 Home About AIMSResearchFacilitiesNewsSearchSite
mapSite
indexTopics
index   |
Species Synopses BLUE MARLIN (Makaira mazara) Blue marlin are the most tropical of all marlins but are distributed throughout the tropical and subtropical regions of the Indian and Pacific Oceans. A single stock is assumed for each ocean. In common with striped marlin, they are rarely encountered in shallow nearshore waters, preferring blue, oceanic waters. There is very strong evidence from Japanese longline data of seasonal migrations of blue marlin in the Pacific Ocean and that the extent of these migrations differs between males and females. Blue marlin occur in equatorial waters year-round but part of the stock makes seasonal migrations to the north and south during the respective summer seasons in each hemisphere. It is believed that these summer migrations are made primarily by "shoals" of mature males between 35kg and 75kg and that year-to-year variability in catch-rates of blue marlin away from the equator are strongly influenced by the numbers of males migrating. Good catch-rates occur when large numbers of males migrate. Males are also smaller than females (see below). An interesting consequence, in the longline fishery at least, is that the average size of fish in waters away from the equator is inversely related to the catch-rate: higher catch-rates mean smaller average sized fish. Blue marlin are sexually dimorphic in size with females reaching 900kg while males may weigh up to 170kg. Males reach maturity at 30-40kg and females between 47-80kg, although substantially larger females may not have reached sexual maturity. While there is considerable difference between maximum size attainable by each sex, their longevities do not appear to differ markedly. Males have been estimated to live to 21 years and females to at least 28 years. Fish probably grow rapidly over 3-4 years to 80kg, and with the onset of sexual maturity, male growth rates decrease, whereas females continue with rapid growth. Spawning is believed to occur year-round in equatorial waters but is limited to summer months at higher latitudes. Peak activity may be centered about the eastern Caroline and the Marshall Islands (Micronesia) in the western Pacific and French Polynesia in the east. There is evidence of spawning in the northwest Coral Sea adjacent to the northeast Australian coast in December - February. web@aims.gov.au
|