Year | Landings (t) | No. samples | No. length measured |
|---|---|---|---|
2000 | 31393 | 167 | 34357 |
2001 | 17230 | 95 | 18563 |
2002 | 19045 | 177 | 32500 |
2003 | 28478 | 149 | 26196 |
2004 | 17564 | 117 | 19640 |
2005 | 20563 | 596 | 93465 |
2006 | 17208 | 325 | 50237 |
2007 | 17372 | 203 | 30107 |
2008 | 24125 | 192 | 32535 |
2009 | 19429 | 168 | 27647 |
2010 | 17642 | 168 | 28464 |
2011 | 11737 | 138 | 21239 |
2012 | 11963 | 69 | 11237 |
2013 | 8761 | 63 | 9360 |
2014 | 9501 | 93 | 15380 |
2015 | 9314 | 58 | 9089 |
2016 | 9537 | 88 | 13026 |
2017 | 8372 | 45 | 8570 |
2018 | 9996 | 27 | 5038 |
2019 | 8715 | 40 | 7509 |
2020 | 11375 | 29 | 5508 |
2021 | 10589 | 26 | 4125 |
2022 | 9465 | 8 | 319 |
2023 | 6675 | 22 | 2045 |
2024 | 2704 | 26 | 3018 |
Key signals
- The total biomass and abundance indices have fluctuated about a constant level since 2003.
- Survey estimates have consistently shown very low abundance of pre-fishery juveniles (< 30 cm) since 2012.
- Length distributions from surveys and fisheries show a progressive shift toward larger fish over time, reflecting an aging population and a long period (2012–present) with very low recruitment.
- Spawning stock biomass (SSB) declined from 1990–2000, was relatively stable from 2000–2016, and has since declined to lowest level.
- Fishing mortality (F) has declined since the mid 1990s and dropped below FMSY in 2024.
General information
Icelandic slope beaked redfish (Sebastes mentella) is a deep-water redfish species, similar in appearance to golden redfish (S. norvegicus) but distinguishable by certain characteristics, notably its deeper habitat (>400 m). Around Iceland, it is primarily found in the warmer waters along the western, southern, and south-eastern continental slope. Like other redfish species, beaked redfish is slow-growing, long-lived, and matures late.
This species is considered a separate biological stock and management unit within the Icelandic waters ecoregion, which encompasses ICES Division 5.a and part of Subarea 14 within the Icelandic 200 NM EEZ. In Icelandic waters, individuals larger than 30 cm are predominantly observed. The East Greenland shelf is believed to serve as the main nursery area for this stock.
Information from the fishing industry
Landings
Total annual landings of Icelandic slope beaked redfish from the Icelandic Waters Ecoregion during 1950–2024 are shown in Figure 1.
From 1950 to 1977, prior to the extension of Iceland’s EEZ to 200 NM, the fishery was primarily conducted by West Germany. Catches peaked in 1953 at around 87 000 t, then gradually declined to approximately 23 000 t by 1977. Following the EEZ extension in 1978, the fishery has been almost exclusively prosecuted by Icelandic vessels.
Landings declined steadily from 57 000 t in 1994 to 17 000 t in 2001 and remained at similar levels until 2010. Between 2011 and 2024, annual landings ranged from 2 500 to 12 000 t. In 2024, the total catch was 2,618 t — a decrease of 4,057 t from the previous year.
Fisheries and fleets
The fishery for Icelandic slope beaked redfish in Icelandic waters is a directed bottom trawl fishery conducted along the continental shelf and slope southwest and west of Iceland, typically at depths between 500 and 800 m (Figure 2). The number of vessels accounting for 95% of the total catch has declined steadily over time (Figure 3).
Sampling from the commercial fishery
Table 1 shows biological sampling from the catch of Icelandic slope beaked redfish in the Icelandic Waters Ecoregion during 2000–2024. Both the number of samples and the number of length measurements have declined since 2012.
Figure 4 displays the number of samples collected by month from 2012–2024, clearly illustrating the reduction in sampling over time. This decline is primarily due to reduced sampling effort by onboard observers from the Directorate of Fisheries.
