Today marked the last official day of shark talks at JMIH/AES, though there will still be plenty of bony fish a reptile talks tomorrow. Most likely I’ll be exploring Minneapolis, and then it’s time for the long trip back and a little mini-vacation. Tonight is the big AES Banquet, where I find out if I won any awards or get to take home any swag from the raffle. In the meantime, let’s see what people were talking about today.
Kevin Weng has been tracking great whites in Southern California in conjunction with the Monterey Bay Aquarium. Eastern Pacific white sharks seem to be one population genetically, but separate off into two “ecological” populations; the sharks around Guadalupe in Mexican waters and those that group around the Farallones. By tagging juveniles found along southern California and Baja California, Kevin and his collegues have found that the two white shark populations in the eastern Pacific may share the same nursery area, which would help explain their continued genetic similarity.
There were a few talks that inhabited more math and modeling-heavy territory. Sebastian Pardo demonstrated how using a fixed size-at-birth can give an unrealistic bias when modeling shark growth using a Von-Bertalanffy curve. This type of curve gets heavy use in fisheries management when performing stock assessments, and biasing the curve can result in a species being managed either too tightly or not at all. This sort of issue is important to work out, since elasmobranch management is already hard enough with often incomplete data. Nick Dulvy showed how he and his collegues calculated the biomass of sharks that would exist worldwide in the absence of fishing. Without fishing, there should be 86 million tons of sharks, rays, and chimeras with an annual production of 6 million tons. However, this may be confounded by factors influencing primary production in marine ecosystems, though their estimate for maximum sustainable yield (1.3 million tons) is fairly close to the current estimate for global catch of elasmobranchs (1.7 million tons).
John Froeschke documented the abundance patterns of the three most common sharks in the coastal estuaries of Texas, finding that while blacktips and bonnetheads behaved exactly as expected by sticking near the inlets, bull sharks dramatically increased in the northernmost estuaries. This may be the result of a ban on gillnets in Louisiana in the 1990s, since the estuaries where bull numbers have really taken off are the closest to the state line.
Rulifson lab member Andrea Dell’Apa presented his Masters work analyzing the effects of the European fisheries law 41/82, basically the equivalent of the Magnusen-Stevens act we have here in the states. However, law 41/82 is concentrated more on economic development than conservation. Most shark landings in the Mediterranean are classified as “smoothhound” and environmental surveys are either unstandardized or woefully inadequate in that area, so any meaningful estimate of species-specific fishing impact is impossible. So Andrea tracked the overall landings of elasmobranchs and found something interesting; the fishery law encouraged fishermen to land an increased number of sharks and rays immediately following its implementation, which was followed by the by-now familiar boom-and-bust pattern seen in most shark fisheries. Fishermen switched to elasmobranchs immediately following law 41/82 to exploit more of the bycatch species and to maintain a dependable source of income as management of bony fishes became more complex. Essentially, the fisheries management law doomed the stocks of medium to small-sized sharks in the Mediterranean.
Simon Gulak brought it back to field work, recounting his experiences tagging dusky sharks along the southeastern coast of the U.S. He’s had some tribulations, but found that although a portion of the Atlantic just off of North Carolina has been designated as essential fish habitat for dusky and sandbar sharks, the duskies may actually be using a patch of ocean called the Charleston Bump more than that area. This is with a depressingly low number of returns so far and some technical difficulties, but still worth a look. Finally, Mike McCallister talked about the juvenile sharks surveys he’s been performing in northeastern Florida. Most of it was pretty standard, but he may have stumbled upon an important nursery area for scalloped hammerheads.
That’s all for this year’s talks, at leas the ones I was both present for and took detailed enough notes to summarize. It’s been a great conference and I’m already looking forward to hitting up AES next year in Vancouver.