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.
The Cape Clawless Otter
Cape clawless otter (Aonyx capensis)
Cover photo by Mark Paxton, CC BY-SA 3.0.
Article cover photo by Peter Chadwick.
The African clawless otter, also known as the Cape clawless otter or groot otter, is the second-largest freshwater species of otter.
As the name indicates these otters do not have claws so identifying them by their spoor is easy. Cape clawless otters can be found in fresh and saltwater habitats and survive in both warm water and cold water areas as their fur is very water resistant and holds in the warmth very well. Staying cool means spending time in the water, and using burrows as a way to escape the highest temperatures of the day. To stay warm, the otters depend solely on their thick fur.
A. Capensis loves to play and they often live in family groups ranging up to six family members but can be seen swimming solitarily, like one spotted in the estuary. They are still around and if one has spare time to sit and watch they can be very entertaining to watch while they are playing with each other or even when they catch fish. They are very inquisitive, and if you sit quietly they may come up very close to see what is going on and to investigate the stranger in their home.
Their diet primarily includes water-dwelling animals, such as crabs, fish, frogs and worms. They dive after prey to catch it and then swim to shore again where they eat. Their forepaws come in handy as searching devices and are great tools for digging on the muddy bottoms of estuaries and rivers, picking up rocks and looking under logs. Their whiskers (vibrissae) are extremely sensitive and detect the movements of potential prey in the water.
The biggest threat to A. Capensis comes from humans. They will often forage in man-made fisheries and become entangled in nets. Overfishing may reduce the food supply available to otters. In forested areas, logging may be a major threat, since erosion leads to greatly increased turbidity in rivers which can in turn greatly reduce the populations of fish on which the otters depend. This may well be a far greater threat to otters than hunting.
With the Breede river having such a high diversity of life not only in the water but on the banks and shore line one is bound to bump into an otter especially in the early morning or late afternoon as this is the time when the otters prefer to go hunting.
Alien invasive plants & water quality
The impact of alien invasive plant species on water quality
Article cover photo by Wouter Haagan (Public Domain).
Aquatic alien invasive species is a worldwide problem. They have a negative effect on native aquatic plants and can also cause big problems for animal life and of course affect the quality of water. Within South Africa alone there are hundreds of invasive plant species in and near water sources. We will concentrate on only one of them and its effect on water quality and the efficient functioning of the nutrient and hydrological (water) cycles.
These cycles are defined as follows:
The nutrient cycle describes how nutrients move from the physical environment into living organisms, and subsequently are recycled back to the physical environment. This movement of nutrients, essential for life, from the environment into plants and animals and back again, is a vital function of the ecology of any region. In any particular environment, the nutrient cycle must be balanced and stable if the organisms that live in that environment are to flourish and be maintained in a constant population (Martin 2010). Currently, large parts of mankind influence the nutrient cycle in such a way that we remove nutrients from the land and discharge them into aquatic environments. On the one hand, this leads to soil depletion on the land, and on the other hand, an overabundance of nutrients and pollution of water sources.
Nutrients are chemical elements that all plants and animals require for growth. On Earth, there is a constant and natural cycle how these elements are incorporated when an organism grows, and degraded if an organism dies. The nutrients used in the largest amounts are the non-mineral elements, i.e. carbon (C), hydrogen (H) and oxygen (O). These elements are mainly taken up by plants as carbon dioxide (CO2) from the air, and water (H2O) by the roots (Joensson et al. 2004). They make up 95-98% of the mass of all living beings (Mahendrappa 2007). But they are, however, not sufficient for life to exist. Further elements are necessary to fuel life on earth: Nitrogen (N) and Phosphorus (P), Potassium (K) as well as Calcium (Ca) and Magnesium (Mg) are highly important, in particular for plant growth and agriculture. These elements are often referred to as macro nutrients. Their uptake is about 100 times that of micro nutrients. Micro nutrients, that plants take up in a much smaller amount and that are essentially consumed by humans, include Boron (Bh), Copper (Cu), Iron (Fe), Chloride (Cl), Manganese (Mn), Molybdenum (Mo), Zinc (Zn) and others.
These nutrients, essentially chemical elements, are continuously in a circular movement. The nutrient cycle is hence a general term that describes how nutrients move from the physical environment into living organisms, and are subsequently recycled back to the physical environment (Martin 2010). Nutrients in the soil are taken up by plants, which are consumed by humans or animals, and excreted again by them, or they are released back into the environment when organisms die (e.g. plants lose their leaves). Microorganisms in the soil break this matter down, and again make nutrients available in their mineral form, which makes it possible for plants to take them up again. Essentially, all nutrients that plants and humans require to survive are cycled in this way. In relation to water management and sanitation, it is mainly N, P and K that are of high priority. They are the most important nutrients to sustain plant growth and agriculture, and thus humanity.
Human-induced alterations in the nutrient cycles lead to an imbalance in the availability of nutrients, whose consequences, in particular with regard to water, are grave. Fertiliser runoff and wastewater discharge contribute to uncontrolled blooms of algae in rivers, lakes and oceans, feeding on nitrogen and phosphorus from fertilisers. When they die, their decomposition depletes the water of oxygen and slowly chokes aquatic life, producing “dead zones.” The largest dead zone in American waters, topping 20,000 square kilometres in July 2008, is off the Mississippi delta. More than 400 dead zones now exist worldwide, covering a combined area of more than 245,000 square kilometres (Castelvecchi 2009).