The spatial distribution of sampling relative to the fishery during 2020–2024 is shown in Figure 5 and indicates that most sampling effort occurs where the fishery is concentrated.
Length distribution from the commercial catch
Length distributions of Icelandic slope beaked redfish from the bottom trawl fishery show a noticeable increase in the number of small fish in the catch in 1994 compared to previous years (Figure 6). A distinct peak near 32 cm in 1994 can be traced through subsequent years, showing approximately 1 cm of annual growth from 1996 to 2002.
From 2004 to 2024, the length distribution has typically peaked around 39–43 cm. In contrast, where data are available, the length distribution from the pelagic fishery shows that the fish caught were generally larger on average than those taken in the bottom trawl fishery (Figure 6).
Catch per unit effort
Trends in non-standardized CPUE (kg/hour) and fishing effort (thousand hours fished) are shown in Figure 7. The CPUE from tows in which more than 50% and 80% of the catch consisted of Icelandic slope beaked redfish declined steadily from 1978 to a record low in 1994. Since then, CPUE has increased consistently, reaching the highest levels in the time series in 2020 and 2021.
Between 1991 and 1994, the decline in CPUE coincided with a substantial increase in fishing effort. Effort has since declined and is now comparable to levels observed in 1980. CPUE and effort data are not available for 2022.
Discard
Although no direct measurements are available, discarding of Icelandic slope beaked redish is believed to be negligible.
Scientific data
The Icelandic autumn survey (IS-SMH), conducted on the continental shelf and slope in Icelandic waters, covers depths down to 1 500 m. Data on Icelandic slope beaked redfish are available for the period 2000–2024, except for 2011 when the survey was not conducted.
Survey indices
The total biomass and abundance indices were highest in 2000 and 2001, declined in 2002, and have since fluctuated around that level without a clear trend (Figure 8).
The biomass index of fish ≥45 cm increased from its lowest point in 2007 to a peak in 2021 but has declined since then (Figure 8). In contrast, the abundance index of fish ≤30 cm (recruits) has remained very low since 2010. No fish smaller than 30 cm were observed in the 2021 and 2022 surveys, and only very few were observed in 2023 and 2024 (Figure 8).
Distribution
Icelandic slope beaked redfish in the Icelandic autumn survey is caught along the continental slope from the south-east to the west of Iceland (Figure 9), with highest abundances observed southwest along the Reykjanes Ridge and west of Iceland (Figure 10). The species is primarily caught at depths between 400 and 800 m (Figure 11).
Length and age
The length of Icelandic slope beaked redfish observed in the autumn survey ranges from 25 to 55 cm (Figure 12). Since 2000, the mode of the length distribution has shifted to the right — from 36–39 cm in 2000 to approximately 42–45 cm during 2012–2024. Over the same period, the mean length of sampled fish increased from 37.4 cm in 2000 to 43.2 cm in 2024.
This is a substantial increase in mean length, particularly given that the species grows slowly (approximately 1–2 cm per year) and that individuals over 50 cm are rarely observed. The absence of smaller size classes and this shift in size structure are consistent with a recruitment failure.
Otoliths from the autumn survey have been collected since 2000, with age readings completed for 10 survey years (Figure 13). The results show that the stock is composed of many cohorts, with ages ranging from 5 to over 50 years. The 1985 and 1990 cohorts were particularly strong and remained relatively abundant in the 2021 survey.
Signs of recruitment failure are evident in the age distributions, with very few individuals aged 10 years or younger observed since 2018.
Maturity
Maturation data from the autumn survey are shown in Figure 14. Males mature at a smaller size and younger age than females. Fifty percent of males reach maturity at approximately 32–33 cm (around 7 years), while 50% of females mature at about 36–37 cm (around 10 years). Most individuals are fully mature by approximately 20 years of age.
Analytical assessment
The stock was benchmarked in 2023 (ICES, 2023) and is now assessed as a Category 1 stock using an age- and length-based assessment model (Gadget). Reference points were defined during the benchmark process and subsequently corrected in 2024 due to an error in the biomass calculations (ICES, 2024).
