D1. Biodiversity and ecosystem services

D1a. Fish size classes in the North Sea


Type: State / Benefit Indicator


Indicator Description

The indicator shows changes in the proportion, by weight, of large individuals equal to or over 40cm in length in fish populations in the North-western part of the North Sea.  Changes in the size structure of fish populations and communities reflect changes in the state of the fish community.  Fluctuations in values between years are expected given inter-annual fluctuations in the distribution and abundance of North Sea fish populations and sampling variation.

This indicator is likely to change in the future to reflect a new indicator being developed to report under the OSPAR Convention.



No new data since the previous publication.

In 2014, large fish in the North-western North Sea made up almost 22% of the weight of the fish community.  This was very nearly the same as the 23% in 1983; however it is an increase from a low of 2.2% in 2001.  While there was a clear decline in the indicator from 1983 to 1993, there has been rapid recovery since 2003 that accelerated after 2010.  


Figure D1ai.  Proportion of large fish (equal to or larger than 40cm), by weight, in the North-western North Sea, 1983 to 2014.


Figure D1ai. Proportion of large fish (equal to or larger than 40cm)

Notes: The line graph shows the unsmoothed trend (dashed line) and a LOESS smoothed trend (solid line) with the shaded area showing the 95% confidence intervals around the smoothed trend.    

Source: Centre for Environment, Fisheries and Aquaculture Science; Marine Scotland.


Assessment of change in the proportion of large fish, by weight


Long term

Short term

Latest year

North-western North Sea

2010 indicator stable

indicator improving

Increased (2014)

Notes: The long-term and short-term assessments have been made by the Centre for Environment, Fisheries and Aquaculture Science (Cefas) by fitting a LOESS smoothed trend to the index.  LOESS is a non-parametric regression method; it may be understood as standing for "LOcal regrESSion”.


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Last updated: December 2015

Latest data: 2014