By: Marty Holtgren, Fisheries Biologist with Michigan DNR
Juvenile Sturgeon from the Muskegon River
The Muskegon River is one of the few rivers on the eastern shoreline of Lake Michigan where a remnant population of lake sturgeon are slowly recovering through natural reproduction. Each year since the early 2000’s research has focused on determining how the sturgeon population is faring. A small and dedicated group has contributed to these assessments including the Department of Natural Resources (DNR), U.S. Fish and Wildlife Service (USFWS), Little River Band of Ottawa Indians (LRBOI), Grand Valley State University (GVSU), the University of Georgia and many volunteers. This research has been supplemented by valuable reports from people that enjoy the river and lake, as we have received numerous calls when sturgeon are observed by fishers, fishing guides and people out enjoying the water.
Because every sturgeon does not spawn every year, the annual spring migration of spawning sturgeon to the Muskegon River is thought to be less than 50 fish, even though the total population is likely between 150 and200 adults. This population is much smaller than historical accounts and the low number demonstrates the need for protection. The estimated abundance of sturgeon is from Mark-Recapture surveys conducted in Muskegon Lake where sturgeon are captured and marked prior to entering the river to spawn, fish are also captured and examined for a mark when they exit the river after spawning. In 2005, during one of these assessments, a 6’3” female sturgeon weighing 135 pounds and carrying over one-million eggs was captured, measured, tagged and released.
To evaluate natural reproduction and recruitment of young sturgeon to the population, surveys have been developed to target 4-7 month old sturgeon in the Muskegon River and older juveniles and adults in Muskegon Lake. The good news is that during both types of surveys we have captured sturgeon and documented natural reproduction. For the in-river surveys researchers go out at night with spotlights in hand and slowly navigate upriver until a small sturgeon is observed. After one is captured the fish will be measured, implanted with a small tag, and a genetic sample collected before being released. In 2014, 70 sturgeon were caught ranging from 5½ to 10 inches in length. During 2015, less effort was put into sampling and a total of 7 fish were captured ranging from 8 to 10 inches in length. Although for both years the numbers were relatively low the findings show that natural reproduction is occurring, the fish were growing well and a good portion were likely to survive. After spending the first few months of life in the river the juvenile sturgeon exit into Muskegon Lake.
Over the past decade GVSU, DNR and other partners have used gill netting in Muskegon Lake during the fall to survey juvenile and adult sturgeon. The nets are set for a short period of time, to avoid killing the sturgeon. Throughout the surveys 27 different year classes were captured, with 2007-2009 and 2011 being the most represented. Not many sub-adult sturgeon (around 10 years old) were captured, however, this should be interpreted carefully as one of the difficulties in sampling this life-stage is how only a portion stay in Muskegon Lake, while some exit into Lake Michigan where targeted sampling is difficult. The last study of this type was conducted in 2015 where a total of 46 lake sturgeon (30 of which were unique and had never been captured before) were captured in only 6 overnight sets of net. The average age of fish captured was 2.8 years old indicating that juveniles produced upriver are surviving well.