Thursday, July 21, 2016

More sharks than we ever imagined

How many kinds of sharks inhabit the oceans?
When I was reading everything I could find about nature as a kid in the 1970s, I remember seeing the figure 300 a lot, as in 300 total species. Figures like 320-330 was pretty common.  But no one - not an amateur, not an ichthyologist - in those days would have claimed there were 500+. 
Well, one official count stands at 512. That may be a little high or low, given the differences of opinion in what's a separate species.  But Douglas Long, writing in DeepSea News, counted six new species in 2015 alone.  These include the small but incredibly cool ninja lanternshark (Etmopterus benchleyi), of the deep waters of the eastern Pacific.  In addition to looking like an evil robot submarine with a black paint job and striking blue eyes (really), it's even cooler because it was named for Peter Benchley, the late Jaws author who turned ardent shark conservationist.  
A "new" species many not be one never seen before. It could, like the half-meter long dark freckled catshark from Brazil, have spent many years being mistaken for a known species. Or it might be a museum specimen never tested genetically before. 
The Dusky Snout Catshark Bythaelurus naylori is an example of a "brand new" species, unseen or at least unnoticed until 2012. It's one of many recent discoveries that turned up in the bycatch of fishing trawlers. No fewer than 41 examples of this species were collected from fishing on Indian Ocean seamounts.  It is, ironically, bad news that some of these are being found, since it reminds us the oceans are being fished out. That's not an exaggeration: read Ellis' The Empty Ocean if you want to be scared to death on this topic. We keep fishing deeper and taking smaller fish, and that has a limit.  
Shark conservation is not a minor issue, either. Species like the basking shark are at risk wherever they occur, but especially in the Indian and Pacific Oceans, to feed the sharkfin soup trade. A recent bust in Ecuador netted three criminals in possession of 100,000 shark fins. That is not a misprint. No animal can withstand this kind of assault. National and international laws are much tougher than they were even ten years ago, but sharks are still in major trouble. One estimate is that humans are killing 200,000 sharks a day

The fast, powerful shortfin mako has the classic look people think of when they hear "shark." (NOAA)

I started this post to celebrate the diversity of the shark world, so let's go back there.  No one doubts there are more sharks to be discovered, both in genetics labs and in the oceans.  Most new species will be small, deep-water varieties, but the oceans encompass a billion cubic kilometers of water. Shark ecologist Paul Clerkin recently found 10 new species in a single two-month cruise with a fishing trawler. It won't be surprising if a few big fish are yet to be landed by science.  Willy Ley, in his 1941 book The Lungfish and the Unicorn, wrote that Timor Sea islanders islanders reported a large bottom-dwelling shark, 3-4 meters long, which he suggested was one of the carpet sharks or wobbegongs. No one has caught one, but there's nothing unreasonable about the story.  The sharks still have some surprises for us.

The U.S. government lists the basking shark, a harmless filter-feeder the size of a small bus, as a "species of concern" because of exploitation for its fins. (NOAA)

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