Date of Award

5-2009

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Joseph Zydlewski

Second Committee Member

Gayle Zydlewski

Third Committee Member

Cynthia Loftin

Abstract

The Rapid River, located in western Maine, has been renowned as a premiere native brook trout (Salvelinus fontinalis) fishery in the eastern United States since European settlement in the late 1800s. Since this time the Rapid River fishery has declined due to numerous anthropogenic effects. Increasing concerns about management and preservation of this brook trout population prompted my research of the history of the fishery in the Rangeley Lakes region (Chapter 1), the effects that the introduction of smallmouth bass (Micropterus dolomieu) may have on the Rapid River brook trout population (Chapter 2), and finally, the effects that heavy fishing pressure may have on the Rapid River brook trout fishery (Chapter 3).

Currently, the greatest threat to the Rapid River brook trout population is speculated to be competition with and predation by introduced smallmouth bass. Over the last 150 years, however, brook trout populations in the Rangeley Lakes region have been exposed to numerous stressors (e.g. over harvest, heavy fishing pressure, multiple introductions of non-native fish species, and habitat degradation from logging activities) that have contributed to their decline. Additionally, the Rapid River brook trout population may also be influenced by more regional (e.g. acid rain) and global (e.g. climate change) environmental conditions, both of which are predicted to intensify in the future.

Summer movement patterns and spatial overlap of native sub-adult brook trout, non-native landlocked Atlantic salmon (Salmo salar), and non-native smallmouth bass in the Rapid River were investigated with radio telemetry in 2005 to assess the potential of competitive interactions between these three species. Fish were captured by angling, surgically implanted with a radio transmitter, and tracked actively from June through September. Most brook trout (96%) and landlocked salmon (72%) displayed long distance movements (>1 km) to open water bodies (28 June to 4 July), followed by periods of time spent in presumed thermal refugia (5 July to 16 September). Summer water temperatures rose above 25 °C, near the reported lethal limits for these cold water species. In contrast, the majority of smallmouth bass (68%), a warm water species, did not make long distance movements (< 1km) from areas of initial capture, remaining in main stem sections of the river (28 June to 16 September). Spatial overlap of smallmouth bass and brook trout in the summer is unlikely because brook trout move to thermal refugia during this time. However, some level of interspecific competition between brook trout and landlocked salmon may occur since they selected similar habitats in this study.

As fish populations decline across their native ranges across the United States, angling regulations such as fly-fishing-only and catch and release are being used by management agencies to conserve fish while maintaining angling opportunities. Post- release mortality, however, may significantly impact age and size structure of protected populations. A deterministic model was used to assess the possible effects of catch and release fishing on brook trout population structure. Data from several sources were applied to create a brook trout population in which 5 age classes occurred. Changes in population characteristics at varying levels of angler effort (0-240 rod hours ha-1 yr-1) and post-release mortality rates (0-14%) were examined. A "trophy" brook trout fishery was sustainable only at low levels of angling intensity (<120 rod hours ha-1 yr-1). As angling effort increased, the proportion of older aged fish (3, 4, and 5 years old) declined significantly. At higher levels of angling effort, 4, and 5 year old fish were no longer part of the population. Increases in post-release mortality rates resulted in similar declines of older age classes. The results of this simulation indicate that heavy angling pressure and post-release mortality, as might be common in catch and release fisheries, significantly shifts the age structure of a population, reducing trophy angling potential.

Knowledge of both the historical and current factors that may limit brook trout is important in informing management decisions for the restoration and recovery of this important native species.

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