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Study shows krill is important food source for Mobulid Rays

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A new study by scientists at the Marine Megafauna Foundation (MMF), Large Marine Vertebrates Research Institute Philippines (LAMAVE), the University of Queensland, and Scripps Institution of Oceanography was published in Royal Society Open Science last week, providing novel insights into the food sources of four mobulid ray species found in the Bohol Sea, Philippines.

Mobulids have slow growth and reproductive rates, making them vulnerable to overexploitation. Targeted and incidental fishing continue to cause population declines in various locations worldwide, and, as a result, Manta birostris and Mobula tarapacana have been listed as ‘vulnerable’ on the IUCN Red List of Threatened Species, and Mobula japanica and Mobula thurstoni as ‘near threatened’.

Dietary studies can inform fisheries and help reduce by-catch through the identification of critical feeding areas, where the occurrence of mobulid rays and targeted fishes overlap. For direct, short-term assessment of diet through stomach contents analyses, access to dead specimens is required, which can be challenging for rare or internationally protected species such as mobulids.

For this study, scientists were granted access to a targeted mobulid fishery which operates out of Jagna, Bohol in the Philippines from November to May. Stomach contents of all examined mobulid species were dominated by the krill Euphausia diomedeae (91% of stomachs contained the species), suggesting that this zooplankton species is abundant during this period. The larger mobulids also contained small mesopelagic fishes in their stomachs in addition to krill.

“Our results show that krill can be an important food source for large filter feeders living in tropical seas with surface waters that are low in plankton at the surface during the day. Krill migrates vertically, staying deep during the day and shallow, including at the surface, at night when the mobulids were caught”, commented Dr Chris Rohner, principal scientist at the Marine Megafauna Foundation. “Some mobulids had empty stomachs, while others had just finished a huge meal, which shows that tropical mobulids have a boom-and-bust strategy, feeding in dense prey patches when they are available and then undergo a period of starvation until they find the next prey patch.”

Stomach content studies provide a direct, but short-term snapshot of a species’ diet, while biochemical analyses can provide an indirect, but longer-term view. In 2016, manta ray scientists at the Marine Megafauna Foundation in collaboration with Proyecto Mantas Ecuador published a study using non-lethal muscle tissue sampling and stable isotope analysis, which revealed that Manta birostris found in the waters off Isla de la Plata, Ecuador, largely feed on prey originating from the mesopelagic zone (200 to 1,000 meters below the ocean surface) rather than on surface zooplankton. The new study from the Philippines now provides direct evidence to the theory that large planktivores in the tropics and subtropics heavily feed on mesopelagic migrating prey.

Photo: Gonzalo Araujo, LAMAVE


The Marine Megafauna Foundation was created in 2009 to research, protect and conserve the populations of threatened marine megafauna around the world. ‘Megafauna’ are large marine species such as sharks, rays, marine mammals and sea turtles – marinemegafauna.org

Large Marine Vertebrates Research Institute Philippines (LAMAVE) is the largest independent non-stock non-governmental organization dedicated to the conservation of marine megafauna and their habitats in the Philippines. LAMAVE strive for conservation through scientific research, policy and education -
 lamave.org

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Dive into Adventure: Limited Space Available for January Socorro Liveaboard Trip with Oyster Diving

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Socorro Giant Mantas, Sharks and Dolphins – 8-16th January 2025

Oyster Diving is offering an unforgettable opportunity to experience one of the world’s most extraordinary dive destinations – Socorro Island. With only one male space left for this January’s liveaboard adventure, divers are invited to join an exclusive trip to explore the waters of Socorro, renowned for its remarkable marine life and incredible dive experiences.

Unmatched Diving in Socorro

Socorro is home to a unique population of giant oceanic mantas that actively seek interaction with divers and snorkelers, making it one of the best places in the world to encounter these majestic creatures. But the adventure doesn’t stop there – the waters surrounding Socorro are also teeming with marine life, including schooling hammerheads and silky sharks, over 10 other species of sharks, playful bottlenose dolphins that love to interact with divers, large schools of pelagic fish, and, during the season, humpback whales.

Luxury Aboard the Nautilus Belle Amie

Diving in such an extraordinary location is made even more special by the Nautilus Belle Amie. Launched in 2015, this modern, spacious liveaboard yacht is designed with divers in mind, ensuring comfort and luxury throughout the trip. The boat offers various suite options, including twin rooms and superior double suites, all with the ambiance of a boutique hotel. Divers will spend 8 days aboard the Belle Amie, with all meals, guided dives, and soft drinks included.

Pricing and Availability

This exclusive Socorro liveaboard trip is available for the following prices:

  • Twin Room (2 people sharing a Stateroom): £3360 per person
  • Superior Double Suite (2 people sharing): £3860 per person

Both prices include Socorro Island fees. A port fee of $35 is payable upon arrival.

Additional Costs:

  • Return economy flights: Approx. £1,000 – £1,300 per person (prices confirmed prior to booking)
  • One night hotel B&B accommodation before the liveaboard: Approx. £100 per person

Book Now

With only one spot left, this opportunity to explore Socorro’s spectacular underwater world is sure to fill up fast. Interested divers are encouraged to get in touch with Oyster Diving Holidays to secure their place today.

