Fish and Shellfish Stocks: 2015 Edition

Nephrops Stocks - Biology and Assessment

Latin name: Nephrops norvegicus

Common names: Norway lobster, scampi, Dublin Bay prawn, langoustine

Introduction

The fishery for Nephrops in Scottish waters has developed from landings of a few tonnes in the early 1960s to over 30,000 tonnes in the mid 2000s. Landings in 2013 of just under 18,000 tonnes had a first sale value of £61.7 million making Nephrops the second most valuable species landed into Scotland. There are Nephrops fisheries on various 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.

Biology and life cycle

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 meters 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, feeding primarily on crustaceans, molluscs and polychaete worms. Female Nephrops usually mature at around three years of age and reproduce each year thereafter. Mating takes place in early summer. Females 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 densities are low, but the animals grow relatively fast, and reach a larger maximum size. The largest animals are colloquially referred to as 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 because 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. Males dominate trawl catches for most of the year and are more heavily exploited than females.

Assessment

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 conversion factor to the relative abundance index, an estimate of the absolute abundance of Nephrops is obtained. A proxy for fishing mortality known as the 'harvest rate' is derived as the ratio of total catch to absolute abundance.

Relative Density of Nephrops Burrows on a Recent UWTV Survey of the Fladen Ground

North Sea : ICES Advice on Management

Information Source: ICES advice 2014

http://www.ices.dk/sites/pub/Publication%20Reports/Advice/2014/2014/Neph-IV.pdf

2015 Position: TAC 17,843 tonnes UK share 15,456 tonnes

2013 Landings: 10,800 tonnes

Stock Health: In most stocks fishing mortality is at or below the FMSY proxy

Importance: Key shellfish species

Location: Widespread on muddy grounds

Latest Assessment: May 2014

North Sea stocks

In the North Sea, Scottish fishermen exploit Nephrops in the Farn Deeps, Firth of Forth, Moray Firth, Fladen Ground and to a lesser extent at the Noup and Devil's Hole. Most are caught by trawlers targeting Nephrops. In some areas, particularly the Fladen Ground, they are also caught by whitefish trawlers.

State of the stocks

In 2014, ICES conclusions about Nephrops stock status were based on trends in the UWTV survey, fishery and catch size composition data.

Farn Deeps: the stock size has declined since 2005 and has been fluctuating near MSY Btrigger since 2007. Harvest rates have been above F MSY for all years except 2008.

Fladen Ground: the stock size has declined from the highest observed value in 2008 and is just above the MSY Btrigger. The harvest rate has declined in recent years, and fell to approximately 3 % in 2013 which is well below F MSY .

Firth of Forth: the stock is well above the MSY Btrigger level. The harvest rate decreased in 2013 to 15.6 % and is now below F MSY .

Moray Firth: the stock declined in 2007-2012 but increased again in 2013. The harvest rate decreased in 2013 to 5.8 % and is now below F MSY .

Management advice

The ICES advice on future landings is provided on the basis of a fixed proportion ('harvest rate') of the UWTV 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 ( F MSY). Target harvest rates corresponding to fishing between F0.1 and F MAX (proxies for F MSY) were recommended.

Total International Landings (tonnes) of North Sea Nephrops.

Distribution of Scottish Nephrops Landings (tonnes) in the North Sea in 2013 ( UK Vessels into Scotland)

On the basis of this approach, ICES has advised the following limits on landings (for the main FUs of Scottish interest) for 2015 ¹:

Farn Deeps	Landings: 1,127 tonnes
	(Catch = 1,281 tonnes)
Fladen	Landings: 10,759 tonnes
	(Catch = 10,759 tonnes, all catches are assumed to be landed)
Firth of Forth	Landings: 1,769 tonnes
	(Catch = 2,050 tonnes)
Moray Firth	Landings: 1,185 tonnes
	(Catch = 1,245 tonnes)

1 Advice for Farn Deeps Nephrops is based on 2014 UWTV survey data while other advice is based on survey data from 2013.

In order to provide information for implementation of the landing obligation, ICES has also given estimates of future catch (shown in brackets above) in addition to landings for 2015. These are based on the assumption that discard rates do not change from the average of the last three years (2011-2013). Note that the catch estimate includes Nephrops expected to survive the discarding process - assumed to be 25% of the total number discarded.

