Overview of marine mammal and seabird bycatch in Icelandic fisheries
Executive summary
Bycatch of marine mammals has been observed in gillnet and trawl fisheries in the last 5 years. The highest bycatch rates were of harbour porpoises in cod gillnets, and of harbour seals and grey seals in lumpsucker gillnets.
Bycatch of seabirds has been observed in gillnet fisheries, longline fisheries, and midwater trawls. The vast majority of bycatch was in lumpsucker gillnets, followed by longlines and cod gillnets.
The most bycaught marine mammal was the harbour porpoise, which was caught in both cod and lumpsucker gillnets. The annual estimated bycatch of porpoises is around 700 animals. The harbour seal was the second most bycaught animal, caught in lumpsucker gillnets, with an estimated annual bycatch of around 500 animals.
The most bycaught seabird was the eider duck, which was only caught in lumpsucker gillnets, with an annual estimated bycatch of 2 245 birds, followed by the common guillemot, caught in both cod and lumpsucker gillnets, with an annual estimated bycatch of around 1 900 birds.
Bycatch of harbour seals needs to be closely monitored, as the population is small and has been reduced by 80% due to direct hunting and culling since the 1980s. The population appears to be slowly recovering, and bycatch rates have dropped in the lumpsucker fishery; it is important to observe if that trend continues.
Bycatch of several bird species with small populations also warrants further monitoring and research. Estimated bycatch of black guillemots is high, given that their population status is uncertain and based on limited data. Estimated bycatch of common loons warrants further investigation, given the small population of this species in Iceland
Introduction
Bycatch of marine mammals, seabirds, and sensitive fish is a worldwide problem and the main source of mortality for some species groups, such as cetaceans globally (Reeves et al. 2013). Iceland, home to a wide variety of marine mammal and seabird species, is no exception.
In Iceland, bycatch in the gillnet fishery for lumpsucker has received most of the attention due to high bycatch rates of both seals and seabirds. Two technical reports, published in (2019) and (2024) have covered that fishery in detail and the summaries of that work are presented in this text.
Bycatch in other fishing gear has not received the same attention, although it has been covered in some detail through the work of the ICES Working Group on Bycatch (WGBYC). Recent developments within that working group have now led to estimates being available for some fishing gears in Icelandic waters, and these estimates are therefore reported here for the first time. A detailed description of the process and methodology behind those estimates can be found in the working group’s report (here)
Reporting of all bycatch of seabirds and marine mammals is mandatory in vessel logbooks according to (Regulation 307/2023). Although all self-reported datasets require certain scrutiny, they can provide additional information, and are reported in this report as an additional source of information.
In this report, all available information on bycatch of marine mammals and seabirds in Icelandic waters is collated. The goal is to provide a holistic overview of the issue in Icelandic waters, along with providing available estimates of bycatch and registered bycatch in logbooks by the fleet.
Description of the datasets
Bycatch estimates for lumpsucker gillnets are based on onboard observations by inspectors from the Directorate of Fisheries (Fiskistofa) between 2020 and 2023. A detailed description can be found in the technical report (here). Bycatch estimates in other gears, as estimated by ICES WGBYC, are based on onboard observations by inspectors from the Directorate of Fisheries (Fiskistofa) between 2017 and 2023 and, in the case of cod gillnets, supplemented by observations in the annual MFRI gillnet survey for cod over the same time period. Reported bycatch from vessel logbooks is presented as received from the Directorate of Fisheries for the 2023 calendar year, although some obvious errors or test reports have been removed.
Methodology for bycatch estimates with precision
For most species/gear combinations, we follow the Bycatch Evaluation and Assessment Matrix (BEAM) data screening and modeling methodology developed within the ICES Working Group on Bycatch (WGBYC). The methodology involves a screening procedure to evaluate the various inputs needed for full quantitative assessments of the population impacts of fisheries bycatch. Criteria considered by BEAM are: 1) BPUE (bycatch per unit effort) quality and analysis, 2) fishing effort data availability, 3) bycatch estimation, and 4) population abundance estimate availability. With regards to the application of criterion 3, only estimated numbers of specimens taken as bycatch are considered. The applied BEAM methodology is scheduled to be benchmarked at the end of 2025 within ICES.
