Rockford, Minn. – More than 30 muskies up to 36 inches long died
thanks to summerkill on one of the DNR’s primary brood stock
The muskies surfaced in the southwest bay of Lake Rebecca – a
250-acre lake near Rockford in Hennepin County. The mortality was
likely a result of warmer water, which holds less oxygen, according
to Dirk Peterson, DNR regional fisheries manager in St. Paul.
Oxygen depletion usually increases overnight, and recent heavy
rains may have spread de-oxygenated water to areas that previously
allowed fish survival, according to Peterson.
In addition to the muskies, which ranged in size from 32 to 36
inches, the DNR also found eight dead bluegills and six dead
Since 1987, Rebecca has been the DNR’s primary source of Leech
Lake strain muskie eggs, and it is estimated that the recent kill
represents 25 to 30 percent of the lake’s brood stock fish.
Periodic stocking helps maintain the lake’s muskies.
The DNR counts on Lake Rebecca for about 600,000 Leech Lake
strain muskie eggs every spring, according to Roy Johannes,
commercial fisheries manager for the DNR in St. Paul.
‘Our program took a little hit and we are concerned,’ Johannes
said, noting that the DNR has a a number of good back-up brood
stock lakes, but they are farther north.
Lake Rebecca’s more southern location and earlier spawning run
is timed well with sucker rearing operations, ensuring plenty of
forage for the young muskies and allowing them to grow to sizes of
10 to 12 inches before being stocked in the fall, Johannes
Taking eggs from later-spawning muskies means a higher
percentage of the muskies stocked in the fall are under 10 inches,
and studies have shown muskies under 10 inches don’t overwinter as
well as larger ones, according to Johannes.
The fish lost on Lake Rebecca were 4 to 6 years old and likely
hadn’t reached sexual maturity, which happens at around 7 years of
age, according to Johannes, who said there will likely be no
short-term effects of the muskie kill.
In the next three years, Johannes expected that there could be
shortfalls in spawning muskies on Lake Rebecca and adjustments will
Since the DNR began using Lake Rebecca as a source of muskie
eggs, this is the first instance where summerkill has been
observed, Johannes said.