prevent_escape_chapter_5.1

seeks to reduce the number of fish that escape from European aquaculture through research to improve fish farming techniques and technologies.

PREVENT ESCAPE is financially supported by the Commission of the European Communities, under the 7th Research Framework Program.

5.1. A NOVEL FORM OF ESCAPE OF FISH FROM SEA CAGES: THE PROBLEM OF ‘ESCAPE THROUGH SPAWNING’ Cite this article as: Somarakis S, Uglem I, Dempster T (2013) A novel form of escape of fish from sea cages: the problem of ‘escape through spawning’. In: PREVENT ESCAPE Project Compendium. Chapter 5.1. Commission of the European Communities, 7th Research Framework Program. www.preventescape.eu ISBN: 978-82-14-05565-8

authors: Stelios Somarakis1, Ingebrigt Uglem2 & Tim Dempster3 Hellenic Centre for Marine Research, Crete, Greece, Norwegian Institute for Nature Research, Norway, 3 SINTEF Fisheries & Aquaculture, Norway 1 2

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Fish farming in sea cages is increasing worldwide, driving an increase in both the volumes of fish produced and the numbers of fish species being cultured. During the last decade, farming of species that may reproduce within sea cages has become more common. Examples of such species within European aquaculture are Atlantic cod (Jørstad et al. 2008) and seabream (Dimitriou et al. 2007). However, knowledge of the extent and ecological effects of reproduction of farmed fish within commercial sea cages is sparse.

The lack of knowledge on the extent and consequences of egg escape in commercial culture restricts our ability to predict the need to implement mitigative actions aimed at reducing escape of fertilised eggs from sea cages. We require a greater understanding of: The lack of knowledge on the extent and consequences of egg escape in commercial culture restricts our ability to predict the need to implement mitigative actions aimed at reducing escape of fertilised eggs from sea cages. We require a greater understanding of s how frequently spawning occurs within sea cages; s how many eggs escape and survive; s whether wild and farmed fish spawn at the same time; s where escaped eggs and larvae disperse to; and s if escaped eggs and larvae mix with those of wild conspecifics.

The EGG Escape WP aimed to build knowledge in these areas using a major ‘industrial’ species, seabream (Sparus aurata), a rapidly ‘emerging’ species, Atlantic cod (Gadus morhua), and a relatively new ‘emerging’ species, meagre (Argyrosomus regius). Answers to these fundamental questions will be central for evaluating the need for mitigation through such measures as inhibiting spawning, recommendations for feeding strategies to reduce the quality of spawned eggs so that egg quality is poor, developing technologies to stop eggs from escaping or recommendations for siting of farms to areas that are distant from spawning areas of wild fish.

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ESCAPE

OF COD THROUGH SPAWNING

In Atlantic cod farms, some fish mature during the first year of culture, while the majority are believed to mature during the second year of culture. This means that almost the entire culture stock in any particular farm has the potential to spawn in sea cages. Efforts to prevent maturation, mainly through manipulation of the light regime in sea cages, have so far been unsuccessful. Although timing of maturation can be changed, it is difficult to inhibit maturation completely (e.g. Hansen et al. 2001, Taranger et al. 2006). The use of hybridization, sterilization and polyploidy to counter this problem are possibilities, but problems such as initially higher mortality, greater fingerling costs, poorer growth and consumer acceptance need to be resolved before they are taken up by industry (Triantafyllidis et al. 2007). Consequently, farmed cod are capable of producing viable eggs and larvae within sea cages, which subsequently mix with larvae from wild cod in the areas around cod farms and survive until one year of age (Jørstad et al. 2008, van der Meeren and Jørstad 2009). Thus, cod farming has the potential to result in unfavourable genetic changes in wild cod populations in the same way as is found for Atlantic salmon (Hindar et al. 2006), but not only through escape of adult fish.

Jørstad et al. (2008) demonstrated that Atlantic cod held within an experimental sea cage are capable of spawning eggs that then dispersed into a nearby fjord system. In the same study, larvae from genetically marked farmed cod were found in plankton net samples up to 8 km away from an experimental farm during the natural spawning season of cod. Furthermore, in the proximity of this farm, 25% of the cod larvae in plankton samples were determined by genetic analyses to have originated from the 1000 farmed cod. This indicates that if spawning occurs within cod farms where numbers of animals are far greater, the contribution of ‘escaped’ larvae to cod recruitment within fjords may be substantial. However, most current farms are located at more exposed locations than the experimental farm studied by Jørstad et al. (2008).