For the estimates of bycatch in the lumpsucker fishery, a ratio-based estimate was used, where observed bycatch per trip is multiplied by the total number of fishing trips in each lumpsucker fishing area. A coefficient of variation (CV) is then calculated around the estimate using a bootstrapping method. A more thorough description can be found (here).
Marine mammal bycatch estimates with precision
The most commonly bycaught marine mammal was the harbour porpoise (Phocoena phocoena) (Figure 1), which is caught in both cod and lumpsucker gillnets. The estimated bycatch of porpoises in these two fisheries is around 800 animals annually. The harbour seal (Phoca vitulina) was the second most common animal bycaught, only in the lumpsucker gillnets, where around 500 animals are estimated to be bycaught annually. Grey seals (Halichoerus grypus) were the third most common animal observed bycaught, with an estimated 160 animals bycaught annually. Harp seals (Pagophilus groenlandicus), ringed seals (Pusa hispida), and white-beaked dolphins (Lagenorhynchus albirostris) were also observed as bycatch, though their estimated numbers are much lower.
Seabird bycatch estimates with precision
The most commonly bycaught seabird was the eider duck Somateria mollissima (Figure 2), primarily caught in lumpsucker gillnets. The estimated bycatch of eiders in this fishery is around 2 300 animals annually. The common guillemot Uria aalge was the second most common bird bycaught, caught in similar numbers in both the lumpsucker and cod gillnets, with an estimated 1 800 animals annually. Black guillemots Cepphus grylle were the third most common seabird observed as bycatch, with an estimated 1 500 birds annually. Among other species, fulmars Fulmarus glacialis were caught in somewhat high numbers in the longline fishery, with an estimated 800 bycaught annually, although uncertainty around this estimate is high.
Reported marine mammal bycatch by the fishing fleet
A total of 462 marine mammals were reported by the fishing fleet in 2023. Most marine mammals (423) were reported in the lumpsucker gillnet fishery. The number of species reported (9) was higher than observed by the onboard inspectors used to calculate bycatch estimates with precision.
Table 1. Numbers of marine mammals reported by the fishing fleet in 2023.
| Fishing gear | Species | # individuals reported |
|---|---|---|
| Gillnets (lumpsucker) | Harbour seal (Phoca vitulina) | 157 |
| Gillnets (lumpsucker) | Harbour porpoise (Phocoena phocoena) | 117 |
| Gillnets (lumpsucker) | Grey seal (Halichoerus grypus) | 47 |
| Gillnets (lumpsucker) | Unidentified seal (Phocidae) | 60 |
| Gillnets (lumpsucker) | Ringed seal (Pusa hispida) | 20 |
| Gillnets (lumpsucker) | Harp seal (Pagophilus groenlandicus) | 16 |
| Gillnets (lumpsucker) | White-beaked dolphin (Lagenorhynchus albirostris) | 3 |
| Gillnets (lumpsucker) | Common dolphin (Delphinus delphis) | 2 |
| Gillnets (lumpsucker) | Bearded seal (Erignathus barbatus) | 1 |
| Demersal trawl | Grey seal (Halichoerus grypus) | 1 |
| Demersal trawl | Unidentified medium sized whale | 1 |
| Gillnets (cod) | Harbour porpoise (Phocoena phocoena) | 30 |
| Gillnets (cod) | Harbour seal (Phoca vitulina) | 5 |
| Gillnets (cod) | Grey seal (Halichoerus grypus) | 1 |
| Handline | Common dolphin (Delphinus delphis) | 1 |
Reported seabird bycatch by the fishing fleet
A total of 3542 seabirds were reported by the fishing fleet in 2023. Similar to marine mammals, most seabirds (2423) were reported in the lumpsucker gillnet fishery. Around 1100 birds were reported in the longline fishery, with fewer in other fisheries. The number of species reported (17) was similar to the number of species observed by onboard inspectors used to calculate bycatch estimates with precision, although not always the same species. For example, several gull species were reported in logbooks that were not observed by inspectors
Table 2. Numbers of seabirds reported by the fishing fleet in 2023.
