Discussion paper on sandeel and herring sensitivities in relation to MPA fisheries management measure advice

Please note - The advice below was produced (February 2023) to assist the development of proposed management measures for fishing activity for Marine Protected Areas (MPAs) and Priority Marine Features (PMFs) (11 most sensitive to bottom contact gear) outwith MPAs. Further considerations were made by Marine Directorate and the final proposed management measures being consulted upon in 2026 are available via Scottish Government’s website.

February 2023

Purpose

This paper has been drawn together to aid internal NatureScot discussions and discussions with Marine Scotland on sandeels, herring and their habitat to inform their protection as a protected feature (sandeels) and as a prey species for mobile species protected in MPAs (including SPAs, SACs and NCMPAs). It summarises the evidence and uncertainties regarding the species and their habitat, in particular in relation to fishing activities and the advice that NatureScot have given for these features in relation to MPAs. 

We will update the Conservation and Management Advice documents for MPAs to reflect the conclusions in this paper. 

The paper covers the following topics and questions and outlines actions where appropriate:

2. Evidence and consistency in relation to NatureScot’s management advice for fishing activities for sandeels as a protected feature and as a supporting prey species in relation to mobile species.
3. Inclusion of advice on important herring habitat.
4. Uncertainties/issues in relation to the evidence and advice.

Background to NatureScot’s management advice

NatureScot provides advice to support management for activities where we consider this may be necessary to achieve the Conservation Objectives for protected features of MPAs. The advice is focused on the activities that cause an effect (a pressure) that a feature is sensitive to. Our advice takes a risk-based approach, i.e. we are focusing on providing advice where we believe there is a risk to achieving the Conservation Objectives. We have identified risks to achieving the Conservation Objectives where there is an overlap between protected features and activities associated with pressures that the features are sensitive to. This advice is presented in section 7 of the Conservation and Management Advice (CMA) documents for MPAs and is based on existing data and information on protected features and relevant activities. We provide our management advice for all activities under three headings:

• management to remove or avoid pressures;
• management to reduce or limit pressures; or
• no additional management required.

For our advice on fisheries management we have also stated where we think this advice should be ‘considered’ or ‘recommended’. The term ‘considered’ is included to highlight that a fishery-feature interaction exists, but circumstances mean that a specific recommendation for action cannot / or need not be made at this point. However, there is sufficient cause to make fishery managers aware and for them to consider if a fishery management measure may be helpful in achieving Conservation Objectives – particularly where there may be a synergy between the benefits of management actions for the fishery and the Conservation Objectives for the feature. The term ‘recommended’ highlights than a fishery-feature interaction exists, there is a reasonable evidence base and a specific recommendation can be made/ justified.

Sandeel advice

Evidence and uncertainties underpinning sensitivity assessment and fisheries management advice

Our management advice is based on our understanding of the sensitivity of sandeels to pressures as outlined in FEAST and the NatureScot & JNCC (2019) Sandeel fisheries guidance note, published as part of the 2019 MPA consultation. The key species of interest as a protected feature of MPAs and as prey species are Ammodytes marinus and Ammodytes tobianus. The key pressures we have considered are in relation to mortality (direct and indirect), disturbance and effects on the habitat they inhabit (structural change, removal). 

In relation to direct mortality, the current focus of managing pressures from commercial fisheries on sandeel populations in Scottish waters is to avoid the targeted removal of sandeels. There is a formal closure of sandeel fisheries along the east coast of Scotland and no targeted fishery for the species on the west of Scotland. NatureScot’s management advice takes this into account and assumes that the current protection/lack of fishing effort in place is maintained. Our management advice also focusses on human activities (including fishing) that have the ability to remove or change the structure of the gravelly sands that sandeels inhabit. Demersal hydraulic fishing gears (those that fluidise the sediment by blowing or sucking water/sediment) have the ability to change the sediment structure. There is however some uncertainty around other forms of demersal mobile fishing, e.g. dredging, trawling and the degree to which they cause direct mortality of sandeels, cause behavioural disturbance (including energetics discussed below) and affect the structure of their habitat to the degree that it is no longer suitable for sandeels to use. There are two key publications, in addition to observations from Marine Scotland Science and expert opinion that have informed our advice, and these are outlined below along with an explanation of the uncertainties and other considerations. 

