サケ・マスの放流効果に関する研究-1-回帰率導出のための数理モデルとその応用〔英文〕

概要

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It is important to estimate the true rate of return when we judge the effect of release. As a first step of the estimation, in this paper, we proposed a mathematical model by which we would like to clarify the variation mechanism of the rate of return. We showed that the rate of return r(t, y) could be written in the following formula under the assumption that it would be determined by the natural mortality coefficient M, the fishing mortality coefficient at the offshore fisheries F(t) in year t and the rate of maturity m(y) of age y: r(t, 3)=m(3)exp [-(2+(3/4))M-(1/4)F(t)], r(t, 4)=(1-m(3))m(4)exp [-(3/4)M-(1/4)F(t-1)-(1/4)F(t)], r(t, 5)=(1-m(3))(1-m(4))m(5)exp [-(4+(3/4))M-(1/4)F(t-2)-(1/4)F(t-1)-(1/4)F(t)]. Using this model it is possible to judge the effectiveness of offshore fisheries, We showed an example of a method of judgement. If F(t) is constant in the above formula r (t, y) is independent of t, so it is possible to estimate that values using the data of the released number and of the returned number by the least square method. As a result we obtained the estimated values values using the data of all Iwate prefecture; r(3)=0.00107, r(4)=0.00380 and r(5)=0.000549.
日本水産學會の論文