Today was the fourth and last day of presentations for this year’s AES. The real shark week ended with a bang, featuring this year’s only concurrent pair of shark sessions. As a result, I definitely missed some talks I wanted to see in order to see other talks I was looking forward to. Here’s the recap:
My day began with an interesting pair of spiny dogfish talks. Chris Gburski looked at vertebral sections vs. dorsal spines for determining the age of Pacific spiny dogfish. The problem with dorsal spines is that they’re exposed to the environment and get broken, warn, or otherwise ruined for the purposes of reading growth rings. By counting rings on sections of vertebrae instead, researchers are able to determine the age of a dogfish with much less error. James Sulikowski looked at dogfish on the Atlantic side in an attempt to figure out how the population rebounded so quickly from overfishing. His lab found pretty convincing evidence that dogfish don’t have a defined spawning season (meaning that on a population level pups can be born any time of year) and possible evidence that the gestation period of dogfish in the Atlantic may be quicker than previously reported (16 months instead of 24). Could these sharks be more resilient to fishing pressure than previously thought?
Steve Kessel looked at very scaled-up dogfish, better known as Greenland sharks, and their tendency to scavenge (or possible prey on) marine mammals in the Arctic. His presentation compiled several sources, including photographs, longline sets, and accounts from native hunters and mammal researchers, and showed that Greenland sharks may actively seek out the migration routes of mammals like seals, narwhals, and belugas. Andrea Kroetz continued the predation theme by setting up mesocosm experiments to see how the feeding rate of bonnethead sharks would respond to the amount of available prey. She found that bonnethead foraging patterns don’t fit any of the three types of functional feeding responses (I – continuous feeding, II – eating until satiation, III – waiting to eat until the prey hits a certain abundance) and instead feed somewhere between Type I and II.
The next couple of talks involved social sharks. Jean Finger studied the social and exploratory behavior of juvenile lemon sharks, and found that more social sharks tended to also be a little less adventurous when exposed to a new area. This has pretty serious implications for conservation, because fishing methods typically pick off more aggressive, adventurous individuals. Tristan Guttridge summarized his methods for identifying social behavior in sharks, which involve a pretty neat acoustic tag that not only pings, but also receives transmissions. Not only that, but it can tell you how roughly close another tagged shark was. Using this technology, it’s possible to identify which individuals a particular shark seems to be “friends” with. Getting back to fishery interactions, John Mandleman attached GoPro cameras, accelerometers, and timers to experimental longlines to look at shark behavior while hooked. He found some interesting results: the amount of time spent fighting the hook and the intensity of the fight varies by species, and in some species the sharks can actually “rest,” saving their energy and improving their survival on the hook.
Makos are the most badass fish in the sea, and several of today’s talks involved makos of some sort or another. Jeremy Vaudo recapped some satellite tagging data on shortfin makos in the Atlantic and Gulf of Mexicos. These tags revealed that makos may have warmer temperature preferences than previously thought, and may not move between the Gulf and ocean that often. Robert Heuter managed to deploy the first pop-off tag ever on a longfin mako, and unlike its shortfin cousins this sharks had no problem moving in and out of the Gulf of Mexico. Dovi Kacev studied the genetic population structure of shortfin makos in the Gulf of California, and found that sharks on either side of the US-Mexico border are likely all one population. This means that effective management will have to involve both countries. Finally, Dave Portnoy checked out population structure in the finetooth shark (which is not a type of mako but sort of looks and acts like one) and got some intriguing results. There are three identified nursery areas for this species; one ranging from South Carolina to northern Florida, one on the Florida Gulf coast, and one around Dauphin Island. All three of these populations are genetically distinct, which is surprising for the Gulf populations, which are only 300 km apart. These populations also only diverged about 5,000 years ago. Genetics really is magic.
And so concludes the real shark week. As always, it’s been a great week and one of the high points of my year. Here’s to next year.