January 2006

River Otter Ecology and Management in Iowa Like much of the rest of

North America, river otter's (Lutra canadensis) were abundant in Iowa during European settlement, but unregulated trapping and hunting, and loss of habitat caused them to be extirpated in the state. Reintroduction efforts since the 1970’s have helped otters make a come back in North America. Iowa’s river otter reintroduction was initiated in 1985 at Red Rock Reservoir. Sixteen otters from Louisiana were released, initiating a pilot project to determine the suitability of Iowa’s aquatic resource for otters. The Red Rock otters survived very well and established normal habitat use patterns. Based on the success of this study subsequent releases were continued until 2003. In total, 345 otter were released in Iowa between 1985 and 2005. This reintroduction coupled with wetland restoration and conservation contributed to the widespread distribution of otters in Iowa at present. Basic Ecology and Habitat Use Otters are full grown at 3 or 4 years of age and by that time are 3-4.5 feet in length with their tail accounting for 35-40% of their total body length. Adult otters weight approximately 30 lbs. The river otter has short, dense, soft fur which is protected by longer, stiff hairs that is still held in high regard in the fur trade. River otters are primarily nocturnal and are active year round. River otters are known to be social and playful animals within the family group. Otter home ranges vary considerably as a function of the distribution of available habitat, food, weather severity, topography of the landscape and season. In habitat where resources are sparse and potential mates are far apart home ranges can exceed 75 miles2 but home ranges might be as small as 30 miles2 in more productive habitat. A study in Missouri found that otters had home ranges of 7 to 48 miles long and reached an average density of one adult per 5 miles of shoreline (0.2 otters/mile). Home ranges were smaller at another area, which supported one adult per 2 1/2 miles (0.4 otters/mile) in more diverse and higher-quality habitat. We estimated linear densities of otters in Iowa based on habitat conditions in the landscape ranging between 1 otter per 10 miles (0.1 otters/mile) in poor habitat in agricultural landscapes to as great as 1 otter per 1 1/3 miles (0.75 otter/mile) in diverse landscapes.

Otters prefer riverine habitats which provide sufficient food resources and shelter. Prey remains found at otter latrine sites at Red Rock indicated that they ate primarily carp and catfish but otters elsewhere have been implicated as important predators of game fish. The telemetry data from Red Rock indicated that otters frequently used log jams and

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January 2006

beaver lodges as resting and denning sites. Landscapes with a diversity of wetland types including rivers with wooded shorelines and nearby wetlands are the most ideal habitat. Dispersal and Movement

Otters have been reported to move up to 26 miles in one day, although daily movements generally average 5-6 miles per day. The telemetry tracking of the Red Rock otters showed male otters moved an average distance of 7 miles while females moved an average of 6 miles from the original release site. Adult males live along large stretches of river, often up to 40 to 50 miles in length and overlap the ranges of a number of females. Females do not move nearly as much as males. Their home ranges are only 3 to 10 miles in length depending on habitat quality and the time of year. Otter Distributions Otters have now been sighted in all counties in Iowa. Figure 1 shows estimated distributions of river otters in Iowa watersheds based on landscape attributes. To reliably monitor population trends across Iowa, we initiated a bow hunter observation survey. As the survey is repeated over the years, we will be able to reliably detect regional differences in sighting of otters. From the 2004 bow season we can clearly see that otters are most abundant in the eastern and northwestern parts of the state. Read the complete report at: http://www.iowadnr.com/wildlife/pdfs/bowobserver_survey2004.pdf

Figure 1. River otter distributions in watersheds throughout Iowa.

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Population Dynamics

Between 2002 and 2004 over 225 river otter carcasses were collected from accidental trapping and vehicle collisions from which we can estimate the age structure and reproductive rate of the population. We estimated survival of young otters in Iowa at approximately 55%. Adults survive better than young. Based on the age structure and the telemetry data we estimated that average annual survival of males was 89%, whereas female survival rate was 73%. The oldest otter recovered was aged 11 years. Even with these accidental losses, the Iowa population continues to increase at approximately 7% each year. The rate of growth of the population would be reduced to zero if 6.5% of the fall population were harvested each year. Conclusions Otter populations have made a substantial recovery from reintroductions and subsequent expansions. Conserving watersheds with a diversity of wetlands and wooded areas along streams and rivers, as well as high water quality that sustains fish populations is important to the sustaining the otter population in Iowa. The goal of otter restoration in Iowa has been successfully accomplished and has resulted in a wide-spread and slowly increasing population. Limited harvest of this population could be sustained. For additional information contact: Dr. William R. Clark Professor – Iowa State University Ecology, Evolution and Organismal Biology Department Ph. (515) 294-5176 Email: wrclark@iastate.eduWebsite: http://www.eeob.iastate.edu/faculty/ClarkW/homepage.html

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