Homing behaviour in herring stocks along the east coast
A fish stock or population is defined as fish that spawn and reproduce together. Fish born within a population will share a gene pool. But the question is: why do certain individuals form a stock? What are the mechanisms that cause one population to be separated from others of the same species? The question is of scientific interest, but it is also important for sustainable fisheries management.
There are two main theories regarding how fish stocks are kept separate. One theory is based on the idea that eggs and fish larvae are carried away by currents and dispersed across different marine areas. Where they ultimately end up will determine which stocks the fish will eventually join. If the fish has the opportunity to spawn several times, it may remain loyal to its initial choice of spawning ground.
The second theory suggests that the fish have the ability to find their way back to their home waters, even if they are carried away by ocean currents as juveniles – the fish are home-tied, i.e. they return to their parents’ spawning grounds to spawn. In this case, it is the behaviour of returning to their home waters to spawn that defines the population.
Many marine fish species, not least commercially important species such as herring and cod, disperse widely in the water column early in their life cycle. Despite this, these species often consist of many small local fish stocks. These small stocks are the ‘production units’ for the fish stock as a whole. Fish such as herring and cod often exhibit a certain degree of home-range fidelity. The homogeneity of the stocks and their degree of home-range fidelity can be investigated using, among other things, otolith chemical methods. The otolith is the fish’s earstone and contains detailed information about the fish’s physiological status and its physical environment from the egg stage onwards.
The project Homing behaviour in herring stocks along the east coast aims to analyse the homing behaviour of herring stocks along the Svealand coast. The project will collect material for otolith chemical studies from various herring spawning aggregations in four spawning grounds along the Svealand coast. The different spawning aggregations are not expected to have any population genetic differences, but may exhibit behavioural differences.
Homing behaviour in herring stocks along the east coast is being carried out by BalticWaters in close collaboration with Stockholm University. The project is funded by the Thuréus Forskarhem och Naturminne Foundation.