Estimation of abundance and catchability by DeLury's method of longheaded eagle ray Aetobatus flagellum (Bloch and Schneider) in Nakatsu of Suo-Nada, Seto Inland Sea, Japan
2010
Fukuda, Y., Oita-ken. Agriculture, Forestry and Fisheries Research Center, Bungotakada (Japan). Fisheries Research Inst. | Zenitani, H.
Abundance (Nsub(0)) and catchability coefficient (q) of longheaded eagle ray Aetobatus flagellum (Bloch and Schneider), which is an important predator on bivalves in Nakatsu of Suo-Nada, the Seto Inland Sea, was estimated by three kinds of DeLury's method (normal approximation model of conditional binomial distribution model, normal approximation model with dispersion parameter, and generalized model using Taylor's power law). In both 2007 and 2008, the time series of catch per unit effort had two peaks, and the ratio of females increased around the second peak. In both 2007 and 2008, we estimated Nsub(0) and q for the two periods, in the first period (males predominantly invade) and the second period (females predominantly invade). The optimal method selected by the Akaike information criterion was the generalized model using Taylor's power law. In the first period and second period, Nsub(0) was 8,338 and 5,616 individuals in 2007, and 2,585 and 7,901 individuals in 2008, respectively, and q was 0.0133 and 0.0169/day/boat in 2007, and 0.0163 and 0.0055/day/boat in 2008, respectively. Our analysis demonstrates that intensive capture of longheaded eagle ray can reduce the ray's consumption of bivalves by 31 to 58%.
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