Wednesday, August 4, 2010

Lake Trout Assessment of Hopkins 2007

Assessment of Lake Trout Spawning Activity in Hopkins Pond, Mariaville, Maine
By J. W. Dembeck IV, Research Fisheries Biologist, Maine Department of Inland Fisheries and Wildlife. December 2007

Introduction
Lake trout (togue) are a long-lived species, and individual fish commonly live for 20+ years. Given the species’ longevity and association with deep, coldwater lakes, fisheries biologists have many questions about Maine lake trout populations that need answers in order to manage the species more effectively. Lake trout currently inhabit 137 lakes and ponds throughout the state, with most populations being wild and self-sustaining because of their ability to spawn along shallow lakeshores and offshore shoals having the appropriate rock and boulder substrate. Detailed studies have been conducted on spawning lake trout in various Maine waters over the past 60 years, but no studies have tracked individual fish over a time period greater than 3 years nor have all available spawning locations in a specific water body been sampled. By knowing the yearly frequency at which lake trout spawn, biologists can better understand the recruitment potential of lake trout populations in specific waterbodies and more accurately assess impacts to the forage base. With this information, managers can implement regulations that will maintain the population while providing quality fishing for anglers. For waters where wild lake trout populations are currently increasing and adversely impacting the forage base (e.g., Moosehead Lake, Sebago Lake, and Beech Hill Pond), a greater understanding of lake trout spawning and recruitment will assist in management of the species as well as the forage populations in these waters.

During September and October 2006, Maine Department of Inland Fisheries and Wildlife (MDIFW) biologists from the Jonesboro Office conducted detailed surveys of lake trout spawning habitat in Hopkins Pond (Mariaville), Phillips Lake (Dedham), and Tunk Lake (T10 SD). Jonesboro and Bangor biologists returned to each of these waters in late October 2006 to sample for lake trout in those areas previously identified as providing suitable spawning habitat. One night of boat electrofishing was conducted on each water resulting in 43 lake trout collected from Hopkins Pond, 8 lake trout from Phillips Lake, and 3 lake trout from Tunk Lake.

To gain knowledge of lake trout spawning characteristics, MDIFW biologists developed a multi-year study of a representative wild lake trout population in Maine. The project consists of a detailed investigation of the spawning activity of wild lake trout in Hopkins Pond (including timing, habitat use, site fidelity, and whether mature individuals spawn annually). The results of this study will assist MDIFW biologists in sampling efforts on lake trout waters throughout the state by identifying key variables that predict lake trout spawning activity. This will allow MDIFW biologists to maximize the relevancy and quality of data gathered on other lake trout waters, and provide for more efficient use of staff time. Additionally, the data on spawning frequency of lake trout will allow for a more accurate assessment of lake trout recruitment, further assisting biologists in managing Maine’s lake trout fisheries.

The objectives of this study are to:

1.Evaluate the characteristics of the spawning lake trout population in Hopkins Pond.
2.Determine the environmental parameters that are the most reliable indicators of the lake trout spawning period.
3.Evaluate spawning frequency (i.e., annual vs. biennial), for tagged male and female lake trout.
4.Determine site fidelity for spawning lake trout.
5.Determine the angler harvest rate for adult lake trout in Hopkins Pond.
Methods
Hopkins Pond was selected as the study water based on the following reasons: the presence of a healthy, wild lake trout population; previous success in collection of lake trout during the spawning period; available spawning areas; adequate boat access; small surface area; and close proximity to the Jonesboro and Bangor offices.

Beginning in October 2007, a minimum of five nights of boat electrofishing will be conducted annually by MDIFW staff and UMO student volunteers at the identified spawning locations in Hopkins Pond. All lake trout collected will be measured, weighed, sexed, spawning status recorded, and implanted with a Passive Integrated Transponder (PIT) tag prior to their release. Each PIT tag is uniquely numbered, permitting identification and data collection for individual lake trout throughout the study period.

During the course of this study up to 400 lake trout will be implanted with PIT tags and marked with an adipose fin clip, with a maximum of 125 individuals to be tagged each year in order to track individual spawning lake trout from a minimum of three consecutive spawning years, 2007, 2008, and 2009. The premise behind tagging mature adults in multiple spawning years is to increase the probability of encountering any fish that do not spawn annually.

The recapture of tagged individuals will allow biologists to monitor their spawning activity and estimate the total spawning population of lake trout in the pond. All captured lake trout will be scanned for the presence of a PIT tag, and if none is present, one will be implanted until all tags are utilized. Environmental conditions (water temperature, air temperature, photoperiod, wind speed, wind direction, weather, moon phase) will be monitored along with spawning activity to determine if one or more variables are reliable indicators of spawning onset and activity. As PIT tags have an unlimited life period, MDIFW biologists are planning to continue annual monitoring of the spawning population in Hopkins Pond, as long as a sufficient number of PIT tagged individuals remain in the pond.
During the winters of 2008, 2009, and 2010 MDIFW biologists will perform winter creel surveys on Hopkins Pond to determine the harvest rate of tagged fish and determine a population estimate of adult lake trout in the pond. Creel surveys will be conducted during January and February each year with biologists surveying one weekday and one weekend day each week.

Results
Six boat electrofishing sampling events were conducted between October 16 and November 2, 2007, collecting a total of 118 individual lake trout. Each lake trout in the sample was implanted with a PIT tag and released back into the pond. The 118 individual lake trout were comprised of 92 males, 23 females, and 3 of undetermined sex due to immaturity during this spawning season. For both males and females, the average length was 21 inches and the average weight 2.9 pounds.

Other species observed during the electrofishing surveys included: landlocked salmon, brook trout, brown bullhead, white sucker, creek chub, common shiner, blacknose dace, rainbow smelt, pumpkinseed sunfish, and redbreast sunfish.

Biologists will begin their creel surveys of ice fishermen on the pond Starting January 1, 2008.

Acknowledgements
The author would like to the thank, D. Jason Seiders (MDIFW- Lake Research Group), Rick Jordan (MDIFW – Jonesboro Regional Office), Greg Burr (MDIFW – Jonesboro Regional Office), Joe Overlock (MDIFW – Jonesboro Regional Office), and Dr. Steve Coghlan (University of Maine – Orono) for assistance in developing the study plan, conducting field activities, analyzing data, and reviewing drafts of the report. Nels Kramer (MDIFW – Enfield Regional Office) provided historic lake trout information from department files. Student volunteers from the University of Maine – Orono provided assistance during some field activities. The Hopkins Pond Association is a supporting group of the study. Funding for the PIT tagging equipment was provided through a grant from the Maine Outdoor Heritage Fund. This report and project has been funded in part by the Federal Aid in Sport Fish Restoration Program, Project F-28-P.

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