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December 2014: New paper: Trade-offs between objectives for ecosystem management of fisheriesGedankenexperimente in ecosystem-based fisheries management. What happens to the ecosystem if we optimise the fishing pattern for yield of biomass (MSY) or for economic rent (EMSY)? And how does that tie in with conservation constraints? Using a trait-based size spectrum model we have been able to extend this classical analysis from a single species to an entire fish community.
The size distribution (top) and the fishing pattern of three fishing fleets (bottom) when fishing to maximize economic rent.

May 2014: New paper: A life-history evaluation of the impact of maternal effects on recruitment and fisheries reference points. The Big Old Fecund Females (the "BOFFs") in a fish stock have been shown to produce more viable eggs and larvae than younger females.  Should we take this into account when we evaluate the producitivity and resilience of a fish stock?  Using a trait-based model of fish stock we show that even though the BOFFs produce more viable offspring their impact on the recruitment of the entire stock is small.  The reason is that the abundance of younger fish is so much larger than the abundance of BOFFs that the main contribution to recruitment comes from the young fish. The only exception is fish stocks which are particularly vulnerable to fishing. For those stocks the recruitment from BOFFs is an important contribution to the resilience of stock.

December 2013: New paper The consequences of balanced harvesting of fish communities. How shall we manage fisheries within an ecosystem approach to fisheries?  A recently proposed solution is to make a "balanced" harvesting of ecosystem components. Balanced harvesting implies that small individuals should be fished harder than large individuals. We make an assessment of balanced harvesting using the size-spectrum modelling concept. We find that balanced harvesting can produce as much biomass yield as current fishing patterns, and it may even do so at a lower risk of compromising other ecosystem components. The price to pay is that the catch is comprised mainly of small individuals. Balanced harvesting can therefore be viewed an attempt to maximise the yield from a forage fishery at the expense of yield from the consumer fishery.

October 2013: Updated the single-species size-spectrum simulator. Now with possibility to simulate "balanced fishing".

April 2013: New paper: Size structure, not metabolic scaling rules, determines fisheries reference points. We develop a comprehensive framework for a size-based model of an exploited fish population. The framework is based on a metabolic assumption at the level of the individual. Despite this, we show that the population-level properties, like fisheries reference points, do not obey metabolic scaling rules. The framework is general and can be used to generalise the impact of fishing across species and for making demographic and evolutionary impact assessments of fishing, particularly in data-poor situations. The model has been implemented as a javascript applet.
The fishing mortality giving the maximum yield (Fmsy) as a function of the maximum size of fish in a population (Woo) (black line). The black dots are Fmsy for selected fish stocks from official ICES assessments. The grey areas represent runs with random parameters of the model (see paper for details).

December 2012: New paper: Control of plankton seasonal succession by adaptive grazing.

March 2012: New paper: Trait diversity promotes stability of community dynamics.  In this paper we show that the dynamic solutions of the community size spectrum model are unrealistic.  We do this by comparing the community model with the same model where we have added trait diversity.  The model with trait diversity has dynamic solutions with much smaller amplitude than the community model (see below).  These results are important because they demonstrate the limitations of the community size-spectrum model.  My student, Lai Zhang, performed the technically demanding calculations behind this exercise.

Phase plot of predator biomass as a function of prey biomass for the simple community size-spectrum model (grey) and the same model where the diversity of individuals is accounted for (black).  The basic model has chaotic dynamics and very large amplitude variation whereas the model with trait diversity has regular and low amplitude oscillations.
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