Assessing Changes in Amphibian Population Dynamics Following Experimental Manipulations of Introduced Fish

Abstract

Sport-fish introductions are now recognized as an important cause of amphibian decline, but few researchers have quantified the demographic responses of amphibians to current options in fisheries management designed to minimize effects on sensitive amphibians. Demographic analyses with mark-recapture data allow researchers to assess the relative importance of survival, local recruitment, and migration to changes in population densities. I conducted a 4-year, replicated whole-lake experiment in the Klamath Mountains of northern California (U.S.A.) to quantify changes in population density, survival, population growth rate, and recruitment of the Cascades frog (Rana cascadae) in response to manipulations of non-native fish populations. I compared responses of the frogs in lakes where fish were removed, in lakes in their naturally fish-free state, and in lakes where fish remained that were either stocked annually or no longer being stocked. Within 3 years of fish removals from 3 lakes, frog densities increased by a factor of 13.6. The survival of young adult frogs increased from 59% to 94%, and realized population growth and recruitment rates at the fish-removal lakes were more than twice as high as the rates for fish-free reference lakes and lakes that contained fish. Population growth in the fish-removal lakes was likely due to better on-site recruitment of frogs to later life stages rather than increased immigration. The effects on R. cascadae of suspending stocking were ambiguous and suggested no direct benefit to amphibians. With amphibians declining worldwide, these results show that active restoration can slow or reverse the decline of species affected by fish stocking within a short time frame.

The importance of phenotypic diversity in conservation: Resilience of palmate newt morphotypes after fish removal in Larzac ponds (France)

“…For instance, the removal of fish from lakes allowed the restoration of frog and salamander populations (Vredenburg 2004;Knapp et al 2007;Pope 2008). This resilience was enhanced in many species of bi-phasic amphibians that are able to disperse on land, and can thus colonise managed aquatic habitats from nearby wetlands.…”

“…However, amphibians could rapidly recover, reaching the same population sizes as in control lakes in only a few years (Funk and Dunlap 1999;Vredenburg 2004;Knapp et al 2007;Pope 2008). The exact dates of fish introduction and extirpation are not known for all sites in Larzac.…”

“…Therefore, fish introductions might have caused populations to lose their potential for paedomorphosis (e.g., alleles for delayed metamorphosis: Voss et al 2012). As shown in frogs (Vredenburg 2004;Knapp et al 2007;Pope 2008), natural populations are thus likely to be recolonised by metamorphic dispersers, but whether the progeny of newts or salamanders could again exhibit the rare paedomorphosis developmental pathway has not been yet demonstrated in the wild. This is a crucial pattern to determine the value of conservation efforts for maintaining such uncommon or endangered phenotypes.…”

The Presence of Micropterus Salmoides (Largemouth Bass) Influences the Populations of Rana Draytonii (California Red-Legged Frog) and Pseudacris Regilla (Pacific Treefrog) in Two Ponds in Santa Barbara County, California

“…Nevertheless, some declines caused by alien species may be reversed relatively quickly (Pope 2008;Knapp et al, 2007;Mullin 2004;Vredenburg 2004). In California, reversal of the negative effects of alien species on amphibians has been suggested by a number of studies showing that the removal or disappearance of the alien species results in the recovery of local amphibian populations (Pope et al, 2008;Knapp et al, 2001;Knapp 2005;Vredenburg 2004).…”

“…In California and much of western North America, amphibian population declines are occurring, and several causal factors have been proposed including disease Kiesecker et al, 2001;Blaustein et al, 2005;, increased use of pesticides and air pollution (Davidson et al, 2001;Relyea and Mills 2001;Kiesecker 2002), habitat destruction (Davidson et al, 2002), over-exploitation (Jensen and Camp 2003;Jennings and Hayes 1985), climate change (Pounds et al, 1999), UV-B radiation Anzalone et al, 1998;Blaustein et al,1998), and alien predators and competitors (Kupferburg 1997;Knapp and Matthews 2000;Vredenburg 2004;Pope 2008). Recent studies have suggested that amphibian declines are potentially influenced by a number of contextspecific interactions of multiple stressors and synergisms between these causal factors (Blaustein and Kiesecker 2002;Kiesecker 2002;Pounds et al, 2006).…”