Játtað í:

Náttúra og náttúrutilfeingi


Minking av laksalúsapláguni í Føroyum


Tróndur J. Kragesteen


Aðrir luttakarar:
Ken H. Andersen, Andre Visser, Knud Simonsen, Lars Asplin, Crawford Revie, Gunnvør á Norði, Kirstin Eliasen


Samlaður kostnaður:

Stuðul úr Granskingargrunninum:

The aquaculture industry has seen a steady high growth over the last two decades and the production of Atlantic salmon was alone 2 m tonnes in 2015. However, there is also a growing challenge to combat sea lice infestations, which has also seen a growth in abundance as well as resistance in the last decade. Managing sea lice has not been effective due to the lack of understanding how sea lice spread in a local and regional scale. Therefore numerical models of the dispersion of sea lice to be used as a managing tool in the industry under development and partly applied in near all salmon producing countries.

This PhD is the first attempt to construct such a numerical management tool for Faroe Islands, the third largest Atlantic salmon producer in Europe. The first step in the project is to investigate how the Faroese aquaculture farms are hydrodynamically connected with reference to salmon lice. Thereafter the research will focus on implementing a SIR model for Faroese salmon farms. This model will provide information on how important the external and internal infections are to the population dynamics at farm location as well for the entire system of fsh farms by integrating into the numerical hydrodynamic model. The third part will focus on improving process descriptions like effects of changing weather situations and salmon lice behaviour and investigate the robustness of the established model system to variabilities in the included parameters. Throughout the development process, the model system will be validated towards available sea lice data.

The final part of the project is to use the model complex to investigate treatment and management strategies to reduce the sea lice infection pressure. In this process location of farms, effects of cleaner fish and traditional treatments methods, effectiveness of fallowing periods will be investigated to develop a first rational management system for the Faroes aquaculture based on knowledge of nature and the conditions that influence it.


Managing diseases is crucial in any farming activity. The vast majority of Atlantic salmon consumed today are raised in an open sea environment where ectoparasitic copepods or sea lice have been a persistent plague for more than half a century. Sea lice and especially the species Lepeophtheirus salmonis or salmon lice are the main obstacle for further growth of the salmon farming industry in the northern hemisphere, because high lice levels have a negative impact on wild salmonid stocks and increases cross-farm infection pressure. Controlling lice levels requires treatments, most of which are harmful for the local environment and are expensive. There have been numerous studies assessing the impact of salmon lice on wild salmonid stocks using bio-physical models and salmon lice population dynamics. However, research on how to optimally manage lice from a farmer's perspective has been limited.

In this thesis, I therefore ask how lice can be optimally managed taken into account the hydrodynamic connectivity between salmon farms. The thesis consists of three scientific papers where the first paper proposes a bio-economic model framework analyzing the profitability of lice management strategies, and the two consecutive papers investigate how to simulate Faroe Islands within the proposed model framework. The general conclusions in the thesis show that idealized salmon farm networks profit the most by keeping a low lice level and concurrently having a minimal impact on the environment.

In the first paper, I investigate the optimal lice treatment thresholds on an idealized salmon farm network. Decreasing treatment threshold mainly comes from the desire to reduce the negative impact lice have on wild salmonid stocks. Somewhat counterintuitive, the paper shows that farm networks obtain the lowest number of treatments and highest profitability be adapting a relatively low treatment threshold (<0.1 gravid lice salmon-1). However, managing lice with a low treatment threshold, places farmers in a tragedy-of-the-commons environment where individual farmers benefit by disregarding legislation at the expense of the rest of the farm network, suggesting high compliance or strict regulation is needed to achieve optimal profitability. In order to gain confidence in the proposed modelling approach, salmon lice growth must be simulated accurately. Here, the Faroe Islands were used as a case site due to its isolated nature, stable water temperature and salinity. In paper two Faroese farms were shown to be highly connected and that lice were able to disperse the entire length of the Faroese archipelago (120 km). External infection pressure and salmon lice population growth rate were estimated based on an extensive time-series of lice counts in paper three. Further, external infection pressure was shown to be correlated with total gravid lice in Faroese waters. Accurate simulations of salmon lice growth were not achieved and further work is needed, however, the bio-economic model showed promise.

