PARENT SESSION
Oral Session #11: Aquatic Ecology: Conservation, Plankton, Invertebrates.
Presiding: C. Cooper
Monday, August 5. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.
Can river otters naturally recolonize the Grand Canyon? Assessment with a spatially-explicit individual-based model.
NIBBELINK, NATHAN*,1, BEN-DAVID, MERAV1, BLUNDELL, GAIL2, 1 University of Wyoming, Laramie, WY2 University of Alaska - Fairbanks, Fairbanks, AK
ABSTRACT- River otters (Lontra canadensis) are piscivorous predators that forage near the apex of the trophic pyramid and readily accumulate high levels of pollutants. Indeed, river otters in North America were reduced throughout much of their historic range by the early 1900s because of pollution, urbanization, and overharvest. Consequently, numerous projects were initiated to reintroduce river otters to areas from which they were extirpated, often with limited success. Recently, a proposal to reintroduce river otters to the Grand Canyon was put forward. This, however, could result in the genetic swamping of endangered L. c. sonora in adjacent watersheds. In addition, such a reintroduction will likely be costly and logistically complicated. Therefore, before such a project is initiated, the feasibility and rate of natural recolonization needs to be assessed. We developed a spatially explicit, individual-based model to evaluate the potential for natural recolonization of the Grand Canyon by river otters that may disperse from known populations in the upper Colorado River Basin. The model uses a population matrix consisting of individual otters at a range of observed densities, male-female ratios and age structures. We then vary survival and reproduction rates, as well as dispersal probabilities and distances. Each year natal dispersal and reproduction can result in colonization of new areas. Survival rates were by far the strongest limitation to population expansion, further questioning the utility of introduction programs, which typically result in low survivorship. Our simulations, assuming no barriers to dispersal and observed otter densities, resulted in range expansion of 2000 to 6000 square kilometers per year. At that rate it would take between 45 &134 years for otters to naturally recolonize the Grand Canyon. Future work will attempt to assess relative effects of movement barriers (e.g. dams, roads, urban areas, unsuitable habitat) to river otter dispersal.
KEY WORDS: individual-based, Lontra canadensis, spatial model, recolonization