News
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.
Dive Travel Curaçao is thrilled to announce the launch of the Curaçao Dive Vacation Guide – 2024 DEMA Special Edition, an expertly curated resource that unveils the unparalleled dive experiences and vacation possibilities awaiting you in Curaçao. Produced exclusively for the Diving Equipment & Marketing Association (DEMA) Show 2024, this special edition guide is packed with exclusive insights, travel tips, and limited-time DEMA offers that make it easier than ever to explore Curaçao’s stunning underwater landscapes and vibrant culture.
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With over 70 diverse dive sites along its southern coastline, Curaçao is a bucket-list destination for divers of all experience levels. From thriving coral reefs and intricate marine ecosystems to historic shipwrecks, the island offers a variety of underwater experiences that are hard to match. The Curaçao Dive Vacation Guide – 2024 DEMA Special Edition provides detailed recommendations for both shore and boat diving, making it a valuable tool for divers seeking the best entry points, pristine reefs, and hidden treasures along the coastline. Whether you are an avid wreck diver, or a beginner interested in shallow reefs, Curaçao has it all.
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This DEMA 2024-exclusive Curaçao guide goes beyond diving to feature insider information on Curaçao’s eco-friendly accommodations, dive resorts, and top-rated dive operators committed to sustainable dive tourism. From all-inclusive resorts that support coral reef restoration initiatives to charming boutique hotels near prime dive locations, the guide helps travelers find the ideal stay to match their vacation goals. It also spotlights trusted dive operators on the island who prioritize environmental preservation, offering travelers a way to enjoy the underwater world responsibly.
Immerse Yourself in Curaçao’s Culture, Culinary Delights, and Adventure
Curaçao offers a vibrant Caribbean culture rich in history, music, and culinary fusion. The guide reveals Curaçao’s hidden gems, including culinary hotspots, historical sites, and eco-tourism opportunities that will appeal to both divers and non-divers. Visitors can explore the island’s iconic architecture, savor a diverse range of dishes influenced by Caribbean, European, and South American flavors, and embark on land-based eco-adventures, such as hiking, cave exploration, and visiting national parks.
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Ho Ho Ho! Vobster Quay’s recording-breaking charity Santa diving event returns on Sunday 15th December 2024 for another round of festive fundraising frivolities. Run in aid of the Royal National Lifeboat Institution (RNLI) and Help For Heroes, this ever-popular annual fundraising event aims to raise sack-loads of cash for these two very deserving charities.
Divers of all levels are invited to grab their Santa outfits – and as much festive cheer as they can muster – and head down to Vobster Quay near Mells, Somerset for a mass sponsored Santa dive in aid of charity. In previous years, the event has attracted divers from the far corners of the UK to join in the festive merriment for a final festive dive before the Christmas and New Year break. Back in 2015, the event smashed the world record for the most Santa divers with 188 divers taking to the waters donning their festive finery – a record that remains unbeaten to this day!
Vobster Santas isn’t just about setting records – it’s also about raising some serious cash for charity. Vobster Quay encourages all divers to get into the spirit of the season to raise much-needed funds for two very deserving charities – the Royal National Lifeboat Institution (RNLI) and Help For Heroes.
Through individual sponsorship and online donations, divers can invite their friends, family and work colleagues to sponsor them to plunge into the balmy waters of Vobster Quay dressed in full festive finery. Since the very first Santa dive in 2007, the event has raised over £52,000 for charity. “It’s been over 17 years since the very first charity Santa dive took place at Vobster Quay and every year the event just keeps getting bigger and better” enthused Vobster Quay owner, Amy Stanton.
“Vobster Santas is a great way for divers to say a massive thank you to the both the RNLI and Help For Heroes – two very deserving charities close to our hearts. We’re immensely proud of all that Vobster Santas has achieved and hope that even more divers will join this year’s event on Sunday 15th December. I’m confident that we can make Vobster Santas 2024 the biggest yet!”.
Divers wishing to participate can get involved by simply registering their attendance at
www.vobster.com/event-vobstersantas.php.
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