Sharks and ecosystem health

Sharks have always been associated with fear. Though thanks to increases in tourism and research, these wonderful creatures are now receiving much more positive attention. This is important as it is now being recognised that these species play integral roles in marine ecosystems. Sharks and rays (elasmobranchs) are upper level predators, which means they have strong influence on prey assemblages and the environments in which they live and they have a stabilising effect on the ecosystems they live in. This role in these systems means that when they are removed there can be huge implications for ecosystem functioning.

Threats

Elasmobranchs are currently subjected to a huge number of threatening processes, most of which are the direct result of human activity. Recent research has indicated that a quarter of all elasmobranchs are threatened with extinction. According to the IUCN Red List of Threatened Species, the authority on the conservation status of all recorded animal species, of the 1,087 described species of Chondrichthyes (the cartilaginous fishes including sharks, rays, skates & chimeras), a whopping 90% are threatened by direct and indirect fishing. Other major threats include development and habitat modification, pollution and climate change. Within the Chondrichthyes, 17% are listed as Threatened and 11% as Near Threatened. These figures are likely higher though as 43% are listed as Data Deficient, meaning there is not enough data available to discern a threat level. In addition, for over 40% of the species listed on the IUCN Red List the assessments are out of date, with the last assessment being done over 10 years ago.

Why are sharks and rays so susceptible to threatening processes?

Many elasmobranchs have 'K-selected life history traits'. This means they are slow growing, they reach sexual maturity at a late age and they have low fecundity, meaning they give birth to only few, well developed young. This makes them particularly vulnerable to threatening processes as it takes a very long time for them to recover from threats, and with these threats increasing in intensity, species can become locally extinct and even lost completely. Adding to this is the fact that many elasmobranchs have a coastal habitat preference, resulting in greater exposure to threats from human activity such as habitat degradation and fishing.

Trophic Cascades

Major ecosystem effects can result from the removal of apex (top) and meso- (mid level) predators, which is a niche that many elasmobranchs occupy. These species play an important role in controlling lower trophic levels. Declines in the abundance of large sharks has been shown to correspond with increases in the abundance of smaller elasmobranchs and marine mammals, which has been linked to the decreased predation pressure experienced by these prey species. This can result in what's called a 'trophic cascade', which is the removal of top level predators resulting in the increased abundance of their prey, which in turn causes a decrease in the abundance of their respective prey. This can ultimately lead to complete ecosystem collapse.

Check out the video below for an in-depth explanation of the relationships within food webs and for some examples of trophic cascades.

Into the future

Studying the role of elasmobranchs as top level predators is difficult due to the complexity of marine trophic assemblages and the migratory behaviours of many elasmobranchs and their prey species. Therefore, with increasing interest in shark conservation and recent technological advances it is only recently that we have been able to model the ecosystem effects of elasmobranch removal. Continued research in this field will provide important data for the development of successful conservation and management plans.

How you can help shark conservation

Something we have realised is that almost everything we read about the peril of sharks doesn't provide us with tangible solutions. So to round off this blog, we thought we would list the best things you can do to help shark conservation!

Educate yourself and others

Continue to learn about sharks and their importance and teach these to your friends and family. Encourage them to teach others. People fear things they don't understand so helping others understand and appreciate our sharky friends goes a long way for changing perceptions. Be the PR manager that sharks need.

Interact with sharks

Go shark cage diving or visit the local aquarium, but be careful. Do your research and choose tour operators that encourage and help conservation efforts. By spending money with these companies you are directly helping to fund conservation efforts.

Reduce your seafood consumption

As mentioned above, fishing activity can dramatically affect shark populations. Fishing can reduce or even completely remove key prey species for sharks. Sharks make up a significant proportion of by-catch from commercial fishing, where they are usually killed in the process. Sharks are also targeted by some fishing, especially for shark fin soup and for 'flake' which is often the fish you will eat at your local fish and chip shop. By reducing your seafood consumption, you a reducing demand and this results in less sharks killed each year.

Avoid shark products

This includes shark meat, such as flake or shark fin soup, but many don't realise that a number of beauty produce contain 'squalene' which is produced from shark liver oil. Shark cartilage is also used in a number of medicines. So be sure to check the ingredients before buying any medical or beauty products. By reducing demand for shark products we can reduce the number of sharks killed for these products.

Reduce pollution

Rubbish kills a huge number of marine species, whether it is by mistaking it for food or by becoming trapped and drowning, and this is no different for sharks. By reducing your use of plastic and single use items, opting for reusable products and recycling items that you no longer need you can help keep trash out of our oceans and keep its inhabitants safe.

Spread awareness

 Along with educating people you know, social media is a powerful tool for spreading awareness to a far broader audience. So be loud, be proud and help raise awareness about the importance of sharks and our oceans.

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Joni Pini-Fitzsimmons