Science Advisory Report 2019/055

Review of existing scientific literature pertaining to fish mortality and its population-level impacts at the Annapolis Tidal Hydroelectric Generating Station, Annapolis Royal, Nova Scotia

Summary

• The purpose of this advisory process was to provide a summary and evaluation of the scientific literature pertaining to the mortality of fish at the Annapolis Tidal Generating Station (Annapolis TiGS) and the population-level impacts associated with this mortality.
• Research at the Annapolis TiGS is dated. The most recent field study at the TiGS identified during this review occurred in 1999. The most recent assessment of changes in life-history characteristics, for American Shad, occurred in 1996.
• There is a diverse fish community present at the Annapolis TiGS. At least forty species have been captured in studies at or near the station. Abundance of each species is not known, although based on sampling in the 1990s, the number of fish moving past the causeway annually would be expected to be in the low millions. Many of these fish are small, including Atlantic Silversides, and young-of-the-year Atlantic Herring, Blueback Herring, Alewife and American Shad.
• The highest priority species for determining population-level impacts are those with COSEWIC designations as extirpated, endangered, threatened, or special concern; and those that support commercial, recreational and aboriginal (CRA) fisheries for which the expected population-level impact, based on a qualitative assessment of the risk associated with the passage at the Annapolis TiGS, is a reduction in abundance greater than 10%.
• There are eight species that were identified in studies in the Annapolis River and estuary that have been designated as extirpated, endangered, threatened, or special concern by COSEWIC. These are: American Eel, Atlantic Salmon, Atlantic Sturgeon, Atlantic Wolffish, White Hake (hake at Annapolis were not typically identified to species), Lumpfish, Spiny Dogfish and Striped Bass. Of these species, only Atlantic Wolffish is listed under the Species at Risk Act, but listing decisions are pending for other species.
• Additional species that support CRA fisheries for which the risk was scored as an abundance decline >10% are: Alewife, American Shad, Atlantic Menhaden, Blueback Herring and Rainbow Smelt.
• There is evidence that mortality of fish occurs at the Annapolis TiGS. This evidence includes: anecdotal reports of dead fish (with injuries consistent with turbine passage) in the vicinity of the Annapolis TiGS, observations of dead fish downstream of the turbine, and in-situ research about survival of fish passing through the turbine.
• There are three routes of passage for fish moving downstream at the Annapolis TiGS: the new fishway, the old fishway and through the turbine tube. Studies of fishway utilization are limited to the summer and fall. Studies do not include larger fish not susceptible to capture in one-meter-diameter nets. Overall, with the exception of Atlantic Silverside, the studies indicate that the majority of fish pass through the turbine.
• There are three studies that provide turbine mortality rate estimates for fish that pass through the turbine. All are limited to quantifying mortality occurring during or shortly after  fish passage.
• When interpreting the turbine mortality rate estimates, it is important to remember that the turbine mortality rate alone does not determine the impact on the population. First, if some portion of the population move past the causeway via the fishways, overall survival will be higher than what is implied by the turbine mortality rate. Second, if fish move back and forth past the causeway more than one time, they may pass through the turbine more than one time leading to lower overall survival.
• Many of the biases associated with turbine mortality rate studies lead to single-pass estimates that are biased high (i.e. turbine mortality rates that are over-estimated).
• A study for adult American Shad in 1986 concluded that 21.3% (90% confidence interval +/- 15.2%) of these fish passing through the turbine die as a result of passage.
• A study in 1999 to trial a new method of estimating turbine mortality rates provided estimates for 12 species of fish. These estimates ranged from 0.0% for Sea Lamprey to 23.4% (95% confidence interval: 6.1% to 58.8%) for young-of-the-year American Shad. These estimates may be biased high because they do not fully account for capture and handling mortality.
• Fish diversion systems, intended to deter fish from passing through the turbine can be either physical or behavioral. Physical barriers have been considered impractical at the Annapolis TiGS due to its large size, debris, and the small size of most fish.
• Behavioral guidance systems have been tested at the Annapolis TiGS, and have shown promise for young-of-the-year American Shad, Alewife and Blueback Herring. Further refinement of the system would likely improve the effectiveness for these species. Whether a behavioral guidance system can be developed that would be effective for all species at the Annapolis TiGS is not known but is unlikely.
• The Annapolis River American Shad population is the only population for which a comparison of their biological characteristics before and after Annapolis TiGS became operational is available.
• Comparison of the characteristics of the American Shad spawning run before and after the turbine came online indicate a decline in the mean size, mean age, maximum observed age, age-at-maturity, and percent of repeat spawners, and an overall increase in the total mortality rate. The direction of these changes is consistent with increased mortality at the Annapolis TiGS. However, the changes cannot be wholly attributed to the turbine without information about fishway usage, the expected number of passes through the turbine each year, and knowledge of other changes that would affect their survival that may have occurred during the 15 years over which these assessments occurred.
• Both genetic and tagging studies have shown that Striped Bass undergo coastal migrations and forage in estuaries other than those at the mouths of their natal rivers. The Striped Bass assemblage in the Annapolis River estuary, at least historically, consisted of fish from more than one population, the relative abundances of which likely changed through time and are not known. This, and the paucity of information about the rates of mortality of Striped Bass moving past the causeway, precludes an evaluation of the population-level effect of the Annapolis TiGS on the Annapolis River Striped Bass population.
• There is weak evidence that there may presently be a population of Atlantic Sturgeon native to the Annapolis River, but its status is not definitively known. If sturgeon encountering Annapolis TiGS are from other populations, the effect on those populations is likely quite low. However, if there is a population native to the Annapolis River, the effects of turbine mortality on a native population would be high.
• Data gaps for estimating population-level impacts of the Annapolis TiGS for the majority of species include: the proportion of populations that would be expected to encounter the turbine; rates of fishway usage and survival; survival of fish of all life stages that pass through the turbine; the expected number of passes through the turbine; and rates of other human-induced mortality.
• Development of reference mortality rates associated with passage at the Annapolis TiGS would help ensure that mortality rates are consistent with DFO’s sustainable fisheries framework and could help inform regulatory decisions under the Fisheries Act and Species at Risk Act. It would also help guide decisions about future research.
• Methods for studying fish behavior and survival have improved significantly since the studies were undertaken at the Annapolis TiGS. For species and life stages large enough to carry acoustic tags, advances with this technology afford the opportunity to address many of the data gaps. For species and life stages that are too small to carry acoustic tags, research to better understand and improve capture and handling methods, as well as capture efficiency, would lead to a better understanding of the impacts of the Annapolis TiGS.
• The focus of this document is turbine mortality at the Annapolis TiGS and its associated population-level impact. While this focus does address the effects of direct mortality, it does  not fully address the impacts of this generating station on fish populations because there is the potential for indirect effects as well. Topics such as changes in habitat quantity and quality, prey availability, or sediment transport that may affect the productivity of clam fisheries in the Annapolis Basin, are not addressed herein. These topics warrant further consideration.

This Science Advisory Report is from the January 9-10 and March 6, 2019 Review of Existing Scientific Literature to Determine the Level of Fish Mortality and Potential Impacts on Fish Populations as a result of the Operation of the Annapolis Tidal Power Facility. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada Science Advisory Schedule as they become available.

Science Advisory Report 2019/055 (PDF, 785 KB)

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