Jared Myers   MSc Candidate Developing and testing models of cisco (Coregonus Artedi) population dynamics in Lake Superior: Implications for restoration in the lower Great Lakes

Some people think of the U.S. Midwest and label it as being flat and boring. I, however, hold the area, and particularly the Great Lakes region, in the highest esteem and proudly call it “home.” Growing up on Sandusky Bay on Lake Erie I realized I could never stray too far from the lakes. This led me to Northland College ( Go Jacks! ), which is situated at the base of Chequamegon Bay (Lake Superior) in Ashland , Wisconsin . Returning home during the summer of my sophomore year, I worked with the USGS Great Lakes Science Center 's (GLSC) Lake Erie Biological Station aboard the R/V Musky II . This opportunity led to further experience with the USGS-GLSC at their Lake Superior Biological Station (LSBS) where, working on the R/V Kiyi with Lake Superior as a backdrop, I realized I would be hard pressed to find a more rewarding job. I joined the “Jones” lab in the fall of 2005 after graduating from Northland in the spring of 2005.  I am working on a project that complements my research interests in the restoration and rehabilitation of indigenous fish communities throughout the Great Lakes Basin .

Historically, cisco (formerly known as lake herring) were found throughout the Great Lakes and played a key role in the food web by serving as a trophic conduit between zooplankton resources and native piscivores. At the turn of the 20 th century, cisco supported major commercial fisheries throughout the Great Lakes . However, most stocks were subsequently decimated. The four lower lakes ( Ontario , Erie , Huron, Michigan ) witnessed the systematic failure of cisco stocks first, followed by the collapse of Lake Superior stocks in the 1960s. Lake Superior stocks have rebounded to support commercial fisheries, yet this population still suffers from highly variable recruitment. Past reintroduction programs have focused exclusively on lean lake trout, yet interest in the reintroduction of native forage species in the lower Great Lakes is emerging amongst managers and the public alike. As a result, the LSBS has devoted a large portion of its future efforts to understanding the factors driving cisco recruitment and population dynamics.

It is generally believed that a native forage base, dominated by indigenous coregonids, would be desirable in each of the Great Lakes . Because cisco are not subject to large-scale die-offs, as occur with alewife populations, cisco will help stabilize prey fish abundances in the lower lakes. Cisco may also facilitate the restoration of native piscivores by reducing the occurrence of Early Mortality Syndrome (EMS), a condition linked to thiamine deficiency and believed to be impeding recovery of lake trout. Rainbow smelt and alewife flesh are high in thiaminase and lake trout that rely on these non-native prey produce thiamine-deficient eggs, preventing successful reproduction in the lower lakes.

Many factors may affect the population dynamics of cisco in Lake Superior . These include but are not limited to: predation and competition, particularly with non-native species; environmental factors such as temperatures; commercial exploitation; and disease. A combination of these factors (that may or may not act independently), functioning at different life stages, likely determine the success of a cohort. I will be using available information on these factors to develop a simulation model that will provide a basis for developing hypotheses about the mechanistic links for growth and survival between life stages. The model will track individual cohorts in a population from eggs to spawning stock. Modeling individual year classes will help us to identify and evaluate the relative importance of mortality between life stages. We are especially interested in examining the influence of hypothesized factors affecting the life stages between egg deposition and age-1 survival because we believe that this period of development determines year class strength. Where data and information are lacking, the model will help reveal the importance of particular sources of uncertainty through sensitivity and uncertainty analysis.

There is also an empirical aspect to my project. In May of 2006 collaborative efforts between the USGS-GLSC-LSBS, Ontario Ministry of Natural Resources, and Michigan State University investigated the long-standing hypothesis that rainbow smelt may act as an impediment to cisco recruitment. Research conducted on inland systems provide strong evidence that predation by rainbow smelt on cisco larvae may be a bottleneck to recruitment. However, this research does not necessarily apply to the much larger Great Lakes and thus the role of rainbow smelt has been the subject of much debate. We are using a comparative field approach to examine the impact of rainbow smelt predation on cisco recruitment in two bays ( Thunder Bay and Black Bay , Ontario ) with contrasting rainbow smelt and spawning cisco abundances. By combining estimates of rainbow smelt and larval cisco densities into a bioenergetics framework, we will be able to estimate the impact of predation as a function of predator density and thus help us better understand the role of rainbow smelt in determining the recruitment of cisco.

By using available information to guide restoration efforts, research directions, and management strategies, we are ensuring that we approach cisco restoration in a pro-active and adaptive manner. It is important that restoration efforts follow a well-focused, scientifically based, and economically sound agenda so that we may increase the probability of achieving self-sustaining populations of native species in the Great Lakes .