Anne Gro Vea Salvanes

Environmental variability in the early rearing environment generates behaviourally flexible cod: implications for rehabilitating wild populations

The release of hatchery-reared fishes for restoring threatened and endangered populations is one of the most controversial issues in applied ecology. A central issue has been to determine whether releases cause extinction of local wild populations. This may arise either through domesticated or non-local fishes hybridizing with wild fishes, or through inappropriate behavioural interactions; for example, many hatchery fishes show exaggerated aggressive and competitive behaviour and out-compete wild counterparts. The impact of the impoverished hatchery environment in shaping behaviour is only now receiving attention. Attempts to counteract hatchery-related behavioural deficiencies have utilized intensive training programmes shortly before the fishes are released. However, we show here that simple exposure to variable spatial and foraging cues in the standard hatchery environment generates fishes with enhanced behavioural traits that are probably associated with improved survival in the wild. It appears that fishes need to experience a varying and changeable environment to learn and develop flexible behaviour. Using variable hatchery rearing environments to generate suitable phenotypes in combination with a knowledge of appropriate local genotypes, rehabilitation of wild fishes is likely to succeed, where to date it has largely failed.

Vertical distribution and trophic interactions of zooplankton and fish in Masfjorden, Norway

Abstract The distribution, biomass, and predator-prey relationships of the pelagic assemblage in Masfjorden, western Norway, was studied in January 1989. The pelagic biomass was dominated by particulate organic matter. Biomasses of copepods, macroplankton, and mesopelagic fishes were of the same order of magnitude, while the biomass of larger pelagic fishes were one order less. Predator-prey relationships seemed most important at intermediate and higher trophic levels. Two sound-scattering layers, consisting of adult Maurolicus muelleri (lower layer) and juvenile M. muelleri (upper layer) performed instantaneous lightdependent vertical migration. Vertical distributions are explained in terms of balancing food demands against predation risk.

Trophic Structure and Community Stability in an Overfished Ecosystem

Gobbled by Gobies A common feature of overfished marine ecosystems is a tendency for biomass to become dominated by jellyfish and microbes, and for the habitat to become anoxic or hypoxic as large fish species are removed. The Benguela ecosystem off the coast of Namibia is a case in point. Utne-Palm et al. (p. 333) describe how the loss of overfished sardines from the Benguela fishery has provided an opportunity for an endemic fish species, the bearded goby, to exploit jellyfish and microbial biomass and to increase in number. These small fish have in turn become the predominant prey species for the larger fish, birds, and mammals in the region. The significance of the goby lies in its ability to forage on resources traditionally regarded as “dead-ends.” The bearded goby has thus become a key stabilizing component to the turnover of energy in the Benguela ecosystem. An endemic goby exploits jellyfish and microbial biomass, partially restoring the food chain in the Benguela ecosystem. Since the collapse of the pelagic fisheries off southwest Africa in the late 1960s, jellyfish biomass has increased and the structure of the Benguelan fish community has shifted, making the bearded goby (Sufflogobius bibarbatus) the new predominant prey species. Despite increased predation pressure and a harsh environment, the gobies are thriving. Here we show that physiological adaptations and antipredator and foraging behaviors underpin the success of these fish. In particular, body-tissue isotope signatures reveal that gobies consume jellyfish and sulphidic diatomaceous mud, transferring “dead-end” resources back into the food chain.

Environmental enrichment promotes neural plasticity and cognitive ability in fish

Different kinds of experience during early life can play a significant role in the development of an animals behavioural phenotype. In natural contexts, this influences behaviours from anti-predator responses to navigation abilities. By contrast, for animals reared in captive environments, the homogeneous nature of their experience tends to reduce behavioural flexibility. Studies with cage-reared rodents indicate that captivity often compromises neural development and neural plasticity. Such neural and behavioural deficits can be problematic if captive-bred animals are being reared with the intention of releasing them as part of a conservation strategy. Over the last decade, there has been growing interest in the use of environmental enrichment to promote behavioural flexibility in animals that are bred for release. Here, we describe the positive effects of environmental enrichment on neural plasticity and cognition in juvenile Atlantic salmon (Salmo salar). Exposing fish to enriched conditions upregulated the forebrain expression of NeuroD1 mRNA and improved learning ability assessed in a spatial task. The addition of enrichment to the captive environment thus promotes neural and behavioural changes that are likely to promote behavioural flexibility and improve post-release survival.

