Montana Fish, Wildlife & Parks biologists say lower Fort Peck Reservoir water levels have had an impact on some fish populations, but benefits are still being realized from good water years in 2008 through 2011.
“Since 2011, water levels have dropped 29 feet and approximately 65,000 surface acres have been lost on Fort Peck,” said FWP Biologist Heath Headley. “That acreage equals nearly two Canyon Ferry Reservoirs.”
Fort Peck Reservoir elevations rose only a foot from January through June of 2013. The impact of these operations is that no shoreline vegetation was flooded during the spring and early summer, resulting in significantly less habitat available for fish to use. With declining reservoir elevations, most fish populations have generally followed a similar declining pattern, Headley said.
Annual netting surveys in 2013 indicated relative abundance of walleye decreased from a record 6.8 per net in 2012 to 4.8 per net. However, Headley noted that this is still above the long-term average of 3.6 walleye per net.
“Walleye in the 15-to-20-inch range continued to be the most abundant due to a very large group of five-year-old fish, but anglers should be encouraged because good numbers of walleye more than 25 inches long continue to be measured during these sampling efforts,” he said.
Northern pike relative abundance decreased from a record 5.0 in 2012 to 3.2 per net in 2013. Similar to walleye, however, northern pike relative abundance is still above the long-term average. Headley said this is attributed to increased spawning and rearing habitat created by the flooded shoreline vegetation over the past few years. Most pike sampled during this time were between 20 and 28 inches long and averaged close to four pounds.
Abundance of shoreline forage fish such as yellow perch, crappie, spottail shiners and emerald shiners decreased in 2013 following declining reservoir elevations. Most of these shoreline forage fish are now at or below long-term averages, he said.
“Unlike the high water years of 2010-12, young-of-year and age-one-plus yellow perch numbers in 2013 declined greatly due to the lack of spawning and rearing habitat as well as increased predation from a growing walleye and northern pike population,” Headley said. “It should also be noted that we observed a decrease in condition of the small-to-medium-sized walleye during our annual sampling. Shoreline forage fish are a critical component for the growth and survival of these smaller walleye.”
In contrast, netting results for cisco, an important coldwater forage fish, showed a substantial increase in young-of-year individuals from less-than-one per net in 2012 to 191 per net in 2013.
“This was more than double the long-term average and the fifth-largest year class recorded,” Headley said. “While this is great news for the medium-to-larger-sized walleye, northern pike, Chinook salmon, and lake trout, it may make things a bit more difficult for anglers. Anglers may have to change tactics in 2014 by fishing deeper as summer progresses and when corresponding water temperatures warm. Warmer temperatures will force cisco to head to deeper, cooler water where larger predatory fish will pursue this abundant food source.”
Several record-breaking fish from Fort Peck Reservoir were also noted in 2013. One angler caught a smallmouth bass that went 6.7 pounds, and another angler caught a channel catfish that weighed in at 34.8 pounds. Also, fisheries staff captured one of the largest Chinook salmon ever during last fall’s egg-taking operation, a lunker that tipped the scales at 29.5 pounds.
“The surge in all types of forage fish numbers created from the high water years clearly gave these species the extra boost they needed to attain trophy weights.” Headley explained.
If Fort Peck continues to be operated in the same manner and there is not a substantial increase in reservoir levels, anglers can expect to see reduced growth and survival of their favorite game fish species.
And that’s despite a snowpack in the Missouri River drainage above the reservoir that currently sits about 122 percent of the 30-year average. If retained in the reservoir – instead of being largely allowed to flow through it — that runoff would contribute to rises in water levels that would benefit fish, Headley said.
(Report by Montana FWP; Feature photo via pbs.org)