Dr. David Ebert is on a global search for the world’s “Lost Sharks”—little known or undiscovered species of sharks that are overshadowed by a handful of high-profile charismatic species (like the great white). Ebert travels the world working with fellow researchers and students to discover and study these overlooked and often threatened marine fishes. His results have considerable application for the understanding—and conservation of global shark—and ray diversity.
Joseph J. Bizzarro: We’re meeting at our favorite sushi restaurant in Santa Cruz. Why aren’t there any sharks or rays on the menu?
David Ebert: Well, there are a few reasons. First off, it would taste pretty awful. Elasmobranchs (sharks and rays) circulate urea and an ammonia-rich chemical called TMAO (trimethylamine N-oxide) for osmoregulation. Both of these compounds taste terrible, and that’s especially true when the fish isn’t bled immediately after capture or when it isn’t cooked. Additionally, the flesh of most sharks and rays is relatively soft, white-muscle tissue and the texture and taste are not up to snuff for sushi-grade fare. Sharks that are strong open water swimmers, such as mako sharks, have highly vascularized, red flesh that is similar in texture and taste to that of swordfish. A seared mako steak makes a fine dinner, but still, you wouldn’t want to try it raw.
So all sharks and rays, collectively, are known as elasmobranchs?
Correct. And elasmobranch literally means “plate gills,” a name referring to the uncovered gill slits visible on the lateral anterior portion of sharks and underside of batoids. There are five pairs of gills in the great majority of elasmobranchs, with six gilled forms occurring in five sharks (frilled sharks (2), sixgill shark (2), and sixgill sawshark (1)) and one ray (sixgill stingray). Two sharks have seven gills. Want to guess what they call them?
I’m going to go with “Sevengill sharks?”
You are correct. The Broadnose sevengill shark, Notorynchus cepedianus, and the narrowsnout sevengill shark, Heptranchis perlo. I worked on these species for my Ph.D. dissertation in South Africa.
You made a generalization about “most sharks and rays,” but sharks and rays are quite different, right?
Well, yes and no. Rays are the sister group (closest relatives) of the sharks. They are essentially “flat sharks,” with the mouth and gills located on the underside of the body. They generally live on or close to the seafloor, with a few exceptions, like the devil, or manta, rays. Rays are actually one type of “batoid,” a term which refers to all the “flat sharks,” including skates, rays, and sawfishes. Currently, there are 1,170 total living elasmobranch species, including 520 sharks and 650 batoids. For convenience, it is common for non-scientists to call all batoids “rays.”
Most people seem to picture a great white or some other large, toothy species when they think of a shark, and think of manta rays as the “typical” ray. Are most sharks and rays of these general types?
Oh no–not at all. This is perhaps one of the biggest misconceptions, especially about sharks. Most species of sharks are small, deep-water dogfish and catsharks. Most batoids—about half of all known species—are skates, which generally live on the seafloor in temperate, boreal, and deep-water regions. These sharks and rays typically are mid-trophic level predators, preying on small fishes, crabs, and shrimps. They serve important ecological roles in energy exchange between benthic and pelagic regions and lower and higher trophic levels, but these are generally species that are < 1 meter in length and certainly not dangerous to humans. The truth is, though, we know very little about most of these species. Even basic biology is unknown for most species and many have just recently been described.
Wow. In an ancient group like the sharks, which evolved what–450 million years ago?–that seems odd. Why are so many species of shark and ray still unknown to science?
Well, most of the dogfish, catsharks, and skates that I’ve mentioned are found in remote or deep-water regions that haven’t been well explored until now. In addition, historically there was little attention paid to sharks and rays by scientists or fisheries. Today, that situation has changed. As the importance of these fishes to the structure and dynamics of marine communities are better understood, and as traditional bony fish resources have been depleted, elasmobranchs are retained and landed more frequently in fisheries.7
Another reason is that these species are very difficult to identify—finding a new species requires a deep knowledge of species identification. My main research program currently involves the search for these undescribed or poorly known species, which I call “Lost Sharks.”
“Lost Sharks,” that sounds interesting. Can you describe this work further?