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 advice and considers that management of fishing mortality on Nephrops stocks would best be achieved if measures, including catch restrictions, were implemented at the level of the functional unit.

West Coast - ICES Advice on Management

Information Source: ICES advice 2014

http://www.ices.dk/sites/pub/Publication%20Reports/Advice/2014/2014/Neph-VIa.pdf

2015 Position: TAC 14,190 tonnes UK share 13,854 tonnes

2013 Landings: 12,700 tonnes

Stock Health: Stocks above Btrigger and fishing mortality fluctuating around the FMSY proxy

Importance: Key shellfish species

Location: Widespread on muddy grounds

Latest Assessment: May 2014 (advice released in autumn to account for 2014 surveys)

West of Scotland stocks

On the west coast of Scotland, there are Nephrops fisheries in the North Minch, South Minch, the Clyde and the the Sound of Jura and to a lesser extent at Stanton Bank. Most of the catch is taken by small inshore trawlers targeting Nephrops, but some are caught by larger twin-rig vessels. Creel fishing accounted for 17 % of landings in the North Minch and almost 20 % in the South Minch in 2013. Creel-caught Nephrops are generally larger and in better condition than those caught by trawling. They attract high prices in the live export market and can provide an important source of income for small local boats. Creels are used mainly in inshore areas and sea lochs, where access by trawlers may be limited by the seabed or legislation. In some areas both fishing methods are used and gear conflicts sometimes occur.

Total International Landings (tonnes) of West of Scotland Nephrops.

State of stocks

In 2014, ICES conclusions about Nephrops stock status were based on trends in the UWTV survey, fishery and catch size composition data.

North Minch: The stock has been above MSY Btrigger for more than 15 years. In 2014 estimated abundance has seen a small 11 % decrease in comparison to 2013. The historical harvest ratios (removals/ UWTV abundance) have fluctuated around the F MSY proxy. The harvest ratio in 2013 decreased to 10.0 % and is below the F MSY proxy.

South Minch: The stock fell below MSY Btrigger in 2012 but has increased since and is now above MSY Btrigger . The harvest ratio (removals/ UWTV abundance) has decreased and is now below F MSY proxy.

Clyde: UWTV abundance remains above the MSY Btrigger . The harvest rate (removals/ UWTV abundance) for Nephrops in the Firth of Clyde decreased in 2013 and is now below the proposed F MSY proxy. Harvest rates for Nephrops in the Sound of Jura have been well below the proposed F MSY proxy in recent years. UWTV abundance in 2013 was at the lowest observed level since 2000, with 2014 showing only a slight increase. The UWTV series remains too short and patchy to propose an MSY Btrigger .

Distribution of Scottish West Coast Nephrops Landings Landings (tonnes) in 2013 ( UK Vessels into Scotland)

Management advice

The ICES advice on future landings is provided on the basis of a fixed proportion ('harvest rate') of the UWTV 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 (equivalent to fishing at F MSY). Target harvest rates corresponding to fishing at F0.1 to F MAX (proxies for F MSY) were recommended. On the basis of this approach, ICES has advised the following limits on landings (by FU) for 2015:

North Minch	Landings: 3,092 tonnes
	(Catch = 3,312 tonnes)
South Minch	Landings: 6,382 tonnes
	(Catch = 6,567 tonnes)
Clyde	Landings: 4,390 tonnes
	(Catch = 4,861 tonnes)

In order to provide information for implementation of the landing obligation, ICES has also given estimates of future catch (shown in brackets above) in addition to landings for 2015. These are based on the assumption that discard rates do not change from the average of the last three years (2011-2013). Note that the catch estimate includes Nephrops expected to survive the discarding process - assumed to be 25% of the total number discarded.

ICES management advice is formulated for Nephrops FUs, whereas management continues to be applied to the larger ICES finfish areas. STECF supports the ICES advice and considers that management of fishing mortality on Nephrops stocks would best be achieved if measures, including catch restrictions, were implemented at the level of the functional unit.