- - precautionary biological limit (Bpa)
The ecosystem of the seas around Scotland supports fisheries for commercially important species. If stocks are in a poor state or overfished it can have a knock-on effect on other parts of the marine ecosystem. Likewise, changes in the wider marine environment can have an impact on the state of the stock. The state of commercial fish stocks may be considered, alongside other indicators, as a proxy for the general sustainability of the marine environment. One measure of the state of a fish stock is the size of its spawning stock biomass (SSB).5 The health of the fish stock can then be indicated by comparing the SSB with a precautionary value, or reference point (Bpa).6
The SSB of North Sea cod stock has been below Bpa since 1984. The SSB increased every year from 2006 to 2013, but the value of 72 kt is still well below the Bpa of 150 kt. The SSB of haddock has been above the Bpa of 140 kt since 2001. The value declined steadily from 2002 to 2011, but has since increased to 258 kt in 2013. The SSB of herring stocks has been above the Bpa of 1,300 kt since 1998. Since falling to 1,444 kt in 2007, it rose to 2,348 kt in 2012 before declining again to 1,996 kt in 2013. The SSB of the North Sea/West of Scotland saithe was estimated to be just over 196 kt in both 2012 and 2013; the value has been gradually declining since 2005 and has fallen just below the Bpa in the previous two years.
The size of these stocks are affected by several factors, including commercial fishing and other factors such as climate change and success of recruitment. A range of management measures are applied to fishing activity in Scotland, with the aim of achieving or maintaining healthy stock levels.7
Email: Callum Neil