AES 2013: Days 1 & 2


The first day of talks was a hodgepodge of general shark and ray ecology.  Cheston Peterson gillnetted and longlined all over Florida’s Big Bend ecosystem (the Gulf Coast shoreline between Tallahassee and Tampa), which also happens to contain one of the largest continuous seagrass beds on the planet.  In the process he got an awesome amount of data on the distribution and habitat preferences of 14 different species of shark or ray.  Mike McCallister found an unusually productive scalloped hammerhead nursery farther up a coastal river in Florida than you’d expect, though recent stormy summers may cause some changes there.  Marcus Drymon proved the usefulness of the good ol’ fishery-independent survey by looking at large-scale (the entire Gulf Coast) and small-scale (just off of Dauphin Island) trends in habitat selection by the area’s sharks.  He managed to find some environmental preferences that were consistent on both scales, particularly for the widely-distributed sharpnose and blacktip sharks.  Pretty inspiring stuff as I try to get my own survey up and running.

A couple talks involved elasmobranchs running up into fresh water.  Jonathan Davis tracked juvenile bull sharks moving in and out of Lake Pontchartrain, where I assume they spend a lot of time stealing bait from the Swamp PeopleGreg Poulakis used stable isotopes to infer the diet of juvenile smalltooth sawfish, and found that the diet wasn’t very different from that of the juvenile bull sharks sharing the area.  The sawfish avoid turf wars by sticking to slightly saltier water.

Some well-studied (but apparently not well-studied enough) coastal sharks rounded out Day 1’s presntations.  Bryan Frazier (who showed me the longlining ropes) looked at age and growth of bonnetheads on the US Atlantic coast.  Turns out they grow larger, slower, and live longer than the population in the Gulf of Mexico.  James Kilfoil presented on the growing recreational fishery for sand tiger sharks (which is almost entirely motivated by the urge to take pictures sitting on sharks) and the potential for post-release mortality.  Though 48 % of the sharks were accidentally gut-hooked, only one actually died during the span of the study.

Day 2 was all about the flat sharks.  This year’s AES included a symposium on durophagous stingrays, more commonly referred to as “the ones that smash shells.”  You may have seen the Twitter coverage with the brilliant hashtag #RaystheRoof.  I’m not usually terribly excited about those flat bastards, but there was a lot of interesting stuff in this symposium.

Neil Aschliman gave what was probably the most entertaining talk about phylogenetics I’ve ever seen.  By looking at a combination of morphological features (like those funky cephalic lobes) and genetics, he was able to piece together how cownose rays, eagle rays, and mantas all fit together.  Turns out mantas are really just derived cownose rays.  Matt Kolman was another speaker who did a great job making a normally dry subject entertaining.  He looked at bite force in cownose rays and how it’s modeled, and found that by the end of their first year of life these rays are already capable of smashing coquina clams.  Christine Bedore studied vision in cownose rays, and found that they are extremely well adapted to traveling in schools and dive-bombing prey on the bottom.  These rays have good vision by ray standards, have a 360-degree field of vertial vision, and can likely see in color.  Oh, and they also may be able to keep their brains and eyes warmer than the surrounding water, much like swordfish.  Crazy animals.

Of course I would key in on feeding ecology, and the ray symposium did not disappoint.  Jack Szczepanski looked at the feeding habits of bullnose rays in Delaware Bay, and found that they really like snails (so much so that hermit crabs using snail shells may be getting caught in the crossfire).  One of their most important prey items seems to be some kind of gastropod that hasn’t been positively identified yet.  Sean Powers (who wasn’t able to make it and had Marcus filling in) studied the diet of cownose rays in Bogue, Back, and Core Sounds in North Carolina, where the infamous Myers et al. paper claimed the big batoids had eaten the bay scallop fishery out of existence.  In the sounds, 80% of ray stomachs contained bay scallops and ray exclusion plots dramatically reduced predation mortality on the delicious bivalves.  This was an interesting contrast to Lyndell Bade’s results.  By using genetic techniques to identify mashed-up bivalves in cownose ray stomachs, she found they mostly like stout razor clams and found no scallops in the diet.  Some of her samples came from the Neuse River, not very far north of Core Sound.

Back to genetics, some interesting stuff is going on with population description for some ray species.  Jennifer Newby tried to find any kind of stock structure in spotted eagle rays, and didn’t even find much of a difference between the Gulf and Atlantic Coast.  However, she did find the good news that the current effective population size is pretty high, so no sign of any of the ill effects of fishing pressure.  Jan McDowell attempted to do the same thing with cownose rays and what she and her team found only muddies the waters more.  Not only might some Brazilian cownose rays be straying north into the Gulf of Mexico, but there might be a third species, currently unidentified, mixed in with cownose ray populations along the Atlantic coast.

The last couple talks of the symposium dealt directly with the interaction between humans and rays.  Dean Grubbs systematically destroyed all the points made by the Myers et al. paper.  Shark declines have not been as dramatic in areas other than North Carolina, cownose rays don’t show up often in the stomach contents of the sharks emphasized in that study, and the collapse of the scallop fishery began decades before the “explosion” of cownose rays.  Sonja Fordham went into the consequences of that paper and the press it got, including attempts to promote cownose ray, a species that currently has no fishery regulations, as a “sustainable” choice.

There were a freakish number of great posters this year, so I’ll just skim a few of them briefly.  If you happen to read this and your poster wasn’t mentioned, don’t take offense, I just only have so much time to bang these recap posts out.  I visited almost every elasmobranch poster at the session, and liked every one that I checked out.  Here are some highlights:

I do love trophic ecology, so posters by Ashley Shaw (assessing the trophic level of large teleosts and juvenile elasmobranchs in South Carolina estuaries, this time with an emphasis on cownose rays) and Jenny Bigman (determining whether predators in Monterey Bay feed mostly out of a benthic of pelagic community) caught my eye.  Mariah Pfelger looked at the genetic differences between deepwater dogfishes in the Gulf of Mexico, and found that Squalus mitsukurii in the Gulf is very different from populations in the Pacific.  Lauran Brewster and Robert Bullock stuck accelerometers to juvenile lemon sharks in Bimini, and were able to find out some pretty cool things about their temperature preferences and activity level on an average day (potentially including how often they chase their prey and for how long).  Brenda Anderson had a nice gory poster identifying shark bites on a right whale carcass that washed up on Florida.

That was Day 1 and 2.  Tomorrow is pretty much all student presentations, including mine.