Draft Fisheries Assessment – Norwegian Boundary Sediment Plain NCMPA: Fisheries management measures within Scottish Offshore Marine Protected Areas (MPAs)

3. Part B – Fisheries Assessment

3.1 Fisheries Assessment overview

Part B of this assessment considers if there would be a risk of the fishing activities identified in Part A, at the levels identified in the relevant date range, hindering the achievement of the conservation objectives for the NCMPA. This is in order to consider whether, and if so, which, management measures might be appropriate for the NCMPA, taking into account all relevant statutory obligations incumbent upon the Scottish Ministers.

The fishing activities and pressures identified in Part A which have been included for assessment in Part B, are demersal trawls and demersal seines, and the pressures abrasion/disturbance of the substrate on the surface of the seabed; penetration and/or disturbance of the substrate below the surface of the seabed, including abrasion; removal of non-target species, and smothering and siltation rate changes (light).

3.2 Fishing Activity descriptions

3.2.1 Existing management of fishing activity within the Norwegian Boundary Sediment Plain NCMPA

No existing fisheries restrictions were identified for the site.

3.2.2 Fishing Activity within the NCMPA

The Norwegian Boundary Sediment Plain NCMPA overlaps ICES rectangles 45F1 and 44F1 and sits within ICES Division 4a. The main gear types for UK vessels are demersal trawls and demersal seines.

The VMS-based estimates and ICES rectangle landings statistics indicate that vessels utilising demersal trawls are the predominant UK vessels that operated within the site over the period 2015-2019.

For the over-12 m vessels, based on the VMS data from 2015-2019, demersal trawls and seines occurred at low levels across the full site.

3.2.3 Demersal Trawls

The aggregated gear method of demersal trawls includes the multiple gears that operated within the Norwegian Boundary Plain NCMPA between 2015 and 2019. These include bottom otter trawls, multi-rig trawls, pair trawls, and other not specified bottom trawl types (Table 1).

The target species for these gear types are demersal fish and nephrops. Similar pressures are exerted by the different gears used for demersal trawling, subsequently the aggregated gear type of ‘demersal trawl’ was used to map activity across the site.

Based on the VMS, the highest intensity of demersal trawl activity within NCMPA occurs in the Northern region of the site, with activity peaking at 12-24 hours per year per grid cell of activity occurring per year between 2015-2019 (Figure 2). The majority of the site has lower fishing intensity (less than 12 fishing hours per year per grid cell).

Swept-Area Ratio (SAR) information averaged over the same time period shows similar levels of fishing intensity as the VMS data with low SAR values (cells swept less than once per year) shown across the full site (Figure 2).

3.2.4 Demersal Seines

Scottish Seine was the only seine gear type found to operate within the Norwegian Boundary NCMPA between 2015 and 2019 (Table 1). These seines target demersal fish.

Based on the VMS, demersal seine activity within Norwegian Boundary Sediment Plain NCMPA was evenly distributed across the full site, showing less than 12 hours per year per grid cell (Figure 3).

Swept-Area Ratio (SAR) information averaged over the same time period shows similar patterns of fishing intensity as the VMS data (Figure 3) with areas of low fishing intensity dispersed throughout the site, which were swept less than once between 2015-2019. The south-east corner of the site shows that the areas were swept one to two times on average throughout 2015-2019.

3.2.5 Summary of fishing activity within Norwegian Boundary Sediment Plain NCMPA

Evidence of demersal trawl activity and potential demersal seine activity were found to occur at very low intensity within the site. Both activities occurred across the full site.

3.3 Fishing activity effects overview

The following sections explore the impacts associated with demersal mobile (demersal trawl and seines) fishing activity within the Norwegian Boundary Sediment Plain NCMPA that were identified as potentially capable of impacting the protected features. The pressures considered in the following sections are:

• Abrasion/disturbance of the substrate on the surface of the seabed;
• Changes in suspended solids (water clarity),
• Penetration and/or disturbance of the substrate below the surface of the seabed, including abrasion;
• Removal of non-target species; and
• Smothering and siltation rate changes (light).

