Status and management of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) in the upper St. Croix River and Namekagon River, Wisconsin, USA

摘要

The upper St. Croix River and Namekagon River have been managed with a closed lake sturgeon (Acipenser fulvescens Rafinesque, 1817) fishing season since 1994. Lake Sturgeon abundance and distribution have not been assessed above the confluence of the two rivers since this regulation was established. We documented abundance, distribution and movement of the Lake Sturgeon in both rivers from their confluence upstream to the first dam on each river during 2008-2012. Captured with boat-mounted direct current electrofishing and by hook and line, 136 sturgeon ranging from 37cm to 140cm total length were tagged. Annual electrofishing catch was only 6% of the catch during the 1960s on a 32km reach of the Namekagon River. Size structure showed that recruitment was significantly higher during the 1960s in the Namekagon River. Lake Sturgeon movement between rivers was documented during both sampling periods with direct line movements of >80km. While still depressed, the A. fulvescens population below the first dam upstream from the confluence of the Namekagon River and the upper St. Croix River is naturally recruiting and appears to have the potential to restore itself with a closed fishing season.