Daniel K. Odell

Structure, Function, and Adaptation of the Manatee Ear

The West Indian manatee, Trichechus manatus, is common throughout the Caribbean yet little is known about its sensory abilities. Hearing in particular is of interest since large numbers of one subspecies, the Florida manatee (T. manatus latirostris), die annually from collisions with boats in shallow coastal waters and canals. There is no published audiogram for Trichechus manatus and the auditory system has not been fully described. Earlier studies of manatee hearing were based on isolated, dehydrated tympano-periotic bones (Robineau, 1969; Fleischer, 1978). This paper describes all major hard and soft tissues of the peripheral auditory system of T. manatus, presents new information on specialized cranial features that may be important for sound conduction, and provides morphometrybased estimates of the frequency range and sensitivity of West Indian manatee ears.

Evidence of Prenatal Infection in the Bottlenose Dolphin (Tursiops truncates) with the Lungworm Halocercus lagenorhynchi (Nematoda: Pseudaliidae)

Adult lung nematodes identified as Halocercus lagenorhynchi were collected from the lungs of four Tursiops truncatus calves. The calves ranged in age from newborn to 3-wk-old and were found on both the Atlantic and Gulf coasts of Florida (USA). This finding suggests the possibility of a more cosmopolitan distribution of prenatal infection with lung nematodes in cetaceans than previously suspected.

Composition of milk of the pygmy sperm whale (Kogia breviceps)

Abstract 1. 1. A 315cm lactating female pygmy sperm whale, Kogia breviceps , accompanied by a 156cm female calf stranded on south Miami Beach, Dade County, Florida, on 13 March 1974, were used in the experiment. 2. 2. A sample of milk from the lactating female contained less fat and more lactose than most cetecean milks previously analyzed. 3. 3. Palmitic and oleic acids predominated in Kogia milk fat and long chain unsaturated fatty acids were lacking. 4. 4. Kogia milk protein contained several unidentified constituents. 5. 5. The chlorinated hydrocarbon residues in the milk were (ppb, wet weight): total DDT—1670; dieldrin—37; PCB—1203.

Reproductive Biology of South American Manatees

The order Sirenia includes the only mammals that are both fully aquatic and herbivorous. The members of this order possess adaptations for both their habitat and their diet. For example, the large fusiform body is almost hairless; external appendages such as the hind limbs and external ear pinnae are absent; the pectoral flippers are reduced and paddlelike; and the tail is modified into a large paddle (manatees) or deeply notched flukes (dugongs) to facilitate locomotion through an aquatic medium. Pachyostotic (swollen) and osteosclerotic (very hard and solid) bones play a role in buoyancy regulation. A peculiar mode of tooth replacement (with an indeterminate number of molars in manatees), presence of horny plates in the mouth, ventral deflection of the rostrum (most pronounced in Dugong), the size, proportions, and structure of the digestive tract, and hindgut fermentation are all adaptations for herbivory. Fossil evidence suggests that sirenians were derived from primitive terrestrial herbivores early in the Tertiary (Reinhart 1971), and biochemical analysis of proteins points to a common origin with elephants and hyraxes (Kleinschmidt et al. 1986).

Ganglion cell distribution and retinal resolution in the Florida manatee, Trichechus manatus latirostris

The topographic organization of retinal ganglion cells was examined in the Florida manatee (Trichechus manatus latirostris) to assess ganglion cell size and distribution and to estimate retinal resolution. The ganglion cell layer of the manatees retina was comprised primarily of large neurons with broad intercellular spaces. Cell sizes varied from 10 to 60 μm in diameter (mean 24.3 μm). The retinal wholemounts from adult animals measured 446–501 mm2 in area with total ganglion cell counts of 62,000–81,800 (mean 70,200). The cell density changed across the retina, with the maximum in the area below the optic disc and decreasing toward the retinal edges and in the immediate vicinity of the optic disc. The maximum cell density ranged from 235 to 337 cells per millimeter square in the adult retinae. Two wholemounts obtained from juvenile animals were 271 and 282 mm2 in area with total cell numbers of 70,900 and 68,700, respectively (mean 69,800), that is, nearly equivalent to those of adults, but juvenile retinae consequently had maximum cell densities that were higher than those of adults: 478 and 491 cells per millimeter square. Calculations indicate a retinal resolution of ∼19′ (1.6 cycles per degree) in both adult and juvenile retinae. Anat Rec, 2012.

