DISTRIBUTION AND ABUNDANCE OF BILLFISH LARVAE 



(PISCES: ISTIOPHORIDAE) IN THE GREAT BARRIER REEF LAGOON 



AND CORAL SEA NEAR LIZARD ISLAND, AUSTRALIA 



Jeffrey M, Leis,' Barry Goldman,^ and Shoji Ueyanagi^ 



ABSTRACT 



Istiophorid larvae were relatively common in plankton samples from the Lizard Island region in 

 November to early March 1980-85. Black marlin, blue marlin, and sailfish larvae were captured. 

 Larvae of all three taxa were most concentrated and abundant in the Coral Sea immediately seaward 

 (= windward) of the outer ribbon reefs. Concentration and abundance within the Great Barrier Reef 

 Lagoon were not usually different from those more than 0.25 nautical miles offshore in the Coral Sea. 

 Size-frequency data combined with the distributional information suggest that spawning or at least 

 hatching of eggs was concentrated in the area within 0.25 nautical mile seaward of the reef crest. 

 Preflexion larvae of blue marlin and sailfish were essentially confined to the upper 6 m of the water 

 column (and perhaps the upper half of that), but not the neuston. Preflexion larvae of all three species 

 dominated the oblique bongo net tows (98%), while postflexion larvae dominated the neuston samples 

 (76%). This suggests an upward ontogenetic movement. 



The horizontal distribution of istiophorid larvae is probably the result of spawning close to the 

 reef front, an area of supposed downwelling, combined with the proclivity of the larvae to occupy 

 surface waters. This should lead to retention of larvae in the forereef area. Some caveats about 

 accepting this hypothesis as a complete explanation for the horizontal distribution of istiophorid 

 larvae are discussed. 



Near-reef areas appear to be important in the early life history of istiophorids at least in the Coral 

 Sea and for the three taxa studied. 



The billfishes of the family Istiophoridae are 

 large, high trophic level, pelagic fishes of consid- 

 erable sport and commercial importance through- 

 out tropical and subtropical oceans (Nakamura 

 1985). Information on their early life history is 

 limited and investigations have been hampered 

 by the relative rarity of the larvae. Studies on the 

 distribution of istiophorid larvae in the Indo- 

 Pacific have dealt with distributions over very 

 broad areas and have not examined distributions 

 on a small scale, particularly those very close to 

 reefs. (The considerable Japanese work was sum- 

 marized by Nishikawa et al. 1985 and the Rus- 

 sian work by Gorbunova 1976.) Size of larvae in 

 relation to horizontal distribution has only rarely 

 been considered. Aside from reports that istio- 

 phorid larvae had been captured in neuston tows 



iDivision of Vertebrate Zoology, The Australian Museum, 

 P.O. Box A285, Sydney South, NSW 2000, Australia. 



2Lizard Island Research Station, PMB 37, Cairns, Queens- 

 land 4870, Australia; present address: Research Associate, The 

 Australian Museum, P.O. Box A285, Sydney South, NSW 2000, 

 Australia. 



^Faculty of Marine Science and Technology, Tokai Univer- 

 sity, 3-20-1 Orido, Shimizu, Shizuoka 424, Japan. 



Manuscript accepted July 1987. 



FISHERY BULLETIN: VOL 85, NO. 4. 1987. 



(e.g., Bartlett and Haedrich 1968; Gorbunova 

 1976) the only published information on vertical 

 distribution of istiophorid larvae was provided by 

 Ueyanagi (1964), who concluded billfish larvae 

 were largely confined to surface waters during 

 the day and dispersed through the upper 50 m at 

 night. 



During studies on the distributional ecology of 

 the larvae of reef fishes in the vicinity of Lizard 

 Island in the northern region of the Great Barrier 

 Reef, Australia, two of us (Leis and Goldman) 

 have sampled extensively in the Great Barrier 

 Reef Lagoon and the near-reef waters of the Coral 

 Sea. In our samples, we captured a relatively 

 large number of istiophorid larvae. This has pro- 

 vided information which sheds light on little 

 known aspects of the early life history of istio- 

 phorids and in view of the widespread interest in 

 istiophorid biology, we have prepared this sum- 

 mary on the horizontal and vertical distribution 

 of istiophorid larvae over relatively small scales 

 and how these relate to development of the lar- 

 vae. Because istiophorid larvae are difficult to 

 identify, we have collaborated to insure accuracy 

 in identification of the larvae. 



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