Acoustic tags track grouper

A new component has been added to the Department of Environment’s continued effort to characterise the Nassau grouper spawning aggregation in Little Cayman.

With the help of a grant from the NOAA International Coral Reef Conservation Program and additional funding from PADI Project AWARE, a multi-year acoustic tagging project on the Little Cayman aggregation has been initiated, said a press release from the DOE.

The initiative is part of a joint project with REEF (Reef Environmental Education Foundation), which has been collaborating with the DOE on the Nassau grouper project since 2001. The project is headed up by Brice Semmens from the University of Washington and Phil Bush from DOE.

The project involves the installation of 15 underwater listening devices, called hydrophones, at strategic sites around Little Cayman. Following the installation of the hydrophones 30 Nassau grouper were acoustically tagged during the January 2005 grouper aggregation and a further 20 will be tagged this summer from inshore reefs, the release said.

The acoustic tags, which are surgically implanted in the belly of the fish, each emit a unique signal that is picked up and recorded by the hydrophone every time the fish passes within 500 meters. The hydrophones will record the presence of the tagged grouper for up to three years (before the tag battery wears out).

Acoustically tagged fish are also tagged with an external Floy tag (often called spaghetti tags) so that they can be visually identified underwater. During the tagging process blood samples are also collected for hormone analysis, to determine the sex of the fish and tissue samples are taken for future DNA analysis.

Project collaborator and fish physiologist, Dr. Scott Heppell from Oregon State University, is coordinating the hormone assays.

Data from the hydrophones will be downloaded every three months for analysis. Additionally, mobile acoustic listening gear is routinely towed by DOE boats to detect groupers in areas that are not covered by the hydrophones including Grand Cayman and Cayman Brac.

The waiting now begins, but initial data gathered is already revealing some interesting results, the release said.

The DOE would like to hear from divers, snorkellers or fishermen who encounter a Floy tagged grouper, so keep a look out for tagged fish along the reefs, especially in Little Cayman.

For more information, contact the Department of Environment at 949-8469.