Knowledge of the extent and causes of escape incidents from sea-cage fish farms varies greatly from country to country across Europe. Several countries, such as Norway, Scotland and Ireland, have legislated reporting requirements whereby farmers are obligated to report escape incidents, their size and cause and when they occur. In contrast, Mediterranean countries have no such requirements; thus no statistics are available on the number of escapes or the underlying causes of escapes (Dempster et al., 2007).
Norway has the most comprehensive record of escapes, dating back approximately 15 years for salmonids and 5 years for Atlantic cod. A total of 722,000 and 963,000 salmon and rainbow trout were reported to have escaped from Norwegian farms in 2005 and 2006, respectively (Norwegian Fisheries Directorate, 2007). The real number of escapes has by some been estimated to be considerably greater (Torrissen, 2007) because not all escape incidents are believed to be reported.
Substantial escape events of salmon have also occurred in other major salmonid producing countries, such as Scotland, Chile and Canada (Naylor et al., 2005 and Soto et al., 2001). Over one million salmon were reported to have escaped from Scottish farms during the period from 2002 to 2006 (Thorstad et al., 2008). The proportion of Atlantic cod that escape is high in comparison to salmon (Moe et al., 2007). In 2005 and 2006, 213,000 and 288,000 cod, respectively, escaped from Norwegian farms.
While no official statistics on the extent of escapes exist for Mediterranean countries, data available from companies that insure fish farm businesses indicate that escapes are a significant component of economic losses claimed by farmers (EU FP-6 ECASA project; www.ecasa.org.uk). From 2001 to 2005, 76 claims accounting for 36% of the total value of all insurance claims made by fish farmers in Greece were due to stock losses from storms, while damage to farm equipment due to storms accounted for 19%. A further, 39 registered ‘predator attacks’ resulted in claims of 10.4% of the total value of all insurance claims, although the proportion of this which relates to stock loss or cage damage is unknown. The existing evidence suggests that escapes are a relatively frequent occurrence on a pan-European scale.
Escapes are caused by a variety of incidents related to farming equipment and their operation. Reports by fish farming companies to the Norwegian Fisheries Directorate following escape events during the period from 2001 to 2006 indicate that escapes can be categorised broadly into structural failure (52%), operational related failure (31%) and biological and/or other causes (17%). Structural failures may be generated by severe environmental forcing in strong winds, waves and currents, which may occur in combination with component fatigue or human error in the way farm installations have been installed or operated (Jensen, 2006). Operational related failures leading to escapes include collisions with boats, incorrect handling of nets or damage to nets by boat propellers. The risks to farm installations from the marine environment largely come from exposure to waves and currents (Lader and Fredheim, 2007 and Lader et al., 2008) and from collisions with seagoing vessels. The further offshore a farm is located, generally the more exposed it is to the elements, thus increasing the risk of escapes.
There is growing evidence that with cod the reasons for escape differ from salmon. This stems from behavioural variations in captivity. Firstly, cod bite the net and might thus increase wear and tear and contribute to the creation of holes (Moe et al., 2007). Secondly, cod show more pronounced exploratory behaviour than salmon and might thus have a higher probability of discovering small holes in the net (Damsgård et al., 2012 and Hansen et al., 2009).
Official statistics and other sources of information which apportion causality to escape events provide little explicit detail to support technological development that will improve farming equipment and modify operations to avoid mistakes that cause escapes. Categorisation of causes may also be inaccurate, as causes are rarely investigated in detail (Valland, 2005). Such detail only comes through thorough investigation of the causes of escape incidents on a case by case basis (e.g. Rist et al., 2004).
This study documents the extent and costs of escapes and presents the biological, technical and operational causes giving rise to escapes of fish from sea-cage fish farms in marine waters in 6 European countries over a three year period.
Results
A total of 242 escape incidents were identified through questionnaires, which were completed across the 6 countries, and using other data supplied by the Norwegian Fisheries Directorate and the Scottish Aquaculture Research Forum. The causes given for these events are shown below in Table 1. Some of the events were as a result of a combination of causes. The majority of escape incidents related to net damage due to predator attacks and abrasion. Storm damage or weather was also a common cause. However, it was not clear from the responses obtained whether the storm losses were due to net, mooring or floater damage.
A total of 8,922,863 fish were reported to have escaped from the 242 incidents. Sea bream accounted for the highest number of escapes at 76.7% followed by Atlantic salmon at 9.2%. Of the 6,846,100 sea bream reported to have escaped, two of the incidents accounted for 1.9 and 3.8 million fish, respectively. It should also be noted that three of the escape incidents relating to sea bream had unknown numbers of fish reported.
Of the 113 Atlantic salmon escape events almost 75% were due to structure failure or operational error. Almost 50% of cod escape incidents were due to biological causes e.g. biting of nets. One major incident involving a trawler accounted for 34% of all cod escapes over the selected period.
The majority of escape incidents (Fig. 1) relate to the enclosure netting, with biting of nets being most common, while the underlying cause for 67% of the number of fish escaping (Fig. 2) was mooring failure. Net biting (Fig. 3) was responsible for the highest proportion of incidents of hole in the net followed by predator damage. This net biting is a behavioural characteristic of both cod and sea bream. While the type of predators causing net failure differs from the Atlantic (e.g. seals) to the Mediterranean (e.g. dolphins/wild fish) the outcome is the same.
