Michigan TU’s New Policy on Lake Superior Splake Stocking

by Michigan TU’s Conservation Committee

Michigan Trout Unlimited recently adopted a new policy regarding stocking splake in Lake Superior. This article introduces our members to the policy and explains its rationale.

Splake are a cross between lake trout and brook trout. However, unlike many hybrid crosses between two different species, the splake currently stocked are reproductively viable and interbreed back with lake and brook trout. Also, their appearance can vary, and they sometimes look quite similar to lake or brook trout, making accurate identification challenging.

Splake stocking started in the 1970s as high sea lamprey populations contributed to an increased downturn in many lake trout populations. It was hoped that perhaps a fastergrowing hybrid might perform better than the long-lived, slow-growing lake trout. As it turned out, splake often spent considerable time in nearshore areas and created a unique fishing opportunity as coaster brook trout populations had long been dwindling to low levels. In the following decades, however, Lake Superior lake trout were restored to healthy and sustainable levels. Still, stocking of splake in Lake Superior waters continued, perhaps because of the local popularity as a nearshore fishery.

Lake Superior is home to several strains of native lake trout, many with specialized adaptations to unique habitats within the lake. Unlike Lakes Michigan and Huron, the native stocks of lake trout were not extirpated in Superior and persist today. Coaster brook trout, brook trout that migrate between streams and the Great Lakes, however, remain at low levels compared with historical accounts. It’s thought that quite a few factors contributed to their decline. Coasters remain present, from well-known populations in the Salmon-Trout River and Isle Royale to lesser-known occurrences in places like the Pictured Rocks shoreline or the Pilgrim River, to even lesser-known occurrences reported in many different areas by anglers lucky enough to catch them.

However, there is much we still do not know about coasters and need to if we are to bring them back to healthy fishable numbers. We need to learn more about the role of genetics and the basis of their migratory behaviors. We also need to embark on diligent efforts to understand better their habitat needs and preferences and their current status and distribution. The Michigan DNR is also working through a long-term research project to assess the degree to which conservative harvest regulations might foster an increased abundance of coaster brook trout.

While enjoyed by many, splake poses several risks of negative impact to lake and coaster brook trout. First, their ability to interbreed with either poses the potential for genetic introgression, which can negatively alter the genetic makeup of the wild lake trout and coaster brook trout (with possible consequences for their fitness and adaptability). There is already evidence of splake using brook and lake trout spawning grounds, and more work is targeted to confirm the extent to which inter-breeding has already occurred.

Second, splake, similar in behavior to both lake and brook trout, act as competitors. More information is needed to understand the extent fully, but splake overlap in habitats and eat similar prey.

Lastly, there are concerns with the misidentification of splake, lake trout, and brook trout. In Lake Superior, the minimum size limit for brook trout is 20” (to help protect and foster coaster brook trout), and only one may be kept per day (waters around Isle Royale are catch and release). However, the minimum length for splake is 15”, and three splake may be harvested. Therefore, if an angler misidentifies a coaster brook trout as a splake, it results in overharvesting coaster brook trout.

There has been growing concern among resource managers and conservation groups over the potential negative impacts that splake stocking in Lake Superior waters may have on the recovery of the wild lake and brook trout populations. The Great Lakes Fish Commission’s Lake Superior Technical Committee (LSTC) recently released a document synthesizing scientific research and natural resource agency data to assess these potential impacts. The report also identified research needs that will better our understanding of risks that splake may pose to lake and brook trout populations. Some of the key points are: 1. Splake backcrossing with lake and brook trout is likely, due to the fertility of splake and the overlap in spawning locations and timing. Thus, splake stocking risks the recovery and long-term viability of lake and brook trout populations. Little evidence exists that introgression has occurred; however, there has been little research. 2. Splake may impact lake and brook trout through ecological dynamics such as competition or predation; however, little research has addressed these interactions. 3. Harvest of splake is low relative to the number stocked. 4. Misidentification of splake may be common given the morphological overlap with lake and brook trout. This results in the harvest of brook trout less than the 20-inch minimum on many Michigan waters of Lake Superior and tributaries.

