Sunday, 11 September 2011

Marine mammals and their future

Marine mammals have borne the brunt of mankind’s unsustainable overexploitation, resulting in population decline and species extinction. Hunting for fur, blubber, and meat in the 19th and 20th centuries resulted in the extinction of three species – the Caribbean monk seal (Monachus tropicalis), Atlantic gray whale (Eschrichtius robustus), and the Steller’s sea cow (Hydrodamalis gigas). The most recent extinction, due to its use in traditional medicine, was that of the Baiji (Lipotes vexillifer) in 2008, a dolphin endemic to the Yangtze River.

In this backdrop, the August 16th edition of PNAS featured an excellent research (it truly is wonderful to come across such), entitled ‘Global distribution and conservation of marine mammals’, by Sandra Pompa and Gerardo Ceballos (National Autonomous University of Mexico) and Paul Ehrlich (Stanford). The mammalian species considered in the study were 129 in total (123 marine and 6 freshwater species), grouped into the orders of Cetacea, Sirenia, and Carnivora (common examples being whales, dolphins, porpoises, otters, seals, and polar bears) .

The researchers created geographic range maps for the 129 species and the map of the water bodies were split into grids of roughly 10,000 km2. They determined the number of species in each grid cell and calculated the total number of cells occupied by each species. Breeding, calving, and feeding grounds, and migratory routes were also factored in. The result was a composite global distribution map of water bodies, revealing locations of ‘global species richness, irreplaceable sites, endemism, and threatened species.'

1. All species can be represented in 20 global key conservation sites that cover at least 10% of the species' geographic range. These sites were determined on the basis: number of species present (species richness), severity of the risk of extinction for each species, and whether the species was endemic to the area.

2. Preserving 9 of such sites (mostly in temperate latitudes located off the coasts of Baja California in Mexico, the Atlantic coast of North America, Peru, Argentina, north-western Africa, South Africa, Japan, Australia, and New Zealand) would protect the habitat of 83.72% (108/129) of marine mammal species (including 5 endemic species) since these have high species richness.

3. The remaining 11 sites (6 freshwater, 5 marine: areas around Hawaiian and Galapagos Islands, Kerguelen Islands in the southern Indian Ocean, San Felix and Juan Fernandez Islands off the coast of Chile, Mediterranean Sea, Lake Baikal in Siberia, Caspian Sea, and major rivers such as the Amazon, Ganges, Indus, and Yang-tze) were tagged ‘irreplaceable key conservation sites’ of great conservation value due to the presence of endemic species, which, consequently, face a greater risk of extinction.
Eg. Galapagos fur seal (A. galapagoensis) and the Mediterranean monk seal (Monachus monachus).

4. Strong correlation of marine mammal species richness with human impacts (Spearman rank correlation (rs = 0.693, n = 46,164, P < 0.01 for climate disruption; rs = 0.666, n = 46,164, P < 0.01 for pollution; and rs =0.678, n = 46,164, P < 0.01 for shipping). The existing deterioration of the marine ecosystems due to anthropogenic activities (and the potential for more deterioration not just at these sites but also elsewhere) was evidenced by around 70% percent of most impacted areas being within or near key conservation areas. Factoring in other impacts such as commercial fishing would result in stronger correlation (and perhaps also global climate change, habitat degradation, ocean acidification, exploitation of natural resources such as oil and gas, hunting, tourism, and plastics?)

5. 10% of all marine mammals were considered to be vulnerable, 11% endangered, and 3% critically endangered. The following vulnerable species were identified:

i. Vaquita (a porpoise species), endemic to the Gulf of Baja California, has the most restricted range. Its population has been declining rapidly and there are only 150-300 individuals in the wild (1/5 of the population are killed in gillnets each year).

ii. Sea lions such as the endemic Australian sea lion (Neophoca cinerea) and the Galapagos sea lion (Zalophus wollebaeki), and the restricted range New Zealand sea lion (Phocarctos hookeri).

iii. Seals such as the freshwater and endemic Baikal seal (Pusa sibirica), and the endemic Galapagos fur seal (Arctocephalus galapagoensis) and Hawaiian monk seal (Monachus schauinslandi).

iv. Whales at the brink of extinction, such as North Atlantic right whale (Eubalaena glacialis) and Sei whale (Balaenoptera borealis), due to overharvesting, pollution, bycatch, and exhaustion of prey-species populations.

v. Dolphins such as the endemic New Zealand dolphin (Cephalorhynchus hectori) and the restricted range Australian Snubfin dolphin (Orcaella heinsohni).

This research could be a useful tool for environmental organisations and governments in identifying conservation areas and anthropogenic threats so as to protect endangered marine mammals and keep the oceans’ ecosystem functional. Mammals hold a lofty position in the food chain- consequently, their population dynamics would affect all other components of an ecosystem (and in human communities, by extension).

Pompa S, Ehrlich PR, & Ceballos G (2011). Global distribution and conservation of marine mammals. Proceedings of the National Academy of Sciences of the United States of America, 108 (33), 13600-5 PMID: 21808012

And the must read:

Image source: Apollo 17

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