It builds on some of the misconceptions of elasmobranchs that we discussed earlier. The public’s perception of sharks often conjures up images of a large, fearsome, toothy predator, with its dorsal fin cutting its way through the water’s surface. However, the reality is that sharks come in a variety of sizes and shapes, from the whale shark (Rhincodon typus), the world’s largest fish, to the dwarf pygmy sharks (Squaliolus spp.). These enigmatic fishes occupy most marine, and some freshwater, habitats. In addition, the batoids and chimaeras (50 current species), along with the sharks, form a distinctive group of fishes collectively referred to as the Chondrichthyans, bringing the overall total to about 1200 species of sharks and shark-like fishes.
The diversity of sharks and their relatives has increased exponentially in contemporary times, with more than 240 new species described over the past 15 years. This represents nearly 20% of all shark species that have been described throughout human history. Most of these new discoveries have come from the Indo-Australian region, followed by the Western Indian Ocean and western North Pacific regions. However, despite such a rich and diverse fauna, the majority of sharks and their relatives have largely been lost in a media age whereby a few large charismatic shark mega-stars overshadow the majority of shark species. While these mega-stars, such the Great White Shark (Carcharodon carcharias), receive much media adulation and are the focus of numerous conservation and scientific efforts, the “Lost Sharks” remain largely unknown not only to the public, but also to the scientific and conservation communities.
How many sharks and rays have you named, Dave?
Overall—either as first or co-author—I’ve discovered scores of new species, or what I believe are new species, but it takes time from discovery to formally naming these new species. To date, I have named 27 new species, often collaborating with my graduate students in describing them.
Is there a particular protocol that is subscribed to in the designation of a new species?
Yes, there is. Typically, the process starts when a friend or colleague sends me a specimen that they can’t identify or I find an odd looking individual (or group of individuals) from a survey cruise or in a fish market. You need to have enough knowledge of external morphological differences between species to recognize an oddball.
The next step is to determine if what you have is really a new species. What constitutes a species is always a fun debate and discussion in science, but—for our purposes—we’ll say that a new species is one that is genetically and morphologically distinct from its closest relative. This is typically determined through combined comparative morphological and genetic analysis. In the past, there was no genetic component. This added aspect has really helped to support and expand on the information we can get from the morphological data alone.
The next step is to write a manuscript detailing your findings and give the species a scientific name. The manuscript must be published in an appropriate peer-reviewed journal for the species description to be valid. The genus name is usually established by relatedness to similar species. Occasionally, a new genus is designated along with a species, but this is not nearly as common. The species name is usually either descriptive (e.g., to indicate color or a distinctive feature) or based on a scientist who worked on other members of the genus or family in question.
Speaking of naming new species—you and a student recently received international media attention about the naming of a new catshark. Can you describe the source of this recent interest in your work?
Yes, one of my students, Victoria Vasquez, and I, along with a colleague, Dr. Douglas Long, described a new species of lanternshark from the Pacific coast of Central America. It is the first known species of this genus from this region.
Last summer was the 40th Anniversary of the release of the blockbuster movie “Jaws.” The author of the book, Peter Benchley became well known in later years as a champion in marine conservation. So we felt it appropriate to name this new species, Etmopterus benchleyi, after him.
What was even more fun was that Victoria was able to engage a group of school kids ages 8 to 14 in helping come up with the common name, which is ninja lanternshark, after the dark black coloration of this species and its stealthy ability to hunt in the dark.
It’s not only small species, like the Ninja Lanternshark, that are poorly known, right? One of the largest sharks, the megamouth, is also largely a mystery to science. You recently had a close encounter with this species, didn’t you?
Yes, last year I collaborated with some colleagues in Taiwan to capture and tag a megamouth shark. It was an awesome experience to go out and find a species that arguably was one of the most spectacular finds of the late 20th Century. My colleagues and I have been aware of a fishing port in Taiwan where about 70 megamouth sharks have been caught over the past few years, but trying to get funding for such a wild expedition was nearly impossible. However, through the magic of the media, the Discovery Channel— through their Shark Week programming—provided the funds for the expedition. So, with another one of my graduate students, we traveled to Taiwan, met up with my Taiwanese colleagues, chartered a fishing vessel, and went in search of megamouth. And we were successful in catching, tagging, and releasing a megamouth. It was definitely a highlight in my career to be able to pull off such a project. Now we will wait and see what exciting data we get back from the tag when it is released.
