Dead dolphins and fish washed ashore in Ghana – The scientific angle

The West Africa correspondent of The Guardian (international edition), Emmanuel Akinwotu, wrote a story entitled “Hundreds of dead fish and dolphins wash up on beaches in Ghana" in the Wednesday 07/04/2021 edition of the newspaper.

The story was earlier widely featured by other local newspapers such as the Daily Graphic, Ghanaian Times, www.ghanaweb.com, among others. The story had it that dead fish (without specific numbers) littered beaches in Accra and about hundred (100) dolphins washed up on the Axim beach in the Western Region.

Consequently, people who might have eaten fish around these communities were encouraged to come forward as authorities investigated sea life deaths. However, www.ghanaweb.com news of Friday, April 9, 2021 reported that an estimated two hundred (200) dolphins were washed ashore in Axim in the Western Region.

There were fears, concerns and agitations of the possibility of public health risk, since contaminated or poisoned fish might have been sold to customers.

Action taken

The Ghana Fisheries Commission took laboratory samples of both fish and water for investigation. Though the causes for the extinction of the fish and dolphins were not immediately known, the Commission’s official, Dr. Peter Zedah, attributed the deaths to “environment” and “stress factors”, a preliminary finding which requires further explanation. It’s also reported by www.ghanaweb.com that the Nzema East Municipal Chief Executive, Frank Okpenyen, swooped on Axim fishmongers and retrieved 68 dolphins out of the suspected 200 washed ashore.

With full-scale investigations announced to be on-going, Ghana’s Minister of Fisheries and Aquaculture, Hon. Mavis Koomson, requested for the cooperation of fishermen as the commission carried out its investigations.

Preliminary investigation by the University of Ghana Marine Science Department (Ghanaweb.com general news of Sunday April 11, 2021) found that nearly all the water quality parameters required for healthy aquatic life were within acceptable limits, except chemical oxygen demand (COD) which was significantly higher, evidence which supported Hon. Koomson’s “stress” theory.

Scientific explanation

As a senior lecturer who teaches second year Bachelor of Technology (BTech) civil engineering students Liquid Waste Management and first year Master of Technology (MTech.) Water and Environmental Engineering students Ecosystems and Ecological Engineering, I posed this question to them a couple of weeks ago:

Under 10% of the liquid waste generated in Ghana is treated before disposal, which means over 90% of it is usually disposed off into our water bodies (such as seas, and large rivers) without treatment. Assuming a huge quantity of organic matter such as excreta (a mix of urine and faeces) is thrown into the sea. What, in your opinion, do you think will happen to the ecosystem?

3.1 Biochemical oxygen demand (BOD)

As none of the students could correctly respond to my question, I hinted that they were required to make use of a term called biochemical oxygen demand (BOD) to answer the question. My question clearly depicts what likely happened to our aquatic life in the Greater Accra city of Osu and the Western Region city of Axim beaches recently.

BOD is the amount of oxygen that is consumed by bacteria to decompose organic matter under aerobic (presence of oxygen) conditions, and usually measured in milligrams per liter. BOD therefore represents the degree of organic matter concentration.

Organic matter is any biodegradable waste – includes excreta (human waste), sewage, food waste, paper waste, among others. It therefore means that huge deposits of excreta into the sea means that bacteria will require significant quantities of oxygen to biodegrade (or decompose) them. At the same time, aquatic life (fishes, dolphins, plants, among others) also requires the same dissolved oxygen in the sea water to survive.

There is therefore competition between aquatic life and bacteria for the limited available oxygen. With huge quantities of excreta thrown into the sea, it is likely that the majority of the oxygen (if not all) will be consumed by bacteria to decompose the organic matter (excreta), leaving none or insufficient quantities for aquatic life.

This situation leads to the state of inadequate oxygen for aquatic life as earlier expressed by Koomson’s “stress” theory. Without sufficient oxygen aquatic life terminates, as the fishes and dolphins will be unable to get enough oxygen and so will die and wash ashore.

The author’s submission is supported by the University of Ghana Marine Science Department’s findings that COD was significantly higher, while all the other relevant parameters of the sea water were within acceptable limits.

3.2 Algae production in the absence of light

Yes, it’s also the case that algae in sea water produce oxygen to support aquatic life and organic matter to decompose, but only when there is sufficient light. Without light algae are unable to produce oxygen. Unfortunately, however, algae terminates oxygen production in the absence of sufficient light, and in turn begins consuming oxygen.

It is therefore also likely that if there was no sufficient light in Axim and Accra over a period of time the fish and dolphins could equally be washed ashore, as aquatic life, algae and organic matter in the water would all be in competition for the limited available oxygen, which might have led to the death of the fish and dolphins.

So yes, as mentioned by Dr. Peter Zedah of Ghana’s Fisheries Commission, the death of the fish and dolphins could be environment related, in this case due to the absence of light for oxygen production by algae to promote aquatic life.

3.3 Eutrophication of aquatic life

Another scientific angle of thought is the issue of eutrophication, which basically is when salts enrich our water bodies and trigger structural changes in the ecosystem. For instance, algae and aquatic plant production may increase, depletion of fishes may occur, and water quality may

subsequently deteriorate beyond human consumption. However, this angle of argument is not likely to be the cause for the extinction of the fish and dolphins in Accra and Axim because the preliminary investigations by the Fisheries Commission included a water quality test which found that the water quality was not degraded.

Discussion

Aquatic life relies on the oxygen in water called dissolved oxygen (DO) to respire. The DO quantity depends on the following parameters: amount of sediments, water temperature, amount of oxygen removed from the system, and the quantity of oxygen added to the water.

Whereas decomposition and respiration of organic matter remove oxygen from the system, aeration, stream flow, and photosynthesizing organisms add/return oxygen to water. BOD and COD are two parameters which describe DO demand by bacteria in water.

It’s common knowledge that a significant quantity of excreta and other organic and inorganic matter are consistently thrown into our water bodies on a daily basis without treatment. This deliberate practice of dumping huge quantities of waste into our water bodies has the potential to trigger two (3.1 and 3.3) of the three factors already outlined and explained above.

There are reports that inhabitants of communities (namely Osu in Greater Accra and Axim in the Western Region) where the fish and dolphins were washed up the beaches consumed them, yet there were no reports of deaths or illness following the consumption of the dead fish. It was therefore not likely that they were poisoned or contaminated.

Conclusion and recommendation

I therefore argue that the death of the fish and dolphins in Accra and Axim beaches was likely caused by the unacceptable indiscriminate disposal of waste without treatment into water bodies, in spite of clear policy guidelines on waste management and disposal.

I therefore recommend massive sensitization and education on the effects of inappropriate waste disposal, particularly without treatment, into our water bodies to prevent future disasters. Beyond education, I further recommend that perpetrators of indiscriminate waste disposal be prosecuted in the court of law to serve as a deterrent to others.