Habitat effects on recruitment, population limitations, and recovery potential in an endangered stream fish

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 81; no. 10; pp. 1468 - 1480
• Main Authors: Gray, John C., Rosenfeld, Jordan S.
• Format: Journal Article
• Language: English
• Published: Ottawa Canadian Science Publishing NRC Research Press 01.10.2024
• Subjects: Dissolved oxygen; Enclosures; Encroachment; Endangered species; Freshwater fish; Habitat utilization; Habitats; High temperature; Juveniles; Phalaris arundinacea; Population number; Recruitment; Riffles; Spawning; Substrates; Temperature preferences; Variation; Vegetation; Vegetation cover; Water conservation; Water temperature
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-2024-0039

Elucidating the habitat-related processes driving variation in juvenile recruitment and population fluctuation is crucial for the conservation of freshwater fishes, particularly for species at risk, where recruitment variation increases at small population size. We used a combination of instream enclosure experiments and habitat use observations to investigate between-stream variation in recruitment of juvenile Nooksack Dace ( Rhinichthys cataractae sp. cataractae), a federally endangered stream-dwelling minnow endemic to the lower Fraser Valley of British Columbia, Canada. There was no evidence for a recruitment bottleneck associated with high water temperature or low dissolved oxygen in spawning riffles at the egg incubation stage, or during a two week juvenile growth experiment in enclosures, although larval dace growth was positively related to temperature. However, immediately post-hatch dace showed a very strong preference for shallow (<5 cm deep), fine substrate marginal shoal habitat with no overhanging or instream vegetation cover, which was associated with well-developed pool-riffle channel structure. Shallow marginal rearing habitat was absent in the stream experiencing recruitment failure, where encroachment by invasive reed canarygrass ( Phalaris arundinacea) created homogenous steep-bank habitat with heavy instream vegetation cover, implicating loss of critical marginal rearing habitat as the recruitment bottleneck.