Scophthalmus maximus 

Scope: Europe
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Pleuronectiformes Scophthalmidae

Scientific Name: Scophthalmus maximus (Linnaeus, 1758)
Regional Assessments:
Common Name(s):
English Turbot, Breet, Britt, Butt
French Turbot
Spanish Rodaballo, Turbot
Pleuronectes cyclops Donovan, 1806
Pleuronectes maximus Linnaeus, 1758
Pleuronectes turbot Lacepède, 1802
Psetta maxima (Linnaeus, 1758)
Rhombus aculeatus Gottsche, 1835
Rhombus magnus Minding, 1832
Rhombus maximus (Linnaeus, 1758)
Rhombus stellosus Bennett, 1835
Scophthalmus ponticus Ninni, 1932
Taxonomic Notes: Previously Scophthalmus maeoticus was regarded as a separate species. Chanet (2003) in a detailed philogenetic study of the familiy Scopthalmidae concluded that S. maeoticus was conspecific with S. maximus. This taxonomic decision has not been accepted by all researches studying these fishes, however for the purpose of the IUCN Red List assessment, the decision proposed by Chanet (2003) will be followed.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2bd (Regional assessment) ver 3.1
Year Published: 2015
Date Assessed: 2013-10-14
Assessor(s): Munroe, T., Costa, M., Nielsen, J., Herrera, J., de Sola, L., Rijnsdorp, A.D. & Keskin, Ç.
Reviewer(s): Kempf, A. & Miller, D.
Contributor(s): Teixeira, C. & Stump, E.
Facilitator/Compiler(s): Nieto, A.
European Regional Assessment: VU

Scophthalmus maximus occurs throughout the Northeast Atlantic from the Arctic circle, North Sea, Baltic Sea to the Aland Sea, Bay of Biscay, and throughout the Mediterranean to depths of 100 m. Scophthalmus maximus is a highly-valued bycatch species which is taken in a variety of gears including beam trawl, gillnet, otter trawl, and static gear. This is a common, widespread species which occurs in low abundance throughout its range. The highest biomasses are observed in the waters around Great Britain. The generation length of T. maximus was estimated using the mid-point of longevity (14 years) and the age of first maturity (4) years using the following formula: Generation length = age at first maturity + 0.5 (maximum age-age at first maturity). This gives a window of 3 generation lengths = 27 years, +/- 2 years due to uncertainties in aging this species and the effects of prolonged exploitation on age structure. Trends in relative Spawning Stock Biomass (SSB) and landing statistics were examined across the range over a time window of 25 to 29 years, and the relative contribution of trends in each region was weighed by average of landings contributed over the last 10 years for each region. This resulted in an 84% contribution by landings to the Northeast Atlantic Fishing Zone, where declines in SSB in the Baltic Sea and North Sea approximated 25%, and a 16% contribution by landings in the Mediterranean and Black Sea Fishing Zones, where declines in landing statistics approached 62%. Trends in landing statistics are used as a proxy for population trends in the absence of other data, and are supported by evidence of poor stock status in parts of the Mediterranean as reported by the European Commission Review of Scientific Advice, and by the poor state of stocks in the Black Sea where SSB is estimated to be <10% of levels seen in the 1970s. An overall decline of 31% in the population of S. maximus was estimated over a 27 to 29 year window. This is a conservative estimate, as this species may be intrinsically vulnerable to exploitation due to its narrow depth range and relatively sedentary nature. Therefore, S. maximus is assessed as Vulnerable A2bd. Scophthalmus maximus has gone through the ICES benchmark procedure in the North Sea, and it is not assessed in other parts of its range.

