Draft Seaweed Policy Statement Consultation Paper

Consultation paper on policy options for seaweed cultivation in Scotland

8 Commercial Harvesting of Wild Seaweeds

8.1 Current Situation

In Scotland

8.1.1 Scotland's wild seaweed 'production' is currently based around the harvesting and picking of wild seaweed stocks on Orkney, Shetland and the Western Isles, with only a small number of small-scale operations in these areas [234] . This industry is estimated to make up only a small part of the European market [235] .

8.1.2 Scottish operators 'harvest' a range of wild brown, red and green seaweed stocks, although the main type harvested is egg wrack ( Ascophyllum nodosum) [236] with around 5,000 tonnes of wild plants harvested from intertidal waters in the Western Isles each year [237] . Smaller volumes of saw wrack ( Fucus serratus) [238] , and kelp in Orkney [239] and Shetland [240] are also harvested on a smaller-scale. Other activities, such as the commercial scale extraction of the rich lime resource in maerl, have been proposed in the Western Isles in the past but have not been taken forward [241] .

8.1.3 'Picking' is a term given to the small-scale removal of smaller species, typically red seaweeds, that live at the top of the shore. Smaller seaweed species such as carrageens ( i.e. Matocarpus stellatus and Chondryus crispus), the channel wrack ( Pelvetia canaliculata), dulse ( Palmaria palmate and Dilsea spp.), pepper dulse ( Laurencia spp.) and laverbread ( Porphyra spp.) are also picked commercially in Scotland [242] .

8.1.4 An unknown quantity of cast seaweed is 'gathered' from the shore in many of Scotland's island communities, for use as a soil conditioner or fertiliser. The Crofters (Scotland) Act 1993 (as amended) gives crofters access to reasonable use of seaweed under Common Grazings regulations, although it is understood that this is largely confined to the gathering of beach-cast Laminaria spp. and other species mixed with it for spreading on machair land in the Western Isles [243] . As such, little information is available about the extent or size of such gathering.

Seaweed Uses

8.1.5 Brown seaweeds such as A. nodosum, Laminaria saccharina and Macrocystis spp. have been harvested for use as alginates, liquid fertilisers and pharmaceutical production [244] . A. nodosum has also been used as an ingredient in animal feedstuffs and fodder supplement.

8.1.6 Red seaweeds, such as C. crispus, Mastocarpus stellatus, Porphyra spp, have been harvested and used as additives in food products and in the pharmaceutical industry. Gracilaria spp and Gelidium spp have been used to produce Agar, an extract used in cell culture [245] .

8.1.7 Green seaweeds have traditionally been harvested for human consumption, albeit on a smaller scale than brown and red seaweeds.

Current Permissions

8.1.8 At present, wild harvesting or picking of seaweed in Scotland does not require planning permission or a licence/permit, other than the permission of the land-owner. In cases where TCE is the landowner, licences for wild harvesting operations are issued to operators, and this can involve the consideration of the following environmental factors [246] :

  • Impacts on the sustainability of wild seaweed stocks and associated habitats and species supported.
  • Potential implications for coastal processes.
  • Use of harvesting methods and frequency including the proportion of individual plant or plant population to be harvested.
  • The particular species and the proposed area for harvesting.
  • Proposed use of rotational fallowing and harvesting regimes.
  • Adoption of monitoring programmes.

Harvesting Methods

8.1.9 Natural seaweed beds have historically been overexploited globally, often with the use of equipment such as dredges and dragnets [247] . In Scotland, hand cutting has previously been the most common method of harvesting in the wild [248] , with tools such as serrated sickles or scythes used from the rocks at low tide [249] . Anecdotal evidence indicates that this method is still being used today.

8.1.10 Mechanical harvesting has also been used in Scottish water where the seaweed and harvest area are amenable to such methods [250] . Mechanized harvesting methods vary, and can involve mowing seaweed areas with rotating blades, cutting seaweed plants with suction methods, and dredging of areas with cutters. Modern harvesting vessels have been specifically developed for these purposes [251] , although harvesting methods vary. For example, some harvesting operators use boats to access harvest areas, and then use mechanized tools to target seaweed floating on the water surface. Others use mechanised equipment to cut the top of the plant stalks as they float beneath the water surface [252] .

