The Management of High Seas Fisheries

A new and acute management problem, now the focus of a major U.N. conference, has arisen in recent years in international fisheries. The problem concerns the management of transboundary fishery resources, in the form of resources to be found in both the coastal state EEZ and the adjacent high seas. The resources are commonly referred to as "straddling" stocks. This article provides a preliminary exploration of the management issue. It reviews the historical and legal background and asks how far the now well developed economic analysis of the management of transboundary fishery resources in the form of resources "shared" by two or more coastal states will take us in examining this second and more recent transboundary fishery management problem. The answer is a very limited distance only. The article concludes by pointing to questions arising from this resource management issue demanding further research.Transboundary fishery resources, straddling stocks, theory of dynamic games, Environmental Economics and Policy, Public Economics,

Beauty is in the eye of the beholder : mate choice in glow-worms depends on perceived, not emitted signals

While the strength of sexual signals is important in mate attraction, the ability to accurately compare signals may also have a major effect on mate choice. Large distances between competitors may reduce competition, as accurate comparison of signals becomes harder. This may be advantageous to weak signallers and detrimental to stronger signallers. We create a mathematical model examining optimal distance from stronger competitors for sexual signallers and test its predictions using the common glow-worm Lampyris noctiluca. Female glow-worms are flightless and attract males by glowing. Males prefer the brightest female if two females are close to each other. Our model gave different predictions depending on whether searchers fly or not. The model and experiment showed that weak signallers should move away from competitors and strong signallers should move closer to weaker competitors when searchers fly. In contrast, the model predicted that the distance between competing signallers has no effect when searchers do not fly. This reveals an unexpected spatial competition between strong and weak signallers. We conclude that, while signal strength is important in sexual selection, location in relation to others is similarly important as ornamentation in determining the result of mate attraction.Peer reviewe

HARVESTING STRATEGIES IN A FISH STOCK DOMINATED BY LOW-FREQUENCY VARIABILITY: THE NORWEGIAN SPRING-SPAWNING HERRING (CLUPEA HARENGUS)

Heavy positively autocorrelated natural fluctuations in a fisheries stock level are problematic for fisheries management, and collapses in the stock dynamics are difficult to avoid. In this paper, we compare three different harvesting strategies (proportional harvesting, threshold harvesting, and proportional threshold harvesting) in an autocorrelated and heavily fluctuating fishery — the Norwegian spring-spawning herring (Clupea harengus) — in terms of risk of quasi-extinction, average annual yield, and coefficient of variation of the yield. Contrary to general expectations, we found that the three strategies produce comparable yields and risks of quasi-extinction. The only observable difference was slightly higher yield and variation in the proportional threshold strategy when the yield is optimized. Thus, it remains an open question as how to characterize the circumstances when it is particularly needful to apply threshold levels in harvest policies.Resource /Energy Economics and Policy,

Fish harvesting, marine reserves, and distribution of individuals over space

Journal homepage: http://versita.com/bl/We analysed exploitation of populations that are partly protected in a marine harvest refuge to prevent their over-harvesting in the remaining unprotected area. We carried out our analysis by introducing the model of ideal free distribution to the population renewal process. In the model, individuals in the target population are distributed so that per capita resource availability becomes matched in the harvested and non-harvested areas. We show that the yield from the harvest effort is strongly affected by the fraction of area protected from harvesting. The harvest effort maximising the yield depends on the relative size of the protected area. Maximum yield is independent of the size of the protected area unless the fraction is > 0.56. If this value is exceeded, annual yield declines rapidly with increasing protected fraction. However, our major - and somewhat surprising - finding is that protected areas can be established without any loss to commercial harvesting if harvesting follows reproduction and population densities are balanced between harvesting seasons according to resource availability

Precautionary management of Baltic Sea cod (Gadus morhua callarias) under different environmental noise and harvesting strategies

Peer reviewe

Ant-associated beetles of Fennoscandia and Denmark

Ants have a negative impact on populations of many arthropod species. On the other hand, numerous arthropod species live in association with ants. In this paper we list ant-associated beetles (including myrmecophiles) of Fennoscandia and Denmark. Data is based on a literature survey and new field observations. We list 369 ant-associated beetle species of which 73 are categorized as myrmecophilous. Our data suggests that there might be numerous beetle species associated with ants, which are not generally known to do so. This indicates that ant colonies may be important habitats for a large variety of beetle species

Outside-host phage therapy as a biological control against environmental infectious diseases

