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Overdispersion in the Estimation of Salmon Escapements by Mark–Recapture Surveys and Its Related Factors
Author(s) -
Miyakoshi Yasuyuki,
Kitada Shuichi
Publication year - 2016
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1080/00028487.2015.1121922
Subject(s) - overdispersion , oncorhynchus , statistics , mark and recapture , estimation , variance (accounting) , negative binomial distribution , maximum likelihood , biology , estimator , escapement , fishery , econometrics , mathematics , fish <actinopterygii> , demography , poisson distribution , population , economics , management , accounting , sociology
The Petersen method, a well‐known mark–recapture method, is frequently used in the estimation of escapement of Pacific salmon Oncorhynchus spp. Robust estimates and associated variances can be obtained when the underlying assumptions of this method are met. However, in field surveys, it is often difficult to meet these assumptions because wild animals are often not randomly distributed. When the sampling variance of the estimator exceeds its binomial variance (resulting in overdispersion), the Petersen model underestimates variance. We assessed the occurrence of overdispersion in the mark–recapture data collected to estimate the escapements of Masu Salmon Oncorhynchus masou in a river in northern Japan in 1998 and 1999. The dispersion parameters estimated from 2‐year data were 2.89 and 2.51 for males and 1.45 and 1.52 for females, indicating that overdispersion occurred in all cases. The magnitude of overdispersion for males exceeded that for females, probably related to differences in the postspawning behaviors of the sexes, as represented by the changes of the sex ratio of Masu Salmon recovered on the spawning grounds. In this paper, we propose a simple procedure to detect the occurrence of overdispersion in multiple‐recovery mark–recapture data. Received February 8, 2015; accepted November 3, 2015