Industrial fishing methods and improper regulation have led to an overexploitation of stocks worldwide and thereby contribute to threaten biological diversity. In addition, the capture of non-target species so called by-catch such as dolphins and turtles but also non-target fish species creates a massive collateral damage to the marine ecosystems. New methods of fishing and fisheries management such as quotas to sustain optimal population sizes are being worked on to develop sustainable means of fisheries.

In order to meet the great demand for fish, industrial fishing uses large ships, huge nets and miles of fishhooks. | Photo: Pixabay

How does fish get to our plate?

Fishing played an important role in humans’ lives long before the concept of livestock existed. Our ancestors made use of prehistoric tools such as spears, arrows, rods, baskets and cast nets to catch fish as food. On one hand, this activity enabled people to become self-sufficient, and on the other hand, increasing specialization created the profession of the fishermen who earn their living with their skills in catching fish. It is only in the past hundred years that these fishing methods have changed drastically, since the 1880s we observe the conversion of a labour intensive manufacture into a technology driven enterprise. Today, besides the small scale artisanal fisheries that still supply local markets, large ships drag vast nets and kilometre-long baited hooklines through the seas, guaranteeing the provision of protein-rich fish for billions of people around the world. 121 million tonnes of fish were caught in 2004 alone. Fifty years before, the amount of fish caught was an approximate 38 million tonnes – an increase of more than two thirds.

However, the fish that we eat does not always come from the seas or rivers, but more and more frequently it is raised in fish farms. These involve either closed recirculation systems or flowing or stagnant waters, where fish are reared and sold as soon as they have reached market size.

Why are fish populations in our seas under threat?

For a long time, the wealth of the sea including the fish populations, were considered an infinite resource which could not be over-exploited. An concept that was proven wrong in many cases already in the Middle Ages, as we learned in retrospect. Today, worldwide demand for fish is rising with the increase of the human population and with increasing awareness in the industrialized countries, but also as a source of animal feed for the rearing of livestock. We have to recognise that the exploitation of our oceans has consequences. Fishing has become one of the most important determinants for the state of our oceans and their inhabitants.

As a result of intensive fishing pressure, especially long lived species such as sturgeon have little chance to reach sexual maturity due to the high risk of capture. Multiple pressures such as intensive traffic, sand and gravel extraction, oil and gas drilling, power production, pollution reaching the sea through rivers and discharge from coastal communities, airbourne pollutants, and climate change contribute to the adverse impacts on the habitats as well as fishing. As such the stocks are exposed to stressors that reduce their capability to withstand these challenges. Many  fish populations of species that end up on our plates are beyond safe biological limits. More than half of worldwide fish populations are under threat.

Fishing, being a semi selective method of obtaining a certain group of water living animals also interferes with other species that share the habitat with the target species such as sea turtles, dolphins and water birds. Non-target animals that get caught by the gear are called bycatch. Especially, air breathing animals such as birds, turtles, dolphins etc. tend to drown when entangled in submerged fishing gear, which leads to a reduction in in the abundance of aquatic species.

Is it possible to eat fish without further reducing biodiversity?

In order to help fish populations recover, specific measures can be applied to different species. Fishing quotas should help ensure that types of fish which are especially under threat are only fished in a specified, amount that is determined to be on the safe side for future population development. Closed seasons and closed areas are measures to exclude direct impact upon certain proportions of the population. Protected marine areas offer fish a safe place to retreat, which mostly applies for feeding spots and spawning areas, where fish typically aggregate. Here, over time a high level of biodiversity can recover. The largest protected marine area in the world is going to be in the Ross Sea in Antarctica, which will comprise an area as big as Germany, France and Great Britain put together.

Aquaculture can also make an important contribution to countering the effects of over-fishing in our seas. Nowadays, it meets a large part of our demand for fish. However, when rearing predatory fish, fish farms often make use of wild fish being processed for food. Rearing in open cages allows the waste to act as a fertilized on the environment and does not prohibit the spread of parasites and diseases on wild fish populations. Fish farming utilizing alternative protein sources and those farms that recycle their rearing water (so called RAS systems) produce fish with less severe impact upon the environment. The certification of products for environmental quality can also help the consumer to find products of more sustainable sources.

To reduce the negative effects of by-catching in the future, the implementation of trawl nets and kilometre-long fishing lines will be more strictly monitored. The development of deterrents such as acoustic signals to shy off sea mammals from fishing nets and baited hooks, the utilization of heahy sinkers to increase the speed of the net to sink into the fishing depth, preventing waterfowl to get into the net, or the development of nets that lift off  the ground for 30-50 cm to prevent sturgeon bycatch in coastal gill-net fishery illustrate that depending upon the target animal, the methods have to be adapted specifically.

These measures can help to ensure that fish stocks and biodiversity are not reduced further without human beings must completely renounce fish.

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