Marine Life & Conservation
New Scientific Report From The Marine Megafauna Foundation: Sharks And Lasers
Laser photogrammetry determines whale shark size segregation and life-history parameters to improve conservation management of the world’s largest fish
The whale shark (Rhincodon typus) is the world’s largest fish. Due to their large size, their tendency to spend a lot of time at the surface and predictable aggregating behaviour in known coastal areas, they are vulnerable to human threats such as directed fisheries, boat strikes and net entanglement. They are globally threatened, but a lack of biological and demographic information prevents an accurate assessment of their vulnerability to further decline or capacity to recover. Determining life-history parameters is therefore crucial to improving whale shark management.
The Marine Megafauna team used paired-laser photogrammetry to describe the size ranges of sharks, assess the length at which males reach sexual maturity and examine whether this technique can detect growth rates over a one to three year period, at two coastal aggregation sites in the Western Indian Ocean; Tofo Beach in southern Mozambique and Mafia Island in Tanzania.
The findings highlight that the size range and sex ratio of whale sharks from Mozambique and Tanzania are similar to those at most other coastal aggregation sites globally, in that mostly male juvenile sharks are present. The size at maturity was ~200 cm longer than for whale sharks in the Atlantic, suggesting biological differences among sharks in the two oceans. Growth rates could not be determined because the slow growth of the sharks in combination with the accuracy of photogrammetry means that a longer time interval is needed. The population segregation by size and sex observed here and elsewhere reinforces the need to determine the whereabouts of newborn sharks, immature female sharks, and mature sharks of both sexes to improve conservation and management for this globally threatened species.
“The segregation by size and sex in whale sharks is intriguing – where are we going to find the newborns, females and mature sharks in the Indian Ocean?”
Laser photogrammetry improves size and demographic estimates for whale sharks
Christoph A. Rohner1,2*, Anthony J. Richardson2,3, Clare E. M. Prebble1, Andrea D. Marshall1,4, Michael B. Bennett5, Scarla J. Weeks6, Geremy Cliff7,8, Sabine P. Winter7,8 and Simon J. Pierce1,4
1 Marine Megafauna Foundation, Praia do Tofo, Inhambane, Mozambique
2 CSIRO Oceans and Atmosphere Flagship, Brisbane Queensland 4102, Australia
3 Centre for Applications in Natural Resource Mathematics (CARM), School of Mathematics and Physics, The University of Queensland, St Lucia Queensland 4072, Australia
4 Wild Me, Praia do Tofo, Inhambane, Mozambique
5 School of Biomedical Sciences, The University of Queensland, St Lucia Queensland 4072, Australia
6 Biophysical Oceanography Group, School of Geography, Planning and Environmental Management, The University of Queensland, St Lucia Queensland 4072, Australia
7 KwaZulu-Natal Sharks Board, Umhlanga 4320, South Africa
8 Biomedical Resource Unit, University of KwaZulu-Natal, Durban 4000, South Africa
Abstract
Whale sharks Rhincodon typus are globally threatened, but a lack of biological and demographic information hampers an accurate assessment of their vulnerability to further decline or capacity to recover. We used laser photogrammetry at two aggregation sites to obtain more accurate size estimates of free-swimming whale sharks compared to visual estimates, allowing improved estimates of biological parameters. Individual whale sharks ranged from 432–917 cm total length (TL) (mean ± SD = 673 ± 118.8 cm, N = 122) in southern Mozambique and from 420–990 cm TL (mean ± SD = 641 ± 133 cm, N = 46) in Tanzania. By combining measurements of stranded individuals with photogrammetry measurements of free-swimming sharks, we calculated length at 50% maturity for males in Mozambique at 916 cm TL. Repeat measurements of individual whale sharks measured over periods from 347–1068 days yielded implausible growth rates, suggesting that the growth increment over this period was not large enough to be detected using laser photogrammetry, and that the method is best applied to estimating growth rates over longer (decadal) time periods. The sex ratio of both populations was biased towards males (74% in Mozambique, 89% in Tanzania), the majority of which were immature (98% in Mozambique, 94% in Tanzania). The population structure for these two aggregations was similar to most other documented whale shark aggregations around the world. Information on small (<400 cm) whale sharks, mature individuals, and females in this region is lacking, but necessary to inform conservation initiatives for this globally threatened species.
For information on this publication please email chris@marinemegafauna.org.
Marine Life & Conservation
Paul Watson Released as Denmark Blocks Japan’s Extradition Bid
Renowned anti-whaling activist Paul Watson has been released from custody in Greenland after spending five months in detention. Denmark’s Justice Ministry rejected Japan’s request for his extradition, citing insufficient guarantees that his time already served in custody would be credited against any potential sentence.
The 74-year-old Canadian-American was arrested on July 21 in Nuuk, Greenland’s capital, when his ship docked to refuel. His arrest was based on a 2012 Japanese warrant related to a 2010 encounter in Antarctic waters. Japan alleged Watson obstructed operations and caused damage to a whaling research ship during efforts to disrupt illegal whaling. Watson has consistently denied these claims, maintaining his commitment to marine conservation.
Denmark, which oversees extradition matters for Greenland, concluded that while the legal conditions for extradition were met, the lack of assurances from Japan regarding time-served credit made extradition untenable.
In a video shared by his foundation, Watson expressed gratitude and relief, saying, “After five months, it’s good to be out… and good to know they’re not sending me to Japan.” He added that the most difficult part of his time in custody was being separated from his two young sons.
Watson is a pioneering figure in marine conservation, known for founding the Captain Paul Watson Foundation in 2022 after decades of activism with the Sea Shepherd Conservation Society. His bold efforts to defend marine life have earned him widespread support, including from celebrities and conservationists. His work has also been featured in the acclaimed reality TV series Whale Wars.
Watson’s lawyer, Jonas Christoffersen, praised the decision, stating, “We are happy and relieved that Paul Watson is now free.” He added that Watson is eager to reunite with his family and continue his vital work.
The arrest occurred while Watson’s vessel, the M/Y John Paul DeJoria, was en route to the North Pacific with a team of 26 volunteers to intercept a Japanese whaling ship. His foundation described the arrest as politically motivated and emphasized that Watson’s actions were focused on ending illegal whaling practices.
Japan resumed commercial whaling in 2019 after leaving the International Whaling Commission, asserting that whale meat is a cultural tradition. Conservationists, however, continue to challenge these practices, highlighting their impact on marine ecosystems.
Despite the challenges, Watson remains steadfast in his mission to protect marine life and bring attention to whaling practices. His dedication to ocean conservation has made him a globally respected advocate for the environment.
Marine Life & Conservation
12 Days of Zero-Waste Fish-mas
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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