Nuhfer A.J.,Hunt Creek Fisheries Research Station |
Wills T.C.,Lake St Clair Fisheries Research Station |
Zorn T.G.,Marquette Fisheries Research Station
North American Journal of Fisheries Management | Year: 2014
We evaluated the effects of steelhead Oncorhynchus mykiss (migratory Rainbow Trout) introduction on the population dynamics of resident Brown Trout Salmo trutta from 1995 to 2008 in a small, low-gradient trout stream. Data on Brown Trout population density, survival, and growth were collected from the treatment section in Hunt Creek, Michigan, where adult steelhead were stocked each spring during 1998-2003, as well as from two reference stream reaches. The presence of steelhead had no apparent effect on the density of age-0 Brown Trout, but the mean density of all age-1 and older (age-1+) Brown Trout year-classes that interacted with juvenile steelhead of the same age was 46% lower than the density of age-1+ year-classes that did not interact with juvenile steelhead of the same age. No differences in density of age-1+ Brown Trout were detected in reference sections between the periods of steelhead presence or absence in the treatment section. Lower annual survival rates for year-classes of age-0 Brown Trout that interacted with steelhead in the Hunt Creek treatment section were the primary reason that density of age-1+ Brown Trout fell to nearly half the levels that existed before steelhead were introduced or after most steelhead had emigrated from the stream. Although our case study showed that the introduction of steelhead into a small, low-gradient stream resulted in lower densities of resident Brown Trout, upstream passage of steelhead into streams with high-quality habitat also offers tremendous potential to increase wild production of juvenile steelhead, thereby reducing fisheries managers' reliance on hatchery-reared fish for stocking the Great Lakes.Received August 16, 2013; accepted January 2, 2014. © 2014 © American Fisheries Society 2014.
Grossman G.D.,University of Georgia |
Nuhfer A.,Hunt Creek Fisheries Research Station |
Zorn T.,Marquette Fisheries Research Station |
Sundin G.,University of Georgia |
Alexander G.,Hunt Creek Fisheries Research Station
Freshwater Biology | Year: 2012
Fisheries models generally are based on the concept that strong density dependence exists in fish populations. Nonetheless, there are few examples of long-term density dependence in fish populations. Using an information theoretical approach (AIC) with regression analyses, we examined the explanatory power of density dependence, flow and water temperature on the per capita rate of change and growth (annual mean total length) for the whole population, adults, 1+ and young-of-the-year (YOY) brook trout (Salvelinus fontinalis) in Hunt Creek, Michigan, USA, between 1951 and 2001. This time series represents one of the longest quantitative population data sets for fishes. Our analysis included four data sets: (i) Pooled (1951-2001), (ii) Fished (1951-65), (iii) Unfished (1966-2001) and (iv) Temperature (1982-2001). Principle component analyses of winter flow data identified a gradient between years with high mean daily winter flows, high daily maximum and minimum flows and frequent high flow events, and years with an opposite set of flow characteristics. Flows were lower during the Fished Period than during the Unfished Period. Winter temperature analyses elucidated a gradient between warm mean, warm minimum and maximum daily stream temperatures and a high number of minimum daily temperatures >6.1°C, and years with the opposite characteristics. Summer temperature analyses contrasted years with warm summer stream temperatures vs years with cool summer stream temperatures. Both YOY and adult densities varied several-fold during the study. Regression analysis did not detect a significant linear or nonlinear stock-recruitment relationship. AIC analysis indicated that density dependence was present in 15 of 16 cases (four population segments×four data sets) for both per capita rate of increase (w i values 0.46-1.00) and growth data (w i values 0.28-0.99). The almost ubiquitous presence of density dependence in both population and growth data is concordant with results from other trout populations and other studies in Michigan. © 2012 Blackwell Publishing Ltd.