Research Document - 2014/007
Assessment of the Recovery Potential for the Outer Bay of Fundy Population of Atlantic Salmon (Salmo salar): Habitat Considerations
By T.L. Marshall, C.N. Clarke, R.A. Jones, and S.M. Ratelle
Abstract
This document addresses the habitat considerations pertinent to the development of Fisheries and Oceans Canada’s Recovery Potential Assessment of Atlantic Salmon of the Outer Bay of Fundy (OBoF) Designatable Unit 16 (DU 16). Considerations include: residence requirements, habitat requirements, spatial extent of the habitat, spatial constraints, habitat suitability, options for habitat allocation, and research recommendations.
Adult Atlantic Salmon require appropriate river discharge and unimpeded access to reach spawning areas, as well as holding pools and coarse gravel/cobble substrate on which to spawn. Eggs, alevins and juveniles require clean, uncontaminated water with a pH generally >5.3 for appropriate development, as well as steady, continuous water flow and areas with appropriate cover during winter and summer to deal with temperature extremes. Smolts need appropriate water temperature, photoperiod and river discharge as cues to migrate and require unimpeded access throughout the length of the river. Immature and mature Atlantic Salmon in the marine environment require access to sufficient prey resources to support rapid growth.
There is an estimated 49.7 km² of productive habitat available to Atlantic Salmon within DU 16, 81% of which is within Canada. Of the combined Canada-USA area, 90% is within the Saint John River Basin; 10% is attributed to ten smaller basins westward to, and including, the St. Croix Canada-USA boundary waters. Within the Saint John River, 21.5 km² is upriver of Mactaquac Dam and 23.2 km² is downriver of Mactaquac Dam. The tidal habitat within the mainstem of the Saint John River Basin is 140 km in length; the estuarine habitat (included in tidal portion) is approximately 60 km in length; the marine habitat is widespread from the Bay of Fundy and Gulf of Maine, to the Atlantic coasts of Nova Scotia, Newfoundland, Labrador and Greenland, including the Labrador Sea.
The upper portion of accessible productive habitat (21.5 km²) of the Saint John River is fragmented by four major hydroelectric dams (Mactaquac, Beechwood, Tinker, and Tobique Narrows) and headponds within Canadian jurisdiction. Each has provisions for upstream but not downstream fish passage. Three dams and flowages (headponds/reservoirs) with upstream but mostly no downstream passage facilities obstruct salmon accessing the majority of habitat in the St. Croix River; one dam with an ineffective downstream by-pass and adjacent pool and weir fishway is located at tide-head on the Magaguadavic River.
Freshwater habitat suitability is largely judged on current abundances of juveniles at electrofishing sites and, to a lesser extent, the availability of stream gradients measured from ortho-photo maps. The assessment of the habitat’s future suitability under biologically based recovery objectives is problematic given increasing river temperatures, decreasing stream discharges, new ecosystems and fish communities established within headponds and some rivers, and escapes from the aquaculture industry. These elements add new uncertainties to the prediction or measurement of success without considering new norms for juvenile abundance and, possibly, revisions to current conservation requirements.
Options for allocation of ‘important’ habitat assume that hydroelectric dams and open pen aquaculture will persist. Similarly, the effects of climate change, urbanization, forestry and agriculture, and the spread and increase in abundance of non-native 'cool' water predators of salmon will likely increase and, therefore, there is likely only to be a decrease in pliable salmon habitat. With this in mind, prioritization criteria for important habitat largely follow criteria developed for the recovery targets related to distribution and favour habitat that is as accessible, productive, and ‘free as possible’ of known threat impacts. Prioritization should, where possible, seek to preserve a cross section of today’s population characteristics and geographic distribution in the faint hope that robustness and adaptive potential of populations will be available for persistence and possible recovery.
Research recommendations are provided in the identification of habitat important or manageable for maintenance or recovery of salmon.
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