It’s day 2 of JMIH/AES, and, as usual, there were too many great talks for me to go through them all. Make sure to check WhySharksMatter and labroides on Twitter to fill in some of the gaps, and if anyone else is reading this and also updating the internets on this conference, let me know and I will steer people your way as well. I have even less spare time to recap the day’s talks than yesterday, so the summaries may be a bit short.
I had a bit of a late start due to the fact that I had to get spiffed up for my own talk this morning. The morning session was comprised entirely of student talks in competition for the Gruber Award, which is given to the best student oral presentation.
The first presentation I made it to was by Chris Mull, who looked at the possible connections between maternal investment and brain size in elasmobranchs. Because elasmobranchs run the gamut of reproductive strategies, from egg-laying to placental live birth, they may have a range of brain sizes as well. The idea is that the more maternal investment involved, the bigger your brain, so a hammerhead giving birth to pups with umbilical cords is probably bigger-brained than a skate laying egg cases. While the connection with the complexity of reproductive mode was somewhat inconclusive, the litter size and gestation period are directly related to brain size. Which means with their two-year gestation period, spiny dogfish might be brainier than the average shark.
I spoke after the first mid-day break, and it seemed to go pretty well. I’m still learning the fine art of finishing my talks on time, and had to rush the last couple slides. I’m not a fan of not leaving time for questions, but I did get some good feedback over the course of the day from audience members.
Aleksandra Malikjovic kicked off a lightning round of stable isotope talks with a look at long-term changes in trophic dynamics using vertebrae taken from sharks caught in the nets set by the Natal Sharks Board. These vertebrae lay down annual rings, and the idea is that the stable isotopes found in those rings can tell you broadly what that shark was eating at that time. It’s very similar in concept to the otoliths studied by Dan. Aleksandra found that smaller sharks like blacktips and spinners show the most apparent gradual reductions in Nitrogen, which may reflect long-term changes in the lower food chain. Makos have apparently seen steady N declines since the 70s, and hammerheads have actually increased in N. This is pretty good evidence that something in the food web leading up to these apex predators has been changing, but whether that’s fishing pressure or climate change is still to be determined.
Rounding out the isotope talks, Aaron Carlisle demonstrated a new use for them by showing that isotopes from vertebrae can show what parts of the North Pacific salmon sharks forage in as they grow. David Shiffman presented some new stuff on his stable isotope analysis on sandbar shark diets, showing that the resolution can get as good as identifying the most common prey species if you have a good enough sample size (and David has the largest sample size of any isotope analysis). Sora Kim wrapped up the isotope talks with analysis of white shark vertebrae from the Pacific obtained from museum collections, and showed that isotopic signatures can show whether great white are feeding on inshore or offshore prey. This is an important distinction in the Pacific where great whites spend a good deal of time out in the pelagic environment.
After many technical difficulties, Jayne Gardiner rallied and presented research on how important each sense is to a shark’s ability to accurately strike its prey. It turns out that all the senses work together in the approach and attack, with smell leading the shark in, the lateral line helping in navigation, vision being used to line up the attack, and the electro-sense guiding the shark in for the final bite. All working together in a nice little symphony of death.
In the non-Gruber talks, Christina Walker presented what should be headline-making research on the effects of the Deepwater Horizon oil spill on the sharks of the Gulf of Mexico. Several species are showing signs of oil contamination, with blacknose sharks acting as the potential best indicator species for oil damage. Greg Skomal filled in for his student Jeff Kneebone, demonstrating that hook-and-line captured sand tiger sharks actually have very good survival on release, despite a high incidence of gut-hooking. Tough critters. The always-entertaining Jim Gelschleichter analyzed the role of the protein relaxin in shark reproduction. It’s been documented that relaxin helps, as you might guess, relax the birth canal in females, but in males may aid in sperm formation and in getting those sperm into the egg for fertilization. Finally Marianne Porter showed that the entire spine of the spiny dogfish is elastic and used in its swimming motion, an energy-saving adaptation and yet another reason why spiny dogfish are cooler than whatever crap you’re studying.
The poster session has some goodies. Notable for me: Jack Szcepanski studying the feeding habits of bullnose rays in Delaware Bay (he may have inadvertently found a new species of snail, yet another use for shark puke), Jenny Kemper looking at the stomach contents of skates off of Alaska, Ryan Ford studying blacknose shark reproduction (there’s a lot of attention on this species lately and for good reason; they may be even weirder than dogfish), and Melissa Giresi trying to tease apart the taxonomy of Triakid sharks (smooth dogfish) in the Atlantic and Gulf of Mexico.
I’m sure I missed plenty of quality talks and posters, so feel free to add more worthwhile mentions in the comments. Meanwhile, I’m going to go celebrate being done presenting for this conference.