Graduate Thesis Or Dissertation
 

An evaluation of attempts to reestablish the sea otter in Oregon

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  • During the summers of 1970 and 1971 a total of 95 sea otter (Enhydra lutris) were shipped to Oregon from Amchitka Island, Alaska. The 1970 shipment consisted of 31 otter which were to be released on the southern Oregon Coast near the town of Port Orford. Two of these animals died in holding pens and 29 were successfully released to the wild on 18 July 1970. A second shipment of 64 sea otter was divided into two groups. On 24 June 1971, 24 otter were released at Port Orford and 40 more were released near Cape Arago. Total documented mortality of the translocated sea otter consisted of eight animals, seven of these were found within 1 week of the releases. During the study period reports of sea otter were distributed from Tillamook Head to Brookings, Oregon, a distance of approximately 276 miles. A single report was received from Tolvana Beach, Oregon, 181 miles north of the nearest release site. Concentrations of otter were established at two locations during 1972, Simpson and Blanco reefs. The number of animals that could.be observed at either of these sites seemed to be related to the season, with most otter using Simpson Reef during the winter months, subsequently moving to Blanco Reef 35 miles to the south as the weather subsided. The use patterns for 1972-73 were similar to those for 1971-72; however, the number of otter using Simpson Reef during the winter of 1972-73 was less than for the previous winter, suggesting that a portion of the herd may have remained in the vicinity of Cape Blanco during winter 1972-73. It is estimated that 30-35 sea otter were on the coast at the termination of this study (5 October 1973). The first sea otter pup was sighted on 20 February 1972, 19 months after the 1970 release at Port Orford. Subsequently nine more pups were observed during the study period: three in 1972 and six in 1973. Data on food habits were gathered at Simpson Reef. Sea urchins (Strongylocentrotus spp. ) comprised the major portion of the sea otter's diet and accounted for nearly 64 percent of the total number of observations. Mollusks accounted for 14.4 percent and several species of crabs comprised 5.2 percent. Underwater surveys of 13 areas indicate that sea urchins are the most abundant macroinvertebrates normally preyed upon by sea otter. They occur at densities of up to 47 purple sea urchins (S. purpuratus) per 0.25 m2 , with red sea urchins (S. franciscanus) occurring as high as an estimated six to eight animals per 1 m2. Results of this study indicate that approximately one-third of the Oregon coastline is suitable for sea otter habitation; approximately 80 percent of the suitable area is situated along the south coast from Coos Bay to the Oregon-California border, with the remainder in the central region near the town of Newport. Both sites chosen for the translocations contain good sea otter habitat; however, because of greater probability of human-related mortality and environmental pollution and the lesser amount of contiguous sea otter habitat in the vicinity of Cape Arago than near Port Orford; the latter appears to have been the better site. It is suggested that in the future, translocated sea otter be tagged to facilitate their identification. Recommended management of the translocated otter in Oregon includes establishment of refuges, protection of the otter and their habitat, and periodic shoreline and aerial surveys to ascertain population growth and range expansion.
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