The escape of eggs will likely be a persistent occurrence in cod culture. The escape of large quantities of eggs from caged cod may be problematic as: 1) coastal cod populations in parts of Norway have decreased considerably over several decades, principally due to overfishing; 2) coastal cod have a high fidelity to specific spawning grounds (e.g. Wright et al. 2006); and 3) sea cage cod farms are often located within short distances of known wild cod spawning grounds (Uglem et al. 2008). Recent research also suggests that cod eggs may be entrained in the vicinity of the spawning grounds long after spawning (Knutsen et al. 2007). Therefore, it is possible for larvae from escaped cod eggs to experience favourable conditions for survival and recruitment to coastal cod stocks.

The extent and effect of spawning within commercial sea cages is largely unknown, even though it is unquestionable that farmed cod have the potential for producing large numbers of “escaped” egg and larvae. The effects of spawning in cages will depend not only on the numbers of egg and larvae which escape, but also on their quality and survival, which in turn is a result of both innate and environmental factors, such as broodstock nutrition, timing of hatching and egg/larval drift following spawning. Further, the ecological effect of this type of escape will depend on the degree to which local adaptations exist in wild cod stocks.

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OF SEABREAM THROUGH SPAWNING

In the Mediterranean region, information about spawning by fish kept in sea cages is limited.

In Greece, the largest EU producer of seabream, a spectacular increase in both the number of fish farms and their production capacity took place over the past decade, accompanied by a substantial decrease in the price of seabream. This industrial development led to structural and functional changes in the rearing process. Farming durations increased from just 12 to 18 months before 1995 to durations of up to 40 months after 1999 (Dimitriou et al. 2007).

Gilthead seabream is a protandrous hermaphrodite species and the increased farming duration has resulted in the production of fish of a size that can reach the stage of sex inversion and female sexual maturation, normally observed at the age of 2 – 3 years in the wild (Mylonas et al.

2011). The aforementioned changes in rearing processes have resulted in the presence of large gilthead seabream individuals (larger than 500 g) in cages during the normal reproductive period of their wild counterparts (November – March: Mylonas et al. 2011). There is evidence that sex inversion and the production of both male and female gametes occur within cages under the present industrial rearing pattern (Dimitriou et al. 2007). A doubling of the population of wild seabream within the Messolonghi lagoon in Greece, based on standardised commercial fishing trap catch returns, correlates with the advent of farming sea-bream to large sizes in the region.

Spawning within sea cages is suspected to have led to greater recruitment to wild seabream stocks (Dimitriou et al. 2007). Ecological and economic consequences of this population shift have ensued. While more wild sea-bream are now available to the fishery, they are of much smaller mean size resulting in an overall lower economic return to local fishers.

The quality of the eggs produced by caged fish and the eventual survival of the larvae is an important yet unknown feature of egg escapes. Cultured cod are known to have different body fat content and fatty acid distributions than their wild counterparts and it is possible that the quality of eggs produced by cultured fish differ from wild fish (Salze et al. 2005). In contrast to Atlantic cod, various fatty acid groups have not been found to differ significantly between wild and cultured seabream, mainly due to the high variability reported in the literature (Grigorakis 2007). However, it has been well demonstrated that cultured fish have higher levels of fat deposits (both perivisceral and peritoneal) and linoleic acid (18:2n-6) when compared to wild fish, the latter being richer in arachidonic acid (Grigorakis 2007, Saglik et al. 2003). How this effects egg production and quality is unknown.

MEAGRE –

AN EMERGING SPECIES OF INTEREST

A species of emerging interest for sea cage aquaculture in the Mediterranean, the meagre (Argyrosomus regius), also has the potential to reproduce during culture in sea cages, as it is typically grown to a commercial size of 40 – 60 cm (1 – 3 kg). If spawning occurs within cages, recruitment of juveniles to wild populations may result. Meagre is uncommon in many areas of the Mediterranean Sea, thus large increases in their abundance in specific coastal areas could lead to ecological changes.

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OBJECTIVES The main objective of the ‘EGG Escape’ work package was to assess the extent and ecological importance of escape through spawning in sea cages and suggest possible mitigation actions.

