Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
Gray's Reef Expedition 2012
Mission Information
 

Tuesday: June 5, 2012
Log Day 6

Dr. Roldan Muñoz
Research Fishery Biologist
National Marine Fisheries Service

Randy Rudd (l) Jenny Vander Pluym (c) and Roldan Muñoz review target fish for their survey

Randy Rudd (l) Jenny Vander Pluym (c) and Roldan Muñoz review target fish for their survey.
(Photo: Debbie Meeks)

I've been working in Gray's Reef National Marine Sanctuary (GRNMS) counting and identifying bottom dwelling fishes for three seasons now (Aug 2010, May 2011, and May 2012) and have never encountered underwater visibility as bad as we've had during our current cruise. Granted, we did just have two tropical storms (Alberto and Beryl) plow right through the Sanctuary, but one foot of visibility makes it extremely hard to do anything underwater. Since differences in underwater visibility can be patchy in the Sanctuary, we tried four different sites that first day (May 31) but were thwarted at every one.

Seaweed Bleeny representative of a prey fish

Seaweed Bleeny representative of a prey fish
(Photo: Greg McFall)

Since 2010, I have been counting and identifying fishes in two different management zones at GRNMS. One zone is open to hook and line fishing and diving and other human uses, and another area, the research area, was completely closed to all use except scientific research in December 2011. Comparing the research area with the open area can help scientists observe natural environmental variation and differentiate whether or not human impacts such as fishing and the deposition of marine debris (fishing line, plastics, bottles, etc) affect the marine community. Similar changes in both management zones would suggest environmental variation, while changes that were unique to only one zone might indicate that human activities were affecting the marine community, or might suggest ecological questions that could be answered with experiments.

Tagged scamp grouper representative of a conspicuous fish

Tagged scamp grouper representative of a conspicuous fish.
(Photo: Greg McFall)

Two activities that I am leading during this cruise are surveys of conspicuous and prey fishes at our study sites distributed throughout the sanctuary. Conspicuous fishes are typically those species that are economically important and highly mobile such as groupers and snappers, and we survey these groups with 50 m x 10 m visual transects for a total survey area of 500 m2. Smaller fishes are surveyed with 25 x 2 m visual transects for a total survey area of 50 m2. These species are often well camouflaged and can either be the juvenile stage of conspicuous species or may remain cryptic and small throughout their life cycles, where they may function as important prey species within the fish community. Counts during the conspicuous surveys tend to target those fish greater than 10 cm in total length (TL), while prey fish surveys are restricted to size classes less than 10 cm in TL. We started these surveys in 2010 but GRNMS has been conducting similar surveys for a number of years.

Coxswain - A.B. Peaks (l) and the Fish Team - Randy Rudd (l) Jenny Vander Pluym (c) and Roldan Muñoz (r) ready for first dive of the day.

Coxswain - A.B. Peaks (l) and the "Fish Team" - Randy Rudd (l) Jenny Vander Pluym (c) and Roldan Muñoz (r) ready for first dive of the day.
(Photo: Debbie Meeks)

Unfortunately during the first three days of this cruise, the low visibility has not allowed us to effectively survey the conspicuous fishes. These larger species startle much easier under conditions of low visibility and we were not able to count them effectively. Luckily, most of the smaller prey species do not feel threatened by divers during conditions of low visibility, and because we have been sampling this group since 2010, we can still compare those data from this year with previous years. Working in the natural environment (what scientists call "the field"); we often have to adjust our research plan in response to the weather.

Luckily, visibility has been steadily improving and the weather has mostly remained calm with light winds. For the first time visibility was great enough (15 ft) for me to feel confident that we could effectively count the both the conspicuous and prey fish communities. In addition, my dive buddy, GRNMS Team Ocean volunteer Randy Rudd, is measuring physical characteristics of the hard bottom (rocky) ledges, sessile invertebrates, and algae (such as ledge and sponge height), because these features can be important in determining the kinds of fishes that settle and live on the hard bottom reefs. Completing our surveys at each site are other scientists in the group that are characterizing the benthic invertebrate community.

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