New fishing techniques may help sea turtles and swordfish fishers

An experimental fishing gear configuration is showing promise in protecting endangered sea turtles and other sensitive species.

The gear is intended to selectively target swordfish at depth, taking advantage of the top pelagic predator’s differential day and night habitat preferences.

If successful, the deep-set longline gear could offer fishers an alternative to drift gillnets – the gear currently used to catch most of the swordfish landed in the state.

Heidi Dewar with NOAA Fisheries Southwest Fisheries Science Center in La Jolla said the idea of the gear modification is based on setting hooks at depths that are below the turtle layer.

Sea turtles and swordfish inhabit the same water depths at night, but during the day, swordfish “go deep in the water column,” Dewar explained.

The trick is to figure out exactly how deep to set the hooks so that swordfish but not protected species are caught efficiently.

To this end, she and her NOAA Fisheries colleagues made 17 deployments of the deep-set longlines in waters off Central and Southern California last fall, with hooks set at an average depth of 235 meters.

With this configuration, researchers caught a range of marketable species, including one swordfish, 37 opah and two albacore tuna. Bycatch was dominated by blue sharks. There were no sea turtle or marine mammal interactions.

“Unfortunately, we have been fishing in very odd years,” Dewar said, explaining the low catch of swordfish. “Few swordfish have been caught by anyone so it is hard to say. Hopefully, we will know more after this year.”

Tagging and tracking of swordfish may help identify strategies for increasing swordfish catches, while still minimizing fishing’s environmental impacts.

Chugey Sepulveda, director of the Pfleger Institute of Environmental Research (PIER) in Oceanside, and colleagues have tagged and tracked 10 swordfish in the Pacific Leatherback Closure Area (PLCA), established to protect the critical habitat of migrating leatherback sea turtles.

“The PLCA is now closed to California’s primary swordfish fishery and the area currently only allows harpoon operations,” Sepulveda said by email. “The data that is collected will be used to identify potential depths that facilitate better targeting of swordfish and also document the degree of vertical separation between target and non-target species of concern.”

“Preliminary findings suggest that swordfish above Point Conception do not display the same depth distribution as swordfish tagged in the Southern California Bight,” he said. “It is apparent that the daytime depths are shallower, but still below the thermocline, and more erratic. We need additional data to ensure that these trends are indicative of the region.”

Swordfish landings in California have declined from more than 4 million pounds in 2000 to about 612,000 pounds in 2012 largely because of regulations on when and where drift gillnetting can occur in federal waters. Gillnetting is banned in state waters.

“We are optimistic that deep-set operations will provide additional fishery options that have minimal interactions with sea turtles and other sensitive species,” Sepulveda said. “However, additional gear testing is needed.”

This project is being supported by CFR West, with funding from the Ocean Protection Council and administrative support  from California Sea Grant.

Below is a summary of the project, published in California Sea Grant’s 2013 Program Directory, with contact information for the lead scientists.

Written by Christina S. Johnson