There is a nearly incomprehensible vastness to our oceans, and a significant portion of it, more than eighty percent, remain unexplored. To put this into perspective, more people have been to our moon than have been to the deepest depths of our oceans - despite them being closer and far more important to our survival and the life of our planet. Despite the increase in deep-ocean research and technological advancements, there is still a deficiency in essential details about many different species that inhabit the deep. Chimaeras, otherwise known as ghost sharks, are such an example.
Image: Painting of an elephant chimaera (Callorhinchus callorhinchus) - Richard Ellis
Multiple different species of chimaeras are informally known as ‘ghost sharks,’ and they all share similar characteristics. Ghost sharks, contrary to the common name, are not true sharks but rather distant cousins to sharks and rays. Part of the class Chondrichthyes, ghost sharks lack bone and have skeletons made of cartilage. Most species have venomous spines just in front of their dorsal fins which are used as defence mechanisms. Most species are also oviparous – females lay eggs from which their young later hatch. These sharks, unlike their cousins, do not have replaceable teeth, but have tooth plates that are used to crush molluscs and worms. Ghost shark species also prefer colder temperatures with the deep-ocean variety (such as Hydrolagus trolli) living at depths of up to 6,600 feet (2,011 meters).
Species at deeper depths are those that present the biggest problems to research endeavours. Practically everything researchers know about these animals is due to the occasional beaching or reported bycatch. In fact, the deep-sea chimaeras are so novel that the first specimen was only just discovered in 2002, and the first camera footage occurred in 2009 - a mere 12 years ago. The combination of inadequate catch reporting and infrequent opportunities for live-specimen research creates concerns that certain species may permanently disappear before we can study them in the wild.
The depths of our oceans are home to untold mysteries - a staggering amount of creatures to learn more about and an unimaginable number of more yet to be discovered. Image: Original
As of 2018, the Species Survival Commission Shark Specialist Group revised the IUCN chimaera database. This revision was based upon estimated data about geographic range (which was just updated in 2016 and continues to change with new research) and population size as reported by the fishing industry. Based on current knowledge, 16% of chimaera species are either threatened or near-threatened, and deficient information for another 15% prevented categorization.
There is a desperate need for information on ghost shark populations (fossil ancestry, behaviour, natural threats, reproductive strategies), and this is correlated with an equal need for additional resources and funding for appropriate research. As quoted by Mike Bennet from The University of Queensland, Australia:
“An understanding of the role of a particular shark species in the ecosystem requires fundamental information about its life history.”
Without this knowledge, not only are we losing the potential to preserve ghost shark populations, but we are also missing essential details about the role they play within their ecosystem. Much like their shark cousins, chimaeras could potentially help maintain trophic level balance, preventing any one species from becoming too populous. The loss of this balance could create a chain reaction leading to an eventual decline in fisheries’ stock, biodiversity, and overall marine health.
All in all, to aid in further research, the best thing to do is first become more aware of the issues. If we can all become more knowledgeable about the deficiencies we still face in scientific research, we can become more cognizant as to how we can overcome these shortfalls and fill in the existing gaps. This starts with all of us. Currently, the Pacific Shark Research Center in Moss Landing, California is a leader in the research of deep-ocean ghost sharks. Please consider following them on Facebook for new information on chimaeras, as well as possible means to promote more research!
Bennett, Mike. (2005). The role of sharks in the ecosystem. SharkBay Seaweek.
Cape Clasp. 5 Facts About Ghost Sharks.(2020). https://wsww.capeclasp.com/blogs/cape-clasp-blog/5-facts-about-ghost-sharks
Finucci, B. et al. (2020). Ghosts of the deep - Biodiversity, fisheries, and extinction risk of ghost sharks. Fish and Fisheries, 1-22.
Reichert, A. et al. (2016). First North Pacific records of the pointy nosed blue chimaera, Hydrolaguscf. Trolli (Chondrichthyes: Chimaeriformes: Chimaeridea). Marine Biodiversity Records, 9(90).
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