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Background and objectives

In 2014 it will be 100 years since Johan Hjort wrote his seminal book ‘Fluctuations in the Great Fisheries of Northern Europe’. The importance of this volume cannot be overstated, in particular Hjort’s new conceptual ideas about the formation of strong year classes based on age determination techniques from fish scales. 

His view that year-class strength varied over time was in sharp contrast to the prevailing theory that migration was the cause of fluctuations in abundance. In his 1914 volume Hjort introduced the key concepts relating to ‘the critical period’ for larvae in relation to availability of proper food. Subsequently, he also introduced the concept of variable larval advection as a cause of recruitment variability. Hjort is widely considered to be the father of modern fisheries science. In addition to his research activities Hjort served as the first fisheries director in Norway (1906-16), was central in the development of ICES (President: 1939-48) and helped to launch joint research activities (e.g., in the North Sea) and extensive cruise programmes (e.g., with ‘Michael Sars’ in the Norwegian Sea). Whilst having wide ranging academic interests, at the same time he appreciated the important management and social implications of fisheries research. Hjort was also interested in providing inputs to other research institutions abroad. His close co-operation with eastern Canada stands out as one clear example. 

Hjort (1914) states that ‘the object can never be fully attained; new questions will constantly arise, as the knowledge obtained creates the demand for new, and it will always be possible to increase and intensify our comprehension of the vital conditions affecting the organisms in question’. In this symposium we would like to address the level of knowledge about these vital rates (natural mortality, growth and recruitment), but also encourage integrated studies including environmental drivers within an ecological framework. In particular, have modern techniques (such as individual-based models and large-scale analytic tools) made reliable predictions possible?

Many of these questions relate to continuing interests and challenges in fisheries research globally. This symposium is convened to recognise Johan Hjort’s legacy, but at the same time identify innovative routes forward within this field of research. This Symposium therefore aims to summarise international state-of-the-art science on the topic of recruitment dynamics and stock variability in different waters.