3D Activity Tracking Enhances Conservation of Caribbean Fish

Written by on April 14, 2015 in Fish, Technology

3D Activity Tracking Aims to Enhance Conservation of Iconic Caribbean Fish
By Evan Lubofsky

The high predictability of spawning times and locations of Nassau Grouper – one of the Caribbean’s most important marine resources – has led to overfishing and fish population declines of 60% over the past several decades (Cornish and Eklund 2003). This has put the species on the International Union for the Conservation of Nature (IUCN) Red List, and spawning aggregations over the past half century have dwindled from tens of thousands of fish to just hundreds at certain sites.

The August 2014 grouper tagging trip crew. Photo credit: Sam Cejtin.

The August 2014 grouper tagging trip crew. Photo credit: Sam Cejtin.

“In the Bahamas, the Nassau Grouper’s reproductive strategy is to migrate hundreds of miles to spawning sites during full moons in the winter,” said Dr. Kristine Stump, a marine biologist with Chicago’s Shedd Aquarium who is leading a multi-year grouper study in the Bahamas. “In the past, these aggregations were really impressive in size. Unfortunately, they are all in very predictable places and times so fishermen decimate them.”

To enhance conservation efforts, Stump and colleagues from the Bahamas Department of Marine Resources (DMR), Bahamas National Trust and University of Exeter are studying grouper movements to learn more about fish activity before, during and after the big event. According to Stump, their movements within spawning sites will be tracked in 3D – a first for this species – in order to yield more precise data.

Deploying a new bottom monitor mooring. Photo credit: Dr. Kristine Stump.

Deploying a new bottom monitor mooring. Photo credit: Dr. Kristine Stump.

To accomplish this, the research team is employing a novel use of acoustic telemetry whereby an array of acoustic receivers with overlapping detection ranges can pinpoint tagged groupers right down to their specific locations in the water column.

“If you have one receiver with a detection capability of 200 meters and a fish swims within range, it could be anywhere within that 200-meter radius,” said Stump. “If you have two receivers, you can narrow down the location. With three, you can get an exact position of the fish in three dimensions when it is paired with a depth-recording tag implanted in the fish.”

The telemetry array, which covers a 120-mile stretch of Bahamas coastline in Andros and Long Island, consists of 18 receivers deployed on the ocean floor which pick up signals from 46 tagged fish. The recorded data will enable the research team to better understand activity leading up to spawning time, assess what the fish are doing once they get to the site, and determine how long they stick around the site after spawning. This, in turn, will help the Bahamas DMR develop a Species Conservation Plan for Nassau Grouper that Stump hopes will allow the region to “help stocks recover before it is too late.”

“There have been places throughout the Caribbean where spawning aggregations are defunct or decimated,” said Stump. “But in some of these places, like the Caymans, they have closed fisheries during spawning times and are starting to see some rebound. We want to see the same rebound happen in the Bahamas so this iconic fishery can continue on for generations.”

Dr. Kristine Stump putting a monitor back on its mooring. Photo credit: Craig Dahlgren.

Dr. Kristine Stump putting a monitor back on its mooring. Photo credit: Craig Dahlgren.

Copyright © 2015 by Marine Science Today, a publication of Marine Science Today LLC.

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