Key signals
Catches (mostly in Breiðafjörður) peaked in the mid 1980s.
The fishery was closed in 2003 due to several factors.
There was an experimental fishery from 2014 to 2019.
A small commercial fishery has operated in Breiðafjörður since 2020.
Biomass index in Breiðafjörður is at a historic low since the start of the camera survey in 2014.
General information
Iceland scallop has been fished in Iceland since the late 1960s. The relatively long lived and slow growing bivalve is not harvested until they are larger than 60 mm (shell height) and do not get much larger than 100 mm. Iceland scallop is mainly found bays and fjords in the west and northwest of Iceland. They generally reside at depths less than 80 m.
The fishery
The fishery began in 1969 in Ísafjarðardjúp with catch of 400 tonnes. In the following year, a fishery started in Breiðafjörður which has been the major fishing area ever since. From 1970 until the closure of the fisheries in 2003, a total of 254 thousand metric tonnes were landed from that area. Landings from other areas were much lower with 18 and 14 thousand tonnes from Húnaflói and Ísafjarðardjúp, respectively
The decline of the stock in Breiðafjörður in 1999-2003, which led to the closure of the fishery, is believed to be caused by several factors (Jonasson et al. 2007). The fishable stock consisted of few year classes and recruitment was scarce. High natural mortality caused by protozoan parasites (gray meat) was evident on all grounds, with annual mortality ratio as high as ~40% in the main fishing ground in the southern part of Breiðafjorður. The intensity of the mortality increased with scallop size and was most pronounced in the fishable part of the stock (>60 mm shell height). Total fishing mortality was also high and in combination with the above factors led to a collapse of the stock. In recent years infection levels have been low and muscle condition good.
Since 2014 there has been limited experimental and then commercial fishing for scallops on specific areas in Breiðafjörður. Within in Breiðasund in southern Breiðafjörður, fishing activity was mainly in western and middle part on conventional grounds (Figure 1). The estimated size of fishing grounds, based on VMS data, was the largest of all areas or 5.64 km2. Within Hvammsfjörður in southeastern Breiðafjörður, fishing activity was on three subareas, two on the northern slope of Breiðafjorður and one on the southern slope (Figure 1). The estimated size of fishing grounds, based on VMS data, was 2.34 km2.
In the Flatey region in northern Breiðafjörður, fishing activity was recorded on four major subareas (Figure 2). The estimated size of fishing grounds, based on VMS data, was 3.83 km2. In the Bjarneyjar region in northern Breiðafjörður, fishing activity was mainly recorded on one large area, that stretched to couple of smaller area to the northeast (Figure 2). The estimated size of fishing grounds, based on VMS data, was 3.26 km2. In the Rúfeyjar region in northern Breiðafjörður, fishing activity was recorded on one relatively thin strip (Figure 2). The estimated size of fishing grounds, based on VMS data, was 1.05 km2. In the Látralönd region in northern Breiðafjörður, fishing activity was recorded on two major and one minor subarea (Figure 2). The estimated size of fishing grounds, based on VMS data, was 4.05 km2.
There is also a small diver operated fishery in the Westfjords. Landings between 2017 and 2021 averaged 2.24 tonnes per annum. Few landings were registered into Fiskistofa’s landings database 2022 and none in 2023 and 2024.
In 2024, 40 tonnes were landed from Breiðasund and 20 tonnes from Hvammsfjörður (Figure 3).
Survey data
In April 2014, a pilot camera survey focused mainly on the Breiðasund area in the southern part of Breiðafjorður, where experimental fishing had been planned. There were also stations on conventional fishing grounds in the southern part of Breiðafjorður. New and grounds that were not covered with an older dredge survey were also surveyed. Those were in Hvammsfjöður, south of Skálmarnes, west of Látralönd and around Sauðeyjar in northwestern part of Breiðafjorður. Large numbers of scallops were found on many of the “new” grounds. Another survey was conducted in December 2014 and covered the area that was fished in the experimental fishing in Breiðasund. During the autumn of 2015–2019 and again in 2024, camera surveys were carried out annually on most of the experimental fishing areas. Results from the survey in Breiðafjörður are presented.
