Download RATS (Rattus sp.) IN GUAFO ISLAND

RATS (Rattus sp.) IN GUAFO ISLAND: THEIR IMPLICATION ON MARINE MAMMALS CONSERVATION.
Mauricio Seguel
Universidad Austral de Chile, Chile
56-09-93819107
[email protected]
SUMMARY
Rats (Rattus sp.) may have a deleterious effect on marine mammal populations. In Guafo Island there are one of the
most important South American fur seals rookeries on Chilean coasts, and a relatively high abundance of the
endangered marine otters. However, these species coexist with a variable population of invasive rat species (Rattus
rattus and Rattus norvegicus). The aim of this project is to analyze the potential competition for food resources
between rats and marine otters, and to determine the role of rats in the transmission of diseases to marine otters and
to fur seals pups at Guafo Island.
DESCRIPTION
GENERAL DESCRIPTION
Invasive species are considered one of the most important causes of biodiversity loss on the planet. Rats (Rattus sp.)
are within the taxonomic groups that successfully invade new ecosystems (Meerburg et al.2009). The impact of
rodents in the loss of biodiversity has been particularly dramatic in oceanic islands, because endemic species from
these places have evolved in the absence of terrestrial predators (Courchamp et al. 2003).
Guafo Island (43º36'S and 74º43'W) is located in southern Chile, and due to its remoteness from mainland has a
large biodiversity of marine mammals and seabirds; however it lacks of endemic land mammals. Among the marine
mammals, highlights the most important breeding colony of South American fur seal (Arctocephalus australis) on
Chilean coasts and the occurrence of marine otters (Lontra felina), an endangered species (IUCN 2010). Among the
seabirds, the largest seabird colony of sooty shearwater (Puffinus griseus) in the world is present in the island
(Reyes-Arriagadaet al. 2007). Rats were introduced to the island probably in the early twentieth century due to the
construction of the Chilean Navy’s Lighthouse and the setup of a whaling station in the northeastern part of the
island, that operated for two decades in that place. Interestingly, the impact of rats on endemic mammals has not
been previously studied in the island.
Rats can produce a strong impact on communities of seabirds and marine mammals through a variety of
mechanisms. The first mechanism is through direct predation, because rats eat the eggs, chicks and even adult birds
and small mammals that live on the ground (Caut et al. 2008). Secondly, another negative effect generated by rats
on native species is the competition for resources. For instance, rats that live at shore eat mollusks, fish and
crustaceans, the same food resources used by sea otters in Chile (Cordoba et al. 2009).
An additional effect that might be more significant for the conservation of species, but least studied, is the
transmission of diseases from rats to wildlife. It is considered that the introduction of invasive species is involved in
more than half of emerging infectious diseases recorded in wildlife (Daszak et al. 2000). Rats are reservoirs for a
wide range of pathogens capable of causing disease in humans and animals (Meerburg et al. 2009). In the case of
otariids and otters, the transmission of Leptospira interrogans,Streptococcus sp. and Salmonella typhimurium are
especially important because these bacteria can cause significant mortalities (Gullandet al. 1996; Kimber and
Kollias 2000; Bruynet al. 2008). At Guafo Island, South American fur seal pups might be affected by an unknown
microorganism, causing encephalitis and death of pups (Seguel et al. in press). Current observations suggest that this
disease may be caused by a microsporidian, parasites that are mainly transmitted by rodents to other mammals.
OBJECTIVES AND HYPOTHESES
General Objective
To estimate the potential ecological impacts of rats (Rattus sp.) on populations of South American fur seals
(Arctocephalus australis) and marine otters (Lontra felina) at Guafo Island. Specific Objectives
To determine the diet of rat populations surrounding the breeding colonies of South American fur seals and marine
otters.
To determine the presence of pathogens in populations of rats close to the South American fur seal and marine otter
colonies.
To determine the presence of diseases in South American fur seal pups, attributable to transmission by rodents.
Hypothesis
H1 = Rats in Guafo Island inhabiting coastal areas prey on a significant percentage of crustaceans, mollusks and
fish, existing trophic overlaps between rats and marine otters (Lontra felina).
H2 = Rats (Rattus sp.) in Guafo Island carry Leptospira interrogans and microsporidian species, representing a risk
agent for the presentation of leptospirosis and microsporidian encephalitis in fur seals and marine otters.
METHODS
To achieve these study objectives, wild rats will be caught by mean of traps (Safeguard Squirrel-Rat Live Trap #
50450-1®). Once trapped, rats will be euthanized by the administration of euthanasia solution (T61®, Hoechst).
Later, postmortem examinations using standard necropsy techniques will be performed. The gastrointestinal system
will be extracted during the necropsy, and frozen at -20ºC for diet and parasites’ analysis that will be performed later
at the laboratory. During the necropsies, samples for serology, virology, bacteriology and histopathology will be
obtained in order to identify any relevant microorganism carried by the rats. To determine the marine otters’ diet,
fecal samples will be collected during regular trips through the rockeries.
The South American fur seal rookery will be checked daily looking for dead pups. Carcasses will be retrieved to
perform a complete necropsy. Samples from all organs and tissues will be collected for histopathological studies,
and samples for serology, virology and bacteriology will be additionally collected in order to determine the cause of
death and to identify any potential pathogen causing the pups’ death.