Background: Environmentally growing pathogens present an increasing threat for human health, wildlife and food production. Treating the hosts with antibiotics or parasitic bacteriophages fail to eliminate diseases that grow also in the outside-host environment. However, bacteriophages could be utilized to suppress the pathogen population sizes in the outside-host environment in order to prevent disease outbreaks. Here, we introduce a novel epidemiological model to assess how the phage infections of the bacterial pathogens affect epidemiological dynamics of the environmentally growing pathogens. We assess whether the phage therapy in the outside-host environment could be utilized as a biological control method against these diseases. We also consider how phage-resistant competitors affect the outcome, a common problem in phage therapy. The models give predictions for the scenarios where the outside-host phage therapy will work and where it will fail to control the disease. Parameterization of the model is based on the fish columnaris disease that causes significant economic losses to aquaculture worldwide. However, the model is also suitable for other environmentally growing bacterial diseases. Results: Transmission rates of the phage determine the success of infectious disease control, with high-transmission phage enabling the recovery of the host population that would in the absence of the phage go asymptotically extinct due to the disease. In the presence of outside-host bacterial competition between the pathogen and phage-resistant strain, the trade-off between the pathogen infectivity and the phage resistance determines phage therapy outcome from stable coexistence to local host extinction. Conclusions: We propose that the success of phage therapy strongly depends on the underlying biology, such as the strength of trade-off between the pathogen infectivity and the phage-resistance, as well as on the rate that the phages infect the bacteria. Our results indicate that phage therapy can fail if there are phage-resistant bacteria and the trade-off between pathogen infectivity and phage resistance does not completely inhibit the pathogen infectivity. Also, the rate that the phages infect the bacteria should be sufficiently high for phage-therapy to succeed.Peer reviewe

Co-evolution as an important component explaining microbial predator-prey interaction

Predator-prey relationships belong to the most important and well-studied ecological interactions in nature. Understanding the underlying mechanisms is important to predict community dynamics and to estimate coexistence probability. Historically, evolution has been considered to be too slow to affect such ecological interactions. However, evolution can occur within ecological time scales, potentially affecting predator-prey communities. In an antagonistic pair-wise relationship the prey might evolve to minimize the effect caused by the predator (e.g. mortality), while the predator might evolve to maximize the effect (e.g. food intake). Evolution of one of the species or even co-evolution of both species in predator-prey relationships is often difficult to estimate from population dynamics without measuring of trait changes in predator and/or prey population. Particularly in microbial systems, where microorganisms evolve quickly, determining whether co-evolution occurs in predator-prey systems is challenging. We simulate observational data using quantitative trait evolution models and show that the interaction between bacteria and ciliates can be best explained as a co-evolutionary process, where both the prey and predator evolve. Evolution by prey alone explains the data less well, whereas the models with predator evolution alone or no evolution are both failing. We conclude that that ecology and evolution both interact in shaping community dynamics in microcosms. Ignoring the contribution of evolution might lead to incorrect conclusions.Peer reviewe

Crayfish population size under different routes of pathogen transmission

We present an epidemiological model for the crayfish plague, a disease caused by an invasive oomycete Aphanomyces astaci, and its general susceptible freshwater crayfish host. The pathogen shows high virulence with resulting high mortality rates in freshwater crayfishes native to Europe, Asia, Australia, and South America. The crayfish plague occurrence shows complicated dynamics due to the several types of possible infection routes, which include cannibalism and necrophagy. We explore this complexity by addressing the roles of host cannibalism and the multiple routes of transmission through (1) environment, (2) contact, (3) cannibalism, and (4) scavenging of infected carcasses. We describe a compartment model having six classes of crayfish and a pool of crayfish plague spores from a single nonevolving strain. We show that environmental transmission is the decisive factor in the development of epidemics. Compared with a pathogen-free crayfish population, the presence of the pathogen with a low environmental transmission rate, regardless of the contact transmission rate, decreases the crayfish population size with a low risk of extinction. Conversely, a high transmission rate could drive both the crayfish and pathogen populations to extinction. High contact transmission rate with a low but nonzero environmental transmission rate can have mixed outcomes from extinction to large healthy population, depending on the initial values. Scavenging and cannibalism have a relevant role only when the environmental transmission rate is low, but scavenging can destabilize the system by transmitting the pathogen from a dead to a susceptible host. To the contrary, cannibalism stabilizes the dynamics by decreasing the proportion of infected population. Our model provides a simple tool for further analysis of complex host parasite dynamics and for the general understanding of crayfish disease dynamics in the wild.Peer reviewe

Outside-host growth of pathogens attenuates epidemiological outbreaks

Opportunist saprotrophic pathogens differ from obligatory pathogens due to their capability in host-independent growth in environmental reservoirs. Thus, the outside-host environment potentially influences host-pathogen dynamics. Despite the socio-economical importance of these pathogens, theory on their dynamics is practically missing. We analyzed a novel epidemiological model that couples outside-host density-dependent growth to host-pathogen dynamics. Parameterization was based on columnaris disease, a major hazard in fresh water fish farms caused by saprotrophic Flavobacterium columnare. Stability analysis and numerical simulations revealed that the outside-host growth maintains high proportion of infected individuals, and under some conditions can drive host extinct. The model can show stable or cyclic dynamics, and the outside-host growth regulates the frequency and intensity of outbreaks. This result emerges because the density-dependence stabilizes dynamics. Our analysis demonstrates that coupling of outside-host growth and traditional host-pathogen dynamics has profound influence on disease prevalence and dynamics. This also has implications on the control of these diseases.Peer reviewe