The drop frame camera survey continued later in 2014, and was conducted annually from 2015-2019 and again in 2024 on scallop grounds in Breiðafjörður. Several tows with dredge are also carried out to obtain information on shell height (SH) and biological samples. Ten camera “drops” are completed on each station and the general procedure is to count every other drop or five drops in total. The area of the image is known and all animals are counted. Scallop height has been measured from images since 2018. Fishable biomass is estimated from the mean number of scallops above 60 mm, based on size distribution from dredges and SH/weight relationship multiplied with the estimated size of fishable grounds. When calculating the ratio of fishable scallops (those than 60 mm to those 60 mm and smaller), scallops less than 25 mm are excluded as they tend to be cryptic and difficult to see when counting from images.
| Gear | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2024 |
|---|---|---|---|---|---|---|---|
| Dredge | 52 | 29 | 32 | 21 | 28 | 38 | 22 |
| Camera | 195 | 83 | 168 | 241 | 192 | 245 | 124 |
Length Distribution
For all grounds in Breiðafjorður combined, the mean shell height in the survey increased from 2014 (66.3 mm) to 2024 (77.6 mm) due decreased abundance of smaller scallops and increased abundance of large scallops (Figure 4). The length distribution plots indicated poor recruitment in recent years.
Changes is overall relative length distribution is observed on the most important individual fishing grounds. While the annual mean shell height in Bjarneyjar did not fluctuate as much as in other areas (Figure 5), the annual mean shell height in Breiðasund increased from 2014 (69.6 mm) to 2024 (74.5 mm). The annual mean shell height in Flatey increased from 2014 (71.5 mm) to 2024 (79.6 mm). The annual mean shell height in Hvammsfjörður increased from 2014 (63.9 mm) to 2024 (77.6 mm) where few scallops were found smaller than the mean annual shell height in 2024. The annual mean shell height in Látralönd increased from 2014 (70.5 mm) to 2019 (74.0 mm), there was no sampling in Látralönd in 2024. The annual mean shell height in Rúfeyjar increased from 2014 (74.8 mm) to 2024 (78.4 mm). The length distribution plots indicated poor recruitment in recent years in all grounds, except Rúfeyjar, sampled in 2024.
Stock assessment
Survey biomass index model
The biomass estimate is based on the numerical estimates obtained from the camera survey/dredge survey. The density of scallops per 0.1 m2 was modeled with a spatial generalized additive model (GAMM) that uses spatial Gaussian Markov random fields using the sdmTMB package (Anderson et al. 2024). It was assumed that the response variable followed a tweedie distribution with a log-link. Depth and year were the explanatory variables.The model was fit to a triangulated barrier mesh to account for the numerous islands in Breiðafjorður. A regularized prediction grid was constructed with 100m intervals. An estimate of depth was assigned to each point using a depth model of Breiðafjorður. One hundred simulations to predict scallop density were run and the mean and 95% confidence intervals for the density estimate at each point on the prediction grid were calculated from the simulations.
Fishable biomass \(FB\) for each scallop ground \(b\) in each year \(y\) was:
\[FB_{b,y} = \bar{D}_{b,y}A_{b}\bar{W}_{b,y}Pr_{60}\] where \(\bar{D}\) is the average density, \(A\) is the size of the scallop bed, \(\bar{W}\) is the average weight of scallops in that bed, and \(Pr_{60}\) is the proportion of the catch over the minimum harvest size of 60 mm.
While Iceland scallops are relatively immobile post settlement, they experience a pelagic larval phase. Thus it is assumed that the scallop grounds in Breiðafjorður constitute a single biological stock. Therefore, the total fishable biomass of the stock is the sum of the annual biomass of each of the six scallop grounds.
The assessment indicates that Iceland scallop stock in Breiðafjörður is at a historic low. Biomass index at each fishing ground indicates that fishable biomass declined at all fishing grounds except Breiðasund between the 2019 and 2024 surveys (Figure 6). These declines follow a downward biomass trend since recent historic peak of 2015.
The application of rfb-rule
- r is calculated as the average of last two years values, divided by average of three preceding years values which results in r = 0.895 (Figure 7). As there was no survey from 2020 to 2023, linear interpolation was used to generate the biomass estimates for the missing years.
- f is the length-based fishing pressure proxy. The mean length from catches in 2024 that are above Lc was 81 mm and the target reference length was 78 mm (Figure 8 and Figure 9). This resulted in a value of f\(^{-1}\) = 1.034, and f = 0.967.
b is the biomass safeguard and is used to reduce catch advice when index falls below the threshold Itrigger. The lowest observed index for Iceland scallop was in 2024, the terminal year of the assessment. Therefore, Iloss for Iceland scallop is 6009, the second lowest year (2014), therefore, Itrigger = 1.4 * 6009 (Figure 7). The biomass index in 2025 was 5153, which is below Itrigger leading to b = 0.61.
m is the tuning parameter and for slow growing species (with von Bertanlaffy K < 0.2), m equals to 0.95.
