• Environment

Relationship between fish, humans and crocodiles in the spotlight

- 2023-08-14 09:11:00

"Humanity wants nice things - big vehicles, industries and wealth - and we are starting to pay the price. I always say it's fine if you want to do and have good things but remember - people somewhere are going to pay the price. Nothing is free. The question we have to ask ourselves is whether this price is acceptable or not. Often things also have a delayed reaction. We have been destroying the planet for so long and we are only now beginning to pay the price for it," Dr Clinton Hay, a senior lecturer in the department of biological sciences at the University of Namibia (Unam), said.
The Ministry of the Environment, Forestry and Tourism; the Ministry of Fisheries and Marine Resources; Unam and the Norwegian Institute for Nature Research (Nina) are currently studying the interaction between people, fish and crocodiles along and in the Kavango River to determine whether the decrease in the river's fish numbers contributes to increased crocodile attacks in the area.
"This is an ongoing project and we don't have any concrete conclusions yet, but we see trends. The purpose of the research is to see what we can do. Destroying all the crocodiles is not an option, because it will cause problems later. I don't know what those problems will be, but there will be a price that people have to pay.
"What we do have to do is to get the growth of the fish population in the river back on track so that the crocodiles and people have enough to eat and everything is back in balance."
According to Hay, it seems as if there is an increase in crocodile attacks on people.
"We are seeing a decrease in the numbers of larger fish species targeted by humans. Two-thirds of the species in the river do not grow very large. They are mainly caught by women and children for household consumption. The men catch the big species because that's where the money is, and their numbers are dwindling."
According to Hay, the diet of a crocodile that is between two and three meters long consists of 98% fish. The larger crocodiles also catch goats and other animals on the river bank and so their diet is slightly more diversified. A decrease in fish numbers affects the medium-sized crocodiles, that now have to look for other food sources because they are too small to catch goats.
Hay and his students have been engaged in research in the Kavango River for more than 30 years. Much of this research was done in the Mahango National Park and they noticed that poaching in the park is on the rise. "We noticed that the crocodiles are moving out of the park in search of food. When you strip the fish, you take away crocodile's food and they will - just like people who have no more food - make a plan to survive."
According to him, this is once again a sign of the sensitivity of the ecosystem - not only in the Kavango but all over the planet.
"Crocodiles and sharks are the top predators and they play an essential role in the ecosystem. If you destroy something small at the very bottom, it might not be such a big deal, but if you destroy something at the top, something will have to take its place and then nature's balance is toppled over. This is the principle of the planet - the moment we damage an ecosystem, it becomes unbalanced and people pay the price. Often, unfortunately, it is not the person who causes the damage who pays the price, but only later generations."
Research
The research that Unam has conducted over the past 30 years is now being taken and transformed into educational material for school children.
"Adults often don't listen and often don't want to change. So, we have to start with the children and inform them. They need to understand what role crocodiles play in nature. What is its place and what they should do in this regard? Yes, they are dangerous, but vehicles are just as dangerous. We need to teach children to be vigilant and respect crocodiles."
According to Hay, people become less vigilant the longer they are in and around the water. They forget to be on their guard just because they don't see a crocodile.
"People forget that crocodiles can stay underwater for more than an hour. They are very patient and they lie in wait. Through our research, we see from the behaviour of crocodiles that they learn. They have been on earth much longer than we have. We also look at the behaviour of fish because they are such an important resource. We look at the behaviour of crocodiles and humans, and then we see how we can intertwine the three and save the crocodiles while making sure that not a single person is caught by them."
The team has equipped 20 crocodiles with transmitters which are attached to the crocodiles' backs and that every hour sends a signal to a satellite that indicated where they are.
"We have again equipped crocodiles with transmitters and the new ones send a signal every three hours and will therefore last longer. They also have solar panels that generate their batteries, so they might last even longer."
Transmitters
"On 14 November 2021, a woman who fetched water from the river at Bagani was attacked by a crocodile with a transmitter that is part of this study. Luckily the woman survived. The crocodile was caught on 24 May 2021 in the Mahango National Park and fitted with the transmitter. It was a male of 2.9 meters long," Hay said.
Through the transmitter, the researchers could see that the crocodile had moved more than 30 kilometres. "He moved from the Botswana border to Bagani and out of Mahango - something that can be attributed to the decline in fish. It could be that he left the protective area in search of food. He was not big for a crocodile and may not have been able to defend a specific area."
It is not always the largest crocodile in an area that is responsible for the attacks on people.
"Just before the attack, we noticed that the particular crocodile was actively occupying areas around footpaths frequented by people and animals. He learned how people moved and knew exactly where and when the people went to fetch water. When we analyzed the movement data, we realised that the crocodile may have stalked several people or animals before targeting specific ones. The crocodile was not afraid of human activities. He occupied areas near places where people went to collect water daily. People have become accustomed to the crocodile in the area, which may have led to them becoming less wary of the threat of crocodiles," Hay explained.
The study showed the use of illegal nets and destructive fishing operations in the Bagani area resulted in a serious decline in fish numbers. Fisheries surveys have revealed that the area where the attack took place has very low biodiversity of fish, which are the resident crocodiles' main source of food.
"You could see the crocodile was watching the people. This is why we humans must equip ourselves with the knowledge to be vigilant at all times. You can fetch water, but then put the bucket down on the river banks and do your laundry. Do not stand in the river. Do not use the same footpath at the same time every day. We can tell people such things, but we need their cooperation to prevent the loss of life.
"Crocodiles follow a certain pattern of behaviour and people have become accustomed to it. Now, with less food, they can change their behaviour. The plan is to get the ecosystem back on track so that crocodiles' behaviour can return to normal. Of course, they are opportunistic and if you swim past one he will try to catch you, but if there are enough fish in the river, they will be less likely to attack people."
In conclusion, Hay said that he is not saying with certainty that fewer fish lead to increased crocodile attacks on people, but it is a logical inference. "It is much easier for a crocodile that is not that big to catch a person or a dog than a goat or other animal." - [email protected]