Environmental Engineering Reference
In-Depth Information
historical population dynamics of the species across six breeding colonies
that represent a range of geographic localities. The observed mismatch
distribution obtained by the authors showed evidences of a population
expansion that would date back to at least 18,000 years before present
and could possibly be as old as 38,000 years. This date coincides with the
height of the last glacial maximum in the area. The authors suggested that
the observed population expansion could be attributable to the high ocean
productivity that characterizes maxima glacial periods that made resources
abundant in the South Atlantic (Martin 1990). On the other hand, the nutrient
content of oceanic waters is thought to decrease substantially during warmer
interglacial periods, particularly in the southern oceans between 22°S and
41°S (Oppo and Horowitz 2000). Thus, current and future global warming
would affect the abundance of Cape fur seals by means of a diminution of
the ocean productivity and prey abundance.
Another case that deserves attention is that of the South American fur
seal,
Arctocephalus australis
. As the South American sea lions,
A. australis
is
distributed along the Atlantic and Pacifi c coasts of South America (King
1983). Breeding colonies are not homogeneously distributed along the
species distribution. They are only found in three areas of the northern
and southern extremities of the species range: the Uruguayan islands; the
southern coast of Chile and Isla de los Estados; and the northern coast of
Chile and Peru (Túnez et al. 2008b). Morphological and genetic studies
support the idea that Uruguayan and Peruvian colonies can be considered
as different Evolutionary Signifi cant Units (ESUs) (Túnez et al. 2007, Oliveira
et al. 2008). South American fur seals have been intensively exploited by
humans (Ximenez and Langguth 2002). However, the most important threat
to the conservation of the species in Peru is the mortality during El Niño
Southern Oscillation (ENSO) events (Oliveira 2011). During the severe ENSO
in 1997-1998, the Peruvian population of fur seal declined a 72% (Oliveira
2011), as a result of low food availability as a consequence of warming of
sea-surface temperatures and primary productivity reduction. Considering
both the intense harvesting and the severe population reduction caused by
the 1997-1998 ENSO, Oliveira et al. (2009) carried out the fi rst bottleneck
test for the Pacifi c and Atlantic populations of
A. australis
based on the
analysis of seven microsatellite loci. Results of the test indicated that
the Peruvian population of the species may have experienced a genetic
bottleneck, while there is no suggestion of the Atlantic population having
experienced a similar phenomenon. The authors conclude that the detection
of the suggestion of a genetic bottleneck in the Peruvian fur seal population,
combined with its small effective population size (Oliveira et al. 2006) and
global warming models that predict stronger and more frequent ENSO
events in the future (NCDC-NOOA 2007), are enough reasons for concern
regarding the survival for the species, and should be taken into account in