Exposure to variable spatial information in the early rearing environment generates asymmetries in social interactions in cod (Gadus morhua)

Many re-introduction programs used for conservation of populations and species threatened with extinction advocate the use of enriched rearing environments to train animals how to behave appropriately in the wild. Curiously, most of the current fish re-stocking programs have paid little attention to lessons previously learned in bird and mammal re-introductions. Many rehabilitation programs that use releases of hatchery fish observe higher mortality in released fish compared to wild, with most mortality arising shortly after release. One explanation for this mortality is based purely on selection processes; many hatchery fish normally selected out of the population thrive in the predator free, food-rich hatcheries. Alternatively, mortalities may be high because hatchery nursery environments fail to shape fish behaviour appropriately. Here, we empirically address the effect of enrichment in the early rearing environment in coastal cod (Gadus morhua). We find asymmetries in aggressive behaviour when fish reared in plain or enriched environments are allowed to interact. Furthermore, cod reared in standard, impoverished, hatchery environments spend less time in shelter, are more active, and show weaker anti-predator responses than fish reared with access to heterogeneous spatial cues. These results suggest that the constant, plain environments of fish farms may generate behavioural deficits that could reasonably be expected to be associated with lower survival in fish released into the wild.

Effects of early experience on group behaviour in fish

Animals that undergo a habitat shift face a number of challenges as they move between habitats; for example, they may encounter new predator species and may be vulnerable as they adapt to their new surroundings. An ability to adapt quickly to the new environment is likely to influence post-transition survival, and an understanding of the development of this ability is important in species that we rear for conservation and reintroduction programmes. Juvenile cod, Gadus morhua, undergo a habitat shift during their development, and they are also a species where reintroduction work has been tried. Here, we describe an experiment that investigated the effects that rearing environment has on cod shoaling behaviour. Cod were tested just after they had undergone the transition from a pelagic to a more benthic existence. We found that cod reared in either an enriched or in a plain, standard hatchery environment differed in terms of their shoaling responses; the shoaling tendency of fish reared in enriched tanks varied between testing environments, but fish reared in plain environments responded in the same way across the testing conditions. We discuss the influence of early experience on the development of appropriate behavioural responses and the importance of this for captive-reared species that are released into the wild.

Effects of formaldehyde and ethanol preservation on body and otoliths of Maurolicus muelleri and Benthosema glaciale

Abstract First of its kind, this study examines effects of preservatives on otoliths as well as on fish size and weight. Effects of200 days of preservation in 4 % seawater fonnaldehyde solution and 80 % ethanol were investigated for the two small, mesopelagic fishes, Benthosema glaciale (REINHARDT, 1837), and Maurolicus muelleri (GMELIN, 1789). The body weight loss was much higher in ethanol (37–39 %) than in fonnaldehyde (13–16 %). The decrease in standard length was small in both preservatives and for both species (0.8–3 %). The weight of the otoliths of B. glaciale was estimated to decrease by approximately 3 % in both formaldehyde and ethanol, while a radius change in one direction could not be demonstrated unambiguously. In contrast, there were no significant changes in the otoliths of M. muelleri in any of the preservatives, thus we can use otoliths from M. muelleri preserved for up to at least 200 days in correctly buffered fonnaldehyde. Growth rate and age can then easily be coupled with other lif...

Dominating sublittoral fish species in a west Norwegian fjord and their trophic links to cod (Gadus morhua L.)

