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RESOURCE STATUS Fishery Interactions Potential interactions between the Japanese longline fishery in the South-West Pacific and the Cairns-Lizard Is. based recreational fishery have been recognised since the recreational fishery began and is the basis of the present management regime in the eastern AFZ. Concerns have also been expressed about interactions between the Japanese longline fishery in the Eastern Indian Ocean and a growing recreational fishery off North-Western Australia. The Pacific-wide catch of black marlin by the Japanese fleet has been decreasing since the mid-sixties. A major decline in the 1970's was caused by the spread of 200mile Economic Fishing Zones (EFZ's) and hence loss of the major black marlin habitat close to land and the introduction of deep longlining where sets are made at depths greater than the normal black marlin habitat where tuna, especially bigeye, are targeted. The black marlin catch of the Taiwanese fleet has been increasing over the same period and to some extent has offset the decrease in catch by the Japanese. The Taiwanese longline fleet does not fish in waters of the AFZ and their catch of black marlin in the Coral Sea is small compared to the Japanese. The increasing catch has presumably been from the North-West Pacific (mainly East China Sea) where the Japanese catch of black marlin has recently been very small. Possible interactions between the Taiwanese fishery in the North-West Pacific and the Australian recreational fisheries can only be clarified with an improved understanding of the relationships of black marlin stocks in the South-West and North-West Pacific and the North-Eastern Indian Ocean, together with better data from the Taiwanese fishery. STOCK STATUS Pacific Ocean Because of uncertainty in total catch figures and stock structure, there have been no attempts to fit production models or estimate maximum sustainable yield for black marlin in any area in the Pacific. Total catch Pacific-wide has been sustained at a level between 2,000 and 4,000 tonnes over a wide range of fishing effort. Because of the lack of variability in catch over a wide range of fishing effort, a stock-production model could not be fitted to the data. However, it is generally recognised that the catch rate has been stable or is recovering in recent years. Indian Ocean Similar limitations in the Indian Ocean data, to those mentioned for the Pacific Ocean, apply. A decline in CPUE, albeit with considerable variation, of black marlin in the Indian Ocean by the Japanese longline fishery occurred over 1952-76 but a shift of longline effort southward into areas of relatively low billfish abundance also occurred over the same period.
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