Reef Grief

In 2020 we were met with a horrifying headlines in the news: "Sharks ‘functionally extinct’ from one in five coral reefs" - ScienceMag". "Reef sharks are in major decline worldwide" - BBC. "Sharks 'functionally extinct' at 20% of world's coral reefs as fishing drives global decline"- The Guardian. A new study, which had sought to assess the populations of reef sharks around the world had found startling results, and conservationists, shark scientists and the public were all left flabbergasted and appalled...

Reef sharks caught on a BRUC camera (Image credit: Janet Greenlee, Source: www.globalfinprint.org)

The study was conducted by an enormous number of shark experts, collaborating internationally; 15,000 baited remote underwater video (BRUV) stations were deployed on 371 different reefs spanning 58 countries! These BRUVs recorded video footage of marine animals, which were attracted to the apparatus by bait attached to the camera frame. This allowed scientists to remotely observe animals in wild conditions. They used to video to count the total number of sharks videoed at any one time, as a measure of abundance for each species. They were especially interested in sharks living on coral reefs, like hammerheads (Sphyrnidae species), reef sharks (Carcharhinidae species) and tiger sharks (Galeocerdo cuvier). All the research teams followed the same methodology and then pooled their knowledge, to assess their respective reef shark populations, and gain some understanding about reef shark abundance globally.

Quite a remarkable display of team work!

BRUV set-up (Image Credit: Andy Mann, Source: Global FinPrint)

Many of the shark scientists were quite disturbed by their findings... They learned that sharks were completely absent from 69 of the 371 reefs they surveyed (that's 1 in 5) and they concluded that reef sharks were "functionally extinct" in at least 8 countries! This means that there would be less than 0.1% chance of seeing these sharks at reefs in the Dominican Republic, the West Indies, Vietnam, Kenya and Qatar (MacNeil et al, 2020).

Tropical reefs where sharks were present (dark grey dots) and absent (lighter grey markings) (MacNeil et al, 2020)

The researchers then performed statistical models to determine what features coincided with sharks being present at different sites - basically they input lots of variables (like each nation's population size and density, and economic features) to assess which were related to shark presence and absence.

Sharks are critical to the health of coral reef ecosystems (Image Credit: frantisekhojdysz / Shutterstock)

They found that several socio-economic features of different nations played a key role in whether sharks were absent from reefs. Firstly, they discovered that countries where people live in large coastal populations were associated with no shark sightings on adjacent reefs. They also found that reefs which were further away from markets where sharks fins would be sold were more likely to have sharks present. Whatsmore, they also learned that nations with high levels of poverty had particularly poor shark sightings on their reefs. Finally, they noted that the areas with the most severe shark declines were those which either had very few fishing regulations or only poorly enforced their regulations (MacNeil et al, 2020).

The researchers concluded that fishing sharks, especially for their fins, is responsible for the decline in sharks on reefs globally, but that areas which are particularly badly affected are those where the local population live in poverty. They suggested that these communities have no choice but exploit declining populations of sharks (MacNeil et al, 2020).

"There has been widespread depletion of reef sharks across much of the world’s tropical oceans"

-MacNeil et al, 2020

However... there was some glimmer of hope (*phew*)! The scientists also learned that sharks were doing very well in many areas; such as the Maldives, French Polynesia, Australia, the Bahamas and the USA. These nations have regulations in place to control the levels of fishing, in order to protect shark populations. So, the good news is, that it seems these regulations DO have some positive effect (MacNeil et al, 2020).

Regions with high shark abundances (larger circles) (MacNeil et al, 2020)

So, they went another step further! They then predicted how shark abundances might change if different types of shark-protective fishing regulations were introduced. On the figure below, you can see every nation they assessed (listed from those with the highest shark abundances at the top (shown in yellow), to the lowest at the bottom (shown in black)) and how the numbers of sharks might increase if legislation were enforced. They found that the nations with the highest "conservation potential" were Madagascar, Hawaii, the British West Indies and Barbados. It is no surprise that creating sharks sanctuaries seemed to give the best results, as these are areas where little to no shark fishing is permitted at any time (in the right column, you can see that the line spreads from "depleted" to "abundant" after the closure). However, they also found that introducing a catch limit (second column from the left) could also be effective for conservation. This would mean that shark fishing would be allowed, but there would be an upper limit to how many could be caught, based on scientific evidence (MacNeil et al, 2020).

Conservation potential of reef sharks in different countries depending on methods implemented (MacNeil et al, 2020)

These findings are of incredible valuable because it teaches us that there is a way to turn shark declines around... it is not a lost cause! Whatsmore, it shows us that there is a way to ensure the survival of declining shark populations, whilst also allowing local fisheries to continue to work. In many nations where sharks are depleted, the community has no option but to rely on fishing for subsistence and/or income. Therefore, it is of critical importance that scientists work together with local communities to develop conservation strategies which can create a sustainable future for everyone - punishing the poorest, most vulnerable people with fisheries closures will not be productive for anyone! If governments, scientists, law enforcement and local people can all work together in shark conservation, there is a way that both sharks and people can flourish together!

"When governments and communities work together, they can protect their sharks. So, you can have both fishing and healthy reefs"

- Mike Heithaus, Shark Research Scientist

References

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By Sophie A. Maycock for SharkSpeak.