TAG A BILLFISH
Hopkins Marine Station - Monterey Bay Aquarium




Project Development
Researchers from Stanford University, the Monterey Bay Aquarium and the National Marine Fisheries Service have worked together to study the movements of the quintessential game fish, the blue marlin, (Makaira nigricans). In the early years of the project, the goals were to test the new technologies, especially as they are applied to blue marlin of a wide range of body sizes. The Billfish Foundation funded the project in the Atlantic. In the Pacific funding was derived from the Monterey Bay Aquarium and the Hawaiian recreational fishing community in association with the Pacific Ocean Research Foundation.
Blue Marlin
Blue marlin are the top predators in open ocean ecosystems. Convention tag and release studies have shown that they travel the length and breadth of the oceans of the world, which indicates inter-ocean movements on a yearly basis, are possible. They forage near the surface in warm mixed layers of temperate and tropical seas. They feed on an assortment of epipelagic organisms. Acoustic telemetry indicates blue marlin prefer the surface lens of the water column and remain above the thermo cline most of the time. Conventional tag and release studies have low resolution and seasonal migratory patterns remain undefined. In the Atlantic ocean, only 123 blue marlin have been recaptured from the 20,123 releases. New methods are urgently needed to gather information about the migratory movements and survivorship of blue marlin.

The New Technology
The single-point, pop-off satellite tag was designed to define movements of pelagic fish. Dr. Paul Howey of Telemetry 2000, of developed the tag in collaboration with researchers at Stanford University and the Monterey Bay Aquarium. The torpedo shaped satellite tag was attached externally on a marlin, released at a pre-programmed time thanks to a corrosive linkage, floated to the surface and then transmitted continuously to ARGOS satellites. The center of buoyancy and mass were such that the tag floated with the antenna extending upward when on the surface. While attached, the antenna extends parallel to the fish and the syntactic foam float provides sufficient lift to keep the tag off the body at low speeds. Each first generation tag logged 61 average water temperature measurements compiled from individual measurements made hourly. The pop-off satellite tags were attached to the marlin around the region of the dorsal fin using a dart machined of titanium.
The Early Accomplishment
Scientists worked in two locations: Madeira, Portugal and Kona, Hawaii in cooperation with sport fishermen. In Madeira, Mr. Stuart Campbell, owner of the FV Chunda hosted the scientists for 4 weeks in August of 1997 while they tagged 5 blue marlin that ranged in size from 350-850 lbs. The fish were caught on lures and fought on heavy tackle. Scientists and the very capable crew aboard the Chunda (Capt. Barkey Garnsey and mate Charles Perry) and the Duyfken, captained by Capt. Peter Wright put on the tags, which were set to stay on the fish for up to 12 months. In addition to the tags, DNA samples were removed to investigate the genotypes of the fish in relationship to their contemporary movements. Four tags released on schedule and showed all of the fish moved south of Madeira. The fish were located 6-9 months later off the western coast of Africa, as well as in the central Atlantic. One 850 lb fish was tagged with two pop-up tags of 6 and 9 month duration. When the first tag surfaced the marlin was in the central Atlantic, 1467 miles south of Madeira and at 9 months it had moved an additional 800 miles further west closer to the Northeast coast of South America. Two tags scheduled to pop-off have not come up and its uncertain whether tag failure or mortality could be the cause. Improvements on second generation tag technology will improve the ability to discern survivorship from this methodology.
In the Pacific, a total of ten tags were deployed during the 39th annual Hawaiian International Billfish tournament. Anglers used 50 and 80 pound class gear and the fish tagged and released were significantly smaller (140-240 lbs). Three tags reported back and a fourth fish was recaptured close to the point of release shortly after the tagging. Remarkably one fish traveled over 2831 miles in 90 days as it headed due east away from the Hawaiian Islands and was to the west of the Galapagos in waters warmed by El Niño when the tag surfaced. One fish was South of the Hawaiian Island chain and headed toward Christmas Island and had traveled 675 nm and a third fish was 586 nm west of the Hawaii.The blue marlin pop up satellite archival tags also provided a brief glimpse of the temperature preferences of blue marlin. Over 10,000 temperature measurements were made indicating the preferred temperatures of the blue marlin along their courses. In the Atlantic, Madeira was the coolest place and as the fish traveled south the water they experienced warmed up from 73ºF to 78ºF. In Hawaii, around Kona, fish remained in water that ranged on average from 78-81ºF. All the Kona tagged blue marlin progressed toward slightly warmer waters that were at maximum 82ºF. The tracks were superimposed upon satellite images of sea surface temperature and ocean color. The information gained with these tags will improve our understanding of the biology of these species and should increase our knowledge of stock structure. In addition to the above research, tags have been attached to longline caught blue marlin and striped marlin in the Pacific Ocean.
The People
Dr. Barbara Block, Prothro Professor of Biological Sciences at Stanford University and co-director of the Tuna Research and Conservation Center, leads the research. Researchers included Stanford Postdoctoral Fellow, Dr. Heidi Dewar, Monterey Bay Aquarium curator of pelagic fishes Charles Farwell and Eric Prince of the National Marine Fisheries Service in Miami.
Significance
Our knowledge of migrations and movement patterns of pelagic fish is incomplete because of the inherent difficulties of studying open ocean fishes and historical lack of adequate tools. Continual advances in the technology of wildlife telemetry and molecular genetics now provide tools to directly examine the short and long-term movement patterns, stock structure and behavior of large pelagic fish (billfishes, tunas and sharks). This program of research is committed to applying the best technology and practice to the issues associated with some of the most important and least understood fishes in the world’s oceans.