Bull Trout (Salvelinus confluentus) (Saskatchewan-Nelson rivers populations): residence description

1 Introduction

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 “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 Bull Trout (Saskatchewan-Nelson rivers populations). The information in these sections was adapted from the “Recovery Strategy for the Bull Trout (Salvelinus confluentus), Saskatchewan-Nelson Rivers populations, in Canada” (DFO 2020). The geographic distribution of the Bull Trout is described in the recovery strategy for this species (DFO 2020).

2 Structure, form and investment

A spawning nest, or “redd” is considered to be the residence for Bull Trout (Salvelinus confluentus). Similar to all salmonids that spawn within rivers, Bull Trout construct redds in locations that contain gravel substrates and exhibit groundwater upwelling. The female digs a redd in the gravel to deposit the eggs and males fertilize the eggs. Once fertilization has occurred, the female moves upstream to dig again resulting in coverage of the fertilized eggs by gravel. This coverage provides protection from predation and keeps eggs from being washed downstream to less suitable habitats in higher flows. Groundwater upwelling is important to ensure that there is a constant supply of freshwater flowing over the eggs so that the eggs do not become desiccated during low water events and so that the locations where eggs are deposited are resistant to anchor ice (a winter time occurrence where ice freezes to the streambed).

During spawning, female Bull Trout excavate a nest, or redd, by turning on their side, arching their body and forcefully beating their caudal fin. Males position themselves alongside the female in the redd where eggs and sperm are released and the fertilized eggs fall into the depression created by the female. The female deposits eggs over several spawning events, each time moving upstream and digging an area, displacing gravel that covers eggs downstream. Redds are typically excavated to a depth of 10 to 20 cm and may range from 40 to 350 cm in length and 15 to 200 cm in width.

3 Occupancy and life-cycle function

Spawning activity can occur at any time between September and late October. Over winter, the eggs remain in the substrate hatching into alevins (the hatchlings) between March and April. Alevins can remain in the vicinity of the redd for several months following hatching. The residence is limited to the redd itself and the spawning and incubation time period that eggs and alevins are present in the redd structure.

4 References