Population dynamics and stock assessment of sailfish (Istiophorus platypterus)in waters off eastern Taiwan
Date Issued
2004
Date
2004
Author(s)
Chiang, Wei-Chuan
DOI
zh-TW
Abstract
Age-growth and reproductive biology of sailfish were studied and the results were applied to yield per recruit (Y/R) and spawning stock biomass per recruit (SSB/R) analysis to assess the current stock of sailfish in the waters off eastern Taiwan.
Length and weight data were collected monthly from a total of 6,279 sailfish (1,927 females and 4,352 males) landed in Shinkang Fish Market during July 1998 to December 2002. The fish sizes ranged from 78 to 239 cm LJFL (lower jaw fork length) or 1 to 60 kg RW (round weight). The proportion of females increased with fish size and reached 100% at fish size larger than 227 cm or 46 kg.
Age and growth were examined by counting growth rings on cross sections of the fourth spine of the first dorsal fin of 1,135 (436 female and 699 male) sailfish. Significant differences were found in length-at-age and estimated growth parameters between sexes. Females grew faster and reached larger sizes than males. The generalized von Bertalanffy growth parameters estimated for females were the following: asymptotic length (L∞) = 343.8 cm, growth coefficient (K) = 0.011 yr-1, age at zero length (t0) = –0.468yr, and the fitted fourth parameter (m) = –1.639. The growth parameters estimated for males were the following: asymptotic length (L∞) = 294.0 cm, growth coefficient (K) = 0.023 yr-1, age at zero length (t0) = –0.704 yr, and the fitted fourth parameter (m) = –1.288.
Monthly variations in gonadosomatic index of 528 sailfish and histological examination on the 391 gonad tissue provided the basis to define the different stages of maturity. This information indicated that the sailfish spawned from April to September. Length at 50% maturity was 166.376 cm and 151.556 cm, respectively for females and males. Sailfish are a multiple spawning species, the spawning frequency was 1.89 days, batch fecundity equaled 0.2–2.48 million eggs. The relationship between batch fecundity in millions (BF) and weight (kg) or length (cm) was: BF = 2.03×10-3 RW1.936 (r 2 = 0.714; n = 18) and BF = 5.46×10-15 LJFL6.283 (r 2 = 0.667).
Via age-length transformation and catch curve analysis, total mortality rate (Z) was estimated as 0.56 and 0.58 yr-1, and the natural mortality rate (M) was 0.26 and 0.27 yr-1 respectively for females and males as obtained using Pauly’s empirical equation. The effects of different levels of M (0.20, 0.26, 0.30, 0.35 yr-1 for females and 0.20, 0.27, 0.30, 0.35 yr-1 for males), fishing mortality (F, 0–1.0 yr-1) and age at first capture (tc, 1–10 yr) on Y/R and SSB/R of sailfish were evaluated. The results showed that at the current tc of 5 yr and the current M of 0.26 yr-1 for females and 0.27 yr-1 for males, the current F values were below F0.1 for both sexes. SSB/R was 14.90 kg and spawning potential ratio (SPR) was 38.6 %. The sailfish in the waters off eastern Taiwan appear to be moderately exploited. However, in view of the recent rapid increase in fishing effort, it is evident that the stock condition and developments in the fishery still need to be monitored.
Subjects
年齡與成長
雨傘旗魚
單位加入生產量
生殖生物學
單位加入產卵親魚量
資源評估
age and growth
eastern Taiwan waters
spawning stock biomass per recruit
yield per recruit
reproductive biology
sailfish
stock assessment.
Type
thesis
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