Nature Conservation Advice from NatureScot and JNCC: Demersal Fisheries Management Plans

3 Risks relating to the designated features of MPAs in Scottish waters

Marine Protected Areas (MPAs) in Scottish waters include Special Areas of Conservation (SACs) and Special Protection Areas (SPAs) which are protected under the Conservation of Habitats and Species Regulations 2017 and the Conservation of Offshore Marine Habitats and Species Regulations 2017, collectively referred to as the Habitats Regulations. Additionally, Nature Conservation Marine Protected Areas (NCMPAs) are designated and protected by the Marine (Scotland) Act 2010 and Marine and Coastal Access Act 2009. Impacts of activities are assessed against the conservation objectives of MPAs, and activities should not have an adverse effect on the integrity of SACs or SPAs and should not hinder the achievement of conservation objectives of NCMPAs.

Fisheries within the Demersal FMPs can potentially impact MPA designated features in 3 main ways:

(iv) through the bycatch of designated features of MPAs

(v) the direct (targeted) and indirect (bycatch) removal of prey species on which designated species depend, and

(vi) physical impacts to seafloor resulting in alterations to habitat feature or supporting habitat condition.

These impacts can affect the designated features of MPAs both inside and outside the boundaries of MPAs.

Assessment of the impact of fishing activity occurring within MPAs in Scottish waters has been carried out by the Marine Directorate of the Scottish Government. Management measures for relevant fishing activities within MPAs have been implemented or are in development, to ensure any fishing within MPAs is compatible with the MPA’s conservation objectives. Therefore, the existing assessment and management pathways mitigate risks arising from fishing activity within Scottish MPAs, and no additional action is suggested for the Demersal FMPs within Scottish MPA site boundaries at this time. Pressures occurring within MPAs have therefore been screened out of this advice. However, potential risks to designated mobile species from bycatch and removal of prey species may remain when they move outside of the MPA. This advice therefore focusses on risks to mobile MPA features from demersal fishing activities occuring outside MPA boundaries.

3.1 Impacts to designated features outside MPA boundaries

The potential for fishing activities outside of MPAs to impact designated features, particularly mobile species that move beyond the protections of MPA boundaries, necessitates broader management consideration.

3.1.1 Risk of bycatch to mobile MPA features from demersal fishing

Much of the evidence presented below comes from the UK bycatch monitoring programme (BMP). The BMP monitors the levels of bycatch in certain fisheries, gear types and areas and extrapolates the data where appropriate to give an indication of the scale of overall bycatch levels (Kingston et al., 2021). The fisheries monitored are nets, pelagic trawls, longlines, and ring nets, as these are currently considered to present the greatest risk.

In general, the findings from the BMP should be considered alongside the caveats of the programme, for example current bycatch estimates will likely underestimate bycatch from larger offshore vessels yet overestimate it for smaller inshore vessels (Kingston et al., 2021).

3.1.1.1 Risk to marine mammals

There are seven marine mammal species designated as features within Scottish MPAs: harbour porpoise, bottlenose dolphin, Risso’s dolphin, minke whale, grey seal, common seal, and otters. Otters, primarily associated with terrestrial SACs and coastal habitats, are excluded from this advice due to their minimal interaction with the relevant demersal gears.

Demersal trawls and seines

Marine mammals, including harbour porpoise, minke whales, Risso’s dolphins, grey and common seals, featured in Scottish MPAs, face a limited risk of bycatch in demersal trawls and seines. Historically, these gear types have not been included in the UK Bycatch Monitoring Programme's sampling regime due to the perceived lower risk compared to static nets or longlines. Incidents of harbour porpoise bycatch, though not common, have been recorded (CEFAS, 2015), but the infrequency of such events suggests a limited impact on the overall population status within MPAs. However, there is a value in continued or expanded monitoring, whether via enhanced observer coverage or remote electronic monitoring, to further refine risk assessments and strengthen mitigation for marine mammals.

