Estimation of the skipjack [Katsuwonus pelamis] migration pattern by a skipjack general migration model
1998
Ito, S. (Tohoku National Fisheries Research Inst., Shiogama, Miyagi (Japan)) | Ogura, M. | Tanabe, T. | Takeuchi, K. | Nonaka, M.
A skipjack general migration model (SGMM) is developed to estimate the migration pattern of young skipjack. SGMM includes two components. One is an ocean general circulation model (OGCM) and the other is a skipjack migration model. First, we integrated the OGCM to obtain steady temperature, salinity and velocity fields and applied these steady states to the ocean condition in the SGMM. In the SGMM, the migration of skipjack is denoted by the sum of the effects of the advection of currents and swimming activity of skipjack. The direction of swimming is assumed to be towards the lower temperature region and the magnitude is assumed to be in the scale of body length per unit second. The results of the SGMM indicate the existence of 1) a boundary which separates the movement of skipjack around 15degrees N, 2) the convergence of skipjack around 5 degrees N and 3) the intensive paths of migration at around 160 degrees E in the shallower depth and around the west boundary region in the deeper depth. These results are consistent with the distribution of adult skipjack confirming the usefulness of the SGMM. Additionally to this basic experiment, two types of parameter study have been carried out. In one experiment, the advection effect only is included. In the other experiment, the swimming activity effect only is included. Although the former could not reproduce the three characters of migration pattern, the latter one was able to effectively reproduce these characteristics. As the result, the swimming activity effect is important to determine the migration characteristics of skipjack. Then the swimming activity is dominated by the temperature fields in the SGMM, the result shows the effect of temperature is very important to the migration pattern
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