Reconstructing migrations of individual cod (Gadus morhuaL.) in the Baltic Sea by using electronic data storage tags

Abstract

AbstractA new methodology is presented to reconstruct migration pathways of individual fish inhabiting ecosystems with moderate‐to‐strong gradients in temperature or salinity. The method uses measurements of ambient pressure, temperature and salinity obtained from electronic data storage tags attached to individual fish and is particularly applicable in areas with negligible tides. We demonstrate the method with Baltic cod. Hydrographic fields obtained from hydrodynamic modelling were used as a geolocation database to identify daily positions of Baltic cod by comparison with the environmental data collected by the tags. Using randomly distributed individual parameter perturbations in the range of the instrument precision of the tag we simulated a cod migrating through the Baltic Sea. The distance between the prescribed and geolocated positions of this artificial cod was on average 2.9 ± 4.7 (SD) km. Subsequently, the method was used to reconstruct migration routes of 10 real cod tagged in the Bornholm Basin of the Baltic Sea in early spring 2003. Differences were compared between the tag data and the geolocation database. The uncertainty in geolocation at recapture day was on average 75 ± 23 (SD) km, as shown by comparison between geolocated position and recapture position.