Namibia’s bottlenose dolphins unique, endangered - researchers

By Jade McClune

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 boat-based 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 near Aphrodite Beach, Walvis Bay.