In this issue
This issue covers our activities for February 2020. We start off with an interesting article on how ocean noise pollution affects marine animals. For the species of the month we look at the Southern Red Bishop, probably one of the most identifiable species along the river. We close off with summaries and data from our routine monitoring projects covering downriver permanent probe data, bird counts and marine debris.
What we have been up to
On the weekend of 21 February was rather a busy one for our rangers. The LBRCT joined forces with Fisheries officials from the Mosselbay & Stilbay offices as well as the Mossel Bay Water Police in a 3 day operation aimed at enforcement of Marine Living Resource regulations in the Breede estuary and along the adjacent coast.
The operation was done under the auspices of Operation Phakisa (Oceans Economy) which is a central government lead initiative. We assisted with logistic support, provided vessels for water patrols and contributed additional manpower.
A number of transgressions were identified and fines were issued. Hopefully these will progress successfully through the legal system. We also got some time to discuss system-specific pain points and initiate planning for future operations.
Turtle Hatchling Rescue
On the 24th of February we had our first turtle hatchling that washed up at Infanta – (this was the second one for the hatchling season). Thank you to Suzette Silbernagl for contacting us and assisting to get the little fellow to us. Also thank you to Martin Fourie from Witsand that transported the hatchling to Paarl where Two Oceans Aquarium retrieved him for rehabilitation.
Deafening the Song of Life
How Ocean Noise Pollution Affects Marine Animals
From the tiniest cricket hiding between the cracks in the bricks, chirping its song to attract females and establish its territory, to birds and frogs and whales, the entire animal kingdom is in a constant state of song. And in the aquatic realm, through sheer physics, this is even more true.
Water is much denser than air, so its molecules are packed tighter together. This means that sound (which manifests through molecules vibrating and pushing against one another) travels much further and faster under water than in air.
Light does not reach far under water. Near the surface in clear water, you might be able to peer a few metres, but at greater depths there is no light to see with at all (unless it is a bioluminescent source of course). On a good day, whales can barely see their tails 16 metres away in turbid waters. But they can maintain their social network acoustically for many miles. Whales see the ocean through sound. Your mind’s eye is their mind’s ear. Many marine animals have evolved to see with sound, using sound for navigation, to avoid predators and hunt prey, and for communicating with other members of their species.
The problem is that man-made sound can interfere with these evolutionary traits. The effects of noise on marine animals are similar to those we experience. If you have ever been left with ringing ears after a rock concert, lived next to an airport or worked in a factory, you know that loud noise can temporarily affect your hearing or even damage it permanently.
Noise interferes with communication. Can you talk above the background noise in a busy cocktail party? It is like the cell phone story, ‘Can you hear me now? Can you hear me now!?’. Excessive noise can change the behaviour of marine animals too. Like a person who decides to move house rather than live next door to a new airport, animals might choose to desert their habitat if things get too noisy because they cannot communicate successfully.
There is a lot of research being done in this field, especially now as new technologies become available to measure sound more accurately underwater. Can we predict what noises and vibrations might be released into the marine environment by new machinery or ships? How does sound propagate through different ocean environments and how far? What are the long-term effects of noise on marine animal populations? One positive is that even though noise pollution travels very fast and very far through the ocean, the moment you switch off the source, the noise is gone. Fortunately, this is very much unlike plastic or chemical pollution. Remove the source of the noise, and the problem goes away. This gives us hope that the impact of noise pollution can be successfully managed in our oceans.
In our next issue we will explore the science of marine noise pollution further, and the known and potential effects it can have on our marine life.
Species of the month:
Southern Red Bishop
Probably one of the most identifiable species along the river during their breeding season, with the males and their scarlet and black colouring, frolicking among the reeds. These birds are seen in high numbers during September in the reedbeds when the males are displaying for females or defending their territory. By December, they become more difficult to spot along the estuary as the breeding season is over and the males take on a duller brown colour. They also disperse to the farmlands but will roost at night in the reedbeds. If you are patient enough, you can still spot them in the reeds this time of the year.
Its scientific name is Euplectes orix, which in Greek translates to “rice weaver” … the weaver part is obvious, the rice … probably because it eats seeds?
They are not a threatened species, having benefitted from human construction of dams and canals, and the increase in seed crops. In the Breede they are an eye-catching element of the native bird life, seen from Bobbejaans and further upriver. Their high numbers are probably due to a mix of the surrounding agricultural fields providing abundant food and also the large reed beds still present in the middle river reaches. However, destruction of natural reed beds could impact their numbers in the future. Removal or cutting of the reed beds by residents while increasing their accessibility and views has unintended consequences for the biodiversity of the river. Due to the current low flow rates, salinity will creep up-river and when landowners remove a reed bed the higher salinity causes a reduction in the reed zone. Those reeds will not grow back as has been observed in Goukou and in turn will affect our weaver population.
Those bright red plumaged ones are the males during breeding season. Out of breeding season they lose their bright colours and are almost indistinguishable from the female. Female and non-breeding male plumage is streaky brown with whitish underparts, which makes them easy to confuse with other species. They can be found throughout southern Africa near open water sources. Reeds beds are their preferred nesting grounds, but they have been known to rarely nest in other plants. Interestingly they are notably absent in the Transkei, probably due to many reed beds being trampled by overgrazing.
Red bishops are colonial nesters, meaning that they breed in close proximity as a group. The nests are an up-right oval shape, with the opening at the top under a “porch”. Males build between 3 to 13 nests in breeding season, each nest can take them 1 to 3 days to complete and are constructed from reed leaf or grass blades.
