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The Deadly Fish Trap

The ephemeral waters of the Okavango Delta are never a guarantee. Some years, like 2019, we get huge droughts. Other years, like 2020, we get a huge flood. And other years, like 2021, we get huge rains. While meteorologists do their best, it is extremely difficult to predict how the Okavango will change from one year to another. But this variability is all part of its success strategy. The residents of the Delta have evolved to cope with everything from below-freezing temperatures in the cold desert nights, to month-long droughts where surface water is completely unavailable over large swathes of the ecosystem. One of the most unpredictable sights you would therefore be lucky enough to see here are the fish traps.

A highlight of any annual Okavango calendar is the arrival of the flood. Between November and April, huge amounts of rain falls in the highlands of Angola over 1,200km away, and, incredibly, 11,000 billion litres of this precious water travel on a slow and arduous journey south to reach the Okavango in the middle of its dry season. Starting at the papyrus and palm-fringed shores of the panhandle, the flood waters spread out into the iconic fan-shape of the Delta. Here it is trapped between two ancient tectonic ridges that damn the waters. The flood is what keeps the Okavango alive and makes it home to some of the greatest abundance of endangered wild animals left on our planet. Without it, this bountiful desert would soon turn to dust, and its inhabitants would be lost forever.

One such resident is the African elephant. These mighty beasts are considered to be ‘ecosystem engineers’ since they use their tusks, feet, and trunks to dig in search of water or mineral sediments that they can detect in underground sources during times of drought. Each time they do this, they may remove several cubic meters of sediment, creating depressions in the ground and tapping into ‘well points’. ‘The Flood’ sounds like a dramatic event, but the reality is quite different. The water moves at a snail’s pace, spreading out like treacle and slowly filling vast floodplains, hippo pools, and river channels. You can race ahead of it, park your car, watch as it oozes out towards you, and, in a matter of hours, your local surroundings will be completely transformed into a wetland oasis. The watering holes created by the elephants will be one of the first things to fill once the flood arrives and one of the last places it remains for months after it disappears, making them vital sources of hydration for countless other animal species. Even the depressions left behind in an elephant's wake footprint are home to tiny frog nurseries.

As the waters trickle southwards, the fish follow. As it fills depressions, common species of fish, including tilapia, bass, barbel, and bream can be found in them, while ferocious tiger fish and pike lurk in the peripheries. The bald hippo, who is particularly vulnerable to drought, takes great delight in the arrival of the waters and their laugh-like grunts can be heard daily during the arrival of the flood. Despite being vegetarians and nature’s natural lawnmowers, hippos do not great make peaceful neighbours. Huge territorial battles between bulls break out over the most lucrative pools (for both mates and resources), and outsiders are simply not tolerated. Forward-pointing, 40cm long incisors and sharp, 50cm-long canines can easily mean a fight to the death. As the waters arrive, they can finally spread out and avoid these antagonistic relationships with their brethren as much as possible. Hippos spend their days feeding on grass, returning to their homes at night. As they do, their bathroom movements in the water create a kind of ‘nutrient conveyor belt’. Research shows that hippos increase the amount of phosphorus and nitrogen in rivers by 25%, which is quickly gobbled up by resident bacteria and algae. The silica from the grass in their diet is also passed on, which makes up an essential component of the cell walls of diatom algae, a key part of the local food chain.

At the height of the flood, fish lay their eggs in this bountiful environment, feeding on the algae that flourish in the hippo's excrement. The three-spotted tilapia takes this to the next level. Males excavate elaborate saucer-shaped nests up to 30cm deep and 75cm wide that can be seen from the air, using just their mouths and fins to dig their elaborate structures. After luring a passing female to his creation, she will lay her eggs and hold them in her mouth where they soon hatch. Their young are occasionally released from their captivity to feed, but at any sign of danger, they will dart back into their cavernous homes. As the flood waters start to recede at the start of the dry season, there is a huge rush of fish out of the floodplains and into the main river channels. This annual event is known as the ‘Barbel Run’, and it is accompanied by huge flocks of birds that take to the sky and dive into the murky waters to feast on the desperate bounty. However, not all fish are lucky enough to make it…

Some fish, who never left in time, remain trapped in the increasingly shallow pools with nowhere to go, cut off from the rivers by the rapidly receding waters. For them, this is normally a death sentence. Huge crowds of birds gather at the banks of these ever-dwindling pools, working as a team to flush out their prey and gobble up the last remaining inhabitants. Black herons create umbrella canopies with their wings and use their feet to flush their prey towards this ‘safe haven’ before skewering them with a stab of the beak. Yellow-billed storks wade with their bills held open snapping them shut when they detect movement. Pelicans use a cooperative formation, beating their wings on the surface of the water and driving their prey into the shallows, where they are scooped up whole. Above, pied kingfishers hover in slow motion, their heads angled down to spot fishes from seemingly impossible distances. Once a target is found, they dive. As their bill parts in the water, their prey may detect the vibrations of their sound waves, but has just half a second to escape a near-certain death.

It's not just fish that feast on this bounty, however. Over 8-years ago, the NHFU released their film, ‘Africa’s Fishing Leopards’. Narrated by David Attenborough, this intimate story followed the life of a leopardess as she raised her cubs in a dangerous new world with our founder, Brad Bestelink, working alongside them to document every step of their journey. ‘Savute’ means ‘mystery’ in the local Bayei language, and it’s a totally appropriate name since this 60-mile-long channel runs and dries seemingly at random. After a hiatus of 28 years, in 2010 it suddenly flowed again, bringing with it an abundance of life and, in particular, barbel (otherwise known as catfish). As quickly as it arrived, it disappeared again. In its wake, it left its catfish inhabitants encapsulating themselves in a mucus slime, absorbing oxygen through their permeable skin, in the hopes that the water would one day return. As the name of this film would suggest, the ever-adaptable leopards that lived in their vicinity were quick to pick up on this food source at the height of the drought.

The existence of fish traps provides sustenance for countless other animals and is thanks to the activities of two of the Okavango's greatest architects: the elephant and the hippo. With climate change wreaking havoc around the world, the expectations are that by 2050, the Okavango will only have enough water to fill its river channels, meaning that its iconic swamps will disappear entirely and so too will most of the fish traps. It all sounds a bit depressing, but with a little help, there is reason to hope. Taking action on climate change requires everyone around the world to make changes in their lives. But they don't have to be dramatic. For example, couldn't you take a local holiday this year, rather than travelling abroad? If we all made these small and tangible sacrifices, then the outcome won't be so terrifying after all.