Tiger Sharks are found throughout the world’s tropical and temperate oceans. While Great White Sharks steal the glory in terms of Hollywood, Tiger Sharks may be even more formidable. Their abundance and cosmopolitan distribution makes them a huge contributor to Earth’s ecosystems. As we lose them from our oceans we permanently damage our ability to recover our planet’s fisheries and climate. Tiger Sharks stop entire ecosystems from collapsing. Here I explore how that is the case and four reasons why Tiger Sharks are really important for rebuilding a habitable world.

We know less about Tiger Sharks than Tigers

Like most large marine animals, Tiger Sharks spend most of their lives in the deep ocean, so we know almost nothing about them. We know less about them than we do about Tigers in the wild. Certainly not enough to do any accurate population counts.

Least of all though, we hardly recognise their contribution to maintaining a habitable planet.

There is no situation where Tiger Sharks can be killed without collapsing marine ecosystems and denying all people the basic human right to fish or live in a habitable world.

When Tiger Sharks congregate near coastlines, they come into conflict with people. Sadly, therefore, most of what we do know about them is due to decline in ‘catch by unit effort’ from fisheries or shark nets.

This is surely damning evidence of our failure to recognise their general importance. After all, it’s mostly due to fishing or persecution that they have been declining for decades. This is up to 71% in just three generations off the coast of eastern Australia, where Government-sanctioned shark killing has ended the lives of 2,500 Tiger Sharks in the last 10 years. Meanwhile, renowned national companies still promote and sponsor competitions which kill mature Tiger Sharks for sport.

The fact remains that, as with most animals, we overlook the significance of even small numbers of Tiger Sharks for global ecosystems. We rely too much on fisheries for conservation. In doing so we neglect the fact that all of our lives depend on maintaining abundant and diverse shark populations.

Tiger Shark conservation can only happen when we recognise their critical importance for rebuilding a habitable world. The value of each animal pointlessly killed for convenience or enjoyment is measured in the lives and livelihoods of everyone in future.

#1 Tiger Sharks support planet-wide ecology

The scale of Tiger Shark impact

Human beings are poor at understanding anything at the spatial or time-scales of many animals. Tiger Sharks cross whole ocean basins and have been manipulating planetary processes for about 5.3 million years. The human footprint is tiny by comparison. Our brains aren’t designed to comprehend things on such a monumental scale. When we only see one or two sharks occasionally we disregard the scale of their importance.

But Tiger Sharks move seasonally across whole oceans. An animal’s ability to migrate is one of its super-powers and it’s a key thing that differentiates many megafauna species from us. Below are several graphs illustrating long-range Tiger Shark movements. Look at these tracks, then multiply them in your mind by a few tens of thousands of individual sharks. You’d see the majority of their home range covered in migration lines.

As sharks get older (and larger) their behaviour changes too. Even within the species, therefore, there is the ability to influence different parts of the food chain and different geographic areas.

The magnitude of Tiger Shark impact

Within their global distribution Tiger Shark activity is densest in the richest and most important ocean areas. Tiger Sharks ‘sample’ places that have the greatest impact – which is also where other animals congregate. Tiger Sharks, like all wildlife, both engineer and use these ecosystem in equal measure. Their ability to amplify processes such as nutrient transfer, carbon uptake, ocean-mixing, food chain balance is alongside a supporting cast of many other ocean creatures.

As we will find out in following sections it’s this patchiness, and the ability to move between hotspots, that makes Tiger Sharks such a powerful ally in creating ecosystem balance.

Here are two examples of the magnitude of Tiger Shark occurrence. The first map shows where sharks move long distances into the Pacific Ocean but also centre a lot of their time around the Galapágos. Needless to say the Galapágos Islands are an important hub for global biodiversity. The other example is from the Gulf of Mexico and show two patches where sharks spend a significant amount of time.

Having Tiger Sharks in the right abundance, in the right place and time, ensures global ecosystem balance is exquisitely maintained. With that in mind, let’s have a look at the intensity of what they do at these locations.

#2 Tiger Sharks stop entire oceans from collapsing

In a healthy ecosystem predators act like a food system control network. This is why the population of prey and predators follows the same cycle.

It is similar to the way shop-owners stock-take and order products strategically. Mediating between different ‘markets’ enables balance to be achieved. Otherwise economies would bankrupt. Similarly, ecosystems collapse, if the moderating influence is removed.

Beth Fulton of Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) said that ‘sharks are the glue that holds marine ecosystems together’. That without sharks, the house of cards falls down. There is little to no direct observation of this happening at sea, as the process is complex and there are few intact shark populations left for us to study. 

