山陰地方における漕刺網漁業について-V

若狭湾における漕刺網のアカアマダイに対する漁獲率

抄録

To obtain the exploitation rate of branquillos of each size in the sweeping trammel net fishery, analyses were made with data on the ratio of catch to fished population size and the length composition of the commercial catch in Wakasa Bay from 1961 to 1970.
As the sweeping trammel net has mesh selectivity for branquillos, the exploitation rate f_i for length l_i was approximated by f₀S_i where f₀ is the rate for the peak of the selectivity curve and S_i the relative efficiency for l_i. Denoting the relative fish number of l_i in the commercial catch by n_i, a theoretical relation of catch C to population size P is presented by
C/P=f₀∑Wini/ ∑Wi(ni/si),
where W_i is the body weight at l_i.
The values of f₀ estimated by this expression showed apparently an exponential pattern in relation to fishing effort and gave the gear efficiency 6.2×10^-4 boat-day^-1, being in agree-ment with that obtained by the other method. Further, it was found that a yearly variation in availability affected the estimation of the rate to some degree.