Extinction and extirpation: balancing ecology & economy

The French government has recently provided economic incentives to fishers on the island of Réunion to begin culling Zambezi (bull) sharks, following a rise in shark attacks on surfers and bathers in the area. This action has been condemned by scientists and conservationists around the world who state that – based on the fact the species is listed as near-threatened by the IUCN Species Survival Commission – this action is not only inhumane but also unsustainable. Termed “legalized extermination” by animal rights groups, many people are questioning the government’s role in promoting human-mediated extirpation of a species at risk. And, perhaps most importantly, leaves us wondering what it actually means – and whether there is any significance – to being a species of conservation concern.

It is indisputable that, as human society has expanded, there has been an accelerated loss of species. In the marine environment this is primarily attributable to the alteration of marine habitats, overfishing, pollution, and associated biological and ecological factors. Many specialists agree, however, that it is virtually impossible to cause the extinction of marine species due to the vastness of the world’s oceans and the mobile nature of many of its inhabitants.
Increasingly, however, scientists are becoming concerned about the rate at which local populations are disappearing from the seas – and what impact, if any, the extirpation of these populations will have on the species as a whole.

Extinction versus Extirpation
Extinction refers to the process through which organisms or a group of organisms (normally a species) cease to exist. Extirpation is the local extinction of an organism or species, where it/they cease to exist in a particular area but continue to exist elsewhere.
What does extirpation mean for species survival?

By removing local populations through human-mediated activities we impact – and limit – the genetic diversity of species. This means many species become less resilient to environmental, ecological and biological changes, making them more susceptible to extinction. In fact, irrespective of the number of organisms, it is thought that genetic diversity is a major key to ensuring the long-term survival of a species. Simply: the more genetic diversity in a population of organisms or species, the better.

What about bull sharks?
Recent studies on bull sharks indicate a general lack of genetic exchange throughout their range. These populations likely diverged thousands of years ago (or more!) due to processes such as continental drift or the shifting of oceanic currents. Even in relatively confined geographic areas (such as the western Atlantic), evidence indicates gene flow – hence genetic diversity – in bull sharks is limited. Combined with inherent biological and behavioural traits which make them more vulnerable than other fishes (e.g., low reproductive rates and reliance on heavily impacted coastal/estuarine ecosystems as essential habitats), bull sharks might just be one of the next candidates for extinction. Particularly if culling programmes – aiming to protect bathers and surfers alike – are permitted to continue around the world.

Balancing the ecology & economy of extinction
One of the “weightiest” questions facing human society today is how best to balance ecological and socio-economic benefits (or costs) of extinction. The glaring reality today is that human actions will continue to cause species extinctions, yet we must take on the (extremely unenviable) task of deciding which species lives and which species dies. Assigning value to a species that we do not easily identify with – think of a mosquito or a fire ant – is quite difficult, especially when faced with a lack of data on the ecological role of that species.

And herein lies one of the biggest threats to bull sharks. Due to public misconception, media propaganda and a lack of information, people around the world are terrified of this species. A governmental call to cull an animal perceived as a threat to our very survival is, therefore, often received with glee by millions of shark-haters around the globe. Yet what these people don’t understand is the extraordinarily valuable role this apex predator plays in regulating the health and integrity of the coastal – and sometimes inland – environment. Even for the scientists who spend their lives studying bull sharks it is difficult to quantify their ecological role with certainty. However, existing global scientific evidence suggests bull sharks be prioritized as a species of international conservation concern – not only because of their ecological role but also because of their increasing value as an eco-tourism draw card.

Based on economy alone perhaps it is time for us – the caretakers of this blue planet – to reconsider our views of this intrinsically rare species. Instead of culling, perhaps the French government should consider long-term sustainable solutions to their “shark attack problem” – holistic solutions which conserve a vulnerable shark species and provide sustainable economic benefits to the people of Réunion.