Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

Sexual size dimorphism in three North Sea gadoids and its implications

The implications of sex-specific dimorphism of life history traits other than fecundity-related traits have hardly been addressed even in case of commercially important fish species but past studies insinuate length differences between females and males in many species. Biological data of whiting, cod and haddock from a long term international survey was analysed to address sexual size dimorphism (SSD) and potential effects on their ecology and their management.


North Sea gadoids show sexual size dimorphism with larger females at the same age as males and length-dependent female:male-ratios.

SSD structures result in higher growth rates of females and a pronounced length-dependent female ratio in the three gadoids in the North Sea analysed. Female-ratios of the three species changed from equality to female dominance at specific dominance transition lengths of around 30, 35 and 60 cm for whiting, haddock and cod, respectively. We assume that SSD and length dependent female-ratios under most circumstances are inseparable.

From the observed sexual size dimorphism and the dimorphism in growth rates higher overall energy demand and energy uptake rate in females must result as a consequence. A number of processes related to feeding, locomotion and physiology could balance the increased energy investment of females.

Potential consequences of SSD and length-dependency of female ratios are the reduction of the reproductive potential of a stock due to size-selective fishing and biased assessment of the true size of the female spawning stock that could distort decisions in fisheries management. Considering that many fish – among these whiting and cod1 – show length dependent association with habitats it is proposed that the female dominance in the upper length range of the population could enable to identify reproduction areas that could be considered separately in the management process.

Relevance for Policy:
  • Common Fisheries Policy
  • Directive on Maritime Spatial Planning and Integrated Coastal Management (forthcoming)
  • Habitats and Birds Directive
Data availability:

Availability: Data is open access; available from ICES DATRAS


  • Keyl, F. (in prep) Distribution of North Sea fish: the gadoid outburst vs. present.

Lead Author:

Friedemann Keyl
vTI-Institute of Sea Fisheries (vTI-SF)
Date of research: October 2014

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Cod, recruitment, temperature and zooplankton

Fish distributions and spatial management measures 

Modelling fishing fleets competing for quota

Response of plaice and sole to climate change 

Spatial overlap and recruitment success of cod 

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
© Vectors 2015. Coordinated by Plymouth Marine Laboratory.