Static nets

Static nets pose a high bycatch risk to marine mammal species and are considered one of the gear groups responsible for the highest level of marine mammal bycatch in UK waters (Sewell & Hiscock, 2005; Moore et al., 2021). They are considered the greatest threat to harbour porpoise populations (Vinther & Larsen, 2004). In 2020, bycatch in UK gillnet fisheries was estimated between 703 and 901 for harbour porpoise depending on ADD compliance and as 356 for seals (Kingston et al., 2021). The approximate bycatch values in Scottish waters (ICES areas 7a, 6b, 4a and 4b) were estimated between 24 and 64 for harbour porpoise, and 49 for seals, reflective of lower gillnetting effort in Scottish waters.

For seals, static nets are the primary source of bycatch mortality. Seals are particularly vulnerable as they are often found in coastal waters where these gears are used.

Although there were no records of bycatch in the BMP over the 2017-2020 period, bottlenose dolphin, Risso’s dolphin and minke whale strandings analysed by the Scottish Marine Animal Strandings Scheme and the UK Cetaceans Strandings Investigation Programme highlight bycatch/entanglement as a common cause of death. These mortalities cannot easily be attributed to active fishing with static nets, but they do indicate a sensitivity to bycatch in static gears. Due to their long lifespans and slow reproductive rates, marine mammals are particularly vulnerable to increases in mortality, such as that caused by static net entanglement. Even a modest rise in deaths among these animals could lead to significant declines in localized populations. Bycatch rates in static nets are much higher than trawls.

Longlines

The risk to marine mammals is expected to be low. In the 2017 to 2020 BMP bycatch recordings by gear type, longlines did not contain any marine mammal bycatch. Generally, the removal of non-target species, especially birds, is considered the highest risk to biodiversity by longline fisheries (Miles et al., 2020).

3.1.1.2 Risk to seabirds

Demersal trawls and seines

Demersal trawls and seines represent a bycatch risk for seabirds, particularly for diving species susceptible to entanglement. Current bycatch levels have not been shown to significantly impact seabird populations or the integrity of Special Protection Areas (SPAs). However, the limited data calls for an enhancement of the bycatch monitoring regime to capture a clearer picture of the risks these gears pose to seabirds.

39 of the 109 UK SPA species and subspecies are seabirds that could potentially be affected by benthic trawling. Historical data and studies point to species such as deep diving shags, scaups, eiders, and cormorants being most vulnerable to this fishing method (CEFAS, 2015; Bradbury et al., 2017). Although the focus of recent research, such as Northridge et al. (2020), reflects the perception that benthic trawling is less risky than set nets or longlines, the existing data gaps on the bycatch exposure of sensitive seabirds warrant caution (Anderson et al., 2022).

Given the current evidence, the risk of significant seabird bycatch affecting population levels or SPA conditions is assessed as low. Nevertheless, improving monitoring through adaptations to existing observer programmes or implementing remote electronic monitoring is advisable to reduce uncertainty.

The bycatch risk to seabirds from demersal seines is assumed to be on par with demersal trawls, especially during hauling when the gear surfaces. However, the risk of bycatch during the sweeping phase might be lower in demersal seines than in trawls due to operational differences such as the use of ropes and the configuration of nets less prone to entrapment. Despite this, there remains a need for additional research to improve our understanding and improve confidence in our assessments.

Static nets

The foraging behaviours of seabirds, including pursuit diving and benthic feeding, make them more susceptible to mortality in gillnet fisheries compared to trawl fisheries; Annually, gillnet fisheries were estimated to result in over 400,000 bird deaths globally (Žydelis ^{et al., 2013)}. Gillnet fisheries pose a significant bycatch risk to diving seabirds in the UK (Cleasby et al., 2022); Species distribution models based on birds' diving behaviour identified areas of elevated bycatch risk where high levels of diving activity and fishing effort coincided. In coastal gillnet fisheries, seabird bycatch is a frequent occurrence, particularly when nets are deployed close to bird colonies, and in shallow waters (Forney et al., 2001).

In the UK, observer data collected between 1996 and 2018 indicates that guillemots have the highest bycatch rate across the gillnet fleet, with high bycatch rates for cormorants and razorbills in the under 10m fleet, and gannets, fulmars and gull spp. in the over 10m fleet. (Northridge at al., 2020). The angler/monk gillnet fishery in Scotland typically sets nets in deeper waters, out of seabird diving range and so the risks to seabirds are somewhat mitigated. However, these gears still present a risk to seabirds when setting and hauling.

