Aarhus University Seal / Aarhus Universitets segl

Fish larvae survey onboard AURORA

Spawning in the Kattegat who, where and when?

Spring spawning in the Kattegat takes place in step with the spring flowering of algae and aquatic fleas, which ensures plenty of food and good conditions for the offspring of the fish. Eggs and larvae from many species of fish can be found floating around the Kattegat. However, since this marine area is heavily affected by water transport between the North and Baltic Sea, it is complicated to identify exactly where, when and which species spawn inside the Kattegat, and how much of the offspring are operating from the outside.

Distributed over the spring of 2021, RS Aurora conducted five three-day research expedition with focus on illuminating the spawning in the Kattegat. The collection of fish larvae took place at 15 stations, distributed across the entire Kattegat, to provide a complete overview of the sea area. Using CTD and features with vertical grids, we collected data on how salinity, temperature, fluroscence and zooplankton composition varied with water depth. Multina trawling made it possible to gather at several different depths, where up to nine fine mesh nets could be used at their depths. Using these methods, it was possible to collect fish larvae at specific depths related to halocline. The halocline is a relatively small water layer with a major change in salinity, and is generally what separates the north and Baltic Sea water into the water column in the Kattegat. By taking exams in specific water masses, we can predict which general direction the collected fish larvae have driven; such as the south of the North Sea or north from the Baltic Sea.

Fish larval collection is a part of Kris-Emil Mose Jørgensens PhD project.

Methods and equipment used:

  • CTD-sonde (Conductivity, Temperature and Density)
  • Multinet trawling
  • Vertikal net sampling