For more information and bookings, please contact:

Oyster Diving Holidays
Phone: 0800 699 0243
Email: info@oysterdiving.com

Don’t miss your chance to dive with mantas, sharks, dolphins, and humpbacks in one of the world’s most pristine marine environments!

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Marine Life & Conservation

12 Days of Zero-Waste Fish-mas

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This holiday period, the Marine Conservation Society, the UK’s leading ocean membership charity, invites you to make some simple changes to eating fish this Christmas to help our seas.

Dr Kenneth Bodles, Head of Fisheries and Aquaculture at the Marine Conservation Society, said, “During the festive season, our consumption increases, but so does waste. Sustainability isn’t just about where food comes from – it’s also about how you use it. By reducing waste and making the most out of your seafood, you’re not only taking steps to be more ocean-friendly, but can also help to cut costs during what is often one of the most expensive times of the year”.

The Marine Conservation Society has compiled twelve tips on how to consume seafood sustainably with zero-waste this Christmas:

Buy whole fish instead of fillets

Instead of fillets, consider buying whole fish such as salmon, hake, or lemon sole. By adopting a “nose to tail” approach with cooking, whole-baked fish not only feeds a crowd, but also helps to minimise waste and maximise sustainability by using up every part of the animal, including bones, skin, and fat.

Make fish stock

Leftover fish bones or shells can be put to good use by boiling them to make a nourishing fish stock or bisque. This can be frozen and preserved for later use and makes for a flavourful base in a soup.

Make your own fish pâté

Avoid waste by turning leftover fish, such as smoked mackerel or salmon, into a delicious pâté by blending with cream cheese and lemon. Perfect when paired with crackers.

The sustainability of salmon and mackerel varies depending on where and how it is caught or farmed. For more information on green-rated options, check the charity’s Good Fish Guide.

Buy frozen

By purchasing seafood that is frozen or vacuum-packed, this helps to reduce waste by extending the shelf life of your food.

Fish pie

If you’re wondering what to do with leftover cooked fish, why not opt for a classic fish pie with mashed potatoes, leeks, and a cheesy sauce? A sure crowd pleaser on Boxing Day.

Use the head

Don’t forget the fish head! The meat is incredibly tender and flavourful. The charity recommends a cod’s head curry or recreating Fallow’s renowned cod’s head in siracha butter.

By stretching your ingredients further, not only is this a more sustainable way to enjoy seafood, but also cost-effective by repurposing leftovers and cooking creatively.

Boxing Day brunch

Mix leftover kippers or smoked salmon with scrambled eggs for a tasty, zero-waste, Boxing Day brunch.

For best choice, make sure you buy kippers, or herring, from the North Sea and the North Irish Sea.

Zero-waste storage

A top tip from the Marine Conservation Society to avoid waste is freezing fish offcuts to save for future use.

Crisp up the skin

Even leftover fish skin can be turned into a quick savoury snack by crisping it up in an air fryer with a little olive oil and salt.

Anchovies two ways

Leftover anchovies can either be blended with butter to make a delicious anchovy butter or tossed into pasta for a hit of umami flavour.

The charity recommends opting for anchovies caught in the Bay of Biscay for best choice.

Fishcakes

For an easy, zero-waste meal, leftover seafood trimmings can be mixed with mash and fried in breadcrumbs to make fishcakes.

Pickled mussels

Try pickling mussels in 1:1 vinegar and water, with a dash of sugar for a sustainable, zero-waste snack that can be enjoyed well beyond the festive season.

Mussels farmed in the UK are a seafood superhero. Grown using low-impact methods and harvested by hand, they get all the food they need from the sea around them. This makes them one of the most sustainable, ocean-friendly, and cost-effective seafood options.

Players of People’s Postcode Lottery have raised £6.6M towards the Marine Conservation Society’s vital work in making seafood more sustainable.

Laura Chow, Head of Charities at People’s Postcode Lottery, said: “Fish is a festive favourite for many, but making sustainable choices when it comes to how we buy and eat seafood makes all the difference for our ocean. Support from players of People’s Postcode Lottery has helped the Marine Conservation Society further its sustainable seafood work, so that we can all enjoy healthier, better protected seas.”

The Marine Conservation Society encourages you to make sustainable seafood choices a year-round habit, not just for Christmas. To check how sustainable the seafood on your plate is, you can visit the charity’s Good Fish Guide. The Guide helps consumers and businesses identify the most sustainable seafood using a simple traffic light system, based on where and how species are caught or farmed. Green is the best choice, amber means improvements are needed, and red indicates fish to avoid buying.

Zero-waste gift idea

Why not embrace a zero-waste Christmas by gifting a membership to support marine conservation? It’s a meaningful, low-waste gift that helps protect our ocean for generations to come. Memberships start from as little as £5 a month – the price of a sandwich and drink from your local coffee shop.

Find the latest sustainable seafood advice for wild-caught and farmed seafood on the Good Fish Guide, downloadable to your phone from www.mcsuk.org/goodfishguide.

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