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Charlotte Amalie
Friday, August 19, 2022
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Undercurrents: Researchers Plumb Depths to Improve Fisheries

A regular Source feature, Undercurrents explores issues, ideas and events as they develop beneath the surface in the Virgin Islands community.

David Olsen doesn’t know what happened to more than 4,000 yellowtail snappers fisherman tagged and released in the waters around St. Thomas and St. John as part of a study begun two years ago. Not one has shown up again – dead or alive.

And all the educated guesses one might make don’t make sense either. The species might be highly migratory, for instance, but past studies don’t suggest that. The tagging might weaken the fish and make them more vulnerable, but the few tagged yellowtail that were sent to Coral World Marine Park had no such problems. Nor have other subjects.

In a 30-plus year career, Olsen, who holds a doctorate in fishery management, hasn’t seen another study that ended in more mystery than the yellowtail research. Funded with a federal grant, the study was conducted by the St. Thomas Fishermen’s Association. Olsen is the association’s chief scientist.

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In sharp contrast, STFA has participated in several studies in the past eight years that have documented everything from the size and abundance of spiny lobsters to the best way to release “by catch” from fish traps.

The purpose of all the studies, Olsen said, “is to try to come up with some guidance for management” of marine resources.

“One of the efforts we’re pretty proud of is our attempts to catch fewer small and non-commercial fish,” he said. Known as “by catch” these are fish that find their way into fish traps but which cannot be sold either because they are under legal size limits or because they belong to a species that is not viable in the local market.

In 2005 and 2006 the association completed projects indentifying the species involved and in 2008 it began experiments with escape vents of varying sizes, trying them in different areas of a trap. The vents allow smaller fish to escape the trap before – or while – it is being hauled, or brought to the surface.

The studies were completed in 2012. The Caribbean Fisheries Management Council now has supplied STFA with 5,000 vents; Olsen said fishermen are installing them as they replace existing fish traps. The move should significantly decrease by-catch and thus promote species growth.

A more recent success is the study of the spiny lobster, which started about two years ago. Although the study has been extended until the end of this year, the association already presented data last month to the Caribbean Fishery Management Council which funded the research and which has regulatory authority over the fishing industry. Now Olsen is drafting a formal paper to be presented in November to the Gulf and Caribbean Fisheries Institute.

In an effort largely paralleling the yellowtail study, fishermen tagged some 4,000 spiny lobsters caught and released in St. Thomas waters. But they had much better luck with the lobsters.

About 350 of them were re-caught, Olsen said. By comparing their size, weight and location between the two captures, researchers were able to learn some new things about their habits, and to document information that was only suspected before.

The peak reproduction period is from March through July, he said. That’s when fishermen found the most lobsters bearing eggs. Further, they caught the most juveniles in September, October and November. It takes about a year and a half for a spiny lobster to grow to adulthood, Olsen said.

The study suggests that lobsters don’t travel much. Although “we’ve had recaptures up to 15 miles” away from the first capture, he said most of the animals were found within a mile of their first encounter with STFA.

Olsen theorizes that the lobsters are drawn not so much by the bait the traps contain – typically old cow skins – as by the shelter they provide. Lobsters don’t like to be exposed, and the traps, set between reefs, offer attractive cover.

The study also led STFA to make a population estimate of 410,000 spiny lobsters in St. Thomas/St. John waters. Olsen said fisherman sell about 50,000 to 60,000 of them each year.

The annual quota for lobsters, set by the Fisheries Council, is not by number but by weight. Currently, the quota for St. Thomas is a total of 105,000 pounds. Olsen believes the study supports raising that quota by up to 15,000 pounds.

He sees things differently for St. Croix. Preliminary findings indicated that the average size of lobsters caught in St. Croix waters has dropped by a centimeter, suggesting that the volume of lobster fishing in that area “is putting a lot of pressure on the resource.”

Fish traps represent the most popular type of fishing in St. Thomas waters, accounting for 450,000 pounds of fish a year. In contrast, hard lines bring in about 110,000 pounds, and seine nets, about 100,000 pounds.

