Jarl Giske

Principles for the Conservation of Wild Living Resources

We describe broadly applicable principles for the conservation of wild living resources and mechanisms for their implementation. These principles were engendered from three starting points. First, a set of principles for the conservation of wild living resources (Holt and Talbot 1978) required reexamination and updating. Second, those principles lacked mechanisms for implementation and consequently were not as effective as they might have been. Third, all conservation problems have scientific, economic, and social aspects, and although the mix may vary from problem to problem, all three aspects must be included in problem solving. We illustrate the derivation of, and amplify the meaning of, the principles, and discuss mechanisms for their implementation. The principles are: Principle I. Maintenance of healthy populations of wild living resources in perpetuity is inconsistent with unlimited growth of human consumption of and demand for those resources. Principle II. The goal of conservation should be to secure present and future options by maintaining biological diversity at genetic, species, population, and ecosystem levels; as a general rule neither the resource nor other components of the ecosystem should be perturbed beyond natural boundaries of variation. Principle III. Assessment of the possible ecological and sociological effects of resource use should precede both proposed use and proposed restriction or expansion of ongoing use of a resource. Principle IV. Regulation of the use of living resources must be based on understanding the structure and dynamics of the ecosystem of which the resource is a part and must take into account the ecological and sociological influences that directly and indirectly affect resource use. Principle V. The full range of knowledge and skills from the natural and social sciences must be brought to bear on conservation problems. Principle VI. Effective conservation requires understanding and taking account of the motives, interests, and values of all users and stakeholders, but not by simply averaging their positions. Principle VII. Effective conservation requires communication that is interactive, reciprocal, and continuous. Mechanisms for implementation of the principles are discussed.

A theoretical model of aquatic visual feeding

Abstract A model for visual feeding by aquatic predators is derived. The predators visual range, which depends on its visual capability, surface light, water clarity, and size and contrast of the prey, is emphasised. Central to the model is the assumption that a prey may be recognized only if the difference in retinal flux, with and without the prey image, exceeds a threshold. This assumption is equivalent to requiring that the product of apparent contrast at retina, retinal background irradiance and area of prey image must exceed a threshold. Visual range ( r ) is found from the equation r 2 exp ( cr + Kz ) = ϱE 0 | C 0 | πs 2 ΔS e −1 , where c is beam attenuation coefficient, z is depth, K is diffuse attenuation coefficient, ϱ is light loss through the surface, E 0 is surface light intensity, C 0 is inherent contrast of prey, β is prey radius and ΔS e is sensitivity threshold of the eye for detection of changes in irradiance. The model predicts that visual range increases non-linearly with increasing predator size and ambient light. Visual range also increases almost linearly with increasing prey size and decreases non-linearly with increasing turbidity. These predictions are compared with experimental data. It is shown that characteristic fluctuations in light regime may be more important to feeding than characteristic variations in prey abundance in aquatic environments. Due to the direct impact of light on the feeding process of several predators (and thereby on the mortality process of prey), we conclude that light should be considered an important top-down control in aquatic ecosystems in addition to the bottom-up control exerted through primary production. Finally, the model is testable, and should stimulate a stronger interaction between theory and experiments in aquatic feeding ecology of visual predators.

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.

Artificial Evolution of Life History and Behavior

We present an individual‐based model that uses artificial evolution to predict fit behavior and life‐history traits on the basis of environmental data and organism physiology. Our main purpose is to investigate whether artificial evolution is a suitable tool for studying life history and behavior of real biological organisms. The evolutionary adaptation is founded on a genetic algorithm that searches for improved solutions to the traits under scrutiny. From the genetic algorithm’s “genetic code,” behavior is determined using an artificial neural network. The marine planktivorous fish Müller’s pearlside (Maurolicus muelleri) is used as the model organism because of the broad knowledge of its behavior and life history, by which the model’s performance is evaluated. The model adapts three traits: habitat choice, energy allocation, and spawning strategy. We present one simulation with, and one without, stochastic juvenile survival. Spawning pattern, longevity, and energy allocation are the life‐history traits most affected by stochastic juvenile survival. Predicted behavior is in good agreement with field observations and with previous modeling results, validating the usefulness of the presented model in particular and artificial evolution in ecological modeling in general. The advantages, possibilities, and limitations of this modeling approach are further discussed.

Implementing behaviour in individual-based models using neural networks and genetic algorithms

Even though individual-based models (IBMs) have become very popular in ecology during the last decade, there have been few attempts to implement behavioural aspects in IBMs. This is partly due to lack of appropriate techniques. Behavioural and life history aspects can be implemented in IBMs through adaptive models based on genetic algorithms and neural networks (individual-based-neural network-genetic algorithm, ING). To investigate the precision of the adaptation process, we present three cases where solutions can be found by optimisation. These cases include a state-dependent patch selection problem, a simple game between predators and prey, and a more complex vertical migration scenario for a planktivorous fish. In all cases, the optimal solution is calculated and compared with the solution achieved using ING. The results show that the ING method finds optimal or close to optimal solutions for the problems presented. In addition it has a wider range of potential application areas than conventional techniques in behavioural modelling. Especially the method is well suited for complex problems where other methods fail to provide answers.

