Scientists use facial recognition technology to track grouper populations in the Cayman Islands

Nassau Grouper. Image credit: Stephanie Archer, Oregon State University

Scientists in the Cayman Islands recently began using facial recognition technology to monitor Nassau grouper (Epinephelus striatus) during their spawning season:

The methods used to count the grouper at aggregation sites have become ever more sophisticated.

This year, scientists used a mix of “floy tagging” – counting the prevalence of previously tagged fish within a group to extrapolate a population estimate – and stereo-video – using two cameras in consort to take a “3-D video” that can be used to estimate length and abundance of fish and a video pan of the whole aggregation site.

They have also begun using facial recognition technology.

Mr. McCoy said each fish has a distinct facial pattern. One regular visitor to the Little Cayman site was christened “The Phantom” because he was black on one side of his face, and white on the other.

The technology aims to take that type of visual recognition to the next level, potentially allowing researchers to identify which individual fish are at the aggregation site each year.

“We take photos of fish faces side on and map the face using reference points that recognize the coloration pattern and store the data. When we retake photos, the software searches in our database of photos to match the facial image.

“The good thing about this is the fact we can use images we have taken over the past 17 years. This allows us to recognize each fish individually due to its unique facial pattern.”

The results of the monitoring have been mixed.  Around Little Cayman, the grouper aggregation has increased steadily in size over the past few years. Around Cayman Brac, the aggregation size has remained relatively constant.  The Grand Cayman aggregation, however, has diminished to worryingly low levels:

“Little Cayman is the real success story and that is due to the efforts of local fishermen who gave up a deep-rooted tradition of fishing the aggregation to comply with the rules and regulations set out for that area,” Mr. McCoy said.

“It is now the largest aggregation of Nassau grouper that we know of in the Caribbean basin, which is something every Caymanian should be proud of.”

At one stage, early in the 17-year research project, there were as few as 1,500 grouper at the site, off the west end of the island.

But a ban on fishing during spawning season has helped revive the population to the point where there are now between 6,000 and 7,000.

The picture on Cayman Brac is also positive, though there are far fewer grouper – between 800 and 1,000 – seen at the site.

Grand Cayman is a different story.

Bradley Johnson, a Department of Environment research officer, said grouper populations had diminished around the main island.

“We are still trying to assess how many fish we have here,” he said. “The population is so low that we are not sure it is functioning as a spawning site any longer.”

Find out more in the full Cayman Compass article.


[Image credit: Stephanie Archer, Oregon State University]

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