Invasive Vertebrate Species Research Articles

Optimising the application of multiple-capture traps for invasive species management using spatial simulation.

Internationally, invasive vertebrate species pose a significant threat to biodiversity, agricultural production and human health. To manage these species a wide range of tools, including traps, are used. In New Zealand, brushtail possums (Trichosurus vulpecula), stoats (Mustela ermine), and ship rats (Rattus rattus) are invasive and there is an ongoing demand for cost-effective non-toxic methods for controlling these pests. Recently, traps with multiple-capture capability have been developed which, because they do not require regular operator-checking, are purported to be more cost-effective than traditional single-capture traps. However, when pest populations are being maintained at low densities (as is typical of orchestrated pest management programmes) it remains uncertain if it is more cost-effective to use fewer multiple-capture traps or more single-capture traps. To address this uncertainty, we used an individual-based spatially explicit modelling approach to determine the likely maximum animal-captures per trap, given stated pest densities and defined times traps are left between checks. In the simulation, single- or multiple-capture traps were spaced according to best practice pest-control guidelines. For possums with maintenance densities set at the lowest level (i.e. 0.5/ha), 98% of all simulated possums were captured with only a single capacity trap set at each site. When possum density was increased to moderate levels of 3/ha, having a capacity of three captures per trap caught 97% of all simulated possums. Results were similar for stoats, although only two potential captures per site were sufficient to capture 99% of simulated stoats. For rats, which were simulated at their typically higher densities, even a six-capture capacity per trap site only resulted in 80% kill. Depending on target species, prevailing density and extent of immigration, the most cost-effective strategy for pest control in New Zealand might be to deploy several single-capture traps rather than investing in fewer, but more expense, multiple-capture traps.

Invasive Vertebrate Species and the Challenges of Management

Invasive vertebrates have had significant effects on native species, ecosystem processes, human health and economies around the world for more than 200 years. However, in the last 30 years, the breadth and impact of invasive specie s has accelerated with the growth and integration of high speed transportation networks. The effects of many non -native species are often difficult to predict prior to establishment. Current efforts to manage invasive species can be broken into the areas of preventio n of introduction and detection of incipient populations, documentation of impacts, and development and implementation of management tools. We address various aspects of these areas under the broad headings of 1) invasiveness and pathways, and 2) impacts, managements, and challenges. One of the biggest challenges of invasive species management is the lack of interest and resources to manage species before they are established. Hence, few tools exist to manage populations once a population is established. As such, much of the focus of current research is dedicated to identifying the impact of species and the development of management tools. Further, these new tools must not only be effective but also adaptable to the ever changing dynamics of the economic, social, and ecological aspects of the locality invaded. The symposia at this conference on various invasive vertebrates highlight both successful and unsuccessful management efforts, investigations to determine the full impact of invasive specie s, and the development of novel control techniques.

Faster but Not Stickier: Invasive House Geckos Can Out-Sprint Resident Mournful Geckos in Moorea, French Polynesia

The House Gecko, Hemidactylus frenatus, is one of the world's most invasive vertebrate species and is spreading rapidly across the South Pacific, displacing other species of geckos that are native or were already resident. We studied the adhesion and locomotor capabilities of H. frenatus and the resident Lepidodactylus lugubris on the island of Moorea in French Polynesia where they are syntopic. Our goal was to determine whether H. frenatus could stick or sprint faster than L. lugubris, two types of performance measures that could underlie superiority of H. frenatus in foraging and agonistic interactions hypothesized in other studies. The clinging ability of H. frenatus and L. lugubris are comparable suggesting that the potential for sticking to vertical and over-hanging surfaces as geckos move through their environments does not differ between species. In contrast, H. frenatus have maximal sprint speeds that are approximately fourfold higher than L. lugubris, an advantage in speed that is even greater than that measured previously for the two species running on horizontal surfaces. Proposed superiority in foraging and agonistic interactions of H. frenatus compared to L. lugubris are potentially traceable to performance characteristics such as adhesion and locomotion. We demonstrate that comparatively high maximal locomotor speeds may contribute to the observed success of H. frenatus over resident geckos in French Polynesia, and possibly in other areas where they have been introduced.

