Long Term Trends and Outlook for Mountain Sucker in the Black Hills of South Dakota

Article excerpt

ABSTRACT.-

The extirpation of native fishes is a major concern in North America, and an understanding of population trends of imperiled fishes is critical to their management and conservation. Mountain sucker Catostomus platyrhynchus is a stream fish native to the Intermountain Region of western North America, and populations in the Black Hills of South Dakota represent the easternmost range of the species. Recently, stream surveys raised concerns about the status of mountain sucker populations in South Dakota. The purpose of this study was to document the current distribution of mountain sucker in the Black Hills of South Dakota for comparison with historic records. We analyzed stream fisheries survey data collected between 1960 and 2010 and found that mountain sucker density generally declined at three nested spatial scales: sample reach, stream, and watershed. At 14 sample reaches and two streams mountain sucker appear extirpated, whereas in remaining areas they persist in varying densities. In 2009-2010, populations exceeding densities of 0.01 fish.m^sup -2^ persisted only in Whitewood, Elk, Boxelder, and Bear Butte Creeks, and tributaries to Upper Rapid Creek. Our study documents the decline of a native fish in the Black Hills of South Dakota, and a comprehensive ecosystem management approach is needed to mitigate further loss of mountain sucker and co-occurring native species, while at the same time maintaining a highly valued non-native salmonid fishery.

INTRODUCTION

Recent studies documented an increase in the number of imperiled freshwater and diadromous fishes in North America since the late 1980s (Jelks et al, 2008). Causes for declines include habitat loss, overexploitation, hybridization, and competition with introduced species. Other recent literature suggests that the rate ?? extinction for freshwater fauna will increase into the future (Ricciardi and Rasmussen, 1999). Fish extinctions (e.g., Snake River sucker Chasmistes murin) and extirpations (e.g., Colorado pikeminnow Ptychocheilus lucius from the lower Colorado River) in North America are most numerous in the West where reservoir construction, non-native fish introductions and water withdrawals altered habitat and established new predators and competitors for native fishes (Minckley and Douglas, 1991).

The ability to detect and quantify long term population trends is the first step in prioritizing conservation actions for imperiled fishes (Williams, 1991). Population parameters including density, natality, immigration/emigration, and mortality are useful in understanding the dynamics of an imperiled population (Bestgen et al, 2007), and comparing a species' present and historic distribution is critical for addressing changes in the status of a species of interest (e.g., Allendorf and Leary, 1988; Dobson et al, 1997). Quantifying population trends and parameters has been used to assess status and set conservation priorities for a variety of declining taxa including: amphibians (Stuart et al, 2004), birds (Kochert and Steenhof, 2002), mammals (Cofré and Marquet, 1999), and fish (Williams et al, 1989; Jelks et al, 2009).

The current status of mountain sucker Catostomus platyrhynchus throughout its range is secure (G5; Natureserve, 2010), but regional trends suggest that the species is in decline at finer spatial scales. In the Black Hills of Soutii Dakota, recent stream fishery surveys raised concern about potential declines in localized mountain sucker populations and extirpations. Mountain sucker occur throughout the western United States and Canada from southern Saskatchewan and Alberta in the north, south and west to eastern California, and east through the Intermountain region to western Nebraska and the Black Hills of South Dakota (Scott and Crossman, 1973). Across the range, it inhabits cool mountain streams with mosdy rocky substrates (Hauser, 1969; Scott and Crossman, 1973; Sigler and Sigler, 1996), but is also found in large rivers (Smith, 1966), lakes (Baxter and Stone, 1995) and as adfluvial reservoir populations in headwater areas (Erman, 1973; Manin and Erman, 1982; Decker, 1989; Wydoski and Wydoski, 2002). …