Geographic Range [top]

Range Description:Scophthalmus maximus is restricted to the eastern Atlantic Ocean, where it is known from southern Iceland and Norway south to Western Sahara (Munroe in press). It is also found in most of the Baltic Sea except for the Bothnian Bay. In the Mediterranean Sea, this species is known primarily from the western and central basins, including the Adriatic Sea (Arneri et al. 2001), Hellenic Seas (Papaconstantinou 1988), and in the Gulf of Lion (Carlier et al. 2007). The species also occurs in the Black Sea, Sea of Marmara, and Azov Sea. The species is found over a depth range from less than 1 m to 100 m (van der Hammen et al. 2013).
Countries occurrence:
Albania; Algeria; Belgium; Bulgaria; Croatia; Denmark; Egypt (Egypt (African part), Sinai); Estonia; Faroe Islands; Finland; France (Corsica, France (mainland)); Georgia; Germany; Gibraltar; Greece (East Aegean Is., Greece (mainland), Kriti); Guernsey; Iceland; Ireland; Italy (Italy (mainland), Sardegna, Sicilia); Jersey; Latvia; Lithuania; Malta; Monaco; Montenegro; Morocco; Netherlands; Norway; Poland; Portugal (Portugal (mainland)); Romania; Russian Federation (European Russia); Slovenia; Spain (Baleares, Spain (mainland), Spanish North African Territories); Sweden; Tunisia; Turkey; Ukraine (Krym, Ukraine (main part)); United Kingdom (Great Britain, Northern Ireland)
FAO Marine Fishing Areas:
Atlantic – northeast; Mediterranean and Black Sea
Additional data:
Lower depth limit (metres):100
Upper depth limit (metres):20
Range Map:198731-1

Population [top]


New European Assessment:
A generation length of 9 years was estimated using the mid-point of longevity (14 years) and age of first maturity (4 years) using the following formula:

Generation length = age at first maturity + 0.5 (maximum age-age at first maturity). This gives a window of 3 generation lengths = 27 years, +/- 2 years due to uncertainties in aging this species and the effects of prolonged exploitation. Trends will be examined over a 27 to 29 year window.

Population decline estimated by using decline in landings in the Mediterranean and Black Sea as proxy for decline in biomass.

A 62% decline was calculated based on % decline between average landings from 1984 to 1986 (1381 t) and landings in 2013 (assumed the same amount landed in 2011 for the region (524 t). 

Decline in the Northeast Atlantic Fishing Zone:
North Sea: Estimates of relative SSB have recently become available from the North Sea. Relative SSB is estimated to have declined by 20-25% from 1984-1986 (average relative SSB of 1.2) to 2012-2014 (average relative SSB of 0.7). It is worth noting that this species is slated to undergo assessment in the North Sea, and is likely to benefit from effort control in this region (ICES 2013).

Declines in the Baltic Sea:
The Baltic Marine Environment Protection Commission (HELCOM) estimated a 30% decline in the population of this species in the Baltic Sea over the last 20-25 years. Declines in the Skagerrak are estimated at 50% over the last 20 to 25 years.

There is no effort information available from the Iberian Peninsula or Bay of Biscay for the latest years. Landings per unit effort (LPUE) show an increasing trend from 1992 to 2005 (Teixeira et al. 2009), and from 2005 to 2011 LPUE declined (C. Teixeira pers. comm 2013). The highest LPUE value obtained was in 2005. LPUE = 0.01 t/vessel. It is assumed that trends seen in the North Sea and Baltic Sea, where this species is relatively well managed, are also occurring in the Iberian Peninsula and Bay of Biscay, where management is scarce.

The Northeast Atlantic fishing zone has accounted for 84% of global landings in the last 10 years
The Mediterranean and Black Sea have accounted for 16% of global landings in the last 10 years

Combined percentage declines over the last 25-29 years in the NEA: 23% + 30% in Baltic Sea, with more weight given to NEA: estimate 25% decline
Med and Black Sea: at least 62% decline, based on reported landings. Likely to be higher due to unreported catches in the region.

25% decline, 84% of weight
62% decline, 16% of weight

This is an approximate decline of 31% throughout this species' range.

