Sea otter, Enhydra lutris, containment management: field studies and feasibility assessment

Limiting sea otter geographic distribution in California (containment management) has long been recognized as being necessary to preserve human recreational and commercial uses of shellfish resources. However, passage of federal legislation that focused preferentially on marine mammal protection and the 1977 listing of the California sea otter population as "threatened" effectively precluded any range-limiting management program. Research, however, that evaluated various non-lethal means of influencing sea otter movements and distribution was encouraged. Our research suggests that herding and acoustical devices may not have any real potential use in this context. Based on research-related capture success rates, capture and relocation techniques may be useful in influencing sea otter geographical distribution. The translocation of sea otters to San Nicolas Island provided the first opportunity to test the technical feasibility of maintaining a large area free of sea otters. Capture success rates were appreciably poorer than those achieved during research-related efforts. We identify several logistical and behavioral influences that contributed to the relatively poor success rate. Based on this evaluation, we discuss the factors likely to limit application of these techniques in the future. We feel that capture techniques can be useful in a long-term management program, if used in conjunction with efforts to limit the sea otter population growth rate. Consequently, we feel future research should focus on assessing individual health effects from using chemical contraceptives and assessing the feasibility of their use to safely control population growth. (12pp.

A review of California sea otter, Enhydra lutris, surveys

Recent surveys (1977 to 1983) of the sea otter, Enhydra lutris, in California were summarized and compared to past surveys, to evaluate the adequacy of current survey design and to-make inferences about current population status. Ground counts within selected index areas provided the best indicator of population trends. These data suggest a rather remarkable stability in the long-term occupied range. Rangewide aerial surveys with ground truth stations provided the best available data for estimating total population size. The most recent (1979) survey yielded a population estimate of approximately 1500 sea otters. Comparisons with past surveys suggest there have been no demonstrable changes in population size since at least 1976. (34pp.

Diablo Canyon power plant site ecological study Quarterly Report no. 6; October 1 - December 31, 1974

During the period October 1 - December 31, 1974, a total of six permanent subtidal stations and ten random intertidal stations were surveyed. Red tides and rough seas limited both the commerical abalone and sea urchin fishery activities. Most activity was concentrated between Diablo Cove and Pecho Rock. Divers, however, did work urchin beds as far north as Lion Rock. Sea otter counts have remained relatively stable with almost all individuals being observed north of Lion Rock. Fourteen random fishing stations were completed. Low catch rates reflected fishing success in areas with a heavy brown algae surface canopy. (12pp.

Diablo Canyon power plant site ecological study Quarterly Report no. 7; January 1 - March 31, 1975

During the period January 1 - March 31, 1975 we relocated and remarked five permanent subtidal stations and surveyed 28 random and two permanent intertidal stations. We failed to find a single giant red sea urchin, Strongylocentrotus franciscanus, around station 16 during a dive in March. Abalone, Haliotis spp., numbers decreased at random intertidal stations in North Diablo Cove and the North Control Area. The commerical sea urchin fishery was inactive, while the commerical red abalone, H. rufescens, fishery continued to operate around Pecho Rock. Counts of sea otters south of Point Buchon increased significantly, 20 to 30 otters are now feeding just north of Pecho Rock. Eight random fishery stations in Diablo Cove, Lion Rock Cove and the North Control Area yielded a substantial increase in catch-per-unit-of-effort. (15pp.

