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The allocation of individual transferable quotas (ITQs) as shares of a total allowable catch (TAC) is now widely practised in fisheries management, but is not without controversy. It is often suggested that the possession of ITQs should provide an incentive for fishers to exercise stewardship of the resource. Quota holders acting in their economic self-interest should collectively exercise stewardship, setting TACs and supporting enforcement measures to maximize the present value of future profit streams. But it is in the economic self-interest of an individual fisher possessing ITQ to take additional unreported catch, through discarding, high-grading, or quota-busting. Thus, ITQs in themselves will not prevent a 'tragedy of the commons', unless there is sufficient compliance monitoring and enforcement to deter hidden catches. ITQs, with adequate enforcement, have been demonstrated to effectively address the race to fish and result in improved sustainability and profitability. There are questions of equity concerning the flow of benefits from the allocations of quotas and associated profit streams and who pays for the management costs required to sustain them. There are also issues around the ability of ITQ-based management to address other social and environmental objectives. Resume: L'allocation de quotas individuels transferables (QIT) comme parts du total autorise des captures (TAC) est communement utilisee dans la gestion des peches, mais elle n'est pas sans soulever des controverses. On indique souvent que la possession d'un QIT devrait inciter les pecheurs a exercer une responsabilite de gerance de la ressource. Les posses-seurs de quotas agissant pour leurs interet personnel devraient exercer collectivement la gerance, en determinant les TAC et en appuyant les mesures d'application des reglements afin de maximiser la valeur actuelle des perspectives futures de profit. Mais c'est dans 1'interet economique personnel du pecheur individuel qui possede un QIT de faire des recoltes addi-tionnelles non signalees, en faisant des rejets, en ecremant les captures ou en depassant les quotas. Ainsi, les QIT en eux-memes n'empechent pas l'arrivee d'une ≪ tragedie des richesses communes ≫ a moins qu'il n'y ait suffisamment de surveillance du respect des reglements et de leur application pour decourager les prises cachees. On a montre que les QIT, avec une application adequate, peuvent gerer de facon efficace la course a la peche et ameliorer la durabilite et la profita-bilite. II y a des problemes d'equite concernant le flux des benefices provenant de 1'allocation des quotas et des lignes de profit associees et au sujet de qui doit payer les coflts de gestion necessaires pour les maintenir. II y a aussi des questions a propos de la capacite d'une gestion basee sur les QIT a atteindre d'autres objectifs sociaux et environnementaux. [Traduit par la Redaction], Introduction While there is debate over the exact state and likely future trends in global fisheries (Worm et al. 2006; Hilborn 2007a), there is general agreement that many stocks are [...]

Since the mid 1990s, Australia's Commonwealth Science Industry and Research Organisation (CSIRO) has developed a biogeochemical (BGC) model for coupling with a hydrodynamic and sediment model for application in estuaries, coastal waters and shelf seas. The suite of coupled models is referred to as the CSIRO Environmental Modelling Suite (EMS) and has been applied at tens of locations around the Australian continent. At a mature point in the BGC model's development, this paper presents a full mathematical description, as well as links to the freely available code and User Guide. The mathematical description is structured into processes so that the details of new parameterisations can be easily identified, along with their derivation. The EMS BGC model cycles carbon, nitrogen, phosphorous and oxygen through multiple phytoplankton, zooplankton, detritus and dissolved organic and inorganic forms in multiple water column and sediment layers. The underwater light field is simulated by a spectrally-resolved optical model that includes the calculation of water-leaving reflectance for validation with remote sensing. The water column is dynamically coupled to the sediment to resolve deposition, resuspension and benthic-pelagic biogeochemical fluxes. With a focus on shallow waters, the model also includes particularly-detailed representations of benthic plants such as seagrass, macroalgae and coral polyps. A second focus has been on, where possible, the use of geometric derivations of physical limits to constrain ecological rates, which generally requires population-based rates to be derived from initially considering the size and shape of individuals. For example, zooplankton grazing considers encounter rates of one predator on a prey field based on summing relative motion of the predator with the prey individuals and the search area, chlorophyll synthesis includes a geometrically-derived self-shading term, and the bottom coverage of benthic plants is generically-related to their biomass using an exponential form derived from geometric arguments. This geometric approach has led to a more algebraically-complicated set of equations when compared to more empirical biogeochemical model formulations. But while being algebraically-complicated, the model has fewer unconstrained parameters and is therefore simpler to move between applications than it would otherwise be. The version of the biogeochemistry described here is implemented in the eReefs project that is delivering a near real time coupled hydrodynamic, sediment and biogeochemical simulation of the Great Barrier Reef, northeast Australia, and its formulation provides an example of the application of geometric reasoning in the formulation of aquatic ecological processes. [ABSTRACT FROM AUTHOR]

Two key challenges in conservation management are: (1) how to quantify and manage the risk that natural populations will fall below critical thresholds and (2) how to fund recovery plans should a population do so. Statistically estimated, process-based simulation models of two distinct fish populations are used to forecast the species population levels, and capture the risk of crossing a management defined trigger point. We show how to calculate the environmental derivative price, which is the amount a risk-neutral investor would require for promising a pay-out should the species abundance fall below the trigger level. The approach provides the potential for environmental derivatives to support species recovery, and a method for measuring the underlying 'health' of a managed population and calculating risk-cost tradeoffs among alternative management strategies. [ABSTRACT FROM AUTHOR]

The blue-green alga(Cyanobacerium) Synechococcus leopoliensis (Racib) Komarek was grown rate, the kinetics of photosynthesis with respect to [DIC]-limited chemostats over the entire range of growth rates. At each growth rate, the maximal rate of photosynthesis (P[SUBmax]) were determined. The half saturation constant for [DIC]-limite photosynthesis (K½[SUPDIC]) for cells growing below 107 d[SUP-1] was constant (4.7μM) whereas for growth rates between 1.7 d[SUP-1] and 2.1 d[SUP-1] (μ[SUBmax]) the kinetics of photosynthesis were multiphasic with an apparent K½ between 1.5-2.0 mM P[SUBmax] increased in a linear fashio with growth rate for growth rates below 107 d[SUP-1] No trend in P[SUBmax] was apparent for growth rates greater than 107 d[SUP-1] These kinetic parameters were used to predict a growth rate versus [DIC] relationship. Results show that the Monod relationship is a physiologically valid expression of growth as a function of [DIC] provided K[SUB½,SUPDIC] remains constant. The major change in K[SUB½,SUPDIC] as μ approaches μ[SUBmax] results in the conclusion that two separate and distinct Monod equations must be used to describe growth as a function of DIC over the entire growth range. These results point to a major discontinuity in the μ vs. [DIC] curve at 1.7 d[SUP-1] which corresponds to the change from high to low affinity photosynthetic kintics. We believe these results account for the previously described deficiencies of the Monod equation in describing [DIC]-limited algal growth. [ABSTRACT FROM AUTHOR]