Impacts of Harvesting on Plant Regrowth

8.1.11 Regrowth of a plant or group of plants after harvesting can vary depending on a range of factors:

  • The species harvested.
  • The proportion of a plant harvested.
  • The age of the plant.
  • The extent and pattern of branching.
  • The level of exposure to waves and coastal processes.
  • The presence or absence of grazers.

8.1.12 From the perspective of an individual plant, the method of harvesting is important to plant regeneration. Harvesting techniques vary and can range from the removal of a whole plant at the holdfast, to cutting of the blades of the plant above the holdfast [253] . Many species, such as A. nodosum, can regenerate quickly if the frond is not cut back to the rock with some studies suggesting that cutting of the blades around 36 cm above the holdfast does not adversely impact on regrowth in this species [254] . The removal of a plant in its entirety or close to the holdfast is unlikely to permit regrowth of an individual plant. This may allow for the natural recolonisation of the harvested area by new plants, whether they be of the same or a different species [255] .

8.1.13 The rate of regeneration and community regrowth can also vary by species. For example, mature kelp forests normally contain an understory vegetation of recruits that can recolonize an area once the adult plants are harvested [256] , and the recolonisation may also be influenced by how successfully invertebrates are able to re-establish themselves in the community [257] and grazing pressures [258] .

8.1.14 Several studies into the impacts of harvesting techniques and regeneration of seaweeds have observed changes in the composition of seaweed communities after harvesting. An Irish study observed short-term increases in cover of some macro-algae species, particularly opportunistic and fast-growing species such as Fucus vesiculosus, after the mechanical harvesting of the targeted seaweed species ( i.e. A. nodosum). These changes are often temporary until the targeted and harvested species has undergone sufficient regrowth [259] .

Lessons Learned

8.1.15 Several countries have adopted protocols and/or regulations to address sustainability and environmental concerns held over wild harvesting. These include:

  • In Norway, harvesting is conducted under harvest plans that outline areas for harvest rotation over a five-year period with specific no-take zones developed for the protection of seabird habitats. In these plans, only one-fifth of seaweed in these harvest areas is harvested every year, allowing the seaweed community in these areas four years of regrowth before being harvested again [260] .
  • In France, seaweed harvesting is regulated by the French Government and the National Syndicate of Marine Algae, a group consisting of representatives from the industry, fishermen and scientific advisers. Licensing of boats for harvesting of specific species ( i.e. L. digitata), restrictions on seaweed landings, and regulation of harvesting times are imposed to allow for the growth, reproduction and regeneration of wild stocks [261] .
  • The Environment and Heritage Service of Northern Ireland ( EHSNI) prepared a position statement and a Draft Environmentally Sustainable Seaweed Harvesting Code of Conduct (CoC) [262] . The position statement outlines the preference for manual harvesting over mechanical means on the basis that it is less ecologically damaging, and adoption of practices such as the preparation of pre-harvesting plans, site-specific baseline reports, rotation cycles, hand harvesting methods for specific species, and use of harvesting records by operators [263] .
  • In Canada, several provinces regulate commercial harvesting in the wild via leases. Those involved in the actual harvest of seaweed must have a valid licence issued by Fisheries and Oceans Canada. These licences and leases detail a series of conditions for harvesting operations and can include stipulations that harvesting be undertaken by hand, limits on the species harvested, where a plant can be cut and how many plants in a given area can be harvested [264],[265] . Licensed operators have also reverted from Norwegian-type mechanical harvesting to hand cutting and a rake-type method of harvesting kelp following over-exploitation of kelp beds by mechanical means in the early 1990s [266] .

8.2 Environmental Effects

8.2.1 The potential impacts of wild seaweed harvesting identified in this SEA are divided into two broad groups:

  • Over-harvesting and Harvesting Practices.
  • Impacts on Coastal Processes from Wild Harvesting.

8.2.2 These impacts are illustrated in Figure 8.1 and the likelihood and significance of these effects is discussed in the following paragraphs.