Population structure:
The stock structure of S. maximus has only recently received attention by fisheries management. Scophthalmus maximus displays low larval dispersal, strong spawning site fidelity, and limited adult migration. A 2012 report by the International Council for the Exploration of the Sea (ICES) recommends that S. maximus in the Skagerrak/Kattegat not be included in the Greater North Sea stock, but be treated separately or combined with the Baltic Stock. Additionally, there may be an additional genetic break between northern North Sea and southern North Sea; however, this break is not strongly supported enough to recommend management actions (ICES IBPNew Report 2012). Genetic data show no structure for the turbot within the Baltic Sea (Nielsen et al. 2004, Florin and Höglund 2007), although Nielsen detected population structure between the Baltic Sea and Kattegat, with a hybrid zone in the Belt Sea (from HELCOM 2013 Red List Assessments). Separate stock structures are indicated by historical data from the Skagerrak-Kattegat area (ICES 2013).

FAO landing statistics summary:
The Food and Agriculture Organization (FAO) common name for this species is Turbot. Landings are declared from the following FAO fishing regions, in order of decreasing landings: Northeast Atlantic, Mediterranean and Black Sea. The overall trend in landings is one of fluctuation until the late 1980s and early 1990s, followed by a period of decline from the early 1990s onward.

Black Sea

There is no formal stock assessment but there is information available from surveys. Survey data indicates that the stock size is at a historical low and is < 10% of the stocks size of the late 1970s (Daskalov et al. 2012). Based on a time series of SSB from 1970 to 2010, SSB peaked in 1980 and followed by continuous decline to 2010. Landings peaked in the early to mid-1980s followed by a decrease after 1988 and stabilized from 1995 to 2010 (General Fisheries Commission for the Mediterranean 2012). The estimated total catch was about 2.44 times higher than the reported landings on average for 2002-2010 (General Fisheries Commission for the Mediterranean 2012). Recent management advice for the Black Sea is provided by Scientific, Technical and Economic Committee for Fisheries (STECF) and states that there should be no directed fisheries for this species in the Black Sea (STECF 2014).

Landings per unit of effort (LPUE) show an increasing trend from 1992 to 2005 (Teixeira et al. 2009), and from 2005 to 2011 LPUE declined (C. Teixeira pers. comm 2013). The highest LPUE value obtained was in 2005. LPUE = 0.01 t/vessel.

North Sea
Scophthalmus maximus
has a low abundance compared to other flatfish species (Daan et al. 1990, van Hammen 2013). This species was formerly widely distributed throughout the North Sea, but since the 1960s has almost disappeared from the northern North Sea, and particularly from an area off the eastern Scotland where it was previously abundant. After the 1960s this species was mainly caught in the central and eastern-central North Sea. In the past two decades the distribution has expanded westwards towards the English east coast and northwards along the Norwegian trench (Kerby et al. 2013).

Fishing mortality (ages 2 to 6) increased from 1975 to the late 1990s and has decreased since then. Spawning-stock biomass for the same time period fell by 60% until the early 2000s and showed a slight increase since then. Present spawning stock biomass is at 50% of the start of the time series. Relative SSB is estimated to have declined by 20-25% from 1984-1986 (average relative SSB of 1.2) to 2012-2014 (average relative SSB of 0.7)(ICES 2013), a time period of 3 generation lengths. It is worth noting that this species is slated to undergo assessment in the North Sea, and is likely to benefit from effort control in this region (ICES 2013). The information does not show that recruitment is not impaired at low levels of spawning stock biomass. Recruitment of S. maximus is variable around the long-term average (ICES 2013).

Baltic Sea: 
Within the Baltic Sea, this species is commonly encountered up to the Åland Sea. It is a species of great local economic importance, especially to the coastal fisheries. The main part of the turbot fishery takes place in the southern and western part of the Baltic Sea, within Danish and German fisheries. The targeted fishery increased in the early 1990s, in eastern Gotland basin and Gdansk Bay primarily due to the Polish, Russian, and Swedish gillnet fishery (ICES 2011). The consideration of landings data, CPUE information from commercial gillnet fisheries, and several fisheries-independent surveys resulted in an estimate of the percent population decrease in the Baltic Sea between 30 and 50% (HELCOM Red List Assessment 2013). This species was assessed as Near Threatened in the 2013 HELCOM Regional Red List Assessments utilizing criteria A2bd. 

