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Sharks are exposed to numerous dangers. What does this mean for our ecosystem?

If the current trend - namely the steady decline in population numbers - does not change, many of the large and well-known shark species will become increasingly rare and eventually extinct. The consequences are unfortunately already clearly visible - and often in very surprising ways.

Unfortunately, we can already see what happens when sharks are gone:

Declining water quality

A similar scenario was seen in the North Atlantic at the turn of the millennium. Here it was not reef sharks that were decimated, but mainly large species like hammerhead and thresher sharks. Along the east coast of the USA, shark populations declined to the point where they could no longer fulfil their role as top predators. During this period, the number of their prey - mainly rays - has increased more than tenfold. The effects have been felt throughout the ecosystem.

But the most obvious was the sudden collapse of the traditional scallop fishery. The highly profitable farming and fishing of scallops and oysters fed an entire industry here. Not only did the disappearance of the sharks lead to a change in the community structure in the sea, but also to the economic demise of an entire region. The impact on the local population was dramatic, with many people losing their entire livelihood within one season.

In the following years, two further consequences could be observed. The large number of rays destroyed the local seagrass beds by constantly uprooting them during their search for food. This resulted in a noticeable decline in food fish that depend on the seagrass beds as a nursery ground for their young. The most surprising consequence, however, was the decline in local water quality. Mussels filter water in search of food - phytoplankton - and thus make a crucial contribution to maintaining water quality. With the collapse of the mussel populations, this filtering system disappeared. The consequence -> increased algal blooms and oxygen-depleted zones.

Disappearing seagrass beds off Australia

Seagrass beds are one of the most important resources in the fight against climate change. Not only do they produce a lot of oxygen, but they also store more CO2 in percentage terms than land plants. Unfortunately, we are losing one to two football fields of seagrass area per day worldwide. Often the reasons lie in coastal development motivated by tourism, but in Australia they are closely linked to the disappearance of animal sharks.

Often, the mere presence of sharks causes their prey to change their behaviour. For example, manatees and green turtles - which feed on seagrass - are often very loyal to their location. This leads to the same areas being grazed over and over again. Sooner or later, this damages the seagrass meadow and leads to either new spread being prevented or whole sections dying.

The presence of tiger sharks leads to avoidance tactics by marine mammals and reptiles. They often change their location, which gives the seagrass enough time to regenerate. Tiger sharks thus indirectly control the structure of seagrass beds and ultimately all communities that depend on the seagrass habitat.
An ocean without sharks is a sad, lonely place. The impact is felt not only by marine life, but also by us. No colourful reefs to dive on, declining catches of edible fish and even more drastic climate change - definitely not a pretty picture.

So if sharks are so important, we might assume that we humans are taking good care of them? Unfortunately, the reality is - once again - completely different. Catch quotas are steadily increasing, population numbers are nosediving and more and more species are moving closer to extinction on the IUCN Red List.

Support us in the fight for legally defined shark protection in Europe: We can't do it without you, sign the EU citizens' initiative: https://eci.ec.europa.eu/012/public/


Shark (c) Klaus-Peter Harter | Sharkproject

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