Hatching Control of Black-tailed Gulls for the Conservation of Japanese Red Pine Forest in Matsushima Bay, Miyagi Prefecture

27 Mar Hatching Control of Black-tailed Gulls for the Conservation of Japanese Red Pine Forest in Matsushima Bay, Miyagi Prefecture

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Abstract

日本三景松島の一部の島々でウミネコの繁殖にともなうアカマツ林の枯死が認められている．アカマツ林の保全対策を策定するため，松島の磯崎漁港内のウミネコ繁殖地において卵の油漬け（オイリング）による孵化抑制試験を行い，土壌へ供給される無機態窒素量の減少効果を検証した．ウミネコの孵化抑制試験区と対照区ではウミネコの営巣密度や産卵数など営巣状況に差はなかった．孵化率は孵化抑制試験区で0％，対照区で38～44％であった．オイリングによってウミネコの孵化をほぼ完全に抑制できることが明らかになった．しかしながら，試験区と対照区間で土壌の窒素含量に有意差が認められなかった．孵化率が低かったことが雛の成長による土壌への窒素供給量の低下につながり，有意差がでなかったものと解釈した

English Abstract

Japanese Red Pine Pinus densiflora forests are declining on several islands in Matsushima Bay, northeastern Japan where Black-tailed Gulls Larus crassirostris breed. Recently, the gull population has increased. In order to conserve the forests, gull eggs were immersed in cooking oil (Oiling) to prevent them from hatching, and the effect on the inorganic soil nitrogen content of the Isozaki fishery port site in Matsushima Bay was evaluated. There were no significant differences in the density of nests, number of eggs, number of nests without eggs, and percentages of nests without eggs between oiling and control sites. No eggs hatched at the oiling site, whereas 38–45% hatched at the control site. Hatching of Black-tailed Gull eggs was completely prevented by oiling. Nevertheless, inorganic nitrogen content in surface soils did not differ between two sites. Low percentages of hatching at the control site would result in a reduced nitrogen supply to the soil.