Sunday, October 14, 2012

Ecology/Fisheries Cruise - October 2012

Blog Post:   14 October 2012 (WB1306)

It’s been a little hard to keep up the blog with sampling going on 24-7. The only down time is about 10-15 minutes per meal and then sleeping for 2-4 hours between hauls using the gear configuration illustrated below across depths ranging from 100 to 2000 meters.

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
Cheston Peterson (Florida State University Biological Science graduate student). — My work has concentrated up until this point on studies of the trophic interactions (feeding relationships) of coastal sharks, using stable isotopes to evaluate long-term feeding patterns in different age fishes. I am extending this work to the deep sea to evaluate the connectivity between these two very different ecosystems. That is, what type of coupling occurs between coastal and deep habitats? Demonstrating that this coupling occurs among shark species has significant management implications for both ecosystems. We know, for instance, that sharks pup in seagrass-rich areas and that seagrass beds and the organisms associated with them can be transported to the deep sea, providing nutritional support in a system that is otherwise nutrient poor. Indeed, a significant portion of the nutrients that end up in the deep sea simply rain down from above as organisms in coastal, offshore, and pelagic realms die and sink to the bottom. So what elements of the diet of deep sea sharks depend on high productivity in coastal habitats, how does that change with ontogeny, and how does it occur over space and time? In addition, can we trace the movement of oil derivatives through the system using this species group?

Graduate Student Brenda Anderson
working up blood samples from sharks
Brenda Anderson (University of North Florida Biology graduate student). — Here’s where the work I’m doing for Jim Gelsleichter comes in. While my master’s work focuses on using non-lethal ways of characterizing reproductive cycles in sharks, primarily by collecting blood to sample sex hormones and using ultrasound to determine pregnancy in these live-bearing animals, the work I’m doing here is toxicological. That is, looking for exposure levels and effects of environmental pollutants (oil and its derivatives, in this case) to determine whether the animals are exhibiting any health- or life-threatening effects. I’m taking bile to test for the metabolites of PAHs, liver to look for the metabolites of PCBs, and blood cells to evaluate DNA for signs of any biomarker that would indicate not only exposure to toxic substances, but the level of exposure.

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
What I’m doing right now is collecting stomach contents for a snapshot of what they’ve been eating, and coupling this with tissue samples that will be evaluated for stable isotope ratios to determine the longer term trophic level at which they normally feed. I’m interested in comparing gut contents and stable isotope ratios between species both in habitats where they coexist and habitats where they do not.

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. 
Kelly Kingon (Florida State University Geography graduate student). – My work related to the Deep-C consortium is to work with the data management team to develop three primary databases: one for references (entered into refbase), one for physical data (geologic, oceanographic, bathymetry and side scan data), and one for biological data (distributions of deepwater corals and other invertebrates, fishes, sea turtles, sperm whales, and other organisms; abundances where they exist). The idea is to compile the historical data from the northeastern Gulf of Mexico in the area of interest into a geo database accessible to everyone in the consortium, and to overlay it with post-spill data, as they become available. All the data will eventually migrate to the Deep-C Data Atlas.

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.

Posted by:
Dr. Felicia Coleman (FSU)

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