Abstract The fish fauna in the sublittoral habitat of Masfjorden, western Norway, has been studied in order to reveal survival and growth prospects of released juvenile cod in a large-scale stock enhancement experiment. Seasonal changes in abundance of dominating fish species and in the diet of potential competitors and predators to juvenile cod were emphasized. A total of 44 species from 17 families of Teleostei and 4 families of Chondrichthyes were recorded at 5–20 m depth of the sublittoral of Masfjorden. Gadids were dominating (50.2 % by numbers, 10 species) and saithe (Pollachius virens), pollack (P. pollachius), poor-cod (Trisopterus minutus) and cod (Gadus morhua) were most numerous. Labrids form a second dominating family (44.7 % by numbers, 5 species) of which Centrolabrus exoletus, Ctenolabrus rupestris, Labrus bimaculatus and L. bergylta were the most abundant. Pollack and saithe had highest abundance during summer and autumn. The labrids and poor-cod had maximum abundance in summer. All labrid...

Is individual variation in competitive performance of reared juvenile cod influenced by haemoglobin genotype

Abstract To succeed in scramble competition for food an individual fish will have to have characteristics that allow it to respond rapidly to encountered prey. A trait such as metabolic rate, which has a positive effect on oxygen consumption and growth rate, is likely to be positively correlated with the traits that determine the speed of reaction. An important factor underlying metabolic rate may be the transport efficiency of oxygen from the gills to the respiring tissue and this is mediated by the structure of the haemoglobin molecule. In cod, two structures of this molecule exist due to polymorphism at the Hb1* locus. An individual cod may be homozygous (HbI*1/1 or HbI*2/2) or heterozygous (HbI*1/2), Evidence exists in the literature that HbI*2/2 fish have higher growth rate and earlier maturation and higher transport efficiency of oxygen at low temperature. However, no study has examined whether this could be associated with fish behaviour. In a study reported here we designed an experiment to test the hypothesis that fish with the HbI*2/2 genotype have a higher motivation to feed and are better competitors than individuals with the other haemoglobin genotypes and that they will eat a larger share of the prey. We use prey capture success early in a feeding trial and the rank of the first prey taken, as proxy-variables for competitive performance. Randomly chosen one-year-old cod Gadus morhua L. in small groups were tested experimentally for individual responses to prey offered sequentially. We analysed the effect on competitive performance of haemoglobin genotype, group, fish size, sex, maturation status and unobserved effects using Components of Variance Analysis, which accounts for repeated observations from the same individuals. The most successful fish were usually among the first to feed and tended to possess haemoglobin genotype HbI*2/2. Other factors such as body size, sex, stage of maturation and group also had effects which may modify the effect set by genotype. Our results suggest that the link between Hbl* genotype and growth is through feeding behaviour and it supports the idea that fish with HbI*2/2 genotype are better able to support an active metabolism. The results obtained are among the first on fish that show that variation in feeding behaviour could be under genetic control.

Individual variability in state-dependent feeding behaviour in three-spined sticklebacks

We studied state-dependent feeding behaviour of three-spined sticklebacks, Gasterosteus aculeatus, during several trials of sequential encounters with 6-mm and 8-mm Asellus aquaticus prey. We used stomach fullness (the number of prey eaten previously) as an indicator for state, which we assumed to affect motivation for feeding. Dummy variable regression was used to study how the per trial energy consumption, the number of events experienced, feeding efficiency and the average time spent on each accepted prey depended on trial number, day and fish. A clear individual variability was found. Feeding behaviour was strongly related to the individuals recent feeding history (within a day). Logit regression models showed that the decision to accept or reject a prey encountered depended on the size of the fish as well as its state (stomach fullness). Although limited, our results demonstrate pronounced heterogeneity in feeding behaviour among individual fish. We discuss this phenomenon in the broader context of population regulatory mechanisms. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.