Scarier than any movie shark that can smell a drop of blood miles away (they can’t, by the way) is this week’s news about sharks’ sense of smell. A team of Australian and American scientists has just shown that smooth dogfishes (also called dusky smooth-hound sharks) can’t smell food as well after living in ocean acidification conditions expected for the year 2100. These “future” sharks could correctly track food smells only 15% of the time, compared to a 60% accuracy rate for unexposed sharks. In fact, the acidification-exposed sharks even avoided food smells!
This surprising result is also pretty sobering, when you consider how important sharks’ sense of smell is to nearly everything they do. Sharks have especially large, complex “nose” organs, which help them find food, mates, and predators, as well as find their way around the oceans. Many sharks, including the smooth dogfish, are very active at night and in the deep, dark ocean, so their sense of smell provides critical information about their surroundings. The researchers note that the sharks’ damaged sense of smell is probably due to the same changes in neurotransmitters reported in coral reef clownfish (yes, Nemo) that love the smell of predators in an acidifying ocean.
Despite their mighty reputation, sharks are under threat from overfishing, pollution, and habitat loss. Sharks that also can’t find food or avoid predators will probably not survive long, causing even more trouble for shark populations. They grow and reproduce slowly, too, meaning that sharks that die young aren’t replaced quickly. Scientists still don’t know yet if the smooth dogfish can adapt over several generations to improve their odds against the ocean acidification we will see over the coming decades, but it doesn’t look good.
Smooth dogfishes live along coasts from Maine to Florida, around the Gulf of Mexico and the Caribbean, and along the southeastern coast of South America. They might benefit somewhat from the actions that East Coast states like Maine and Maryland are taking against ocean acidification, but as species that migrate long distances, our best bet is to cut carbon dioxide emissions globally.