To help animal populations, stop harvesting adults, focus on juveniles
http://www.bbc.com/news/science-environment-34011026
Very interesting study, with huge possible implications for how we approach management of fishing and hunting.
This concentration on large adult prey is triggering extinctions, as well as driving an evolutionary shift towards smaller fish sizes and disrupting global food chains, say the authors.Prof Tom Reimchen, a UoV co-author on the study, uses a financial analogy to explain the damaging consequences of hitting adult populations hardest.
He calls the adults the system's "reproductive capital" - the equivalent of the capital held in a bank account or a pension fund. And he says we are eating into this capital when we should really be living off the interest - the juveniles, which many species will produce in colossal numbers, expecting a good fraction to be doomed from the moment they are born via predation, starvation, disease, accidents and more.
The heavily biased preference for adults was not a sustainable strategy long-term, which ought to be clear from fundamental biology, argued Prof Darimont: "In the overwhelming number of cases as fishes age, they become more fecund. That is to say, they produce more eggs, have more babies, and, in fact, in many cases, many of those babies are more likely to survive and reproduce themselves.
"So when a predator targets that reproductive age class and especially the larger more fecund animals in those populations, we are dialling back the reproductive capacity of populations."
However, much of the standard conservation management today is based on the notion that it is the "tiddlers" that should be let go, to ensure robust numbers for the next generation. Trawl nets are often designed specifically to support this approach.Doing it the other way would be challenging, but the technical solutions were available, said Prof Reimchen.
"There are traps that can define the entrance to a net, which then very easily allows you to exclude fish above a certain size - in other words, the reproductive capital. Once the motivation is in place, clever people will work out how this transition from the reproductive capital to the interest could be brought about."
As for quotas, these should more closely align with the numbers taken out by natural predators, the team suggests.