Geology topics
Galen B. Rathbun
Publications and source records attributed to Galen B. Rathbun.
Fixed-wing airplane versus helicopter surveys of manatees (Trichechus manatus)
The abundance of manatees, as with most marine mammals, is difficult to determine because they are visible for only short periods of time while at the surface of the water (Eberhardt et al. 1979, Powell et al. 1981). Aerial surveys are generally considered to be the most accurate method of counting manatees, although there is no doubt that some undetermined proportion is missed (Irvine and Campbell 1978, Shane 1981, Kinnaird 1985, Packard et al. 1985). When designing aerial censuses for manatees two types of aircraft are usually considered: fixed-wing and rotary-wing airplanes (Irvine 1982). Fixed-wing airplanes normally are used because helicopters are prohibitively expensive to hire (often over twice that of a fixed-wing airplane). Helicopters, however, have been assumed to yield more accurate counts for manatees (personal observations; J. Fletemeyer and J. Provancha, personal communication) because their slower air speed and greater maneuverability reduce the proportion of animals missed due to some of the biases inherent in fixed-wing airplane counts (Caughley 1974). To assess how effective fixed-wing aircraft are in determining the number of manatees in an area, a series of paired total-count aerial surveys were done in winter 1978-79. A Bell 47G helicopter was used to obtain a “count” to compare with counts made from a Cessna 172 fixed, high-wing airplane. The experiment was conducted at two different sites and on five consecutive days at each site. The first location was Crystal River, which is a clear, spring-fed river that flows about11 km into the Gulf of Mexico on the central west coast of Florida. The second site was an 8-km-long section of the Indian River, which is a large, turbid estuary adjacent to Cape Canaveral on the east coast of Florida.
Status of dugongs in waters around Palau
The dugong, Dugong dugon , is widely distributed throughout the Indo-Pacific region in shallow tropical and subtropical waters (Nishiwaki and Marsh 1985).The International Union for Conservation of Nature and Natural Resources lists the species as vulnerable (Thornback and Jenkins 1982), as it is severely depleted or extinct in many parts of its former range (Nishiwaki and Marsh 1985). Many populations at isolated archipelagos have been exterminated through direct human exploitation. Husar (1975) cited evidence of the former existence of dugongs around the Mascarene, Laccadive, Maldive, Barren, Narcondom, Cocos (Keeling), Christmas, and Lesser Sunda islands. An isolated dugong population still occurs around Palau (Republic of Belau), Western Caroline Islands, about 850 km from both Papua New Guinea to the south and the Philippines to the west. The first aerial surveys of this population, in 1977 and 1978, indicated that it was small and other evidence suggested it was subject to persistent poaching (Brownell et al. 1981). We resurveyed this population in 1983 to reassess its status and attempt to detect any changes in distribution or abundance. With the assistance of the Palau Department of Natural Resources, we also interviewed fishermen and knowledgeable residents about dugong abundance, distribution, mortality, and natural history. Surveys were conducted from 19 through 26 August, using a Cessna 206high-wing airplane flown at an altitude of 150 to 300 m and an airspeed of about 170 km/h. An observer sat in each rear seat, and a third observer, who also navigated and recorded the data directly onto maps, sat in the right front seat. Small animals close to another dugong were considered calves. The survey route, based on that of Brownell et al. (19Sl), covered much of the approximately 1,380 sq km of dugong habitat within the archipelago. The islands are surrounded by very deep water, which restricts dugong habitat to lagoon areas within about 3 km of shore. Surveys were flown about 0.5 km offshore and the same distance inside the fringing reefs, with transects about 1 km apart across the larger lagoons. The coast was divided into the same 12 segments used by Brownell et al. (1981) (Fig. 1). However, the area outside the western fringing reef was not surveyed because no dugongs were sighted there in either1977 or 1978. We surveyed the entire archipelago twice and carried out replicated surveys of the lagoon areas and Malakal Harbor, which had been used by relatively large numbers of dugongs in 1977 and 1978 (Table 1). The total survey time was 15 h.265Help Volumes Main Menu
Status of sea otters (Enhydra lutris) in Mexico
Sea otters in North America historically were distributed from the Near Islands in the western Aleutian Archipelago to about Punta Morro Hermoso on the Pacific coast of Baja California (Kenyon 1969, Rodriguez-Jaramillo and Gendron 1996). During the 18th and 19th centuries they were so common that they formed the basis for a lucrative fur trade (Ogden 1941), but by the early 1900s they were exploited to extinction in Baja California (Kenyon 1369).
Interactions between northern elephant seals and vehicles near Point Piedras Blancas, California
Northern elephant seals, Mirounga angustirostris , were nearly extirpated in the late 19th and early 20th centuries. However, they have recovered to the point where they are now locally abundant (Stewart e t al. 1994). Stimulated by the report of human/northern elephant seal interactions in Baja California Sur (Webster and Baird 1998), we report here on an unusual terrestrial example of the increasing conflict between the growing populations of these two species in central California.
Status of translocated sea otters at San Nicolas Island, California
In the 1970s about 1,650 southern sea otters (Enhydra lutris nereis) were restricted to the central California coast (Riedman and Estes, 1990), and a high volume of oil was being shipped through the region. Because of the vulnerability of sea otters to contamination from oil (Costa and Kooyman, 1982; Williams and Davis, 1995) that would likely spread wide- ly along the shore after a large spill (Van- Blaricom and Jameson, 1982), the subspecies was listed as threatened in 1977 under the United States Endangered Species Act.
Temporal and spatial distribution of manatees in Kings Bay, Crystal River, Florida
No abstract available.