Fernando González-Costas assesses American Plaice in NAFO Division 3M; 2025 near series mean biomass.

An assessment of American plaice (Hippoglossoides platessoides) in NAFO Div

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Serial No. N7739 NAFO SCR Doc. 26/020

SCIENTIFIC COUNCIL MEETING – JUNE 2026

An Assessment of American Plaice (Hippoglossoides platessoides) in NAFO Division 3M

Fernando González-Costas1

1 Instituto Español de Oceanografía , CSIC-IEO fernando.gonzalez@ieo.csic.es.

GONZÁLEZ-COSTAS, F. 2026. An Assessment of American Plaice (Hippoglossoides platessoides) in NAFO Division 3M. NAFO Scientific Council Research Document, SCR Doc. 26/020: 1-28.

Abstract

The present assessment evaluates the status of the 3M American plaice stock. Due to the lack of ALKs for recent years the previous models used to assess this stock were not update, therefore not analytical assessment was carried out and the assessment is done base on the catches and the survey trends.

All of the 1991 to 2005 year-classes were estimated to be weak. Two pulses of recruitment were observed from 2008-2012 and 2015-2018 but with less strength than those before the middle 90s, since then the recruitment is poor. Both EU survey stock biomass and abundance recorded a minimum in 2007, due to consistent year-to- year recruitment failure from the 1991 to 2005 year-classes. Both indices show an increased trend since 2007 due to improved recruitment and in 2025 are about the series mean values. Fishing mortality index (C/B) declined from the mid-1980s to the mid-2000s and since then fluctuated around low levels within its time series.

Introduction

General considerations

On Flemish Cap American plaice mainly occurs at depths shallower than 600 m. The last analytical full assessment based on model results was done in 2020 (Alpoim, 2020), and the last not analytical full assessment base on the catches and the survey information was done in 2023 (Alpoim, 2023).

Catch trends and TAC regulation

Nominal catches from 1960-2025 were obtained from NAFO Secretariat and recalculated from NAFO statistical data base, using the NAFO STATLANT 21A Extraction Tool 27 May 2026. The STATLANT 21A for 2021-2025 are incomplete. STACFIS catches, since 1988, were estimated based in several sources, but in recent years are estimated by the NAFO Catch Estimation Strategy Advisory Group (CESAG). In the early-1960’s catches were relatively low with the exception of 1961. Catches were high between 1964 and 1966, with a peak in 1965 of 5 341 tonnes. Till the end of the 1960’s catches remained at a low level within 80 tonnes and 150 tonnes, jumping to a higher 600 - 1 100 tonnes level on the early-1970’s. Since 1974 this stock became regulated and catches ranged from 600 tonnes (1981) to 5 600 tonnes (1987). After 1987 catches declined to 300 tonnes (1996), following the fast decline of the stock biomass and the reduction of the Spanish directed effort (1992). From 1986 to 1989 and in 1995 catches exceed the TAC. Since 1997 catches have remained low and declined to a

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www.nafo.int 2 historical minimum in 2012 (63 tonnes). Catches increased afterwards, oscillating between 100 tonnes (2021) and 371 tonnes (2025) and are taken as bycatch mainly in the Div. 3M cod and redfish fisheries. Since 1974 till 1993 a TAC of 2 000 tonnes has been in effect for this stock with the exception of 1978 (TAC of 4 000 tonnes). A reduction to 1 000 tonnes was agreed for 1994 and 1995, and finally a moratorium was agreed thereafter (Table 1 and Fig.1).

Survey data

The plan of stratification of the Flemish Cap (Bishop, 1994) used by the surveys is presented in Fig. 2.

In the 2002 assessment (Alpoim et al., 2002 - SCR 02/62) and in the 2003 update (Alpoim, 2003 - SCR 03/44) of the status of the stock several historical survey data were analysed, this analysis is summarized in Fig 3. Since 2003 only EU-Spain/Portugal survey was conducted. This was the only survey updated and used in this assessment.

EU-Spain/Portugal Survey (1988-2025) (González Troncoso et al, 2026 - SCR 26/003).

EU- Spain/Portugal has conducted a random bottom trawl survey up to a depth of 730 metres (400 fathoms) on Flemish Cap since 1988. All surveys had a stratified design following NAFO specifications. The surveys were conducted in June-July of each year. Towing speed was around 3.5 knots. Trawling effective time is 30 min. The fishing gear used was a Lofoten gear with effective 30 mm mesh size in the codend. The full description of the survey could be found in the survey protocol (Vázquez et al, 2014).

In June 2003 a new Spanish research vessel, the RV “Vizconde de Eza” (VE), replaced the RV “Cornide de Saavedra” (CS) that had carried out the whole EU survey series, with the exception of the years of 1989 and 1990. In order to preserve the full use of the 1988-2002 survey indices available for several target species, the original time series needed to be converted to the new RV units.

