Sharks! Coming back from the depths
Valerie Taylor, an Australian underwater photographer, now in her late 80s, could almost certainly, had she wanted to, become a movie actress. As a young woman, she had dabbled in theatre acting, and had the movie-star looks, intelligence, poise, sense of humor, and the self-confidence that all help in that profession. Her interests, however, lay elsewhere: in the oceans and their life. Starting out as a competitive surfer and spear fisherman (at a time when few women were either), she soon, with her husband Ron, also a spear fisherman and photographer, became an underwater wildlife photographer and conservation advocate.
Yet, in her own way, she did become a film star: Ron frequently filmed her underwater, with her signature pink wetsuit and bright hair ribbon swimming near their marine animal subjects. And there was one particular kind of animal whom the Taylors found particularly fascinating: sharks! They swam with them and filmed them, often up close, including Great White Sharks. Hence, to Valerie’s other admirable qualities, add “courage”.1
And it was in that way they entered Hollywood film history in a small way. Some of their Great White Shark footage, shot in South Australian waters, was used in a film being made by a then young and largely unknown director named Stephen Spielberg in 1973-74. Based on a novel by the American writer Peter Benchley, it was called Jaws. Valerie and Ron also were drafted as consultants for the film. As everyone knows, it was a big hit and provided the launch-pad for Spielberg’s career, as well as boosts for many of the others involved, including three of the main actors (Richard Dreyfus, Roy Scheider, Robert Shaw). The film was nominated for several Oscars, including best film. (It lost to One Flew Over the Cuckoo’s Nest.) In effect, for the people involved in making Jaws, it was, despite all sorts of difficulties in its making, a positive experience.2
Sadly, for sharks, it was anything but. No sharks were killed in the making of Jaws since the shark “actors” in the film were animatronic devices specially built for it but the damage Jaws did to sharks was to their image, giving them the reputation as ruthless killers of humans. Indeed, the Great White Shark, depicted in the film as a mindless killing-machine, became the emblem in the public’s mind for sharks generally. That image lasted for decades with the result that killing sharks of all kinds, for food, sport, or just for being sharks, was considered perfectly all right.
This included the vast majority of species who never interfere with humans at all. In fact, world-wide, shark attacks on humans are relatively rare, estimated at about 30 per year on average. (Compare that to the murder rates in many countries where humans are the agents of violence.)
An irony of the situation was that the Taylors, who had long been advocates of sharks, as animals of great interest and value in themselves, and who had long promoted shark conservation – and continued to – had inadvertently created an image that they then had to fight in their professional work in trying to protect and conserve shark life in the oceans.
Today, however, sharks are coming back from those reputational depths into a new era of appreciation as constructive participants in their ecosystems. I will give an idea here of this more realistic and constructive perspective.
First of all, let us note a bit of evolutionary history and something about the biodiversity of sharks. The Latin name for the sharks is the Elasmobranchi and they are one of two sub-classes of the class of vertebrates known as the Chondrichthyes or the “cartilaginous fish”. As that designation indicates, their skeletons are made of cartilage, not bone, and sharks share membership in the Elasmobranchi with skates and rays (and an usual kind of fish termed the “sawfish” whose snout looks indeed like a double-bladed saw). Because cartilage decays much faster than bone, the fossil record of sharks is poorer than it would be if they had bony skeletons. Yet, their teeth are more resistant to decay after death than their skeleton and there is a comparatively rich record of shark teeth in the fossil record, from which it is possible to deduce something of their long evolutionary history.
Those remains point to the origins of shark-like animals in a distant period in the geological record, the Devonian period (419-359 million years ago or mya). Indeed, there are some still earlier possible precursors in still earlier periods, the Ordovician and Silurian. Remains of what are considered “modern” sharks (members of the family Selachimorpha), however, go back only to the early Jurassic, about 200 mya. That, of course, is still a long time ago, allowing much opportunity for shark diversification. Because of their longevity and diversity, sharks can be considered not just one of the oldest kinds of vertebrate animals but one of the most successful groups.
Today, there are reckoned to be 536 shark species, probably an underestimate. Worryingly, considering their now-recognized importance in many of their ecosystems, they have undergone a rather precipitate decline in numbers over the last 70 years or so, the period for which the numbers are most reliable.3 However, for certain reef-dwelling sharks, estimates can be made from fossilized teeth and the hard tooth-like structures of their skin, their “denticles”, over the last few thousand years. Those estimates indicate a decline over that period too. It is ascribed to fishing by indigenous fishermen, long before modern, Western-style commercialized fishing.
How can we characterize sharks as a whole today? Probably as one of the most diverse groups of vertebrates. They range in size, as adults, from the 7 inch pelagic (deep water) dwarf lantern shark to the approximately 40 feet whale shark, one of the largest animals on Earth. Their diets are equally diversified. To be sure, the famous big predatory sharks (the Great Whites, bull sharks, tiger sharks), the so called “apex predators”, are great hunters and kill and eat other large fish, sea mammals (seals, sea otters) and sea reptiles (sea turtles) but smaller sharks eat smaller fish and several species eat zooplankton, the small sea animals and larvae. This includes the whale shark, which despite its huge size and what appears to be a fearsome aspect, with its more than yard long mouth, is a gentle beast, eating zooplankton (specifically krill, jellyfish and crab larvae). There is even one omnivorous species, the bonnet head shark, which is known to eat sea grass though how much nutrition it gets from it is unknown. Correspondingly, one can swim in the ocean around many shark species, with no fear at all. 4
As one would imagine from such varied diets, different sharks play multiple and different roles in their respective ecosystems, whether swimming in the ocean along coasts or in deep waters or living near reefs. Since coral reefs are home to an incredible diversity of living forms, sharks that live in and around reefs are, correspondingly, part of the ecosystem of reefs in the most varied ways.
