Sharks of the Abyss

Latest update July 2, 2019 Started on March 7, 2017
sea

Little is known about sharks in Sri Lanka; from those in the shallow reefs all the way to the deep sea canyons just off our shoreline. We aim to observe them and collect information necessary to ensure their survival.

March 7, 2017
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Preparation

Technology plays a crucial role in improving our understanding of cryptic marine species. For example, while we have managed to collect extensive data on various sharks from fishery landing sites, our knowledge on these species’ habitats and behaviour when alive, is still extremely limited. And this is where we hope to use specialised equipment to gain new insights.


The Trident ROV provides a unique opportunity to undertake such an endeavour. While the deep-sea sharks are likely captured at depths beyond current capabilities given that fishing takes place above canyons that are around 300-900 meters deep, there are two possible alternatives to be investigated. The first is to utilise the topography of the fishing area. For instance, given that these locations are just a couple of nautical miles offshore, they are all in areas where the bottom drops down from around 40 meters to 900 meters within a few hundred meters. This allows us to deploy bait canisters that would hopefully entice the sharks to come closer onto the steps that range from 60-90-meter depths. Then we can send the Trident to monitor any activity around the bait cans, along with documenting the surrounding topography. The second opportunity is to accompany the shark fishers, and place the ROV near its maximum operating depth in order to record the behaviour and status of the shark as they are brought up. Furthermore, given that these deep-sea shark fishers occasionally capture species that are discarded, the ROV can follow and monitor the released specimen from a safe distance in order to determine its immediate responses, and to monitor status to ascertain whether survival post-release is likely.

Moving to our shallow water sharks that are found among the coral reefs, we would be able to use the Trident to investigate not just the occurrence and behaviour of species frequently observed in the fisheries (e.g. bamboo sharks), but also simultaneously assess the health of their associated habitats, particularly in light of current bleaching events that are occurring at more frequent intervals. Data collected over the last few years has clearly demonstrated that it is insufficient to simply monitor species, and that studying their habitat and impacts on habitat is as important. Video transects from the Trident would also enable us to map reefs and identify new sites at a significantly faster pace. Additionally, in combination with equipment such as the Sofar Spotter Buoy that could be deployed in the same areas, we could obtain real-time information that is essential to monitor factors that may have an impact on coral bleaching, which in turn would have likely knockdown effects on the already vulnerable sharks living within these ecosystems.

Finally, technology such as the Trident ROV will not only improve our knowledge but also entice young scientists to study the oceans surrounding the island that is Sri Lanka! Opportunities to demonstrate this technology during public lectures and at schools will highlight that it is not merely government agencies or heavily funded research centres that can utilise modern technology to study the species and habitats encountered in the depths of our oceans!

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In The Field

While most sharks are captured for their fins and meat, some species are targeted for their liver oil! Since sharks lack swim bladders, they have large livers that are lighter than water, enabling them to compensate for their body density and maintain buoyancy. Deep sea sharks have even larger livers given the depths they are found at.


Shark liver oil contains a natural organic compound called squalene, which is used in cosmetic products such as moisturising lotion, sunscreen, lipstick etc., and is also purported to have medicinal properties. Given concerns on the pressures faced by sharks, there is now increased extraction of squalene from vegetable sources or biosynthetic processes.

However, it is still a lot easier and cheaper to extract squalene from shark liver oil. It is these deep sea shark fisheries that we are monitoring in order to identify unusual or potentially novel species, in addition to collecting data to better understand the biology of these species. It is known that deep-water sharks have even more conservative life histories than other sharks, and therefore targeted fisheries, as documented in other countries over the last few decades, are very likely to result in population collapses if not extremely well regulated.

While the local fishing communities are already regulating this deep sea shark fishery by limiting the number of vessels operating and the duration of the fishing season, we intend to use data from our research to ensure such regulations reflect, and are in line with, scientifically based management recommendations.

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Preparation

Check out this paper by D.A. Ebert, K.V. Akhilesh, and S. Weigmann on the description of a new species of the pygmy false catshark (Planonasus indicus). Of the 4 specimens used to describe it, one of them was encountered during our surveys in Sri Lanka and is now a designated Paratype in our collections.


https://link.springer.com/article/10.1007/s12526-018-0915-4

https://www.researchgate.net/publication/326866177PlanonasusindicusspnanewspeciesofpygmyfalsecatsharkChondrichthyesCarcharhiniformesPseudotriakidaewithareviseddiagnosisofthegenusandkeytothefamily

Blue Resources Trust Collections: https://www.blueresources.org/collections

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Expedition Background

Elasmobranchs are facing intensive global threats from overfishing as a consequence of growing demand for shark fins, oil, mobulid gill plates, skin, and more recently, domestic consumption of meat.
Sri Lanka, although one of the largest shark and ray fisheries in the Indian Ocean and among the largest in the world, lacks scientific data to effectively manage these threatened species. The 28-year civil war exacerbated the situation, hindering data collection and resulting in a rapid expansion of fisheries post-conflict.

In order to best protect these species, a baseline study that evaluates species presence, composition, in addition to biological parameters is crucial. Our data collection began in March 2017 and we have been surveying landing sites, documenting all the sharks and rays we encounter. This has led to the identification of unique species (https://www.researchgate.net/publication/332382361), making us curious to investigate them in further detail.

This expedition will predominantly focus on the sharks found in the abyss! Each year for a few months, fishers from some communities in Sri Lanka travel a couple of nautical miles off our shoreline and lower lines. But this is not just at any location - they are fishing above deep sea canyons dropping several hundred, and sometimes thousands, of meters down. And they are hauling up diverse deep sea sharks, rarely encountered in other parts of the world - in fact one dead specimen that we encountered now forms part of our collection, and is one of three documented specimens of this species in the entire world! We will be looking at using technology (Trident ROV) to film some of these species at depths of up to 100 meters as they are brought up into the shallows, hoping to get a glimpse into their lives.

The use of technology will also help nurture growing interest by young scientists for the marine environment surrounding Sri Lanka, and it is essential that we support and enhance such capacity by providing additional research opportunities for them. We therefore intend on using the Trident ROV to capture insights into some of our coastal, shallow water shark species as well. These species, found on coral reefs around the country, are also captured by fisheries and yet little is known. Our partner project, studying the health of coral reefs paints a bleak picture, where reefs are under extreme stress due to bleaching and other direct anthropogenic pressures. How will these sharks, that rely upon coral reefs for their habitat, survive?

Furthermore, given the conservative life histories of many elasmobranchs, particularly these deep sea species, where gestation periods, litter size, age at maturity, and maximum age is more comparable to mammals like leopards and whales than tuna and billfish, they are easily over-harvested resulting in rapid and severe population declines. To ensure sustainable fisheries that protect both species and fisher livelihoods, management measures such as phasing out indiscriminate fishing techniques, promoting the use of bycatch mitigation tools, introducing catch and export quotas, time and/or area closures, must be identified. Our research, collecting in-depth biological data from dead specimens at landing sites, combined with upcoming studies to observe these species alive in the wild, will provide the data necessary to build upon our previous successes in transferring science to policy and inform effective management measures that are up-to-date, practical, and enforceable. Without positive change, the future of sharks and rays, their marine ecosystems, and all associated livelihoods will hang in the balance.

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