So, I thought I’d mention some of the primary sampling objectives of the cruise. The first one is to collect specimens across habitats so that we can examine differences in the species assemblages and relative abundances of demersal fishes associated with the eastern and western walls of De Soto Canyon and the adjacent continental slope and shelf edge. This includes sampling within the Madison Swanson Marine Reserve.
Every dominant species of fish that is brought on board is sampled for liver, bile, and blood to examine spatial and depth-mediated differences in exposure to polycyclic aromatic hydrocarbons (PAHs). Muscle tissue is taken from all animals (fish and invertebrates) collected for stable isotope analyses as part of a study of trophic interactions (feeding relationships), as well as determining radiocarbon ratios to examine attenuation of long-term exposure to hydrocarbons. Given that we are encountering a number of rare or even species that are new to science, we are collecting whole specimens as vouchers to help resolve phylogenetic uncertainties and improve our understanding life history traits in collected taxa.
In addition to this rather general overview, each scientist onboard has a specific set of objectives. Let’s hear it from the grad students.
|Graduate student Cheston Peterson |
and six-gill shark, Hexanchus griseus
|Graduate Student Brenda Anderson |
working up blood samples from sharks
Jo Imhoff (Florida State University Biological Science graduate student). — I’m interested in the feeding behavior and movement patterns of sharks. In particular, I’m studying niche partitioning among groups that broadly overlap in their geographic ranges to determine what allows them to coexist. The first part of my study involves two species of dogfish (Family Squalidae) -- the Cuban dogfish Squalus cubensis and the shortspine dogfish species complex Squalus cf mitsukurii – that have similar morphologies (although Cuban dogfish is smaller) and life history strategies. The second part involves sharks from two different families, the dogfishes and the gulper sharks (Family Centrophoridae), so named because of their ability to swallow large prey.
|Graduate student Jo
Imhoff (FSU) working up sharks |
caught on the slope of the De Soto Canyon
Following movement patterns is going to be a bit trickier. Vertical migrations have not yet been tracked for most of these species. Are they feeding on benthic organisms (on the sea floor) or mesopelagic (in the water column at depths from 150 – 1000 m)? This is an important question in terms of whether or not species are contaminated with oil because it will influence the amount of residual oil showing up in their tissues. That is, those animals feeding in the mesopelagic zone are anticipated to have been impacted less than those feeding on the bottom. The best model species for making these determinations in the shortspine dogfish, which is more robust than the other species of interest and so can be successfully tagged with satellite tags to track their vertical movements.
A follow up question relates to the apparent separation of species on the eastern and western slopes of the De Soto Canyon. What we have discovered during the Deep-C study thus far is that the dogfishes are dominant on the eastern side while the gulper sharks are dominant on the western side. The question is, how does feeding and movement play into determining their community structure and their apparent niche partitioning? I’ll be working on this problem for the next three years.
|Kelly Kingon FSU graduate student |
doing a very nice impersonation
of Dr. Jim Gelsleichter, UNF.
I’m also posing as Dr. Jim Gelsleichter, UNF (sorry, Jim, you’ve been replaced), to work with grad student Brenda Anderson to process the data she describes above. This has just been fascinating for me and quite different from the types of things I work on as a geographer.
Dr. Felicia Coleman (FSU)