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CURRENT STATUS AND MONITORING OF LAKE STURGEON (ACIPENSER FULVESCRENS) IN THE ST. CROIX RIVER

CURRENT STATUS AND MONITORING OF LAKE STURGEON (ACIPENSER FULVESCRENS) IN THE ST. CROIX RIVER

G. Nathaniel Painovich, Minnesota Department of Natural Resources
Rod Ramsell, Minnesota Department of Natural Resources
John Frank, Minnesota Department of Natural Resources
Larry Damman, Wisconsin Department of Natural Resources

The Lake Sturgeon (Acipenser fulvescens Rafinesque, 1817) continues to persist in the Upper Mississippi River watershed despite having to endure changes in habitat and the effects of commercial exploitation over time. One of the major tributaries in this watershed is the relatively infertile St. Croix River that originates in Douglas County, Wisconsin and meanders 164 miles SSW to its confluence with the Mississippi River. Historically, the St. Croix River supported a thriving lake sturgeon population, but over-harvest and environmental impacts have led to a decline in their overall abundance. Currently, little is known about the status of lake sturgeon in the St Croix River. Growing interest in this species as a sport fish has caused some concern from the public and government agencies as to whether present populations in the St. Croix River are stable enough to support targeted angling pressure. The primary objective of this project is to assess the long-term status and relative health of the lake sturgeon population in the St. Croix River.

The St. Croix River is divided into two sections (Upper and Lower) by a hydroelectric dam located in St. Croix Falls, Wisconsin. The height and design of this dam establishes an impassible barrier to the upstream migration of lake sturgeon, however, it would be possible for fish to emigrate downstream. The Upper St. Croix is entirely riverine in nature and averages less than 200 yards in width. A closed season was implemented on this portion of the river in 1993 to protect lake sturgeon from over-harvest. The Minnesota Department of Natural Resources (MDNR) and the Wisconsin Department of Natural Resources (WDNR) have been working together to assess the population and develop a long-term strategy for managing lake sturgeon in the Upper St. Croix River. The WDNR has drafted the Upper St. Croix River Basin Lake Sturgeon Plan, which outlines specific management objectives.

The upstream half of the Lower St. Croix is similar to the Upper section, but the lower half, called Lake St. Croix, averages nearly a half-mile wide and is an open system to the Mississippi River. There is a short open season for lake sturgeon angling on the Lower St. Croix from September 1 to October 15 each year. One fish over 50.0 inches may be harvested each year by anglers purchasing and possessing a harvest tag in advance. Currently, the Lower St Croix is primarily being sampled by MDNR in an attempt to build on information gathered by WDNR in 1986-87.

This project began in 2003 with efforts centering on capturing and tagging individually numbered fish and releasing them back into the river system. Ongoing sampling efforts monitor for recaptures of previously marked fish in order to generate an estimate of the current abundance of lake sturgeon in the population. Collected data on all fish allows us to assess the dynamics of the population for all sizes of individuals. Some of the parameters reviewed to date include length-frequencies, growth, age composition, length-weight regression, condition, and catch-per-effort. To date, over 600 individual lake sturgeon have been captured and tagged on the St. Croix River during this study. Methods, data, and initial population estimates will be presented and compared for both the Upper and Lower sections of the river.