| Fishing gear | Species | # individuals reported |
|---|---|---|
| Gillnets (lumpsucker) | Eider (Somateria mollissima) | 953 |
| Gillnets (lumpsucker) | Black guillemot (Cepphus grylle) | 635 |
| Gillnets (lumpsucker) | Cormorants (Phalacrocorax carbo and Phalacrocorax aristotelis) | 424 |
| Gillnets (lumpsucker) | Common guillemot (Uria aalge) | 302 |
| Gillnets (lumpsucker) | Puffin (Fratercula arctica) | 17 |
| Gillnets (lumpsucker) | Brünnich’s guillemot (Uria lomvia) | 8 |
| Gillnets (lumpsucker) | Razorbill (Alca torda) | 8 |
| Gillnets (lumpsucker) | Long-tailed duck (Clangula hyemalis) | 6 |
| Gillnets (lumpsucker) | Common loon (Gavia immer) | 5 |
| Gillnets (lumpsucker) | Northern fulmar (Fulmarus glacialis) | 5 |
| Gillnets (lumpsucker) | Red throated loon (Gavia stellata) | 3 |
| Gillnets (lumpsucker) | Northern gannet (Morus bassanus) | 2 |
| Gillnets (lumpsucker) | Kittiwake (Rissa tridactyla) | 1 |
| Gillnets (lumpsucker) | Alcids (Alcidae) | 36 |
| Gillnets (lumpsucker) | Unidentified birds (Aves) | 18 |
| Gillnets (cod) | Alcids (Alcidae) | 16 |
| Longline | Northern fulmar (Fulmarus glacialis) | 1 000 |
| Longline | Great black-backed gull (Larus marinus) | 32 |
| Longline | Northern gannet (Morus bassanus) | 31 |
| Longline | Lesser black-backed gull (Larus fuscus) | 19 |
| Longline | Herring gull (Larus argentatus) | 9 |
| Longline | Glaucous gull (Larus hyperboreus) | 3 |
| Longline | Kittiwake (Rissa tridactyla) | 3 |
| Longline | Black guillemot (Cepphus grylle) | 1 |
| Longline | Alcids (Alcidae) | 3 |
| Longline | Unidentified seagulls (Larus spp.) | 2 |
Population status of bycaught marine mammal species
The population of harbour porpoises in Icelandic waters has been estimated using two different methods. In 2007, (survey) estimated the population around 43 000 animals around the country. Due to the difficulties and costs associated with such surveys, it has not been repeated since. The second method uses close-kin mark-recapture genetics (Babyn et al 2024), which estimates relative population size based on the probability of detecting parent-offspring pairs in a dataset. This method was applied over two time periods. 1991–2000 and 2011–2018, using samples from bycaught and stranded animals. The results of this analysis suggest that the harbour porpoise population has doubled in number between these time periods (NAMMCO 2019), likely due to a lower bycatch risk as gillnet effort has reduced considerably since around mid 2000s. Bycatch levels are currently likely well within the biological tolerances of the species, but this could change if gillnet effort increases in the future (see Fisheries overview
The population of harbour seals around Iceland has been monitored with regular aerial surveys since 1980. In the latest survey conducted in (2020), the estimated population size was 10 319 animals. This estimated population size was approximately 9% larger than in 2018 but 69% smaller than when the population was first assessed in 1980. Most of the population decline can be attributed to systematic culling and bounty programs aimed at reducing the population size, which lasted until the 2000s. Direct hunting of seals was banned in 2019 (Regulation 1100/2019), and bycatch in the lumpsucker fishery has reduced considerably. Regular monitoring of both the population and bycatch levels is recommended due to the size of the population and the considerable bycatch numbers observed in the past.
The Icelandic grey seal population has been assessed regularly since 1982. The population size is estimated based on aerial counts of pup production. Based on pup production, the total grey seal population size in (2022) was estimated to be 6 697 animals. The population was estimated to be 27% smaller than the first estimate in 1982 but corresponds to an increase of 6.8% since the 2017 estimate. Regular monitoring of both the population and bycatch levels is recommended due to the size of the population and the considerable bycatch numbers observed in the past.
The white-beaked dolphin population around Iceland is considered very large, estimated at around 160 000 animals (Pike et al. 2019), and the low bycatch numbers observed are unlikely to affect the population.
The three species of Arctic seals that were observed bycaught, harp seals, ringed seals, and bearded seals are all considered vagrants in Icelandic waters and are part of large populations to our north. These low bycatch levels are unlikely to affect the populations of these species in the region.
