Interactions between escaped farmed and wild cod. Research supported by the Norwegian Research Council (2006-09, Projects ' Interactions' and 'Vertical'). Unless otherwise cited, all content is by Justin J. Meager and Jon Egil Skjaeraasen.

QUICK LINKS Introduction Project objectives Juvenile experiments: territorial competition antipredator behaviour coping styles Adult experiments spawning competition (mesocosm) natural spawning ground Research staff and collaborators Further reading

Have you caught a cod with an external tag/ har du fanget en fisk med ytre merker?

INTRODUCTION

Cod is a new target species for aquaculture in the north Atlantic (Fig. 1). Most farmed cod are produced in net-pens in sheltered coastal areas used as habitat by coastal cod. To date, the rate of escapes from cod farming has been much higher than that of salmon, and it has been estimated that a half a million cod escaped in Norway between 2000 and 2005 (up to 6% of the yearly farmed stock) (Moe et al. 2007; Hansen et al. 2008). In 2008, 228 000 cod were reported to have escaped from net pens along the Norwegian coast (official statistics, Norw. Directorate of Fisheries). This has been attributed mainly to the small size at which they are on-grown in net- pens (~10-20 grams) and the tendency of farmed cod to bite the net-pen walls and explore new openings (Moe et al. 2007). As future expansion of the industry is expected, interactions between farmed escapees and local coastal stock are inevitable.

The main risks that escapees pose to native cod stocks include genetic alteration, competition for space and resources, disruption of social behaviour, cannibalistic predation and transmission of pathogens (see review by Naylor et al. 2005, Fig. 2). Genetic introgression from escapees has caused fitness depression in wild salmon populations and similar effects may occur with cod. Coastal cod populations have a localised genetic structure that may make them particularly vulnerable to introgression from farmed fish (Bekkevold et al. 2006).

The impact of farm escapees does not necessarily depend on fish surviving to reproduction. If the escapee population is continually replenished they may still have deleterious effects on earlier life history stages (Naylor et al. 2005). Hence, to understand fully and to avoid potential impacts of escapees on wild stocks, detailed information on how farmed fish compete and interact with wild fish in both nursery habitats and spawning grounds is required (Fig. 2).

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Figure 1: licenses for cod sea-cage farming in Norway (red circles), 2007. Data from Norw. Direct. of Fisheries.

Figure 2: Summary of risks imposed by escapees on wild stock. Text in bold: assessed by our research.

PROJECT OBJECTIVES

We aimed to address the potential impacts of escapees on wild stocks by providing detailed information on how farmed fish compete and interact with wild fish in both nursery habitats and spawning grounds. Specifically, we aimed to test if:

1. Escaped juvenile farmed cod compete for space and reduce the ability of local populations to avoid predators

2. Escaped adult farmed cod disrupt spawning events and hybridise with wild populations

We addressed objective (1) in laboratory experiments and objective (2) using laboratory and field experiments.

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JUVENILES: TERRITORIAL AND ANTIPREDATOR BEHAVIOUR

Escapees may displace wild cod from sheltering sites and aggressive interactions between wild and escapees may decrease predator vigilance (Jakobssen et al. 1995). Escapees are also likely to compete with wild cod for resources, because large liver energy reserves (Grant et al. 1998; Kristiansen et al. 2000) and the availability of alternative food items (Nordeide & Salvanes 1991) are believed to sustain farmed cod until they have overcome an initial foraging disadvantage (Nordeide & Fosså 1992; Steingrund & Fernö 1997).

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COMPETITION BETWEEN FARMED AND WILD JUVENILES

Little is known of competition for space between farmed and wild cod. Social interactions between juvenile cod can be quite plastic, ranging from group tactics such as shoaling (e.g. Laurel et al. 2004; Anderson et al. 2007) to territorial defence (Tupper & Boutilier 1995a,b; Gotceitas & Brown 1993) depending on factors such as habitat availability, the density of conspecifics and the threat of predation. In areas of complex substrata, juvenile cod are thought to have a restricted home range (Hawkins et al. 1980) and defend territories around shelter sites (Tupper & Boutilier 1995a,b).

Experiments at the University of Bergen (UiB) have shown that the early rearing environment affects the development of agonistic behaviour (Salvanes & Braithwaite 2005). Cod from conventional rearing environments were less aggressive than cod from enriched rearing environments. Although wild cod were not examined and the influence of the rearing environment on the development of territorial behaviour in cod is yet to be tested, the hatchery environment impairs the ability of salmon to compete for territories with wild fish (Metcalfe et al. 2003). If there is a similar effect in cod, wild populations may be quite robust to competitive displacement by escapees.