Based on the information presented in this document and the sound rationale behind the risks identified, it is the position

of Michigan TU that splake stocking in Lake Superior be ended or at least significantly reduced until critical data is obtained regarding the impacts of splake on the wild lake and brook trout populations. While ongoing and future studies may indicate the effects are minimal, we feel that it is not worth continuing to put valuable wild populations at risk until sufficient research is carried out.

We understand that a segment of recreational anglers feel strongly that splake stocking continue, and this likely includes a portion of Michigan TU membership. Splake provide an important nearshore fishery in several locations within Michigan waters of Lake Superior. With this in mind, our policy offers a suite of actions that may reduce the potential negative impacts of splake on lake and brook trout populations while still providing a productive nearshore fishery.

Risks & Proposed Actions

1. Risk: Genetic introgression of splake in lake and brook trout populations reduces fitness and hinders recovery. Action 1. Cease splake stocking in Michigan waters of Lake Superior. Action 2. Reduce splake stocking in areas in close proximity to remnant coaster brook trout populations. 2. Risk: Unintentional harvest of coaster brook trout less than 20 inches due to misidentification. Action 1. Increase the minimum size limit on splake to 20 inches. Action 2. Implement a 100% mark (adipose clip) on stocked splake. 3. Risk: Costs associated with raising and stocking splake are disproportionate to the anglers utilizing the fishery, and the “return-to-creel” investment of splake stocking has previously been reported by the DNR as low (costly). Action 1. Reallocate resources from raising and stocking splake to habitat restoration projects to improve wild fish populations. Action 2. Replace splake stocking with coaster brook trout stocking.

Efforts to stock coaster brook trout have been minimal and overall unsuccessful. Many of the attempts on Lake Superior’s south shore used brood stock from other locations, such as Isle Royale. We believe that coaster stocking should be revisited, and the use of local wild stocks be considered. If successful, these populations may become self-sustaining, not require annual stocking, and could once again provide the nearshore fishery that splake intended to augment.

Research Needs

Introgression of Splake in Lake and Brook Trout Populations

Assessing the genetic introgression of splake into wild brook and lake trout populations may be the most critical data needed at this point. We understand that analyses are underway at Michigan State University in collaboration with USFWS, DNR, and Michigan Tech University. This work will determine if splake

Photo by Captain Travis White, Keweenaw Charters genetics are present in samples identified as a lake or brook trout in field surveys. Continuing regular assessments of genetic material sampled from wild fish will be necessary for monitoring the potential introgression of splake with wild populations. Extent of Splake Migration Our understanding is that the DNR is beginning a project using alternating fin clips to identify where recaptured splake were planted, thus providing information on the extent to which these fish may migrate after stocking. We are in full support of this project. Currently, an extensive network of acoustic receivers is deployed throughout Michigan waters of Lake Superior. Implanting a sample of stocked splake with acoustic tags may provide additional and essential data on migrations and not require that the fish be physically recaptured. Existing Coaster Brook Trout Populations With regard to coaster brook trout, we know relatively little about where remnant populations exist. Identifying these locations is critical but is challenging given the environmental conditions and remoteness of many tributaries potentially supporting coasters. Exploring the use of newer technologies, such as remote sensing with cameras or environmental DNA detection, may help identify existing populations. Based on existing information, Michigan TU feels that splake stocking in Lake Superior should be ceased or significantly reduced because of the potential impacts on the wild lake and brook trout recovery. Critical data needs should be addressed in the coming years to understand better how splake may or may not negatively affect recovery efforts. We recognize the challenges associated with altering an established fish stocking program that provides an opportunity for some recreational anglers. Hopefully, as anglers become more aware of the potential impact of splake, support for the actions outlined will increase. We believe that decisions should be made based on the best available scientific data, and Michigan TU fully supports obtaining information needed to give managers the best chance at restoring self-sustaining wild lake and brook trout populations in Lake Superior and tributaries in Michigan.