自食性鱼类种群动态的分析模式

THE ANALYTIC MODEL OF POPULATION DYNAMICS FOR CANNIBAL FISHES

自食性鱼类是一些捕食同种幼鱼的鱼类,在补充时期自食性鱼类的幼鱼大量被同种鱼作为饵料而捕食。自食性鱼类一般在长到一定年龄(t_n龄)后才开始捕食自己同种幼鱼,所以这种鱼类在补充时期的自然死亡和本种群的t_n。龄以上鱼的数量有关。如果t_n龄以上鱼的残存量愈大,补充群体被捕食死亡部分就愈多。本文分:(Ⅰ)t_n=t′_ρ;(Ⅱ)t_n>t′_ρ;(Ⅲ)tn<t′_ρ三种情况,推导出单位补充量产量方程如(3)、(4)、(5)和(6)、(7)、(8)等式。 应用东海群带鱼各参数计算的结果,用自食性鱼类模式得出的最高产量出现在t′_ρ=1龄左右,而用Bevreton-Holt模式得出的最高产量出现在t′_ρ=3龄左右。显然自食性鱼类模式计算的结果比较符合现实情况。

Beverton-Holt Model is used in fish population dynamics. It is based on some assumptions, such as, fish population recruit into an exploitable phase when they reach a certain age, the recruitment of the year class spreads evenly over the year, the abundance of recruitment is constant regardless of the spawning amount, the natural mortality keeps constant, the growth pattern of each year class is same and the yield over the lifespan of a certain age class is equal to the total yields of each age class in one year. But these assumptions sometimes do not conform to some fish population and the result of Beverton-Holt Model may be inappropriate, for example the cannibal fishes prey on their own juveniles. So the natural mortality coefficient treated as a constant is not suitable. The cannibal fishes begin to prey on their own juveniles at the age t_n. During the time of recruit, their natural mortality is related to the abundance of the cannibal fishes over the age t_n. If the number of survivors over the t_n age is large, then the mortality of predators also becomes large correspondingly. Under the condition (Ⅰ) t_n=t′_p, (Ⅱ) t_n>t′_p, (Ⅲ) t_n<t′_p, the author has developed the equations for yield of each recruitment: as (3) (4) (5) and (6) (7) (8).Notation:Y——yield by weightC——yield by numberR——number of recruitst_λ——the end of life-spant′_p——age of recruitmentt_p——the average age at which they enter to fishing groundF——fishing mortality coefficientM——normal natural mortality coefficientW_t——weight of fish at t age(?)——average weight of juvenile fish during predationk——ratio of juvenile fish to feedstuffThe equation was examined for the hairtail fish population of Dong Hai. The result proved that the equation was closer to the actual situation than to the Beverton-Holt Model.