Challenges Associated with Eradicating Invasive Rodents from Islands: Lessons Learned

Abstract

Removal of introduced rats from islands is a proven and powerful conservation tool that can help restore ecosystem functioning and/or processes. Haida Gwaii, British Columbia, Canada, is an isolated marine archipelago with distinct flora and fauna that have evolved during 14,000 years of isolation from the mainland. Approximately 1.5 million seabirds from 13 species nest on the islands of Haida Gwaii, including 50% of the global ancient murrelet population, a federally designated species at risk in Canada. Within Gwaii Haanas National Park Reserve and Haida Heritage Site (located at the southern end of Haida Gwaii) there are 9 designated Important Bird Areas (IBAs), established primarily to denote important seabird nesting sites. However, unintentional historical introductions of rats to islands within IBAs and throughout Haida Gwaii have led to the demise of several seabird nesting colonies. In September 2013, Parks Canada Agency, in partnership with Coastal Conservation and Island Conservation, implemented Canada's first aerial broadcast eradication of black rats from two islands within the Ramsay Island and Northern Juan Perez Sound Islands IBA, where seabird colonies and ecosystem processes have been negatively impacted by this species. The eradication of black rats from Murchison and Faraday Islands posed several challenges including ensuring adequate bait density to maximize the probability of eradication success while minimizing risks to native species. Our planning efforts focused on addressing bait competition by non-target species, the consequence of bait interception by the forest canopy, minimizing bait entering the marine environment, mitigating potential negative impacts to non-target species, and determining the ideal timing for the eradication operation. We present here a summary of these challenges and the measures that were implemented to address them. Proc. 26 th Vertebr. Pest Conf. (R. M. Timm and J. M. O'Brien, Eds.) Published at Univ. of Calif., Davis. 2014. Pp. 118-124.

RapidRat: Development, validation and application of a genotyping-by-sequencing panel for rapid biosecurity and invasive species management

“…To meet seabird recovery goals and to protect ecological and cultural integrity [35], Parks Canada and other agencies started managing invasive rats in the 1990s primarily through whole-island eradications. Since 1997, invasive rats have been successfully eradicated from five islands throughout the archipelago (Fig 1); however, brown rats were re-detected on the Bischof Islands following two eradication attempts in 2003 and 2011, and brown rats were detected on Faraday and Murchison Islands four years after a successful black rat eradication in 2013 [29,30,36,37]. Brown rats have now also spread to Hotspring, Ramsay, and Agglomerate Islands, all of which have been historically rat-free (C. Bergman, pers.…”

Rattus population genomics across the Haida Gwaii archipelago provides a framework for guiding invasive species management

“…using poison regimes aimed at reduction rather than removal) is ineffective in species with high fecundity, density-dependent reproduction and the capacity to adapt through bait resistance or neophobia (Damin-Pernik et al, 2017;Emlen, Stokes, & Winsor, 1948;Takács, Kowalski, & Gries, 2016;Zipkin, Kraft, Cooch, & Sullivan, 2009). Both species of rats were successfully eradicated from the northern islands of Langara, Lucy and Cox (1997); the southern St. James Island (1998); and the east-central island of Arichika (2011) (Gaston et al, 2008;Gill, Wein, Howald, & McClelland, 2014;Golumbia, 1999;Kaiser et al, 1997). Black rats were successfully eradicated from Faraday Island and Murchison Island (2013), but they have both since been invaded by brown rats.…”

“…and the east-central island of Arichika (2011) (Gaston et al, 2008;Gill, Wein, Howald, & McClelland, 2014;Golumbia, 1999;Kaiser et al, 1997). Black rats were successfully eradicated from Faraday Island and Murchison Island (2013), but they have both since been invaded by brown rats.…”

Managing non-target wildlife mortality whilst using rodenticides to eradicate invasive rodents on islands

“…On Murchison and Faraday Islands, Canada, prior to rodent eradication, removal of Sitka black-tailed deer (Odocoileus hemionus sitkensis) through planned culls was conducted. This was done to minimize risk of secondary poisoning for native wildlife species such as bald eagles, common ravens (Corvus corax), black bears (Ursus americanus) and other wildlife species that could scavenge deer carcasses (Gill et al 2014). Once eradication was completed, after 418 hours search time, common ravens (n = 11) were the only scavenger species recovered on Murchison and Faraday.…”