Killing more fish to increase a fish population may seem like a paradox, but a study published in a recent issue of the Proceedings of the National Academy of Sciences demonstrates just that.
Arne Schrder, Lenart Persson and Andr de Roos carried out a series of experiments in which they selectively removed (at different rates) individuals from groups of the poeciliid Least killifish (Heterandria formosa) maintained in tanks.
The individuals removed from the tank were either all juveniles (fish under 9 mm long) or all adults (males larger than 12 mm, females larger than 14 mm).
The remaining fish were allowed to reproduce and were measured regularly. The authors found that selectively removing adults at an intermediate rate (0.015 individuals per day) led to the greatest increase in the population size, as did selective removal of juveniles at 0.008 individuals per day.
This confirmed the results of a theoretical study published in 2007 by de Roos and coauthors using mathematical models.
Although the total number of fish in a population declines when fish are killed (or removed), this removal also results in less competition for resources (e.g. food) among the remaining individuals.
This enables the remainder to exploit this relaxation in competition and to grow into larger, stronger adults faster.
This would, in turn, lead to these adults producing more offspring (in what is known as biomass overcompensation) that more than compensates for the number of individuals lost in the first place.
For more information, see the paper: Schrder, A, L Persson and AM de Roos (2009) Culling experiments demonstrate size-class specific biomass increases with mortality. Proceedings of the National Academy of Sciences 106, pp. 2671"2676.