高屏溪日本鰻族群動態及永續利用:YPR和SPR模式的應用

Population dynamics and sustainable use of Japanese eel (Anguilla japonica) in Kao-Ping River: application of YPR and SPR models

林裕嘉(Yu-Jia Lin)

指導教授 ： 曾萬年

國立臺灣大學/生命科學院/漁業科學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.00612

摘要

日本鰻(Anguilla japonica) 為一高度經濟價值的物種。由於過度捕撈，鰻魚族群量急劇下降，因此急切需要管理及保育。本研究藉由估計成長參數、死亡率以及成熟參數來探討南台灣高屏溪下游鰻魚族群之族群動態，且利用單位加入生產量及加入親魚量模式估計過漁的風險，進而評估當地鰻魚資源的永續利用。並將估計參數時所產生的誤差，利用蒙地卡羅法納入兩模式中考量。經過已知年齡之養殖鰻，以及野生鰻的耳石邊緣成長率的驗證，確認年輪形成之年週期性，顯示可以利用耳石來估計當地鰻魚的年齡及逆算年齡形成時的體長。經由資訊理論的判定，范氏成長方程式(von Bertalanffy growth model)為最符合推套用逆算體長之成長方程式。當利用標誌放流法估計死亡率時，發現死亡率估值會受到標誌鰻的來源(野生或養殖)或是標示方式(微晶片或剪鰭)所影響。當用銀鰻來代表鰻魚之成熟並估計族群的成熟曲線時，發現成熟曲線有顯著的雌雄差異，顯示了鰻魚在銀化上之兩性差異。
雌雄成長性過漁的風險相對為小，其風險在1 到40 % 左右。然而加入性過漁的風險相對較高，在24 到98 %之間。漁獲死亡率降低時，成長性及加入性過漁的風險也隨之降低。當漁業受到最小捕獲體長的管制時，最小捕獲體長越大，成長性過漁之風險明顯地減少，然而加入性過漁的風險只有些許的降低。當漁業受到最大捕獲體長的管制時，將最大捕獲體長向下調整時越小，成長性過漁的風險只有些許的降低，但加入性過漁的風險有顯著的降低，顯示限制最大捕獲體長可以有效地保護產卵親魚量。在現今的捕撈水準下，發生成長性過漁的風險相對較低，但加入性過漁的風險卻相當有可能，甚至可能已經發生。為了永續利用鰻魚資源及提供足夠的產卵親魚量，本研究建議將現有之漁獲死亡率下降40%，或是執行不小於500公厘之最小捕獲體長及不大於850公厘的最大捕獲體長管制。

關鍵字

日本鰻 ； 生命參數估計 ； 單位生產量模式 ； 成長性及加入性過漁

並列摘要

Japanese eel (Anguilla japonica) is a highly-priced commercial fish in Asia. Due to heavy exploitation, the Japanese eel population declined drastically and thus conservation and management of the eel population are urgently needed. In this study the population dynamics of the eel population in the lower reaches of Kao-Ping River in the southern Taiwan were examined by estimating its growth, mortality rate and maturation parameters. The sustainable use of the eel population was evaluated by assessing the risks of growth and recruitment overfishing using yield per recruit (YPR) and spawner per recruit (SPR) models. Uncertainties in parameter estimation were incorporated into the models by Monte Carlo simulation.
In order to obtain accurate age estimates, otolith annuli were validated by known-age cultured eels and otolith marginal increment ratio of the wild eels. Then the back-calculated lengths-at-age from otolith were used to estimate the growth parameters in von Bertalanffy growth model, which best fitted the lengths-at-age data according to information theory. Mortality rates estimated from mark-recapture data were found different between eel origins and marks. The maturation curves, described by the silvering of the eels, were found to be different between females and males, indicating a sexual dimorphism in the silvering of the eels.
Analysis of YPR model indicated that the risks of growth overfishing (GOF), defined as probabilities that current fishing level were larger than Fmax at which the YPR was at its maximum, ranged 1 to 5 % for both sexes. A more conservative risks of GOF, defined as the probabilities that current fishing mortality exceed F0.1 at which the increase in YPR was 10 % of that when the eels were not exploited (F = 0), were from 30 to 40 %. Two risks of recruitment overfishing (ROF), defined as the probabilities that the SPR under current fishing mortality was less than 40 and 50 % of that when F = 0, were relatively higher, 23.9 to 84.8 % and 67.0 to 97.6 %. When the minimum legal sizes increased, the risks of GOF decreased considerably but the decreases in risk of ROF were less apparent. When the maximum legal sizes decreased, the risks of GOF decreased a bit but the risks ROF were effectively reduced due to better protection of larger spawners. The risks of GOF for the eel fisheries in the study area were low to considerable, while the risks of ROF were substantially higher. To sustain the eel resources, especially for supplying sufficient amount of glass eels for eel culture, control of fishing mortality rate, and exploitation rate, e.g. a 40 % reduction, and the enforcement of minimum legal sizes of not smaller than 500 mm or a maximum legal sizes of not larger than 850 mm were recommended for the eel fisheries in the lower reaches of Kao-Ping River.

並列關鍵字

Japanese eel ； Estimation of vital parameters ； YPR and SPR models ； Growth and recruitment overfishing ； Sustainable use

參考文獻

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