Science Advisory Report 2018/041

Review of the Science Associated with the Inner Bay of Fundy Atlantic Salmon Live Gene Bank and Supplementation Programs

Summary

• The inner Bay of Fundy (iBoF) Atlantic Salmon Live Gene Bank (LGB) program supports Objective 1 in the Inner Bay of Fundy Atlantic Salmon Recovery Strategy (conserve iBoF Salmon genetic characteristics and re-establish self-sustaining populations to iBoF rivers), and is a part of the larger iBoF Salmon recovery program that also includes hatchery supplementation involving the release of juveniles and adults into native river habitat.
• This review provides an assessment of the LGB program following 3 generations (i.e., approximately 15 years) of iBoF Salmon population maintenance activities, which will inform the development of an updated 5-year plan for the LGB program.
• Results are summarized below for each of the five Terms of Reference for this review, followed by a summary of considerations for the future management of the LGB program. Additional program results and recommendations are contained in the text of this report.

Evaluate Success of Conserving Genetic Characteristics of the iBoF Salmon Population Across Three Generations of Captive Breeding and Rearing

• Sufficient information concerning both genetic variability and fitness is available to evaluate this objective for the Stewiacke River population only.
• The original collection of 1,029 Stewiake Salmon (i.e., the group of parr collected from the wild between 1998 and 2001, which include the primary founders) exhibited very high levels of family structuring.  
• Levels of genetic variation in the present day Stewiake population may have been markedly higher, and levels of inbreeding lower, if initial founder collections were initiated even two years earlier.
• High variability in the genetic contributions of the parents of the originating founders has resulted in elevated rates of loss of founder parent variation (e.g., founder parent alleles and founder parent genome equivalents) over time, and higher than anticipated rates of accumulation of inbreeding in subsequent generations.
• Overall, variance in family size was lower for captive-reared versus wild-exposed groups from a given brood year.  
• Overall, rates of loss of molecular genetic variation between the Stewiacke founder and second generation Salmon were low, though some slight reductions were observed.

Investigate Levels and Origins of Inbreeding in iBoF Salmon

• The estimated effective number of Stewiacke breeders under the wild-exposed offspring management regime is probably sufficiently large that ongoing rates of loss of genetic variation due to random genetic drift, and rates of accumulation of inbreeding, are not expected to be high.

Evaluate the Effects of the Overall Program on Fitness-related Traits in iBoF Salmon

• There was no evidence for possible effects of parental early juvenile rearing environment (captive versus wild) on early offspring survival in the wild.
• In some years, the parental early juvenile rearing environment (captive versus wild) may have influenced size-at-age of offspring in their first year in the wild, with offspring of wild-exposed Salmon exhibiting greater length and weight compared to offspring of exclusively captive-reared parents.
• No evidence was found for possible cumulative negative effects of ancestral (parent and grandparent) early juvenile captive rearing environments on early offspring survival in the wild.
• In some years, a possible negative influence of increasing number of generations of captive breeding and rearing on survival in the wild was observed and, although the effect was small, the number of generations across which comparisons were possible was very limited.
• No association between measures of molecular genetic variation or pedigree inbreeding and either survival in the wild or the incidence or percentage of fry deformities was observed.
• Female parent age, but not male parent age, was found to have a large effect on multiple offspring performance traits, including survival in the wild from release to Age 1, and this effect was consistent across multiple years; part of this effect appears to be due to egg size, but female parent age was also associated with increased survival independent of egg size in some years.
• Generally, most monitored traits in the Stewiacke population did not show any discernible trends over the course of the program. 

Assess the Status of Atlantic Salmon in the iBoF Designated Unit based on DFO Information and, Where Possible, Evaluate the Efficiency and/or Appropriateness of the Different Release Strategies

• The observation that juvenile Salmon are no longer present, or if present are at extremely low densities, indicates the lack of returning truly wild iBoF Salmon and that iBoF Salmon would likely be extirpated without the LGB program.
• Based on the genetic analysis, about 24% of the small Salmon returns on the Big Salmon River and the majority of the adult returns to White Rock Dam on the Gaspereau River have been the direct result of the LGB program.
• On the Big Salmon River, the mean annual smolt production from 2003 until 2016 has been approximately 13,400 smolts. Over this time period, the annual contributions by origin breakdown is as follows: adult spawners have contributed 4,729 fish, LGB unfed fry releases have contributed 4,646 fish and adipose-clipped LGB fall and spring parr releases have produced 4,034 fish.
• Both Gaspereau and Big Salmon rivers remain well below conservation egg requirement due to poor marine survival. The smolt to small Salmon return rate from the combined group of adult spawners, LGB fry, and LGB parr has been consistently below 1% and has averaged 0.32% from 2002 to 2016 on the Big Salmon River.
• The mean smolt to small Salmon return rate for the smolts that originated from LGB fry is 0.20%, which is about three times better than the mean return rate for LGB origin smolts released as parr.

Provide Information Concerning Introgression of Non-native Wild and Aquaculture Genetic Material into iBoF Populations

• Genetic structuring between outer Bay of Fundy and Big Salmon River Salmon appears to be decreasing over time. Results from several population genetic analyses are all consistent with extensive and ongoing gene flow from non-local (likely outer Bay of Fundy) sources into the Big Salmon River gene pool, and this could represent a risk to the conservation of iBoF genetic characteristics in the Big Salmon River LGB population.
• European farm Salmon ancestry, the proximate source of which appears to be the local (Bay of Fundy/Gulf of Maine) industry, has been detected in Salmon collected from the Upper Salmon and other iBoF rivers. European farm escapes, or their European farm/North American farm hybrid offspring, appear to have been spawning in the iBoF during the period spanning 1997 to 2012, including during all or most years within this period.
• Analyses indicate that farm Salmon escapes exhibiting European ancestry have successfully reproduced in several iBoF rivers and appear to have spawned with endangered iBoF Atlantic Salmon.
• European farm/North American hybrids may exhibit reduced early juvenile survival relative to pure Stewiacke parents, in wild Stewiacke River habitat.

Considerations for Future Management of the LGB Program

• The likely number of adult returns to individual rivers in the iBoF (0 to 10 in most years with the exception of the Big Salmon River) is probably too low for natural selection to be effective at maintaining or increasing survival under current and possibly changing marine conditions. For natural selection to impact or improve smolt-to-adult survival, a sufficient number of smolt must exit a given iBoF river for a small to moderate number of adults to return to either reproduce in native river habitat, or be incorporated into LGB populations directly as spawners. This may require increasing the number of fish released from the LGB program.
• There are several possible paths to maintaining large effective population size in iBoF LGB programs, each involving variable levels of expenditure of different resources; an optimal approach can be selected based on scarcity of each resource at a particular point in time.
• If a shift in focus of the iBoF Recovery program from maintenance of genetic variation to re-establishment of wild self-sustaining populations were to be considered, the extent to which resources ought to be redirected should reflect both costs (e.g., reduced efficacy of conserving genetic variation) and benefits (e.g., the likelihood of making progress toward re-establishing self-sustaining populations, given current marine conditions).

This Science Advisory Report is from the June 13-16, 2017, Review of the Inner Bay of Fundy Atlantic Salmon Science Associated with the Live Gene Bank. 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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