There has been only one published study we are aware of that describes mortality of sandeels as a result of scallop dredging. Eleftheriou and Robertson (1992) undertook experimental scallop dredging over shallow sandy substrates in Loch Ewe and reported that the experiment caused high mortality of the greater sandeel Hyperoplus lanceolatus. Whilst this inshore species of sandeel is a different species from the one on which sandeel fisheries are focused (Ammodytes marinus) and the results weren’t quantified, the authors highlighted the mortality should be taken into account when considering the possible effects that commercial dredging might have on sandeel fishing grounds.  However, H. lanceolatus is approximately twice the size of A. marinus and therefore the likelihood of individuals being caught in the teeth of the dredge bar is greater is this species (and hence higher mortality could be expected). NatureScot and JNCC consulted with scientists at Marine Scotland Science (MSS) in the development of the Sandeel fisheries guidance note (NatureScot & JNCC 2019). MSS commented that, “There is some evidence that scallop dredges can kill sandeels buried in the sediment but work from Marine Scotland Science has shown that even when equipped with a fine mesh net to sample sandeels, the efficiency is <12% (MSS unpublished data) and not therefore considered to pose a significant risk”. Further clarification from MSS indicates that this is the catchability seen with this equipment. Video evidence during tows shows that most sandeels escape the dredge, with the addition of the hood (fine mesh net) increasing catchability. However, there is potential for sandeels that escape dredges to be injured and subsequently die so levels of mortality could be different to levels of catchability. The time of year is also expected to have an impact and mortality is likely to be higher during colder temperatures (winter) and at night when they bury themselves in the sediment, compared to during the spring/summer and during the day when they are feeding in the water column.

It is also important to take account of the movements and connectivity of sandeels when considering the ability of local sandeel grounds to recover from mortality impacts. The evidence is summarised in Wright et al. (2019) but the key conclusions were: sandeel larval dispersal between banks situated less than 67 km apart is common but over distances of more than 200 km, dispersal is very low; and the movement of settled individuals/adults is very low and banks situated more than 30 km apart exchange very few or even zero individuals. Therefore, whilst there is the possibility of replenishment from a nearby source of larvae following local depletion (whether due to overfishing or other causes) reoccupation of an area by sandeels after such impact may take some time. Additionally larval dispersal relies on hydrodynamic processes which need to be accounted for as some areas are more isolated than others.

There is also a study by Tien et al. (2017), who used a model (GLMM) to examine the presence of three sandeel species A. tobianus, H. lanceolatus and A. marinus off the Dutch coast in relation to sediment characteristics (particle size), water velocity near the seabed, and to fishing effort of the beam trawl fishery targeting flatfish and shrimp. Beam trawls targeting flatfish use tickler chains which dig through the top layer of sediment to target the partially buried fish.  The presence of all three species was found at lower levels of fishing effort and not at higher levels of intensity. Presence of A. marinus and A. tobianus was negatively correlated with flatfish fishing effort. This relationship was not found for the shrimp fishery for these two species and Tien et al. (2017) outline that that the shrimp fishery uses lighter gear that doesn’t dig into the seabed which may offer an explanation. Tien et al. (2017) suggest that the relationship between fishing intensity and the presence of A. marinus and A. tobianus could arise if the flatfish fishery targeted habitat that was unsuitable for sandeels. However, they outline that the intensity of beam trawl flatfish fishing was higher at locations where it was the preferred habitat of sandeel (lower silt content, higher sand content, and higher water velocity). They note that this supports the hypothesis that beam trawl fishing using a tickler chain has a direct negative effect on the presence of these species. Interestingly, for H. lanceolatus there wasn’t a significant effect of flatfish fishing intensity on their presence but there was a significant negative correlation with the intensity of the shrimp fishery. The authors conclude that further work is needed to look at ecophysiology of sandeels and relationships between mobile/active demersal fishing pressure/intensity and sandeel distribution. This study was not considered in the NatureScot & JNCC (2019) Sandeel fisheries guidance note or within other NatureScot advice to date.

Sandeels are reactive to disturbance near the seabed and will emerge from the sediment with the passing of fishing gear. A possible effect would be the energetic costs of repeated disturbance, i.e. from multiple fishing events, particularly during the overwintering period. This could result in effects on their survivability due to increased predation, reduced foraging, and lower reproductive success from higher energy outputs e.g. from increase burst swimming. Whilst empirical evidence is lacking, expert opinion supports this rationale. 

It is also worth noting that there may also be additional displacement of the scallop fishery due to additional spatial management, e.g. PMF fisheries management and developments e.g. offshore wind. This may lead to areas with sandeel habitat that had not previously been targeted for scallops being potentially impacted. 