For Ireland, Norway and Scotland it was possible to obtain official figures for the total number of escapes. These were used as a basis for calculating the value at point of first sale of the escapees. The number of escapees per annum was multiplied by the average harvest weight in kilogrammes for farmed salmon in each country and the result was multiplied by the average value per kilogramme of salmon sold, for that year in each country. Average weight at harvest and average first sale prices were obtained from representative organisations, national statistics and other recognised sources of such commercially sensitive information. The results are presented in Table 2. The total value of escaped salmon in terms of first sale value was estimated at €4.7 million per annum.
For Malta, Spain and Greece official statistics on escapes are not compiled. In these countries, the results obtained in the questionnaire and supplemented by follow-up investigations and interviews were used as the basis for calculating the number of escapees. The number of escapees recorded was taken as a representative subsample and the estimated total calculated by reference to the proportion of the total production sampled (Table 3). For example if 20% of the farm production was sampled the resulting figure was raised by a factor of 5 to give an estimate of the national total. Where the subsample was large, such as Malta (> 60%) there is a higher confidence regarding the accuracy of the resulting estimate than where the sample represents a smaller proportion of the national production. FAO and Globefish statistics were used to calculate value at point of first sale and the size at point of sale was set at 500 g.
Over a three year period a total of 242 escape incidents were documented representing a variable proportion of the farms in operation in each country. This percentage varied from a low of 20% to a maximum of 75%.
In northern European countries, national statistics are available on total escapes due to mandatory reporting requirements. Where available these were used as a basis for calculations. Results indicate that the cost to the industry in terms of loss of sales revenue at point of first sale is in terms of tens of millions of euro per annum. The Prevent Escape partners are currently carrying out a scoping exercise to attempt to produce a validated figure for an average annual cost for the European industry in terms of euro per tonne of licensed production. This figure could then act as a baseline to measure improvements in efficacy of containment against, and to derive cost–benefit metrics for, improvements in containment.
Discussion
Out of a total of almost 9 million escapees recorded in the study period over 75% were accounted for by escapes of sea bream. Of these over 5 million occurred in two catastrophic escape incidents. The most significant factor in terms of number of fish escaping (Fig. 2) was mooring failure. In terms of numbers of fish escaping this factor accounts for over two thirds of all escapees recorded in the study.
By far the most significant cause in terms of numbers of escape incidents was a hole in the net due to either biting (16%), predator damage (14%) or other causes. When the causes of holes in the net are examined (Fig. 3) it can be seen that taken together, net biting and predator damage, account for almost half (47%) of escape incidents due to a hole in the net.
The present study did not address the issue of negative environmental impacts associated with escapes from fin fish farms. There are a number of studies (Dimitriou et al., 2007 and Jensen et al., 2010) which raise issues in this regard. Two key issues highlighted are the possibilities for genetic interactions (McGinnity et al., 2003) and the risk of competition with wild stocks.
The number of escapees recorded in northern Europe was much lower than in the Mediterranean. The total number of salmon and cod recorded as escaping during the study period was 1.27 million or less than 15% of the total number of escapees recorded. This may, as suggested by Jensen et al. (2010), in some measure be related to the more highly developed standards for equipment and structures including mooring arrays. It may also be due in part to the codes of good practice introduced by the industry themselves in these countries.
One example is The Code of Good Practice for Scottish Finfish Aquaculture (http://www.thecodeofgoodpractice.co.uk/index.php) which has been in place since 2006. The Norwegian government has enacted legislation called NYTEK, first version mandatory from 2006, updated version mandatory from 2012, with some parts not mandatory until 2013 in which it specifies the technical standard NS9415, first edition in 2003 revised in 2009.
This technical standard relates to cages, mooring systems and other components. Since the implementation of this legislation there has been a reduction in both the number of escape incidents and the numbers of fish escaping ( Jensen et al., 2010). In Scotland, similar containment standards are presently under development and training programmes to improve husbandry staff understanding of containment management have been implemented (http://www.scotland.gov.uk/Topics/marine/Fish-Shellfish/18364/18692).
The role of holes in the net in a large number of escape incidents points towards the need to improve surveillance of net integrity, preventative maintenance programmes and testing and inspection of nets before deployment or redeployment. Where such programmes are widely employed numbers of escapes are significantly lower.
The study identified that the number one cause of escape incidents was due to net biting and the number one cause of large escape numbers was mooring failure. It was also concluded that there was a large variation in the level of awareness of the necessity of both training of staff and procedures or Standard Operating Procedures on containment related issues.
Conclusions
There were significant numbers of finfish escapes in all of the areas studied (8.9 million fish over the period of the study). The nominal cost of these escapes at point of first sale is very significant in terms of lost income (€47.5 million per annum). Implications of the escape incidents have been shown to have negative effects on the viability of individual commercial concerns. The public perception of the aquaculture industry has also been adversely affected by publicity surrounding high profile escape incidents.
Two key drivers towards reducing escapes identified by the industry were standards for materials and site specific procedures and processes to ensure the use of appropriate equipment and its maintenance.
Further Reading
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