August 2, 2019 at 12:55 pm
By Fisheries Biologist Wes Ashe
Along the Midcoast and south-central part of the state, there are very few wild trout populations in Maine’s larger lakes and ponds. Whether it’s a result of competition and predation, degraded water quality, a lack of suitable spawning grounds, and/or some other habitat-related variable, conditions just aren’t suitable for wild salmonids. However, there is one notable exception. Lake trout (aka togue, in Mainer-talk) have taken up shop in a handful of waters and wild fish now exist in six Region B waters including Sheepscot Pond (Palermo), Swan Lake (Swanville), Wassookeag Lake (Dexter), Maranacook Lake (Winthrop), Lower Narrows Pond (Winthrop), and Echo Lake (Fayette).
Some of Region B’s wild lake trout populations have been around for decades, and a few including Wassookeag (stocked from 1958-78), Swan (1971-81), and Sheepscot (1956-85) are now entirely self-sustaining without any supplemental stocking from state hatcheries. Lower Narrows (1937-2015) and Maranacook (1975-2015) have also been stocked for decades, but it wasn’t until the past few years that wild togue were confirmed in each water.
At the same time of these togue confirmations, regional biologists received dozens of togue reports from regional anglers. Typically, togue reports are from anglers who land lunker fish in the 10-20-lb range, but these accounts were different. Anglers were catching small (~6-14”), juvenile togue by the bucketful. Most of these angler reports were from Sheepscot and Swan, but smaller, wild togue were also landed on the other waters at higher rates.
It’s typical for a given togue population to fluctuate over time. Lake conditions may favor togue recruitment over consecutive falls and strong year-classes may result. As these strong year-classes grow older and their diet transitions from zooplankton to insects to fish, the forage base (e.g. rainbow smelt) may not be able to sustain the new army of hungry mouths. Without a robust forage base, togue population dynamics change and a stockpiling of smaller, sub-legal individuals may occur and can be problematic. This process is common on any given togue water, but it’s not normal when it happens on every single regional togue water at the very same time.
To gain a better understanding of the environmental conditions that may have led to this togue infiltration, regional fisheries biologists are currently gillnetting all six togue waters. Summer is an ideal time to gillnet togue as lake thermoclines are well established and cold, oxygenated water is easy to pinpoint. In setting small meshed nets at these very depths, biologists can capture juvenile togue with very little bycatch. To date, juvenile togue have been successfully collected in all netted waters. Adult togue were also collected, but unlike the juveniles, the smaller mesh greatly limited their mortality.
In the lab, immature togue were measured to length and weight, stomach samples were analyzed, and otoliths were removed. Stomach samples varied by water, but rainbow smelt (adult & YOY), Daphnia (water fleas), Chaoborus (phantom midges), Chironomids (non-biting midges), and plankton were most common in diets. Otoliths are tiny, bone-like structures located in the inner ear cavity that provide balance and can also be used to determine age.
Once all togue waters have been netted, the otoliths will be analyzed and ages will be determined. It is the hopes of regional fisheries biologists that we will be then have the ability to not only uncover the ages of those fish most represented, but also link them across waters to determine a specific spawning season that produced the majority of juveniles. Hopefully we can then match specific environmental variables (e.g. lake water level, precipitation amount, air temperature) that resulted in this togue explosion across Region B waters.