Longlines

Between 1996 and 2018, 4 MPA protected marine bird species have been recorded as bycatch in UK offshore longline fisheries; northern fulmar, northern gannet, great black-backed gull, and black-legged kittiwake (Northridge et al., 2020). Over 90% of these captured birds were fulmars, and the majority were found to be deceased upon retrieval of the lines. In 2019, the BMP also recorded a single northern skua as bycaught in longline fisheries in Scottish waters.

The greatest risk of bycatch in longline fisheries occurs during setting and retrieval of the gear. A study by Rouxel et al. (2022) found that hooks from floated-demersal longlines are readily open to seabird attacks. The study estimated that up to 10,000 seabirds, including 2,600–9,000 fulmars could be bycaught each year by the UK’s hake longline fishery. In the 2019 BMP report, of the 101 recorded seabirds bycaught, 91 were attributed to longlines and 89 were fulmars.

In Scottish longline fisheries, observer notes and questionnaire survey results highlighted that seabird bycatch rates are highest in summer and in the more northern part of the fisheries range (Scottish Government, 2022). Bycatch rates may also be affected by the behaviour of the birds, the time of day the lines are set, and the prevailing weather conditions.

3.1.1.3 Risk to fish

Demersal trawls and seines

Demersal trawls and seines present a potential bycatch risk to certain fish species that are integral to the biodiversity of SACs and NCMPAs. Among these, Atlantic salmon, river lamprey, and sea lamprey spend critical parts of their lifecycle within coastal and marine waters protected by SACs in Scottish waters. Similarly, NCMPAs are designed to safeguard species like basking shark and flapper skate which utilise coastal habitats and likely overlap with fishing areas for a number of the targeted demersal fish species covered by the Demersal FMPs.

Flapper skate are considered vulnerable to bycatch impacts, owing to their slow growth, late age at maturity and site fidelity. Landings of flapper skate are prohibited. However, demersal trawls are known to take flapper as bycatch (adults, juveniles, and eggs) (STECF, 2017; Fox, 2010). Mitigation of bycatch risk is possible (e.g. the removal of tickler chains on trawls to reduce bycatch, Kynoch et al., 2015). For example, this measure in combination with temporal/spatial restrictions forms part of the management measures used in the Loch Sunart to the Sound of Jura MPA (Loch Sunart to the Sound of Jura Marine Conservation Order 2016).

Static nets

Reports of a single basking shark, 3 gulper shark, and 1416 skate listed as ‘common skate complex’ which includes blue and flapper skate, were recorded as bycatch in the gillnet fisheries sampled through the BMP over the 2017-2020 period. None of these bycatch incidences have occurred in Scottish waters. The high skate numbers are attributed to 3 trammel nets hauls on two separate trips in the southwest of the UK, which accounted for 1357 of these bycaught skate. Further evidence is required to downgrade a precautionary risk rating in the Scottish demersal fisheries.

Longlines

The Northern Shelf longline fishery for hake is considered to be quite specialised with limited bycatch of non-target fish species, with anecdotal evidence that bait choice can help to mitigate this impact. However, there is limited monitoring of bycatch for commercial species, including those fish and elasmobranch species designated as protected features of the West of Scotland MPA

3.1.1.4 Conclusions and recommendations relating to bycatch risk

While the risk to the conservation status of mobile species that are designated features of MPAs through bycatch from demersal trawls and seines is generally considered low, given the broad scale of the demersal fisheries covered in this assessment and the significant gaps in the available evidence, the risk rating for bycatch in demersal trawls and seines is assessed as moderate. Certain fish species such as the basking shark and flapper skate as well as several deep-water fish species, including elasmobranchs, may be at greater risk owing to their life histories. Continued or enhanced monitoring and research has the potential to improve our understanding of risk and is essential for directing management in relation to these more sensitive species.