Skagerrak and Kattegat (North Sea: Division IIIa)
There is insufficient information to determine the fishing mortality trend but spawning stock biomass has been stable from 2005-2012 (ICES 2013). In the Baltic International Trawl Survey (BITS) no trend in CPUE (N/h) was indicated in the dataset from 1996- 2011 (ICES 2013). Cardinale et al. (2009) performed an analysis of a re-constructed time series of biomass, maximum body size, and spatial distribution in the Kattegat-Skagerrak using standardized research surveys extending back to 1925. This analysis showed biomass declines of 86%, maximum body size decreased by 20 cm (from 50 cm to just above 30 cm), and the northern component of this population nearly vanished.  In the Kattegat, IBTS shows a decrease in captures (N/h) of large fishes (larger than 30 cm) of 65% between 1985 to 2011 (HELCOM Red List).

Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Habitat and Ecology
Scopthalmus maximus is a benthic species which lives on sandy, rocky or mixed substrata, it is rather common in brackish waters. It feeds mainly on other bottom-living fishes (sand-eels, gobies, etc.), and also, to a lesser extent, on larger crustaceans and bivalves. Scophthalmus maximus is a visual predator, feeding on other demersal and pelagic fishes. 

Life History and Reproduction
While S. maximus spawns at specific locations in shallow waters during the summer, this species generally occurs in spatially separated stock units. Tagging studies from different areas in the Baltic Sea show that Turbot have high spawning site fidelity, with 95% of fishes moving less than 30 km from the spawning cite. Larval dispersal is low and adults have restricted movement. This species exhibits strong spawning site fidelity (ICES 2013). Migrations of this species from the nursery grounds in the southeastern part to more northern areas have been recorded in the North Sea. Adults of this species can tolerate cooler water temperatures in the northern areas of the North Sea which are too low for juveniles to survive (ICES 2013). Spawning season is between April and August, eggs are pelagic. This species may reach weights of 25 kg (Frimodt 1995). Spawning usually happens between the months of February and April in the Mediterranean Sea and from May to July in the Atlantic. Sequenced spawning occurs every 2 to 4 days. Growth rate differs between sexes, such that females become much larger than males (van Hammen et al. 2013, Florin et al. 2013).

In the North Sea this species is a summer spawner, with spawning generally occurring from April to July. The size at maturity was 46 cm, at an age of 4.46 years in 1974 (Jones 1974).

In the Baltic Sea, females mature at 20 cm at an age of 4 years, while males are mature a year earlier at 15 cm. This is in contrast to the Swedish west coast, where mature females and males are about 30 and 25 cm, respectively. A generation length of 8.5 years was used to assess this species in the 2013 Regional HELCOM Red List Assessment. In the spring, juveniles and adults move to the coast, and in winter they move towards deeper waters (in excess of 30 m in the central Baltic) (Florin 2005). Spawning occurs in shallow waters at depths of 10 to 15 m in the central Baltic. Eggs have an optimal development at 15 psu, while eggs from the North Sea have an optimum between 20 and 35 psu and do not survive in the lower salinities of the Baltic Sea. Based on age-structure data in the Baltic Sea, the average age was about 7 years.

In the Mediterranean, the maximum recorded size is 79.0 cm TL and the length at maturity for females is 50.0 cm TL and for males is 42.5 cm TL (Tsikliras and Stergiou 2014). 

Generation length:
A generation length of 9 years was used to assess this species. Generation length derived from the following data:

The oldest available ages for S. maximus are as follows:  
In the Adriatic Sea, maximum age was 18 years, with individuals above 10 years of age being rare in samples (Arneri et al. 2001).
In the Black Sea, a maximum age of 10 years was observed (Zengin et al. 2006).
In the North Sea maximum age appears to be 13 years (October 2012).
There is a report of the oldest individual recorded in the North Sea reaching ages 35 years, however it could not be verified. 

