There are a number of challenges with regard to maintaining fish populations in the marine and fresh water environments. These include over-fishing, sustaining edible fish populations, regulations and Marine Protected Areas, harvesting fish of the right age to protect breeding cycles and maintenance of fresh water environments.
One needs to identify what fish you are eating in order to avoid eating the wrong species, i.e. those species that are threatened. The World Wildlife Fund (WWF) organisation SASSI (South African Sustainable Seafood Initiative) has a rating for different species of fish according to how sustainable their populations are. There are three categories – the green category is what you can eat with the least impact. Orange category means ‘think twice’ before you eat it and Red Category means don’t eat it. The difficulty lies in knowing which species is which and so SASI provides an illustrated guide to fish types.
We tend to rely on those who supply the fish to make the decision for us but we need to take responsibility for identifying the fish ourselves. If ‘foodies’ concentrate on using ‘trash fish’, i.e. low-value species for eating and find ways of making dishes palatable instead of focussing on high-value species. For example tuna used to be a low-value species but now it is a high-value species because of things like the popularity of sushi – so the tuna species is now under considerable pressure.
The job of regulators is to protect the Marine Protected Areas, which are important because they allow fish species to recover and as well as providing a yardstick to measure species populations by providing an example of what the sea should look like.
In determining at what size fish can be harvested, we make the provision that each fish should breed at least once before being harvested. So that determines at what size the fish can be caught without affecting the population. Other factors to consider when deciding what fish to eat include how widely dispersed populations are – the wider the geographic spread of a fish population, the more likely it is to survive. Pelagic fish are a big resource – they grow fast and there are lots more of them and so are more sustainable.
Fisheries officials do monitoring but mainly in the harbours. The problem is policing the extent of the coastline. Also fines are levied for unlicensed fishing, but the fines are less than the value of the fish.
Fresh water fish are substantially different from marine fish – it is easier to introduce foreign or exotic species into fresh water environments. This has had a huge impact on fish conservation. But reservoirs change the nature of rivers because they stop the flow of water and that changes the habitat permanently. So a lot of endemic fish have lost their habitat and their numbers have declined dramatically. So while people alter the environment to suit their needs, this has an impact on fish species. Compounding the problem is that new fish species are then introduced to the rivers from other countries and they feed on the indigenous fauna.
Fish gills are only one cell thick, so any pollutants or toxins in the environment are absorbed immediately and this leads to large-scale fish die-offs. Another problem is that algae produce CO2 gas at night, and this can deplete the amount of oxygen in the water to such an extent that the fish die. So throwing waste such as sewerage or chemicals into fresh water can lead to algae growth which then affects the environment. Wetlands function to filter out nutrients and toxins, but by building on wetlands we reduce the ability of the planet to filter water systems.