Assessment
Data
The model uses multiple disparate datasets. The input data include:
Length-disaggregated survey indices from the autumn survey (IS-SMH) for 2000–2024, excluding 2011.
Length distributions from the Icelandic commercial bottom trawl fleet for 1975–2024.
Landings by 6-month periods from Iceland for 1975–2024.
Age–length distributions from the autumn survey.
Maturation data from the autumn survey.
An overview of the input data and their annual availability is shown in Figure 15.
Model settings
The model runs from 1975 to 2025, with each year divided into two 6-month time steps.
Two sub-stocks are modeled:
- Immature stock: age range 3–20 years.
- Mature stock: age range 5–50 years.
The oldest age group (50+) is treated as a plus group.
Movement from the immature to the mature stock occurs through:
- Maturation, based on a length-based ogive.
- Ageing, where all 20-year-old fish are transferred to the mature stock at the end of the year.
Modelled lengths range from 5 to 60 cm, in 1 cm increments. No mature individuals are assumed to be below 50 cm.
Recruitment to the immature stock occurs at age 3.
Survey length bins are: 10–30 cm, 30–35 cm, 35–40 cm, 41–45 cm, and 46–55 cm (five bins in total).
One commercial fleet is included in the model: bottom trawl.
Model processes
Natural mortality:
- Natural mortality (Ma) was fixed at 0.05 for all ages, based on values used in other redfish stock assessments.
Growth:
- Growth follows a length-based von Bertalanffy growth function, with parameters k and L∞ informed by age–length frequencies.
- The β parameter of the beta-binomial distribution controls the spread of the length distribution.
- Maximum growth per length group was set at 5 cm per timestep.
- Length–weight relationship parameters (αs, βs) were fixed using mean values from log-linear regressions of autumn survey data.
Maturity:
- A logistic, length-based maturity ogive was applied, with parameters αm and l50 estimated from autumn survey data.
Recruitment:
- Annual recruitment occurs in the first timestep, with one parameter per year (Ry, where y ∈ 1970–2024).
- A recruitment scalar (Rc) is applied to all Ry values to aid optimization.
- Mean length at recruitment (l0) is estimated.
- The coefficient of variation (CV) for length at recruitment is fixed at 0.1, based on autumn survey data.
Initial population:
- Total initial abundance (N0) for both stocks is estimated.
- Initial numbers-at-age are calculated as:
N0,a = N0 × e^(−a(Ma + F0)),
where F0 is an additional mortality parameter reflecting historical fishing pressure (estimated). - Initial numbers-at-age are split between immature and mature stocks using an age-based ogive. The age at which 50% of the stock is mature (a50) was fixed based on autumn survey data, while the slope parameter (αa) of the ogive was estimated.
- Initial mean length-at-age values are derived from the von Bertalanffy growth function.
- Variance in initial length-at-age is fixed and based on autumn survey length distributions for each stock.
Fleet operation:
- Two fleets are modeled: the commercial bottom trawl fleet and the autumn survey fleet.
- Each fleet uses a logistic selection function with fleet-specific parameters (αf, l50).
Length-weight relationship
The conversion from length to weight is based on the following formula:
\[ W_{l} = \alpha \cdot l^{\beta} \]
In the model, the parameters α and β are fixed, based on estimates derived from biological data collected during the Icelandic autumn survey. The observed values and the fitted length–weight relationship are shown in Figure 16.
Diagnostics and model fit
Survey indices for Icelandic slope beaked redfish can be highly variable due to the influence of a few very large hauls. The index data used in the model consist of the total raw number of fish caught (within defined length bins) across the entire autumn survey. While these indices are intended to represent the full stock, no data pre-processing or standardization was applied to reduce variability, making them inherently noisy.
This variability is reflected in the model’s fit to the survey index data (Figure 17). Overall, the model captures historical stock trends reasonably well. However, it underestimates abundance for the 10–30 cm, 30–35 cm, and 35–40 cm length groups during the period 2000–2003. In the terminal year, model estimates align closely with observed values across all length groups (Figure 17).
Length and age distribution
The model-estimated catch composition is illustrated in Figure 18 through Figure 22, with corresponding residual plots for each component shown in Figure 23.