Radio-Tracking and Survivorship of Two Rehabilitated Bottlenose Dolphins ( Tursiops truncatus ) in the Indian River Lagoon, Florida

Despite an increase in the number of stranded dolphins rehabilitated and returned to the wild, the survivorship of these cetaceans is poorly documented. Since rehabilitation and release programs remain limited in scope, the release of dolphins from different age and sex cohorts provides information that is pertinent to protocols for future release candidates. Novel opportunities to track the survivorship of two rehabilitated bottlenose dolphins with radio transmitters occurred in 2001 and 2003 in the Indian River Lagoon (IRL), Florida. Both dolphins were male and had been identified prior to rehabilitation during a photoidentification monitoring program. Dolphin C6 stranded with multiple life-threatening shark wounds in 2000, at age 24, and was released after a successful 6-mo period of rehabilitation. This dolphin re-established an existing male pair-bond with dolphin C7, traveled 67 km from the release site, and survived 100 d before he died from asphyxiation by an exotic fish that lodged in his pharynx. Carter, a calf orphaned in 2003 at 1 y of age, was released following a 3-mo period of care that provided adequate nutrition and weight gain needed for survival in the wild. This young dolphin remained within a 10-km radius of the release site, failed to form a stable relationship with other dolphins, and appeared to have survived only 7 d when radio transmissions from an acoustic tag ceased. These two cases represent the radio-tracking studies of the oldest and youngest known bottlenose dolphins rehabilitated and released in the IRL.

New records of the West Indian manatee (Trichechus manatus) from the Bahama Islands

Abstract The first positive sighting of a manatee ( Trichechus manatus ) in the Bahama Islands in more than 70 years was made on 12 September 1975 at West End, Grand Bahama Island. The only previous record was from the Bimini Island group in 1904 . A dead manatee was found near Freeport, Grand Bahama Island, in November 1975 . The skull, which was preserved, had a condylobasal length of 36·8 cm. Speculation concerning the origin of these animals is offered: a local population; immigration from Florida or other islands in the Bahamas; and importation by man. The manatee population in the Bahamas might be limited by freshwater sources. An aerial survey should be conducted to assess the manatee population, if any, in the Bahama Islands.

Marine Parks and Zoos

Publisher Summary This chapter discusses the different aspects of marine parks and zoos. It also provides worldwide counts of zoos and aquariums. The mission statements of most zoological parks and aquaria include recreation, education, conservation, and research in one form or another. Behavior, including acoustic emissions, can be observed and recorded 24 h/day if desired. Animals can be trained to hold position for body measurements, collection of body fluids (blood, urine, and milk), various medical procedures (i.e., ultrasound examinations), and collection of exhaled breaths for air composition analyses. Animals can be trained for a variety of visual, acoustic (hearing, echolocation), locomotion, and learning studies. The birth, growth, and development of offspring can be detailed. Research on wild marine mammals, especially cetaceans, is often expensive and subject to the vagaries of environmental conditions, among other things. Modern technology has made huge contributions to various studies of free-ranging marine mammals. Nevertheless, it is our opinion that there is still much that cannot be learned from wild animals that can be learned from marine mammals in zoological parks and aquariums.

Sirenian Life History

Publisher Summary Sirenians are unique among the marine mammals in that they are herbivores. The manatees, as their common names suggest, are distributed in the coastal tropical and subtropical regions of the Atlantic Ocean. The dugong is found in the South Pacific and Indian oceans. The manatees and the dugong are considered endangered or threatened under various national laws and international conservation schemes. The Stellers sea cow is the exception: not only is it extinct but it inhabited the islands in the western reaches of the Aleutian archipelago in the North Pacific Ocean. Detailed age estimation studies have only been done for the Florida manatee and for the dugong. Female Florida manatees reach sexual maturity between 2.5 and 6 years of age. Male Florida manatees reach sexual maturity between 2 and 11 years of age based on the presence of active spermatogenesis in the testes. Even though the estimated maximum life expectancy for the dugong is similar to that of the Florida manatee, dugongs appear to mature at greater ages, and the age at sexual maturity may vary among populations. In both manatees and dugongs the male plays no apparent role in the care of the young. After mating, males and females go their separate ways. Florida manatee calves average about 120 cm in length at birth, but viable calves may have a birth length ranging from about 80 to 160 cm. This, along with variable individual growth rates, results in a highly variable length at age distribution. A key factor in assessing fecundity is the gestation period, which, despite numerous conceptions and births of Florida manatees, is not known for any sirenian species. Even though the Florida manatee and the dugong have been studied intensively since the 1980s, detailed data on many aspects of their life history are only beginning to be elucidated and there is considerably less information on the other species of sirenians.