Minimising number killed in long-term vertebrate pest management programmes, and associated economic incentives

AbstractManagement of invasive vertebrate species often requires the use of lethal control tools such as toxins, traps, or shooting. However, because these pest species are sentient and have the capacity to suffer, the application of such tools raises concerns about welfare impacts. To address such concerns, research, policy and regulation have focused most often on the welfare impacts (humaneness) of the tools at the individual animal level (ie the ‘quality’ of the impact) with no attempt to assess welfare at the population level (ie the ‘quantity’ of the impact). Because control programmes often target large numbers of animals, we suggest that when the welfare costs of pest control operations and strategies are being evaluated, the numbers of individuals involved should be considered in addition to the intensity and duration of individual suffering. We explore this concept using a modelling framework and three New Zealand case studies (brushtail possums [Trichosurus vulpecula], ship rats[Rattus rattus], and Bennett's wallabies[Macropus rufogriseus])to assess the extent to which typical control strategies used by land managers influence the numbers of animals killed. We test whether a predicted relationship between numbers killed and position on the population growth curve holds across these scenarios, and identify whether it would be economically viable for end-users to adopt more welfare-friendly control strategies (ie those that kill fewer individuals to achieve the required management outcomes) for these pest species, or whether some form of incentive would be required. Computer modelling showed that for four simulated brushtail possum control strategies, the number of animals killed on a 1,000-ha area over 30 years ranged from approximately 13,000 to 26,000. Similarly, for two ship rat control strategies, numbers killed over a 20-year period were 977 for an aerial strategy versus 1,517 for a ground-based strategy. For both species, the strategies that killed fewest animals generally also cost the least. For Bennett's wallabies, because farmers only carry out control for production benefits, the control strategy they are most likely to select would result in the highest number of wallabies killed. To reduce the number of wallabies killed while allowing farmers to achieve some production benefits, farmers would need to receive some additional financial benefit. The concept of welfare incentive then raises questions such as ‘what willingness is there to pay for increased welfare’ and ‘to what extent can reducing control costs substitute for incentive payments in reducing numbers killed?’

Ecological Restoration of Sub-Antarctic Macquarie Island

Author(s): Springer, Keith | Abstract: Invasive vertebrate species have had devastating impacts on the flora, fauna and landforms of Macquarie Island over a period of 200 years. Following the successful eradication of weka by 1989 and feral cats by 2001, planning for the eradication of ship rats, house mice, and European rabbits began in 2004. Funding of AUD$24.7M was secured in 2007 for a multi-year project based on aerial baiting targeting rabbits and rodents followed by ground hunting targeting surviving rabbits. The first aerial baiting attempt in 2010 was abandoned due to unfavourable weather and shipping delays. The degree of non-target seabird species mortality from limited baiting in 2010 led to a renewed examination of non-target mitigation options. Rabbit Haemorrhagic Disease Virus (RHDV) was introduced in February 2011 to reduce the pre-baiting rabbit population and thus minimise non-target mortality amongst scavenging seabirds. Aerial baiting resumed in May 2011 using 4 AS350 helicopters and a team of 27 people, and was completed by July 2011. No rodents have been detected post-baiting, and the estimated rabbit population of 150,000 has been reduced to fewer than 30 at the conclusion of baiting. The rabbit hunting phase commenced in July 2011 using a team of 15 hunters and 12 dogs and is ongoing, with 3 rabbits accounted for. Hunting and monitoring is expected to take a total of 5 years post-baiting and will be based on annual progress reviews. A minimum of 2 years monitoring will be conducted. Rodent detection dogs will deploy in 2013 to assist in determining rodent eradication success. Six months after baiting, vegetation recovery was already evident, and increased burrownesting seabird activity has also been observed in the first breeding season post-baiting.

Applying the 3Rs (Reduce, Refine, and Replace) to Vertebrate Pest Control in New Zealand

New Zealand has many invasive vertebrate species that adversely affect native biota, compete with livestock, and spread diseases. Large-scale management of the most critical pests is achieved mainly by lethal control. This includes aerial application of the controversial toxin sodium fluoroacetate (1080), despite vociferous opposition from those concerned about potential non-target deaths, environmental contamination, and animal welfare impacts. We have borrowed a framework from animal welfare science, namely the ‘3Rs’ (reduction, refinement, and replacement), to address some of the concerns about the use of aerial poisoning while sustaining its cost-efficiency. The first aim was to reduce the amount of toxin used so that undesirable nontarget impacts are minimised. A range of projects have: 1) developed a method to identify the high-risk habitat within a landscape that needs to be targeted and, equally importantly, the low-risk habitat over which toxic bait does not need to be sown; and 2) optimised the combinations of prefeeding, sowing rate, and bait distribution to achieve the desired percentage kills at the lowest cost and lowest sowing rate of poison bait. To address the second aim, refining toxin use, we have improved target specificity by developing repellents to minimise unintended bykill of non-target species such as deer, and by identifying long-term strategies that minimise the total number of animals killed. The final aim, replacement of 1080, focuses on the search for alternatives, such as fertility control. It also involves development of complementary tools, such as tuberculosis vaccines, that may reduce the frequency or need for repeated use of 1080. This integrated ‘3Rs’ approach has quickly led to changes to operational practice by management agencies, with some operations now using up to 92% less toxic bait than usual, and other operations switching from aerial 1080 poisoning to ground-based non-1080 approaches for ongoing control. Looking forward, the ‘3Rs’ approach offers a framework for continuous improvement in the use of control tools for a wide range of species, whilst also providing a clear pathway to complementary or alternative approaches.