The model provides a good fit to the length distributions (Figure 19, Figure 21, and Figure 22). However, in some years (notably 2012–2015), the model does not fully capture the observed peak around 40–45 cm in the autumn survey data (Figure 19).
Fits to the age distribution from the autumn survey are less accurate for the oldest age groups (30+), where the model tends to underestimate abundance (Figure 18). In addition, the model overestimates certain cohorts that can be tracked across years: first appearing as 12–19-year-olds in 2009, and then as 20–28-year-olds in 2017 and 2018.
The fit to the commercial age–length distribution is poorer, likely due to the limited number of age readings per time step (Figure 20). Despite these issues, the residuals for all catch composition components show no clear patterns, indicating a generally unbiased fit (Figure 23).
Growth
For the autumn survey, the growth patterns predicted by the model closely follow observed growth from approximately age 10 onwards. However, growth is consistently underestimated for ages below 10 (Figure 24). This systematic deviation across years suggests that allowing for age-specific variation in growth could improve model performance.
The model also fits the growth data from the bottom trawl fishery reasonably well, although a similar underestimation of growth in younger ages is evident in 2001 and 2002 (Figure 25). This pattern implies that the model may be overestimating the mean length at recruitment.
It should be noted that (1) age–length data are relatively sparse for the younger ages, and (2) because the stock does not enter the fishery until later ages, the beta-binomial length update would have produced more realistic length-at-age standard deviations by that point in the model.
The model’s fit to the maturation data is shown in Figure 26.
Fleet Selectivity
Estimated length-based selection by fleet is shown in Figure 27. Fishing patterns differ considerably between fleets, which is explained by the longer time series of catch data.”
Model results
Annual outputs from the final model are shown in Figure 28. The spawning stock biomass (SSB) declined sharply from the late 1980s to the early 2000s, followed by a period of relative stability throughout the 2000s and a gradual decline during the 2010s. The SSB is currently at its lowest point in the time series.
Since a recruitment spike in 2003, annual recruitment has shown a steady decline. From 2010 onwards, recruitment has remained at exceptionally low levels, contributing to a continued reduction in total stock size and a stock structure increasingly dominated by older, mature individuals.
Fishing mortality has decreased since the 1990s, stabilizing around 0.09 during 2013–2019, increasing slightly to 0.1 from 2020–2023, and falling to 0.03 in 2024.
Retrospective analysis
The analytical retrospective analysis is shown in Figure 29. All retrospective revisions fall within the confidence intervals of the base model. The Mohn’s rho values for Fbar (−0.071) and SSB (0.056) are well within accepted limits.
In contrast, the Mohn’s rho for recruitment is notably high, likely reflecting substantial uncertainty due to the low survey selectivity for the younger age classes.
Reference points
Reference points and their bases area shown in Table 2:
Approach | Reference point | Value | Basis |
|---|---|---|---|
MSY approach | MSY Btrigger | 217 563 | Bpa |
FMSY | 0.041 | Fishing mortality that leads to MSY; estimated using stochastic simulations | |
Precautionary approach | Blim | 156 568 | Bloss. Median SSB (2000–2005) |
Bpa | 217 563 | Blim × e1.645σ, σ = 0.2. | |
Flim | 0.079 | Fishing mortality that in stochastic equilibrium will result in median SSB at Blim | |
Fpa | 0.041 | Maximum F at which the probability of SSB falling below Blim is < 5% |
State of the stock
The stock is currently at a low level. Since 2007, survey estimates have consistently indicated very low abundance of pre-fishery juveniles (<30 cm), raising concerns about the stock’s productivity. Without a significant increase in recruitment, biomass levels are likely to continue declining.
Short term forecast
Maturity, growth, and the length–weight relationship used in the forecast are based on the processes estimated within the model. Similarly, commercial fleet selectivity is assumed to remain as estimated by the model.
The intermediate catch reflects landings from the current fishing year (January–August), while fishing mortality for the remaining period (September–December) is set to FMSY. Recruitment in the forecast is assumed to be the average of the last five years (2020–2024).