Diablo Canyon power plant site ecological study; Quarterly Report No. 11; January 1 - March 31, 1976

Permanent subtidal stations 6, 11 and 16 were surveyed. Appreciable increases in densities of one species of brown algae and five species of macroinvertebrates were noted at station 6. Winter surveys of random and permanent intertidal stations were completed. There was little or no change in black and red abalone, Haliotis cracherodii and H. rufescens, densities at the various random study areas. There was a noticeable increase in black abalone numbers at permanent station 2A located in North Diablo Cove. Three new permanent stations were established and counts of abalone completed. Approximately 100 sea otters, Enhydra lutris, have moved from the Point Buchon area to the area around Pecho Rock. We fished at 13 random stations in Diablo Cove and five stations in North Cove and North Control to determine the catch rate of common sport fishes. A good percentage of the 1975 bull kelp, Nereocystis luetkeana, population weathered the winter storms. We calculated an approximate 18% over-wintering survival rate. Daily observations of foam in Diablo Cove continued; large amounts of piled-up foam have been observed during low tides in the South Diablo intertidal during periods of northwesterly winds. On a recent reconnaissance dive in Intake Cove, fish numbers appeared to be on the increase and visibility appeared to be improving. (15pp.

Diablo Canyon power plant site ecological study Quarterly Report no. 10; October - December 31, 1975

Field work during the quarter included surveys of permanent and random subtidal and intertidal stations. At permanent subtidal stations densities of the brown algae Laminaria and Nereocystis decreased as did densities of giant red sea urchins, Strongylocentrotus franciscanus. Counts of small invertebrates within one-quarter meter square (1/4-m2) quadrats at random subtidal stations were begun. A total of 32 quadrats was completed. Balanophyllia elegans was the most abundant and most common animal encountered. The annual surface count of bull kelp (Nereocystis) was not possible because of the increased density; instead we utilized subtidal counts to estimate the surface canopy. An estimate of 33,000 plants was made for this year's canopy; this compares with a count of 18,000 plants last year. Sampling of random intertidal stations for the Davidson period began; 15 stations were surveyed. In addition, permanent intertidal stations 1, 2 and 3 were surveyed for abalone densities. The sea otter, Enhydra lutris, herd continued to occupy the area around Point Buchon. In November daily observations were initiated on foam location and abundance in Diablo Cove. (13pp.

Diablo Canyon power plant site ecological study Quarterly Report No. 13; July 1 - September 30, 1976

Surveys of 39 random 30-m2 subtidal stations and 56 random 1/4-m2 subtidal stations in Diablo Cove and the North Control were completed. The mean density of red abalones, Haliotis rufescens, in Diablo Cove was greater this year (0.02/m2) than last year (0.005/m2). This difference probably reflects sampling variation rather than density change. A total of 29 sportfish catch-per-unit-of-effort stations was sampled in Diablo Cove and 12 in the North Control. Foam observations in Diablo Cove were continued. The cooling water pumps were not in operation. The amounts of foam appeared to be about the same during certain weather conditions as those when the pumps are in operation, although not as thick. The number of sea otters, Enhydra lutris, decreased substantially between Pt. Buchon and Pecho Rock. This was due to their annual migration (or "pulling back") into the more central parts of their range. Random surveys of the intertidal areas during the upwelling period were completed. (11pp.

Diablo Canyon Power Plant site ecological study Quarterly Report No. 3; January 1 - March 31, 1974

During the period January 1 - March 31, 1974, winter surveys of the permanent subtidal stations were initiated. Three stations were surveyed. We completed our winter random intertidal surveys; a total of 14 stations in Diablo Cove and the North Control Area were visited. The commercial sea urchin fishery resumed and we began interviewing fishermen again. Very little commercial abalone fishing occurred due to the one-month closed season and winter storms. We observed a sea otter in North Cove for the first time and harbor seals were also observcd on the eastern end of the south breakwater for the first time since we began our studies. (17pp.

Uniqueness Results for Second Order Bellman-Isaacs Equations under Quadratic Growth Assumptions and Applications

In this paper, we prove a comparison result between semicontinuous viscosity sub and supersolutions growing at most quadratically of second-order degenerate parabolic Hamilton-Jacobi-Bellman and Isaacs equations. As an application, we characterize the value function of a finite horizon stochastic control problem with unbounded controls as the unique viscosity solution of the corresponding dynamic programming equation