Science Advisory Report  2014/021

Recovery Potential Assessment for Outer Bay of Fundy Atlantic Salmon

Summary

• The Outer Bay of Fundy (OBoF) Designatable Unit 16 (DU 16) of Atlantic Salmon was assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada in November 2010.
• There are 20 rivers considered to either contain or to have historically contained OBoF Atlantic Salmon populations. Only the habitat within Canadian boundaries was considered when assessing threats, as well as setting abundance and recovery targets for the OBoF DU.  The Saint John River and its tributaries upriver of the Mactaquac Dam are considered a single watershed and one of the 20. All 20 rivers are either influenced by the incursion of tidal waters or directly meet with the Bay of Fundy tides.
• Despite recent declines in population size, measures of within-population genetic variation in the sample populations of OBoF Atlantic Salmon analyzed were relatively high.  They were greater than that observed in comparable sample collections from Inner Bay of Fundy and Southern Upland populations, but similar to, or slightly lower than those from Eastern Cape Breton and Northern New Brunswick populations. In among-population comparisons of microsatellite variation, OBoF populations cluster together and separate from all other populations analyzed from the Maritime Provinces (including those from the nearby Inner Bay of Fundy).
• A log-linear (regression) model and a step function (ratio) model were used to predict declines in population abundance over the past 15 years. Analysis of trends for the entire OBoF DU indicates similar declines of 64 and 65% in total adult salmon population abundance over the past 15 years.
• Over the same time period, one-sea-winter (1SW) returns in the DU have declined between 68-73%, slightly more than the decline of 52-68% determined for multi-sea-winter (MSW) returns.  MSW salmon include those fish which return following two or more winters at sea and repeat spawners. The greatest decline rates have been observed for total returns to the Magaguadavic River (80-92%).
• In 2012, total (hatchery and wild) estimated 1SW returns were 194 salmon and total estimated MSW returns were 371 salmon for a combined total return of only 565 salmon estimated for the entire DU, which is the lowest in the time-series.
• Record poor adult returns observed in 2012 followed two years of increased adult abundance when the estimated DU returns were about 11,500 (2010) and 8,000 (2011).
• In 2009, electrofishing surveys of 189 sites within most of the rivers or tributaries in the outer Bay of Fundy region indicated that salmon (juveniles) are still present in 15 of the 20 salmon rivers but at low abundance in most rivers.
• The proposed recovery target for OBoF DU salmon has both an abundance and distribution component. The short-term distribution targets were based on seven criteria designed to maintain genotypic, phenotypic, and geographic representation of the DU while offering the best opportunity for recovery. Abundance targets are set using conservation egg requirements of 2.4 eggs per m² of productive habitat.
• Short-term distribution target rivers include the Saint John River upriver of Mactaquac Dam (specifically the Tobique, Shikatehawk, and Becaguimec tributaries), five rivers downriver of Mactaquac Dam (Keswick, Nashwaak, Canaan, Kennebecasis, and Hammond), and one river from the outer Fundy complex (Digdeguash).  Combined, these rivers represent 56% of the productive salmon habitat in the OBoF region.
• The short-term abundance target for the OBoF DU is to annually achieve the conservation egg requirement in the seven priority rivers selected for distribution targets. This target translates to approximately 54.4 million eggs which could be produced by 23,500 adult salmon (17,000 1SW and 6,500 MSW salmon) within the 22.62 million m² of productive habitat area.
• The long-term abundance target, based on 2.4 eggs per m² is 97 million eggs in the currently accessible 40.46 million m² of productive habitat area. This egg deposition could be produced by 41,200 adult salmon (29,700 1SW and 11,500 MSW salmon based on current biological characteristics).
• The maximum lifetime reproductive rate (the maximum number of spawners produced per spawner throughout its life at very low abundance) for the Nashwaak population has decreased from an average of 2.49 in the 1973-1982 time period, to an average of 1.13 during the 2000s. These rates are very low for Atlantic Salmon and are indicative that the Nashwaak population is at risk of extinction due to a reduced capacity to recover from years of low survival that may occur either due to environmental events or due to human activities.
• Population viability analyses indicate that the abundance of the Nashwaak River population, an index of populations in the Saint John River below the Mactaquac Dam, will continue to decline under current conditions.  Increases in freshwater productivity are expected to result in an increase in population abundance and a decreased extinction probability. Increases in both freshwater productivity and at-sea survival are required to meet recovery targets with higher probabilities (>90%).
• For the Tobique River population, the number of spawners replaced from one generation to the next, the maximum lifetime reproductive rate was estimated to be 0.18 indicating that spawners are well below replacement and the population is not viable. The Tobique population will be extirpated unless this rate improves. Freshwater production, downstream fish passage survival, and marine survival for the Tobique River population all have to improve to achieve recovery targets.
• Redds have characteristics that meet the residence requirement criteria.
• The seven rivers/tributaries identified in the short-term distribution target and their estuaries are important habitat and are required for OBoF DU salmon to complete their life cycle. Information is not sufficient to determine important marine habitat boundaries other than a general range of occurrence between the OBoF and the Labrador Sea.
• Functional components of freshwater habitat, including their associated features and attributes are well known for OBoFDU salmon.
• There is an estimated 41.75 million m² of historically accessible productive freshwater  habitat available in the area occupied by OBoF Atlantic Salmon, of which 40.46 million m² remain currently accessible. Fish passage facilities provide access to 41.1% of this area. Anthropogenic barriers on the Monquart, Nackawic and Musquash totally exclude salmon from approximately 1.30 million m² of productive habitat; other barriers (they number over 200 in the region) and passage issues at some road crossings affect connectivity for habitat in the region.
• Based on tagging information, the marine habitat for OBoF DU salmon includes a wide spatial range and temporal distribution from the Bay of Fundy and Gulf of Maine to the Atlantic coasts of Nova Scotia, Newfoundland and Labrador including the Labrador Sea and west coast of Greenland.  There is no evidence that the range in the marine environment has been reduced. However, the functional components of marine habitat are relatively less well known.
• In freshwater, hydroelectric dams and illegal fishing activities are identified as the threats of highest concern.
• Removal of adult salmon from OBoF rivers constitutes a severe threat to the populations and a direct loss of spawners.
• For many activities, where the level of harm is very low, the effect on extinction risk is likely not measurable. For example, in the case of bridge or culvert construction, only a small portion of the population may be affected by the activity. In other cases, for example scientific activities (e.g. monitoring the juvenile populations by electrofishing), habitat improvement, or recreational fisheries for other species, the small increase in extinction risk may be offset by other benefits, such as improved conditions for salmon or increased knowledge of population status.
• Potential freshwater mitigation measures/actions for high level threats include: implement/improve downstream fish passage, remove or refurbish reservoirs/dams, increase education and awareness activities, public outreach, and increased enforcement in areas of concern.
• Marine threats of high concern (importance not implied by order) are: shifts in marine conditions (which affect temperatures, currents and predator prey interactions), salmonid aquaculture, depressed population phenomenon, and disease and parasites.
• Potential marine mitigation measures/actions for high level threats include: application of science based siting criteria for aquaculture operations, escape management regimes, improved fish health management, increased compliance and enforcement of best management practices, and enhanced education and training for industry.

This Science Advisory Report is produced from the February 19-22, 2013, Recovery Potential Assessment for Atlantic Salmon (Outer Bay of Fundy Designatable Unit). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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