Movement and spatial use patterns of California sea otters

Abstract

Movement patterns of sea otters (Enhydra lutris) were followed by daily monitoring of 40 individuals with implanted radio transmitters. Otters of all age and sex classes were most often found within 1–2 km of their locations on the previous day. However, individuals often remained within a small area for an extended period and then suddenly moved a much greater distance within a short time period. There were significant differences among age–sex classes, but not months, in the mean monthly distances between successive daily locations and between extreme locations of individual otters. There were significant differences among both age–sex classes and months in the harmonic mean distance deviation. For all three measures, juvenile males tended to move the greatest distances. Adult males tended to be more sedentary than adult females over the short term, but traveled over greater distances in the long term. Individuals within age–sex classes had different movement patterns, and individuals often had different movement patterns during the same month in successive years. Estimates of the area used by individual otters during a single 24-h period (6.9–1166.4 ha) overlapped previous estimates of home-range size based on much longer time periods.

Sea otter population status and the process of recovery from the 1989 'Exxon Valdez' oil spill

“…Adult sea otter home ranges are relatively small and stable, commonly including a few to 10s of km of coastline (Jameson 1989, Ralls et al 1996. Generally, male sea otters exhibit greater movements than females, and juveniles exhibit greater movements than adults and are more likely to disperse from natal areas (Riedman & Estes 1990, Ralls et al 1996.…”

“…Adult sea otter home ranges are relatively small and stable, commonly including a few to 10s of km of coastline (Jameson 1989, Ralls et al 1996. Generally, male sea otters exhibit greater movements than females, and juveniles exhibit greater movements than adults and are more likely to disperse from natal areas (Riedman & Estes 1990, Ralls et al 1996. If population recovery resulted from reproductive recruitment from within the affected population, the sex ratio in the recovering population should favor females, because young males exhibit greater movements and are more likely to be excluded from reproductive areas by territorial males.…”

Long-term impacts of the Exxon Valdez oil spill on sea otters, assessed through age-dependent mortality patterns

“…These differences, combined with the demographic results reported here, suggest that oil-affected areas may continue to represent a population ''sink'' that benefits from immigration from healthy segments of the greater WPWS sea otter population. Although sea otters generally occupy relatively small home ranges, longer-range movements, particularly by males and͞or young animals, are common (41,42).…”

Point Mugu Sea Range Marine Mammal Technical Report

“…This population has diminished to about 17 animals (Rails et al 1996;USFWS 1996). The San Nicolas Island experimental population is discussed further in Section 3.7.4.4.…”