Estimation de la capacité biotique du gaspareau (Alosa pseudoharengus) dans le bassin hydrographique de la rivière Skutik (Sainte-Croix) en fonction de l'habitat

Abstract

Alewife are a small anadromous, iteroparous fish native to the Skutik River watershed that spawn in lakes and slow flowing bodies of water. Alewife productivity is partly determined by the density dependence of the juvenile life stage in freshwater lakes. Nursery areas for alewife in the Skutik River were estimated using satellite imagery and shapefiles from the National Hydrographic Network. Theoretical carrying capacity and theoretical spawning stock biomass in the absence of anthropogenic effects (SSB0) for Skutik River alewife were estimated by applying the meta-analysis of the habitat carrying capacity for alewife to the estimated nursery area. Biological reference points in accordance with the Fisheries Management framework were not estimated in this process. Methods from a previously reviewed meta-analysis of the habitat carrying capacity for alewife were applied according to the framework for the assessment of river herring. The Skutik River watershed contains 104,762 acres of accessible or potentially accessible nursery area, 121 acres of naturally inaccessible nursery area, and 3,403 acres of artificially inaccessible nursery area which combine for a total of 108,286 acres of alewife nursery area, when including waterbodies greater than 10 acres. The theoretical carrying capacity and SSB0 for accessible and potentially accessible nursery area was estimated to be 21,817 mt (10th percentile of 12,734 mt, 90th percentile of 37,380 mt) and 20,661 mt (10th percentile of 12,059 mt, 90th percentile of 35,399 mt), respectively. A number of uncertainties are outlined, with the largest being the wide range of the confidence intervals for theoretical carrying capacity and SSB0 derived from the meta-analysis of the habitat carrying capacity for alewife, and that the nursery area and alewife population of the Skutik River are typical and well-represented by the populations modeled in the meta-analysis. The estimates of theoretical carrying capacity and SSB0 presented here are calculated under the assumption of 100% fish passage at anthropogenic barriers, where passage efficiency less than that will limit population growth. It is unlikely that fish passage will be 100% at any barrier. The nursery area quantified here captures the nursery area as it currently is, including the potential nursery area that was artificially created by building dams and impoundments throughout the watershed. Any future changes to the quantity of nursery area by removing dams or providing access to currently inaccessible nursery areas would require updating the estimated quantities herein.