Case Study: A Simulation Model of the Spawning Stock Biomass of Pacific Bluefin Tuna and Evaluation of Fisheries Regulations

Abstract

This study proposes a simulation model that well reproduces the spawning stock biomass of Pacific bluefin tuna. Environmental factors were chosen to estimate the recruitment per spawning stock biomass, and a simulation model that well reproduced the spawning stock biomass was developed. Then, effects of various fisheries regulations were evaluated using the simulation study. The results were as follows: 1) arctic oscillations, Pacific decadal oscillations and the recruitment number of the Pacific stock of Japanese sardine were chosen as the environmental factors that determined the recruitment per spawning stock biomass; 2) spawning stock biomass could be well reproduced using a model that reproduced the recruitment per spawning stock biomass and the survival process of the population that included the effect of fishing; and 3) the effects of various fisheries regulation could be evaluated using the simulation model mentioned above. The effective regulation in the simulations conducted in this paper was a prohibition of fishing for 0-and 1-year-old fish in terms of recovering the spawning stock biomass. The reduction of fishing mortality coefficients for all age fish to 50% of actual values also showed a good performance. The recent reductions of the recruitment and spawning stock biomass were likely caused by heavy harvesting, especially of immature fish, since 2004.

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

“…The results coincided well with those for the Pacific stock of Japanese sardines [10] and Pacific bluefin tuna [12].…”

“…Recently, however, Sakuramoto proposed a new concept of the mechanism of the SRR which did not assume any density-dependent effect [8] [9] [10] [11] [12]. The purpose of the present study is to elucidate whether or not the density-dependent effect is essential to explain the population fluctuation of pink salmon and to propose a new model that can reproduce the population fluctuation of pink salmon.…”

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

“…In contrast, the results of this paper show that no relationship between recruitment and SSB could be easily detected for stocks which have a high age at maturity. For instance, the SSR of Pacific bluefin tuna showed no relationship between R and SSB, and the plots were widely scattered without any trend [12] [13]. The Beverton and Holt model or hockey stick model is usually applied as the SSR for Pacific bluefin tuna, and the management procedure has been widely discussed.…”

“…Recently, Sakuramoto proposed a new concept of SRR mechanisms [8]- [13] and showed the mechanisms that explained clockwise or anticlockwise loops emerged in the SRR, using a simulation study. That is, when recruitment, R, fluctuates cyclically in response to environmental factors, and the spawning stock biomass (SSB) also fluctuates cyclically with a time lag (mainly determined by age at maturity), the SRR shows a clockwise loop or an anticlockwise loop for each period of environmental change.…”

Correction of “A Recruitment Forecasting Model for the Pacific Stock of the Japanese Sardine (Sardinops melanostictus) That Does Not Assume Density-Dependent Effects”

“…The same correction was conducted for the paper on Pacific bluefin tuna that was analyzed by Sakuramoto [5] [6]. In the case of Pacific bluefin tuna, the effect of the error was more serious than in this case, because the error influenced the maturity rates for ages 3 and 4.…”