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Marine Life & Conservation

Fish Conditioning: Do fish become conditioned by contact with divers?

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In Mauritius, some of the species are completely relaxed, and others extremely nervous around divers. The most remarkable are the sharks in the shark pit in Mauritius. We have been there with a small group to find as many as 23 sharks finning around in the washing machine current. To them we do not exist. They completely ignore us.

Once they have got used to the fact that the air-breathers are harmless they go about their business happily, unafraid of the invaders.

In Mozambique the Potato Bass are happy to interact with divers, lying on the sand, eyeing them hopefully, swimming beside them and rubbing against them. The legendary Bert was among these.

The controversy over Cage Diving and chumming for sharks rages on, and although we enjoy the adrenalin rush of the Tiger Shark Dive at Aliwal Shoal, there is always a nagging doubt that we are supporting something that could lead to later danger. It is extremely rare for a diver to be attacked by a shark, unless he is in a bait ball or in the wrong place, or behaves foolishly. The Dive Operators who offer these extreme experiences have never themselves felt in any danger.

The raggies at Aliwal shoal are like bull terriers. They are completely familiar with divers, and they are unfazed by photographers. The pregnant females at Sodwana fin trance-like around groups of divers.

I watched Walter Bernardis brush a piece of sardine away from my buddy’s head just as a Black Tip was diving for it, and the Black Tip veered away from his hand. Shark diving is exhilarating, but I have never felt threatened by the animals themselves. After five years of diving with the Tigers, I have noticed that the grey reef and black tips that come to feed are no longer wary of divers. They brush you out of the way to reach the bait ball. Once they lose their fear of divers, these sharks are completely relaxed in the water.

The one animal that always seems completely aloof, has never changed, and which completely ignores diver and which typifies the apex predator is the Tiger. Nothing changes their behaviour that I have ever seen. They are always looking for something to taste. They are always alert to anything new in their world. They will always nibble on anything unfamiliar, and a nibble from a tiger can remove most of your torso.

Is it a bad thing for fishes to become conditioned to the presence of divers in their private domain? Theoretically, anything that changes the behaviour of a creature in its natural habitat is unwarrantable interference. However, the test of stress in a creature is whether it continues to live, to eat and to breed and the evidence of stress-free fish life is everywhere.

In the bad old days, Dive Masters in Mauritius used to conceal pieces of uneaten cheap Government bread in their BC pockets. Unnoticed by the early naiive Resort Course divers, the DMs crumble the bread into the water around them, and are soon mobbed by shoals of damsels, who like nothing more than a little French loaf for breakfast.

When you dived with certain Dive Operators there you had to swat away the aggressively seeking damsels. They bit your hands or the naked areas on your face. Their teeth are too small to draw blood, but the nip was painful nonetheless. Conditioned to expect something from divers? Absolutely.

At Sodwana Bay on Stringer Reef and on Quarter Mile Reef the Sergeant Majors (Abdadufduf abdadufduf ) lay their eggs in nests in the hollows of the eroded rocks and caverns. In December they can be seen hovering anxiously over their nests, but if a diver gets too close they dart away, and the wily wrasses pile in and gobble their eggs.

Incredibly, the Wrasses know they fear divers, and we have often been plagued by colourful wrasses weaving seductively in front of the camera lens, and then darting towards the Sergeant Majors’ nests hoping we will follow them. It’s almost as though they are saying, “Come on guys, come and look at these eggs, come and photograph these fish.” We have often seen pairs of mournful-looking Sergeant Majors rushing back to their eggless nests after an oblivious dive group has finned down for a closer look.

Conditioning? Looks like it.

Less obvious conditioning is on new or undiscovered reefs, where the fish are much more nervous when a group of divers arrives, and whole shoals will fin away from the intruders. I’ve seen this happen at little –known Reefs like Fusilier, or Snapper College at Sodwana.

Perhaps, just as we are learning about Reef Fish, they are learning about us – and if their behaviour is anything to go by, once they get to know us, they simply accept us.


Words Jill Holloway

Pic David Holloway

Copyright Ocean Spirit

www.osdiving.com

Jill Holloway lives in Mauritius and at Sodwana Bay Isimangaliso Wetland Park in South Africa. A PADI qualified Nitrox diver with over 1,500 dives, she is a passionate observer and preserver of the marine environment, and has a database of over 35,000 fish pics and hundreds of Gopro videos on fish behaviour, which she shares with her readers.

Marine Life & Conservation

New report shows simple measures needed to cut beach plastic pollution

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The Marine Conservation Society has launched its annual State of our Beaches 2023 report, highlighting the need for less single-use plastic items and more refillable options.

The charity’s beach cleaning programme, now in its 30th year, asks volunteers to record all litter that they find within a 100-metre stretch of beach. By gathering vital data from across the UK and Channel Islands, the charity creates change for cleaner seas and a healthier planet through policy and industry change. Last year, over 148 kilometres of beach were surveyed by volunteers, who removed 17,208kgs of litter from our coast.

Using data collected by over 14,000 volunteers, the State of our Beaches 2023 report shows that half of all litter collected came from public sources – either dumped, blown or washed onto our beaches.

Drinks-related litter, such as plastic bottles, caps and cans were one of the most found items, with an average of 16 found per 100 metres of beach surveyed. This figure is up 14% compared to the charity’s 2022 report.