They are polygynous, with males attracting between 3 to 8 females in breeding season. Once a female selects a nest, she will start lining the interior with downy materials. They will lay 1 to 5 five eggs that are a pale blue to turquoise colour. Eggs are incubated for about 13 days, and the fully-fledged chicks leave the nest about 15 days later. Red bishops are also parasitized by the Diderick Cuckoo (called a brood parasite) which will lay its eggs in the red bishop nests and leave the red bishops to raise the cuckoo’s offspring. Nests are abandoned after the chicks have fledged and are frequently occupied by other bird species and mice.
Adults are preyed upon by Cattle Egrets and other large birds like Peregrine Falcons and Western Barn Owls. Predation by snakes, rodents and other small mammals and the occasional flood is the most important cause of nest failures. They forage in flocks with other weavers and sparrows, and even breeding males will leave their territory to join a foraging flock. Their diet consists mostly of seeds and small invertebrates like beetles, caterpillars, dragonflies and spiders.
Roberts Bird Guide – Second Edition Oct 2016.
Craig, A.J.F.K. Red Bishop. Avian Demography Unit. Accessed 23 October 2019.
In the data
Monthly routine monitoring
Downriver permanent probe data
Unfortunately our mobile probe gave up the ghost again during February. We downloaded the data from the permanent probes both down and up-river, to compare the effect of tidal influences on the shallower areas, and the effect of flow generated from rain in the catchment, had on the estuary.
Spring tide 10 January
From the graph we can see that high tides bring in lower temperatures with salinity, with the surface elevation increasing by a maximum of 1.19 m with high tide and drops by 18 cm with low tide.
Neap tide 17 January
During the neap tide, the changes are less drastic, with a maximum surface elevation of 75 cm during high tide, and drops 27 cm with low tide.
Spring tide 24 January
This spring tide looks a lot more interesting. The preceding rains of 17-22 January caused significate flow to come down from the catchment. You can see the sharp rises in salinity as the high tides start pushing in hard, but drops off sharply as the upstream flow gains the upper hand and forces the salinity do drop sharply. Surface elevation peaked at 1.08 m, and at low tide only dropped by 3.4 cm.
Neap tide 2 February
This neap tide we can still see the effect the steady upriver flow has on the lower estuary salinity.
Flow and tides compared on rainy 20-22 January
The top graph shows the drastic increase in flow coming down from the catchment with the rains. Compared with the second graph, we can see that it takes approximately a day for the fresh water flow from the catchment to have a very noticeable effect on downriver salinity, pushing it all the way down from 30 to 0.9 PSU.
January / February bird counts
A relatively low number of species for summer were seen during this survey (27 species), but compared with the 29 species seen in January. This could be attributed to the observed high boating activity up during the surveys. The exposed mud banks at Groenpunt are important for many bird species such as African Spoonbill, Black-winged Stilt, Whimbrel and multiple tern species which feed and rest at this site during low tide. While the number of species recorded was low, over 1200 birds were seen during the survey, which compares favourably with the 1161 birds seen in January.
High numbers of summer migrants were seen which is to be expected on the Breede River Estuary. This included Common ringed Plover (265 birds), Whimbrel (58 birds) and Grey plover (48 birds). Many other summer migrants were still seen during February: Common Sandpiper, Curlew Sandpiper, Bar-tailed Godwit and Common Greenshank. These migrants only start leaving our shores in March.
Resident waterfowl were abundant with Egyptian Geese (172 birds), South African Shelduck (247 birds) and Yellow-billed Ducks (158 birds) seen in high numbers. All three of these duck species are common birds in South Africa.
January / February marine debris
Most of the litter recorded in February was found on Main Beach (62.9%) followed by Oysterbeds (15.9%), Blokke (12.5%) and finally Gov. Slip (8.7%). In each of the four survey zones, plastic was the most abundant litter type. The highest contribution of plastic-related litter was found on Main Beach (73.8%) and the lowest at Gov. Slip (47.4%).
In the Blokke survey site, the most abundant plastic-related litter were pieces of different sizes. This makes it difficult to determine the origin of these pieces. However, plastic bottles and bottle caps from beach users were also found in high numbers. Plastic that likely originated from local users was important at the Gov. Slip and Oysterbeds sites. Single-use plastic bags as well as beverage bottles and bottle caps were found in large numbers in these two sites. Main Beach also recorded high numbers of these items, but plastic pieces, particularly microplastics dominated the litter picked up.
Other litter types that were important in the Blokke survey area, were pieces of rope (12.2%) from the marine environment and glass-related litter (4.9%) which is from beach users within Witsand. Gov. slip saw high numbers of cigarette butts (24.6%) and food wrappers (7.02%) which is indicative of littering by beach users. Main beach saw litter that originated in the marine environment, specifically pieces of rope (14.3%) an important litter type. Cigarette butts were the next important litter type in this area. Oysterbeds has the highest percentage of glass pieces found (8.7%), often from beer bottles. Cigarette butts and packaging accounted for 7.7% of all litter picked up in this area. Food wrappers, primarily chip packets were also recorded (7.7%). Often the litter in this area was hidden in the vegetation above the high tide line.
Get involved and help keep our beaches clean! Anchorage Restaurant and Bar still has their coffee for trash initiative going. Why not go pick up a bucket from the restaurant and fill it with litter for a free cup of coffee.
Cumulative marine debris collected for all areas:
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 email@example.com.