Status of the resident bottlenose dolphin population in the Sado estuary : past, present and future
Abstract
The main aim of this work was to determine the past, present and future conservation
status of the bottlenose dolphin population inhabiting the Sado estuary region, Portugal,
using a long term (photo ID) data set. Resident animals, identified from their strong
resighting pattern, were confined to the estuary region. There is little evidence of social
interchange with other coastal bottlenose dolphins and the role of emigration and
immigration is unclear. This is a very small population. Numbers of animals have
decreased in the past but now seem to be increasing. A mark-recapture analysis of
individual capture histories showed that time changes in age-specific survival explained
the observed changes in number of animals. Survival was lower, particularly in young
animals, in earlier years which have resulted in a long period of lack of recruitment to
adulthood. In the most recent years survival has increased, especially for calves in their
second and third years. Fecundity has also been higher. Protected areas and proposed
marine SACs reflect the importance of the Sado estuary region; this is also an area of
intense anthropogenic activities that threaten the dolphin population. Population
viability analysis was conducted using the software VORTEX incorporating estimates
of past or current vital rates. The likely future of the resident population is for it to
decline, especially during the next few decades. A viable population was only predicted
if maximum values of vital rates were used or if regular immigration occurred. A
number of proposals for management action are discussed. This work constitutes an
example in conservation biology where life history parameters were estimated, and used
to predict future viability and thus to indicate management actions that could increase
the chance of saving a very small marine mammal population.
Type
Thesis, PhD Doctor of Philosophy
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