Aspects of the biology of billfish (lstiophoridae) from the equatorial western Indian Ocean*

Abstract

With 17 figures in the text)A tuna longline survey of billfish was carried out in the equatorial western Indian Ocean during 1964-67, in which 265 specimens of five species (Zstiophorus platypferus, Tetrapferus audax, T. angustirostris, Makaira indica and M. nigricans) were caught. The comparative morphometric evidence obtained is used in confirming the conspecificity of these istiophorids with Pacific Ocean forms. However, the insufficient depth and detail of the data allow only preliminary observations on populational differences. The distribution and seasonal abundance of the species are discussed in terms of percentage catch rate. The weight-length relations of the species are examined. The size composition of the catches is shown by the analysis of length and weight frequencies, and tentative estimates of the year classes present in the catches of T. audax are given. An examination of the sex ratio of the species is made. Gonad maturation indices for males and females are established, based on both macroscopic and histological evidence. The indices are used to study breeding in the species caught in the survey area. Relative gonad weight is also considered as a means of assessing the stage of gonad development. The results of the gonad examination indicate that little spawning occurs in the area, and it is suggested that seasonal abundance of certain species is related to feeding. Preliminary observations on the size at first maturity are made, and the fecundity of female I. platypferus, T. audax, and T. angustirosfris is examined.

Reproductive biology of blue marlin Makaira nigricans around Yonaguni Island, southwestern Japan

“…Oocytes in the early yolk stage are thought to develop rather rapidly with no noticeable growth in body length, so the minimum length at maturity was considered to be 183 cm LJFL (159 cm EFL). Various authors have reported the smallest size of mature female blue marlin for their region by various criteria [11,12,[14][15][16]. Except for the eastern Pacific [11], the minimum mature lengths are larger in other regions compared to that for Yonaguni Island.…”

“…Previous studies on the reproductive biology of blue marlin in the eastern Pacific Ocean [11], western Indian Ocean [12,13], Atlantic Ocean [14,15], and Hawaiian waters [16] focused on determining spawning season and size at sexual maturity. However, in the western North Pacific, where most blue marlin populations are concentrated, these biological parameters are poorly understood [17,18].…”

Reproductive biology of female striped marlin Kajikia audax in the western Pacific Ocean

“…(). Fecundity was estimated at 12 million eggs for a female K. audax of 182 cm L EF in the western Indian Ocean with a gonad mass of 1532 g and the mean diameter of MAGO was 470 µm (Merrett, ). The fecundity estimated from three females (155–180 cm L EF ) in the eastern Pacific Ocean ranged 11·3 to 28·6 million eggs; ovaries weighed 2580–3550 g and the mean diameter of MAGO was 600 µm (Eldridge & Wares, ).…”

“…Kume & Joseph () estimated size at maturity and spawning season by developing a gonado‐somatic index ( I G ) for K. audax in the northern and southern Pacific Ocean. Merrett (, ) identified the gonad development and estimated size at maturity in the western Indian Ocean. The appearance of the gonads was described by Eldridge & Wares () who also estimated size at maturity, fecundity and spawning season in the eastern Pacific Ocean.…”

Seasonal occurrence and feeding habits of black marlin, Istiompax indica, around Yonaguni Island, southwestern Japan

“…Gonad observations indicate that spawning of black marlin does not occur in the East China Sea (Morita 1960), the equatorial western Indian Ocean (Merrett 1971), the Mauritian waters (Cyr et al 1990), and the west coast of Panama (de Sylva and Breder 1997). The South China Sea is also thought to be one of the spawning grounds based on the seasonal change in sex ratio (Nakamura 1941(Nakamura , 1942.…”