"Some things still need to be said about the world". Pliny the Elder, Naturalis Historia
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".
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).
National Institute of Aquatic Resources, AQUA
Technical University of Denmark
Jægersborg Allé 1