Sakutaro Yamada

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

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.

Age and growth of yellowstriped butterfish, Labracoglossa argentiventris, around Izu Oshima Island

Age and growth of the yellowstriped butterfish, Labracoglossa argentiventris, around Izu Oshima Island were studied using a total of 1450 fish. Age was determined by counting the edge of the opaque zones as a ring mark on sectioned sagittal otoliths. Formation of the first ring was observed during spring or summer, corresponding to 1.5 years after hatching. Thereafter, one ring was formed each year in the same season as the previous year. The growth of the butterfish was rapid until 2 years of age. The maximum likelihood method was applied to the age and length data for estimating parameters in von Bertalanffy, Gompertz, and Logistic growth models. The selected model, based on the Akaike Information Criterion, was the von Bertalanffy growth model, which indicated differential asymptotic length and variance by sex.

Estimation Problem on a Tagging Experiment Including Incomplete Reports.

The estimation of population size by a tagging experiment including incomplete reports of the number of recaptured tagged fishes is considered. It is assumed that the sample is classified into two classes. In class 1 the reporting rate of recaptured tagged fish is 1, and in class 2 the rate may be less than 1. In this case the Petersen estimator and the Chapman type estimator based on the observation in class 1 (CTE) have been proposed, although large sample in class 1 is not expected. In this paper, we examine the effects of the observation in class 2 as additional information for the estimation of population size. Some estimators which include the observations in both classes, such as the modified maximum likelihood estimator (MMLE), are evaluated in senses of the bias and the mean squared error. As a result, if the sample size in class 1 is small and true reporting rate is high, then the MMLE is preferable to the CTE. In the other case, however, the CTE is superior to the estimators based on the observations in both classes.