Quote from ‘Wildlife in the Balance: Why Animals are Humanity’s Best Hope‘.

Sharks are large and mobile. That makes them the connectors between different parts of the marine system. There is a bewilderingly complex network of creatures they hold in balance. I could show you a diagram with sharks at the top but this would be a gross over-simplification.

The bewildering complexity of food webs

Below are simplified models of plankton food webs. The balance of ocean systems depends on these components being diverse and that’s where animals come in. If we remove sharks we end up with a homogenised plant-based system that lacks the kind of richness and integrity complex animals like us need to survive. Our destiny is shared with sharks because we have similar needs and we’re part of the same survival system.

It’s not only a little hard to imagine this, it’s almost impossible to describe scientifically. For instance, in response to submissions about culling large sharks from WA waters, CSIRO had this to say:

A full understanding of the potential impacts of the removal of up to 300 tiger sharks per annum would require a full ecosystem model populated with empirical data on trophic relationships between sharks and their prey as well as relevant linkages to other species in the region. These data are not available (and may never be available).

The key point being that the data ‘may never be available’.

How do we reconcile the knowledge that entire ocean systems collapse without sharks, with the fact we can never know this significance fully? This is barely accepted yet, despite the enormous importance to our civilisation’s future.

We can instead, only imagine the intensity of this effect at a global level, between thousands of ecosystems across whole oceans involving hundreds of thousands of different species.

#3 Tiger Sharks recycle carbon back into the food chain

The largest Tiger Sharks are about five metres long. We found this Sperm Whale carcass floating in about 3,000m of water in the Banda Sea in October 2022. There were at least fifteen Tiger Sharks present though there could have been more. The largest we estimated to be about four metres and there were others about half the size too.

Studies on the importance of wildlife for carbon and climate regulation have found that whales are particularly important. Each animal absorbs as much carbon as thousands of trees. But it’s not just a case of carbon-laden carcasses sinking to the seafloor. As the above video shows, the carcass is recycled. Sharks are a major part of that process.

Beyond the sharks was an oil-slick many miles long and there were hundreds of Wilson’s Storm Petrels feeding on it. These birds breed thousands of miles away on Subantarctic islands. Animal abundance increases when animals are smaller. So, the overall effect of one Sperm Whale might be the same as an equivalent weight in Tiger Sharks or Storm Petrels. Perhaps one whale = 100 Tiger Sharks = 10,000 Storm-Petrels.

The amplification factor

In other words, the Sperm Whale’s influence is multiplied because of the other animals that gather around it.

Another way of thinking about this, is that the animals operate together, amplifying their individual effect on the environment. The reintroduction of nutrient into surface waters by Tiger Sharks and Storm-Petrels (from defecation) will dramatically increase the growth and diversity of algae and plankton. Without this extra nutrient the system shuts down quickly as resources are instantly exhausted. Wildlife keeps this process turning over and prolongs the effect.

A Sperm Whale carcass is not, therefore, of importance on its own. But when combined into a food chain, the carbon is recycled back into a vibrant system that provides benefits for everyone. This includes our own fisheries and climate. Ultimately, the movement of carbon back into places where it’s of most use, limits the risk it escapes into the atmosphere.

#4 Tiger Sharks protect coastal livelihoods and fisheries

Shallow reefs, seagrass and mangroves, are essential for protecting our coastal cities. These ecosystems provide a natural buffer against storm-surges. In recent years small increases in sea level have increased the likelihood of coastal erosion but at the same time, these ecosystem buffers are disappearing. It’s hardly any wonder that the consequences are becoming more severe. Today, some 634 million people are at risk from rising seas.

Tiger Sharks are responsible for the maintenance of healthy seagrass. This in turn keeps coastal sand banks intact, protects mangroves, provides most of the world’s nurseries for fish, and absorbs wave energy.

As we discovered earlier, sharks move in and out of areas seasonally. When they move in, they reduce herbivory from animals like dugongs or turtles, and this allows seagrass time to rest. The result is it bounces back even healthier, more diverse and stores more carbon. Without Tiger Sharks it would become less healthy and the ecosystem collapses.

In a similar way, removing Tiger Sharks will cause collapse of all ecosystems in which they previously occurred. We haven’t even begun to acknowledge the devastating impact that deliberate and grossly negligent levels of persecution of sharks is already having on our coastal livelihoods.

There is no situation where Tiger Sharks can be killed without collapsing marine ecosystems and denying all people the basic human right to fish or live in a habitable world.