News
Study shows krill is important food source for Mobulid Rays
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
After a two-year tour of UK art galleries, community spaces and aquariums, the Shark Trust’s acclaimed Oceanic31 exhibition takes its final bow at the Royal Geographical Society later this month. And the unique collection of artwork, depicting 31 species of oceanic sharks and rays, donated by 31 artists, is now open for bids from art lovers and shark enthusiasts. The online auction, launched today, will close on the 7th December at 8pm (BST). The money raised will support the Shark Trust Oceanics Programme.
People can now bid on 27 of the artworks by visiting this website:
https://superstars-auctions.com/sharktrustauction
It is a chance to own a beautiful piece of original art and to support the Shark Trust. The timing of the auction also means that these would make a very special Christmas gift for any shark-lover.
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- Bigeye Thresher Shark by Janina Rossiter
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- Carcharodon carcharias by Jimmy Higgs
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- Croc VR 2030 by Tom Mead
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- Oceanic Whitetip by ATM
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- Silky Street by ScapaJoe
The diversity of pieces mirrors that of the sharks and rays they represent. You can bid on paintings, digital creations, sculptures, mixed media and more. You can pick your favourite artist or species of shark. Or you can select the perfect artwork to make a statement in your home or office. Whichever you choose, you will be supporting the work to protect these amazing animals.
One of the pieces of art has been selected to be auctioned live by Steve Backshall at the For the Love of Sharks event at the Royal Geographical Society in London on the 29th November. In addition to this, two further pieces will be raffled at this event, giving people a chance to win an incredible piece of shark art. For the Love of Sharks is the Shark Trust’s flagship evening. A night to celebrate sharks. Steve Backshall is the headline speaker at this event that will see other prominent shark advocates join him on stage.
Tickets for the event can be snapped up here:
https://thesharktrust.org.uk/Event/flos24
Those that would like to see the Oceanic 31 exhibition have one final chance. It is being displayed at the Pavilion at the Royal Geographic Society from 26th November until the 7th December. Entry is free.
Find out more here:
https://www.rgs.org/events/upcoming-events/oceanic-31
Paul Cox, Shark Trust CEO, Said “This exhibition has given us the opportunity to reach out to a new audience. And inspire more people with the wonderful sharks and rays on which our Big Shark Pledge campaign is based. We are immensely grateful to the 31 artists who have worked so hard to create these works.”
Bid for your favourite Oceanic 31 artwork here:
https://superstars-auctions.com/sharktrustauction
Banner Image: Smooth Hammerhead by Alicia Hayden
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