3.5. GENERAL CONCLUSIONS & RECOMMENDATIONS FOR PREVENTING AND MITIGATING ESCAPE-RELATED FISH BEHAVIOUR

Fish escapes from aquaculture can be economically and environmentally detrimental to the aquaculture industry and its surrounding environs. In farmed species that exhibit a propensity to inspect and bite the cage wall, determined efforts should be undertaken to understand a) the motivation behind these behaviours, b) the factors that can increase the risk of these behaviours occurring, and c) the measures that can be taken to reduce or mitigate against these risks.

The Pre-Escape work package of the Prevent Escape project was tasked with these specific objectives. Three key European aquaculture species that can exhibit escape-related behaviours: Atlantic cod (Gadus morhua L.), European seabass (Dicentrarchus labrax L.) and gilthead seabream (Sparus aurata L.) were used to assess the factors that can increase or mitigate against these behaviours. These species are primarily farmed in northern Europe (Atlantic cod) and southern Europe (seabass and

Cite this article as: Noble C, Hedger RD, Uglem I, Papadakis VM, Papadakis VM, Papadakis IE, Glaropoulos A, Kentouri M, Smith CJ, Zimmermann E, Fleming IA, Høy E, Damsgård B (2013) General conclusions & recommendations for preventing and mitigating escape-related fish behaviour. In: PREVENT ESCAPE Project Compendium. Chapter 3.5. Commission of the European Communities, 7th Research Framework Program. www.preventescape.eu

authors:Chris Noble1, Richard D. Hedger2, Ingebrigt Uglem2, Vassilis M. Papadakis3, Ioannis E. Papadakis3, Alexios Glaropoulos3, Maroudio Kentouri3, Christopher J. Smith4, Emily Zimmermann5, Ian A. Fleming5, Erik Høy6 & Børge Damsgård1

1 Nofima, Norway, 2 Norwegian Institute for Nature Research, Norway, 3 University of Crete, Greece, 4 Hellenic Centre for Marine Research, Greece, 5 Ocean Sciences Centre, Memorial University of Newfoundland, Canada6 SINTEF Fisheries & Aquaculture, Norway

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ISBN: 978-82-14-05565-8

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Findings from the Atlantic cod experiments undertaken during the Pre-Escape WP included:

Feed deprivation increased net inspection and biting frequency (Damsgård et al. submitted, see also Moe et al. 2007, Hansen et al. 2009). Tank studies also showed that poorly repaired areas of the net wall, specifically where a contrasting coloured thread was used to repair net damage, also increases net inspection and biting frequency.

With regard to Atlantic cod (see Figure 3.5.1), the Pre-Escape Work Package showed that there were a number of husbandry factors that can increase the frequency of escape-related behaviours. We showed that Atlantic cod do interact with, inspect and bite the net wall. This behaviour has also been noted in previous studies (Moe et al. 2007, Hansen et al. 2009) and net biting does have the potential to damage cage netting materials (Høy et al. 2011).

RECOMMENDATIONS FOR PREVENTING AND MITIGATING ESCAPE-RELATED BEHAVIOURS IN ATLANTIC COD

seabream) and mean the work package addresses the problem of behaviourally driven escapes on a pan-European scale. Prior to the Prevent Escape project, the biological and husbandry factors that may drive and augment the risk of fish exhibiting escape-related behaviours were poorly understood. The Pre-Escape work package was designed to address this shortfall.

Figure 3.5.1 Atlantic cod (Gadus morhua) in a sea cage. Photo: Frank Gregersen, Nofima

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To reduce the prevalence of net inspection and biting behaviour in Atlantic cod farmers should:

Limit the length of time that they deprive cod of feed. Short-term feed deprivation is a common husbandry practice when cod are being graded and transported. Farmers should be aware that cod will increase net inspection and biting in the days during and following these periods of feed deprivation.

Although a short-term, 50% feed restriction did not emerge as a risk for increasing net inspection behaviour, farmers should be aware that net biting can increase if fish are underfed.

If seaweeds (or other macro net fouling materials) build up around the net walls, farmers should attempt to remove these as quickly as possible as long seaweed strands increase net inspection and biting behaviour in Atlantic cod.

Net repairs should be carried out diligently, with no loose thread left exposed at the end of each repair. Where possible, the colour of the repair thread and net colour should be matched.

In sea cages where cod were fed a full satiation ration during autumn/winter, fish directed their inspection behaviour at the net panel and the net frame, rather than at different types of repair.

The frequency of escape related behaviours may have a seasonal aspect - the overall number of net inspections and bites decreased during autumn and winter when water temperature and daylength decreased.

The majority of the sea cage studies showed that the number of inspections and bites decreased during feeding. This suggests the presence of feed in the water column distracts the fish from browsing the net wall.

Short-term, 50% feed restriction did not increase the frequency of net inspections. However, low level net biting frequency did increase during feeding when fish were fed reduced rations

Biofouling with a long-term algal biofilm did not emerge as a risk factor for net inspection or net biting behaviour during spring. However, biofouling with seaweeds did increase the frequency of both net biting and inspection behaviour.

There was no clear relationship between short-term changes in stocking density and the frequency of net inspection behaviours.

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To reduce the prevalence of net inspection, biting or escape-related behaviour in European seabass, farmers should:

Ensure that there are no loose threads inside the net wall, on commercial farms. This will markedly reduce the frequency of bass biting and interacting with the net wall, and reduce the risk of further net damage.

Seabass seemed to move away from the net when personnel were present. If a hole in the net is suspected, personnel should stay above the site until the net can be inspected and repaired.