Reef-visiting sharks contribute to the reefs in multiple ways. First, they eat the smaller fish and prevent the latter from having boom-and-bust population cycles. Second, they often bring in nutrients for the reef that are found in their excretions; this frequently involves nutrients derived from their prey in deeper waters. Third, they also do so with their bodies when they die in or near reefs. Then there are the knock-on effects from their predations on other species, which contribute to the richness and resiliency of the reef ecosystems. There is a host of interactions in these ecosystems which contribute to their health and survival; take sharks out and the life of reefs would become impoverished.5
Why does this matter? If you are like me, valuing the natural world as a good thing in itself, any substantial or long-term reduction in its richness is simply wrong in itself. If, however, one wants to tot up benefits from reef life for humans, it is still wrong. Reef systems around the world contribute, disproportionately to their mass, to the economies of their countries, in supplying food (fish and shellfish) and other goods, and in tourism. For the latter, if reef life were to vanish or be greatly diminished, tourism in marine areas would be badly hit. Even not counting indirect benefits, which are hard to quantitate, the measurable economic gains are in many billions of dollars. And beyond that, reef systems contribute over-all to the health of the oceans, which in turn are vital to life on land.
If one were to eliminate sharks, or even greatly reduce their numbers, the consequences for all living things in the ocean would be severe. With an estimated 70% reduction, over-all, in shark numbers, there are almost certainly consequences today, whose effects will be felt soon. Nor is it just coastal and reef populations of sharks that have experienced these effects. Pelagic shark populations are suffering too, though it is too early to judge the full extent of the defaunation and its consequences.6
There is nothing surprising about this ecological view. Eliminating, or greatly reducing, predators from terrestrial systems has tremendous and deleterious effects on those ecosystems, while restoring them can reverse or ameliorate these effects. Wolf and coyote restorations illustrate this. Of course, similar processes would occur in the seas.
There are three major factors contributing to the loss of sharks in the oceans. Probably most seriously, there is general fishing, where sharks are by-catch, sometimes in considerable numbers. However, there is also substantial loss from directed hunting of sharks, for their fins and their oil. The various international laws and regulations governing protection of fish populations have hardly been invoked yet to protect sharks. The attitude that sharks are a kind of marine vermin, though not shared by marine biologists or conservationists generally, undoubtedly comes into this neglect.
Second, there is the destruction of habitats along the coasts by commercial development, not just reefs but the many mangrove swamps, a high proportion of them under threat. Third, and related to this, is global warming which is most certainly affecting ocean temperatures, sea chemical composition, and, of course, the marine creatures that live in the oceans. In response, many fish just migrate to cooler marine regions, toward the poles, and expand there. However, this can have deleterious consequences in those new home ranges, with some reduction of the richness of those regions.
The above provides only a sketch of what is happening as a result of the great loss of shark populations to the marine ecosystems of the world but the references given in the footnotes will expand the picture for those interested. Yet, the interest of sharks goes beyond their vital roles in the ecology of the oceans. They are simply fascinating animals and their diversity of size, and forms, diets and habits helps make them so. That diversity, however, goes beyond that of the different species characteristics.
Sharks even of the same kind or species have their individual differences. About this, let us finish this piece with a comment from Valerie Taylor, with whom we began, commenting on shark personality: “They all have different personalities. Some are shy, some are bullies, some are brave. When you get to know a school of sharks, you get to know them as individuals.” This is quite far from the images of Jaws, isn’t it?
See the National Geographic documentary, Playing with Sharks (2021).
For a recounting of the Taylors’ part in the making of the film, see “The woman who capture Jaws, then worked to undo the damage” by Ashley Spencer, The New York Times, September 29, 2021. The making of Jaws was quite a drama in itself, with a 100 day over-run in the filming, and a lot of personal tension amongst some of the actors, recently captured in a Broadway play about it.
A very informative review, which covers this material and much else is that of Dedman, S. et al. (2024). Ecological roles and importance of sharks in the Anthropocene Ocean. Science 385, ead12362 (Aug 2)
In 1993, I made a visit to Cairns, Australia and had a boat trip out to the Great Barrier reef. Scuba diving, we were close to a number of white-tipped sharks, roughly 4-5 long, and they did not seem aggressive at all, though at first I was a bit nervous.
For the multiplicity of ways that sharks contribute to their ecosystems, again see the review by Dedman et al. (note 3)
For the impoverishment of deep sea sharks, see Finnuchi, B. et al. (2024) Fishing for oil and meat drives irreversible defaunation of deepwater sharks and rays. Science 383, 1135- 1141.