Figure 8.1: Potential Impacts for Commercial Wild Harvesting of Seaweed

Loss of Seaweed Stocks and Habitats for Marine Fauna

8.2.3 Factors such as the frequency, magnitude and seasonality of harvesting activities can all influence the ecological impacts of seaweed harvesting operations [267] (see Section 8.1). The main risk in expanding wild harvesting in Scotland is likely to be over-harvesting and the use of harvesting practices that impair the regeneration capability of seaweed communities ( i.e. removal of plants at or close to the holdfast). These can lead to significant changes in the composition of the seaweed communities ( i.e. fewer species or changes in species proportion) and have secondary impacts on the marine ecosystems that they inhabit ( i.e. adverse impacts on biodiversity of marine fauna).

8.2.4 Studies into the effects of intensive harvesting ( i.e. near-total removal of plants from an area) indicate that significant changes such as reductions in both seaweed numbers and animal abundance can occur [268] . By contrast, the regeneration of some species and seaweed communities can be comparatively quick and successful if harvesting is appropriately undertaken. Frequent harvesting of the same natural seaweed communities, even if just a proportion of the plant is harvested, may limit effective regrowth and contribute to long-term loss of habitat in consequence and adversely affect future harvest yields. Several countries ( i.e. Canada and Norway) have set limits on harvesting in the wild, including measures such as setting protected areas, five-year harvest cycles, and rotation of harvest areas (see Section 8.1.15).

8.2.5 Harvesting of wild seaweed stocks may also lead to a range of secondary effects, including:

  • Increased susceptibility of marine fauna to predation.
  • Greater susceptibility of marine fauna and seaweed communities to wave effects.
  • Scouring through loss of cover.

8.2.6 In the short-term, increased predation and greater susceptibility to wave patterns can be a consequence of harvesting simply due to a loss in seaweed cover. In the longer-term, regular seaweed harvesting can reduce the structural diversity of a marine community, with seaweed beds gradually changing from complex to more simple structures. Over time, and with the added effects of predation, this could lead to further changes in community structures [269] .

Increased Competition for Resources

8.2.7 A reduction in natural seaweed volumes after harvesting of a given area would likely see reductions in nutrient inputs from seaweed, if only over the short-term. This could create increased competition amongst flora and fauna for fewer resources [270] , with potentially adverse effects for some species, particularly those that are vulnerable.

Loss of Seaweed Species

8.2.8 The potential for over-harvesting of Scotland's seaweed communities may create opportunities for invasive non-native species, such as S. muticum [271] , to spread and colonise in Scottish waters via transport or dispersal in water currents [272] .

8.2.9 In general terms, non-native species are considered to present a significant threat to Scotland's marine biodiversity and economy [273] . This could potentially be exacerbated by other factors including the predicted effects of climate change ( i.e. milder sea temperatures) and our adaptation to them ( i.e. likely increases in marine shipping) which could contribute to altering of the composition of seaweed communities by creating conditions suitable for non-native species to spread and survive in Scottish waters [274] . Given the important role that seaweeds play in supporting Scotland's many varied marine ecosystems, the potential also exists for adverse effects on marine biodiversity.

Potential Damage from Harvesting Activities

8.2.10 The potential may also exist for additional impacts from undertaking harvesting activities, including:

  • Harvesting methods, particularly relating to the use of mechanised systems.
  • The capture or injury to non-targeted species ( i.e. by-catch).

8.2.11 The extent and scale of such impacts will depend on several factors, most notably the harvesting equipment used, the nature and sensitivity of the benthos in the vicinity of the harvesting site, and the species being harvested. For example, harvesting of species with generally low biodiversity, such as A. nodosum, is likely to contain smaller levels of by-catch than other seaweed species known to host greater biodiversity [275] .

8.2.12 However, the extent of by-catch from harvesting of seaweed in the wild, and its significance is not presently known. It is noted that discussion with the industry through the consultation may assist in informing this assessment.

Storm Protection and Coastal Processes

8.2.13 The removal of seaweed could potentially alter wave patterns and impact on coastal processes, and affect the stability of nearby coastlines, particularly those susceptible to erosion or accretion. It can increase the susceptibility of coastlines to impacts from storm events, particularly the high energy coasts located in Scotland's Western Isles where the role of L. Hyperborea in the Western Isles has been documented in providing important ecosystem services such as the reduction of wave energy [276] . Potential changes to coastal processes are considered by The Crown Estate in granting individual leases for harvesting in the wild [277] (see Section 8.1), and this should not change under the proposed SPS.

