Marine Ecological Studies

• Steller Sea Lion Study
• Prince William Sound and Kodiak Island
• FLOE Technology Development

Steller Sea Lions

Steller Sea Lion photo by Rolf Ream, NOAA/NMFS

The fish lidar is part of an airborne package that includes visual observations, digital video, and thermal imaging. Visual observations provide counts of sea lions, whales, and sea birds. The digital video provides similar information, but color processing allows the video to see deeper into the water. The thermal imager can see marine mammals and birds at night, so that the day/night distributions can be compared. There is some evidence that sea lions may remain away from the shore at night, and this could affect the accuracy of feeding patterns based on collection of scat on the shore. Night surveys using the thermal imager will help to answer this question.

The airborne surveys are coupled with ship surveys using echo sounders and sample catches. The ship surveys can reach deeper into the water column than the lidar surveys and see fish that are too deep for the lidar. Generally, the lidar can see the fish that are most useful to the sea lions. These are the herring, capelin, and sand lance that have high fat content. It can also see juveniles of pollock. The adult pollock are generally too deep for the lidar to see, and are captured by the echo sounder. The speed of the aircraft allows the lidar to survey the entire area in a single flight, and to do day and night surveys on the same day. This helps resolve space/time scales that are impossible to resolve with at ship speeds. The lidar is also able to survey in very shallow water, where the ships cannot work.

Prince William Sound and Kodiak Island

A number of studies have been completed in Prince William Sound and around Kodiak Island. The objective has been to develop improved techniques for measuring various elements of the ecosystem, including:

Plankton

In May 2002 two studies of lidar detection of plankton were performed. The first was a study, done in collaboration with the Prince William Sound Science Center, of zooplankton in Prince William Sound. We were particularly interested in Neocalanus, a tiny shrimp. These form a large component of the diet of young salmon in the spring. A comparison of the lidar results and the ship survey revealed a correlation of almost 80% between the two techniques. The conclusion is that Fish Lidar can also be used as Plankton Lidar. The other study was an investigation of the extent of thin plankton layers in the Gulf of Alaska. Patchy layers were observed all across the Gulf from Kodiak to Juneau. A very strong nonlinear wave perturbed this layer in the open waters of the Gulf. This perturbation showed up very clearly in the oscillation of the layer up and down as the aircraft moved across.

Salmon

Salmon

In September 2002, the imaging lidar was flown over Kitoi Bay on Afognak Island in Alaska. The lidar was able to record images of salmon that were in the bay near the surface. The picture is an example of a school of pink salmon. A paper describing this work has been accepted by Applied Optics.

J. H. Churnside and J. J. Wilson, "Airborne Lidar Imaging of Salmon," Appl. Opt. (in press).

Pollock

In August 2001, the lidar was flown over regions of extensive ship surveys of pollock east of Kodiak Island. While pollock are too deep to be seen by the lidar, we showed that juvenile pollock can be surveyed. The reason lies in the behaviour of juvenile pollock. During the day, they stay away from the surface to avoid being eaten by birds. At night, the birds cannot see to hunt, so the pollock can come up to the surface to feed. A lidar survey at night can detect these fish. To prove this, we compared the daytime results from the ship survey with our nighttime results. The correspondence between our data and the distribution of juvenile pollock was just over 70%, once the lidar data were filtered to remove the plankton scatter.