Main costs to the sector

Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 103-106)

Investigations into the costs relating to INNS in the aquaculture sector have led to a general impression that INNS do not cause a specific issue to the industry. For example, we are unaware of costs incurred by the off-shore fisheries industry as a result of INNS. This is not necessarily because INNS do not affect the sector, but rather that the industry requires that all fish are kept pest free, whether the pest is a non-native species or not. However, species including slipper limpet (Crepidula fornicata), signal crayfish (Pacifastacus leniusculus) and wireweed (Sargassum muticum) have some effect on the industry, even if the impact is hard to quantify. The most common impacts of INNS on this sector are fouling, competition for resources, predation and vectoring of diseases.

A potential major impact is that of fouling (nets, cages, buoys, moorings, boat hulls etc), which can be a significant problem for approximately four months a year, and cause costs of approximately £13 million per annum (David Fraser, pers. comm.). However, various sources have indicated that INNS are generally not considered to be the main cause of these additional costs to the industry. A recent paper suggested that fouling is not a great enough issue for the mussel industry to spend time and money on (Leblanc et al. 2003). The main reason for the lack of focus on INNS is that there are also native fouling species and current management practices target fouling organisms in general, and do not consider whether the species that are being removed are native or non-native. The advice for boat


owners is, and has been for a number of years, to lift their boat out of the water and clean the hull on a regular basis (e.g. British Marine Federation, Green Blue book, BW guidance).

However, as some of the species fouling a hull are non-native a cost estimate is made for hull cleaning, and anti-fouling measures.

The cost of hull cleaning through pressure washing is estimated as £25 m-1 vessel length (based on pricing information provided by Milford Haven Ship Repairers). Treatment with antifouling paint costs approximately five times as much, and is therefore estimated at £125 m-1. The advice for boat owners is to clean the hull once per year, but treatment with antifouling paint is required less frequently, generally once every five years. There are 5834 fishing vessels49 with an average length of 9.88m, and therefore the cost of annual cleaning is estimated at £1,440,998. In addition 20% of these boats will be treated with antifouling paint each year at a cost of £1,440,998, giving a total cost for control and treatment of hull fouling of £2,881,996.

Gollasch (2002) found that 57% of the species in samples (ballast, sediment and hulls) collected from shipping vessels arriving from outside the North Sea area were non-native to that area. No estimates could be found of the percentage of hull area covered by non-native fouling organisms, but is it possible that fishing vessels travel less to different marine ecological zones than international shipping vessels, and therefore have less exposure to non-native species and have a lower percentage of non-native organisms fouling their hulls.

Therefore, assuming that only 25% of organisms fouling fishing vessels are non-native, the estimate for the cost of fouling to fishing vessels is reduced to £721,000.

Fouling can cause additional costs to the shellfish industry and it is estimated that the European shellfish industry experiences a loss of 5-10% (FAO) due to the cost of labour to clean fouled produce. The time and cost spent in cleaning shellfish can be 20% of the market price (GISP 2008). Therefore, based on the estimate of market value of the shellfish industry in Scotland (£7.6 million) and England and Wales (£14.1 million; CEFAS 2009) the annual cost of removing fouling species from shellfish could be more than £1.52 million in Scotland and £2.8 million in England and Wales. However, native species (e.g. tubeworms and barnacles) are also targeted and it is unknown what fraction of the fouling organisms are INNS and whether there has been a change in cleaning costs as a result of INNS. It is therefore difficult to estimate incurred costs due to INNS accurately. However, even if INNS only make up 20% of fouling species the cost incurred by the shellfish industry due to these species could be £864,000 (£304,000 in Scotland and £560,000 in England and Wales).