All five pressures, as exerted by demersal trawls and demersal seines were considered capable of impacting the Ocean quahog aggregations and the supporting Offshore subtidal sands and gravels features within Norwegian Boundary Sediment Plan NCMPA.

Given the similarity between ‘abrasion/disturbance of the substrate on the surface of the seabed’ and ‘penetration and/or disturbance of the substrate below the surface of the seabed’, these two pressures are considered together in the text below.

Information on the impacts of demersal trawls and demersal seines on the protected features is presented below and is informed by the JNCC and NatureScot Fisheries Management Guidance document for Arctica islandica, JNCC and NatureScot Fisheries Management Guidance document for Offshore subtidal sands and gravels, JNCC Marine Pressures-Activities Database v1.5 and Advice on Operations package for the site.

3.3.1 Summary of impacts associated of demersal mobile gear on Norwegian Boundary Sediment Plain NCMPA protected features

Towed bottom fishing gears (including demersal trawls and seines) are used to catch species that live in, on or in association with the seabed and therefore are designed to remain in close contact with the seabed. That interaction with the seabed can lead to disturbance of the upper layers of the seabed. As a relative comparison of gear types, otter trawls tend to have less physical impact on the seafloor than beam trawls (and dredges) with their heavy tickler chains, although the doors of an otter trawl do create recognisable scour of the seabed ((Hinz, Murray, Malcom, & Kaiser, 2012); (Polet & Depestele, 2010); (Lart, 2012);(Paschen, Richter, & Köpnick, 2000)). The magnitude of the immediate response to fishing disturbance, cumulative effects and recovery times varies significantly according to factors such as the type of fishing gear and fishing intensity, the habitat and sediment type, levels of natural disturbance and among different taxa ((Collie, Hall, Kaiser, & Poiner , 2000); (Boulcott, Millar , & Fryer, 2014);(Kaiser, et al., 2006); (Hinz, Prieto, & Kaiser, 2009); (Kaiser M. J., Collie, Hall, Jenning, & Poiner, 2003)).

There is some evidence that otter trawl doors may impact ocean quahogs by bringing them to the surface (Rumohr & Krost, 1991), however there is insufficient evidence to assess the mortality caused by this gear at a population level. The northern North Sea is primarily fished by otter trawls and ocean quahog does not appear to have declined to the same extent as seen in southern areas. However, ocean quahog within the NCMPA are currently considered to be in unfavourable condition.

As with demersal trawls and dredges, demersal seines may impact the structure and function of sedimentary habitats and the long-term survival of their associated species. There are currently no direct studies on the physical impacts of demersal seines. Modelling studies suggest that demersal seines have a large overall footprint (i.e. the surface area covered during one hour fishing) (Eigaard, et al., 2016). Hiddink, et al., (2018) suggest that depletion of biota is highly correlated with seabed penetration depth by trawls. Seines lack the heavy gear components (e.g. otter doors, trawl shoes) of other demersal mobile gears ((Suuronen, et al., 2012) ;(Donaldson, Gabriel, Harvey, & Carolsfield, 2010)) and therefore, despite the relatively large footprint, impacts associated with penetration into the sediment are likely to be lower. Eigaard, et al., (2016) modelled surface (<2 cm) and subsurface (>2cm) impacts and found that demersal seines have some of the smallest proportions of subsurface impact.

No evidence was found on the effects of shellfish dredging. However, the physical effects of scallop dredging on seabed sediments are similar to those of beam trawls (penetration to depths >5 cm) and so the effects on ocean quahog are likely to be similar. Hydraulic gears penetrate sediments more deeply than other gears and so could be expected to cause a greater mortality, particularly where ocean quahog is the target species (although there is no known direct exploitation of the species in the UK).

