By Hannah Corsini, Freelance Writer

Published January 23rd, 2023

An 11-year study by scientists in Mozambique has revealed the significance of Závora Bay to reef manta ray populations migrating up and down the Inhambane coast.

It is easy to tell how the manta ray was given its name. With the word manta meaning cloak or blanket in Spanish, it seems perfectly matched to such an oddly-shaped fish, whose extra-long pectoral fin gives it its infamous physiology. However, global trade in ray gill plates, which has experienced a particularly significant increase in the last two decades, has meant that the manta ray has been overfished.

This has left species like the giant manta ray (Manta birostris) and the reef manta ray (Manta alfredi) dangerously close to extinction in some parts of the world. Both species are now listed as ‘vulnerable’ on the International Union for the Conservation of Nature.

In Mozambique, manta ray populations are severely and rapidly declining. A 16-year long study was conducted in the Praia do Tofo region, during which estimated annual manta ray populations peaked at 836 in 2004 to 2005. An 88% decrease in their populations was observed in the decade which followed, with only around 100 individuals sighted in the years following 2013.

Manta rays were not protected by Mozambique law until last year, wherein sweeping reforms were made to commercial fishing regulations and community-led management initiatives were set up in attempts to ease the transition for local fishermen.

‘Manta rays were not protected by Mozambique law until last year.’

Part of the reason for the new legislation is the impact that manta rays have on the tourism industry—visitors flock from around the world to snorkel and dive with the variety of megafauna in Mozambique’s waters.

Závora is a remote Mozambican fishing village, which offers dive sites for the chance to catch a glimpse of the manta rays. In spite of a wealth of pre-existing manta ray monitoring schemes in Mozambique, the number of manta rays in Závora bay had never been extensively assessed until 2010, when a group of University of Cape Town researchers embarked on an effort to consistently survey reef manta ray (M. alfredi) populations.

During the 11-year study, which ended in 2021, researchers had taken photos of the unique ventral markings of each manta ray so that they could tell when individuals returned to the region.

Manta rays often aggregate at so-called ‘cleaning stations’—areas where small marine fish called wrasse clean the dead skin and parasites from the bodies of larger animals. In Závora, this cleaning site is called Red Sands, a rocky reef filled with coral and sponges which acted as a point of return for the Mozambican manta rays. One individual returned as many as 18 times throughout the 11-year study period.

The manta rays tended to return to Red Sands seasonally, with abundances peaking between July and November. In other parts of the world, this is thought to be due to shifts in monsoonal winds and seasonal currents. Here, the scientists propose that it is due to ontogenetics, that is, the biological development of the manta rays causing specific forms of behaviour.

Unlike their giant counterparts, M. birostris, reef manta rays tend to prefer open oceans. This is what makes the Mozambican Inhambane coastline so special, and part of why the rays’ presence in this area is transitory.

‘One individual returned as many as 18 times throughout the 11-year study period.’

This area experiences highly productive intervals—times where it is particularly teeming with plant and animal life—due to sporadic nutrient upwellings caused by an eddy. Eddies are circular currents of water which rotate extremely fast at their centre, transporting water from one area to another.

With them, they bring blooms of phytoplankton from the deep ocean, attracting larger organisms from higher up the food chain such as zooplankton. The fluctuation of nutrients along the Mozambican coast may drive the movements of the reef manta rays up and down the coast.

What does this mean for manta ray conservation? Well, scientists have suggested previously that for highly mobile ocean species such as manta rays, protecting key areas is more feasible than protecting their home range.

For example, the authors of the Závora bay study recommend the immediate implementation of a marine protected area (MPA) specific to the Red Sands cleaning area. An MPA is an area of the marine environment governed by a specific set of laws which place restrictions on human activity in that area. Some outlaw fishing altogether.

Since the 1992 Rio Earth Summit, several countries have attempted to establish networks of MPAs. The UN Convention on Biological Diversity set the target of protecting 10% of the world’s coastal and marine areas by 2012—but when 2010 rolled around and only 2% of these areas were protected, they extended the deadline to 2020.

Today, around 8% of coastal and marine areas count as marine protected areas. Meta-analyses have shown that fish population densities, biodiversity, biomass and size are all generally higher inside MPAs than outside them.

‘The authors recommend the immediate implementation of a marine protected area specific to the Red Sands cleaning area.’

However, marine protected areas are not immune to criticism. Ray Hilborn, a marine biologist and fisheries scientist at the University of Washington argued to Mongabay that marine protected areas increase fishing pressure in other areas of the world.

Other scientists have expressed concern about the impacts felt by fishermen, who often depend on the industry for survival, and describe no-take MPAs as a type of fortress conservation.

‘Fortress conservation’ was an ideology which rose during the new wave of environmentalism in the 1960s, and asserted that the best practice for conservation was to exclude humans entirely from areas of nature.

Opponents to fortress conservation believe that it diminishes human connection to nature and causes socio-economic harm—in this case, to small-scale fishermen whose livelihoods may be jeopardised.

MPAs which limit fishing rather than outlawing it entirely allow the fish to reproduce and maintain their populations, meaning people can continue fishing there for years to come without their stock being depleted. Although, it has been argued that limited fishing privileges some fishermen and excludes others—whereas prohibiting fishing for everyone is at least more equitable.

However, much of the fishing which occurs in Mozambican waters is carried out by industrial fisheries, with the Japanese and Spanish fishing industries having a particularly strong presence. The fish that they catch are typically exported from Mozambique to other countries, despite 80% of their workers being local to Mozambique.

‘Much of the fishing which occurs in Mozambican waters is carried out by industrial fisheries.’

Previous investigations of industrial fisheries in the Global South have found workers who are paid slave wages, and that physical, emotional and sexual abuse can be rife. Reports from Cambodia and Ghana have revealed that children—sometimes as young as four—can be forced to work on these boats.

Emergent solutions aiming to protect sites as important as the Red Sands cleaning station in Závora should also account for those who live in the fishing village. Preventing the exploitation of Mozambique’s biodiversity by wealthy industrial giants could be the key to defending both its marine life and its fishermen.

‘Community conservation’, an alternative to fortress conservation, stresses the importance of including and amplifying the voices of the people local to the conservation area.

One potential solution under this model could be the establishment of cooperative fisheries, where members pool together resources and make collective decisions, such as fishing quotas in particular areas.

Cooperative fisheries established previously in the Global South have seen successes in regenerating biodiversity along with facilitating economic stability and the autonomy of their members. This has been seen elsewhere in Mozambique, with the NGO Fish Forever aiding communities to institute MPAs managed by the community members themselves, with local fishermen given exclusive rights.

Using this type of framework could address the socio-economic issues of poverty and worker exploitation, whilst simultaneously preserving integral marine sites such as Red Sands cleaning station for generations to come.

Featured image: Anett Szaszi | Ocean Image Bank

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