Ok. Not all sharks look or act like white sharks, but they are still thriving after millions of years of evolution. Why has this group been so successful?
Well, in terms of number of species, elasmobranchs are far less diverse than bony fishes. Only about 3% of all living fish species fall into this category. However, this group of fishes has a disproportionate influence on the organisms with which they interact. Large, upper trophic level species—like tiger sharks, white sharks, and oceanic whitetips—can not only prey upon other large marine organisms—such as seals, billfishes, and manatees—but they can also influence the behavior of these species, reducing their fitness. Rays that either crush hard prey (“durophagy”) or excavate feeding pits on the seafloor to uncover buried invertebrates can influence the structure and composition of benthic and infaunal communities through a combination of predation and disturbance.
Elasmobranchs have several predatory adaptations that represent advantages over bony fishes and have facilitated their continued presence and influence in a wide variety of oceanic systems. One of these adaptations is an acute ability to detect electrical currents, like those generated by other marine life.14 For instance, some rays can detect a worm wiggling a foot beneath the seafloor, and pelagic sharks, like the silky shark, can isolate a single wounded mackerel in a school of thousands of fit individuals—and they can do this in complete darkness. Therefore, the predatory advantages of elasmobranchs often are most pronounced at night and at crepuscular periods, when shadows are present.
In addition, sharks and rays have a highly advanced sense of smell. Some species can detect scents (e.g., blood, pheromones) that are present in concentrations of 1 part per 25 million parts seawater—from distances of more than half a kilometer. Sharks and rays also lack swim bladders (instead storing fat in their livers for buoyancy), which allows highly mobile species to move rapidly through the water column without suffering pressure effects.
The diversity of morphological adaptations for feeding also are remarkable – from crushing teeth for hard-shelled prey, to piercing teeth for spearing fishes, or circumscribed mouths to slurp up eels and polychaete worms—like we see in torpedo rays. Tiger sharks have slanted, serrated teeth that can saw through turtle shells, whereas the teeth of manta rays are barely present and they instead filter organisms inside their oral cavity (using gill rakers, which are like modified teeth on the back of gill filaments). Elasmobranchs are also generally large relative to bony fishes, and many species give birth to few, well-developed young as a result—often late in life. This is a common strategy of other top marine predators like mammals and sea birds, but it is not common of bony fishes. It makes elasmobranchs disproportionally more vulnerable to added mortality, such as that from fishing pressure.
What is the global status of elasmobranchs? Are they in trouble?
Some are, some aren’t. It’s problematic to over-generalize the situation. Some species are no doubt in trouble. Large species that venture into freshwater, like sawfishes and the Zambezi River shark, are facing extinction. Guitarfishes are also in trouble, mainly because of overfishing on their nursery grounds throughout subtropical and tropical regions. In some regions, like the Gulf of California, large, predatory sharks like bulls and tigers have been virtually extirpated. However, just to the north of California, white shark and soupfin shark populations have rebounded dramatically and appear to be in fine shape. Large, nearshore skates, such as the ironically named common skate of the northeast Atlantic, are among the most threatened of all marine fishes. In addition, the assemblage structure of skates and other species has been markedly impacted by a combination of intense fishing pressure and environmental change. Some species, especially relatively small, short-lived species, have increased in abundance, whereas other large, long-lived species generally have declined.
On the other side of the spectrum, there are many deep-water and boreal species that are new to science and beyond the reach of most fisheries or other anthropogenic impacts. The population status of these and many other elasmobranchs, such as those in remote, tropical regions (including the Pacific Coast of Central America) are virtually unknown but presumed to be healthy. It’s remarkable, though, that we are still finding new species in areas that have large, historic populations and are heavily fished – like the Carolina hammerhead of the southeastern U.S. and Gulf of Mexico, or the Flapper skate of the northeastern Atlantic. These are two cryptic species—they resemble the scalloped hammerhead and common skate morphologically—that persisted, unknown to science, for centuries. Only through the incorporation of genetic techniques were these species finally detected, and their occurrence has profound effects on fisheries management in both regions. Finding and describing these “lost sharks” is therefore crucial to understanding and maintaining elasmobranch diversity. After all, we can’t effectively manage species and calculate population parameters if we can’t figure out what they are.