Preliminary Analysis of CPR and Other Environmental Data for the Waters around Shetland


This project comprised a preliminary analysis of the long-term Continuous Plankton Recorder (CPR) data from the Fair Isle Channel, and waters around Shetland, along with other long-term environmental data series from this area.

Start Date and Duration

The project ran from February to June 2006.


The project was partly funded by the University of the Highlands & Islands under their Staff Sabbatical Scheme.

The cooperation and assistance of the Sir Alister Hardy Foundation for Ocean Science (SAHFOS) in making available the CPR data used in this project is gratefully acknowledged.

Download the Project Report

Napier, I. (2006). A Preliminary Analysis of CPR and Other Environmental Data for the Waters Around Shetland. NAFC Report.


A preliminary analysis has been carried out of data from the Continuous Plankton Recorder (CPR) survey A route (Lerwick to Aberdeen) for the period from 1946 to 2004. Further work is required on these and other environmental data from this area, but the following is a summary of the main results obtained:

Phytoplankton Colour Index
There has been a marked increase in phytoplankton colour (indicating an increase in phytoplankton biomass and primary production) over the last 60 years. However, the pattern of change seen after the mid-1980s differs from that described for other areas of the North Sea and northeast Atlantic. It is suggested that this may be a result of variations in the influence of oceanic water in the area.

Plankton Indicator Species
There has been a marked increase in the abundance of oceanic indicator species, suggesting a greater inflow of Atlantic water, over the last 20 to 25 years. There appear to have been peaks in inflow about 1985-90 and 2000-04, greater than any since the early 1960s. There have also been dramatic increases in the abundance of some indicator species characteristic of more southerly water masses, suggesting an increase in the inflow of Atlantic water of more southerly origin.

Copepod Indicator Assemblages
The area has been dominated by copepod species belonging to the Temperate and Shelf assemblages throughout the last 60 years, although there has been a long-term decline in the numbers of these species present (but not the numbers of individuals). There has been a substantial increase in the frequency and abundance of warm-water assemblages, but there has not been an equivalent decline in cold-water assemblages.

Significant negative correlations were found between seabird breeding success at Fair Isle and Sumburgh Head and both the abundance of oceanic indicator species (especially southern species), and the abundance of southern Copepod Indicator Assemblages. These results suggest that seabird breeding success is lower during periods of increased Atlantic inflow, especially when the inflowing water has a southerly origin. The sensitivity of seabird species varied, but (with a few exceptions) was broadly in line with previously proposed rankings of seabird sensitivity to variations in sandeel abundance.

North Sea Herring
Significant correlations were found between Atlantic inflow (the abundance of Atlantic indicator species) and the recruitment of North Sea herring the following year. Prior to the mid-1980s the correlation was positive, suggesting that increased inflow resulted in increased recruitment. Since then, however, during which time the inflow has been characterised by water of more southerly origin, the correlation was negative, suggesting that increased Atlantic inflow now results in reduced recruitment.

No correlations were found between the CPR data and Shetland sandeel survey data, but there were significant correlations with the Shetland annual sandeel catch (which may provide a better index of annual sandeel abundance). The results suggest that increased Atlantic inflow has a negative impact on sandeel abundance.


The main finding from this preliminary study is that variations in the strength of the Atlantic inflow, and especially the recent apparent increase in the inflow of more southerly water, has an important influence on Shetland’s seas, and may help explain observed changes in the marine environment.