Examining the Density-Dependent Effect on the Growth of Dolphinfish, Corphaena hippurus in the Eastern Taiwan Waters

Abstract

本研究係利用1996年10月至1998年7月間，連續22個月於台東新港漁港所量測之鬼頭刀體長頻度資料（雌魚7054尾，雄魚2626尾），以體長頻度分析軟體(ELEFAN)估計其成長參數、死亡率、開發率及加入型態。並檢驗兩個時期之間（1996-1998和2004-2005年間）台灣東部海域鬼頭刀之成長是否有密度相依效應。以ELEFAN所估計之季節性本托蘭斐成長方程式(seasolonal von Bertalanffy)參數如下，雌魚：極限體長L(下标 ∞)=160 cm，成長係數k=0.56yr^(-1)，理論零體長之年齡t0=-0.183yr，季節性震盪幅度C=0.9，冬季成長最低點WP=0.77；雄魚：L(下标 ∞)=172.25cm，k=0.7yr^(-1)，t0=-0.142yr，C=0.5，WP=0.17。雌、雄分別可分離出4個(0(上标 +)-3(上标 +))與3個(0(上标 +)-2(上标 +))年齡群且每年均有兩個加入群，加入的高峰期在6月和10月。雌魚各年齡平均尾叉長1歲為78.04cm，2歲為113.19cm，3歲為133.26cm。雄魚各年齡平均尾叉長1歲為94.59cm，2歲為133.69cm。雌魚全死亡率Z=1.466yr^(-1)，自然死亡率M=0.752yr^(-1)，漁獲死亡率F=0.714yr^(-1)，開發率E=0.487；雄魚Z=1.897yr^(-1)，M=0.853yr^(-1)，F=1.044yr^(-1)，E=0.550。相較於1996-1998年，2004-2005年的鬼頭刀成長速率較快，極限體長較小，顯示在這兩個時期之間，鬼頭刀之成長可能有受到密度相依效應之影響。A 22-month length frequency data set including 7054 females and 2626 males collected at Hsinkang fish market, Taitung County from October 1996 to July 1998 were used to estimate the growth parameters, mortalities, exploitation rate and recruitment pattern of the dolphinfish (Coryphaena hippurus) with ELEFAN. The possibility of density-dependent growth of the dolphinfish in the eastem Taiwan waters was examined on the two periods of 1996-1998 and 2004-2005. Parameters of the von Bertalanffy growth equation with seasonal fluctuations were estimated as follows: asymptotic fork length (L (subscript ∞))=160 cm, growth coefficient (k)=0.56 yr^(-1), age at zero length (t 0)=-0.183 yr, amplitude of seasonal growth oscillation (C)=0.9, winter point (WP)=0.17 for females; and L (subscript ∞)=172.25 cm, k=0.7 yr^(-1), t0=-0.142yr, C=0.5, WP=0.17 for males. Four (0 (superscript +)-3 (superscript +)) and three (0 (superscript +)-2 (superscript +)) age classes were identified for females and males, respectively. Mean fork lengths of age classes 1, 2, and 3 were estimated as 78.04, 113.19, and 133.26 cm for females. Mean fork lengths of age classes 1 and 2 were estimated as 94.59 and 133.69 cm for males. The total mortalities (Z) were estimated to be 1.466 and 1.897 yr^(-1) for females and males, respectively. Natural mortalities (M) estimated from Pauly's empirical formula were 0.752 and 0.853 yr^(-1) for females and males, respectively. Fishing mortality (F) and exploitation rate (E) were estimated to be 0.714 yr^(-1) and 0.487 for females and 1.044 yr^(-1) and 0.550 for males. The recruitment of dolphinfish in both sexes occurred in Jun. and Oct. annually. Comparing with the fish during 1996-1998, a higher growth rate and smaller asymptotic length of the dolphinfish during 2004-2005 suggested that the density-dependent effect on the growth might exist in the two periods.