Input values for the interim year are provided in Table 3, and the results of the forecast are shown in Table 4.
Variable | Value | Notes |
|---|---|---|
F (2025) | 0.04 | F that corresponds to assumed catch in 2025 |
SSB (2026) | 92 057 | Projected from the assessment; tonnes |
Recruitment age 3 (2026) | 0.038 | Geometric mean of recruitment from 2020-2024; millions |
Recruitment age 3 (2027) | 0.038 | Geometric mean of recruitment from 2020-2024; millions |
Catch (2025) | 3 800 | Allocated catch for 2025; tonnes |
Basis | Catch (2026) | F (2026) | SSB (2027) | SSB change (%)1) | TAC change (%)2) | Advice change (%)3) |
|---|---|---|---|---|---|---|
MSY approach | 0 | 0.00 | 91 171 | -1.0 | -100 | 0 |
Other scenarios | ||||||
FMSY*SSB2025/MSY Btrigger | 1 466 | 0.02 | 89 746 | -2.5 | -61 | |
FMSY | 3 284 | 0.04 | 87 977 | -4.4 | -14 | |
F2026 = F2024 | 2 500 | 0.03 | 88 739 | -3.6 | -34 | |
1) SSB in 2027 relative to SSB in 2026 | ||||||
2) TAC value for 2025/2026 relative to TAC value for 2024/2025 (3800 t) | ||||||
3) Advice value for 2025/2026 relative to advice value for 2024/2025 (0 t) | ||||||
Uncertainties in the assessment and forecast
Only the fishable portion of the stock is found in Icelandic waters, while recruitment likely originates from East Greenland. The connection between the Icelandic slope stock, the East Greenland stock, and the deep pelagic stock remains unknown.
Currently, limited age data are available. As a result, retrospective analysis is sensitive to the removal of years, which substantially affects model outputs. Reduced uncertainty is expected as additional age data become available.
Basis for advice
ICES MSY approach agreed during the WKBNORTH meeting (ICES 2023).
Management considerations
Beaked redfish is a slow-growing, late-maturing deep-sea species and is therefore considered vulnerable to overexploitation. As such, management advice must be precautionary and conservative.
Regulations and their effects
There is no species-specific management in place for Icelandic slope beaked redfish. The stock is managed under the general Individual Transferable Quota (ITQ) system.
Management
The Ministry of Industries (MI) in Iceland is responsible for the management of Icelandic fisheries, including the Icelandic slope beaked redfish fishery, and for the implementation of fisheries legislation within the Icelandic Exclusive Economic Zone (EEZ). However, there is no explicit management plan in place for Icelandic slope beaked redfish.
The Ministry issues annual regulations for commercial fishing for each fishing year (1st September–31st August), including the allocation of Total Allowable Catch (TAC) for stocks subject to such limits. Redfish — comprising golden redfish (Sebastes norvegicus) and Icelandic slope beaked redfish — has been included in the Individual Transferable Quota (ITQ) system since its inception.
Until the 2010/2011 fishing year, Icelandic authorities issued a joint quota for the two redfish species, and fishers were not required to report catches separately by species. Since 1994, MFRI has provided separate scientific advice for both species. Quota separation was implemented starting with the 2010/2011 fishing year.
Figure 30 shows the net transfer of quota to or from Icelandic slope beaked redfish by fishing year. For the first five years (2010/2011–2014/2015), quota transfers were minimal and the set quota was generally taken. During the 2015/2016–2020/2021 fishing years, substantial portions of the beaked redfish quota (approximately 10–20% per year) were transferred to other species, and the full quota was not landed. In contrast, over the last three fishing years (2021/2022, 2022/2023, and 2023/2024), this pattern reversed, with quota being transferred from other species to beaked redfish, resulting in landings exceeding the set quota by more than 20%.
References
ICES. 2023. Benchmark workshop on Greenland halibut and redfish stocks (WKBNORTH). ICES Scientific Reports. 5:33. https://doi.org/10.17895/ices.pub.22304638
ICES. 2024. Northwestern Working Group (NWWG). ICES Scientific Reports. 6:39. https://doi.org/10.17895/ices.pub.25605738