1. Marine Laboratory, PO Box 101, Victoria Road, Aberdeen AB11 9DB, Scotland, UK,
2. National Research Institute of Fisheries Science, 2‐12‐4, Fukuura, Kanazawa‐ku, Yokohama 236, Japan,
3. Ocean Research Institute, University of Tokyo, 1‐15‐1 Minamidai, Nakano‐ku, Tokyo 164, Japan,
4. Nansei National Fisheries Research Institute, 6‐1‐21, Sanbashi‐dori, Kochi 780, Japan