During 2003 and 2004 Flemish Cap surveys, 130 pairs of parallel hauls (selected at random from the annual coverage of the bank) were performed simultaneously by the two vessels, at depths less than 730 m. Those pairs of parallel hauls were distributed over the swept area trying in one hand to maximize the sampled area and on the other to guarantee a large enough number of hauls with acceptable catches of all target species, namely the ones from severely depleted stocks (cod and American plaice). Both vessels were fishing with the same gear, a Lofoten trawl gear with 35 mm mesh size at the codend, which remained unchanged throughout the series. With the comparative fishing trials concluded and the conversion factors estimated, the indices from R/V CS were transformed to the R/V VE scale to make them comparable. The results of the calibration shown that the new RV VE is 33% more efficient than the former RV CS as regards American plaice (González-Troncoso and Casas, 2005 – SCR 05/29). Data from 1988-2002 R/V CS were converted to R/V VE, 2003-2025 data are original from R/V VE (González-Troncoso et al, 2026 - SCR 26/003).

The methodological aspects and results of the calibration are presented in SCR 05/29 (González-Troncoso and Casas, 2005).

Biomass and abundance estimates

Estimates for biomass and abundance are presented in Table 2 and Fig. 3.

Stock length composition

The EU Flemish Cap survey biomass length composition matrix was updated since the last assessment (Alpoim, 2023; González-Troncoso et al, 2024, 2025 and 2026). EU Flemish Cap survey biomass length compositions from 1988 to 2025 are present in Table 3 and Fig. 4.

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www.nafo.int 3 Length weight relationships

Length weight relationships for the 3M American plaice (1988-2025) were calculated with EU survey length/weight data from both males and females (González-Troncoso, pers. comm. 2026) and used in this assessment on an annual basis (Table 4).

Stock abundance-at-age

Unfortunately, the age length keys (ALK) for the years 2020-2025 were not available. Therefore, it was not possible to update any age-dependent data, matrices or analyses. Consequently, it was not possible to update any age-dependent data, matrices or analyses, for either the stock or the catches.

Recruitment proxy

The maximum mean length for ages 1 to 4 were calculated based on the EU survey mean length at age 1988- 2025 matrix. The abundance less than 16cm was considered a proxy for age 1, the abundance less than 24cm was considered a proxy for ages 1 to 2, the abundance less than 32cm was considered a proxy for ages 1 to 3 and finally the abundance less than 36cm was considered a proxy for ages 1 to 4. The trends of these survey recruitment abundances are shown in Fig. 5.

Commercial Data

Length composition of the commercial catch and by-catch

The total catches length composition matrix was updated since the last assessment (Alpoim, 2023). The length compositions presented in the 2024 Portuguese and Russian Research Reports (Vargas et al., 2024; Fomin and Pochtar, 2024) were used to estimate the length composition of the 2023 total catch. The length composition presented in the 2025 Portuguese and Russian Research Reports (Alpoim et al., 2025; Fomin and Pochtar, 2025) were used to estimate the length composition of the 2024 total catch. The length compositions presented in the 2026 Portuguese, Russian and Spanish Research Report (Alpoim et al., 2026; Fomin and Pochtar, 2026; Gonzalez-Costas et al., 2026) were used to estimate the length composition of the 2025 total catch.

For each year of the 2023–2025 period, a sample weight was estimated for each of the available catches length distributions based on the available length-weight relationship (Table 4). These were extrapolated to the total catch for each of the countries with available size distributions. Each year, the catches length distributions from the countries with available data were summed, and the total was scaled up to the total STACFIS catch.

The breakdown of the total catch is presented in Table 5. The commercial catch at length matrix (Alpoim, 2023) was updated with the 2023, 2024 and 2025 data (Table 6 and Fig. 6).

Assessment

Due to the lack of ALKs, the previous models used to assess this stock were not update, therefore not analytical assessment was done and the assessment is done base on catches and the survey trends.

Comments on trends on stock indicators

The two former USSR-Russian survey series showed a decreasing trend in biomass and abundance between 1976 and 1993 (Fig. 3). The Russian surveys in 2001-2002 show very low estimates of biomass and abundance. From 1978 till 1985 Canadian series was stable, with survey biomass and abundance around 6 700 tonnes and 10 million fish. A continuous decline in abundance and biomass is observed since the beginning of EU survey 1988 (Tables 2 and Fig. 3) till 2007 when the abundance and biomass reached the lowest values of this series (1 053 tonnes and 1.4 million fishes). From 2008 to 2025, due to improved recruitment (in particular from 2008-2012 and 2015-2018), biomass and abundance indices show an upward trend, reaching in 2025 levels about the mean values of the series, there have been two peaks in recruitment from 2008-2012 and 2015-2018

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www.nafo.int 4 but with less strength than those before the mid-1990s. Since then, recruitment levels have been poor. Results of the 1996 Canadian survey are comparable with the 1996 EU survey (Fig. 3) (Alpoim et al., 2002; Alpoim, 2003; González-Troncoso et al, 2026).

The recruitment proxy indicates that the best represented year-classes at the beginning of the series (1988) lost its strength (Tab. 3 and Figs 4 and 5). In the period between 1992 and 2007, all the recruiting was poorly represented in the EU survey. Two pulses of recruitment were observed from 2008-2012 and 2015-2018 but with less strength than those before the middle 90s, since then the recruitment is poor (Fig 5).

Commercial catches of American plaice resulting from bycatch in other fisheries have increased over the past three years, reaching 371 tonnes in 2025.

A proxy to fishing mortality (F) has been giving by the ratio between catch and EU survey total biomass. Despite the variability, decreased, from high values in the beginning of the series (1988), to 0.016 in 2005. Since then this F index fluctuated at or below 0.05 (Table 7, Fig. 7). Over the last three years, F has increased from 0.01 to 0.03.

Conclusions