Population status of bycaught seabird species
Population assessments of seabirds are not conducted by the MFRI. The Icelandic Institute of Natural History (website) is responsible for monitoring and assessment of these species in Icelandic waters. The best available population estimates are published in the (Icelandic Red list for birds), even though the information is in some cases quite outdated
Out of the species most commonly bycaught, eider ducks are considered vulnerable on the Red List due to a 20–25% decline over the last three generations. It is, however, still a large population of approximately 850 000 birds. Further investigation into the possible impacts of bycatch on the population is perhaps warranted if this trend continues.
Common guillemots are also considered vulnerable due to a 30% decline over the last three generations. Like the eider, it is still a very large population of around 1.3 million birds, and the bycatch numbers observed are unlikely to affect the population. This species is also hunted, so cumulative mortality has to be considered.
Black guillemots were the third most commonly bycaught species and are also considered endangered on the Red List. Unlike eiders and common guillemots, the population of black guillemots around Iceland is considered small, and there is high uncertainty surrounding the estimate of 20 000–30 000 birds due to difficulties in surveying the birds. Bycatch likely has or had an effect on the population, especially when combined with direct hunting which was banned in 2017.
Fulmars were the fourth most commonly bycaught species and are considered endangered on the Red List due to a sharp population decline in recent years. The population is still large, over 1.2 million birds, and bycatch on its own is unlikely to explain the decline.
Other species were caught in smaller numbers, and for the most part, bycatch is unlikely to affect their populations, with a few exceptions. Estimated bycatch of common loons warrants further investigation, given the small population of this species in Iceland. The Red List listing and population estimates of all the species observed as bycatch can be found in the table below.
Table 3. IUCN conservation status, and best available population estimate as published by the Icelandic Institute of Natural History of all seabird species that were observed bycaught.
| Species | Red list criteria | Population estimate |
|---|---|---|
| Eider | Vulnerable | 850 000 |
| Common guillemot | Vulnerable | 1 200 000 |
| Black guillemot | Vulnerable | 20 000–30 000 |
| Northern fulmar | Endangered | 1 200 000 |
| Northern gannet | Vulnerable | 80 000 |
| Cormorants (Great cormorant and common shag) | Least concern/vulnerable | 9 162/11 600 |
| Herring gull | Near threatened | 5 000–10 000 |
| Brünnich’s guillemot | Near threatened | 654 000 |
| Lesser black-backed gull | Data deficient | 100 000 |
| Long-tailed duck | Near threatened | 110 000 |
| Razorbill | Near threatened | 626 000 |
| Common loon | Vulnerable | 600 |
| Puffin | Critically endangered | 4 000 000 |
| Kittiwake | Vulnerable | 1 160 000 |
| Red throated loon | Least concern | 1 000–2 000 |
| Greater black-backed gull | Critically endangered | 12 000–16 000 |
| Glaucous gull | Endangered | 4 800 |
Appendix 1 - Tables of estimated bycatch
Table 4. Bycatch of marine mammals estimated with the ICES WGBYC BEAM data screening and modelling methodology. Number of individuals refers to the number of individuals observed by onboard inspectors or MFRI staff in 2017-2023, BPUE for bycatch per unit effort, and total annual bycatch number of animals estimated to be taken as bycatch by that fishery annually. Lower and upper refer to 95% confidence intervals.
