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COMMERCIAL FISHERY There is no domestic commercial fishery for black marlin. Japanese longline fisheries making significant catches of black marlin began in both the NW Coral Sea and off NW Australia in 1953. Since the declaration of the 200-mile AFZ in November, 1979, access of this fleet to Australian waters has been subject to annually reviewed bilateral access agreements (see below). The terms and conditions addressed include limits on the number of boats permitted to fish in the AFZ, the access fee, ports available for victualling and repair, the placement of Australian observers and procedures for reporting activities to Canberra. Size of the longline boats varies from 200-350 GRT, 38-45m LOA. Campaigns generally last from 6 to 18 months depending on the size of the vessel. During a campaign the average duration of a boat in the AFZ is 60 days. Longlines comprise a mainline approximately 80km long with a series of branchlines and a total of approximately 3,000 hooks. Usually one set of a single mainline is made in any 24 hour period. Traditional sets fish at approximately 50m to 150m depth. Targeting of deeper-dwelling big-eye tuna since the mid 1970's has led to the development of "deep" longlines fishing to a depth of 250m. These sets use the same gear as the traditional sets but with fewer floats on the mainline. While deep sets now predominate in many fishing grounds, particularly near the equator, the great majority of sets in the Eastern AFZ remain at the traditional depth. The Indian Ocean fishing grounds with highest catch rates of black marlin in the Indian Ocean are east of 110oE, between 9-20oS, south of Java and the Lesser Sunda Islands and off NW Australia. Maximum catch rates off NW Australia are between November and April. During the 1980's, maximum catches and catch-rates by the longliners off NW Australia ranged between 12-24oS, peaking between Exmouth and Broome, offshore of the Rankin Gas Field. The NW Coral Sea longline grounds account for the major part of the SW Pacific black marlin catch and were, historically, bound by 142-150oE and 10-20oS [Fig]. Catch and catch-rates peaked in October-December between 14-19oS in the Queensland and Townsville troughs. The present fishing grounds are much more restricted due to area closures (see below). Target group: Spawning/pre-spawning aggregation (Coral Sea). Nature of NW Australian fishery is unclear at present. By Catch: Yellowfin tuna, Albacore, Broadbill Swordfish, Blue and Striped Marlin. Incidental catch (from non target fisheries): Black marlin are an incidental catch in the Japanese longline fishery throughout much of the AFZ. CATCH STATISTICS The catch of black marlin by Japanese longline vessels is now considerably less than it has been historically as a consequence of area closures and a shift to other higher-value species (Table 1). MARKETS Japanese The majority of black marlin caught by Japanese longliners is sold as frozen sashimi in Japan. Average annual price per kg for processed and frozen black marlin at Yaizu fish market was 532 Yen ($A 5.08) in 1988, 525 Yen ($A 4.82) in 1989 (Bergin MS) and 448 Yen ($A 3.87) in 1990. Average price of fresh black marlin in the Tokyo Fish Market rose from around 300 Yen/kg in 1970 to a maximum during 1985 (year of latest data) of approximately 1250 Yen/kg. Domestic Black marlin is banned from sale in NSW due to extremely high mercury levels in the flesh. The mean concentration of 7.3ppm found in the muscle of fish caught in a gamefishing tournament off Cairns (October 1973) is one of the highest yet recorded values for teleost (bony fish) muscle. Forty two fish, ranging in size from 68 to 572kg were examined. Mercury concentrations were highly variable but nonetheless significantly correlated with size. Sale of all marlins is banned in Western Australia to protect the recreational resource. Table 1. Numbers of black marlin taken by Japanese longliners fishing Australian waters.
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