Tracking and speed evaluation of cod schools in the 2014 Nordic Seas experiments

Abstract

Observing and tracking fish shoals over long periods enables us to understand and establish the behavior processes of fish shoals in their ecosystem and different phases of migration, spawning and feeding. In the past, researchers have observed fish shoals for days and even weeks for that purpose. However, previous studies were limited by conventional methods such as echosounders and acoustic tagging of fish, which are only able to track one or a few schools at a time with low spatial sampling. In 2014, the Ocean Acoustic Waveguide Remote Sensing system (OAWRS) was employed in the Nordic Seas for the study of fish shoal behavior in that region. The OAWRS system enables the study of multiple shoals simultaneously over long periods. The experiment took place in three main spawning areas on the shores of Norway, and lasted from Feb 18 to Mar 8 for the study of three commercially important species: cod, herring, and capelin. In this paper, we use the data gathered by the OAWRS system in the Nordic Seas experiment to track fish schools in the Lofoten area by comparing two methods of calculating their track: 1) calculating and tracking the centroid of the school, and 2) calculating the shift of the school between pings to establish its new position. We calculate the speed of schools along theirs tracks and compare it with known cod speeds. We find that the general heading of all the schools investigated here is towards offshore. We suggest that the speed calculated for these small scale schools might aid in identifying a school's species, when lacking other means.