Drones, dry ice may help prevent damage caused by great cormorants(カワウ対策にドローン一役 高所の巣にドライアイス)

 
A group of great cormorants rests in the tree on the shore of Lake Inawashiro.Photos courtesy of the Fukushima prefecture government.(ドローンで空撮した猪苗代湖岸のカワウ。木の上に集団で巣を作り生息している=4月24日撮影(県提供))

 The Fukushima prefectural government is conducting a demonstration project using drones to control the reproduction of great cormorants. Great cormorants are colonial nesting birds that are prone to eating large amounts of freshwater fish, causing as much as 200 yen-300 million yen in damage to marine resources a year. Found all over Japan, the species' population has increased in recent years and damage to trees caused by their dung has also been a problem. As a result, urgent countermeasures are needed.
 In the project, dry ice is being dropped via drones into the birds' nests because they have a habit of nesting in high places. Doing so will cool their eggs and keep them from hatching. The prefectural government will verify the effects over several years and aims to make the results available throughout the prefecture.

 県は本年度、小型無人機ドローンを使い、川魚を食べるカワウの繁殖抑制に向けた実証事業に取り組んでいる。カワウによる漁業被害は深刻で、県内の被害額は年間約2億~3億円に上るなど対策が急務となっている。カワウは木の上など高所に営巣する習性があるため、ドローンでドライアイスを運んで巣に落とし、卵の温度を下げて孵化を抑える。県は数年かけて個体数抑制の効果を検証し、県内全域への普及を目指す。

 The project started in April on the shores of Lake Inawashiro, where groups of great cormorants build their nests. A private firm responsible for countermeasures to damage caused by animals was commissioned to conduct a monthly survey of the cormorants through the use of drones. About 5 million yen for related expenses has been included in the initial budget for this fiscal year.
 So far, dozens of birds have been observed in five conducted surveys. After the great cormorants finish laying eggs in March next year, dry ice will be dropped into their nests to observe the effects on hatching.

 実証事業は、カワウが集団で巣を作っている猪苗代湖岸で4月に開始。獣害対策を担う民間業者に委託して月1回、ドローンでカワウの様子を調べており、これまでに5回の空撮で数十羽の生息を確認した。カワウが産卵を終えた来年3月にドライアイスを落とし、孵化の状況を調べる。

 Removing the birds with guns is difficult because of the safety risk it poses for residents if nests are found in places such as riverside urban areas or on lakeshores facing major roads. Expectations are for the demonstration project are high, because it can be carried out in residential areas.
 According to the prefectural government, there was a precedent in Yamanashi Prefecture where dry ice was used to tackle the issue. When dry ice was manually placed into a nest located in a shrub, a fixed effect of hatching suppression was observed. However, dealing with nests in high places where people were unable to reach, remained unsolved.
 "Through the use of drones, we can efficiently place dry ice in high places," an official at the Nature Conservation Division of the prefectural government said. "We hope to have a method established through this project to reduce [the amount of] damage."

 市街地や幹線道路に面した川辺、湖岸に巣がある場合、住民の安全性から猟銃での駆除が難しいため、人の生活圏で行える対策としての期待も高い。本年度当初予算に関連経費約500万円を盛り込んだ。
 県によると、ドライアイスを使ったカワウ対策は山梨県で先行例がある。低木の巣に人の手でドライアイスを入れたところ、孵化の抑制に一定の効果がみられたが、手の届かない高所での作業に課題を残したという。県は「ドローンを使うことで効率的にドライアイスを投入できる。実証事業で手法を確立させ、被害減少につなげたい」(自然保護課)としている。

 According to the prefectural government, 1,000 to 1,500 great cormorants are believed to live in the prefecture. Numbers of freshwater fish such as sweetfish, Japanese dace and carp, which have been bred and released by fisheries cooperatives in various parts of the prefecture, have severely dropped. The annual damage of more than 200 million yen exceeds that of agricultural products caused by animals such as bears and wild boars, which accounts for around 150 million yen annually.

( Translated by The Japan News )

 県によると、県内には1000~1500羽のカワウが生息しているとみられ、各地の漁協が繁殖、放流したアユやウグイ、コイなどの淡水魚を中心に被害が拡大。年間2億円を超える被害額は、クマやイノシシなどの有害鳥獣による農産物の被害額(例年1億5000万円前後)を上回っている。

 【 2020年8月11日付・福島民友新聞掲載 】