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Trawling with Zombies: Deep-Sea Creatures Up Close and Personal

posted Dec 11, 2012, 12:12 PM by Kirk Sato

    Stepping onto the ship early Saturday morning was very surreal.  As a coastal ecologist, there has never been a reason for me to get on a giant research vessel; and the thought of not jumping in the water to dive during a research expedition seemed bizarre to me.  I was amazed at the volume of microscopes, analytical tools, cold vans, and technology that outfitted the Melville.   This is a far cry from the BINKE nets (small nets to capture fish while scuba diving) and personal coolers filled with seawater to collect fish that I use for my research.  But I soon became comfortable with the set up and it was only a matter of hours before we were headed straight to work, decked out in foul weather gear, steel toed rubber boots, safety vests, and hard hats. 

Map of station locations in the San Diego coastal region. 

D= Del Mar line, L = La Jolla, P = Pt. Loma, SDT = San Diego Trough

    I am a volunteer for the “Shelf Team” aka the “Zonation Zombies” and our job is to collect fish and invertebrates from the seafloor at different depths (or zones) and relate that data to the oxygen minimum zone.  We use an otter trawl, which is essentially a weighted net with a mouth opening about 10 m wide.  The net descends to the benthos and collects anything residing on the bottom: fishes, worms, sponges, crabs, octopus, and echinoderms.  Our sites are mapped out using Google Earth which has been surprisingly accurate.  Knowing the distance of our otter trawls is very important because it helps us calculate the average density of each taxon during a trawl.  Our first two otter trawls were at 3 and 4 a.m. on Sunday morning (remember science does not conform to the circadian rhythms of human beings!) and they were very successful.  There is an evident difference in biodiversity among the various zones we are sampling, and it is impressive to see such high biodiversity and biomass in an area many consider to be inhospitable for organisms.  


Zonation Zombies haul in a benthic otter trawl collected from 400 m. 

Once the trawl made it back on the deck, the zombies were running around at full speed grabbing buckets, fish, brains …. oops, I mean urchins, and inverts.  We separated the organisms as best we could and acquired counts and sizes of all organisms. Total counts of organisms were being called every which way and Mike Navarro, the record keeper, would echo back the calls in confirmation.  It was a veritable round of science harmony.  Yuzo Yanagitsuru and I worked in tandem to identify and count the fishes. Natasha Gallo measured the standard length of all fishes with economic importance.  Amanda Netburn (Scientific American Blog) photographed larger animals that were too big for preservation, and Kirk Sato reserved two representatives of each species to be used as teaching aids or as a voucher species.  These specimens will be catalogued and archived into a database that is maintained by the Scripps Benthic Invertebrate and Vertebrate Collection.   The work was long, but it is so satisfying to watch sunrise standing on the deck of a ship counting deep-sea animals.

Posing with a deep-sea octopus.

    But the day was not over yet!  We still had a ROV dive planned, and another otter trawl in the evening.  The ROV performed brilliantly, with Kirk and Mike (the zombie leaders) directing the techs where to maneuver the machine.  It is interesting to see the difference in the diversity of species that we see with the ROV versus the otter trawl.  Some species, like the heart urchins (Brisaster latifrons and Brissopsis pacifica) burrow into the sediment and cannot be counted on ROV transects; but we see many of these species in the otter trawl.   Alternatively, there are mobile species that we cannot collect with an otter trawl that we see during an ROV dive. These two techniques (the otter trawl and the ROV) complement one another well to acquire accurate and comprehensive data. 

    In the evening we had our third otter trawl of the day, and brought up an even wider array of species.  As we were finishing the counts, the zombies stopped for a short time to watch the sunset as dolphins swam along the ship.  Days as long as this force upon you some introspection and I could not think of anywhere I would rather be.   This ship is decorated with Christmas lights, the company is great, and there is an endless supply of ice cream sandwiches.  What more could you ask for?

-  Katie Sievers, Masters Student in Ecology at San Diego State University