Key signals
Survey biomass indices declined sharply in the early part of the time series, reached low levels around 1997–2002, increased gradually from 2003 to 2016, and have remained relatively stable since 2017. The most recent spring survey index is comparable to levels observed in the early 1990s.
The biomass index for larger plaice (>47 cm) has increased substantially since the low period in 1997–2002 and reached a new peak in 2024.
The recruitment index (<20 cm) has remained low since 1998, with only occasional small peaks. Recruitment is poorly covered by the spring and autumn surveys, as the main nursery areas are located in shallow habitats.
Both survey and commercial catch data show a gradual shift in length distributions towards larger fish. Mean length has increased in both the catch and survey time series.
The analytical assessment indicates that fishing mortality has declined and spawning stock biomass has increased in recent years. Available indicators suggest that the stock is currently in good condition.
Assessment uncertainty remains, primarily due to limited information on recruitment from the survey data.
General information
Plaice (Pleuronectes platessa) is found on the continental shelf surrounding Iceland, with highest abundance in the southwest and west. It primarily inhabits sandy or muddy substrates at depths ranging from the coastline down to 200 meters, and occasionally deeper (Jónsson and Pálsson 2013).
Plaice exhibit sexual dimorphism: females grow larger than males and reach maturity at a larger size. Few males exceed 45 cm in length, whereas females can reach up to 85 cm; a similar proportion of females exceed 55 cm as males exceed 45 cm. Size at sexual maturity also differs by sex — about 50% of males are mature at 33 cm, while females reach that level at around 38 cm. Spawning occurs mainly at depths of 50–100 meters in the relatively warm waters south and west of Iceland, with limited spawning activity off the northwest and north coasts (Sigurðsson 1989; Solmundsson, Palsson, and Karlsson 2005).
After metamorphosis, 0-group juveniles settle in shallow coastal waters, typically just below the tidemark during their first summer (Hjorleifsson and Palsson 2001; Gunnarsson, Jonasson, and McAdam 2010).
Genetic studies (Le Moan, Bekkevold, and Hemmer-Hansen 2021; Hoarau et al. 2004) indicate that plaice on the Icelandic and Faroese shelves are genetically distinct from those elsewhere. Tagging experiments have shown that plaice remain on the Icelandic continental shelf, although they move between regions (Solmundsson, Palsson, and Karlsson 2005). Combined with observed seasonal shifts in distribution between spring and autumn surveys, these findings suggest little variation in population structure within Icelandic waters.
Fishery
Landing trends
Plaice landings in Division 5.a peaked historically at around 14.5 thousand tonnes in 1985. Since then, landings have declined and stabilized over the past two decades, typically ranging between 5 and 8 thousand tonnes annually (Figure 1). In 2025, landings were estimated at approximately 6737 thousand tonnes (Figure 1 and Table 2).
Before the expansion of the Icelandic Exclusive Economic Zone (EEZ) to 200 nautical miles in 1975, foreign vessels accounted for a substantial share of plaice landings (Figure 1). They dominated the fishery prior to World War II, but during the war, the Icelandic fleet increased its catches. From around 1960 onward, most plaice landings have been by Icelandic vessels.
Demersal seine is the primary gear used (Figure 2), accounting for 59–71% of the catch since 2011, followed by demersal trawl (23–37%). A small share is also caught with gillnets and longlines (Table 2). Seiners dominate the coastal fishery, while trawlers operate in deeper and more offshore areas.
Since 2000, the number of vessels reporting plaice catches annually has declined, while total catches have increased in recent years (Figure 3 and Table 2). The most notable decrease has occurred in the demersal seine fleet, which fell from 125 vessels in 2000 to 36 in 2024. The number of trawlers has also gradually declined over the same period, reaching around 52 vessels in 2025.
The main fishing grounds for plaice are located on the southwestern, western, and northwestern part of the Icelandic shelf, with smaller fishing areas in the southeast and several fjords in the north (Figure 4; Figure 5). Since 2000, the spatial distribution of the plaice fishery has remained relatively stable, with around 60% of the catch taken from the western and northwestern shelf (Figure 5).
Plaice is typically caught in relatively shallow waters, with 60–80% of the catch taken at depths between 21 and 80 meters (Figure 6).
Catch per unit of effort (CPUE) and fishing effort
Catch per unit of effort (CPUE) estimates for plaice in Icelandic waters are not considered representative of stock abundance, as they are not standardized for changes in fleet composition or technological improvements.
Non-standardized CPUE for demersal seine (kg/set) is calculated from sets where plaice made up more than 10% of the catch. These estimates increased gradually from about 120 kg/set in the early 2000s to over 450 kg/set in 2016 (Figure 7), and have fluctuated around that level in recent years.
For demersal trawl (kg/hour), using hauls where plaice constituted more than 10% of the catch, CPUE increased rapidly between 2000 and 2015, peaking at 260 kg/hour. Since then, CPUE has declined and was approximately 150 kg/hour in the most recent year.
Landings and discards
All landings in Division 5.a before 1982 are derived from the ICES STATLANT database. This also applies to foreign landings in 5.a up to 2005. Between 1982 and 1993, landings by Icelandic vessels were collected by the Fisheries Association of Iceland. From 1994 onward, landings by Icelandic vessels are provided by the Icelandic Directorate of Fisheries. Foreign landings (primarily by Norwegian and Faroese vessels) were recorded by the Icelandic Coast Guard until 2014; after that, they have also been recorded by the Directorate of Fisheries.
Discarding is banned by law in the Icelandic fishery. Discard rates for plaice have been estimated as negligible since at least since 2001 (MRI 2016). Various measures in the management system, such as converting quota shares between species, are widely used by the fleet and are believed to discourage discarding in mixed fisheries. To further prevent high grading and quota mismatches, vessels are allowed to land catches that exceed their quota. These landings are not counted against the vessel’s allocated quota, provided the proceeds from the sale go to the Fisheries Project Fund (Verkefnasjóður sjávarútvegsins).
Data and sampling
Commercial data
Biological sampling from the main gears (demersal seine and bottom trawl) in commercial plaice catches is generally considered to be good, providing satisfactory spatial and temporal coverage of the fishery. Prior to 2014, approximately 6,000–7,000 fish were aged annually from around 150 samples per year. Following a reduction in sampling intensity in 2014, the number of samples taken annually from demersal seine has ranged from 24 to 58, and from bottom trawl from 21 to 53. No samples are collected from other gear types, as these account for only approximately 5% of the total plaice catch. An overview of the number of samples per month is presented in Figure 8 and sampling coverage by gear in 2025 is shown in Figure 9.
Length composition
An overview of available length measurements from Division 5.a is provided in Table 3. Most measurements come from the two main fleet segments — demersal trawls and seines (Figure 10).
The size distribution of plaice caught by these gears has remained relatively stable, with most fish ranging between 35 and 55 cm in length. However, there has been a gradual shift toward larger sizes in the catch, reflecting an increase in the effective minimum landing size in both fleets. As a result, the average length in commercial catch samples increased from 35 cm in 1991 to 44.6 cm in 2021, and has decreased slightly since then. Mean length differs by gear type, with trawlers generally landing larger plaice.