シカ・イノシシなどによる獣害対策の3つの提言
全国的に獣害問題が深刻化し,農林業被害だけで年200億円を超え,毎年10億円以上の割合で増加し続けています。そのうち,シカとイノシシによる被害が50%以上を占めています。シカやイノシシとの衝突による交通事故も増える一方です。イノシシ,クマによる人身傷害事故も増えています。シカによる被害は特に深刻で,農林業だけでなく,全国各地で,植生破壊,野生動物種の減少絶滅,土砂流失崩壊など,自然生態系の被害が年々激しさを増しており,最近では被害の奥地化を進んでいます。しかし,いっこうにシカのコントロールは進まず,被害の沈静化はいささかも認められません。
地域社会では,住民の後継者不在のままの高齢化,国民の狩猟離れなどによる狩猟者の消滅が予測され(3年後の銃刀法の切り替え時に急減し,2020年までにほぼ消滅),シカ,イノシシの個体数調整は完全に行き詰まることは目に見えています。以後は,シカの野放図な食害により森林原野の荒廃は広域的に進み,土砂災害などの多発が予想されます。こうした状況を踏まえ,次の3つの緊急対策の同時実現を提案しています。
1 奥山:絶滅種オオカミの再導入
現在のシカ,イノシシなどの中大型哺乳類の増えすぎは,明治時代のオオカミの絶滅に第一の原因を求めることができます。それゆえに,絶滅種オオカミと同種です。絶滅種コウノトリやトキの再導入による復活となんら異なるものではありません。本州,四国,九州の場合,中国に生息するオオカミを,北海道には沿海州のオオカミを再導入することによって実現することができます。ちなみに,オオカミのシカやイノシシの生息密度調節効果,生態系の復元,低下した生物多様性の回復効果は,米国や欧州での研究で実証済みです。また,人に危害を及ぼす可能性はほとんどありません。これもヨーロッパの研究者グループの共同研究によって実証されています。奥山の自然地域(たとえば,南アルプスの高山帯や富士山麓の原生林地帯など)での侵入防止柵の建設は,技術的,財政的に難しいばかりでなく,その建設自体が自然破壊です。こうした地域は,オオカミを頂点とする食物連鎖による自然調節に任せるべきです。
2 里山・人里:ハンターの自治体雇用による常勤体制化
獣害激増の第2の原因は,明治以来約100年間,オオカミ絶滅による生態学的な穴を埋めてきたハンターが,今,急激に力を失い,オオカミの後を追うように絶滅の危機に直面していることです。ハンターの存続が必要です。従来の獣類のコントロールはレクリエーションハンターのボランティアに依存してきました。そうしたハンターに代わって,今後は,自治体が雇用する常勤ハンターが必要です。しかし,常勤ハンターの雇用には財政的な限界が予想されますので,耕作地,林業地,居住地域などいわゆる里山地帯が活動地域となります。奥山はオオカミ,里山・人里は常勤ハンターで有害獣のコントロール体制の実現を早急に進めるべきです。
3 シカ・イノシシに対する広域的侵入防止柵(壁)の建設
オオカミの復活と限られた人数の常勤ハンターだけでは,被害防除は完全ではありません。そこで,人里・里山を囲む広域的な半恒久的な有害獣侵入防止柵の建設が必要です。
Three proposals
Three proposals of the anti-beast harm measure for deer and wild boar
Animal environmental harm is a serious problem, causing just over 200 billion yen in agricultural and forestal damage to date. If current trends continue, expected damage could top more than 10 billion yen annually. Particularly, deer and wild boar account for over 50 percent of the damage. Also, traffic accidents involving deer and wild boar are on the rise. Injury to people by wildlife such as wild boars and bears are frequent results of these automobile accidents. Particularly alarming is the damage caused by deer, not only in terms of agriculture and forestry, but natural ecosystem damage is increasing annually in different parts of the country. This includes destruction of vegetation, destroyed sediment, and wildlife reduction or extinction. Recently, the damage has crossed into interior mountain areas. So far, local governments have yet to present a plan to control deer overpopulation. If careful control of the deer population doesn’t improve, the damage will continue.
In the local community, aging residents who actively engage in hunting will certainly substantially decrease by 2020 with few young residents continuing the hunting tradition. Deer and wild boar population control by hunting will certainly reach a standstill. Without population control, the voracious appetite of deer for planet life will be a prime factor in the destruction of forestland, shifting to a wide area that could lead to frequent sediment-related disasters. To prevent these future situations, we propose the following three emergency measures.
1.For deep mountain areas: Extinct species/wolf reintroduction
The primary reason why middle and large size mammals including deer and wild boar are overpopulated is due to the extinction of wolves during the Meiji era. The reintroduction of wolves into their once natural habitat is completely akin to the circumstances that brought about the reintroduction of storks and the Japanese crested ibis. In the case of the Japanese mainland,ShikokuIslandandKyushuIsland, reintroducing wolves from a habitat inChinawould be appropriate. For theHokkaidoregion, reintroducing wolves from the habitat of the Primorskij district,Russia, would be appropriate. The research of resurgent wolf populations in theUSandEuropehas proven effective in controlling deer and wild boar densities, in addition to ecosystem restoration, and increased biodiversity.
Furthermore, it should be added that there is very little chance for harmful interaction between wolf and the human population as proven by various research groups in European countries.
One common proposal for dealing with overpopulation has been the utilization of exclusive fences. In deep mountain areas, it is not only difficult to build exclusive fences, but also the construction of these barriers destroys the natural environment.
For these areas, the reintroduction of a wolf population would provide a natural method of population control via the food chain.
2.Full-time employment system of hunters by the local governments
The second cause of increased animal harm is the fact that hunters have been filling the predatory role of wolves within ecosystems for the last 100 years since the extinction of wolves in the Meiji era. Now, these hunters are fast becoming extinct as well. Hunter intervention is required. Originally, we have depended on recreation and volunteer hunters to control animal overpopulation. Instead of these types of hunters, local governments need to employee full-time hunters. However, there are financial limits to having full-time hunters. They should supervise only arable land, forestry areas and residential areas, such as human activity zones. The animal control system should be implemented as such: wolves in deep mountain areas; hunters in human populated areas.
3.The construction of a wide-area fence (wall) for deer and wild boars to prevent their intrusion.
Resurrection of the wolf population in combination with the limited number of full-time hunters an area can provide can hardly manage to prevent all damage by animal intrusion. Therefore, construction of fences our rounding large human populated areas that prevents intrusion of harmful animals is required.