'Climate change' is a term that we are all now familiar with. We see evidence of our shifting climate on the news regularly; extreme hurricanes decimating American coastlines, massive bushfires roaring across Australia, hotter summers, milder winters, floods, droughts... Air temperatures are predicted to rise by as much 2 - 5°C all over the world, but it is not just the terrestrial environments which will be affected by rising temperatures... Marine environments do not escape unscathed. So how is climate change going to affect the marine environment? And how will it affect sharks?
It is now a scientific fact that human beings are altering our climate by releasing an excess of greenhouse gases into the atmosphere. Since the industrial revolution, atmospheric carbon dioxide (CO2) levels have already increased from a natural level of 280 ppm, to 380 ppm and are predicted to rise up to 1020 ppm by the year 2100 (Rosa et al, 2014).
As a result, sea surface temperatures have already risen by 0.5 - 0.6°C and it is predicted that these temperatures will only continue to rise. Whatsmore, as CO2 reacts with seawater, pH reduces into acidic levels and it is predicted that the drop in oceanic pH will decrease by as much as 0.14 - 0.5 units by 2100 (Rosa et al, 2014).
Baby, It's Warm Outside
So what affect will rising temperatures and ocean acidification have on marine animals, like sharks? A recent study attempted to begin answering this question, by simulating climate change conditions in aquariums to see how the brown-banded bamboo shark (Chiloscyllium punctatum) was affected. Researchers increased the water temperatures by 4°C and dropped the pH by 0.5, in line with the worst predictions from climate change modelling and then assessed the impact on the sharks' early development; both as embryos in their eggs and as newly hatched neonates (Rosa et al, 2014).
Their results were alarming... They found that predicted climate change conditions affected the sharks as they were eggs and after they were born. The developing embryos used their yolk very rapidly and their growth rates were significantly higher, and immediately after hatching, the neonate's body condition was considerably worse. As they grew, the juveniles metabolisms and ventilation rates were significantly altered. These physiological impairments reduced juvenile fitness significantly and lead to a 50% mortality rate! (Rosa et al, 2014).
To put it simply, the conditions which are predicted to arise due to climate change will be outside the range of tolerance for this species and will affect their ability to breed successfully (Rosa et al, 2014).
In Hot Water
Brown banded bamboo sharks are currently flagged as Near Threatened on the International Union for the Conservation of Nature's Red List of Threatened Species. If they are not able to breed properly, it is likely their populations will begin to decline. This could mean climate change may directly threaten their survival in the near future (Rosa et al, 2014; IUCN, 2023).
Whilst the effects of climate change will vary between species of sharks, scientists have voiced concerns that more active species (which have higher energetic demands) will likely suffer similar or even worse impacts than the brown-banded bamboo shark. They also worry that the effects of climate change will likely be most severe for estuarine, reef and coastal species of sharks (Rosa et al, 2014).
As many species of sharks are already experiencing population declines globally, increased juvenile mortality due to climate change, will seriously hamper the recovery of decimated populations (Rosa et al, 2014).
If we are to protect marine animals from the effects of climate change, it is critical that we act now! These researchers assessed the impact upon sharks using the worst-case-scenario temperature rises and ocean acidifications that models have predicted... Every fraction of a degree in temperature that we can claw back and every molecule less of CO2 that we put into our atmosphere will be beneficial to the sharks of the future. We must all make great efforts to move towards living more sustainably NOW, so that we can minimise the effects that climate change will have on sharks and other marine life!
Kempster R, Hart Nathan & Collin S (2009). Survival of the stillest: predator avoidance in shark embryos. PloS One, 8, e52551. Access online.
Rosa R, Baptista M, Lopes VM, Pegado MR, Paula JR, Tru ̈benbach K, Leal MC, Calado R & Repolho T (2014). Early-life exposure to climate change impairs tropical shark survival. Proceedings of the Royal Society B, 281:1793. Access online.