Lots of cool talks today as this conference continues to be very good at keeping me busy. Check below the jump for the rundown on what I found interesting.
The behavior session was today, and had some of the more entertaining talks I’ve seen at an AES conference. Chris Lowe kicked things off by describing a plan to create a fleet of shark-tracking robots. Using AUVs equipped with acoustic sensors, he and his collegues can follow a shark indefinitely while sampling environmental conditions, apparently all without affecting the shark’s behavior. The future is now…
Shark reproductive behavior was the focus of two talks. Nurse shark guru Wes Pratt found some very interesting behaviors in the species he’s been working on for decades. It’s well-known that shark mating can be pretty rough, and it turns out that both male and female nurse sharks use cooperative behaviors in their sexual conflict. Males will work together to get females out of their refuge areas and some males will even altruistically give up their chance at mating to help their bros out. Females, on the other hand, will form a phalanx of interlocking pectoral fins to resist the males. So far the females have the upper hand (fin?), with the male behaviors only having a successful result about 40% of the time. On the more pelagic end of the shark spectrum, Hannah Calich looked at mating scars on tournament-caught female blue sharks and back-calculated the size of the males. It turns out that off of the east coast of Canada mature male blues are mating with immature females. However, these females are usually in the “almost mature” range, so there’s a possibility that these females actually store sperm until they’re capable of producing eggs. This may answer the question of how female blues in the Atlantic, which tend to stay on the totally opposite side of the ocean from the males, end up getting pregnant. Sharks are weird.
It should be noted that both of these talks were only improved by off-color commentary from old-school shark legends George Burgess and Jack Musick. The fact that these were combined with actual, insightful questions and observations made it even better.
Stephen Kaijura flew over huge aggregations of sharks practically in the surf zone of Palm Beach, and estimated that there are over 1,000 sharks/km in that area. Why are they all bunched up there? The Gulf Stream and the continental shelf break are both close to shore there than anywhere else on the east coast, which squeezes all the coastal sharks into a narrow, shallow area as they migrate to the Keys for the winter.
Jeremy Vaudo presented more work from the awesome tiger shark research going on in the Bahamas and Bermuda. Last year it was revealed that tigers in the Atlantic spend a lot more time in the open ocean than previously believed. It also turns out that they sometimes make dives as deep as 600 m (nearly 2,000 feet) while they’re offshore. Individually, their behavior ranges from occasional divers to sharks that oscillate back and forth between the surface and the deep the entire time they’re out in the ocean.
Any Nosal continues to give the best genetics talks I’ve ever seen with his discussion of multiple paternity in leopard sharks. Multiple paternity, which occurs when not every pup in the litter comes form the same father, is widespread in sharks but the frequency of it varies by species. In Andy’s leopard sharks, only about 36% of females were carrying pups from more than one male, and there were never more than two fathers represented. Even more interesting, one father usually seemed to be dominant, with a little as 0.5% of the pups coming from the secondary father. Among shark species, the frequency of multiple paternity may reflect the amount of sexual segregation in that species, which means that multiple paternity is not an evolutionary adaptation, but just a consequence of the way sharks make little sharks. And here we are, back to shark sex.
Will White gave an interesting talk about the importance of taxonomy. Bad taxonomy can potentially ruin conservation and management of sharks and can make some endangered species even more endangered. And we can’t just rely on genetics, because fishermen and managers can’t all be carrying sequencers.
Ashley Shaw, who also had a poster about this at last night’s poster session, used stable isotopes to check out dietary overlap between six species of coastal sharks and three species of bony fish (flounder, red drum, and spotted seatrout) in the South Carolina estuary of Bulls Bay. It turns out that sharks are more specialized than bony fishes when it comes to feeding, and finetooth sharks are the most specialized at all. Of the sharks, bonnetheads showed the highest overlap (and potential competition for food) with the bony fish. This is because bonnies tend to eat more crustaceans, which are also more prevalent in the diet of the non-sharks.
Speaking of the poster session, Jenny Bigman showed off the results of her combined puke/isotope diet study on Pacific spiny dogfish, and found that their feeding habits have no odifferences in size or sex like researchers (including me) have been finding in the Atlantic species. This might be because the west coast has almost no continental shelf so females aren’t able to hang out over the shelf away from the males and juveniles like they are on the east coast. It’s cool to be able to compare notes with people working in different areas.
That concludes today’s recap of shark nerdiness. I give my talk tomorrow, so if you’re interested in a potential blood feud between spiny dogfish and striped bass, I’ll be in the Elasmobranch Ecology 2 session at 10:30 Vancouver time. I’ll see you there.