The amount of water on earth has been constant over centuries. It is in permanent circulation and regeneration and is therefore a renewable resource. However, most of the water on earth is salty (97%) and thus not suitable for the majority of uses. Only roughly 2.5% is freshwater in rivers, lakes, groundwater, fixed in soil or frozen in icecaps and a mere 0.5% of the total is easily accessible for human use (Inforesources Focus 2006). This liquid water travels the earth constantly in the water cycle. Humans largely influence the water cycle today, be it quantitatively, by using large parts of the water available, or be it qualitatively, by changing the quality of water (e.g. pollution). On the Earth, water never occurs in pure form, it always contains dissolved substances, be it minerals, nutrients, and also pollutants. The water cycle is thus inherently linked to the nutrient cycle. The water cycle involves the exchange of energy, which leads to temperature changes. For instance, when water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment. These heat exchanges influence climate. The evaporative phase of the cycle purifies water which then replenishes the land with freshwater. The flow of liquid water and ice transports minerals across the globe. It is also involved in reshaping the geological features of the Earth, through processes including erosion and sedimentation. The water cycle is also essential for the maintenance of most life and ecosystems on the planet. For both the nutrient and hydrological cycles to occur neither one of them may be interrupted.
Let us take Eichhornia crassipes, better known as common water hyacinth, for example. It is an aquatic plant native to the Amazon basin, and is often considered a highly problematic invasive species outside its native range. Outside of the Amazon, water hyacinth is a aquatic weed that can be found in lakes, rivers and ponds or areas filled with freshwater. It is a perennial aquatic plant and lives for more than 2 years.
These plant species are known as a free-floating weed but may be anchored in more shallow water. The invasive status which indicates to what extend the level of invasion is “transformer”. Transformer means that it can, as a monospecies, dominate or replace a natural or semi-natural ecosystem, altering its structure, integrity and functioning.
One of the fastest growing plants known, water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. Each plant can produce thousands of seeds each year, and these seeds can remain viable for more than 28 years (Sullivan & Wood 2012). Some water hyacinths were found to grow up to 2 to 5 metres a day in some sites in Southeast Asia (Gopal 1987). The common water hyacinth are vigorous growers known to double their population in two weeks.
When not controlled, water hyacinth will cover lakes and ponds entirely; this dramatically impacts water flow, blocks sunlight from reaching native aquatic plants, and starves the water of oxygen, often killing fish and other aquatic life.
There’s a number of factors that ensures that the quality of water is sufficient. Water flow can also be influenced due to the formation of dense mats by water hyacinths. These dense mats increases silt build-up in water bodies and the diffusion of oxygen is decreased resulting in lower concentrations of dissolved oxygen.
In conclusion the quality of water decreases because of lower oxygen concentrations combined with the increased amounts of organic detritus that collect beneath these floating mats, increases sediment accumulation rates and accelerates hypertrophication* processes that is harmful and eventually lethal to fish and other aquatic life, causes algal blooms and renders water toxic and uninhabitable for indigenous animal and plant species.
*Hypertrophication is the ecosystem’s response to the addition of artificial or natural substances, mainly phosphates, through detergents, fertilisers, or sewage, to an aquatic system. One example is the “bloom” or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Negative environmental effects include hypoxia, the depletion of oxygen in the water, which may cause death to aquatic animals.
September water quality
September’s water quality run was conducted on incoming spring high tides over 21 sites. At each site environmental variables are recorded every half a meter from just below the surface to as close to maximum depth as possible. The Breede River Estuary salinity, expressed as Practical Salinity Units (PSU), recorded near the mouth on the estuarine bed was below that of seawater (35 PSU) with a peak of 31.89 PSU at Gov. Slip.
The salinity decreased from Gov. Slip to the Malgas pont which is a result of the tidal influence decreasing the further you travel upstream. The effect of freshwater on the salinity is greater in the upper reaches of an estuary. The water temperature showed a longitudinal temperature gradient developing with lower temperatures recorded near the estuary mouth (16.53 °C) and higher temperatures in the upper reaches (18.45 °C at the pont). The water temperature in the lower reaches is influenced by the sea temperatures.
September bird count
Spring has arrived! The LBRCT staff were joined by Helen Jarman of Barry’s Accomodation. A total of 41 species were recorded on the day’s outing, with 29 of these water-associated birds. Higher numbers of migrant birds were recorded compared to the winter months, such as Whimbrel (39 birds) and Common Greenshank (24 birds).
New arrivals since last month were two Common Sandpipers. We usually only record a few of these non-breeding birds overwinter. The most abundant water-associated bird recorded were Southern Red Bishops. These birds build nests in reeds that are found along the Breede River. The bright red and black males can be seen puffing themselves up like a bumblebee in the reeds. Over 650 Southern Red Bishops birds were counted. Egyptian Geese were the next most abundant bird seen (102 birds) followed by Whimbrel (39 birds) and then South African Shelducks (34 birds).
Other birds seen on survey were Cape Vulture, Peregrine Falcon, Yellow-billed Kite, Great-striped Swallow and Yellow Bishop.
September 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:
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.