Prosopium coulterii (Eigenmann and Eigenmann, 1892)
Basis for Listing
The Pygmy Whitefish (Prospium coulterii) is restricted to deep waters of Lake Superior, where it was not discovered until 1952. This population is disjunct and more than 1000 miles (1609 km) from the nearest population in western Montana. The species is widely distributed but rare in Lake Superior (Becker 1983). It is currently listed as special concern in Wisconsin and abundance trends from Lake Superior are uncertain (Lyons et al. 2000). The species’ isolated population and its rarity in Lake Superior prompted listing the Pygmy Whitefish a special concern species in Minnesota in 2013.
The Pygmy Whitefish is a small fairly cylindrical whitefish that is typically 10-13.5 cm (3.9-5.3 in.) total length, withna maximum of about 17.5 cm (6.9 in.). Distinguishing characteristics include an adipose fin, lateral rows of diffuse round spots, about the size of the pupil but faint in specimens greater than 10 cm (3.9 in.) total length, 16-20 short gill rakers, single flap dividing nostrils, subterminal mouth lacking jaw teeth, and cycloid scales that usually range 56-66 in the lateral line, 33-37 scales around the body, and 16-20 around the caudal peduncle. Breeding males exhibit numerous body tubercles, while females have few (Lyons et al. 2006).
Pygmy Whitefish inhabit the deep cold waters of Lake Superior. In Michigan’s Keeweenah Bay, specimens were most abundant at 46-71 m (151-233 ft.). Young of the year prefer shallower depths, from 24 to 33 m (79 to 108 ft.) (Becker 1983).
Biology / Life History
Pygmy Whitefish spawn in Lake Superior during November and December. Some males reach sexually maturity as early as their second growing season. At least 50% of females are sexually mature in their third season. Young of the year exhibit rapid growth. Specimens collected in October ranged from 47-51 mm (1.9-2.0 in.). Females live to nine years old, males to seven. Females are larger than males beginning at age three (Stewart et al. 2016)
Conservation / Management
Long-term monitoring of Pygmy Whitefish is needed to study the effects of climate change and detect impacts on the species’ abundance, distribution, age, and growth. In 2008, Department of Fisheries and Oceans Canada biologists collected the species from Winnange Lake about 35 miles (56 km) east of Kenora, Ontario, and 200 miles (322 km) northwest of Lake Superior. This occurrence suggests additional surveys of large and deep lakes between the Lake Superior and western populations may reveal the species has a more continuous distribution than previously assumed (Schmidt and Rohde 2012). That saie, recent cisco (Coregonus spp.) surveys of 75 lakes in northeastern Minnesota and southwestern Ontario, using similar sampling gear and methods, did not collect Pygmy Whitefish (D. Etnier, pers. comm.).