Satellite Tracking Shows Marlin Vulnerable to Longliners

HOBART, Tasmania, Australia, August 30, 2001 (ENS) - A satellite tag found by a beachcombing dog has recorded the journey of a black marlin tagged last November off Cairns. The satellite archival tag was attached to the fish for a month before detaching automatically.

While attached, the tag travelled 1,100 kilometers (680 miles) before washing up at Brunswick Heads in northern New South Wales. It was mailed back for analysis to the scientists at CSIRO Marine Research at Hobart who originally tagged the marlin.


Black marlin in the waters off Cairns, Australia (Photo courtesy CSIRO)
CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is an agency in the Industry, Science and Resources government portfolio.

The black marlin was one of five tagged by John Gunn of CSIRO Marine Research and Dr. Julian Pepperell of Pepperell Research in a pilot project supported by the Game Fishing Association of Australia Research and Development Foundation.

"This was the first time we used the A$8,000 pop-up satellite tags on black marlin in Australia," Gunn says. "All five tags used in the project clearly show that black marlin swim away from the Coral Sea following the spring early summer spawning."

The tag showed that the 80 kilogram (175 pound) fish swam south-easterly with the East Australian Current. Pop-up tags transmit details of diving patterns, water temperatures and daily locations to satellites, after they have become detached from the fish.

The volume of data tags can transmit is limited by battery power. A full record of the fish's movements can only be recovered in the rare event that a tag is returned.

Black marlin are the ultimate prize for gamefish anglers in Australian waters, but catches in the A$40 million Cairns fishery have been declining in recent years.

"Black marlin congregate and spawn off the Great Barrier Reef north-east of Cairns each spring, then depart suddenly in December," Dr. Pepperell says.

Pop-up satellite tags have the potential to help reveal links between recreational fishing and commercial longlining in the Pacific Ocean, helping scientists to assess the impact of commercial fishing on black marlin populations. A satellite tag recovered last year showed a marlin had travelled from Australia to Costa Rica, a journey that may have placed it in the path of longliners.

"The fact that the fish travel so far means they may be vulnerable to longline fisheries on the high seas, but few tags are received from the longline fleets, so information on their catch levels is sketchy," Gunn says.

The project's next phase is planned for the 2001 season in Cairns around December, and possibly later in the 2001-2002 Australian summer, as black marlin are caught along the east coast of Australia during their southward migration. The aim is to tag 20 more fish in the Cairns fishery.

The single point, pop-off satellite tag was designed to define movements of deep ocean fish. Dr. Paul Howey of Telemetry 2000, of developed the tag in teh mid-1990s in collaboration with researchers at Stanford University and California's Monterey Bay Aquarium. Conventional tag and release studies have low resolution and seasonal migratory patterns remained undefined until the use of satellite tags.

In the past decade, sport fishermen have strongly supported the tag and release of blue marlin, according to the Pacific Ocean Research Foundation of Kona, Hawaii. Their Tag-A-Marlin project utilizes pop-up satellite archival tags to examine post-release survivorship and gather much needed information about the movements of blue marlin.

The release ethic was developed in response to the overfishing of many marine resources, and in Hawaii, a 25-year history of blue marlin research includes the recreational anglers of Kona working to gather information in association with the Pacific Ocean Research Foundation.

Similar efforts are taking place in the Atlantic Ocean with cooperative tagging occurring along the U.S. Eastern seaboard especially in the Carolinas, in Madeira and off Bermuda. This cooperative effort of scientists and fishers has resulted in a large increase in knowledge about blue marlin.

Survivorship of billfishes after tag and release is not well documented and is critical information for assessing the costs and benefits of the practice for marlin caught in recreational and commercial fisheries.

The CSIRO scientists say their study shows that when fish are handled and tagged carefully by experienced crews, their chance of survival is high.