On the Spatial Distribution of Salmon by Means of the Analysis From the Catch of Fish Per Unit Net

Abstract

Salmon in the North Pacific Ocean are widely distributed and migrate from the open sea to the coast in a broad area. When they have been captured by the drift gill-net, it has been bserved that they are gathered densely here and there in the net. But, the characteristics of their spatial distribution have not been clarified yet in this area. Judging from these phenomena, it is considered that salmon must have the gathering instict and make social grouping in these areas. The authors applied the method in which the number of captured fish for the net was taken as the stochastic process for analysis of these phenomena and tried to clarify the spatial distribution of the salmon in the above mentioned area. The number of fish include the four species; that is, pink, chum, red and silver salmon. Put the captured number of fish in the net as variables X(i) against numerical order of the net T, these variables fluctuate for their mean value as an irregular phenomenon. The auto-correlation coefficients and power spectra for the variables are calculated with regard to the fluctuations in the stochastic process. According to these calculations, it was deduced that the existences of remarkable power in the spectra would mean the grouping of the salmon. Using the data of 1960 and 1963 from the Okhotsk Sea, 1961 and 1963 from the Pacific Ocean, the calculations were performed by the equations (1), (2), (3) and (4). According to the results of these calculations, the various periodic components in the power spectra indicate the characteristics spatial distribution of the school.

A collective navigation hypothesis for homeward migration in anadromous salmonids

“…We note that Mishima et al (1965) documented evidence of salmon grouping at sea based on catches in gillnets. Using acoustic surveys, Nero and Huster (1996) found many small schools (2 4 individuals) of salmon (species unknown) spaced uniformly at small scales (2 200 m) and aggre gated at larger scales (400 2000 m).…”