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Relationship between spawning behavior of spear squids (Loligo bleekeri) and structures of the port

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  • In early spring, spear squids (Loligo bleekeri) lay their egg capsules on top of hollows in reefs and cavities in structures of Hokkaido ports on the Sea of Japan. Therefore, the role of port structures is important for propagation of spear squid. Research on the spawning conditions of spear squids around reefs and structures was conducted on the Sea of Japan coast of Hokkaido in 1995. Width, height and depth of hollows or cavities for applied the spawning ground were decided based on that research data. Then, the new 3 types of concrete blocks designed as a spawning ground were developed; these were placed on breakwaters. The research was conducted the spawning properties, survival rate of eggs, and physical environment on new type concrete block under wave-dissipating blocks from 1995 to 2000, and this research date was compared with other spawning grounds. The survival rate of eggs was 83.4% on the new type concrete block after 3 months, but it was 20.5% on other spawning grounds. Since spawning grounds on reefs are not deep enough in many cases, the maximum intensity of illumination was 10,000 lux. In highly illuminated spawning grounds, diatoms adhere to the surface of egg capsules and the survival rate was decreased. And, in spawning grounds with little current, silt adheres to the surface of egg capsules and also decreased the survival rate. As a result, it would be possible to create good environment for spawning grounds using artificial structures such as a breakwater.
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  • Kitahara, Shigeshi, Sadayuki Oka, Akihiro Honma, Kenji Yano, Hideto Narumi, Kiyoto Koganezaki. 2004. Relationship between spawning behavior of spear squids (Loligo bleekeri) and structures of the port. Peer Review: No. In: Proceedings of the Twelfth Biennial Conference of the International Institute of Fisheries Economics & Trade, July 20-30, 2004, Tokyo, Japan: What are Responsible Fisheries? Compiled by Ann L. Shriver. International Institute of Fisheries Economics & Trade, Corvallis, Oregon, USA, 2004. CD ROM. ISBN 0-9763432-0-7
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