Sources and Limitations Of Larval Walleye Production In a Heterogeneous Waterway In Northern Michigan

Walleye represent the focus of a shared harvest fishery in the interconnected system of Mullett, Burt, Pickerel and Crooked Lakes (Michigan’s Inland Waterway). However, a walleye population estimate in 2009 in Mullett Lake was 82% lower than an estimate conducted in 1998, which spurred interest in factors affecting overall walleye recruitment in this system. We conducted a survey of young-of-year walleye recruitment dynamics within the Inland Waterway and connecting rivers in the spring and summer of 2011-2012 in order to determine if low natural reproduction is contributing to the low walleye population.  We hypothesized that low recruitment is a likely consequence of low larval walleye production and inadequate food resources to support larval walleye in this system.  We sampled Ichthyoplankton and zooplankton concurrently in lake and river habitats to determine the spatial distribution and abundance of larval walleyes and their primary food source.  Initial results indicate that rivers adjacent to Burt Lake (Sturgeon River) and Mullett Lake (Black River) are the primary sources of walleye recruitment within the Inland Waterway system, both supporting peak larval densities of between 13 and 91 walleye/1000m3 in 2011-2012.  However, the abundance of large-bodied zooplankton (calanoid copepods, Daphnia) is much lower in Mullett Lake (2011: 0.17 org./L and 2012: 0.50 org./L) compared to Burt Lake (2011: 1.41 org./L and 2012: 2.0 org./L). These findings suggest that recruitment within Mullett Lake may be limited by the lack of suitable forage base for larval walleyes, which likely contributes to low production of walleye in this lake.