Langoustine (Nephrops norvegicus) is the most valuable resource landed into Scotland and over one third of world landings are made there. A number of stocks are located around the Scottish coast and in 2009 31,490 tonnes were landed at a value of nearly £78.27 million.

Most of the landings are taken by trawlers, with smaller vessels operating on the inshore grounds and larger vessels operating in more mixed fisheries offshore. On the west coast, a creel fishery is taking increasing quantities of this important crustacean shellfish. However, landings from creel caught methods still only account for approximately 5% of the total weight landed.

Various industry groups in Scotland have used the Marine Stewardship Council's environmental standard for sustainable fisheries to assess the sustainable operation of a number of Nephrops fisheries around Scotland. Two are currently certified under the MSC standard; the Stornoway Nephrops trawl fishery and the Loch Torridon creel fishery. Two other Nephrops fisheries in the Clyde and North Sea are also currently in the process of assessment to this standard. 

Nephrops occur in areas of suitable muddy sediment in which they construct burrows. Populations are found in depths as shallow as a few meters in sheltered sealochs, 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. When they are inside their burrows, most animals are protected from trawls so that the emergence patterns are very important from a fisheries perspective. The timing of emergence appears to be related to light level, and greatest catches are often taken at dawn and dusk, although this varies with water depth and a number of other factors. Males tend to dominate trawl catches for most of the year and are more heavily exploited than females which rarely come out of the burrow when carrying eggs ('berried').

Female Nephrops mature at about three years of age and usually reproduce annually. Mating occurs in early summer followed by spawning in September, females remain berried until they hatch their eggs in April or May. The larvae develop in the plankton before settling to the seabed six to eight weeks later.

Growth and maturity in Nephrops in different areas appears to be related to the density of animals which appears to vary with sediment type. On soft muds, density is low, but the animals grow relatively fast, and reach a larger maximum size. On sandier mud, Nephrops density is far higher, but the animals grow more slowly, and are smaller ('beetles'). The diet of Nephrops is extremely varied and includes many bottom living animals and species swimming close to the seabed. Nephrops also scavenge. In common with other crustaceans, Nephrops cannot be aged and so cannot be assessed using methods commonly employed for fish stocks exploited in Scotland. Instead, the main method relies on fishery independent television surveys.

 

 

In 2009, ICES conclusions about Nephrops stock status were based on trends in the underwater TV (UWTV) survey, fishery and catch size composition data. For areas lacking UWTV survey information (Noup and Devil's Hole), ICES did not update its advice on stock status in 2009.

Farn Deeps: the UWTV survey, fishery data and length frequency data all point to the stock at the start of the 2008 fishing season continuing to be at a low level. Recruitment signals for Nephrops in 2008 appear to indicate low recruitment.

Fladen Ground: the UWTV survey indicates that the stock is fluctuating without obvious trend with estimates for the last 2 years increasing to the highest abundance in the series. Taken together with stable mean sizes in the length composition of catches, this suggests that the stock is being exploited sustainably. The decline in mean length of smaller individuals in the catch may be indicative of recent good recruitment.

Firth of Forth: the UWTV survey suggests that the population has been at a relatively high level since 2003. Taken together with information showing stable mean sizes, this suggests the stock is being exploited sustainably.

Moray Firth: the UWTV survey suggests that the population is stable but at a lower level than that evident in 2003-2005. Taken together with information showing stable mean sizes, this suggests the stock is being exploited sustainably.

North Minch: the stock is being exploited unsustainably. The UWTV survey indicates that the population has declined by around 40 % over the past two years from a previous time series high in 2006. Harvest ratios in this period were above the values associated with high long term yield and low risk of stock depletion.

South Minch: the UWTV survey indicates that the population has declined from record high in 2004 to record low in 2007 but has increased in 2008. Harvest ratios since 2006 have been above F0.1.

Clyde: the stock is being exploited unsustainably. The current harvest rate is well above Fmax. The UWTV survey indicates that the population has been at a relatively high level since 2003 except for 2007.

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.

The advice for the North Sea and west of Scotland aims to control exploitation rate by suggesting TACs for individual FUs which are estimated as a fixed proportion ('harvest rate') of the underwater TV abundance estimate. ICES advised that this 'harvest rate' should be at a level which is consistent with high long term yield and low risk of depletion of production potential. Target harvest rates corresponding to fishing at F0.1 to FMAX were recommended. For a number of FUs the advised harvest rate implies a significant reduction in catch. In these cases ICES has suggested that since there does not seem to be any immediate biological risk to the stocks then incremental reductions in fishing mortality towards the target could be considered.

ICES management advice is formulated for Nephrops FUs, whereas management has continued to be applied to the larger ICES finfish areas. STECF supports the ICES ACOM advice for management at a smaller scale and emphasised the need for effort management and whitefish by-catch mitigation measures.

	EU TAC	UK share
North Sea	24,688	21,384
West coast	16,057	15,677

Marine Scotland - Science (MSS) has been involved in the development of underwater television (UWTV) surveys for estimating Nephrops abundance for a number of years and this continues with the refinement of both the technological aspects and analysis of video recorded material. During 2009 MSS made major contributions to an ICES workshop which developed a method for providing TAC advice from the UWTV estimates of abundanceFRS