Stable lead isotopes evidence anthropogenic contamination in Alaskan sea otters
No abstract available.
Alaska↗
Geology topics
Research about Amchitka Island
Source-linked reports with geographic coverage including Amchitka Island.
Inter-decadal change in diet and population of sea otters at Amchitka Island, Alaska
After having been hunted to near-extinction in the Pacific maritime fur trade, the sea otter population at Amchitka Island, Alaska increased from very low numbers in the early 1900s to near equilibrium density by the 1940s. The population persisted at or near equilibrium through the 1980s, but declined sharply in the 1990s in apparent response to increased killer whale predation. Sea otter diet and foraging behavior were studied at Amchitka from August 1992 to March 1994 and the data compared with similar information obtained during several earlier periods. In contrast with dietary patterns in the 1960s and 1970s, when the sea otter population was at or near equilibrium density and kelp-forest fishes were the dietary mainstay, these fishes were rarely eaten in the 1990s. Benthic invertebrates, particularly sea urchins, dominated the otter’s diet from early summer to mid-winter, then decreased in importance during late winter and spring when numerous Pacific smooth lumpsuckers (a large and easily captured oceanic fish) were eaten. The occurrence of spawning lumpsuckers in coastal waters apparently is episodic on a scale of years to decades. The otters’ recent dietary shift away from kelp-forest fishes is probably a response to the increased availability of lumpsuckers and sea urchins (both high-preference prey). Additionally, increased urchin densities have reduced kelp beds, thus further reducing the availability of kelp-forest fishes. Our findings suggest that dietary patterns reflect changes in population status and show how an ecosystem normally under top-down control and limited by coastal zone processes can be significantly perturbed by exogenous events.
Alaska↗
Aleuts, sea otters, and alternate stable state communities
Reexamination of stratified faunal components of a prehistoric Aleut midden excavated on Amchitka Island, Alaska, indicates that Aleut prey items changed dramatically during 2500 years of aboriginal occupation. Recent ecological studies in the Aleutian Islands have shown the concurrent existence of two alternate stable nearshore communities, one dominated by macroalgae, the other by epibenthic herbivores, which are respectively maintained by the presence or absence of dense sea otter populations. Thus, rather than cultural shifts in food preference, the changes in Aleut prey were probably the result of local overexploitation of sea otters by aboriginal Aleuts.
Alaska↗
Depredation of sea otter pups by bald eagles at Amchitka Island, Alaska
No abstract available.
Alaska↗
Hydraulic tests in hole UAe-2, Amchitka Island, Alaska
Inflatable straddle packers were used to isolate and test 19 intervals ranging from 56 to 747 meters (183 to 2,450 feet) each in hole UAe-2, Amchitka Island, Alaska. Packer seats were poor in part of the hole because of unstable wall conditions. Thus, some zones had to be tested several times. The static water levels in the intervals tested ranged from 14.2 meters (46.6 feet) below land surface in the upper interval to 33.7 meters (110.6 feet) below land surface in one of the intervals near a depth of 1,500 meters (4,900 feet). The specific capacity of the open hole from 83.5 to 1,980.6 meters (274 to 6,498 feet) was 3.26 cubic meters per day per meter (0.182 gallon per minute per foot) of drawdown after the hole had been jetted at an average rate of 763 cubic meters per day (140 gallons per minute) for about 41 hours. Transmissivity computed from the recovery of water level after jetting stopped was 2.97 cubic meters per day per meter (239.2 gallons per day per foot). The relative specific capacities of isolated intervals ranged from 0.001 cubic meter per day per meter (less than 0.001 gallon per minute per foot) of drawdown to 2.765 cubic meters per day per meter (0.155 gallon per minute per foot) of drawdown.
Alaska↗
Hydraulic tests in hole UA-1 and water inflow into an underground chamber, Amchitka Island, Alaska
Hole UA-1 was center punched (a small-diameter exploratory hole drilled ahead of the large-diameter emplacement hole) from 1,524.0 to 1,981.2 meters (5,000 to 6,500 feet) and hydraulically tested to determine an ideal location for mining a chamber. Fifteen zones were tested; minor amounts of water bypassed the packers during five of the tests. The tested intervals ranged in length from 37.5 meters (123 feet) to 211.5 meters (694 feet). For purposes of comparison relative specific capacities were calculated from comparable 60.4-meter (198-foot) intervals of tested rock, and ranged from 0.1162 cubic meters per day per meter (0.0065 gallons per minute per foot) of drawdown to 0.0039 cubic meters per day per meter (0.0002 gallons per minute per foot) of drawdown. The interval 1,745.0 to 1,836.4 meters (5,725 to 6,025 feet) appears to be the best location for mining a chamber so far as water inflow is concerned. This interval, 91.4 meters (300 feet), consists of about 27.4 meters (90 feet) of breccia and 64.0 meters (210 feet) of basalt. The inflow to a spherical chamber 18.3 meters (60 feet) in diameter and placed in the center of the proposed 91.4-meter (300-foot) interval, was calculated to be about 175 cubic meters per day (32 gallons per minute) after the first day and would stabilize at about 57 cubic meters per day (10.5 gallons per minute) after about 200 days.
Alaska↗