Academic journal article The American Midland Naturalist

Characteristics of a Naturalized Kokanee Salmon Oncorhynchus Nerka Population in Atypical Habitat

Academic journal article The American Midland Naturalist

Characteristics of a Naturalized Kokanee Salmon Oncorhynchus Nerka Population in Atypical Habitat

Article excerpt

INTRODUCTION

The kokanee salmon is a dwarf, landlocked, freshwater form of the sockeye salmon (Oncorhynchus nerka) native to the Pacific coast of northwestern North America and northeastern Asia (Scott and Crossman, 1973). It is a coldwater lake species that prefers water temperatures below 18 C and dissolved oxygen levels above 6 mg/1 and that cannot tolerate temperatures above 24-25 C and dissolved oxygen below 2.5-4 mg/1 (Brett, 1952, 1971; Davis, 1975; Brett and Blackburn, 1981; Ruggerone, 2000; Eliason el al., 2011; Chen et al., 2013). The kokanee salmon is a popular sportfish and a potentially important prey for larger species, and consequently it has been widely and successfully introduced into many deep lakes and reservoirs in mountainous areas of western North America (Scott and Crossman, 1973; Sigler and Sigler, 1996; Moyle, 2002; Wydoski and Whitney, 2003). Numerous introductions have also been attempted in eastern North America, but establishment there has been limited, and only a handful of naturalized populations are known east of the Mississippi River (Scott and Crossman, 1973; Smith, 1985). Lakes where kokanee salmon have been successfully introduced tend to have relatively large amounts of cold water habitat during summer because of either their large surface (> 100 ha) area and great depth (> 30 m) or their location in cooler climates at high elevation (> 1000 m) or high latitude (> 50°N). Florence and Upper Bass lakes, connected water bodies in northeastern Wisconsin, have perhaps the most unlikely naturalized populations in eastern North America, the lakes being much smaller, shallower, lower elevation, and southerly and having much less suitable oxythermal habitat in the water column during summer stratification than typical kokanee salmon waters. Yet kokanee salmon have persisted in these two lakes without stocking for more than 50 yr (Lyons el al., 2000).

The ability of kokanee salmon to survive in marginal habitats such as Florence and Upper Bass lakes has implications for understanding the response of the species to environmental impacts that will likely reduce habitat suitability for coldwater lake species, especially increasing lake eutrophication and a warming climate (e.g., Colby et al., 1972; Ficke et al, 2007; Berge, 2009; Martins et al, 2011; Young, 2016). To better understand possible reasons for its persistence, the kokanee salmon population in Florence Lake and its tributary, Drew Creek, were studied from 1997-2016. Objectives were to characterize habitat use and population attributes, particularly size and age.

MATERIALS AND METHODS

STUDY AREA

Florence and Upper Bass lakes and their tributary, Drew Creek, occur in the upper portion of the Wolf River drainage of the Lake Michigan basin in northeastern Wisconsin (Fig. 1). Both lakes are spring-fed, relatively small and shallow, and mesotrophic (Florence: Latitude 45.123°N, 88.890°W, 21.4 ha surface area, 7.6 m maximum depth, elevation 381 m; water clarity trophic state index = 45 [Carlson, 1977]; Upper Bass: 45.111°N, 88.879°W, 49.8 ha, 15.5 m, 380 m; trophic status index = 42). Drew Creek is a third-order cold water stream (summer water temperature < 24 C) with extensive spring input and a baseflow of approximately 0.5 m3/s that enters Florence Lake and then exits the lake and flows about 1 km to Upper Bass Lake. Upper Bass Lake then outlets to the West Fork of the Wolf River. There are no barriers to movement between the lakes or into or out of Drew Creek, but we have no data on fish movements except from Florence Lake into Drew Creek. Drew Creek upstream of Florence Lake has habitat that, based on qualitative observations and descriptions in Parson and Hubert (1988), appears suitable for kokanee salmon spawning, but the channel between Florence Lake and Upper Bass Lake is slow moving with primarily soft sediments (sand and silt) and is not suitable for spawning.

Kokanee salmon were introduced into Florence and Upper Bass lakes accidentally. …

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