Challenges for Diadromous Fishes in a Dynamic Global Environment

Restoration of Diadromy in an Endangered Fish: Do Atlantic Whitefish Covet the Sea?

Adam M. Cook and Paul Bentzen

doi: https://doi.org/10.47886/9781934874080.ch73

Diadromy is a tactic employed by many fish species around the globe. However, its significance as a strategy integral to species survival is often unknown. Numerous examples in the literature document cases where species, generally regarded as diadromous, harbor populations or cohorts that are freshwater residents and never descend rivers, or marine contingents that never fully ascend estuaries (Skaala and Nævdal 1989; Tzeng et al. 2000). As such, diadromy may be viewed as a plastic trait only displayed by some individuals or populations. Situations arise, occasionally, where the only remaining population of a diadromous species is found in a land-locked form. Prior to restoring diadromy to this population, information is required on their propensity for saltwater.

Atlantic whitefish Coregonus huntsmani is an endangered, endemic Nova Scotian species documented only in the Petite Riviere and the Tusket River. Historically, Atlantic whitefish in the Tusket River made diadromous upriver migrations in autumn. The form of diadromy used by this population was unknown as spawning locations were never identified, and unfortunately, this population was extirpated at some time during the 1970s or early 1980s (Edge and Gilhen 2001). Diadromy in the Petite Riviere population could not be quantified as the river has been dammed, with no fish passage, for the past 30–35 years (Bradford et al. 2004). The importance of diadromy to the population, and hence species recovery, is not known.

The aim of the present work was twofold: first, to determine the form of diadromy exploited by Atlantic whitefish by testing salinity tolerance of gametes, and second, to determine the salinity tolerance and preference of developing larvae and juveniles.

Three Atlantic whitefish males were stripped manually of milt. Three treatments were performed on each batch of milt, such that 1 μL of milt was activated in one drop of either freshwater, brackish water, or seawater, on a hanging drop microscope slide. Each treatment was replicated three times for each batch of milt. The mixture was observed and video recorded, while active, at 1003 magnification.