Use of Mobile Hydroacoustics to Manage Commercial Harvest of Cisco In the Minnesota Waters of Lake Superior

The historic cisco Coregonus artedi fishery in the Minnesota waters of Lake Superior remains the largest commercial fishery (kg harvested) in Minnesota.  The fishery yield was over 2.3 million kg annually from 1924 – 1941 and supported over 400 licensed operators.  Eventually, over-fishing resulted in a rapid decline in harvest.  Similar trends occurred in other Lake Superior jurisdictions and each of the other Great Lakes.  By the early 1970s, most Lake Superior fish management agencies had placed extreme harvest restrictions on cisco.  In Minnesota, a fishing closure during the spawning period was imposed, along with effort and gear restrictions.  In 1984, the first strong cisco year class in over 40 years was documented, which began the rehabilitation of cisco in Lake Superior.  By 2005, abundance was considered high in some areas of Lake Superior, and commercial harvest increased.  In 2003, mobile hydroacoustic surveys began in Minnesota that targeted pelagic prey fish.  Of specific interest was the biomass of large cisco (>250mm) in Minnesota waters.  Based on this information, Minnesota changed its cisco management in 2006 from an unlimited harvest fishery with a spawning period closure, to a year round fishery with an established annual total allowable catch (TAC).  Discussions with commercial fishers led to a consensus that the TAC would be set at 10% of the estimated biomass of cisco greater than 250mm based on the results from annual hydroacoustic surveys.  This presentation highlights the strategies used to establish the TAC, the annual hydroacoustic survey design, and the allocation of the TAC among commercial fishers.  The current management of the cisco fishery in the Minnesota waters of Lake Superior may have potential application to the rehabilitation of corregonid fisheries around the world.