Bycatch (i.e. discarded catch) is associated with almost all fishing activities and is related to factors such as the gear type and its design (i.e. its selectivity), the targeted species and effort. There are significant concerns over the impacts of discards on marine ecosystems, including changes in population abundance and demographics of affected species and altered species assemblages and food web structures ((Alverson, Freeberg, Murawski, & Pope, 1994)(Kaiser M. J., Collie, Hall, Jenning, & Poiner, 2003)).

Benthic trawls most frequently result in bycatch of fish, crustaceans and other invertebrates ((Gubbay & Knapman, 1999)(Sewell & Hiscock, Effects of fishing within UK European Marine Sites: Guidance for nature conservation agencies, 2005); (ICES, 2013); (Pierpoint, 2000); (Bergmann & Moore, 2001);(Catchpole, Frid, & Gray, 2005); (Tulp, Piet, Quirijns, Rijnsdorp, & Lindeboom, 2005)). There are relatively few studies of the non-fish bycatch composition from demersal seines, however, it is probably similar to that of demersal trawls e.g. crustaceans and other invertebrates, etc, although quantities of such bycatch are likely to be lower than that of other gear types such as beam trawls ((Suuronen, et al., 2012); (ICES, 2011); (Donaldson, Gabriel, Harvey, & Carolsfield, 2010)(Walsh & Winger, 2011)).

Ocean quahog are classed as having medium sensitivity to the pressure removal of non-target species (including lethal) in FEAST^[2]. Hamon et al. (2020) also report ocean quahog as being sensitive to demersal seine fishing due to their capture as bycatch in the southern North Sea, however, this assessment is associated with uncertainty due to the sampling technique not being representative of deep burrowing species and larger epifaunal species. Overall, demersal seines may have a relatively lower impact on ocean quahog compared to other demersal towed gears, as the gear is lighter and has no trawl doors or warps.

This is supported by evidence suggesting that Arctica islandica can be caught or damaged by beam trawls (Witbaard and Klein 1994; Klein & Witbaard 1993), with an individual pass of the gear causing around 20% mortality (Bergman and van Santbrink 2000). Population density has been found to be inversely related to beam trawling effort (Craeymeersch et al, 2000).

The JNCC and NatureScot Fisheries Management Guidance document for Arctica islandica states that demersal towed and hydraulic gears that penetrate the sediment (beam trawls, dredges and hydraulic gears including those operated by divers) are likely to reduce the abundance of ocean quahogs. The degree of impact will depend on the intensity of fishing. Further research will be required to determine the amount of fishing with these gears (if any) that would be compatible with maintaining the feature in good condition. Current evidence suggests that additional management is unlikely to be required for demersal otter trawling at low intensity levels due to limited penetration of the sediment. However, to determine the effects of otter trawl at high levels of effort would require further research.

Impacts from siltation rate changes, and changes in suspended solids may result from physical disturbance of the sediment, along with hydrodynamic action caused by the passage of towed gear, leading to entrainment and suspension of the substrate behind and around the gear components and subsequent siltation ((Sewell, Harris, Hinz, Votier, & Hiscock, 2007); (Gubbay & Knapman, 1999);(Lart, 2012); (Kaiser M. J., Collie, Hall, Jennings, & Poiner, 2002); (Riemann & Hoffmann, 1991); (O'Neill, Summerbell, & Breen, 2008); (Dale, Boulcott, & Sherwin, 2011); (O'Neil & Summerbell, 2011)).

