Parasites as biological tags of stocks of neon flying squid (Ommastrephes bartramii) in the North Pacific Ocean
Nagasawa, K.; Mori, J.; Okamura, H. (1998). Parasites as biological tags of stocks of neon flying squid (Ommastrephes bartramii) in the North Pacific Ocean, in: Okutani, T. Contributed papers to International Symposium on Large Pelagic Squids, July 18-19, 1996, for JAMARC's 25th anniversary of its foundation. pp. 49-64
In: Okutani, T. (1998). Contributed papers to International Symposium on Large Pelagic Squids, July 18-19, 1996, for JAMARC's 25th anniversary of its foundation. Japan Marine Fishery Resources Research Center: Tokyo. 269 pp., more
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| Authors | | Top |
- Nagasawa, K.
- Mori, J.
- Okamura, H.
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| Abstract |
The stock structure of neon flying squid (Ommastrephes bartramii) in the North Pacific Ocean was examined by using parasites as biological indicators. A total of 1,516 neon flying squid was collected over an extensive area (24°-47°N, 147°E-135°W) of the North Pacific Ocean from January to October during 1991-1995. These squid were examined for the occurrence of the following helminth parasites: ascarid third-stage larvae of Lappetascaris sp. Type A in the musculature of the mantle; tetraphyllidean metacestodes of Phyllohothrium sp. in the lumen of the caecum; and trypanohynch metacestodes of Tentacularia sp. on the inner surface of the mantle. The area of capsules formed by ascarid third-stage larvae of Lappetascaris sp. Type B on the stomach wall was also recorded as an indication of intensity of infection. As the North Pacific neon flying squid consists of two cohorts (i.e., winter-spring cohort and autumn cohort), levels of intensity of infection with each parasite in both cohorts were statistically compared between the western (west of 170°E), central (170°E-160°W), and eastern (east of 160°W) regions of the North Pacific Ocean (north of 35°N). Based on this analysis, the winter-spring cohort is separated into two stocks: the western North Pacific stock and the central-eastern North Pacific stock. The border of the distribution range of these stocks is 170°E. It is impossible to separate the latter stock into smaller regional groups, due to the small sample size trom the eastern region. The autumn cohort is divided into two stocks: the central North Pacific stock and the eastern North Pacific stock, which occur west and east of 160°W, respectively. |
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