Michigan Trout Unlimited
16
by Michigan TU’s Conservation Committee
Summer 2022
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
Photo credit: Captain Travis White, Keweenaw Charters
MICHIGAN Trout
Michigan TU’s New Policy on Lake Superior Splake Stocking