This thesis contributes to our understanding of how to optimally manage lice in salmon aquaculture. It provides a model framework which can be applied to specific farm networks giving authorities and farmers the capacity to optimally manage lice on a national, regional or farm level. Feeding a growing human population requires optimal and sustainable food sources and results shown here suggest that salmon aquaculture can increase food supply while reducing its environmental impact.


Scientific articles, books, thesis etc.

Kragesteen, T. J., Simonsen, K., Visser, A. W., & Andersen, K. H. (2018). Identifying salmon lice transmission characteristics between Faroese salmon farms. Aquaculture Environment Interactions, 10, 49-60.

Kragesteen, T. J., Simonsen, K., Visser, A. W., & Andersen, K. H. (2019). Optimal salmon lice treatment threshold and tragedy of the commons in salmon farm networks. Aquaculture, 512, 734329.

Kragesteen, T. J. PhD thesis. Lice management in salmon Aquaculture - Using the Faroe Islands as a case site.

Other results, such as unpublished articles, patents, computer systems, original models and new procedures

Kragesteen, T. J., Simonsen, K., Visser, A. W., & Andersen, K. H. (2019). Estimation of vital rates of salmon lice infections in the Faroe Islands. In Prep

Kragesteen, T. J., Salmon lice bio-ecomonic model. Desribed in Kragesteen et al., (2019).

Publications outside the scientific community, i.e. lectures, periodicals, articles in newspapers, television and radio

Kragesteen T.J. et al., Connectivity and Dispersal of Salmon Lice in a Tidal Energetic System: Faroe Islands. Price for second best lecture: at the 11th International Sea Lice Conference 27 Sep. 2016, Westport, Ireland.

Kragesteen T.J. et al., Connectivity and Dispersal of Salmon Lice in a Tidal Energetic System: Faroe Islands Dansk Havforskermøde 27 Feb. 2017, Helsingør, Dansk national råd for Oceanologi.

Kragesteen T.J. et al., Tidal Driven Connectivity and Dispersal of Salmon Lice in Faroe Islands Presentation held at Dept. of Health Management 8 Sep. 2017, University of Prince Edward Islands (UPEI), Canada.

Kragesteen, T. J. et al., Poster: Sjóvarfalsdrivið smittu samband millum aliøkir í Føroyum Reseach in the Faroes, Fróskaparfelagið 16 Nov. 2017, Norðlandahúsið, Tórshavn.

Kragesteen, T. J. et al., Optimal Salmon Lice Treatment Threshold and Tragedy of the Commons in Salmon Farm Networks. Vísindavøka á ferð 25. sep. 2018, Granskingarráðið, Tekniski Skúlin, Klaksvík.

Kragesteen, T. J. et al., Winner of poster pitch: Sjóvarfalsdrivið smittu samband millum aliøkir í Føroyum Vísindavøka 28. sep. 2018, Granskingarráðið, Sjóvinnuhúsið, Tórshavn.

Kragesteen, T. J. et al., Eingin sleppur undan lúsini (2018). Frøði 1/2018.

Kragesteen, T. J. et al., Optimal Salmon Lice Treatment Threshold and Tragedy of the Commons in Salmon Farm Networks Lecture at the 12th International Sea Lice Conference 6 Nov. 2018, Patagonia, Chile.

Kragesteen, T. J. et al., Optimal Salmon Lice Treatment Threshold and Tragedy of the Commons in Salmon Farm Networks. Aliráðstevnan 1 Mars 2019, Tórshavn, Faroe Islands.

Storage and access rights til collected data

Faroese Lice database: access right are owned by Bakkafrost, Mowi and Luna.

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