Spatial and temporal migration modeling for stock of Pacific saury Cololabis saira (Brevoort), incorporating effect of sea surface temperature

Abstract

A model is proposed that expresses the spatial and temporal migration pattern for stock of Pacific saury Cololabis saira (Brevoort), in order to investigate the effect of sea surface temperature (SST) on migration rates. Two factors are considered: (i) Saury emigrate to waters of an optimal SST zone; and (ii) saury immigrate from water zone that is extremely cold for saury. Parameters of migration and initial levels of stock are estimated with a maximum likelihood method based on catch per unit effort (CPUE) data for 1995-2001. The best model was selected using Akaike's information criteria. The results suggested that the emigration rate to southern adjacent regions is dependent on the coverage proportion of their waters under some threshold temperatures; 20 ° C to Doutou and Sanriku, 23 ° C to Joban and Izu.

Comparisons of monthly and geographical variations in abundance and size composition of Pacific saury between the high-seas and coastal fishing grounds in the northwestern Pacific

“…Environmental changes, such as variations in temperature, salinity, wind field, and currents, can affect both the productivity and the distribution of fish stocks [39,40]. Temperatures associated with oceanographic conditions have been found to be strongly linked to the migration route, distribution, and abundances of Pacific saury fishing stocks in the NWP, which results in annual variations in saury abundances and beginning times of the fishing season [3,7,28,30,32,41]. In our study, the monthly distribution pattern (Fig.…”

“…6). The SSTs below 10°C and above 20°C were the threshold temperatures of the extremely cold and warm SST waters, which correlate closely with the closure of the fishing season and a hard barrier blocking the southward migration of the saury, respectively [28]. Pacific saury prefer cold waters as migration routes, and the first and second Oyashio intrusions are important southerly migration routes for the species [30].…”

“…Pacific saury prefer cold waters as migration routes, and the first and second Oyashio intrusions are important southerly migration routes for the species [30]. The fishing grounds of Pacific saury are formed in the Oyashio water, along the oceanic front between the Oyashio cold waters and warm waters originating from the Kuroshio [28,30]. In contrast, most SWTs [15°C in the fishing grounds were an indicator of low stock abundances for the Pacific saury [32].…”

“…The sea surface temperature (SST) in the Kuroshio region in winter and in the Kuroshio-Oyashio Transition Zone and Oyashio region has been found to affect abundances of the large-sized (winter-cohort) and medium-sized (springcohort) groups of Pacific saury, respectively [3]. Recently, a modeling of the spatial and temporal migration of the Pacific saury stock in the NWP was proposed to incorporate the effect of the SST [28]. However, the high-seas data were sparse in the northern region, located east and north of 149°E and 40°N, respectively, and had to be assumed in the modeling process.…”

“…Yamamura [19] suggested that, under this landing limitation, fishermen would discard the small-sized saury that had been found in the stomachs of demersal fishes to maximize their profits. Fish sorting machines began to be used by fishermen on boats to selectively land members of the larger-sized class of Pacific saury with a higher price starting in the mid-1990s [27,28], making the issue of discarding worse [6]. In consequence, there was a series of price collapses caused by the excessive supply of large-sized fish in the 2000s, and the fishermen decided to remove the sorting machines from their vessels in 2006 [6].…”