Okavango fish traps

by Grant Atkinson and Helena Faasen (Okavango Wilderness Safaris)

The recent high water levels in the Okavango Delta are now a thing of the past. One result of this year’s big flood is the exciting bird viewing that is taking place as thousands of fish become trapped by the receding waters.

These fish become a magnet for many species of waterbirds, and on a recent visit to Chitabe Camp we got to experience some of the action associated with these so-called ‘fish traps.” Instead of viewing birds just flying overhead, or standing somewhere, the fish traps bring many species together and the interaction that occurs between them is fascinating. Forced into close proximity with one another, the birds compete, co-operate, fight and steal from one another. The particular pool that we spent most time at near Chitabe was dominated for a while by a pair of Saddle-billed Storks. The pair were happy to share the pool with several smaller species of birds, but objected to a flock of Yellow-billed Storks, and some Pink-backed Pelicans, that joined in the action. For almost an hour the two Saddle-billed Storks chased all the other storks and pelicans away, but eventually they either grew tired of the effort, or else they had caught enough fish for themselves.

Birding action like we observed will be happening all over the Okavango over the next few months, and it will last until the annual floodwaters arrive and once again bring the sanctuary of deep water to the fish.

Too much of a good thing?

With the Okavango River at its highest flood level for decades at present, there have been great expectations for good birding as water reaches areas that have been dry for a long time. Throughout the Delta, water levels are high, and this has had the somewhat unexpected effect of forcing wading birds into peripheral areas. The result is that the central parts of the Delta are noticeably devoid of birds.

July is the month for the African Waterbird Counts, and long-standing transects that have been counted in the Okavango so far are turning up very few birds. The heronries at Xakanaxa, Gadikwe and Gcobega have been surprisingly quiet, and the same applies to other areas. Water at Lake Ngami is deeper and more extensive than at any other time in the recent past, and waterbirds are conspicuous by their absence.

However, along the fringes of inundated floodplains such as the Khwai and Gomoti, birding is much better. Unusually, sizeable flocks of Wattled Cranes are being seen along the Khwai River, an area previously considered marginal for this flodplain specialist. These are likely to be birds forced out of their normal areas by high water, or they may simply be taking advantage of the improved conditions at Khwai. The Gomoti floodplain is teeming with Slaty Egrets, Glossy and African Sacred ibis and a variety of ducks and geese.
Glossy Ibis probing the shallow floodplain margins (Photo: P Hancock)

Please keep the BirdLife Office in Maun informed of any build-up of waterbird numbers anywhere in the Okavango Delta system.

A Little Piece of the Okavango Restored

There have been some interesting attempts to manage the Okavango Delta in the past, to ‘improve’ the provision of the ecosystem’s goods and services, but it is doubtful whether many of these were successful. The system is very dynamic and fluctuates hugely within natural bounds, moving to its own rhythm.

During the 1970s and 80s, the flood levels in the Okavango were higher than average, but by the end of this period they declined and the outflow down the Thamalakane and Boteti Rivers no longer reached Rakops and the Mopipi reservoir at the distal end. Since large quantities of water were needed at the Orapa diamond mine, the Nhabe Channel was blocked, thereby diverting water down the Boteti River towards the Mopipi reservoir from whence it was pumped to Orapa. Of course, this deprived people living along the Nhabe from their water supply, but by the mid-nineties this did not make any difference since the Okavango waters ended in Maun, some 25 kilometres short.

The position of the bund at the start of the Nhabe channel

Now with the return of higher floods imminent, Debswana has removed the bund at the mouth of the Nhabe Channel. This is in line with the Okavango Delta Management Plan, and is a highly commendable action aimed at restoring the Nhabe Channel. This watercourse flows westwards to Lake Ngami, some 80 kilometres distant. If it flows this year, it will recreate valuable waterfowl habitat, as well as improving the quality of life for people living along its length, illustrating once again that what is good for birds is generally good for people too. Despite the Nhabe being blocked, Lake Ngami has actually filled to varying extent over the past five years, being fed by the Kunyere Channel, and this is likely to continue, with any water reaching the Lake from the Nhabe being an added bonus.

Work in progress - the pipes have been removed and the bund is being levelled (Photo: P Hancock)

The Nhabe Channel is likely to support significant numbers of ducks and geese once flows are restored, particularly Red-billed and Hottentot teal, White-faced Duck, Comb Ducks and Southern Pochard. For some reason, channels that have been dormant for a number of years (whether due to natural or man-made changes) attract vast numbers of waterfowl when they flow again, possibly due to a build-up of nutrients in the form of dung from the herbivores that graze along the channels when they are dry. It is expected that African Fish-Eagles and other piscivores such as Reed Cormorant and African Darter will soon recolonise the area.

It is likely that the Nhabe Channel will once again support large numbers of waterfowl (Photos: W Tarboton)
Once the Nhabe Channel becomes more permanent, aquatic vegetation in the form of reeds, sedges and waterlilies will become re-established, and provide suitable habitat for African and Lesser jacanas, African Pygmy-Geese and Whiskered Terns. The riparian woodland that has degenerated over the past two decades will also recover and boost numbers of frugivores such as Meyer’s Parrot, Burchell’s and Meves’s starling, Black-collared Barbet and Grey Go-away-bird.

African Fish-Eagles will quickly colonise the Nhabe