Plastics caps and lids were recorded on 89% of surveys, with over 30,000 found in total. Plastic bottles were also commonly collected, with 73% of surveys finding this single-use item – a 4% increase compared to 2022. The charity’s inland litter pick survey, Source to Sea, also reported finding plastic bottles on 92% of cleans.

However, the charity’s State of Our Beaches 2023 report also indicates that some types of litter are on a downward trend. Although still in the top 10 litter items, disposable plastic cutlery, trays and straws were found on 5% fewer beaches across the UK, showing that bans on these plastic items between 2022 – 2023 could be working. The presence of plastic cotton bud sticks also dropped by 14%.

Lizzie Price, Beachwatch Manager at the Marine Conservation Society, said, “Half of the litter found on our beaches originates from public sources, underscoring the pressing issue of single-use plastic. Evidence shows that refillable alternatives and litter return schemes effectively reduce rubbish, as demonstrated by the decline our data has shown in items like plastic bags and disposable cutlery.

“Urgent and decisive action from UK governments is needed to accelerate our shift towards a circular economy, where we reuse, repair and recycle. The public needs greater access to refillable products and systems need to be implemented in which manufacturers are responsible for their waste.”

Governments across the UK have committed to delivering deposit return schemes from October 2025. However, the proposed scheme in England does not include glass items, despite glass being found on 52% of beaches in 2023. The charity is calling for governments across the UK to introduce compatible all inclusive deposit return schemes as soon as possible. This would see aluminium cans, and plastic and glass bottles have a 20p deposit which would be returned when recycled which would reduce drinks-related pollution.

Businesses are, however, starting to take refillable and reusable options into their own hands. Supermarket chain, Aldi, the largest corporate funder of the charity’s 2024 Beachwatch programme, is already leading the charge in refillable items by trialling refillable options for cereals and porridge oats in their stores over the past 5 months.

Plastics and Packaging Director, Luke Emery, from Aldi, who are running 4 beach cleans for staff and volunteers in 2024, said, We are continually working to reduce single-use plastics and packaging, and making unpackaged product options more commonplace for our customers is a key part of this. We are really pleased with the uptake of our refillable range so far by customers. Not only are we making sustainable shopping more accessible, but we also offer refill products for a better price than the packaged alternative, helping our customers save money.”

Marine litter is one of the biggest threats to our seas, with plastic breaking down over time into microplastics and threatening marine life which can ingest or become entangled in them. The Marine Conservation Society is urging the UK Government to move faster on its policies to cut down plastic waste and prevent items from reaching our seas.

To find out more about the charity’s beach cleans and how to get involved, please visit mcsuk.org/beach-cleans

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Guarding Against Coral Invaders

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Protecting (Dutch) Caribbean Reefs from Unomia stolonifera

Recent reports highlight the concerning spread of the invasive soft coral, Unomia stolonifera, currently devastating Venezuela’s marine ecosystems and detected in Cuba. With the potential threat of its expansion to the (Dutch) Caribbean islands, urgent action and awareness are essential to safeguard marine biodiversity and local economies from possible catastrophic consequences.

Invasive species are animals or plants from another region of the world that don’t belong in their new environment. These species can have major ecological effects by decimating native flora or fauna. They can also cause large economic losses and impact human health. Invasive species also pose a significant threat to marine ecosystems worldwide, including the Dutch Caribbean. Among these invaders is the octocoral species Unomia stolonifera or “Pulsing Xenia”, originally from the Indo-Pacific. With its rapid growth and lack of natural predators, this species can outcompete native species and disrupt fragile marine habitats such as seagrass beds and coral reefs.

Background

The invasive soft coral U. stolonifera was first identified in 2014, off the coast of Venezuela. It is believed to have been introduced via the illegal aquarium trade.  Since this species can reproduce sexually and asexually (or fragment), even small pieces can regenerate to spread.  Once introduced it quickly took over shallow reefs and hard substrate at depths of 0-50 meters, outcompeting local corals and seagrass for space.  Follow on surveys found that this coral species exhibited average percentage cover as high as 80%, vastly outcompeting native corals. In highly colonized areas, fish are disappearing due to loss of habitats.

In 2022, during a survey conducted in Cuba by the University of Havana, an unknown octocoral was discovered which was later identified as the invasive Unomia stolonifera. It is suspected that the coral larvae arrived in ballast water from fossil fuel ships originating from Venezuela, as nearby sites adjacent to Venezuelan ports have been heavily affected by the invasion.

How to help

Prevention through continuous monitoring, particularly in high-risk areas such as marine harbors and oil facilities, is paramount. Early detection plays a pivotal role in mitigating the threat posed by Unomia stolonifera.

The public’s involvement and awareness are also vital. Local communities, recreational divers, tourists, and all stakeholders are urged to participate in early detection efforts by reporting sightings (photo, location and date) of this invasive coral to their respective Protected Area Management Organization (PMO’s)- the Fundacion Parke Nacional Aruba (FPNA)STINAPA BonaireCARMABI Curaçao Saba Conservation Foundation (SCF)Nature Foundation St. Maarten (NFSXM) and St. Eustatius National Parks (STENAPA). If an invaded area is confirmed, follow the recommendations by the local PMO’s.

Keys to Success

Despite the challenges, early detection is key to mitigating the threat posed by Unomia stolonifera. With continued vigilance, research, and community engagement, there is hope for containing this potential issue before it becomes a major threat.

About the DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports (science) communication and outreach in the Dutch Caribbean region by making nature related (scientific) information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article.

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