8.2.14 It is noted that the predicted effects of climate change may place greater importance on the ecosystem services provided by seaweed communities, particularly in relation to wave dissipation and the protection of coastal areas from erosion. Predicted increases in sea level, increased frequency of storm surges and larger waves have the potential to significantly alter the coastline shape and the depth of near-shore areas, which could have associated impacts on the distribution and abundance of seaweed in these areas.

Coastal Biodiversity and Stabilisation

8.2.15 The removal of wild seaweed stocks through harvesting may lead to a reduction in the deposition of cast-weed on nearby beaches. This could result in secondary effects, including a reduction in the availability of beach-cast weed for gathering at nearby locations, and reduction in the supporting services that cast weed provides for shoreline biodiversity and the sand dune development process.


8.2.16 Scotland's natural seaweeds are an important resource. However, sustainable management is not straightforward and experiences in other countries indicate the importance of implementing sustainable practices to avoid adverse impacts on both the local and wider marine communities, and demonstrate their successful implementation.

8.2.17 There is presently no evidence that seaweed harvesting in the wild is currently resulting in adverse environmental impacts in Scotland. However, the SEA has identified that the adverse effects are possible with the future growth of this industry, particularly relating to marine biodiversity and coastal processes, and that this may be further exacerbated in the future with the predicted effects of climate change.

8.2.18 Harvesting practices, most notably the extent and scale of harvesting ( i.e. frequency of harvesting, the proportion of a seaweed community harvested, and the proportion of an individual plant harvested) and the species harvested have been identified as key factors in ensuring plant regeneration and recovery of harvest areas, and ensuring the sustainability of the resource and the biodiversity it supports. Many of the potential impacts are likely to be site-specific and will be largely dependent on the composition and resilience of the areas to harvesting.

8.2.19 It is considered that engagement with the commercial wild harvesting industry and stakeholders on a number of topics ( i.e. regulation of the industry, assessment of environmental impacts for proposed wild harvesting operations) may prove beneficial in promoting sustainable development in the future growth of the industry.

8.3 The Consultation Document and the Proposed SPS

8.3.1 Scotland's current operations for the commercial harvesting of seaweed in the wild are small in scale and are not currently regulated. The practice of commercial harvesting in the wild has been reviewed in this SEA to inform the SPS development through the identification of potential impacts of these practices that may be associated with the future growth of this industry.

8.3.2 While the consideration of harvesting in the wild in the proposed SPS is currently limited, the Consultation Document raises these issues and provides a vehicle to consult with stakeholders on options such as development of guidance and promoting good practice in managing the future sustainability of the industry.

8.4 Mitigation

8.4.1 While harvesting operations, by their very nature, are likely to result in a degree of impact at the local level, the scale and permanence of any impacts is likely to be limited if these activities are undertaken in a sustainable manner. As such, it is not considered that expansion of the wild harvesting industry is likely to have significant adverse effects on the marine and coastal environments at the national level, provided adequate mechanisms are in place to prevent over-harvesting and ensure sustainable harvesting practices are implemented by industry operators.

8.4.2 Many of the potential environmental impacts identified in this SEA are likely to be both site and operation specific. Factors such as wave patterns, coastal processes, ecosystem composition and sensitivity, species harvested, scale of harvesting operations, the proximity to sensitive marine areas, and harvesting techniques are likely to exert influence over the occurrence and extent of any such impacts. The potential benefit in identifying likely adverse impacts has been noted from undertaking project level and ecosystem-based environmental assessment of prospective wild harvesting or picking operations. As such, this has been raised in the consultation to gauge stakeholder views.

8.4.3 The SEA also identified potential benefits in the development of guidance, such as a Code of Practice (CoP), for commercial harvesting in the wild for promoting the use of sustainable practices, particularly for new operators entering this industry. As such, the SEA prompted the inclusion of the development of guidance as an option for discussion in the Consultation Document.

8.4.4 Whilst not necessarily in the remit of the proposed SPS or this SEA, the potential for benefits in aiding coastal protection and reducing the gathering of cast weed on Scotland's beaches (through education on the role of beach-cast weed to coastal ecosystems in stabilisation and supporting biodiversity) was also identified.


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