All catches of living specimens will be made following the bioethics protocols for animal research from the National
Commission on Science and Technology of Chile (CONICYT).
ANALYTICAL APPROACH
To evaluate the importance of each prey’s taxon present in the diet consumed by otters and rats the following
indexes will be calculated:
Percentage of total number (%PTN): Nº of individuals of a prey item * 100 / Total number of prey.Percentage of
occurrence (%PO): Nº of feces with an item * 100 / Total number of analyzed feces.
The diversity of preys in the diet will be determined using the software DIVERS, which will calculate ShannonWeaver’s diversity index (H’), species abundance and uniformity of prey species.
The Berger and Parker dominance index (D) will be employed to know which prey items constituted the main prey
resource for each species.
To calculate the similarity between rats and otters diets and their potential overlap the Schoener’s similarity index
will be used.
SIGNIFICANCE FOR THE CONSERVATION OF THE SPECIES
The data obtained will be useful to estimate the influence of rats on the rate of South American fur seal pups’
survival, and whether these invasive species play a role limiting the growth of marine otter populations. South
American fur seals have experienced a population’s decline close to 57% on Chilean coasts, and marine otters are an
endangered species, therefore the information generated in this study will be useful to support conservation
programs on both species, especially in island waters.
TIMELINE OF THE PROJECT
This project is to be completed during 2012 according to the following schedule: Field work (January, February),
Laboratory work (March, April, May), Analyses of data and presentation of preliminary results (May, June), Final
Report (July).
BUDGET
The budget presented below covers the expenses related to travel to field site and feeding during the permanence
time at the camp (these funds are requested to the Society for Marine Mammalogy). The rest of the necessary inputs
are provided by the organizations mentioned in the section "Other funds available."
Item
Cost/unit ($ U.S)
Units
Total ($ U.S)
Land transportation
115
2
230
Sea transportation
195
2
390
Feeding
400
2
800
Total of funds requested
1420
The cost per unit of land transportation and sea transportation include go and back tickets.
The cost of feeding per unit is calculated on basis of the rations used by one person during 60 days (based on
personal field work experience at Guafo Island).
All items include two units. One unit is for the researcher that requests the funds and the other for an unpaid field
assistant. For logistical and security reasons the travel might not be done without at least one assistant.
LEGAL PERMITS
This project will be performed in accordance with current Chilean regulation regarding marine mammals.
REFERENCES
Bruyn, P., A. Bastos, C. Eadie, C. Tosh, M. Bester.2008. Mass mortality of adult subantartic fur seals: Are alien
mice the culprits?.Plos ONE 3, e3757.
Caut, S., E. Angulo and F. Courchamp. 2008. Dietary shift of an invasive predator: rats, seabirds and sea
turtles. Journal of Applied Ecology, 45: 428–437.
Córdova, O., J. Rau, C. Suazo and A. Arriagada A. 2009. Comparative study of the feeding ecology of the top
predator Lontra feline (Molina, 1782) (Carnivore: Mustelidae) in Chile. Revista de biología marina y
oceanografía,44: 429-438.
Courchamp, F., J.L. Chapuis and M. Pascal. 2003. Mammal Invaders on Islands: Impact, Control and Control
Impact. Biological Reviews, 78: 347–383.
Daszak, P., A.A. Cunningham and A.D. Hyatt.2000. Emerging infectious diseases of wildlife; threats to biodiversity
and human health. Science, 287:443–449.
Gulland, F., M. Koski, L. Lowenstine, A. Colagross, L. Morgan, T. Spraker. 1996. Leptospirosis in California sea
lions (Zalophus californianus) stranded along the central California coast, 1981 1994.Journal of Wildlife
Diseases, 32: 572–580.
IUCN 2010.IUCN Red List of Threatened Species.Version 2010.2.< www.iucnredlist.org>.
Downloaded on22 July 2010.
Kimber, K. and G. Kollias. 2000. Infectious and Parasitic Diseases and Contaminant Related Problems of North
American River Otters (Lontra Canadensis): A Review. Journal of Zoo and Wildlife Medicine, 31: 452–472.
Meerburg, B., G. Singleton and A. Kijlstra. 2009. Rodent-borne diseases and their risks for public health.Critical
Reviews in Microbiology,35: 221–270
Reyes-Arriagada, R., P. Campos-Ellwanger, R. Schlatter and C. Baduini. 2007. Sooty Shearwater (Puffinusgriseus)
on Guafo Island: the largest seabird colony in the world? Conservation and Biodiversity, 16 : 913-930.
Seguel, M., E. Paredes, H. Pavés, R. Molina, F. Henriquez, F. De Groote and R. Schlatter. 2011. Pathological
findings in South American fur seal pups (Arctocephalusaustralis) found dead at Guafo Island, Southern
Chile. Journal of Comparative Pathology, in press.
OTHER FUNDS AVAILABLE
The Animal Pathology Institute (Universidad Austral de Chile) will provide the following implements.
Necropsy equipment ($600 U.S), Samples containers ($150 U.S), Fixation solutions ($50 U.S)=Total ($ 800 U.S)
The Animal Pathology Institute will fund all tests that will be performed at the institute labs (Histological,
parasitological, serologic and bacteriological tests). The amount of the investment it depends on the amount of
samples and the complexity of each case.
Curriculum Vitae
MAURICIO SEGUEL