The slipper limpet can substantially reduce incomes in the shellfish industry by acting as a competitor for space and food. In Brittany, the scallop industry has lost an estimated 97% of the harvestable area (FitzGerald 2007). In Great Britain, slipper limpet occurs from Yorkshire to Pembrokeshire, with two recorded locations in Scotland with no recorded impact on commercially exploited shellfish. The population is localised, but populations occur in the Solent and Essex estuaries, Poole harbour, Lyme Bay, Truro Bay and Milford Haven. After a period of limited increases in population density, the population increase has been rapid in the past decade (Walker 2007). Currently, slipper limpet occurs in densities that are far higher than oysters and mussels together in Truro Bay (FitzGerald 2007). Where slipper limpet is present the efficiency of dredging for scallops is reduced, it takes longer to sort the catch, clean it and the quality of the catch is reduced. In Lyme Bay for instance, 10 kg of slipper limpet can be lifted for every 50 kg of scallops (Syvret and FitzGerald 2008). There do not appear to be any assessments of the costs of slipper limpet to GB, but even if additional costs and reduced catch cost the scallop industry 10%, an average of losses estimated by the FAO and GISP, then this cost could be £3,530,000 per annum (at an annual value of £35.3 million for UK scallop production (Seafish 2008)). In addition, recent increases in population density suggests that similar competition may occur to that found in France at present or in the near future and therefore costs are likely to increase.

The slipper limpet is also known to compete with oysters, in particular reducing the ability of young oysters to establish themselves. Oysters are also predated by the American oyster drill, which feeds on young oysters and is known commonly to cause 50% mortality in oyster spat (GISP, undated). There is a limited distribution in Britain, with records existing in only seven 10 km2 squares along the south and south-eastern coast of England (NBN).

Wireweed can also adversely affect the oyster industry (as well as fishing lines and nets) by smothering growth. Based on the amount of oysters produced and landed in England, Scotland and Wales50 (CEFAS 2009 and using a value of £3,000 per tonne for native oysters and £2,500 per tonne for pacific oysters (pers. comm.)), the oyster industry can be valued at £10.4 million in England, £2.6 million in Wales and £1.3 million in Scotland.

Therefore, assuming that the presence of both slipper limpet and the American oyster drill increase costs by 10% then the cost to the oyster industry is £1,430,000, (England

£1,040,000, Wales £260,000 and Scotland £130,000).

The development of a Standard Operating Procedure for checking that shipments of mussel seeds are free of slipper limpet for the Menai Strait cost ca. £5,000 and each inspection costs approximately £2,000 (Andy Woolmer, pers. comm.). In 2009, the number of formal


inspections was 4 (James Wilson, pers. comm.). The total cost of implementing a code of good conduct in the Menai Strait was estimated at £20,000 (Gabrielle Wyn, pers. comm.).

The four mussel companies fund a PhD project to examine the ecological requirements for slipper limpet establishment at an annual cost of £12,000 and authorisation to export mussels to the Netherlands costs approximately £5,000 per year (James Wilson, pers.

comm.). Finally, the Environment and Heritage Service are very careful about mussel movements from the Menai Strait, which costs one of the mussel companies, Deepdock Ltd, in excess of £500,000 per year, as they cannot move mussels to their finishing grounds in Northern Ireland (James Wilson, pers. comm.). The total cost of slipper limpet on mussel production in the Menai Strait can thus be estimated at £550,000.

Other species, such as the Chinese mitten crab (Eriocheir sinensis) and topmouth gudgeon (Pseudorasbora parva), predate on native fish eggs or can damage nets (NNSS51). In addition, topmouth gudgeon carries a parasite that affects both salmon and trout breeding cycles, thus affecting coarse fish production in England. Current efforts to control topmouth gudgeon amount to £190,000 over 4 years, (£50,000 p.a., Britton et al. 2010). However, part of these costs can be attributed to either the biodiversity and conservation sector and the tourism and recreation sector, due to the effect of topmouth gudgeon on native fish species, and the effect on recreational coarse fishing.

Dans le document The Economic Cost of Invasive Non-Native Species on Great Britain (Page 103-106)