Static nets and longlines, primarily associated with the hake and anglerfish fisheries, present a considerable bycatch risk for birds and other mobile species which are designated features of MPAs in Scottish waters. Bycatch in static nets is considered the greatest threat to harbour porpoise, and the primary source of bycatch mortality among seals. Gillnet fisheries pose a significant bycatch risk to diving seabirds such as common guillemots, razorbills, and European shags. There are also concerns about the seabird bycatch in the Scottish and UK offshore longline fisheries, with fulmars being particularly vulnerable to bycatch in this gear type. Based on current evidence, the risk rating for bycatch in static nets and longlines is considered high. This is primarily driven by risk of bycatch of marine mammals in gillnets and of birds in longlines. A continuation of current monitoring effort, supported by enhanced data collection and research to fill gaps is required to understand the scale of the problem and improve the ability to assess risk. This risk may be revisited in future as the evidence base develops.

3.1.2 Risk of prey depletion of important prey species to mobile MPA features from demersal fishing

Within the Demersal FMPs, some target species may also be considered as key prey species for marine mammals and birds, particularly small gadoids.

Harbour porpoise are generalist foragers, feeding primarily on small fish from both pelagic and demersal habitats (Santos and Pierce, 2003; IAMMWG, 2015). Recorded prey species include sandeels, gobies, various gadoids (whiting, pout, cod), clupeids (herring and sprat), and scad/horse mackerel (Santos and Pierce, 2003; Santos 2004; De Pierrepont 2005; Ransijn et al., 2019; Ransijn et al., 2021). Porpoise are shown to switch between prey species in response to changes in prey availability (Fryxell & Lundberg, 1994), indicating some flexibility in their diet and foraging strategies.

A study on the stomach contents of ten bottlenose dolphins stranded and by-caught around Scotland between 1990 and 1999 found that cod, saithe, and whiting were the main prey, along with other fish species including salmon and haddock, and cephalopods (Santos et al., 2001). This indicates that bottlenose dolphins in Scottish waters target a variety of prey but some of the demersal species listed in the Demersal FMPs may contribute significantly to their diet.

The diet of seals around Scotland, including both grey and harbour seals, shows considerable variation, consisting of gadoids (such as whiting and cod), sandeels, pelagic fish, like herring, and cephalopods. Studies highlight a broad dietary range that suggests flexibility and opportunistic feeding behaviours by seals, likely driven by the availability of prey species in their respective habitats.

Small gadoids also feature in the diets of several seabird species, including the European shag, the black-legged kittiwake and the common guillemot (Swann et al., 2008).

Given that marine mammal and seabird predators feeding on these species tend to have varied diets, the direct risk to mobile features of MPAs from reducing the availability of prey species' numbers might be relatively low, however, marine foodwebs are complex and poorly understood. Given the breadth and scale of fisheries included in the Demersal FMPs, it is possible, either through targeted fishing, bycatch or downstream impacts on spawning and recruitment, that there will be a reduction in the availability of juvenile gadoids and other prey species to marine predators designated within the Scottish MPA network. Seabirds in particular are likely to exhibit greater sensitivity to localised depletions in their key prey, owing to site dependency during the breeding season.

3.1.2.1 Conclusions and recommendations relating to prey depletion risk

Juvenile gadoids are an important component of the diet for a variety of marine predators and are thus considered a key forage fish species. Forage fish are essential to marine food webs, often serving as the primary food source for higher trophic levels, including marine mammals and seabirds. Given the breadth and scale of fisheries included in the Demersal FMPs, it is likely, either through targeted fishing, bycatch or downstream impacts on spawning and recruitment, that there will be a reduction in the availability of juvenile gadoids and other prey species to marine predators designated within the Scottish MPA network. Recognising a potential impact pathway but lacking sufficient evidence to provide a confident conclusion, we advise that the risk of prey depletion to designated features of MPAs from demersal fisheries be considered moderate. Work done by the Demersal FMPs to ensure fisheries eventually meet the precautionary and sustainability objectives of the Fisheries Act will help to ensure stocks are fished sustainably, but additional consideration of predator needs is recommended.

Certain fisheries are likely to present a greater risk than others, but further work is needed to help disentangle these risks. In the short-term improvements to achieve greater certainty in bycatch estimates would result from a more systematic approach to data collection, particularly large offshore demersal fisheries. This approach would also generate better understanding of the temporal and spatial patterns of bycatch estimates, and demographic information about which individuals are bycaught. This information could then be used to highlight species and areas most at risk and enable possible pilot area(s) for more focussed development of mitigation trials and monitoring to be identified with stakeholders.