抄録
北海道東部の知床半島を流れる小河川のオショロコマの食性と,市販のストマックポンプによる胃内容物中の被食生物の採集効率を調べた。胃内容被食生物中で優占した生物は,2004年5月と10月にはハエ目幼虫,6月にはヨコエビ亜目,7,8月にはトビケラ目幼虫,9月はサケ科の魚卵であった。ストマックポンプによる胃内容被食生物の採集効率は,7月の湿重量を除いて,調査期間を通じて65%以上を示し,個体数組成は回収物と胃内容物で差がなかった。ただし,被食生物として大型のトビケラ目とサケ科魚卵が優占した7,8,9月に採集効率は低下し,尾叉長と採集効率,胃充満度と採集効率の間に負の相関が認められた。よって,オショロコマなどの河川性サケ科魚類の食性調査にストマックポンプは有効であるが,大型の個体や携巣付きのトビケラ目幼虫やサケ科魚卵などの大型の生物を偏食している個体に対しては若干の補正が必要と思われた。これらの詳細な補正条件を明らかにすることは今後の課題として残された。
Feeding habits and removal efficiency of prey in stomach content (RE) of fluvial Dolly Varden of a standard length larger than 10cm were investigated by a stomach pump in a stream located in Shiretoko Peninsula. Dominance taxa in the stomach contents were chironomid larva in May and October, Gammarids in June, caddis larva (Goera spp.) in July and August, and salmonid eggs in September, 2004. RE by the pump showed over 65% during the study period. There were no significant differences in the prey-type compositions between samples by stomach pump and by operation. Sometimes, when the fish fed entirely on larger preys like cased caddis or salmonid eggs, RE of the pump was low. There were negative correlations between standard length or stomach fullness index and RE. Therefore, the stomach pump seemed to be effective for the feeding investigation of streamdwelling salmonid fishes without killing. However, when the fish fed entirely on large preys and the fish was lager than 15cm (standard length), the modification for the estimation of RE is required. It is a future tasks to clarify various conditions for this modification.
