When logbooks show the path: Analyzing the route and timing of capelin (Mallotus villosus) migration over a quarter century using catch data

Migration routes of exploited marine resources are often investigated using tracking methods such as satellite tags or Data Storage Tags (DSTs). However, this type of research crucially depends on the tagging and recapture effort, and is often unfeasible for small migratory pelagic fish such as capelin because of size constraints. We investigated the spawning migration route of capelin along the shelf break from the north and east of Iceland to spawning grounds located south and west of Iceland using catch data. Fishing vessels usually follow the front of the capelin migration as soon as it appears in fishable concentrations at the beginning of the year. This provides a good opportunity to assess the reliability of the catch data to assess the migration path of this species. The results show that capelin fishery starts in the first week of January along the Icelandic shelf and gradually moves towards the southern area in a clockwise manner, which is reflected in the fleet behavior. In addition, by analyzing catches for two different time periods encompassing more than two decades, we were able to detect slight changes in the timing and route of the capelin migration. We argue that in the case of small migratory pelagic fish, logbook data could be used to assess migration route and timing and its changes over time.