Science Advisory Report  2013/009

Recovery Potential Assessment for Southern Upland Atlantic Salmon

Summary

• Available indices show that abundance of Atlantic salmon is very low in the Southern Upland designatable unit and has declined from levels observed in the 1980s and 1990s.   
• Annual adult abundance in four rivers declined 88% to 99% from observed abundance in the 1980s, a similar trend is observed in the recreational catch.    
• Region-wide comparisons of juvenile density data from more than 50 rivers indicate significant ongoing declines between 2000 and 2008/2009 and provide evidence for river-specific extirpations.
• Population modeling for two of the larger populations remaining in the Southern Upland designatable unit (LaHave and St. Mary’s) indicates a high probability of extirpation (87% and 73% within 50 years for these two populations respectively) in the absence of human intervention or a change in survival rates for some other reason. 
• Population viability analyses indicate that the loss of past resiliency to environmental variability and extreme environmental events is contributing to the high risk of extinction.
• Juvenile Atlantic salmon were found in 22 of 54 river systems surveyed in 2008/2009. Given the reductions in freshwater habitat that have already occurred and the current low population size with ongoing declines, all 22 rivers include important habitat for Southern Upland Atlantic salmon.  Restoration of these populations is expected to achieve the distribution component of the recovery target. If additional rivers are found to contain salmon, the consideration of these rivers as important habitat would have to be re-evaluated.
• The estuaries associated with these 22 rivers are considered to be important habitat for Atlantic salmon as successful migration through this area is required to complete their life cycle.
• While there is likely to be important marine habitat for Southern Upland Atlantic salmon, given broad temporal and spatial variation, it is difficult to link important life-history functions with specific marine features and their attributes.
• Proposed recovery targets for Atlantic salmon populations in the Southern Upland designatable unit have both abundance and distribution components.  Abundance targets for Southern Upland Atlantic salmon are proposed as the river-specific conservation egg requirements.  The distribution target should encompass the range of genetic and phenotypic variability among populations, and environmental variability among rivers, and would include rivers distributed throughout the designatable unit to allow for gene flow between the rivers/populations. There is the expectation that including a wider variety of populations in the distribution target will enhance persistence as well as facilitate recovery in the longer term.
• Interim recovery targets for Southern Upland Atlantic salmon can be used to evaluate progress towards recovery.  First, halt the decline in abundance and distribution in rivers with documented Atlantic salmon populations. Next, reduce the extinction risk in rivers with documented Atlantic salmon populations by increasing the abundance in these rivers.  Then, as necessary, expand the presence and abundance of Atlantic salmon into other rivers currently without salmon to fill in gaps in distribution within the Southern Upland designatable unit and facilitate metapopulation dynamics.
• Recovery targets will need to be revisited as information about the dynamics of the recovering population becomes available. Progress towards recovery targets can be evaluated using survival and extinction risks metrics.  
• Two dwelling places were evaluated for their potential consideration as a residence for Atlantic salmon. Of these, redds most closely match the definition of a residence because they are constructed, whereas home stones are not. 
• Threats to persistence and recovery in freshwater environments identified with a high level of overall concern include (importance not implied by order): acidification, altered hydrology, invasive fish species, habitat fragmentation due to dams and culverts, and illegal fishing and poaching.
• Threats in estuarine and marine environments identified with a high level of overall concern are (importance not implied by order): salmonid aquaculture and marine ecosystem changes.
• From analyses of land use in the Southern Upland region, previous and on-going human activities are extensive in the majority of drainage basins and have likely altered hydrological processes in Southern Upland watersheds.  Watershed-scale factors have the potential to override factors controlling salmon abundance at smaller spatial scales (i.e., within the stream reach). 
• River acidification has significantly contributed to reduced abundance or extirpation of populations from many rivers in the region during the last century. Although most systems are not acidifying further, few are recovering and most are expected to remain affected by acidification for more than 60 years.
• Acidification and barriers to fish passage are thought to have reduced the amount of freshwater habitat by approximately 40%, an estimate that may be conservative.  However, given the low abundance of salmon at present, habitat quantity is not thought to be currently limiting for populations in rivers where barriers and acidification are not issues. Whether freshwater habitat becomes limiting in the future depends on the dynamics of recovered populations.
• Population modeling for the LaHave River (above Morgan Falls) and the St. Mary’s River (West Branch) salmon populations indicated that smolt-to-adult return rates, a proxy for at-sea survival, have decreased by a factor of roughly three between the 1980s and 2000s. Return rates for Southern Upland salmon are currently about ten times higher than they are for inner Bay of Fundy salmon populations.
• In contrast with inner Bay of Fundy salmon populations, for which at-sea survival is so low that recovery actions in fresh water are expected to have little effect on overall viability, recovery actions focused on improving freshwater productivity are expected to reduce extinction risk for Southern Upland salmon.
• Remediation actions to address land use issues will not produce immediate population increases for Southern Upland salmon.  However, large-scale changes are the most likely to bring about substantial population increase in Southern Upland salmon because they should have a greater impact on total abundance in the watershed rather than on localized density, and they would address issues at the watershed scale.  Coordination of activities at small scales may produce more immediate effects but of shorter duration than addressing landscape-scale threats.
• Population viability analyses indicate that relatively small increases in either freshwater productivity or at-sea survival are expected to decrease extinction probabilities. For example, for the LaHave River (above Morgan Falls) population, increasing freshwater productivity by 20% decreases probability of extinction within 50 years from 87% to 21%, while a freshwater productivity increase of 50% decreases the probability of extinction within 50 years to near zero. Larger changes in at-sea survival are required to restore populations to levels above their conservation requirements. 
• Sensitivity analysis examining the effect of starting population size on population viability highlights the risks associated with delaying recovery actions; recovery is expected to become more difficult if abundance continues to decline, as is predicted for these populations.
• Atlantic salmon is one of the most-studied fish species in the world. Readers are referred to the supporting research documents, which form part of the advisory package for this designatable unit, for more information than is contained in this summary document.

This Science Advisory Report is from the May 22-25, 2012, Recovery Potential Assessment for Southern Upland Atlantic salmon. 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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