| Fishing gear | Species | # individuals observed | BPUE (lower-upper) | Total annual bycatch (lower-upper) |
|---|---|---|---|---|
| Gillnets (cod) | Harbour porpoise (Phocoena phocoena) | 254 | 0.207 (0.063–0.685) | 559 (312–1 033) |
| Gillnets (cod) | White-beaked dolphin (Lagenorhynchus albirostris) | 4 | 0.004 (0.001–0.018) | 7 (2–35) |
| Gillnets (cod) | Harp seal (Pagophilus groenlandicus) | 31 | 0.036 (0.002–0.088) | 61 (24–153) |
| Gillnets (cod) | Ringed seal (Pusa hispida) | 3 | 0.003 (0.001–0.011) | 5 (1–21) |
| Otter trawl | Harp seal (Pagophilus groenlandicus) | 1 | 0.001 (0.001–0.003) | 3 (1–18) |
Table 5. Bycatch of marine mammals in the lumpsucker gillnet fishery. Total bycatch is estimated using standard raising by effort method, stratified by lumpsucker fishing area. Number of individuals refers to the number of individuals observed by onboard inspectors in 2020-2023, and total annual bycatch number of animals estimated to be taken as bycatch in that fishery annually. Bootstrapped CV is shown in brackets
| Fishing gear | Species | # individuals observed | Total annual bycatch (CV) |
|---|---|---|---|
| Gillnets (lumpsucker) | Harbour seal (Phoca vitulina) | 46 | 501 (43) |
| Gillnets (lumpsucker) | Grey seal (Halichoerus grypus) | 12 | 159 (83) |
| Gillnets (lumpsucker) | Harbour porpoise (Phocoena phocoena) | 11 | 108 (62) |
Table 6. Bycatch of seabirds estimated with the ICES WGBYC BEAM data screening and modelling methodology in all fishing gear except lumpsucker gillnets. Number of individuals refers to the number of individuals observed by onboard inspectors or MFRI staff in 2017-2023, BPUE for bycatch per unit effort, and total annual bycatch number of animals estimated to be taken as bycatch by that fishery annually. Lower and upper refer to 95% confidence intervals.
| Fishing gear | Species | # individuals observed | BPUE (lower-upper) | Total annual bycatch (lower-upper) |
|---|---|---|---|---|
| Gillnets (cod) | Common guillemot (Uria aalge) | 643 | 0.558 (0.318–0.977) | 984 (587–1 647) |
| Gillnets (cod) | Northern fulmar (Fulmarus glacialis) | 14 | 0.013 (0.005–0.289) | 25 (11-57) |
| Gillnets (cod) | Brünnich’s guillemot (Uria lomvia) | 10 | 0.009 (0.003–0.028) | 18 (6–55) |
| Gillnets (cod) | Northern gannet (Morus bassanus) | 6 | 0.006 (0.003–0.013) | 11 (5–25) |
| Gillnets (cod) | Red-throated loon (Gavia stellata) | 1 | 0.001 (0.001–0.007) | 2 (1–13) |
| Longlines | Northern fulmar (Fulmarus glacialis) | 146 | 0.056 (0.008–0.0371) | 763 (115–5040) |
| Longlines | Northern gannet (Morus bassanus) | 25 | 0.039 (0.009–0.017) | 534 (123–2316) |
| Longlines | Lesser black-backed gull (Larus fuscus) | 5 | 0.011 (0.002–0.073) | 152 (23–992) |
| Midwater trawl | Common guillemot (Uria aalge) | 2 | 0.007 (0.001–0.050) | 133 (18–1 009) |
Table 7. Bycatch of seabirds in the lumpsucker gillnet fishery. Total bycatch is estimated using standard raising by effort method, stratified by lumpsucker fishing area. Number of individuals refers to the number of individuals observed by onboard inspectors in 2020-2023, and total annual bycatch number of animals estimated to be taken as bycatch in that fishery annually. Bootstrapped CV is shown in brackets
| Fishing gear | Species | # individuals observed |
|---|---|---|
| Gillnets (lumpsucker) | Eider (Somateria mollissima) | 217 |
| Gillnets (lumpsucker) | Black guillemot | 143 |
| Gillnets (lumpsucker) | Common guillemot (Uria aalge) | 87 |
| Gillnets (lumpsucker) | Cormorants (Phalacrocorax carbo and Phalacrocorax aristotelis) | 33 |
| Gillnets (lumpsucker) | Long-tailed duck (Clangula hyemalis) | 5 |
| Gillnets (lumpsucker) | Brünnich’s guillemot (Uria lomvia) | 5 |
| Gillnets (lumpsucker) | Northern fulmar (Fulmarus glacialis) | 4 |
| Gillnets (lumpsucker) | Razorbill (Alca torda) | 3 |
| Gillnets (lumpsucker) | Puffin (Fratercula arctica) | 1 |
| Gillnets (lumpsucker) | Kittiwake (Rissa tridactyla) | 1 |
| Gillnets (lumpsucker) | Northern gannet (Morus bassanus) | 1 |
| Gillnets (lumpsucker) | Common loon (Gavia immer) | 1 |