We assessed the potential of farmed escapees to competitively displace wild fish, using the classic ‘intruder-resident’ experimental setup (Fig. 3). These experiments also compared aggression between farmed and wild fish, and were the basis of Masters research defended at UiB in June 2008 by Gisle Sverdrup. Collaborators for these experiments included Justin Meager, Anders Fernö, Jon Egil Skjæraasen, Torbjorn Järvi and and Anne Gro Salvanes.

Publications

Sverdrup, G.K.; Meager, J.J.; Fernö, A.; Rodewald, P.; Skjæraasen, J.E.; Järvi, T.; Salvanes, A.G. (in review). Territorial and agonistic interactions between farmed and wild juvenile Atlantic cod (Gadus morhua L.). Aquaculture Research

Sverdrup, G.K. (2008). Territorial and agonistic interactions between farmed and wild juvenile Atlantic cod (Gadus morhua L.). Masters Thesis, Department of Biology, University of Bergen. 67 pp.

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Figure 3: Schematic representation of experimental tank, with the intruder (1 x 0.8 m, 0.5 m depth) and defender sections (2 x 0.8 m, 0.5 m depth) separated by a sliding door operated by a pulley system. The defender section was provided with a gravel substratum, shelter and a feeding station, whereas the intruder section had only a feeding station (Sverdrup 2008).

ANTIPREDATOR BEHAVIOUR OF FARMED AND WILD JUVENILES

Ineffective antipredator behaviour (Nordeide & Svåsand 1990, Nødtvedt et al. 1999) is believed to explain the initial poor survival of reared cod in nature (Svåsand et al. 2000). Wild juvenile cod have a flexible behavioural repertoire towards predators that is threat sensitive. Cod are able to assess predation risk and respond, by sheltering (Goceitas et al. 1995), shoaling (Grant & Brown 1998), or by freezing/decreasing activity (Nødtvedt et al. 1999). Little is known about how this differs between farmed and wild cod. We recently compared the responses of farmed and wild juvenile cod to a standardised fright stimulus in the laboratory, and investigated behavioural reactions in terms of sheltering, swimming activity and escape responses at the level of individuals. We also investigated the antipredator behaviour of farmed and wild cod in mixed shoals towards visual signals from a live predator (Fig. 4). These experiments were the basis of Master's research defended at UiB by Petra Rodewald in April 2009. A range of approaches was used, such as motion analysis (MotionGrab, Robert S. Batty, SAMS, Oban) and high-speed video (Fig. 5). Collaborators include Justin Meager, Anders Fernö, Paolo Domenici, Jon Egil Skjæraasen and Torbjorn Järvi.

Publications

Meager, J.J.; Rodewald, P.; Domenici, P. Fernö, A.; Skjæraasen, J.E.; Järvi, T and Sverdrup, G.K. (in prep. ). Antipredator responses of hatchery-reared and wild cod (Gadus morhua L.) to mechano-acoustic stimuli. Journal of Fish Biology

Petra Rodewald (2009). Antipredator reactions of wild and reared juvenile Atlantic cod to fright stimuli (Gadus morhua L.)'. Masters Thesis, Department of Biology, University of Bergen. 68 pp.

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Figure 4: Video screen capture of an experiment comparing the behaviour of wild and farmed cod in a simulated natural environment. Mixed shoals of farmed and wild juvenile cod were given the choice of three habitats representing a gradient of risk and foraging return from (1) to (3). (1) structure, (2) no structure and food, (3) food and a predator, (4) an overhead view of the entire 3 m tank. A glass barrier prevented predator movement out of section (3) (Rodewald 2009).

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Figure 5: Juvenile cod (15 cm SL) escaping from a predator model with a fast-start. The sequence is in slow motion.

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COPING STYLES OF FARMED AND WILD COD

Domestication and hatchery-rearing affects the way fish respond to stress compared to their wild counterparts, by providing differential experience, survival within a single generation and selection for traits over generations (see Huntingford 2004 for review). This causes rapid phenotypic and genotypic divergence between farmed and wild fish (Gross 1998; Huntingford 2004), and may influence the ability of farm escapees to cope with challenges imposed by the natural environment and the outcome of interactions with wild fish that they encounter. We are currently comparing coping styles and neuroendocrine stress indicators between farmed and wild cod. Collaborators include Justin Meager, Anders Fernö, Ian Mayer, Jon Egil Skjæraasen and Svante Winberg.