After a net has been damaged, the close proximity of neighbouring cage structures may decrease the risk of seabass swimming through a hole in the net. If farmers wish to reduce the potential number of escapes through a hole in the net wall, they could install a floating net near or around the cages until the hole is repaired.

RECOMMENDATIONS FOR PREVENTING AND MITIGATING ESCAPE-RELATED BEHAVIOURS IN EUROPEAN SEABASS

With regard to European seabass, work carried out during the Pre-Escape WP also identified a number of husbandry factors that promote net biting and inspection behaviours, and also increase the prevalence of fish swimming through a hole in the net.

Findings from the seabass experiments carried out within the WP included:

Studies carried out on commercial farms showed that seabass had a propensity to bite loose thread on the cage wall. Contact with this thread was primarily through simple biting, but also with more physical tearing at the thread. However, this biting behaviour was only observed in commercial and not experimental studies.

The level of interaction with the cage wall and loose thread can change both within and between days on a commercial farm.

Reduced rations or short-term starvation had no effect on the escape activity of seabass.

The proximity of neighbouring cage structures reduced the frequency of escapes.

Exit of fish through the hole seemed to be dependent on proximity of the shoal to the net wall.

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With regard to gilthead seabream, both small and large scale experiments carried out during the Pre-Escape WP also identified a number of husbandry factors that promote net inspection, biting (Figure 3.5.2) and the propensity for bream to swim through a hole in the net (Figure 3.5.3).

RECOMMENDATIONS FOR PREVENTING AND MITIGATING ESCAPE-RELATED BEHAVIOURS IN GILTHEAD SEABREAM

Figure 3.5.3 Photo-sets showing the escape sequence of gilthead seabream. Photograph a) shows the fish locating the hole, b) and c) shows the fish entering and exiting the hole and d) shows the fish on the other side of the net. Total time required

for escaping through the hole was less than 333 ms. Photo-set: University of Crete.

Figure 3.5.2 Photo-sets showing gilthead seabream biting the net. Photograph a) fish

approaching the net wall, b) fish bends to the right and bites the twine , c) - g) fish

repeatedly pulls the twine, h) fish terminates the biting and begins to leave the area.

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To reduce the prevalence of net inspection, biting or the frequency of gilthead seabream swimming through net holes, farmers should:

Be diligent about seabream increasing the frequency of their escape-related behaviours when held at higher stocking densities.

Match feed delivery to appetite, and neither underfeed nor completely starve fish for prolonged periods.

Maintain net cleanliness. If biofouling materials build up on or around the net walls, farmers should attempt to remove these as quickly as possible.

Findings from the seabream experiments undertaken during the Pre-Escape WP included:

Stocking density does increase the risk of seabream inspecting a net wall and escaping through a hole (Papadakis et al. 2012). This contrasts with our findings on Atlantic cod, and shows the need for research to be carried out on escape risks at a species-specific level.

Both reduced rations and feed deprivation increased net inspection and the frequency of bream escaping through a hole in the net (Glaropoulos et al. in press).

White netting material increased the number of net inspections in comparison to dark coloured nets in seabream.

Biofouling also increased the frequency of net biting behaviour in seabream.

Studies carried out in commercial cages showed that the incidence of escapes can be low when compared with seabass.

However, larger seabream do appear to browse upon and damage the net wall, as markings on the cage wall may be evidence of net biting on loose threads and removal of the antifouling coating.

Commercial cage studies showed that interactions with a hole in the net were not very dependent on the position of the shoal in relation to the net; a number of fish were observed to be moving along the wall of the cage, independent of the shoal.

Close interactions with a net hole did not often lead to an escape in cage-held seabream on a commercial farm.

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Damsgård B, Høy E, Uglem I, Hedger RD, Izquierdo-Gomez D, Bjørn PA (in press) Net-biting and escape behaviour in farmed Atlantic cod, Gadus morhua: Effects of feed motivation and net traits. Aquaculture Environment Interactions

Glaropoulos A , Papadakis VM, Papadakis IE, Kentouri M (in press) Escape-related behavior and coping ability of seabream due to food supply. Aquaculture International

Hansen LA, Dale T, Damsgård B, Uglem I, Aas K, Bjørn P-A (2009) Escape-related behaviour of Atlantic cod, Gadus morhua L., in a simulated farm situation. Aquaculture Research 40:26–34

Høy E, Volent Z, Moe-Føre H, Dempster T (2011) Loads applied to aquaculture nets by the biting behaviour of Atlantic cod (Gadus morhua). Aquacultural Engineering 47:60-63

Moe H, Dempster T, Sunde LM, Winther U, Fredheim A (2007) Technological solutions and operational measures to prevent escapes of Atlantic Cod (Gadus morhua) from sea-cages. Aquaculture Research 38:90–99

Moe H, Gaarder RH, Olsen A, Hopperstad SO (2009). Resistance of aquaculture net cage materials to biting by Atlantic cod (Gadus morhua). Aquacultural Engineering 40:126–134 Papadakis VM, Papadakis IE, Lamprianidou F, Glaropoulos A, Kentouri M (2012) A computer-vision system and methodology for the analysis of fish behavior. Aquacultural Engineering 46:53-59

REFERENCES CITED

Seabream are attracted by loose threads and damage the net wall (Glaropoulos et al. in press). If the net is repaired out of the water, ensure all seams, knots and loose threads are on the outside of the net. Further, all repaired seams should have smooth finishes inside the net and there should be no loose threads inside the net. Tie-wraps/cable-ties are very useful for quick repairs until the net can be removed during scheduled maintenance.

Seabream seemed to move towards the net if personnel were present. If a hole in the net is suspected, personnel should stay away from the site until the net can be quickly inspected and repaired.

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