Type: State Indicator

Indicator description

The indicator shows the number of rivers in which salmon spawning levels have met or exceeded agreed standards for sustaining salmon stocks.  Between 1997 and 2009, the number meeting agreed standards fluctuated markedly, varying between 13 and 28 rivers with the data showing an improvement in alternate years. Although there was an increase between 2004 and 2008, the number of qualifying rivers fell sharply in 2009 to 16 rivers, similar to the number seen in 2001 and 2003.

Figure 13.1.  Number of rivers meeting their agreed standards for sustainable salmon stocks, 1997 to 2009

Source: Environment Agency

Assessment of change in the number of rivers meeting agreed standards for sustainable salmon stocks
	Long term	Since 2000	Latest year
Number of rivers with sustainable salmon stock			Decreased (2009)

Relevance

Under the EU Habitats Directive, a ‘good’ conservation status must be maintained for salmon in freshwater.  If numbers fall below agreed standards then a stock may not be sustainable and the threat of losing that individual stock and its associated genetic diversity is high.

Background

In order to assess salmon stock levels, Conservation Limits are set for each of forty principal salmon rivers in England.  The Conservation Limit is set at a stock size below which further reductions in spawning numbers are likely to result in significant reductions in the numbers of juvenile fish produced in the next generation.  Conservation Limits range from 70 eggs per 100 m² for the Wyre and 395 eggs per 100 m² for the Tamar.  These Conservation Limits are used by the Environment Agency as an indication of the minimum desirable spawning stock level below which stocks should not be allowed to fall.

Table 13.1. Conservation Limits for salmon stocks in the forty rivers included in the assessment

Source: Environment Agency

On most rivers, procedures to evaluate compliance with the Conservation Limit involve deriving egg deposition estimates from reported rod catch data. 

Spawning levels fell sharply in 2009 from the improved levels evident over the previous 5 years. The underlying causes of this sharp downturn are not clear; however the numbers of grilse (or 1-sea winter salmon) returning to rivers in England as well as the rest of the UK and Ireland were widely reported to be well down on usual levels. Grilse form the dominant component on most of our rivers and their widespread pattern of decline in 2009 suggests that conditions in the sea may have been less favourable for survival than in recent years.

Where conservation measures are required, steps continue to be taken to reduce the numbers of fish killed by net and rod fisheries through voluntary and statutory means. Similarly, efforts to improve the quality of the freshwater environment are ongoing, including initiatives in pollution control, better land management and the removal of man-made obstructions to fish passage.

For example, on historically polluted rivers such as the Mersey and Trent, salmon have been returning in response to major improvements in water quality. However, multiple pressures from factors such as siltation, acidification, pesticide residue and climate change continue to affect fish stocks on many systems.

Initiatives such as those described above have helped protect salmon numbers in English rivers against a background of general decline in abundance evident here and throughout the North Atlantic over the last 30-40 years (see reference below).

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