Emerging Challenges of Managing Island Invasive Species: Potential Invasive Species Unintentionally Spread from Military Restructuring

Author(s): Pitt, William C.; Stahl, Randal; Yoder, Christi | Abstract: The U.S. Department of Defense is in the process of restructuring military assets in the Pacific Basin that includes moving more troops to Guam. As a result of this process, the potential risk of vertebrate invasive species may increase across Micronesia. We identified the pathways through which goods and materials are moved throughout the Pacific basin and then developed a list of the most likely invasive vertebrates that could be moved in these pathways. We reviewed the available literature, interviewed experts, and evaluated pathways according to a fixed set of criteria to determine the risk of the pathway to transport invasive species. Some of the potentially high-risk pathways are military and commercial aircraft and vehicles, mail, shipping containers, and aquaculture. The following are species that may spread or become established in the Pacific without the implementation of measures to reduce risk: brown tree snake, habu, Asian beauty snake, common wolf snake, anole, gecko, coqui frog, cane toad, red-vented bulbul, Indian myna, and Indian mongoose.

Invasive vertebrate species in Chile and their control and monitoring by governmental agencies

Entregamos una revision del estado actual de las especies de vertebrados invasores en Chile, actualizando informacion sobre las especies exoticas terrestres y documentando la situacion de las especies exoticas de peces dulceacuicolas. Ademas, revisamos la legislacion pertinente y los programas que el gobierno chileno ha implementado para limitar la entrada de especies exoticas al pais o para minimizar su impacto sobre la flora y fauna nativas y los ecosistemas naturales. Documentamos lo que se conoce sobre la introduccion de 26 especies exoticas de peces a las aguas continentales de Chile, discutiendo la distribucion y efectos putativos de 11 especies que pueden considerarse invasivas. De la lista previa de 24 especies invasoras de vertebrados terrestres, nosotros retiramos la tortuga argentina (Chelonoidis chilensis), el reno (Rangifer tarandus) y el muflon (Ovis ammon), porque no hay evidencias de que hayan logrado asilvestrarse. Por otra parte, agregamos la tortuga dulceacuicola de orejas rojas (Trachemys scripta), la cotorra argentina (Myiopsitta monachus) y el cardenal de cresta roja (Paraoria coronata), manteniendose asi el total de invasoras constante en 24 especies. La principal agencia a cargo de implementar las leyes y regulaciones existentes con respecto a la importacion de especies exoticas de peces es el Servicio Nacional de Pesca (SERNAPESCA), una dependencia del Ministerio de Economia. La principal agencia a cargo de aplicar las leyes y regulaciones vigentes sobre la importacion de especies exoticas terrestres a Chile es el Servicio Agricola y Ganadero (SAG), una dependencia del Ministerio de Agricultura. Actualmente, el SAG no solo controla los pasos fronterizos, puertos y aeropuertos de Chile, sino tambien financia estudios para monitorear y controlar los invasores ya presentes en el pais. Ademas, la Corporacion Nacional Forestal (CONAF) tambien se involucra con especies invasoras, pero solo si ellas entran al Sistema Nacional de Areas Silvestres Protegidas del Estado (SNASPE)

Captive Care and Breeding of Marine Toads, Bufo marinus

ABSTRACT Marine toads, Bufo marinus, also known as cane toads, were introduced into Australia in 1935 as a biological control agent for native beetles in sugarcane plantations. They were unsuccessful in controlling the beetles and have since become a pest in their own right. They now rank as one of Australia's most serious invasive vertebrate species. We are seeking a means to control the marine toad population and have established a marine toad colony to provide a continuous supply of various life stages to aid our research. We describe here the establishment and maintenance of a breeding colony of Bufo marinus.