Addressing constraints on anadromous salmon productivity in the Rocky River: ouananiche and habitat use

Description: The Rocky River has the largest drainage (296 km2) on the Avalon Peninsula, and a natural waterfall at its mouth has historically inhibited access of anadromous salmon to the watershed (see map). It has 10823 units (1 unit = 100 m2) of rearing habitat and 2191 ha of lacustrine habitat that is suitable for Atlantic salmon (Bourgeois et al. 1992, Bourgeois 1998).

The only fish in the river prior to 1984 were resident ouananiche Atlantic salmon, brook trout, brown trout, American eel and three-spined stickleback. In 1984, the Salmonid Association of Eastern Newfoundland (SAEN), with support from DFO, initiated the introduction of anadromous Atlantic salmon with the hopes of establishing a robust, self-sustaining population and recreational fishery. In conjunction with the introduction, a functional fishway was constructed. While a self-sustaining run of anadromous salmon was successfully established, it has never achieved the Limit Reference Point of returning adults to the system (i.e. the target egg deposition), and currently sits at just 28% of the conservation egg requirement and its status is considered “critical” (Kelly et al. 2023).

The proposed project aims to identify potential factors that are inhibiting the recruitment of anadromous salmon, specifically whether it is caused by interactions with resident ouananiche and/or limited habitat use by anadromous salmon. Native ouananiche were present throughout much of the system prior to the introduction of anadromous fish (Meaney 1984), and there is evidence of subsequent hybridization between the two genetically distinct populations (Mason 2018). This has raised concern regarding the impact of ouananiche on the establishment of anadromous fish, through either hybridization and/or direct competition. Does hybridization affect the likelihood of individuals to migrate (i.e. are they more likely to become resident), and if they do migrate does it affect their survival at sea (i.e. are they less adapted for marine migration)? In terms of competition, do anadromous, ouananiche and hybrid juveniles occupy the same habitats, both broadly within the watershed and more locally within stream reaches, and if so, are they competing for the same food sources that may affect their growth and survival? Alternatively, is habitat use by anadromous fish restricted to particular parts of the watershed (i.e. are they preferentially in breeding particular areas and making limited use of the available rearing habitat) and how does this relate to what is known about the habitat from previous surveys (e.g., Meaney 1983, Patey and Whitaker 1993). The availability of scale samples from immediately prior to (1983), during (broodstock of fry released) and following introduction (1987, 1989) allows the possibility to examine both life history and genetic change that has occurred to the anadromous and ouananiche populations since. This can provide an understanding of how the Atlantic salmon in the Rocky River have responded following the introduction of anadromous fish in 1984.

The project will involve sampling and measuring salmon fry and parr systematically throughout the watershed in both fluvial and lacustrine habitats to quantify distribution and habitat use both on a broad and fine spatial scale. A sample of the fry will be analyzed for stable isotopes and lipids/fatty acids to determine diet overlap among coexisting fry of anadromous, ouananiche and hybrid origin. Smolts and returning adults will also be sampled at DFO’s counting facilities located near the mouth of the Rocky River to assess marine survival of salmon of the differing origins.

Genetic analyses of samples will be undertaken using a panel of microsatellites (Bradbury et al. 2018) to determine fish identify – anadromous, ouananiche or hybrid.