Evolutionary consequences of trophy hunting and fishing

[Andrew]

A recent study (actually, I compilation of many studies) detailing how the harvest of the largest animals (game and fish), and even plants, affects the evolution of these populations has been published and has gotten a lot of press. The take-home message is that by harvesting the biggest and best, we're changing the genetic make-up of the populations so that they reproduce earlier and at smaller sizes. This isn't exactly new news, but the rate at which it occurs is much faster than previously thought, and much faster than that caused by other forms of selection.

Below I've pasted the abstract from the original paper, and a link to an article about the paper in the NYT.

Abstract (Summary) from the original paper:

The observable traits of wild populations are continually shaped
and reshaped by the environment and numerous agents of natural
selection, including predators. In stark contrast with most predators,
humans now typically exploit high proportions of prey populations
and target large, reproductive-aged adults. Consequently,
organisms subject to consistent and strong ‘harvest selection’ by
fishers, hunters, and plant harvesters may be expected to show
particularly rapid and dramatic changes in phenotype. However, a
comparison of the rate at which phenotypic changes in exploited
taxa occurs relative to other systems has never been undertaken.
Here, we show that average phenotypic changes in 40 humanharvested
systems are much more rapid than changes reported in
studies examining not only natural (n=20 systems) but also other
human-driven (n=25 ystems) perturbations in the wild, outpacing
them by >300% and 50%, respectively. Accordingly, harvested
organisms show some of the most abrupt trait changes ever
observed in wild populations, providing a new appreciation for
how fast phenotypes are capable of changing. These changes,
which include average declines of almost 20% in size-related traits
and shifts in life history traits of nearly 25%, are most rapid in
commercially exploited systems and, thus, have profound conservation
and economic implications. Specifically, the widespread
potential for transitively rapid and large effects on size- or life
history-mediated ecological dynamics might imperil populations,
industries, and ecosystems.

http://www.nytimes.com/2009/01/13/science/13fish.html?_r=1

[Jon]

Andrew - this is very interesting and makes a lot of sense from the perspective of population dynamics (how many MORE reasons do we need??) It seems like a credible study.

I've also heard it argued that to produce a bigger average weight of fish a sensible harvest of very small fish might be applied, particularly in nutrient poor water bodies where food is scarce.

Jon

[Andrew]

Yes, I think it often comes down to what kind of fishery we want - big fish, small fish, numerous fish, rare fish, etc. Lots of big fish is of course what we'd all like, but competing interests and the inevitable biology that gets in the way makes this a tough goal to achieve.