Fifteen Years of River Otter Monitoring by Citizen-Science Volunteers in Northern California: Litter Size

Abstract We solicited and collated citizen-science volunteer observations of North American River Otters (Lontra canadensis) over 15 y in Humboldt, Del Norte, and adjacent counties in northern California. The occurrence of River Otter reproduction is thought to be an indicator of watershed and wetland health. We described when and where observers reported sightings of pups and litters. Citizen volunteers reported 3540 River Otter observations, of which 371 included required information about number and size of smaller pups. From these records, 148 litters were identified in 39 waterbodies. Five to 17 litters per year were reported. Average litter size was 2.0 (SE 0.1; range 1 to 4 pups). Litter size did not vary significantly among years or waterbodies, including coastal and inland sites. The number and size of River Otter litters reported did not increase (or decline) over the study period.