|Latitudinal variation in the recruitment dynamics of small pelagic fishes in the western North Pacific|
Watanabe, Y. (2007). Latitudinal variation in the recruitment dynamics of small pelagic fishes in the western North Pacific, in: Yamashita, Y. et al. (Ed.) Proceedings of the Sixth International Symposium on Flatfish Ecology, Part II, held at Maizuru, Kyoto, Japan from 20-25 October 2005. Journal of Sea Research, 58(1): pp. 46-58
In: Yamashita, Y.; Nash, R.D.M.; van der Veer, H.W. (Ed.) (2007). Proceedings of the Sixth International Symposium on Flatfish Ecology, Part II, held at Maizuru, Kyoto, Japan from 20-25 October 2005. Journal of Sea Research, 58(1). Elsevier: Amsterdam. 1-112 pp., more
In: Journal of Sea Research. Elsevier/Netherlands Institute for Sea Research: Amsterdam; Den Burg. ISSN 1385-1101, more
Latitudinal variations; Pelagic environment; Population dynamics; Recruitment; Marine
The subarctic Oyashio Current flows south-westward and the subtropical Kuroshio Current flows north-eastward in the western North Pacific, converging in the waters off northern Japan to form the Kuroshio-Oyashio transition region. Some small pelagic fishes inhabit the subarctic or subtropical waters, and others seasonally migrate north and south across the major ocean fronts. Environmental conditions in the subarctic and transition waters are variable, whereas in the subtropical Kuroshio waters conditions are relatively stable. Latitudinally different environmental conditions may affect vital parameters and recruitment variability of small pelagic fishes inhabiting the various waters. Pacific saury Cololabis saira migrate seasonally from the Kuroshio to Oyashio waters and spawn in the transition waters in autumn and spring and in the Kuroshio waters in winter. During 1990-1999, the coefficients of variation (CVs) of daily growth rates (G) and instantaneous mortality coefficients (M) were large for larvae and juveniles spawned in the northern transition waters, but relatively small for those from the southern Kuroshio waters. The Pacific stock of chub mackerel Scomber japonicus spawns in the Kuroshio waters in spring and early summer and migrates to the subarctic Oyashio waters in summer for feeding, whereas the Tsushima Warm Current stock spawns in the East China Sea in spring and fish remain in the subtropical warm waters throughout their lifetime. The Pacific stock had CVs > 100% for the fish aged 0-5 during 1970-2002. In contrast, the Tsushima Warm Current stock had CVs of 34-40% during 1973-2002. Pacific herring Clupea pallasii, which inhabits subarctic waters, had CVs of 118-178% for the fish aged 3-8 y during 1910-1954. Japanese sardine Sardinops melanostictus, which spawn in the subtropical Kuroshio waters and migrate to the subarctic Oyashio waters in summer for feeding, had CVs > 120% for the fish aged 0-4 during 1976-2003. Contrasting with these subarctic Oyashio associated species, subtropical round herring Etrumeus teres had a CV of 26% over the total catch during 1976-2003. For these small pelagic fishes, latitudinal variation in early life parameters and recruitment was evident at the levels of cohorts (C. saira), stocks (S. japonicus), and species (Clupeidae). Large variations were observed in the subarctic Oyashio and the Oyashio-affected transition waters, whereas relatively stable results were recorded for the subtropical Kuroshio and its branch, the Tsushima Warm Current. Because the cohorts of Pacific saury and stocks of chub mackerel are not genetically distinct, it is likely that the large variability in the northern waters was environmentally induced in these species. The differences in CVs among clupeids are probably the result of differences in specific reproductive strategies and the environmental characteristics of the waters inhabited by the different species.