Dynamics of harvestable resources

Temporal changes in the abundance of harvested marine animals are common. Such changes are likely driven both by direct anthropogenic impacts, e.g. fishing, and individual level responses to the prevailing biotic and physical environment with these drives commonly also interacting.

There is thus a need for an in-depth understanding of the underlying processes affecting species productivity, especially considering the complex ecosystem changes expected under climate change. The Hjort Centre aims to disentangle and understand the causes of variability in harvested marine resources in the past, present and future. Central to this goal is i) to understand how prolonged harvest may have caused changes in important life-history traits such as offspring production and age at maturity of exploited species and how this may impact their resilience to further exploitation and climate change, ii) the underlying population structure and associated population - specific life-history traits of harvested species and iii) to use new emerging knowledge to improve contemporary management advice.

Relevant projects involving Hjort Centre members

ConEvolHer: Can Contemporary Evolution explain the many enigmas in recent dynamics of Norwegian spring-spawning Herring?
Project leader: Katja Enberg, Institute of Marine Research
Funding source: RCN (HAVKYST)
Period: 1.7.2015 - 31.8.2018
In collaborations with: University of Bergen, Norway; University of California, Santa Cruz, USA;  IFREMER, Laboratoire Ressources Halieutiques, France
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 from 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.

EcoNorSe: ECOsystem dynamics in the NORwegian SEa - new methods for under-standing recent changes
Project leader: Katja Enberg; Institute of Marine Research
Funding source: RCN (HAVKYST)
Period: 1.1.2015-31.12.2018
In collaboration with: University of Bergen, Norway; Marine Research Institute, Iceland; HAVSTOVAN Faroe Marine Research Institute; Instituto Español de Oceanografía, Centro Oceanografico de A Coruña, Spain; Greenland Institute of Natural Resources. 
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 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.

AHA - Adapted Heuristics and Architecture: toward an understanding of personalities and phenotypic diversity
Project leader: Jarl Giske, Department of Biology, University of Bergen
Funding source: RCN FRIMEDBIO
In collaboration with: Univ. Bristol; Univ. California Santa Cruz; Univ. California Berkeley

The classical methods of evolutionary ecology, optimization and games, assume as a simplification that organisms are able to trade-off conflicting demands and optimize their behavior. We have, however, shown that two types of increased realism may change this picture. One of them is to replace the assumption of perfect behavior with heuristics: rules for fast and quite likely good decisions. The other is explicit architecture: a description of the major pathways in the organism from genes and perceptions to behavior. We have seen in simulation models that evolution in populations of individuals with adapted heuristics and architecture yield populations with higher evolutionary robustness and evolvability and with personality variation among individuals. Focusing on architecture has the potential to change how we think about behavior, ecology and evolution. We will use rich individual-based models in classical evolutionary ecology scenarios, such as patch choice and patch leaving rules and producer-scrounger games.