Namibia’s bottlenose dolphins unique, endangered - researchers

FRESH research into an isolated  population of bottlenose  dolphins in the waters  around Walvis Bay indicates that  there are generally very few such  animals to be found in Namibian  waters, and that this population is  both unique and endangered.  Based on the findings of the  long-range study, the average  number of bottlenose dolphins in  Namibian waters is estimated at  82 per annum, but they are said to  face a number formidable threats.  The authors of the report, which  covers a five-year period, concluded  from the data that Namibia’s  coastal population of common  bottlenose dolphins (scientific  name Tursiops truncates) is regionally  isolated and unique.  Moreover, the study – published  last week in the African Journal of  Marine Science – found that “This  population faces several potential  anthropogenic (man-made) threats,  especially in Walvis Bay, including  boat-based tourism, a commercial  harbour undergoing expansion, and  aquaculture for oysters and mussels.”  The authors said a review of the  data based on 238 boat-based surveys  showed that between 2008 and  2012, there were 170 encounters  with bottlenose dolphins in the area.  The overall group sizes varied from  one to 45 individuals (with the mean  at 10.7).  The researchers, Elwen,  Leeney and Gridley found that  encounter rates, the group sizes  and the total numbers of dolphins  identified were notably  higher in winter than in summer  field seasons.  “The highest numbers estimated  were in the first and last  years of the study, with estimates  of 74 to 82 in 2008 and 76 to 77  in 2012.” The statistical data had  an upper 95% confidence limit.  According to the marine researchers,  “The only previously  available data, from an incomplete  study in the early 1990s,  suggested that the population  was between 100 and 150 individuals  at the time. Although no  linear trend in population size  was obvious during the current  study, the clear evidence of isolation,  small population size, low  annual birth rate, and potential  long-term decrease in numbers  since the early 1990s is concerning.”  “The number, survival and immigration  parameters of bottlenose  dolphins using Walvis Bay  were investigated using robust  design and Huggins closed-population  mark-recapture models,”  they said, but it is difficult to  gauge whether there have been  major changes in the local dolphin  population since.  The release of the latest data  comes shortly after the Namibia  Dolphin Project reported its latest  recue of two bottlenose dolphins  that were stranded south  of Walvis Bay near the end of  March.  According to earlier media  reports, a volunteer marine scientist  at the Namibian Dolphin  Project, Jack Fearey, said they  were alerted to the two bottlenose  dolphins that were stranded  near Lover’s Hill by two boatbased  tour guides who work in  the area. The team of marine scientists  later identified the stranded  dolphins as two “sexually immature  males” of about seven  years, each weighing 200kg.  It is understood the dolphins  became stuck in the shallow waters  while scouting for fish, and  that this was not too uncommon.  “We have both these boys on our  records and know them quite  well as they are frequent visitors  to the lagoon. They usually swim  up in the lagoon to feed,” he told  the press.  In the event of sighting a dolphin  stranding, residents and  visitors to the coast are encouraged  to contact the Namibia  Dolphin Project on 081-6876461  for assistance, whose volunteers  have gone to great and admirable  lengths to assist distressed  dolphins and whales.  The latest study cited above,  entitled ‘Abundance estimates of  an isolated population of common  bottlenose dolphins Tursiops  truncatus in Walvis Bay,  Namibia, 2008–2012’, concluded  that “further work to collect data  on demographic parameters  [of local bottlenose dolphins] is  urgently recommended with a  view to obtaining increased protection  for this species.”  A bottlenose dolphin takes a  dive in the waters nearAphrodite  Beach, Walvis Bay.