Latin name: Nephrops norvegicus
Common names: Norway lobster, scampi, Dublin Bay prawn, langoustine
The fishery for Nephrops in Scottish waters has developed from a few tonnes in the early 1960s to over 31,000 tonnes in 2009, and Nephrops is currently the second most valuable species landed in Scotland (£78.3 million in 2009). There are Nephrops fisheries on grounds around Scotland, the largest being the Fladen Ground in the North Sea. Most Nephrops are caught by trawlers, but creel fisheries are also important, particularly on the west coast of Scotland. Scotland is allocated the majority of the Total Allowable Catches (TAC) in both the North Sea and on the Scottish west coast and takes over one third of the landings worldwide.
Nephrops distribution is limited by the extent of suitable muddy sediment in which animals construct burrows. There are populations in the North Sea and waters to the west of Scotland, in open waters and sea lochs at depths ranging from a few metres down to over 500 m on the shelf edge, west of the Hebrides.
Nephrops spend most of their time in burrows, only coming out to feed and look for a mate. They are opportunistic predators, primarily feeding on crustaceans, molluscs and polychaete worms. Female Nephrops usually mature at three years of age and reproduce each year thereafter. After mating in early summer, they spawn in September, and carry eggs under their tails (described as being 'berried') until they hatch in April or May. The larvae develop in the plankton before settling to the seabed six to eight weeks later. Reproductive timing may be slightly delayed in the deeper areas of the Fladen Ground.
Nephrops in different areas grow at different rates and mature at different sizes. This variation is related to the density of animals and sediment type. On the softest mud, Nephrops density is low, but the animals grow relatively fast, and reach a larger maximum size ('clonkers'). On sandier mud, Nephrops density is much higher, but the animals grow relatively slowly, and are smaller ('beetles'). In the North Sea there are differences in growth between stocks, while on the west coast, there are also differences between areas within the same stock.
Since most Nephrops fishing is by trawling, and animals are protected from trawls when in burrows, the emergence patterns affect catch rates. The timing of emergence to feed appears related to light level, and greatest catches are often taken at dawn and dusk, although this may vary with water depth and clarity. As 'berried' females rarely come out of the burrow, they are naturally protected from trawlers, and males dominate trawl catches for most of the year, and are more heavily exploited than females.
For the purposes of stock assessment, Nephrops around Scotland are split into a number of stocks or 'functional units' (FUs) based on the discrete patches of mud which they inhabit. Unlike fish, Nephrops cannot be aged directly and therefore the assessments make use of size composition data from catches, combined with information on stock abundance obtained from underwater television (UWTV) surveys. UWTV cameras are used on research vessel surveys to estimate Nephrops burrow density on the seabed. The information gathered provides an index of stock abundance for each FU which is independent of the fishery and burrow emergence patterns. By applying a number of 'correction' factors to the index, an estimate of the absolute abundance of Nephrops is obtained.
The graph below shows change in Nephrops relative catch rate over a 24 hour period in the Moray Firth.