Management
The Ministry of Food, Agriculture and Fisheries is responsible for the management of Icelandic fisheries and the implementation of legislation. Throughout the period 1993–2000, the total allowable catch (TAC) in Breiðafjörður was relatively stable at about 8000–8500 tonnes (Figure 3). At that time, the recommended annual TAC was 10% of the total estimated biomass from dredge surveys; since 1994, the national TAC and the landings have been in accord with the recommendations. Between 2003 and 2013 the MRI advised that no fishery should be conducted on scallop grounds in Breiðafjörður. In 2014 the advice was no fishery on conventional grounds, but small- scale fishing experiments were allowed in areas outside the limits of the dredge survey. The same advice has been given in 2015–2019 and fishing trials continued, mainly on new grounds, but later also on traditional grounds where scallops were found in fishable quantities. The experimental fishery ended in the 2019/2020 quota year. Since then, a small quota has been issued only for the southern grounds because poor recruitment was observed in the northern grounds. The quota was reduced by 20% for the 2023/2024 quota year as a precautionary measure due to the uncertainty regarding the stock status. As there was no new assessment available last year, the quota was maintained.
References
Anderson, S. C., Ward, E. J., English, P. A., Barnett, L. A. K., & Thorson, J. T. (2024). sdmTMB: An R package for fast, flexible, and user-friendly generalized linear mixed effects models with spatial and spatiotemporal random fields [Preprint]. bioRxiv. https://doi.org/10.1101/2022.03.24.485545
ICES. 2025. “ICES Guidelines - Advice rules for stocks in category 2 and 3,” February. https://doi.org/10.17895/ices.pub.28506179.v2.
Jonasson, J.P., Thorarinsdottir, G., Eiriksson, H., Solmundsson, J., Marteinsdottir, G., 2007. Collapse of the fishery for Iceland scallop in Breidafjordur, West Iceland. ICES J. Mar. Sci. 64, 298-308
Comments on the assessment and Advice
Following ICES guidelines for data-limited stocks (ICES, 2025), the ICES rfb-rule was utilized for the assessment of Iceland scallop in 2025. The method incorporates life-history traits, exploitation characteristics, and other relevant parameters for data-limited stocks into an empirical assessment rule (ICES, 2025). The rfb-rule has the following form:
\[A_{y + 1} = A_{y}rf^{-1}bm\] where Ay+1 is the advised catch, Ay is the current advice (issued in the previous year).The parameter r corresponds to the rate of change in the biomass index (the ICES “2 over 3” rule), f is a length-based proxy for the exploitation level (an MSY reference length divided by the mean catch length), and b is a biomass safeguard (reducing the catch when the biomass index drops below a trigger value).
The parameter r is calculated by dividing the mean of the last two survey index (I) values by the mean of the three preceding survey index values:
\[r = \frac{\sum_{i = y - 2}^{y - 1}\left( I_{i}\text{/}2 \right)}{\sum_{i = y - 5}^{y - 3}\left( I_{i}\text{/}3 \right)}\]
The length-based fishing pressure proxy f is calculated as follows:
\[f = \frac{L_{F = M}}{{\overline{L}}_{y - 1}}\]
where \({\overline{L}}_{y - 1}\) is the mean length in the survey that is above the length at first capture (Lc). The length at first capture is defined as the length at 50% of modal abundance (Figure 8). The target reference length (\(L_{F = M}\)) is the expected mean length when fishing at MSY and is calculated via:
\[L_{F = M} = 0.75L_{c} + 0.25L_{\infty}\]
where Lc is the length at first capture (see above) and L∞ is von Bertalanffy growth parameter. This assumes that the ratio \(M/K\) is equal to 1.5.
The biomass safeguard b is used to reduce catch advice when the index falls below a threshold denoted by Itrigger:
\[b = \min\left\{ 1,\frac{I_{y}}{I_{trigger}} \right\}\,\]
where Itrigger = 1.4Iloss, and Iloss is the lowest observed index value (Figure 7). As the terminal year of the assessment was the lowest index value, the second lowest index value was used for Iloss. Note that b cannot exceed a value of 1.
The multiplier m is based on stock growth. The von Bertalanffy growth parameter K for Iceland scallop is 0.139 (Jonasson et al. 2007) which is less than 0.2, therefore m = 0.95 (ICES, 2025).
Analysis of the assessment and advice
The assessment is based on the rfb-rule for ICES category 3 data-limited stocks. The fishable biomass estimated from the drop camera survey was used as the index for the stock development. The advice follows the equation outlined above (Ay+1 = Ay rfbm), and with parameter values inserted, Ay+1 = 75 * 0.895 * 1.034 * 1 * 0.95. The advice for the fishing year 2025/2026 is 40 t in Breiðasund, which is a -46% less than the previous year (75 t). Further it is advised that only Iceland scallops larger than 60 mm in shell height be landed.