PhD defence on straying of sea trout in a fjord system

Salmonids, such as Atlantic salmon and brown trout, possess a remarkable ability to return to breed in the same area where they were born, a behavioural trait referred to as natal homing. While a large proportion of the population is expected to display tendencies of natal homing, there is often a group of salmonids that do not return to their home river to spawn, but stray to other rivers instead. 

As natal homing has become rooted into the description of salmonid life cycle, straying is often unexplored. Yet, knowledge about straying is important in determining population borders and dynamics, particularly when making management decisions about fish populations and their habitats. 

During her PhD project at DTU Aqua, Kristi Källo investigated prevalence and patterns of straying among sea trout populations in Mariager Fjord, Denmark, using electronic tagging, otolith microchemistry and genetics. Her studies reveal a significant prevalence of straying in this system, with an average of 37% of sea trout documented as strayers in Mariager Fjord. Furthermore, strayers were found to make up a significant proportion of spawners in all of the investigated rivers. Straying rates documented in this PhD project are the highest rates of straying known in wild sea trout straying among multiple rivers. 

Kristi Källo has further investigated patterns of straying among repeat spawners, an understudied life-history phase in salmonids. The results revealed that straying was also common in this group of fish, with repeat spawning strayers displaying high variability in migratory patterns. Furthermore, her research documented that the high level of straying had left its mark on the genetic structure of sea trout originating from different rivers of Mariager Fjord, to an extent that all the rivers make up one genetically uniform population.  

Furthermore, Kristi Källo’s studies show that strayers display various spatial and temporal migratory patterns, which for example included strayers migrating between multiple rivers and straying being more prominent towards the bigger rivers. Straying was further documented to be an inherent part of life-history of sea trout, which was linked to multiple life-history factors at different life-stages. 

About the PhD defence

Kristi Källo will defend her PhD thesis "Do all roads lead home? Straying of anadromous brown trout (Salmo trutta) in a fjord system” on Monday 3 July 2023, 10:00 on Zoom and at DTU Aqua, Vejlsøvej 39, 8600 Silkeborg. 

Supervisors

• Principal supervisor: Professor Kim Aarestrup, DTU Aqua
• Co-supervisor: Senior Researcher Henrik Baktoft, DTU Aqua
• Co-supervisor: Researcher Martin Lykke Kristensen, DTU Aqua

Examiners

• Senior Researcher Jakob Hemmer Hansen, DTU Aqua (Chair)
• Researcher II Line Elisabeth Sundt-Hansen, Norwegian Institute for Nature Research, Norway
• Assistant Professor Anna Sturrock, School of Life Sciences, England

Chairperson at defence

• Senior Researcher Niels Jepsen, DTU Aqua

Learn more

A copy of the thesis is available by e-mail on request. Please contact Kristi Källo, kkal@aqua.dtu.dk