The work consisted of both an extensive field program and a modelling component. In the field program, farmed fish were randomly collected at selected Atlantic cod (Gadus morhua), seabream (Sparus aurata) and meagre (Argyrosomus regius) farms in Norway, Greece and Spain, respectively. The three species were selected to include: a) a major industrial species (seabream) with increasing potential to spawn within cages; b) a species (cod) initially predicted to make a transition from an emerging to a major industrial species within a few years, which is known to spawn within cages; and c) a new emerging species (meagre) that was suspected to spawn within cages.

The specific objectives of WP5 were to: s evaluate the extent and timing of spawning within sea cage fish farms at an industrywide scale; s assess the quality of released eggs; s assess the survival and distribution of escaped eggs; and s evaluate the need for implementation of mitigative strategies for reducing or preventing escape of eggs

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REFERENCES

CITED

Dimitriou E, Katselis G, Moutopoulos DK, Akovitiotis C, Koutsikopoulos C (2007) Possible influence of reared gilthead seabream (Sparus aurata, L.) on wild stocks in the area of the Messolonghi lagoon (Ionian Sea, Greece). Aquac Res 38:398-408 Grigorakis K (2007) Compositional and organoleptic quality of farmed and wild gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax) and factors affecting it: A review.

Aquaculture 272:55-75 Hansen T, Karlsen Ø, Taranger GL, Hemre GI, Holm JC, Kjesbu OS (2001) Growth, gonadal development and spawning time of Atlantic cod (Gadus morhua) reared under different photoperiods. Aquaculture 203:51-67 Hindar K, Fleming IA, McGinnity P, Diserud O (2006) The genetic and ecological effects of salmon farming on wild salmon: modelling from experimental results. ICES J Mar Sci 63, 1234-1247 Jørstad KE, van der Meeren T, Paulsen OI, Thomsen T, Thorsen T, Svåsand T (2008) “Escapes" of eggs from farmed cod spawning in net pens: Recruitment to wild stocks. Rev Fish Sci 16:285295 Knutsen H, Moland OE, Ciannelli L, Heiberg ES, Knutsen JA, Simonsen JH, Skreslet S, Stenseth NC (2007) Egg distribution, bottom topography and small scale cod population structure in a coastal marine system. Mar Ecol Prog Ser 333:249-255 Mylonas CC, Zohar Y, Pankhurst N, Kagawa H (2011) Reproduction and broodstock management.

In: Pavlidis MA, Mylonas CC (eds) Sparidae: Biology and Aquaculture of gilthead seabream and other species. Blackwell Publishing, pp. 95-131 Saglik S, Alpaslan M, Gezlin T, Cetlinturk K, Tekinay A, Guven KC (2003) Fatty acid composition of wild and cultivated gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax).

Eur J Lipid Sci Technol 105:104-107 Salze G, Tocher DR, Roy WJ, Robertson DA (2005) Egg quality determinants in cod (Gadus morhua L.): egg performance and lipids in eggs from farmed and wild broodstock. Aquac Res 36:1488-1499 Taranger GL, Aardal L, Hansen T, Kjesbu OS (2006) Continuous light delays sexual maturation and increases growth of Atlantic cod (Gadus morhua L.) in sea cages. ICES J Mar Sci 63:365-375 Triantafyllidis A, Karaiskou N, Bonhomme F, Colombo L, Crosstie D, Danancher D, GarcíaVázquez E, Gilbey J, Svåsand T, Verspoor E, Triantaphyllidis C (2007) Management options to reduce genetic impacts of aquaculture activities. In: Genetic Impact of Aquaculture Activities on Native Populations. GenImpact Compendium (http://genimpact.imr.no/compendium)

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Uglem I, Bjørn P-A, Dale T, Kerwath S, Økland F, Nilsen R, Aas K, Fleming I, McKinley RS (2008) Movements and spatiotemporal distribution of escaped famed and local wild Atlantic cod (Gadus morhua L.) in a Norwegian fjord. Aquac Res 39:158-170 van der Meeren T, Jørstad KE (2009) Fanger torsk på vidvanke. Nytt fra havbruk 2009(2), 1 (In Norwegian) Wright PJ, Galley E, Gibb IM, Neat FC (2006) Fidelity of adult cod to spawning grounds in Scottish waters. Fish Res 77:148-158

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