Projects

Katja Enberg

Program leader, docent

katja.enberg@imr.no

(+47) 4100 6368

 

Institute of Marine Research

Research and Advice Program Norwegian Sea

PO Box 1870 Nordnes

5817 Bergen

Norway

 

Visiting address: Nordnesgate 33, Bergen

Projects

Can contemporary evolution explain the many enigmas in recent dynamics of Norwegian spring-spawning herring?

 

Fisheries-induced life history changes in terms of for example reduced age at first spawning have been observed in many demersal fish species. However, such changes have not been observed in pelagic species, although they too are under constant fishing pressure. Does this mean that the theory is wrong, or is there something else going on with pelagic species? Norwegian spring-spawning herring is one of the largest pelagic fish stocks in the world. At the same time, it is most likely the best documented pelagic stocks with time series data on catches back to 1899, on population dynamics back to 1904 and biological data on individual starting from 1935. A number of changes in life history traits in accordance with the expectations of life history theory have been observed in this population. At the same time, stock assessment is overestimating population size year after year. Based on massive amount of data on Norwegian spring-spawning herring collected over the years, life history theory and statistical modeling, this project will examine how these observed patterns are connected, and how much of the changes are caused by evolution. The results of this project can help with population estimates and sustainable management of this commercially and ecologically important population, while they are also going to increase our understanding of human-induced evolutionary changes in natural populations. Please visit the project home page for more information.

 

 

Ecosystem dynamics in the Norwegian Sea – new methods for understanding recent changes

 

The ecosystem in the Norwegian Sea has been under constant change during the last decades. Ecologically and commercially important pelagic fish stocks; Norwegian Spring Spawning herring, North East Atlantic mackerel, and blue whiting, have all had their turn in being the most abundant pelagic species, however, the exact nature of the interspecific interactions between these species is still poorly understood. In the last decade the summer feeding area of the NEA mackerel stock has been expanding drastically and in 2014 mackerel was observed all over the Nordic Seas. While mackerel stock is thriving, Norwegian spring spawning herring stock is currently at its lowest level in 20 years. Some hypothesize that the absence of strong year classes of Norwegian spring spawning herring is a direct result of expansion of mackerel as they prey upon herring larvae. In addition to the suggestion that mackerel is competing for food with herring, it has also been hypothesized that by eating herring larvae, the mackerel would worsen the already dire conditions of many sea bird populations along the Norwegian coast. In the spirit of ecosystem based fisheries management the supposedly detrimental effect of mackerel on other fish stocks and sea birds should be taken into account in the management of the Norwegian Sea Ecosystem. In this study we aim at improving our understanding about the species interactions and the dynamics of the Norwegian Sea ecosystem by developing and using modern methods for identifying and quantifying the diet of these ecologically and economically important pelagic fish populations. We will use modern statistical methods to scrutinize these data, and end-to-end ecosystem models to test the hypotheses regarding ecosystem dynamics from plankton, via fish, to sea birds under the current climate change. This project is an investment in understanding and long-term monitoring and management of the Norwegian Sea and other ecosystems. Please visit the project home page for more information.

 

Katja Enberg