By Peter G. H. Evans, Ian Stirling (auth.), Peter G. H. Evans, Juan Antonio Raga (eds.)
Interest in marine mammals has elevated dramatically within the previous couple of a long time, as evidenced via the variety of books, medical papers, and meetings dedicated to those animals. these days, a convention on marine mammals can allure among one and thousand scientists from worldwide. This upsurge of curiosity has ended in a physique of information which, in lots of circumstances, has pointed out significant conservation difficulties dealing with specific species. whilst, this data and the linked actions of environmental businesses have served to introduce marine mammals to a receptive public, to the level that they're now perceived through many because the dwelling icons of biodiversity conservation. a lot of the impetus for the present curiosity in marine mammal conservation comes from "Save the Whale" campaigns all started within the Nineteen Sixties through environmental teams world wide, in accordance with declining whale populations after over-exploitation via people. This public strain ended in a global moratorium on whaling urged in 1972 through the United countries convention at the Human surroundings in Stockholm, Sweden, and finally followed by means of the foreign Whaling fee ten years later. This moratorium principally holds sway to this present day, and additional protecting measures have incorporated the delimitation of in depth components of the Indian Ocean (1979) and Southern Ocean (1994) as whale sanctuaries.
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Additional resources for Marine Mammals: Biology and Conservation
Example text
For a number of cetacean species, a further constraint upon the number of young a female may produce in her lifetime is that, beyond a certain age, she may cease reproducing at alL In toothed whales with a matrilineal and polygynous social structure, such as sperm whale, killer whale, short-finned and long-finned pilot whales, the pregnancy rate declines with increasing age, and conception ceases 18-27 years before the age of maximum longevity, although females may remain receptive to mating attempts (Kasuya, 1995).
Similar changes in life history parameters in response to exploitation have been found in several seal species. , Lile History Strategies olMarine Mammals 45 1962) began breeding at an earlier age and their population growth rates increased after their numbers were reduced by commercial harvesting. , 1962). The average age of breeding bulls was 10 years (with a maximum of 20 years) at Signy Island and 6 years at Macquarie Island, whereas males reached sexual maturity at 4 years at South Georgia (Laws, 1953, 1956).
Among polygynous and sexually dimorphic species, a female should produce a male offspring when she is in good condition since she will then be best able to provide it with sufficient maternal care for it to be successful reproductively, compared with others. If she is in poor physical condition (or is of subordinate social status), she may be better to produce female offspring since these will have less trouble finding a mate and are therefore more likely to reproduce irrespective of their size or dominance status.