On a Catch-Forecasting Model for the Pink Salmon Oncorhynchus gorbuscha in the Maritime Province of Siberia

Abstract

The aim of this paper is to elucidate the fluctuation mechanism in the catch of pink salmon Oncorhynchus gorbuscha harvested in the Maritime Province of Siberia. We used catch data on pink salmon born in odd-and even-numbered years. Monthly indices of the Arctic Oscillation and the Pacific Decadal Oscillation were used as the environmental factors. We assumed that the catch in year t, C t , and that in year t + 2, C t+2 , could be used to represent the spawning stock biomass and recruitment, respectively, and C t+2 /C t could then be used to represent the recruitment per spawning stock biomass. Under these assumptions, we adopted the equation C t+2 /C t = g (environmental factors) as the model that forecasted the trajectories of the catch. The results were as follows: 1) the trajectories of the catches of pink salmon born in oddand even-numbered years can be well reproduced by the model mentioned above. No density-dependent effect was detected in the relationship between C t+2 and C t , which corresponds to the stock-recruitment relationship (SRR), for catches in both odd-and even-numbered years. The relationship between C t+2 and C t for odd-numbered years showed a clockwise loop; however, that for even-numbered years showed an anticlockwise loop. It is believed that this difference occurs in response to the negative relationship between the catches born in odd-and even-numbered years. Pink salmon is one of the typical fish species to which a density-dependent SRR can be applied; however, this study indicates that the assumption of a density-dependent SRR is not valid.

Clockwise Loops and Anticlockwise Loops Observed in a Stock-Recruitment Relationship

“…In the case of the Seto Island Sea stock of Japanese Spanish mackerel, the first seven lines appear to show clockwise loops (See Figure 4(d)). Hasegawa et al [24] noted the possibility that even when the age at maturity is low, the SRR could show anticlockwise loops when strong species interactions can be assumed to exist. Further, the direction of the loops would be strongly influenced by the cycle of en-…”