Brook Trout Removal as a Conservation Tool to Restore Eagle Lake Rainbow Trout

Abstract

Abstract.-Nonnative brook trout Salvelinus fontinalis are abundant in Pine Creek and its main tributary, Bogard Spring Creek, California. These creeks historically provided the most spawning and rearing habitat for endemic Eagle Lake rainbow trout Oncorhynchus mykiss aquilarum. Three-pass electrofishing removal was conducted in 2007-2009 over the entire 2.8-km length of Bogard Spring Creek to determine whether brook trout removal was a feasible restoration tool and to document the life history characteristics of brook trout in a California meadow stream. After the first 2 years of removal, brook trout density and biomass were severely reduced from 15,803 to 1,192 fish/ha and from 277 to 31 kg/ha, respectively. Average removal efficiency was 92-97%, and most of the remaining fish were removed in the third year. The lack of a decrease in age-0 brook trout abundance between 2007 and 2008 after the removal of more than 4,000 adults in 2007 suggests compensatory reproduction of mature fish that survived and higher survival of age-0 fish. However, recruitment was greatly reduced after 2 years of removal and is likely to be even more depressed after the third year of removal assuming that immigration of fish from outside the creek continues to be minimal. Brook trout condition, growth, and fecundity indicated a stunted population at the start of the study, but all three features increased significantly every year, demonstrating compensatory effects. Although highly labor intensive, the use of electrofishing to eradicate brook trout may be feasible in Bogard Spring Creek and similar small streams if removal and monitoring are continued annually and if other control measures (e.g., construction of barriers) are implemented. Our evidence shows that if brook trout control measures continue and if only Eagle Lake rainbow trout are allowed access to the creek, then a self-sustaining population of Eagle Lake rainbow trout can become reestablished.

Restoration of native Mediterranean brown trout Salmo cettii Rafinesque, 1810 (Actinopterygii: Salmonidae) populations using an electric barrier as a mitigation tool

“…Chemical methods include the use of the piscicides antimycin, rotenone or ozone, and have mainly been used to eradicate exotic fish populations, or fish which may spread disease, in order to protect threatened or endangered species (Gresswell 1991;Demong 2001;Allen et al 2006;Buley et al 2017). Mechanical methods include the use of gill netting (Knapp & Matthews 1998;Tiberti et al 2017), and repeated electrofishing (Kulp & Moore 2000;Carmona-Catot et al 2010;. The use of chemical methods for eradication is often controversial due to harmful effects on nontarget species, and lethal effects on aquatic invertebrates and the larval forms of amphibians (Mangum & Madrigal 1999;Ling 2003;Buley et al 2017).…”

“…Over the last two decades, native salmonid species have been the focus of important conservation projects, owing to population reduction and extinction in many countries Araguas et al 2008Araguas et al , 2009Carmona-Catot et al 2010;Caputo Barucchi et al 2015). In particular, the introduction of non-native Atlantic trout has included foreign genes into Mediterranean brown trout populations, and has altered the traits of the native gene pool (Berrebi et al , 2017Nonnis Marzano et al 2003;Caputo et al 2004;Querci et al 2013;Gratton et al 2014;Splendiani et al 2016).…”

Long-term captive breeding does not necessarily prevent reestablishment: lessons learned from Eagle Lake rainbow trout

“…They were soon abundant in areas that ELRT used for spawning and rearing; today densities of brook trout average ca. 16,000 ha -1 , with local densities up to 30,000 ha -1 , which are among the highest recorded for California (Carmona-Catot 2009). It is likely that brook trout further suppressed the already diminished ELRT population through competition and perhaps predation on early life stages.…”

“…In addition, small numbers of native Tahoe sucker, Lahontan redside and speckled dace are present (Carmona-Catot et al 2010). The occurrence of ELRT is described in the next section.…”

“…The ability of large numbers of fish to make spawning migrations has still not been conclusively demonstrated although there is evidence it is possible (Pustejovsky 2007;Thompson et al 2007). There is ample evidence that juvenile ELRT can persist and grow in small numbers even in the presence of dense populations of aggressive, predatory brook trout (Carmona-Catot et al 2010). Brook trout, however, clearly present an obstacle to full recovery, while also demonstrating the capability of Pine Creek for supporting high densities of juvenile ELRT in the absence of brook trout.…”