Sustainable fishing requires deeper knowledge of fish populations

In his thesis Stefan Skoglund demonstrates that if we don't take into account the migratory patterns of spawning fish, we might make inaccurate estimates of annual fish population growth. When using his models on data for Baltic salmon (Salmo salar), he discovered that that these fish not only return to their native river to spawn but specifically to their exact birthplace.

"Parts of the current models we use in salmon management fail to consider the distribution of salmon within a river, and thus potentially introducing errors in our models," says Stefan Skoglund, PhD at the Department of Aquatic Resources (SLU Aqua).

He also developed a method to predict the size and age at which salmon undergo smoltification, i.e. the physiological changes where young salmonid fish adapt from living in fresh water to living in seawater.

"In this study, I show that it is possible to use the length distribution of the younger age groups, known as stirrings, to estimate the age and size of the smolt. The method also makes it possible to transfer what we know from one river where the smolt is measured to another river where only the stirrings is measured.”

Finally, Stefan Skoglund looked at the competitive interactions between salmon and trout (Salmo trutta), finding that trout seem to do better in warmer temperatures, while salmon dominate when in cooler temperatures.

"The experiment showed that the two species seem to compete with each other in the first stage of life, but which species was the dominant one varied between the experimental years. This difference is probably temperature-dependent, as it was the factor that differed between the different years.”

Read the thesis Population regulatory processes in the Baltic salmon (Salmo salar)