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Grand Bahama Acoustic Tracking Study Summary


INTRODUCTION

Throughout the islands of The Bahamas, bonefishing is not only a popular sport, but also an important component of the tourism industry that contributes greatly to the economic health of many communities. For such a valuable fishery, surprisingly little is known about bonefish movements, particularly when it comes to migrations associated with their reproduction.

Although bonefish pre-spawning aggregations have been documented near deepwater drop-offs along the coastlines of Eleuthera, Abaco, and Andros, only anecdotal information exists for the island of Grand Bahama. Although bonefishing guides have noted that large schools of bonefish occur on the south side of the island during the winter months, it is unclear where these bonefish originate. Historically, at least some of the large bonefish populations on the north side of the island were reported to have used Hawksbill Creek to move to the south side. While building the port in the 1950s and 1960s, however, Hawksbill Creek was blocked by the construction of a causeway.  Since then, however, the man-made Grand Lucayan Waterway (GLW), a canal that now bisects the entire island, provides a way for bonefish to traverse the island…but, the question is: Do they use it?

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Our Grand Bahama Acoustic Tracking Study of bonefish is now part of the Ocean Tracking Network (OTN). The telemetry data from our tagged bonefish will be added to the Ocean Tracking Network’s global database. The Ocean Tracking Network is helping to develop the global infrastructure needed to build a comprehensive dataset on the movement of sea animals in relation to the ocean’s changing physical properties.

THE STUDY

A small transmitter is surgically implanted in the body cavity of the bonefish, which is then held in a pen until the fish is fully recovered. The implantation process takes about 10 minutes.

A small transmitter is surgically implanted in the body cavity of the bonefish, which is then held in a pen until the fish is fully recovered. The implantation process takes about 10 minutes.

The specific objectives of this project were:

1) to assess if bonefish use the GLW to traverse the island and/or if they swim around the East or West ends of Grand Bahama to get to the spawning grounds, and

2) to identify the location(s) of pre-spawning aggregations of bonefish on Grand Bahama.

Before the spawning season, the team deployed VEMCO acoustic receivers in strategic locations around the entire island, including 32 receivers provided by the Ocean Tracking Network, for a total of 67 VEMCO acoustic receivers in the final array. These additional receivers greatly increased our ability to track bonefish, and all of our telemetry data will be added to the Ocean Tracking Network’s global database.

A total of 56 bonefish were implanted with acoustic tags in locations all around Grand Bahama. Once released, these acoustic tags allow us to track the movements of these bonefish to their spawning sites.

WHAT DID WE FIND OUT?

The results of the first year of the study revealed that some of the fish tagged on the North side did indeed use the Grand Lucayan Waterway as a movement corridor for migrations during spawning season. Others went around both the east and west ends of the island. This data also confirmed that bonefish are forming pre-spawning aggregations only on the south side of Grand Bahama.

In year two, which focused on pinpointing the locations of pre-spawning aggregations and has now been completed, early data analysis has revealed that there are only three pre-spawning aggregation sites on Grand Bahama, with multiple bonefish going there to spawn on multiple days during the study (late October 2014 – early June 2015).

Dr. Karen Murchie presented the findings at the International Fish Telemetery Conference  in Halifax in July, 2015.

Dr. Karen Murchie presented the findings at the International Fish Telemetery Conference in Halifax in July, 2015.

Some of the interesting findings were:

  1. Bonefish continued both to use the Grand Lucayan Waterway as a corridor to reach spawning locations, as well as to swim around both ends of the island.
  2. The longest round trip migration was one of at least 180 miles from north of Dover Sound all the way to the south side of the island around East End.
  3. Several fish spawned at least five times during the study.
  4. Two fish used multiple pre-spawning aggregation sites.

With only three pre-spawning sites on the island, commercial development or illegal fishing in any one of these three areas could destroy a local fishery. These findings emphasize that protecting critical habitats are essential to keeping the multi-million-dollar bonefish fishery healthy for years to come.

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IT TAKES A VILLAGE

There are a lot of behind the scenes efforts and coordination needed for such a large project to succeed, and this project would not have been possible without the extraordinary support and personal assistance from Jason Franklin and Greg Vincent of H2O Bonefishing, as well as Paul Adams and the bonefishing guides at North Riding Point Club. They provided both excellent advice and support, including boats, guides, lodging, and refreshments, which is no small feat for a project of this size.

We would also like to recognize the members of our science team: Dr. Karen Murchie (College of the Bahamas); Dr. David Philipp and Julie Claussen (FCF); Dr. Aaron Adams and Justin Lewis (Bonefish & Tarpon Trust); Aaron Shultz, Eric Schneider, Nick Balfour, and Malcolm Goodman (Cape Eleuthera Institute); Dr. Steve Cooke (Carleton University); Drs. Jeffrey Stein and Cory Suski (University of Illinois).

Murchie_findingsThe findings for year one of the study were published in the journal Environmental Biology of Fishes.

Abstract: Development on Grand Bahama in the Bahamian Archipelago during the 1950’s to 1970’s resulted in substantial changes to the island’s geography. Hawksbill Creek, which potentially served as a natural migration route for fish from the north side to the south side of the island, was severed and replaced by a man-made canal called the Grand Lucayan Waterway (GLW). Bonefish (Albula spp.), a sport-fish that contributes more than $141 million to the Bahamian economy annually, is one such species that may have been affected. The purpose of this study was to determine contemporary movement corridors of adult bonefish during their spawning season (October to May) in Grand Bahamian waters. This was accomplished by using a passive acoustic telemetry array of 17 receivers and 30 transmitter-implanted individuals. A total of 26,108 detections were logged from 20 of the fish. Eight bonefish tagged on the north side used the GLW to access waters on the south, whereas no transmitter-implanted fish tagged on the south side fully traversed the man-made canal, suggesting that primary spawning areas may be located on the south side of the island. This result is consistent with previous reports that bonefish spawn near deep water which is easier to access on the south side of Grand Bahama. Further supporting this finding, two other bonefish tagged on the north side forayed around the east end of the island and were detected on receivers approximately 88 km from their tagging locations. Additionally, two other bonefish tagged on the north side were detected at the west end of the island, with one individual continuing its movements along the south side of the island for an approximate straight-line distance of 80 km. Canal use typically corresponded to days immediately prior to or after new or full moons, indicating that movements were related to spawning. This study suggests that despite historical habitat modifications, bonefish today use the GLW as a movement corridor for migrations during spawning season, emphasizing the importance of protecting the canal from any activities that could impede connectivity.

See photos from our Grand Bahama study here.

GB Tracking pics

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Champaign, IL 61825
info@fishconserve.org

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