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Dry Tortugas Cruise Day 5 - August 29, 2007
at the end of the 30th transect.
Photo credit: Shelby Moneysmith
small boats from which dive
operations are executed (note the
"diver down" flag), with
the Nancy Foster in the background.
Photo credit: Shelby Moneysmith
Day five of the cruise began with beautiful weather. Many eager cruise participants were ready to kick off the day before the sun rose. Cruise operations began as usual with three dive teams deploying in the morning right after breakfast. The morning’s sites included two shallower sites (54 and 61 ft), and one deeper site (97 ft). On the bottom, one team saw mutton snapper and several species of grouper, which disbanded as the team of scuba divers began their survey. Another team observed many juvenile groupers. Increased abundance of juvenile groupers is a positive sign, indicating healthy levels of reproduction of these heavily harvested fishes.
Many of today’s sites were within Dry Tortugas National Park. This year, the Park has established a no–take Research Natural Area (RNA). As the name implies, the RNA will be used for non–extractive research and monitoring activities. Five of CCFHR’s 30 sites lie within the RNA boundary. This gives us the opportunity to compare reef communities at these sites before and after implementation of the no–take RNA. Unlike Tortugas Ecological Reserve, a limited amount of fishing is permitted in the Park outside of the RNA. Establishment of the RNA is intended to benefit fish and invertebrate populations not only within the RNA, but within the rest of Dry Tortugas National Park, and surrounding waters.
of macroalgae that will be assessed
for the presence of ciguatera–
causing dinoflagellates.
Photo credit: Shelby Moneysmith
During the day’s dive operations, teams completed the usual fish, photo, and video surveys. In addition, they added a new task to collect macroalgae. At each site, a diver collected a random sample of macroalgae from the seafloor and placed it in a resealable plastic bag filled with seawater. Back on the Nancy Foster, the bag of macroalgae was shaken up to release any small organisms that might be living upon the algae. The water was filtered through a small sieve so that only organisms of small size were collected. The filtered water will be returned to scientists at CCFHR to look for tiny organisms called dinoflagellates, some of which produce the toxin that is responsible for ciguatera poisoning. These CCFHR scientists are interested in assessing the spatial distribution of ciguatera–causing dinoflagellates in Florida.
Our surveys require not only knowledgeable and competent divers, but also a wide range of equipment. On a typical dive, team members are equipped with still cameras, video cameras, dive computers, pop–floats (‘safety sausages’) and reels, a back–up air supply, clipboards, and tools. The gear is split up among team members. The video and still cameras used to collect video and photo footage are housed in watertight cases. During today’s dives, two teams were reminded of the challenges that can arise when using electronic equipment underwater. Because an underwater housing unit is not foolproof, divers must make sure it is well sealed. They must be attentive to any signs of leakage, such as bubbles at the seals or condensation inside the housing. Unfortunately, today we had leaks in both still and video camera housings, a rare occurrence. Divers returned the malfunctioning gear to the surface, where it was dried and assessed for repairs.
camera. Photo credit: Amy Uhrin
collected in the beam trawl.
Photo credit: Brett Harrison
With seven dives completed today, all 30 of the survey sites have been visited. All survey activities were reviewed to determine which sites needed revisiting to obtain a complete set of data. Problems with equipment, environmental conditions (i.e., strong current or poor visibility), or limited bottom time are all factors that can account for incomplete surveys at some sites. We will revisit these sites tomorrow to complete the surveys.
Between dive operations this afternoon, the science party and ship’s crew surveyed more drop camera sites. Drop camera surveys are used to ground truth the acoustic seafloor classification and characterize the habitat sampled by beam trawls during evening and night operations. Deployment and recovery of the drop camera and beam trawl from the ship requires extensive support from the ship’s crew members. Like all previous nights, the crew will work late into the night operating the A–frame from the ship’s stern in hopes of finishing up the beam trawl sites. This operation takes quick and concise communication from the lab, bridge and deck.
Today’s website contributors are Vanessa McDonough and Shelby Moneysmith from Biscayne National Park. Both have served as photographers during dive operations.
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