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Pengurasan Waduk Bantu Salmon & Kurangi Predator

Pengeringan atau pengurasan waduk dengan biaya murah pada waduk atau danau buatan (reservoir) di Oregon, Amerika Serikat (AS), membantu ikan salmon remaja (young salmon) migrasi ke hilir dan hilang secara bertahap dua spesies predatornya. Begitu hasil riset Christina Murphy, mahasiswi doktoral pada Oregon State University (OSU) sebagai ketua tim peneliti, Gregory Taylor dan Todd Pierce dari Korps Insinyur Angkatan Darat AS (U.S. Army Corps of Engineers) di Amerika Serikat. Proyek penelitian ini didanai oleh U.S. Army Corps of Engineers di Amerika Serikat (Oregon State University, 21/5/2019).

Pemindahan spesies dua predator, ikan kakap (largemouth bass) dan ikan air tawar keluarga mola-mola di Amerika Utara (crappie), dari Fall Creek Reservoir, sekitar 30 mil tenggara Eugene di kolam Willamette River (Amerika Serikat), dapat mempengaruhi tata kelola waduk-waduk yang telah dimasuki oleh spesies-spesies tertentu ikan predator—yang memangsa ikan lainnya (Science Daily, 21/5/2019).

“Even though the strategy appears extreme, it's both helping juvenile salmonids pass downstream and promoting a  native species-dominated reservoir. Bass and crappie, which are major predators in the reservoir, have been pushed out and into the Willamette. That can be worrying because filling the river with invasive, warm-waterfish seems like a bad idea, but these reservoirs are leaking warm-water fish all the time. The good news is that they were pushed downstream in the fall and winter, when the water is cold and the flow is faster, so they should be at a disadvantage in the Willamette River -- compared to when they leak out of the reservoir in the summer,” ungkap Christina Murphy (Oregon State University, 21/5/2019).

Selama beberapa tahun terakhir pada musim gugur, Korps Insinyur Angkatan Darat telah menguras Fall Creek Reservoir di Amerika Serikat, untuk membantu salmon chinook musim semi remaja bergerak keluar dari waduk dan migrasi ke hilirnya. Tim peneliti asal Oregon State University, US Forest Service Pacific Northwest Research Station dan Corps of Engineers menganalisis data penangkapan ikan tahun 2006-2017 --pengeringan atau pengurasan air tahunan dimulai pada paruhan periode ini -- untuk meneliti perubahan-perubahan waktu keluar danau itu dan perbandingan jumlah spesies ikan (Science Daily, 21/5/2019).

“We have also been sampling fish within the reservoir during the summer. In 2012, we could capture 10 bass an hour. This went down each year. By the summer of 2015 we only caught one during all of our sampling and in 2016, we didn't capture any. This change was reflected in the data from the trap downstream too. The decline occurred with crappie, but faster,” papar Christina Murphy (Oregon State University, 21/5/2019).

Tim peneliti itu menemukan bahwa pengurasan atau pengeringan waduk usia 50 tahun itu membawa hasil yang diinginkan yakni memberi jalan keluar ikan salmon chinook keluar dari waduk atau danau buatan itu dan pada saat bersamaan, jumlah ikan crappie dan kakap mulai berkurang hingga sama sekali tidak ada (Science Daily, 21/5/2019).

“This extreme draining management is only about a week in duration, but has implications for the whole ecosystem. It makes the reservoir begin to act as a natural river again affecting the entire fish community,” ungkap Ivan Arismendi, asisten profesor pada The Department of Fisheries and Wildlife pada College of Agricultural Sciences, Oregon State University (OSU), yang menjadi co-author studi ilmiah ini (Oregon State University, 21/5/2019).

“This type of research and monitoring before and after major changes in management of a reservoir is crucial for improving our ability to balance water availability while maintaining native species,” papar Sherri Johnson, ekolog peneliti pada The U.S. Forest Service Pacific Northwest Research Station (Oregon State University, 21/5/2019). Hasil riset itu dirilis oleh jurnal Ecohydrology, edisi Mei 2019 (Christina A. Murphy, Gregory Taylor, Todd Pierce, Ivan Arismendi, Sherri L. Johnson, “Short-term reservoir draining to streambed for juvenile salmon passage and non-native fish removal”, Ecohydrology, 2019).

Oleh: Servas Pandur