For researchers, managers and policymakers trying to conserve fish species diversity it is important to understand the potential impacts of non-native species. Cucherousset and Olden (2011) did a review of studies reporting ecological impacts of non-native freshwater fishes, focusing on the negative impacts of fish introductions. They found several types of ecological impacts spanning multiple levels of biological organization. At the genetic level, noted impacts are the disruption of gene transcription and hybridization and introgression. Disrupting gene transcriptions means that genes can be expressed or suppressed (turned on or off depending on their normal state). Hybridization and introgression can reduce reproductive efficiency, result in hybrid vigor and decrease genetic integrity. At the individual level, introductions of non-native fishes can cause changes in behavior of native species, changes in morphology and impact vital traits. Upon introductions of non-native species, native species can be forced to adapt to new selection pressures which can result in changes in morphology. Non-native species are known to have strong impacts on vital traits like growth, reproduction and survival. At the population level, non-native species can carry parasites that infect native populations, non-native species can act as parasites themselves, can modify the structure of the native population and can affect the distribution of native species by displacement and predation. At the community level, introductions of non-native species can cause extinctions of native species, rearrange the biogeography of native species and alter food webs. At the ecosystem level, introductions of non-native species can modify biochemical cycles, modify the exchange of nutrients, energy and organisms between ecosystems (e.g. freshwater/marine and aquatic/riparian), and alter habitats because some non-native species act as an engineer species.
The following are examples of impacts by non-native species familiar to northern Midwest anglers: Round gobies’ Neogobius melanostomus aggressive behavior and ability to eat eggs and embryos can reduce recruitment of native species. Sea lamprey Petromyzon marinus parasitism contributed to the dramatic decline of lake trout Salvelinus namaycush. In streams invaded by brown trout Salmo trutta, brook trout Salvelinus fontinalis move to small headwater streams for refuge. The feeding behaviors of common carp Cyprinus carpio can change the trophic status of a body of water from clear to turbid. In Chinook salmon Oncorhynchus tshawytscha spawning streams, redd construction decreases abundance of mosses, algae, macrophytes and benthic invertebrates.
Implications for anglers: Invasions of non-native species are generally irreversible so prevention must be a management priority. Anglers can transport non-native species in a variety of ways. Anglers need to follow all the regulations regarding species introductions and invasive species on the bodies of water they fish. Also, invasions by non-native species are inevitable, anglers should be prepared to change fishing practices, including tactics and target species.
Selected definitions:
Ecological: The relationship between organisms and their environment.
Transcription: The synthesis of RNA from a DNA template.
Population: A localized group of individuals that belong to the same species.
Community: All the organisms that inhabit a particular area, living close enough for potential interaction
Ecosystem: A community and its physical environment.
Riparian: The area situated on the banks of a river.
Engineer species: Any organism that creates or modifies habitats.
Recruitment: When juvenile organisms survive to be added to a population.
Trophic status: The level of growth or productivity of a lake as measured by phosphorus content, algae abundance, and depth of light penetration.
Cucherousset, J., J.D. Olden. 2011. Ecological impacts of non-native freshwater fishes. Fisheries. 36: 215-230.
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