RiverWise
Issue 17 ~ August 2019
The monthly newsletter of the Lower Breede River Conservancy Trust
Season & Visitor Checklist
Remember to collect your angling and bait collection permits from your local Post Office during week days. Witsand, Heidelberg and Swellendam Post Offices can run out of stock during peak season due to high demand, and do not sell permits over weekends.
Did you know you can reserve your boat licence online and pay by EFT? Book online and collect at our Witsand office or Malagas Hotel, no more queues and paper forms to complete!
The Indian Ocean humpback dolphin
Humpback Dolphins (Sousa plumbea) in the Breede River - Why should we care and why are they important?
by Sasha Dines
PhD candidate University of Stellenbosch / SeaSearch research and conservation Core member of The SouSA project
Photographs courtesy of Bridget James (SeaSearch)
Humpback dolphins are the rarest species of resident dolphin in southern Africa and little is known about them by scientists and the public alike. Population studies since the 1990s have shown a clear reduction in group size, sighting rates, and abandonment of previous ‘hotspots’. The Indian ocean humpback dolphin, Sousa plumbea, one of four species of humpback dolphin, occur along the southern and eastern coasts of South Africa. However unlike other top predators in South African waters their home ranges are limited to extremely shallow, nearshore environments and over relatively short along-shore ranges.
It is these characteristics that result in high individual exposure to human induced pressures compared to other species, which range further from shore. On the one hand, this makes humpback dolphins one of the most ideal indicator species in South Africa, to monitor the impacts of anthropogenic (human caused) changes in the marine environment. However, it means that they’re also one of the most difficult dolphin species to study. Surveying their movements and collecting Photo ID data from a boat is often difficult, due to inaccessible coastline, poor weather, and large swells. It is for this reason that the presence of humpback dolphins in the Breede River are so important for studies of this species. The fact that they are regularly sighted in the river far upstream and also happily feeding could be an indicator of strong ecosystem health and also provides a safe and easier (in theory!) area in which to study these animals.
Over the past few years scientists have been trying to increase the sightings data on these elusive dolphins and increase the size of the photo ID catalogues across South Africa. These photo ID catalogues contributed to research published in 2017 that identified 247 uniquely well marked humpback dolphins in South Africa. From this scientists were able to produce a first national abundance for the population that was far below previous estimates of 1000 individuals, with numbers possibly closer to 500. They also have a very small range of only around 120km with dolphins in the south coast of South Africa likely forming one single population at the western end of the species’ global range, separate to the KZN population. However, more information is needed to fully understand the species’ total population abundance, population dynamics and ecological needs.
Scientists have been concerned for the health of the South African population for some time and showing concern for good reason. This small population size combined with slow population growth, may result in failure of these animals to withstand growing environmental pressures. This is concerning, especially in view of South Africa´s aim to increase the use of ocean resources in the near future. Other dolphin species whom have had small isolated populations and local pressures such as the Baiji (Chinese river dolphin), which numbered in the thousands of animals a few decades ago, have already gone extinct. The vaquita of the Gulf of California also currently numbers less than 19 animals, and there has been an estimated total population decline of 98.6% since 2011. These populations of dolphins all underwent similar pressures. Luckily for the humpback dolphins of southern Africa, people have already recognised the need to assess their status and understand their population structure, before it’s too late. These efforts have led to an up-listing in their conservation status from Vulnerable, to Endangered, during the local Red List Assessment and they are currently considered the country’s most endangered resident marine mammal.
Over the past few years the LBRCT and local community have run a successful sightings network where the community can provide sightings data which is key to understanding and protecting this dolphin species.
To continue reporting marine mammal sightings in the river to help contribute to this research please head to the SouSA Project or submit sightings to the LBRCT Marine Mammal whatsapp group (email your number to marinemammalspottersbreede@gmail.com). In particular include if you can, information on group size, behaviours and any high quality photos you may get.
Or better yet, download the Seafari App to your phone, where you can log all of your dolphin sightings from any location, and directly contribute to this research! Your sightings data is important to helping us understand how these dolphins use the river, as an indicator of overall river health and ultimately how we can better protect them for future generations.
August water quality
The water quality run in August got off to a rocky start as the sites between the Breede River Lodge and Mudlark could not be sampled due to a strong high tide current pushing the probe to the surface.
The bottom salinity at Goudmyn showed a high marine influence with 31.38 Practical Salinity Units (PSU) as seawater is around 35 PSU. The salinity dropped substantially after that with a much lower 11.98 PSU by Karoolskraal. From White House to Bush Pub the water was less than 0.3 PSU and freshwater conditions were recorded about 26 km upstream.
The water temperature ranged from 14.8 ºC to 15.21 ºC.
August bird count
The bird count for August recorded the lowest number of birds this year with 328 birds. However, there was a higher species count than we expected. A total of 38 species were recorded with some interesting species seen on the day.
Juvenile Lesser Flamingos were seen at Groenpunt with Black-crowned Night Herons, Southern Red Bishops and a Giant Kingfisher were seen. The four most abundant birds were Yellow-Billed Ducks (77 birds) followed by Egyptian Geese (50 birds), Black-winged Stilts (26 birds) and Cape Shovellers (19 birds).
August marine debris
At Oysterbeds towards Groenpunt, the two main categories of litter were plastic (27.4 %) and smoking (23.5 %). The two most important plastic-related litter recorded was plastic packaging (5.5 %), particularly glowstick packets and other plastic bags (4 %). Cigarette butts were the most abundant type of smoking-related litter and accounted for 16.8 % of all the litter found. This meant that 76 cigarette butts were picked up. Litter associated with cigarette packaging was the next most important smoking-related litter (6 %). The majority of this were cigarette boxes. Other litter that was found were food wrappers (16.1 %), particularly chip packets.
On Witsand Main Beach, a small 50 m patch of beach was covered for the litter survey and 912 pieces of litter were recorded. Plastic-related litter (93.4 %) dominated the litter found. The most abundant plastic-litter type was microplastic (plastic pieces smaller than 2.5 cm) which itself accounted for 61 % of all litter. Other important plastic categories were nurdles (129 pieces) and large plastic pieces (84 pieces). Rope pieces were the next most common category and accounted for 4.1 % of all litter picked up.
The litter picked up between Gov. slip to Skuitbaai was mainly foam-related litter (46 %), particularly small polystyrene pieces. Several buried plastic bags were also picked up. Plastic-related litter was the next most abundant (30 %). Smoking-related litter was also an important litter type with 11 % of all litter picked up.
Cumulative marine debris collected for all areas:
Thank you for reading
We hope you enjoyed this months' issue. Should you have any feedback, questions, or matters you would like us to cover in a future issue, please do not hesitate to write to us at news@breede-river.org.