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

Abstract

Length and mass data for 1260 (536 females, 683 males, 41 sex unknown) striped marlin Kajikia audax were collected at the fish markets of Tungkang, Singkang and Nanfangao from July 2004 to September 2010. Of these samples, 534 gonads (236 females and 298 males) ranging from 95 to 206 cm in eye- to- fork length (LEF) and 8 to 88 kg in round mass (MR), were collected. Chi- square tests indicated sex ratios were homogeneous among months in 2004 and 2006- 2008, but not in 2005, 2009 and 2010; and there were significant differences in sex ratio by size. The overall sex ratio (RS) differed significantly from the expected 0 center dot 5. Kajikia audax are sexually dimorphic and the proportions of females increased with size between 140 and 210 cm LEF. Reproductive activity was assessed using a gonado- somatic index (IG), external appearance of the gonads and histological examination and results indicated that the spawning season occurred from April to August with a peak in June to July. Based on histological observations and the distribution of oocyte diameters, K. audax are multiple spawners and their oocytes develop asynchronously. The estimated length- at- 50% maturity (LEF50) was c. 181 cm (c. 4 center dot 8 years of age) for females. The proportion of reproductively active females in the spawning season with ovaries containing postovulatory follicles (0 center dot 27) indicated that they spawned every 3 center dot 7 days on average. The hydrated oocyte method estimated mean +/- S. D. batch fecundity (FB) to be 4 center dot 4 +/- 2 center dot 02 million eggs; average relative fecundity was 53 center dot 6 +/- 13 center dot 9 oocytes g- 1 MR; and the average annual fecundity was 181 center dot 3 +/- 48 center dot 3million eggs. The parameters estimated in this study are key information for stock assessments of K. audax in the north- western and central Pacific and will contribute to the conservation, management and sustainable yield of this species. (c) 2017 The Fisheries Society of the British Isles