Sex ratios, size at sexual maturity, and spawning seasonality of sailfish Istiophorus platypterus from eastern Taiwan
Lower jaw fork length (LJFL), round weight (RW) data, and 246 female gonads from 6279 sailfish ranging in size from 78 to 239 cm LJFL (or 1–60 kg RW) were randomly sampled at the Shinkang Fishing Port in southeastern Taiwan from July 1998 to December 2002. Sixty-nine percent of these sailfish were males. The sex ratio defined as the proportion of females in the sample increased as the LJFL increased beyond 145 cm and reached 98.6% at sizes > 227 cm LJFL (or 46 kg) (sex ratio = 3.07 × 10−7 LJFL 3.9782). Female gonads were classified into seven stages of maturity based on histological structures. Sexually mature individuals were defined as females with ripe ovaries or advanced oocytes. Estimated mean LJFL at sexual maturity (L 50) was 166 cm for females, and the smallest mature female was 162 cm LJFL. Monthly variations in gonadosomatic indices of 313 mature sailfish peaked during April–September, which is coincident with the histological findings that females were in spawning and recently-spawned stages during this time, indicating this to be the spawning period off eastern Taiwan.
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Document Type: Research Article
Publication date: 01 November 2006
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