Leah Johnson: Fish Identification & Pisces Farewell, August 1, 2015

NOAA Teacher at Sea
Leah Johnson
Aboard NOAA Ship Pisces
July 21 – August 3, 2015

Mission: Southeast Fishery – Independent Survey
Geographical Area of Cruise: Atlantic Ocean, Southeastern U.S. Coast
Date: Saturday, August 1, 2015

Weather Data from the Bridge:
Time 12:13 PM
Latitude 033.995650
Longitude -077.348710
Water Temperature 24.37 °C
Salinity 36.179 ppt
Air Temperature 27.4 °C
Relative Humidity 83 %
Wind Speed 15.95 knots
Wind Direction 189.45 degrees
Air Pressure 1012.3 mbar

Science and Technology Log:
I am still amazed at the wealth of data collected aboard the Pisces on this survey cruise. I am getting better at identifying the fish as they are hauled up in the traps, as well as when I see these fish on video. Because of light attenuation, many fish look very different in color when they are underwater. Light attenuation refers to the gradual loss of visible light that can penetrate water with increasing depth. Red light has the longest wavelength on the visible light spectrum, and violet has the shortest wavelength. In water, light with the shortest wavelength is absorbed first. Therefore, with increasing depth, red light is absorbed, followed by orange, then yellow. Fish that appear red in color at the surface will not appear red when they are several meters below the sea surface where they are captured on camera.

For example, we hauled in some blackfin snapper earlier this week. At the surface, its color is a distinct red like many other types of snappers, and it has a black spot near the base of its pectoral fin. When I looked at the videos from the trap site, I did not realize that all of the fish swimming around with yellow-looking tails were the very same blackfin snappers that appeared in the traps! When I remembered that red light is quickly absorbed in ocean water and noticed the black spot on the pectoral fin and shape of the dorsal fin, it made more sense.

Top: Blackfin snapper collected from trap.
Bottom: Video still of blackfin snappers swimming near trap.

I tell my geology students every year that when identifying minerals, color is the least reliable property. I realize now that this can also apply to fish identification. Therefore, I am trying to pay closer attention to the shape of the different fins, slope of the head, and relative proportions of different features. The adult scamp grouper, for example, has a distinct, unevenly serrated caudal fin (tail) with tips that extend beyond the fin membrane. The tip of the anal fin is elongated as well.

scamp grouper

Scamp grouper

Another tricky aspect of fish identification is that some fish change color and pattern over time. Some groups of fish, like wrasses, parrotfish, and grouper, exhibit sequential hermaphroditism. This means that these fish change sex at some point in their lifespan. These fish are associated with different colors and patterns as they progress through the juvenile phase, the initial phase, and finally the terminal phase. Some fish exhibit fleeting changes in appearance that can be caught on camera. This could be as subtle as a slight darkening of the face.

The slight shape variations among groupers can also lead groups of scientists to gather around the computer screen and debate which species it is. If the trap lands in an area where there are some rocky outcrops, a fish may be partially concealed, adding another challenge to the identification process. This is no easy task! Yet, everyone on board is excited about the videos, and we make a point to call others over when something different pops up on the screen.

warsaw grouper

We were all impressed by this large Warsaw grouper, which is not a common sight.

I have seen many more types of fish and invertebrates come up in the traps over the past week. Here are a few new specimens that were not featured in my last “fish” post:

Did You Know?

Fish eyes are very similar to those of terrestrial vertebrates, but their lenses that are more spherical.

lens from fish eye

Lens from fish eye

Personal Log:

I love being surrounded by people who are enthusiastic about and dedicated to what they do. Everyone makes an extra effort to show me things that they think I will be interested to see – which I am, of course! If an interesting fish is pulled up in the trap and I have stepped out of the wet lab, someone will grab my camera and take a picture for me. I continue to be touched by everyone’s thoughtfulness, and willingness to let me try something new, even if I slow down the process.

me, standing on the deck at the stern

Me, on the deck of the ship. We just deployed the traps off the stern.

As our cruise comes to an end, I want to thank everyone on board for letting me share their work and living space for two weeks. To the NOAA Corps officers, scientists, technicians, engineers, deckhands, and stewards, thank you for everything you do. The data collection that takes place on NOAA fishery survey cruises is critical for the management and protection of our marine resources. I am grateful that the Teacher at Sea program allowed me this experience of a lifetime. Finally, thank you, readers! I sincerely appreciate your continued support. I am excited to share more of what I have learned when I am back on land and in the classroom. Farewell, Pisces!