In the North Sea, age at 50% maturity was 4.5 years (Jones 1974). In the Baltic Sea, females mature at 20 cm at an age of 4 years, while males mature a year earlier at 15 cm (HELCOM Red List Assessment Project). 

Generation Length (years):9
Movement patterns:Full Migrant

Use and Trade [top]

Use and Trade: The northeast Atlantic has driven the global catch trend of S. maximus since 1950, followed by Mediterranean and Black Sea fisheries (FAO 2011). In the North Sea, Scophthalmus maximus is valuable as bycatch in flatfish and demersal species fisheries using beam trawl, gillnet, otter trawl, and static gear.

ICES did not provide advice for S. maximus fisheries until 2012 (ICES 2013). In the Skagerrak and Kattegat targeted fisheries probably did not begin until before the 1960s when the S. maximus stock was large. Currently, this species is only caught as bycatch and gillnet fisheries in the area. Landings from 2012 were ~189 t which is almost double that of the previous year (ICES 2013).

Scophthalmus maximus is bred in captivity and is thought to be an excellent candidate for aquaculture in Europe (Devauchelle  et al. 1988, Imsland et al. 1997).

Threats [top]

Major Threat(s): Intrinsic vulnerability to exploitation
Scophthalmus maximus is found in relatively shallow waters at depths ranging from 0 to 100 m. Its entire depth range is within the range of commercial fishing activity. As such, this species is taken as bycatch in a number of fisheries. Because S. maximus is fast-growing and large relatives to other flatfishes, gear with smaller mesh sizes may catch younger, smaller individuals resulting in high fishing pressure on immature fish (David Miller pers. comm. 2014). This species is sexually dimorphic, with females reaching larger sizes than males and more likely to be taken by fisheries (Florin et al. 2013). Additionally, this species displays high fidelity to spawning sites and is relatively sedentary.

Fisheries characterization 
The principal threat to S. maximus is over-exploitation. Population declines have been documented throughout this species' range. Scophthalmus maximus is a valuable bycatch species which is taken in fisheries targeting flatfishes such as sole and plaice. This species is caught with beam trawls, seines, trammel nets, longlines, gillnets and otter trawls. It is a highly-esteemed food fish (Frimodt 1995) which is subject to high fishing pressure. Due to the size dimorphism and current regulation of minimum landing size the majority of landed fish consist of females (Florin et al. 2013).

Conservation Actions [top]

Conservation Actions: Scophthalmus maximus is likely to benefit from effort reductions for targeted species such as Sole and Plaice (Kerby et al. 2013). In the North Sea, ICES advises that catches of S. maximus should not exceed 2,978 t. An official minimum landing size has yet to be implemented for this species but Belgian and Dutch producer organizations have adopted voluntary minimum landing sizes of 25 cm to 30 cm (ICES 2013). In the Skagerrak and Kattegat (North Sea: Division IIIa). ICES advises that catches for this area not exceed 102 tonnes in 2014 (ICES 2013). HELCOM recommends a management plan to regulate the fishery in the HELCOM area. Area or time-specific protection of spawning and nursery habitats have been suggested. In the Baltic Sea, ICES advises that catches not exceed 220 tonnes in the region (ICES 2013). Turbot is currently protected from fishing during spawning season in the Southern Baltic Sea and also benefits from a Swedish marine reserve in the Baltic proper (Florin et al. 2013).
Scophthalmus maximus was regionally assessed as Near Threatened in the Mediterranean (Abdul Malak et al. 2011).

Citation: Munroe, T., Costa, M., Nielsen, J., Herrera, J., de Sola, L., Rijnsdorp, A.D. & Keskin, Ç. 2015. Scophthalmus maximus. The IUCN Red List of Threatened Species 2015: e.T198731A45790581. . Downloaded on 19 September 2018.
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