Date of Award

8-2010

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Stephen Coghlan

Second Committee Member

Joseph Zydlewski

Third Committee Member

Joan Trial

Abstract

Anadromous Atlantic salmon populations in New England have declined precipitously and now persist in only a handful of Maine rivers. Smallmouth bass have been established in most of the last remaining watersheds containing endangered anadromous Atlantic salmon, yet little is known about the ecological interactions between the species. The goal of this research is fill key gaps in knowledge regarding the effects of competition for habitat from smallmouth bass on Atlantic salmon. We used snorkel observation to identify the degree and timing of overlap in habitat use and to describe habitat shifts by Atlantic salmon in the presence of smallmouth bass in natural conditions. We also used a simulated stream, to monitor age 0 Atlantic salmon and age 0 smallmouth bass diel habitat use and movements in sympatry and allopatry. In late July, 2008, we observed substantial overlap in depths and mean water column velocities used by both species in sympatry, and an apparent shift by age 0 Atlantic salmon to shallower water coinciding with the period of high overlap. We detected no overlap or habitat shifts by age 0 Atlantic salmon in the presence age 1 smallmouth bass, and low overlap and no habitat shifts of Atlantic salmon and age 0 smallmouth bass in fall 2008. Summer floods in 2009 resulted in a near complete reproductive failure of smallmouth bass in our study streams, thus compromising our ability to replicate our 2008 experiments. In laboratory experiments Atlantic salmon did not change their habitat use in the presence of conspecific or heterospecific invaders. However, Atlantic salmon did forced smallmouth bass out of riffle habitats during daytime. Atlantic salmon and smallmouth bass displayed different diel activity patterns, which were affected by heterospecific introductions. From our field experiments, we suggest that environmental conditions of temperature and discharge mediate interactions of these species, and may determine the potential outcomes of competition. In our laboratory experiments the level of interspecific competition for habitat was low. Under certain conditions, Age 0 Atlantic salmon and smallmouth bass may be able to avoid intense interspecific competition through spatial and temporal habitat partitioning.

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