This week is shark week, so given that they’ve been around for 420 million years, I thought it time to show a little love for these vital and efficient predators.
As I mentioned in a previous post, we need sharks because they’re apex predators, and when shark numbers drop, we get top-down trophic cascades. That means that when the apex predators drop, the creatures they feed on increase, and other creatures lower down the food chain can die out altogether (as happened with the scallop fishery in the previous post).
An alternative scenario is that the creatures that sharks feed on become weaker and die out: sharks tend to catch weak or sick individuals, and hence keep populations healthy, so the lack of sharks means that diseases can spread throughout the population, while weak individuals can pass on weak genes.
Then of course there’s the question of phytoplankton: many sharks eat smaller fish which eat phytoplankton, which produces oxygen. Less sharks, more smaller fish, less phytoplankton, less oxygen. Bad for everything that needs oxygen, including us.
But despite sharks being necessary for a lot of reasons, and worth preserving in themselves, humans still kill about 100 million sharks a year. On the sharks’ side, they’ve killed slightly over one human per year for the past 500 years (unprovoked). That’s one human death for every 100 million sharks. We kill sharks accidentally as ‘bycatch’ in industrial fishing, and deliberately, whether for food (shark fin soup) or in attempts to make beaches safe for recreational activities.
It’s estimated that up to 73 million sharks die each year just due to ‘finning’: the cruel process of cutting off the fin, often while the shark is still alive, then dumping it back in the water to bleed to death or drown. Given that sharks take 12 – 15 years to mature, and reproduce extremely slowly, it takes a long time for populations to recover, if they ever do. Because of the threats of overfishing, finning, and bycatch, the International Union for Conservation of Nature (IUCN) has estimated that 32% of open ocean sharks are threatened with extinction.
That’s bad news for all of us: if the sharks die, many fish and shellfish populations die, and many people who depend on those fish to live will suffer. But there are things we can do. Laws can be enacted and enforced to reduce their loss via bycatch; campaigns against shark fin soup can be begun; the word can be spread that we need sharks, and that they rarely threaten us without provocation; and if we want to venture into their realm, there’s a new style of wetsuit being developed that makes divers and surfers invisible to sharks.
If we can do all that, then all they’ll have to worry about is being dropped from the sky onto a golf course.
[Featured image: Great white shark at Isla Guadalupe, Mexico, August 2006. Shot with Nikon D70s in Ikelite housing, in natural light. Animal estimated at 11-12 feet (3.3 to 3.6 m) in length, age unknown. Photo by Pterantula (Terry Goss) at en.wikipedia. Licensed under the GNU Free Documentation License version 1.2 or later.]