The quantity of suspended material, its spatial and temporal persistence and subsequent patterns of deposition will depend on factors associated with the gear (such as type/design, weight, towing speed), sediment (particle size, composition, compactness), the intensity of the activity and the background hydrographic conditions ((Sewell, Harris, Hinz, Votier, & Hiscock, 2007); (Kaiser M. J., Collie, Hall, Jennings, & Poiner, 2002);(Dale, Boulcott, & Sherwin, 2011); (O'Neil & Summerbell, 2011)). Sediment remobilisation and deposition can affect the settlement, feeding, and survival of biota through smothering of feeding and respiratory organs. Prolonged exposure of an area to the pressure may result in changes in sediment composition ((Kaiser M. J., Collie, Hall, Jenning, & Poiner, 2003);(Sewell, Harris, Hinz, Votier, & Hiscock, 2007);(Gubbay & Knapman, 1999);(Kaiser M. J., Collie, Hall, Jennings, & Poiner, 2002); (O'Neil & Summerbell, 2011)).

The extent to which mobile gear impacts on the supporting sand and gravel sediment habitat can vary considerably according to the type of gear, the intensity of fishing and the sediment composition. In high energy locations, sediments can become naturally disturbed, whilst in lower energy locations, such as muddy sands and sand in deep water, sediments tend to be more stable. The Norwegian Boundary Sediment Plain NCMPA is a shallow sandy plain, with EUSeaMap noting the area to be low energy and thus more likely to be potentially exposed to relatively higher levels of natural disturbance.

The predictive habitat map, EUSeaMap, used to indicate extent of supporting habitat is the result of work undertaken by a consortium lead by the JNCC to combine physical data describing the marine environment with information from biological sampling, generating a broad-scale habitat model of seabed habitats from which a predictive map was created (Cameron & Askew, 2011). The habitat map from the model predicts that suitable habitat for colonisation by Ocean quahog occurs throughout the NCMPA. More specifically, the following habitats are predicted to be present: A5.15 Deep circalittoral coarse sediment and A5.27 Deep circalittoral sand (the dominant habitat type covering 97% of the NCMPA). These components are all considered suitable habitat type for ocean quahog colonisation (Witbaard & Bergman, 2003); (Sabatini & Pizzolla, 2008). Very little data is available on these habitats however they are likely to be more stable than their shallower counterparts and characterised by a diverse range of polychaetes, amphipods, bivalves and echinoderms.

The JNCC and NatureScot Fisheries Management Guidance document for Offshore subtidal sands and gravels states that the variability in the sensitivity of sand and gravel sediments to fishing disturbance is such that site by site consideration of management options is likely to be the best approach. However, there are general points that can be applied. In lower energy locations, such as muddy sands and sand in deep water, sediments tend to be more stable and their associated fauna less tolerant of disturbance (Kaiser et al., 2006, Hiddink et al., 2006). Stable gravels often support a ‘turf’ of fragile species which are easily damaged by trawling and recover slowly (Collie et al., 2005; Foden et al., 2010). The requirement for management of fishing is therefore more likely in lower energy areas, such as those found within the NCMPA.

Gears that penetrate deeply into the sediment (>5 cm) would generally be of more concern than those with only surface impacts (e.g. light trawls, seines). In most cases, good information on the distribution and intensity of fishing activity and good knowledge of the current condition of features relative to their potential recovered condition will be required to inform management options. The VMS data for the NCMPA shows that low levels of demersal trawling and seine netting takes place at a low level across the site, and no other gear types were utilised from 2015 -2019.

Given the evidence outlined above regarding the physical impacts of gear interacting with the seabed, of the gear types occurring within the site, demersal trawl and demersal seine do not carry a risk to hindering Ocean quahog aggregations or the supporting habitat at current levels of activity. Accordingly, Scottish Ministers conclude that the demersal trawl and demersal seine occurring within the site at current activity levels would not hinder the achievement of the conservation objectives of Ocean quahog and its supporting habitat of Offshore subtidal sands and gravel for Norwegian Boundary Sediment Plain NCMPA.

3.4 Part B Conclusion

The assessment of impact of fishing pressures at current activity levels on Ocean quahog aggregations features and the supporting habitat of Offshore subtidal sands and gravels of Norwegian Boundary Sediment Plain NCMPA has indicated that demersal trawl and demersal seine when considered in isolation, will not hinder the achievement of the conservation objectives of the site.