Ghost sharks – unraveling the mysteries of these strange and elusive sea monsters

A team of intrepid researchers from the University of Florida and the Seattle Aquarium are poised to embark on a unique expedition this summer. Plunging a hundred meters beneath the surface of the Pacific Northwest’s waters, they aim to unravel the enigmas surrounding a denizen of the deep – the elusive ghost shark, also known as chimaeras.

The scientists, utilizing remotely operated underwater vehicles (ROVs), will be hunting for the nesting grounds of a specific variety of ghost shark known as the Pacific spotted ratfish, or Hydrolagus colliei. Often found haunting the ocean floor, these spectral creatures have a mystique that has intrigued scientists for years.

Gareth Fraser, an assistant professor of biology at the University of Florida, is leading this daring expedition.

“We know very little about these elusive relatives of sharks and even less about their spawning habits and embryonic development,” Fraser said. He added that the goal of this mission is to use ROVs to discover where these ghostly sharks lay their eggs.

Ghost sharks, or chimaeras as they are formally called, have been separated from their shark and ray relatives by a chasm of nearly 400 million years of evolution.

What do ghost sharks look like?

This mysterious group of fish, often relegated to the ocean’s murky depths, remain one of the most understudied and enigmatic creatures. However, during the summer months, these chimaeras often frequent the more shallow waters of the Salish Sea along Washington’s coast to breed and feed.

Understanding the developmental processes of the ghost sharks could help unravel the secrets of their unique biological characteristics, or morphologies. Ghost sharks are known for their large, round, rabbit-like eyes that help them navigate in the dark. They also possess ever-growing tooth plates, much like a rodent, earning them the nickname ratfish.

Interestingly, while shark skin is covered in teeth, ghost sharks have smooth skin. Male chimaeras boast a peculiar bulb on their forehead. This is called a tenaculum, which sprouts spiky teeth that resemble those of a shark.

Fraser elucidated, “We think they use this head clasper like a second ‘jaw’ on their head to bite down and attach to the female during copulation. Ghost sharks are a very strange group of shark relatives whose biology makes them a bit other-worldly. When we get a chance to find these obscure fish where they feed and breed, we have to go for it.”

Studying these creatures is no easy task

Despite recent success in locating adult chimaeras through deep-water trawling projects, the study of mature fish has offered limited insights into their developmental processes. The upcoming exploration for ghost shark nesting areas this summer is groundbreaking – a first-of-its-kind for this species.

“Last year, we found different stages of the fish, from newly hatched babies to fully mature adults. This year, we’re going back to find their nursery grounds,” said Fraser.

The expedition was funded through a National Science Foundation grant and Fraser’s UF start-up grant. The scientists also aim to unearth clues about the origins of teeth. This knowledge could potentially unlock valuable insights for regenerative dental research in humans.

Setting out from Seattle on June 11, the team commenced their four-day expedition from a pier. The researchers piloted the ROV, essentially an underwater drone, about 10 meters deep. From there, they scoured the ocean floor for ghost shark nesting sites.

The drone, laden with cameras offering 360-degree views, will send back images to construct a virtual reality depiction of the ocean’s depths. This will offer scientists an immersive view of the ghost shark’s environment.

Fraser said, “This will take us to the waters off Washington state, so that we can swim with these ghost sharks virtually and get an up-close, panoramic view of their environment.”

For Karly Cohen, a UF biology postdoctoral fellow in the Fraser Lab, who originally identified the potential ghost shark nursing sites, this project is a golden opportunity to bolster conservation efforts.

Cohen remarked, “It’s important to learn about these understudied deep-water fish and their reproductive strategies. Ultimately, we want to protect this really charismatic species.”

More about chimaeras

Chimaeras, also known as ghost sharks, ratfish, or rabbit fish, are a unique group of fish belonging to the subclass Holocephali. They share the class Chondrichthyes with sharks and rays. This article offers a detailed examination of their unique characteristics, habitat, reproduction, and scientific significance.

The name “chimaera” originates from Greek mythology, referring to a creature composed of parts from various animals. The diverse physical attributes of chimaeras reflect this mythical association. They exhibit traits akin to several distinct animals.

For instance, their large, rabbit-like eyes, rodent-esque incisor teeth, and smooth, scaleless skin distinguish them from other marine species.

Chimaeras have several characteristics distinguishing them from their shark and ray relatives. Among these, they possess a permanent notochord, a feature present in the earliest vertebrates. Male chimaeras also display a distinctive adaptation for reproduction: retractable sexual organs on their foreheads.

Habitat and diet

Chimaeras frequent temperate ocean floors, descending to depths of up to 2,600 meters. Few species venture into shallower depths below 200 meters.

The expansive, flat heads of most species facilitate the scanning of the seafloor for food. Their diet mainly consists of small benthic invertebrates.

Physical characteristics

Chimaeras are characterized by an elongated body shape, with a bulky head and a slender, whip-like tail. Some species bear a venomous spine preceding the dorsal fin.

Their large pectoral fins resemble wings. Some species employ these in a bird-like manner for swimming, appearing to “fly” through the water.

Reproduction

Chimaeras are oviparous, or egg-laying creatures. Some chimaeras produce eggs encased in a leathery shell, often with extended filamentous tendrils.

The males display unique mating behavior. They utilize a pair of claspers (modified pelvic fins) for the transfer of sperm to the female during copulation.

Evolution and relation to sharks and rays

While grouped with sharks and rays under the class Chondrichthyes, chimaeras diverged from these relatives approximately 400 million years ago.

Similar to sharks and rays, chimaeras have skeletons composed of cartilage instead of bone.

Scientific significance

Chimaeras remain relatively understudied due to their deep-sea habitats, despite their unique traits and evolutionary history. As a subject of scientific interest, they offer fascinating insights into marine life’s diversity and development.

Their specialized characteristics, from their mating behavior to their cartilaginous skeletal structure, provide valuable opportunities for further exploration and research.

Conservation

As of 2021, conservation efforts primarily focus on expanding our understanding of these elusive creatures. The deep-water habitats of chimaeras render them relatively inaccessible.

This fact complicates scientific efforts to study their life cycles, population dynamics, and vulnerability to human activities such as deep-sea fishing. Conservation strategies will benefit from comprehensive research, enhancing our ability to protect these intriguing species.

In summary, chimaeras, with their enigmatic lifestyle and unique biological attributes, represent an exciting frontier for marine biology and evolutionary study. Although we have much to learn about these ghostly denizens of the deep, their existing data opens up a window into the vast diversity of life present within the world’s oceans.