Three-Dimensional Visualization of Cod Spatial Dynamics and Vertical Movements in European Waters

Cod stocks in European waters are in serious decline recently, drawing media coverage to that subject. Danish Institute for Fisheries Research (DIFRES) participated in a television program about threatened and endangered fish species on the national Danish Channel DR2 shown in March 2004. The program focuses on biologists’ work in estimating stock size for different fish species. One of the items produced for the show by DIFRES is a video clip in which ArcGIS 3D Analyst was used to show the movements of a single tagged cod.

The three-dimensional picture shows the movement of a single cod for 55 days from April to June 2003. The cod was tagged with an electronic data storage tag (green dot on picture) and caught (red dot on picture) at locations approximately 27 kilometers from each other. The three-dimensional visualization illustrates the movement of the cod showing that the cod mainly stayed in two different locations: one location to the southeast of Bornholm where it was found in the water column and another location to the southwest of Bornholm where it was found at the bottom. The scientific interpretation of these results is that the cod was probably spawning in the water column while residing in the first area and feeding at the bottom while residing in the second area.

The full video clip can be seen on the DIFRES home page at www.difres.dk. There is also another video clip produced with ArcGIS Tracking Analyst for the same television program. This clip shows the distribution area of cod in the Bornholm Basin in the Baltic Sea since the 1950s.

Two small maps explicitly show the geographic extent of the bottom area covered by water with an oxygen concentration greater than two milligrams per liter and a salinity greater than 11 in the Bornholm Basin of the Baltic Sea during the 44 years that the video clip covers. Biological surveys along with measurements of physical and chemical parameters indicate that these conditions, highlighted by the bright green area on the maps, characterize the main cod distribution area in this region. In 1971, the area for cod distribution was at its lowest with an area less than 9,000 square kilometers. In 1968 and 1974 the area was at its largest extension with approximately 33,000 square kilometers. The average for the 44 measured years is approximately 20,000 square kilometers per year.

All three maps are in the Mercator projection, and the three-dimensional map was produced with a vertical exaggeration of 200X.