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A regular Source feature, Undercurrents explores issues, ideas and events as they develop beneath the surface in the Virgin Islands community. David Olsen doesn’t know what happened to more than 4,000 yellowtail snappers fisherman tagged and released in the waters around St. Thomas and St. John as part of a study begun two years ago. Not one has shown up again – dead or alive. And all the educated guesses one might make don’t make sense either. The species might be highly migratory, for instance, but past studies don’t suggest that. The tagging might weaken the fish and make them more vulnerable, but the few tagged yellowtail that were sent to Coral World Marine Park had no such problems. Nor have other subjects. In a 30-plus year career, Olsen, who holds a doctorate in fishery management, hasn’t seen another study that ended in more mystery than the yellowtail research. Funded with a federal grant, the study was conducted by the St. Thomas Fishermen’s Association. Olsen is the association’s chief scientist. In sharp contrast, STFA has participated in several studies in the past eight years that have documented everything from the size and abundance of spiny lobsters to the best way to release “by catch” from fish traps. The purpose of all the studies, Olsen said, “is to try to come up with some guidance for management” of marine resources. “One of the efforts we’re pretty proud of is our attempts to catch fewer small and non-commercial fish,” he said. Known as “by catch” these are fish that find their way into fish traps but which cannot be sold either because they are under legal size limits or because they belong to a species that is not viable in the local market. In 2005 and 2006 the association completed projects indentifying the species involved and in 2008 it began experiments with escape vents of varying sizes, trying them in different areas of a trap. The vents allow smaller fish to escape the trap before – or while – it is being hauled, or brought to the surface. The studies were completed in 2012. The Caribbean Fisheries Management Council now has supplied STFA with 5,000 vents; Olsen said fishermen are installing them as they replace existing fish traps. The move should significantly decrease by-catch and thus promote species growth. A more recent success is the study of the spiny lobster, which started about two years ago. Although the study has been extended until the end of this year, the association already presented data last month to the Caribbean Fishery Management Council which funded the research and which has regulatory authority over the fishing industry. Now Olsen is drafting a formal paper to be presented in November to the Gulf and Caribbean Fisheries Institute. In an effort largely paralleling the yellowtail study, fishermen tagged some 4,000 spiny lobsters caught and released in St. Thomas waters. But they had much better luck with the lobsters. About 350 of them were re-caught, Olsen said. By comparing their size, weight and location between the two captures, researchers were able to learn some new things about their habits, and to document information that was only suspected before. The peak reproduction period is from March through July, he said. That’s when fishermen found the most lobsters bearing eggs. Further, they caught the most juveniles in September, October and November. It takes about a year and a half for a spiny lobster to grow to adulthood, Olsen said. The study suggests that lobsters don’t travel much. Although “we’ve had recaptures up to 15 miles” away from the first capture, he said most of the animals were found within a mile of their first encounter with STFA. Olsen theorizes that the lobsters are drawn not so much by the bait the traps contain – typically old cow skins – as by the shelter they provide. Lobsters don’t like to be exposed, and the traps, set between reefs, offer attractive cover. The study also led STFA to make a population estimate of 410,000 spiny lobsters in St. Thomas/St. John waters. Olsen said fisherman sell about 50,000 to 60,000 of them each year. The annual quota for lobsters, set by the Fisheries Council, is not by number but by weight. Currently, the quota for St. Thomas is a total of 105,000 pounds. Olsen believes the study supports raising that quota by up to 15,000 pounds. He sees things differently for St. Croix. Preliminary findings indicated that the average size of lobsters caught in St. Croix waters has dropped by a centimeter, suggesting that the volume of lobster fishing in that area “is putting a lot of pressure on the resource.” Fish traps represent the most popular type of fishing in St. Thomas waters, accounting for 450,000 pounds of fish a year. In contrast, hard lines bring in about 110,000 pounds, and seine nets, about 100,000 pounds.