Sharks of some description have been on this planet for hundreds of millions of years. They have weathered major changes in climate – periods of glaciation and warmth – but the rapid and acute change that they’re currently experiencing is something new.
By releasing greenhouse gases into the atmosphere, humans are changing the global climate in ways that are affecting the marine environment in terms of weather patterns, water temperature, sea level, ocean chemistry, currents, coastal erosion and the frequency of storms. We have already observed many of these effects, but scientists are expecting them to become more severe as climate change continues. Changes to the foundations of the marine environment such as this are likely to affect marine creatures’ food supply, migration patterns, distribution, reproduction and relationships with other parts of the food web. These changes could also affect the way animals behave. Sharks are no exception.
Scientists recently made predictions that two shark species in Australia, for example, may move southwards – away from the equator – at a rate of 40 miles per decade to escape warming waters. And scientists are already finding evidence that fish are moving polewards in this way, so their predators – like sharks and rays, seabirds and marine mammals, among others – will have to follow them.
Sharks are slow to evolve – they generally grow slowly, mature late in life and have long generation times – so it is difficult for them to adapt to the new conditions brought about by the rapid climate change we’re inducing now.
Climate change is happening now; it is ongoing and it is going to get worse before it gets better. Even in the midst of this change, we don’t know for sure what to expect. Nevertheless, scientists conduct experiments day by day and observe how the earth’s climate and environment are changing, giving us more information about what’s happening and what to expect. This is particularly important when it comes to species that are already endangered and exposed to a multitude of threats – and sharks and rays qualify in both respects. As we gain more knowledge, we are able to make informed decisions about how to mitigate the threats and manage our behaviour for the benefit of the planet – and, by extension, ourselves.