著者

高島 義信 高田 壮則 工藤 敬太 松村 英樹 蓑輪 直幸

出版者

北海道東海大学

雑誌

北海道東海大学紀要. 理工学系 (ISSN:09162097)

巻号頁・発行日

vol.8, pp.51-60, 1996-03-21

---

The variation in the weight of individuals with same age and the age-specific maturation ratio of white-spotted charr Salvelinus leucomaenis are examined in Furuu River in Hokkaido. The variance in the age-specific weight is extremely high and the strong intraspecific competition is expected to occur in the population. The maturation ratio of females in the stream is zero at any age and that of males in the river ranges from about 21 % to 58 % depending on age. It is shown that (1) it is a rare event for females to mature in the river, (2) the proportion of maturing in the river is about 21 % in males with 2+ age and (3) there is a possibility that both males and females with 5+ age in the river migrate to the sea. (4) about 25 % of sea-run individuals are immature.

著者

谷野 賢二 鳴海 日出人 斎藤 二郎 本間 明宏 北原 繁志 黄金崎 清人

出版者

北海道東海大学

雑誌

北海道東海大学紀要. 理工学系 (ISSN:09162097)

巻号頁・発行日

vol.11, pp.35-47, 1999-03-25

---

In Hokkaido ports on the Sea of Japan and along the Tsugaru Straits, which are along the course of the spawning migration of spear squids, Loligo bleekkeri, their eggs were found on breakwaters and other port structures. Therefore, research has been conducted on the spawning properties of spear squids and survival rates of eggs on breakwaters, as well as on related physical environment properties. On breakwaters and other structures, spear squids lay their egg capsules in cracks in vertical concrete walls of breakwaters and quays, as well as in the cavities of wave-dissipating works and armor blocks. In deep cavities created by wave-dissipating works and armor blocks, more eggs were found on blocks which were deeper in the cavities than the second row from the end of the slope. Since spawning grounds on reefs are not deep enough in many cases, the irradiance may be high at some parts to which egg capsules adhere. In highly illuminated spawning grounds, diatoms adhere to the surface of egg capsules and the survival rate decreases. In the port with little current, silt adheres to the surface of egg capsules and also decreases the survival rate. The cavities of wave-dissipating blocks, on the other hand, are washed by swift waves and the irradiance is low. There are no substance adhered to the surface of egg capsules and the survival rate is high.