Possibility of forecasting the abundance of the firefly squid Watasenia scintillans immigrating into Toyama bay, southern Japan sea [Japan]
1998
Nishida, H. (Japan Sea National Fisheries Research Inst., Niigata (Japan)) | Uchiyama, I. | Hirakawa, K.
Methods for elucidating the mechanism of interannual variability in the firefly squid (Watasenia scintillans) biomass were examined on the catch data (adult females only) obtained using set nets in Toyama Bay from 1982 to 1995, in relation to changes in both biotic and abiotic factors. It is indicated that the reproductive activity (mean egg abundance from March to May) of the squid in a certain year is not linked to the catch (from March to June) in the following year. Among several environmental factors, water temperature, phytoplankton (diatoms) density and possibly zooplankton biomass in spring (April or May) contribute to a significant increase n the squid catch (April) increasing from 1986 to 1990 (density-independent effect). However, such an effect has not always been recognized from 1991 to 1995 when the peaks and troughs of the squid catch were not synchronized with those of their mantle length in April, and the annual catches decreased gradually due mainly to density-dependent effects. On the other hand, in the light of top-down control, there are significant relationships between the catches of the squid and those of predators such as walleye pollack and mackerel during the period from 1982 to 1995. Results from multiple regression analysis suggest that water temperature (implying plankton biomass as an index of food availability), salinity and predation pressure are valid factors for forecasting the catch of this population immigrating into the bay from spring
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