Smallmouth bass (Micropterus dolomieu) have experienced substantial range
expansions in northern Ontario over the past century, with adverse consequences for
native salmonid predators. It is unclear how climate-induced water clarity shifts will
affect interactions between native dark-adapted walleye (Sander virteus) and invading
smallmouth bass in northern Ontario. This study used stable isotopes of nitrogen
(15N/14N) and carbon (13C/12C) in fish muscle tissue to investigate how resource
partitioning between walleye and smallmouth bass is related to water clarity in 34 small
(100-200 ha) Boreal Shield lakes (ranging from 1 to 8.5 m Secchi depth, and from 3.2 to
13.1 mg/L DOC). Quantitative metrics of trophic niche dimensions (based on the size,
position, and dispersion of multivariate ellipses drawn around sampled individuals in
δ15N vs. δ13C biplot space) were calculated for each individual population and used to
determine trophic interactions and niche overlap between sympatric walleye and
smallmouth bass. Linear and multiple regressions were then used to explore potential
relationships between trophic interactions and water clarity. Available habitat and fish
assemblage data was also explored for potential influences on isotopic niche dimensions
and trophic interactions of walleye and smallmouth bass. Total occupied niche space
decreased significantly with increasing water clarity for smallmouth bass as populations
occupied a narrower range of trophic levels and made greater use of pelagic resources. In
contrast, walleye trophic niche dimensions did not respond significantly to water clarity.
Isotopic niche overlap ranged from 0 to 65%, but no metric of trophic overlap was
significantly related to water clarity. Other abiotic and biotic variables, however, did have
a significant influence on the similarity between some aspects of walleye and smallmouth
iv
bass isotopic niche dimensions (but not interaction). Both species fed on more
isotopically similar carbon sources as lakes became shallower, which may be a result of a
lack of distinct littoral and limnetic habitats. Walleye and smallmouth bass niche size also
became more similar with increasing DOC but this may be a result of lower prey
diversity. Both species also occupied more similar average food web positions as yellow
perch relative abundance increased, indicating that the exploitation of yellow perch by
both species increased with perch abundance. Together with other studies that have found
little evidence for an impact of smallmouth bass on walleye fitness and abundance, this
research suggests that, unlike salmonid and cyprinid species, walleye may be resilient
against smallmouth bass invasions regardless of water clarity conditions in oligotrophic
boreal lakes.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OSUL.10219/2008 |
| Date | 30 July 2013 |
| Creators | Stasko, Ashley D. |
| Publisher | Laurentian University of Sudbury |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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