Environmental Engineering Reference
In-Depth Information
seals are declining and, in some cases, face an escalating risk of extinction
under current projections for Antarctic warming (Barbraud et al. 2008).
Marine mammals comprise several orders that are very well adapted
to life in the water, among these mammals being cetaceans including
whales and dolphins, carnivores with polar bears, sea otters, sea lions,
seals and walruses between this particular group and fi nally the sirenians
including manatees and dugongs (Bastida and Rodriguez 2009). Fossils
show that cetaceans arose from terrestrial ancestors more than 50 millon
years ago (Fordyce 2002). Pinnipeds predecessor inhabit coastal regions
approximately 23 to 29 million years ago, during Oligocene. Polar bears
and sea otters are a group of modern species with the last emergence of
aquatic carnivores, recently during the Pleistocene of the Quaternary Era
(Bastida and Rodriguez 2009). Marine mammals and bats are probably the
mammals whose anatomy and physiology have undergone the greatest
modifi cations. Marine Mammals adapt very well to living in oceans and
seas. Some of them (cetaceans) adapt better than others (carnivores and
sirenians). Discussion of evolution depends on an agreed phylogenetic
approach. On the other hand, evolutionary processes at the species level
have likely a different mechanism as natural selection, sexual selection, co-
evolution and others. The processes involved were different across different
marine mammals. On geological timescales evolution and paleoecology
are inextricably linked, for evolution occurs through natural selection and
adaptation to the environment (Fordyce 2002).
The impact of the climate change induced changes in marine ecosystems
is increased by anthropogenic reasons. Human activities are polluting,
warming, and acidifying the oceans, melting sea ice, overharvesting
fi sheries, and altering entire food webs (Davidson et al. 2012, Halpern et al.
2008, Hoegh-Gouldberg and Bruno 2010). Fisheries' by-catch causes deaths
of more than 650,000 marine mammals each year (Read 2008). Overfi shing
has depleted food supplies by reducing fi sh populations by 50-90%, and
industrial-scale krill harvesting will likely further deplete food resources
(Myers and Worm 2003, Hilborn et al. 2003, Schiermeier 2010). In addition,
polar oceans are warming at rates twice as fast as the global average (Hoegh-
Gouldberg and Bruno 2010); this has already altered whale migrations,
reduced prey populations, and caused declines in seals and polar bears
(
Ursus maritimus
) whose lifestyles are dependent on sea ice (Moore 2008).
The International Union for the Conservation of Nature (IUCN) Red List
currently classifi es 25% (32 of 128 species) of marine mammals as threatened
with extinction. Examination of the threats on the basis of the Red List
shows that nearly half of all species are threatened by two or more human
impacts, with pollution being the most pervasive, followed by fi shing,
