Hand harvesting of seaweed: evidence review to support sustainable management

Wilding, C, Tillin, HM, Stewart, EJ, Burrows, M and Smale, DA 2021 Hand harvesting of seaweed: evidence review to support sustainable management. NRW Bangor, 275pp. (573)

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Natural Resources Wales commissioned this literature review to improve understanding of the range of potential impacts of hand gathering seaweed and to review potential management measures. The report will support managers to provide clear, evidence based and consistent advice to applications while protecting the seaweed resource. The majority of hand harvesting activity is for food use, with limited amount taken for cosmetics and pharmaceuticals. Little evidence for collection of beach cast weed was found in Wales and England, which is thought to be opportunistic and seasonal following winter storms, with applications as fertilizer or soil conditioner. A small amount of mature adult plants are also hand harvested to provide fertile material for seaweed cultivation. Commercially in Wales and England, Sea spaghetti (Himanthalia elongata), dulse (Palmaria palmata), Ulva spp., Porphyra spp., carrageen (Chondrus crispus), Fucus serratus (some F. vesiculosus) and the kelps Laminaria digitata and Saccharina latissima are the key species targeted. Recreational harvesting activity targets a range of species, with some overlaps with commercially harvested species. Of these, Laver, (Porphyra spp). is of particular importance to recreational harvesters in South Wales, followed by F. vesiculosus, pepper dulse (Osmundea spp), kelps, carrageen (C. crispus and Mastocarpus stellatus) and P. palmata). Growth rates, life history, seasonality and reproduction underpin recovery from harvesting. These are species and site specific and may vary over time. Dispersal potential of propagules is poorly understood, but is a key recovery mechanism and is thought to be low for most species. For key targeted species, evidence for distribution and these life history parameters is presented in the appendices as a series of species dossiers. The report identifies how management should take these into consideration and highlights differences between species. The wrack Ascophyllum nodosum is the most slow growing and long lived of harvested species, followed by the kelp Laminaria hyperborea, other kelp and wrack species, and perennial red seaweeds. Conversely Ulva spp. and Porphyra spp. are fast growing and quick to mature and able to rapidly colonise newly cleared rock. Seaweeds support the natural ecosystem and people through primary production/ carbon fixation and nutrient cycling that underpins marine food webs. Seaweeds provide and modify habitats for a wide range of organisms, including commercially targeted fish and shellfish species. The contribution to ecosystem function and services varies with kelps and brown seaweeds being of particular ecological importance. The impact of harvesting varies according to species, scale, technique and local environmental conditions. By removing seaweeds, harvesting reduces growth rates and population dynamics, this reduces nutrient cycling and reduces habitat availability and provision. While recovery may take place in some instances, changes in community composition can occur as a result of competition and grazing pressure. These impacts should be considered within harvesting management plans to mitigate adverse effects. Invasive non-native species are a key risk for native species and habitats. A rapid evidence assessment identified 33 invasive species of concern, likely to be associated with harvested seaweeds, these include thirteen invasive seaweeds, thirteen attached or 19 fouling species and seven mobile species that may shelter amongst seaweeds. The risks from these were prioritised based on impact on native species and habitats, relevance of seaweed harvesting to dispersal and current distribution. Fourteen priority species were identified, three of which may be of commercial interest. Measures to reduce risk of spread include avoiding or reducing by-catch and ‘check clean dry’ equipment are suggested. Existing harvesting guidance documents are centred around codes of conduct which are not legally binding. Effective management will be site and species specific. Management approaches may be voluntary (e.g. codes of conduct) or statutory (e.g. quotas), and can be summarised as follows. • Harvesting methods - Cutting height, leave a proportion of the plant (holdfast and some frond) remaining at the base; - Selectively cut with scissors rather than plucking or uprooting to support recovery and reduce by-catch; - Avoid by-catch of epiphytes and vulnerable species - Avoid harvesting reproductive material if possible (or only take half from each plant in the case of H. elongata); - For certain species (e.g. for F. serratus and F. vesiculosus), only harvest part of mature plants • Harvesting period - Harvest during active growing season; - Avoid harvesting during the reproductive season; • Harvesting frequency - Fallow periods for recovery of canopy in A. nodosum and perennial kelps • Harvest limits - Quotas, volumes or bag limits; - Proportion of standing stock biomass removed/left remaining • Harvesting spatial considerations - Harvest sparsely, leaving unharvested plants between those taken; - Shape, size and spacing of harvested areas (i.e. between harvested plants or patches); Knowledge of the available resource is essential for sustainable management of hand harvesting of seaweeds. Simple methods of assessing and monitoring biomass were discussed and some initial estimates of biomass of intertidal seaweed provided. Due to gaps in evidence uncertainty remains regarding the lifecycle and recovery capacity of certain species, particularly red seaweeds and the standing stock biomass of all species available for harvest. This report has identified management approaches that are well supported and based on ecological considerations such as life-history and recovery mechanisms. However, it is recognised that advice and action by managers for those seaweeds where uncertainty exists regarding biomass and recoverability will need to be precautionary. Effective management will be site and species specific, utilising a combination of management approaches. Seaweed harvesting activities provide an opportunity to involve stakeholders to conduct applied research projects, monitoring sites before, during and after harvesting and to trial effective management issues. Continued monitoring in some form by harvesters could be a condition of any license to exploit wild stocks.

Item Type: Publication - Report (UNSPECIFIED)
Additional Keywords: Seaweed, Hand harvesting, Sustainable Management, Natural Resources Wales
Subjects: Aquaculture
Ecology and Environment
Marine Sciences
Divisions: Marine Biological Association of the UK > Ocean Biology
Depositing User: Tamar Atkinson
Date made live: 29 Apr 2022 14:49
Last Modified: 09 Feb 2024 16:50
URI: https://plymsea.ac.uk/id/eprint/9637

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