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ADULTS: REPRODUCTIVE BEHAVIOUR

Very little is known of the potential of escaped cod to hybridise with wild stock, however the experience with salmon aquaculture indicates the risk of genetic introgression and fitness depressions in wild populations through interactions with escapees (Naylor et al. 2005). Escaped salmon now occur in all aquaculture regions (Naylor et al. 2005). Even at very limited levels of hybridisation, fitness depression can occur and may threaten vulnerable populations (McGinnity et al. 2003; Araki et al. 2007).

Coastal cod have a localised population structure (Bekkevold et al. 2006) and strong fidelity to known spawning locations, where shoals may persist for months (Robichaud & Rose 2001, 2003; Espeland et al. 2007). Experimentally released farmed cod are known to navigate to local spawning grounds (Svåsand et al. 1990; Wroblewski et al. 1996; Nøstvik & Pedersen 1999; Uglem et al. 2008), and cod farms are often located close to cod spawning grounds in sheltered coastal areas. It is therefore likely that farm escapees will join local spawning shoals.

However, the presence of escapees on spawning grounds does not necessarily imply hybridisation. Behavioural deficits in courtship behaviour can limit hybridisation between farmed and wild salmonids. Wild male salmonids have a much higher reproductive success than farmed males (Fleming et al. 1996, Petersson & Järvi 1997, Weir et al. 2004), due to their aggressive dominance behaviour and the failure of reared males to release sperm concurrently with female egg release (Fleming et al. 1996, Weir et al. 2004). Farmed females were readily accepted by wild males (Fleming et al. 1996, 2001), and are therefore a likely vector for genetic introgression of farmed genes into wild populations (Fleming et al. 2001, but see Weir et al. 2004).

Addressing the risk of hybridisation and courtship disruption thus depends on an understanding of the spawning behaviour of cod. Most of what we know of cod spawning behaviour comes from laboratory experiments (e.g. Brawn 1961; Hutchings et al. 1999), echosounding (e.g. Rose 1993) and presence-absence data (see review by Windle & Rose 2006). Cod are thought to use a lekking mating system (Hutchings et al. 1999, Nordeide & Folstad 2000), which is an aggregated male display that females attend primarily for fertilisation (Höglund & Alatalo 1996). During spawning, males act aggressively towards each other and court females using acoustic and visual displays (Brawn 1961, Hutchings et al. 1999, Skjæraasen 2003). These behavioural interactions are directly correlated to individual male reproductive success (Skjæraasen & Hutchings in prep).

Definitive support for these observations from the field requires observations of the behaviour of cod over fine spatial and temporal scales. Resolving the behaviour of rapidly moving individuals under low-light conditions in the ocean has to date, proved to be challenging to researchers. Behaviour also needs to be considered in three dimensions, as the spawning behaviour of cod also involves considerable vertical movement (e.g. Brawn 1961; Hutchings et al. 1999; Rose 1993). Our research therefore aims to not only address the risk that escapees pose to wild cod, but to test some basic predictions of the reproductive behaviour of cod in the wild.

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SPAWNING COMPETITION BETWEEN FARMED AND WILD COD

Ventral mount in the laboratory tank above. The male is underneath the female: click the image to enlarge.

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Publications

Skjæraasen, J.E.; Meager, J.J; Karlsen, Ø.; Mayer, I.; Dahle, G.; Rudolfsen, G.; Haugland, T. and Fernö, A. (in press) Mating competition between farmed and wild cod: wild females choose wild males. Marine Ecology Progress Series

Skjæraasen, J.E.; Meager, J.J. and Hutchings, J.A. (2010). The cost of male reproductive behaviour in Atlantic cod. Canadian Journal of Zoology 88(6):595-600.

Meager, J.J.; Skjæraasen, J.E. ; Fernö, A.; Karlsen, Ø.; Løkkeborg, S.; Michalsen, K. and Utskot, S.O. (2009). Vertical dynamics and reproductive behaviour of farmed escapee and wild cod (Gadus morhua). Marine Ecology Progress Series 389, 233-243.

Skjæraasen, J.E.; Mayer, I.; Meager, J.J.; Rudolfsen, G.; Karlsen, Ø; Haugland, T. and Kleven, O. (2009). Sperm characteristics and competitive ability in farmed and wild cod. Marine Ecology Progress Series 375, 219-228.

Skjærraasen, J.E.; Meager, J.J.; Karlsen, Ø (2008). Expression of secondary sexual characteristics in recruit and repeat spawning farmed and wild cod. ICES Journal of Marine Science 65, 1710-1716.

Skjaeraasen, J.E., Rowe, S., & Hutchings, J.A. (2006) Sexual dimorphism in pelvic fin length of Atlantic cod. Canadian Journal of Zoology 84, 865-870.

