Under‐Ice Population Density Estimation of Alaska Blackfish

Abstract

The Alaska Blackfish Dallia pectoralis is an understudied but ecologically important mudminnow occurring in lentic ecosystems of subarctic and Arctic Alaska. We sampled a population of Alaska Blackfish during the winter months in an upland pond near Fairbanks, Alaska, and we used a simple mark–recapture estimator to provide the first population estimate for this species. We found that Alaska Blackfish density in the pond was approximately 0.27 individuals/m2, equating to an estimated biomass of 15 g/m2 of pond surface area, which is similar to density estimates reported for other mudminnow species. We tested capture methods and found that under‐ice minnow trapping was a poor method during early winter (September–December) but was highly effective near methane sumps and areas of high muskrat Ondatra zibethicus activity in late winter (March–April). Qualitatively, nearshore minnow trapping, seining, and kicknetting during the ice‐free season were less effective than under‐ice trapping. Cursorily, pelvic fin clips were more effective for batch marking of Alaska Blackfish than two types of subcutaneous tags, given the high numbers of individuals we captured and the species’ relatively small body size and dark skin, which hindered tag visualization. We demonstrated that Alaska Blackfish can occur at high densities in their typical habitat, underscoring their importance as forage fish in Alaskan freshwater ecosystems that support subsistence and sport fisheries for piscivorous fishes. Extending this approach across the geographic range of Alaska Blackfish will improve understanding of the ecological role of this species in the varying aquatic ecosystems where it occurs.

How do muskratsOndatra zibethicusaffect ecosystems? A review of evidence

“…Alaska blackfish Dallia pectoralis and catfish Ictalurus spp. are associated with winter activities of muskrats, because muskrat movements maintain open, well‐oxygenated water during winter (Errington 1957, 1961, 1963, Fraley et al 2018). Smaller fish species, such as eastern mudminnow Umbra pygmaea , use muskrat burrows as refugia (Bean 1903).…”

Distribution and Characteristics of Blackwater Rivers and Streams of the Contiguous United States

“…The term “blackwater” is commonly used to describe low‐gradient rivers and streams with characteristically tea‐colored waters due to high levels of tannins from decaying vegetation. Other terms used globally to describe these systems include “tannic” (Fraley et al., 2018; Largier, 1986), “brownwater” (Benedetti et al., 2006; Clair & Freedman, 1986; Lotzkes et al., 2021; Stahle et al., 1985), “humic” (Heikkinen, 1994), and “stained” (McKinley, 2013; Waldo, 2019). Blackwater rivers and streams exist around the world with substantial numbers existing in Africa (Anwana et al., 2021; Thieme et al., 2005), Asia (Alkhatib et al., 2007; Lotzkes et al., 2021), Europe (Grzybkowska et al., 1996; Heikkinen, 1994), North America (Benke & Wallace, 2015; Meyer, 1990; Zampella et al., 2007, 2008), and South America (Duncan & Fernandes, 2010; Ríos‐Villamizar et al., 2013; Vegas‐Vilarrubia et al., 1988).…”