The collected works

The dugong (Dugong dugon) is the only herbivorous mammal that is strictly marine. It has a range spanning some 37 countries, including tropical and subtropical coastal and island waters. This plan presents a global overview of the status of the dugong and its management throughout its range. It contains information on dugong distribution and abundance, threatening processes, legislation, and existing and suggested research and management initiatives for the countries and territories in the dugongs known range. It is hoped that the comparative information provided will enable individual countries to develop their own, more detailed, conservation plans.

Dugong : status report and action plans for countries and territories

Living on the edge: dugongs prefer to forage in microhabitats that allow escape from rather than avoidance of predators

Background Protocetidae are middle Eocene (49–37 Ma) archaeocete predators ancestral to later whales. They are found in marine sedimentary rocks, but retain four legs and were not yet fully aquatic. Protocetids have been interpreted as amphibious, feeding in the sea but returning to land to rest. Methodology/Principal Findings Two adult skeletons of a new 2.6 meter long protocetid, Maiacetus inuus, are described from the early middle Eocene Habib Rahi Formation of Pakistan. M. inuus differs from contemporary archaic whales in having a fused mandibular symphysis, distinctive astragalus bones in the ankle, and a less hind-limb dominated postcranial skeleton. One adult skeleton is female and bears the skull and partial skeleton of a single large near-term fetus. The fetal skeleton is positioned for head-first delivery, which typifies land mammals but not extant whales, evidence that birth took place on land. The fetal skeleton has permanent first molars well mineralized, which indicates precocial development at birth. Precocial development, with attendant size and mobility, were as critical for survival of a neonate at the land-sea interface in the Eocene as they are today. The second adult skeleton is the most complete known for a protocetid. The vertebral column, preserved in articulation, has 7 cervicals, 13 thoracics, 6 lumbars, 4 sacrals, and 21 caudals. All four limbs are preserved with hands and feet. This adult is 12% larger in linear dimensions than the female skeleton, on average, has canine teeth that are 20% larger, and is interpreted as male. Moderate sexual dimorphism indicates limited male-male competition during breeding, which in turn suggests little aggregation of food or shelter in the environment inhabited by protocetids. Conclusions/Significance Discovery of a near-term fetus positioned for head-first delivery provides important evidence that early protocetid whales gave birth on land. This is consistent with skeletal morphology enabling Maiacetus to support its weight on land and corroborates previous ideas that protocetids were amphibious. Specimens this complete are virtual ‘Rosetta stones’ providing insight into functional capabilities and life history of extinct animals that cannot be gained any other way.

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New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism

Distribution, abundance and conservation status of dugongs and dolphins in the southern and western Arabian Gulf

Study of the gonads of 108 dugongs from north Queensland indicates that neither females nor males are continuously in breeding condition. The gonadal activity of males in a population is not synchronized. Ovaries tend to be active in the latter half of the year. There is no evidence for females coming into oestrus soon after giving birth but conception can occur during lactation. In the Townsville-Cairns area, dugongs calve from August-September through December. Neonates are between 1.0 and 1.3 m long and weigh 20-35 kg. Dugongs of both sexes less than 2.2 m long are likely to be immature, those over 2.5 m long are probably mature, and the status of animals between 2.2 and 2.5 m long is uncertain. The pre-reproductive period seems to be very variable but is a minimum of 9-10 years for both sexes. The gestation period is about 1 year and lactation can last at least 1.5 years. The usual litter size is one. The secondary and tertiary sex ratios are 1:1. Estimates of the calving interval based on pregnancy rates, the rate of accumulation of placental scars, and calf counts from aerial surveys and photographs, range from 3 to 7 years for various populations. A simple population model has been used to calculate the relationship between calving interval and adult mortality rate for stationary populations with different pre-reproductive periods and juvenile mortality rates. Even the most optimistic schedule of reproduction and juvenile mortality demands an adult survivorship of about 90% per year for population maintenance.

LM Marsh

Papers

Breeding Cycle, Life History and Population Dynamics of the Dugong, Dugon dugon (Sirenia: Dugongidae