In conclusion, there is limited evidence that can be drawn upon to inform our management advice but there is sufficient to highlight that an interaction exists that needs to be considered. There would be value in additional research, to explore the unknowns outlined above and help improve our understanding.

Current NatureScot management advice for sandeels 

Sandeels are a Priority Marine Feature and a protected feature of some MPAs within Scotland (Mousa to Boddam MPA and North-east Lewis MPA inshore and North-west Orkney MPA and Turbot Bank MPA offshore). Our current management advice in relation to fishing activity where sandeels are a protected feature of MPAs is outlined within Conservation and Management Advice (CMA) documents e.g. North-east Lewis MPA and is summarised in Table 1. 

Sandeels are key prey for seabirds and marine mammals, e.g. bird species protected within SPAs, harbour porpoise, seals, minke whale protected in SACs and MPAs, but also for predatory fish like whiting, haddock and flatfish (some of which are Priority Marine Features). Our management advice where sandeels are a prey species of a protected feature is summarised in Table 1, taken from information contained within CMA documents, e.g. Inner Hebrides and the Minches SAC, Sea of the Hebrides MPA, Outer Firth of Forth and St Andrews Bay Complex SPA. The key premise of this advice is that removal of sandeels or disturbance of key areas of sandeel habitat could, by impacting the sandeel populations, negatively affect the mobile species that rely on them for food. 

Our advice for sandeels as a protected species and prey species is consistent across designation types in relation to pelagic fisheries, hydraulic dredging and static gear, but currently inconsistent regarding mobile/active demersal gear (trawls, dredges). 

Table 1. Summary of NatureScot advice to support management in relation to fishing activities for sandeels as a protected feature and a prey species within MPAs. *Note that demersal mobile gear has been split into mechanical trawls/dredges and hydraulic dredges for the SPA advice and for the purposes of this summary table, but they are not currently separated in the MPA/SAC advice tables in the CMA documents.

Activities considered capable of affecting the protected features	Sandeels advice (as protected feature of MPAs)	Minke whale/Harbour porpoise advice (in relation to sandeel as prey species)	SPAs advice e.g. seabirds, Great northern diver, red-throated diver, Slavonian grebe, red-breasted merganser (in relation to sandeel as prey species)
Fishing - demersal mobile/active gear (inc. mechanical trawls and benthic trawls)*	No advice given	No advice given	Whilst we have limited understanding about the extent of interactions between benthic fisheries and prey supporting habitat within the site, we recommend that a principal objective of the management of the relevant fisheries should be to ensure that the fishing activity does not cause such disturbance to the benthic habitats that it adversely affects the abundance and availability of prey.    Reduce or limit pressures (removal of prey species and abrasion of prey-supporting habitat) associated with fishing that has the potential to damage seabed habitat (in particular, sandeel habitat).
Fishing – hydraulic dredges*	Remove or avoid pressures The exclusion of hydraulic fishing methods from habitat supporting sandeels within the site is recommended.	Remove or avoid pressures  The exclusion of hydraulic fishing methods from the habitat of sandeels (as a key prey species of minke whales/harbour porpoise) within the site is recommended. (NatureScot considers that hydraulic dredging includes suction dredging and also fishing methods that use jets to blow/move the sediment and then pass a dredge over this seabed. These forms of fishing can significantly alter the sediment and penetrate it to a point where they affect its ability to support sandeels.)	Hydraulic dredging has the potential to cause significant disturbance to the sediment habitats that support the prey species of the protected features, particularly for sandeel.    We recommend  that a principal objective of the management of the relevant fisheries should be to ensure that the fishing activity does not cause such disturbance to the benthic habitats that it adversely affects the abundance and availability of prey.    Remove or avoid pressures (removal of prey species and disturbance of prey-supporting habitat) associated with hydraulic fishing that has the potential to damage seabed habitat (in particular, sandeel habitat).
Fishing – static gear*	No additional management required	No additional management required	No additional management required
Fishing – pelagic*	Remove or avoid pressures The exclusion of targeted fishing for sandeels is recommended.	Remove or avoid pressures  The exclusion of targeted fishing for sandeels is recommended because of the importance of sandeels as a prey species for minke whale/harbour porpoise.	Remove or avoid pressures (removal of key prey species) associated with fishing for sandeels. There is no current targeted sandeel fishery within the SPA, this position should be retained.