Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi): residence description

1 Introduction

The Species at Risk Act (SARA) states that

“no person shall damage or destroy the residence of one or more individuals of a wildlife species that is listed as an endangered species or a threatened species, or that is listed as an extirpated species if a recovery strategy has recommended the reintroduction of the species into the wild in Canada.” [section 33]

Also, SARA defines a residence as:

“a dwelling place, such as a den, nest, or other similar area or place, that is occupied or habitually occupied by one or more individuals during all or part of their life cycles, including breeding, rearing, staging, wintering, feeding, or hibernating.” [subsection 2(1)]

Sections 2 and 3 below provide a description of a residence for the Westslope Cutthroat Trout, Alberta populations. The information in those sections was adapted from the “Recovery Strategy for the Alberta populations of Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi) in Canada” (DFO 2014). The geographic distribution of the Westslope Cutthroat Trout, Alberta populations, is described in the recovery strategy for this species (DFO 2014).

2 Structure, form and investment

Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi) are known to have one type of residence: a redd. In Alberta, Westslope Cutthroat Trout generally spawn in small gravel-bottomed streams where the female prepares a redd in the gravel by thrashing her tail to displace gravel until a depression about 30 cm wide and 12 cm deep is dug. Eggs are deposited into the redd and a male fertilizes the eggs. The redd containing the eggs is covered with gravel by the female dislodging gravels just upstream of the redd (Nelson and Paetz 1992; Scott and Crossman 1973). Redds created and used by Cutthroat Trout for spawning demonstrate that there is significant investment in the creation and to some extent, in the protection of the residence (filling with gravel) by Westslope Cutthroat Trout. Thus, a redd is considered to be the residence of this fish. The residence is limited to the redd itself and the spawning and incubation time period during which eggs and alevins are present in the redd structure.

3 Occupancy and life-cycle function

Spawning takes place between May and July depending on location, and usually occurs when water temperatures reach 10°C (Nelson and Paetz 1992) (6°C in high elevation populations; S. Humphries pers. comm.). Incubation is also temperature dependent and generally lasts six to seven weeks. Once the eggs hatch, alevins will remain in the redd for another one to two weeks (Nelson and Paetz 1992; Scott and Crossman 1973). Following emergence, fry migrate to low energy lateral habitats, which are areas with low water velocity and appropriate cover.

Currently, genetically pure populations of Westslope Cutthroat Trout inhabit only a small portion of the original Westslope Cutthroat Trout distribution and a residence for this species would only occur within habitat considered critical to the survival and recovery of this species. The residence for this species may occur anywhere within the population of genetically pure Westslope Cutthroat Trout and is restricted to areas considered to be critical habitat.

4 References