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BEHAVIOUR OF FARMED AND WILD COD ON A NATURAL SPAWNING GROUND

We examined sex-based patterns of movement and behaviour of farmed escapee and wild coastal cod on a spawning shoal in western Norway in February 2007. We released 93 farmed cod (F1 progeny of local broodstock) and 54 wild coastal cod from the spawning shoal. A subset of 48 fish was implanted with acoustic tags, including 12 fish of each type (farmed or wild) and sex, and the remaining fish were externally tagged with conventional tags. A stationary positioning system (Vemco VRAP) was used to track the 3-D movements of the fish on the spawning ground for 35 days.

Additional data were provided by a range of other techniques, such as hydroacoustics, passive acoustics, underwater video, fishing re-captures and egg sampling. Ultrasound was used to assess the reproductive status and sex of fish prior to release (Karlsen and Holm 1994), and the gonads of re-caught fish are being examined with histology. Data were also collected for environmental factors such as temperature, surface light, water currents, wind, turbidity and salinity, and fish depths were converted to distance from the seafloor using a bathymetric map from echosounding. An array of hydrophone receivers (VR2W) monitored broad-scale movements, presence/absence and depth dynamics of fish between 2007 and 2009.

Preliminary results were presented at the Second International Symposium on Tagging and Tracking Marine Fish with Electronic Devices in 2007 (Donostia-San Sebastian, Spain), and the Ecological and Evolutionary Ethology of Fishes conference (Boston USA) and the 5th World Fisheries Congress (Yokohama, Japan) in 2008. More details will be available soon.

Publications

Meager, J.J.; Skjæraasen, J.E. ; Fernö, A.; Karlsen, Ø.; Løkkeborg, S.; Michalsen, K. and Utskot, S.O. (2009). Vertical dynamics and reproductive behaviour of farmed escapee and wild cod (Gadus morhua). Marine Ecology Progress Series 389, 233-243

Meager, J.J.; Skjæraasen, J.E.; Fernö, A. and Løkkeborg, S. (2010). Reproductive interactions between fugitive farmed cod and wild cod in the field. Canadian Journal of Fisheries and Aquatic Sciences Canadian Journal of Fisheries and Aquatic Sciences 67: 1221-1231.

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PROJECT STAFF

Aquatic Behavioural Ecology Group, University of Bergen

Anders Fernö (Project co-ordinator, Professor)

Jon Egil Skjæraasen (Principal investigator and project manager, Researcher II)

PROJECT COLLABORATORS

University of Bergen

Ian Mayer: (Associate Professor, Developmental Biology of Fishes)

Anne Gro Vea Salvanes: (Professor, Leader of Aquatic Behavioural Ecology Group)

Institute of Marine Research

Svein Løkkeborg: (Researcher, Fish Capture Technology)

Kathrine Michalsen: (Researcher, Fish Stocks and Ecosytem)

Ørjan Karlsen (Researcher, Feed, Feeding and Quality)

Geir Dahle (Researcher, Population Genetics)

International

Jeffrey A Hutchings (Professor, Dalhousie University, Canada)

Gudrun Marteinsdottir (Professor, University of Iceland)

FURTHER READING

'Listen to the Cod', article published about our field study in a local newspaper 'Marsteinen' , by Dorthea M. Møgster, February 15, 2007 (Nynorsk). Click to enlarge.

Hva skjer når oppdrettstorsk møter villtorsk? [What happens when farmed cod meet wild cod]. 'Havbruk' newsletter (Norwegian) ?

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CITED REFERENCES

Anderson JL, Laurel BJ, Brown JA (2007) Diel changes in behaviour and habitat use by age-0 Atlantic cod (Gadus morhua L.) in the laboratory and field. J Exp Mar Biol Ecol 351:267-275

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Bekkevold D, Hansen MM, Nielsen EE (2006) Genetic impact of gadoid culture on wild fish populations: predictions, lessons from salmonids, and possibilities for minimizing adverse effects: Gadoid mariculture: development and future challenges. ICES J Mar Sci 63:198-208

Brawn VM (1961) Reproductive behaviour of the cod (Gadus callarias L) Behaviour 18:177-197

Fernö A, Jarvi J (1998) Domestication genetically alters the anti-predator behaviour of andadromous brown trout ( Salmo trutta ) - a dummy predator experiment. Nordic Journal of Freshwater Research 74: 95-100

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Gross MR (1998) One species with two biologies: Atlantic salmon (Salmo salar) in the wild and in aquaculture. Can J Fish Aquat Sci 55:131-144

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