The Department of Wildlife and National Parks has attributed the mysterious death of countless fish in the Okavango Delta to changes in water quality and temperature in the river system, following the heavy downpours from the last two weeks.
North West Regional Wildlife Officer, Dimakatso Ntshebe said upon learning about the fish dying, the department dispatched a team of veterinary experts to investigate. Last week, he told The Patriot on Sunday their investigations into the mysterious fish mortality unearthed nothing sinister. Ntsebe said they have concluded that the fish died naturally due to changes in the delta ecosystem. He further highlighted that this is a natural phenomenon that happens when there are changes in the environment; citing the recent heavy downpours over Shakawe, which caused changes in water quality and the temperature of the river system.
Ntsebe said a team of veterinarians spent the whole of last weekend sampling up to 400 fish but turned up nothing, pointing to natural causes. Botswana University of Agriculture and Natural Resources (BUAN) Fish Biologist, Professor Keta Mosepele explained that the Okavango Delta fish die at the onset of new floodwaters from Angola.
He noted these deaths are caused by changes in water quality where anoxic water (i.e. water with low dissolved oxygen content) are flushed out from beneath the papyrus and onto the main water body (i.e. either the river channels or lagoons of the Okavango Delta). He said it is the same phenomenon experienced worldwide, where fish experience mortalities due to changes in water quality, generally induced by natural dynamics.
Professor Mosepele also noted that other potential causes of fish deaths in natural systems like the Okavango Delta are disease outbreaks, sharp temperature changes and fire outbreaks. The EUS (Epizootic ulcerative syndrome) is also a major fish disease whose outbreak has been recorded in the Okavango Delta in the past. The Professor, however, stressed that fish dying from Epizootic ulcerative syndrome have significant lesions on their skin, which has not been recorded in the recent fish deaths in the Delta.
“Sharp temperature changes can also cause fish mortalities, although the impact of this is usually localised and may not, therefore, explain the recent fish deaths in different parts of the panhandle,’ he stated.
Professor Mosepele also emphasised wildfire outbreaks followed by heavy rains where ash is washed out onto the river channel can also result in fish mortalities. This occurs when ash depletes oxygen levels in the water body, which may result in fish mortalities, he stated. He further noted that fish could die of unknown causes, particularly in the absence of systems that are designed to monitor fish populations in the long-term.
It emerged that fish populations in the Delta’s panhandle are not monitored as they previously were. With long-term monitoring systems in place, experts can quickly observe, analyse and find the answers that explain occurrences such as mysterious fish mortalities, he said.
Professor Mosepele noted that this task previously fell within the remit of the Fisheries Division in the Department of Wildlife and National Parks (DWNP) under the Ministry of Environment, Natural Resources and Tourism. However, the Division appears to have been disbanded and its research activities absorbed into the Research Division of the same Department (i.e. DWNP). He explained that there is currently not any research into fisheries, possibly due to overstretched financial and human resources.
Professor Mosepele said fish is a key source of cheap yet highly nutritious food for people the world over, including socio-economically marginalised communities such as the Okavango Delta communities. He said on that basis, optimum utilisation of fish can also help slash Botswana’s food import bill. He said the lack of investment in fisheries research will gradually erode the utility of this resource for Botswana’s marginalised communities as well as the public purse.
He stressed there is a clear and urgent need for investment into research to re-establish long-term fish monitoring, to allow science to provide immediate answers to various observed phenomena.
For the complete article: http://www.thepatriot.co.bw/news/item/8694-environmental-changes-kill-fish-in-okavango-delta.html
