No abstract

Dams are ubiquitous in coastal regions and have altered stream habitats and the distribution and abundance of stream fishes in those habitats by disrupting hydrology, temperature regime and habitat connectivity. Dam removal is a common restoration tool, but often the response of the fish assemblage is not monitored rigorously. Sedgeunkedunk Stream, a small tributary to the Penobscot River (Maine, USA), has been the focus of a restoration effort that includes the removal of two low-head dams. In this study, we quantified fish assemblage metrics along a longitudinal gradient in Sedgeunkedunk Stream and also in a nearby reference stream. By establishing pre-removal baseline conditions and associated variability and the conditions and variability immediately following removal, we can characterize future changes in the system associated with dam removal. Over 2years prior to dam removal, species richness and abundance in Sedgeunkedunk Stream were highest downstream of the lowest dam, lowest immediately upstream of that dam and intermediate farther upstream; patterns were similar in the reference stream. Although seasonal and annual variation in metrics within each site was substantial, the overall upstream-to-downstream pattern along the stream gradient was remarkably consistent prior to dam removal. Immediately after dam removal, we saw significant decreases in richness and abundance downstream of the former dam site and a corresponding increase in fish abundance upstream of the former dam site. No such changes occurred in reference sites. Our results show that by quantifying baseline conditions in a small stream before restoration, the effects of stream restoration efforts on fish assemblages can be monitored successfully. These data set the stage for the long-term assessment of Sedgeunkedunk Stream and provide a simple methodology for assessment in other restoration projects.

By identifying individual Atlantic salmon (Salmo salar) smolts (age 1+, mean weight 95 g), a tank study with four treatments (n = 175 fish per tank) indicated that maturation as grilse is associated with changes in somatic growth over many months, from July of the first summer in seawater onwards. The grilse rate in both sexes was associated with a relatively high condition factor from July onwards, but was independent of fork length. Food deprivation in either early winter , late winter (February-April, 0.7-4.0°C), or both early and late winter (double deprived) reduced the female grilse rate (p < 0.01) to 4, 7, and 2% versus 18% in the control, whereas male grilse rate was reduced by a lesser degree (p > 0.05), 43, 39, and 33% versus 44% in the control. Mean condition factor among both maturing and immature fish decreased by a similar degree due to food deprivation but from spring onwards increased by a faster rate among incipient grilse. In a large experiment in four sea cages (each n = 3885 fish) using similar food deprivation treatments, the reduction in grilse rate was statistically significant in both sexes: among males, 28-36 versus 43% in the control; among females, 3-4 versus 6% in the control.Résumé : Dans une étude en bassins avec quatre traitements (n = 175 poissons par bassin) dans laquelle des smolts de saumon atlantique (Salmo salar) (âge 1+, poids moyen de 95 g) étaient identifiés individuellement, on a observé que la maturation précoce (madeleineaux) était associée avec des changements dans la croissance somatique sur de nombreux mois, à partir du mois de juillet du premier été en eau de mer. Le taux d'apparition des madeleineaux chez les deux sexes était associé à un coefficient de condition relativement élevé à partir de juillet, mais était indépendant de la longueur à la fourche. La privation de nourriture au début de l'hiver (novembre à décembre, 8,2 à 4,1°C), à la fin de l'hiver (février à avril, 0,7 à 4,0°C) ou durant ces deux périodes (double privation) a réduit le taux d'apparition des madeleineaux femelles (p < 0,01) à 4, 7, et 2% contre 18% chez les témoins considérant que le taux d'apparition des madeleineaux mâles a été réduit par un peu de degré (p > 0,05), 43, 39 et 33% contre 44% chez les témoins. Le coefficient de condition moyen parmi tous les deux mfrissant et non mfrs les poissons a diminué par un degré semblable df à la privation de nourriture mais à partir du printemps a agumenté à une vitesse plus rapide parmi les madeleineaux naissants. Dans une expérience de grande envergure effectuée dans quatre cages marines (n = 3 885 poissons par cage) utilisant les mêmes traitements de privation de nourriture, la réduction du taux d'apparition des madeleineaux a été statistiquement significative chez les deux sexes : dans le cas des mâles, il a été de 28 à 36 contre 43% chez les témoins, et dans le cas des femelles, de 3 à 4 contre 6% chez les témoins.[Traduit par la Rédaction] Duston and Saunders 207

Co‐evolved diadromous fishes may play important roles in key life history events of Atlantic salmon (Salmo salar) in northeastern U.S. rivefine ecosystems. We reviewed available information on the historic and current abundance of alewives (Alosa pseudoharengus), blueback herring (Alosa aestivalis), American shad (Alosa sapidissima), rainbow smelt (Osmerus mordax), and sea lamprey (Petromyzon marinus) for several rivers in Maine. Historically, these diadromous fishes were substantially more abundant and were able to travel much farther inland to spawning and rearing areas in comparison to contemporary conditions. At historic abundance levels, these diadromous fishes likely provided several important functions for Atlantic salmon such as providing alternative prey for predators of salmon (i.e., prey buffering), serving as prey for juvenile and adult salmon, nutrient cycling, and habitat conditioning. Restoring the co‐evolved suite of diadromous fishes to levels that sustain these functions may be required for successful recovery of the last native Atlantic salmon populations in the United States.