coast. Nephrops lives on patches of soft mud, in which it excavates burrow systems. The distribution of the species is therefore limited by the extent of these mud patches, which are found in the Firth of Forth, Moray Firth, the North and South Minches, the Clyde estuary, and the Fladen ground, in the centre of the North Sea. Juveniles and females spend most of their time inside these burrows, with males venturing out more frequently. This difference in behaviour, coupled with the inherent problem in measuring the age of crustaceans, means that standard stock assessment techniques cannot be used. Nephrops stocks are assessed by surveying their habitat with TV cameras to count the number of burrows. This is then used to calculate an average population density, and from their to calculate a biomass for a particular area. The total allowable catch is set as a proportion of this biomass. Nephrops stocks in the North Minch have decreased considerably in recent years (ICES). The creel fishery in Loch Torridon was first certified as sustainable in 2003 by the Marine Stewardship Council but the certificate was suspended on 11 January 2011. Pelagic sector The commercial performance of this sector suffered a near terminal setback during the 1970s, when the herring fisheries in the North Sea and west of Scotland collapsed and had to be closed. As stocks recovered and as it became possible to separate the catching of herring and mackerel, the sector recovered. It became apparent that the domestic market for herring had disappeared, and mackerel became the dominant source of earnings. These trends encouraged a number of enterprising fishermen to set about investing in the modernisation of the fleet through the commissioning of new, state-of-the-art vessels. The pelagic fleet is now highly centralised, based in Shetland and north east Scotland, with a fleet of 27 vessels generating gross earnings of £98M. The general view is that substantial profit and excellent returns on investment are being achieved by this sector. 2006 raids by the Scottish Fisheries Protection Agency (SFPA) on a number of fish processors revealed large-scale misreporting of landings by pelagic vessels. This led to the Scottish component of pelagic quotas being reduced for several years to "repay" this over-exploitation. Fish processing industry The Scottish fish processing industry accounts for 49 per cent of the turnover of UK fish processing industry. Geographical distribution of the turnover of the Scottish industry