Day 3 of AES included pretty much all the talks up for the Gruber award, an award given to the best student presentation. Holy crap there were some good talks today. My talk was among them, and having seen my competition, I will gracefully concede to whoever wins. Some of the talks were also about spiny dogfish, and you know that always gets me excited. Here’s what I found interesting today:
Bianca Prohaska demonstrated a nonlethal approach to assessing reproductive stage in three species of elasmobranch, each one representing a different reproductive strategy (placental live birth, aplacental live birth, and straight-up laying eggs). By taking a quick muscle biopsy and looking at the hormones, she was able to determine not only which reproductive stage the sharks were at, but also predict the size of reproductive organs and even developing pups. Speaking of the wee sharks, Ryan Kempster showed that bamboo sharks developing in their egg cases will respond to the electrical signals put out by a potential predator, but will eventually acclimate to them. This has serious implications for shark repellants based on electrical fields (you don’t want a curious tiger shark getting used to the buzz after 20 minutes).
Many of the talks had pretty serious conservation implications. Teagan Gray used genetic methods to determine the potential number of breeding-age adults (and therefore the effective population size) of sand tiger sharks in Delaware Bay. The typical standard for an animal that’s doing “okay” is an effective population of 500-1000, and Delaware’s sand tigers fit right in there with 721-1031. Granted, that’s the minimum standard for a recovering population, but good news is good news. Melissa Giresi showed a very useful guide for telling smooth dogfish species apart in the Gulf of Mexico (thankfully only one species, the smooth dogfish itself, makes it as far north as North Carolina, saving me that ID nightmare). Austin Gallagher closed out the morning session by looking at which species are most affected by longline bycatch mortality. It turns out the specialists (species like threshers and hammerheads) do much worse than the generalists (tigers and blue sharks) at surviving interactions with fishing gear. This is a cool idea that he plans to explore in greater detail.
There were some trophic talks too. Ashley Shaw used stable isotopes to describe the feeding ecology of 6 species of shark, 1 species of ray, and 3 species of bony fish that all coexist in coastal South Carolina estuaries. She got some cool results, including finding that cownose ray and finetooth shark diets overlap very little with the other species, most likely due to difference in prey (for the cownose ray) or possible difference in feeding location (more likely for the finetooth shark, which eats a lot of the same fish also eaten by the other shark species). Ornella Weileli used good ol’ gut contents plus genetic identification methods to assess the diet of juvenile lemon sharks in developed and undeveloped areas of Bimini. In spots where the natural mangrove habitat has been plowed over to build resorts, lemon sharks show dramatic diet shifts and actually expand their diets to include more scavenging. Jenny Bigman made a second appearance on these recap posts by talking about the diet of North Pacific spiny dogfish in Monterey Bay, which has a very different bathymetry to most environments dogfish feed in. Because the Monterey submarine canyon brings deep environments almost right up to the shore, dogfish in the bay feed on a lot more krill than they do elsewhere.
Speaking of dags, Amy Carlson recapped the findings of her satellite tagging project involving spiny dogfish, and found evidence for two different populations split up by Cape Cod. She was even able to tease out some environmental preference differences, with the more southern sharks occupying shallower water. It may be possible that previously undescribed offshore movements caught by the tags might result in NMFS surveys missing a significant portion of the dogfish population. My talk reported the results of the captive feeding project I was running in Morehead City. I’ll have a more detailed post on the results up sometime after AES, but the main take-home is that current food web models for the US Atlantic coast may be overestimating the amount of food dogfish need to eat. If someone wants to kick me some funding, I’ll even keep these feeding trials going…
Dave Shiffman gave the most unique talk of the day, focusing not on sharks so much but on the perception of shark conservation issues on Twitter. Shark conservation NGOs are much better represented on Twitter than scientists, and as a result their perception of conservation issues and policy (which can be very different from what the best science recommends) is much more prevalent online. The potential problem is that many of these tweeters represent the “no shark fishing ever” crowd, which is a problem when scientists are trying to promote responsible management of these species. Very interesting stuff (full disclosure: I’m among the group of people who have been helping Dave with some of the organization and analysis of his data).
Good stuff today. Tomorrow will be hectic because it’s the only day this week with two simultaneous shark sessions. Hopefully I don’t miss anything cool, and as always feel free to bring up anything you think deserves a mention in the comments.