Ecology in Mare Pentium: an individual-based spatio-temporal model for fish with adapted behaviour

Abstract A conceptual approach to study spatial movements of fish using an individual-based neural network genetic algorithm model is presented. Artificial neural networks, where the weights are adapted using a genetic algorithm, are applied to evolve individual movement behaviour in a spatially heterogeneous and seasonal environment. A 2D physical model (for the Barents Sea) creates monthly temperature fields, which again are used to calculate zooplankton production and predation pressure. Daily fish movement is controlled by reactive or predictive mechanisms. Reactive movement governs search for local optimal habitats, whereas predictive control enables adaptation to seasonal changes. Levels of growth and predation pressure at the time of decision are used to assess whether to apply reactive or predictive movement control. To make the model realistic on a large scale, each of the individuals are scaled up to represent a clone of one million siblings acting and growing synchronously. The fish lives for up to two years, and may reproduce in its second year. In order to spawn it has to be at the designated spawning area in the south-western part of the lattice in January. During spawning it produces a number of offspring in proportion to its body size. The “genetic constitution” of offspring (the weights of the synapses in the neural networks) is a mix of their “mothers” and a randomly picked member of the population. The model is able to solve the problem of navigating in a heterogeneous and seasonal environment. The movement of the artificial fish follows a seasonal pattern, typical for migrating pelagic fish stocks. During summer and autumn the distribution is widespread whereas during spring it is more concentrated. When trophic feedback is removed (i.e. zooplankton survival is independent of fish predation) the distribution of the fish is less dispersed which shows that the model allows for density dependent behaviour. Large-scale migration is an interplay between reactive and predictive movement control and when only one of these is allowed, the individuals are unable to adapt properly. Throughout most of its life the fish relies heavily on reactive movement, but during the spawning migration predictive movement control is applied almost exclusively.

Ontogeny, season and trade-offs: Vertical distribution of the mesopelagic fish Maurolicus muelleri

Abstract To investigate the validity of static optimization models, the vertical distributions of two age groups of Maurolicus muelleri is compared to the optimal annual ontogenetic growth rate: mortality risk trade-offs as determined from generation-time based life-history equations. Calculations indicate that juvenile feeding rate was near the maximum for efficient conversion to growth, and at times constrained by digestion rate. Feeding rate of adults seems not to have been high enough to sustain body mass. Juveniles seem to follow the static ontogenetic trade-off between growth and survival, while adults in winter emphasize feeding far less than predicted from static optimization. Static trade-offs are thus inadequate in predicting their distributions, and models accounting for time- and state-dependencies are required. The difference between the two age groups with respect to following the annual trade-off, is explained by their different feeding-to-fitness functions: the relation between adult feedi...

A dynamic optimization model of the diel vertical distribution of a pelagic planktivorous fish

Abstract A stochastic dynamic optimization model for the diel depth distribution of juveniles and adults of the mesopelagic planktivore Maurolicus muelleri (Gmelin) is developed and used for a winter situation. Observations from Masfjorden, western Norway, reveal differences in vertical distribution, growth and mortality between juveniles and adults in January. Juveniles stay within the upper 100m with high feeding rates, while adults stay within the 100–150m zone with very low feeding rates during the diel cycle. The difference in depth profitability is assumed to be caused by age-dependent processes, and are calculated from a mechanistic model for visual feeding. The environment is described as a set of habitats represented by discrete depth intervals along the vertical axis, differing with respect to light intensity, food abundance, predation risk and temperature. The short time interval (24h) allows fitness to be linearly related to growth (feeding), assuming that growth increases the future reproductive output of the fish. Optimal depth position is calculated from balancing feeding opportunity against mortality risk, where the fitness reward gained by feeding is weighted against the danger of being killed by a predator. A basic run is established, and the model is validated by comparing predictions and observations. The sensitivity for different parameter values is also tested. The modelled vertical distributions and feeding patterns of juvenile and adult fish correspond well with the observations, and the assumption of age differences in mortality-feeding trade-offs seems adequate to explain the different depth profitability of the two age groups. The results indicate a preference for crepuscular feeding activity of the juveniles, and the vertical distribution of zooplankton seems to be the most important environmental factor regulating the adult depth position during the winter months in Masfjorden.

Making predictions in a changing world: The benefits of individual-based ecology

Ecologists urgently need a better ability to predict how environmental change affects biodiversity. We examine individual-based ecology (IBE), a research paradigm that promises better a predictive ability by using individual-based models (IBMs) to represent ecological dynamics as arising from how individuals interact with their environment and with each other. A key advantage of IBMs is that the basis for predictions—fitness maximization by individual organisms—is more general and reliable than the empirical relationships that other models depend on. Case studies illustrate the usefulness and predictive success of long-term IBE programs. The pioneering programs had three phases: conceptualization, implementation, and diversification. Continued validation of models runs throughout these phases. The breakthroughs that make IBE more productive include standards for describing and validating IBMs, improved and standardized theory for individual traits and behavior, software tools, and generalized instead of system-specific IBMs. We provide guidelines for pursuing IBE and a vision for future IBE research.

Food, predation risk and shelter: an experimental study on the distribution of adult two-spotted goby Gobiusculus flavescens (Fabricius)

Abstract Adult two-spotted gobies Gobiusculus flavescens (Fabricius) distributed themselves according to the Ideal Free Distribution (IFD) when 10 individuals were offered equal amounts of prey items at two sites in aquaria. As ratios between the prey supply at the two sites increased, however, increasing deviations from the IFD were observed. It is suggested that perceptual constraints within the time scale of the experiments hampered optimal foraging at increased food supply ratios. Introduction of a predator caused a pronounced deviation from the IFD. It is suggested that in the trade-off between food availability and predation risk more emphasis is put on survival than feeding. Introduction of shelter at one of the sites had little or no effect on the observed distribution of gobies when a predator was absent. In the presence of a predator, however, shelter had a pronounced effect on goby distribution. G. flavescens spent up to five times more time in the vicinity of the predator when shelter was present.