Moosehead Lake wild brook trout study

January 2010 –

The Maine Department of Inland Fisheries and Wildlife is partnering with NextEra Energy, The Natural Resource Education Center at Moosehead, and Plum Creek to conduct a two year study of the wild brook trout population in Moosehead Lake. Moosehead Lake is a 75,000 acre oligotrophic lake with wild brook trout, lake trout, and landlocked salmon fisheries. It is the largest wild brook trout lake east of the Great Lakes. The recreational fishery in this lake and its tributaries and outlets are of major economic value to the region and to the State.

The Eastern Brook Trout Joint Venture (EBTJV) identified Maine as the “Jewel” of the eastern range with the most intact wild populations of any state in the northeast. In addition, Maine is the only state with large lakes (over 5,000 acres) of self-sustaining populations of brook trout. We are the last stronghold for wild brook trout and represent a unique opportunity for research to improve the knowledge base and to promote better stewardship and restoration projects across the northeast. In March 2008, the EBTJV identified 10 areas of study needed for brook trout in large lakes and rivers. The Moosehead Lake project has multiple objectives which address several of these research needs. This study will quantify the difference in population size and any changes in sex/maturity or age/growth. We will also be able to compare the number of brook trout utilizing Socatean Stream in 2009 to data collected in 1958, when Fisheries Biologist Roger Auclair constructed a wooden weir on the stream.
The specific research needs identified in that 2008 meeting that will be addressed during this study include:
1. Movements of brook trout in large lakes and rivers.
2. Interactions between brook trout and exotic salmonid fish species.
3. Interactions between brook trout and exotic non-salmonid species.
4. Factors influencing brook trout spawning survival.
5. Determination of persistent population size.
6. Effectiveness of regulations for brook trout management.

Our assessment will include a major initiative to evaluate all of the major and minor spawning tributaries in two years. Specifically, we plan to fabricate and operate a fish weir on two major brook trout spawning tributaries to capture the entire runs beginning in 2009. Trapnets will be used to capture brook trout at the mouths of smaller tributaries and at potential shoreline spawning sites. Thirty mature brook trout from the Roach River, Socatean Stream, and various shoreline sites will have a radio transmitter surgically implanted in the body cavity. All mature brook trout captured will receive an individually coded PIT tag and a fin clip. We will install stationary dataloggers on the source streams to identify fish moving into and out of the stream/river. Aerial flights will be conducted bi-weekly during the fall and monthly during the remainder of the year.
Tracking will allow us to locate specific spawning areas, areas of winter refuge in the streams, areas of winter refuge in the lake, identify mortalities and estimate post-spawning mortality, and track general fish movements in this large lake system with multiple inlets and outlets. Winter angler surveys and angler counts in combination with the PIT tag information will allow us to estimate angler use, harvest, and exploitation of wild brook trout in the winter fishery. Population data collected from Socatean Stream will be comparable to work completed by Roger Auclair in 1957.

The study has already begun.

The weir was installed on Socatean Stream in late August and we immediately began catching mature wild brook trout moving into the stream in preparation for the fall spawning. Clearly, flow was the most important factor on trout movement into the stream. Each time we saw an increase in flow, there was an immediate response of more trout moving into the stream (and the weir). In fact, it was extremely dry in early September and we stopped catching trout in the weir. So, we took a day to survey the entire stream and remove debris/beaver dams. We removed several large beaver dams which created a small, short term increase in the stream flow as the beaver flowages were drawn down. At the end of the day, we observed several trout in the weir and more came in over night due to this flow increase. Each time we had a rain event; more fish would come into the stream. Peak movement occurred during peak flows and movement quickly dissipated as the natural flows receded.

The weir operated from late August through late October. We had hoped to operate it through November; however, a large rain event the weekend of Oct 24th caused scouring and washing under and around the structure and it could not be reset in the high flows. Therefore, we removed it later that week.

We caught 372 wild brook trout in our weir during the study. Most of the fish were 14-17” in length. We took one large female that was just over 21” and 3 lbs. We know we missed many fish as well. Several times we had holes appear under the weir and fish were able to pass. We observed dozens pass around our feet one day while trying to patch the holes. In late October, we seined a pool of trout to count the number of tagged vs. untagged fish to try to estimate the number we missed. We seined 39 trout and only 10% were marked! Overall, we were very impressed with the numbers of fish in the stream. Socatean Stream still has a strong run of wild brook trout.

We were able to implant radio telemetry transmitters into 40 fish. All other fish were PIT tagged. We tracked the radio tagged fish through the fall and were able to locate many spawning areas in the stream (Note the antenna protruding from male trout in photo!). We only observed 1 mortality in the tagged fish prior to the onset of spawning. These radio tags have mortality switches which emit a different signal when the fish dies. We expected to see high post-spawning based on a similar study at Chamberlain Lake and the work conducted on Socatean Stream in 1957. To date, we have seen 58% mortality on these fish. This is very similar to data collected at Chamberlain Lake.

We will continue to track these fish from a plane during the winter months to locate areas of winter refuge. We will install our antennas on the stream next spring to see if and when any fish return to Socatean Stream. We also received grant for nearly $12,000 from the Maine Outdoor Heritage Fund (The instant lottery ticket fund) to conduct the same study on the Roach River beginning next August.