. Bio-telemetry data indicated potential spawning migration corridors in the Northeast, Southeast, and East regions of Eleuthera. In addition, the team was able to track the nighttime movements of spawning aggregations in the Southwest region of the island. Although, transmitter detections in the Northwest part of the island were limited, the fact that the timing was coordinated with spawning-related movements in other regions suggests that they were potentially spawning-related. Interestingly, bonefish tagged in each of the areas were not detected moving into another region, perhaps indicating these populations are unlikely to mix. Overall, five migration corridors have been identified, with additional data suggesting there are likely at least five bonefish spawning sites on Eleuthera, although more study is needed for confirmation.

Given the success of last year, the bonefish telemetry project officially kicked off its second year of data collection to answer the following questions:

  1. Where are bonefish forming spawning aggregations in the five regions of interest on Eleuthera?
  2. How do abiotic factors (season, moon phase, temperature, current, tide, etc.) influence bonefish spawning migrations in South Eleuthera?
  3. What is the energetic cost of spawning migrations?
  4. How do predators interact with the bonefish spawning aggregation?
VEMCO receivers are attached to cinder blocks with rebar posts. This receiver has a SYNC tag positioned above it, allowing for triangulation of position with other nearby receivers and allowing for the fine scale movement of bonefish to be assessed.

VEMCO receivers are attached to cinder blocks with rebar posts. This receiver has a SYNC tag positioned above it, allowing for triangulation of position with other nearby receivers and allowing for the fine scale movement of bonefish to be assessed.

Two VEMCO positioning arrays were deployed to assess the broad- and fine-scale spawning migration movements of bonefish in Eleuthera. Forty-two receivers in the broad-scale array were concentrated around zones of interest in each region (identified from last year’s study) to further the understanding of bonefish spawning migrations and staging areas. This increase in coverage, combined with manual tracking and visual observations, should provide further evidence and confirm our previously identified sites of interests as critical spawning areas. Transmitters will be implanted in 30 bonefish at strategic locations around Eleuthera ,allowing for the fine-scale movements of these fish to be collected. Additionally, these fish will add to the 39 bonefish tagged last year to provide unprecedented data on this important species. By simultaneously tracking bonefish from several areas of Eleuthera, we can better determine which environmental cues bonefish use to form spawning aggregations, such as moon phase and tides.

At the previously identified spawning aggregation site of interest in South Eleuthera, 31 receivers were placed in an overlapping fine-scale array to track the movements of the bonefish aggregation on an almost continuous basis. This array will allow the team to answer questions related to: how abiotic factors (current, moon phase, seasonality, tide) influence bonefish spawning, how predators interact with the aggregation, understanding the energy expenditure of bonefish when migrating to their spawning site, and potentially the physical act of spawning, which is yet to be described. Furthermore, the fine-scale array will fill critical knowledge gaps regarding the movements of tagged predatory species, such as great barracuda, Sphyraena barracuda, and blacktip shark, Carcharhinus limbatus.  In addition to the basic positional transmitters being deployed, the team will be deploying 20 acoustic transmitters fitted with accelerometer sensors to determine energy expenditure of bonefish during spawning, as well as 20 acoustic tags in predatory species to assess predator interactions with the bonefish spawning aggregation.  Collectively, findings from this study will be used to develop a management and conservation framework for bonefish and predatory species surrounding Eleuthera, The Bahamas.

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This project is being conducted in partnership with Fisheries Conservation Foundation (FCF) with additional funding from the Hutchins Family Foundation. Georgiana Burruss is conducting this study as part of her MSc thesis at Michigan State University. This year, the team is supported by visiting researchers from FCF, Illinois Natural History SurveyFlorida Institute of Technology, and Florida Fish and Wildlife Conservation CommissionCocoloba ToursFishbone Tours, and the Rainbow Inn have provided support in the form of lodging and guiding.

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