domingo, maio 23, 2010

Why fishing magnifies fluctuations in fish abundance


It is now clear that fished populations can fluctuate more than unharvested stocks. However, it is not clear why. Here we distinguish among three major competing mechanisms for this phenomenon, by using the 50-year California Cooperative Oceanic Fisheries Investigations (CalCOFI) larval fish record. First, variable fishing pressure directly increases variability in exploited populations. Second, commercial fishing can decrease the average body size and age of a stock, causing the truncated population to track environmental fluctuations directly. Third, age-truncated or juvenescent populations have increasingly unstable population dynamics because of changing demographic parameters such as intrinsic growth rates. We find no evidence for the first hypothesis, limited evidence for the second and strong evidence for the third. Therefore, in California Current fisheries, increased temporal variability in the population does not arise fromvariable exploitation, nor does it reflect direct environmental tracking. More fundamentally, it arises from increased instability in dynamics. This finding has implications for resource management as an empirical example of how selective harvesting can alter the basic dynamics of exploited populations, and lead to unstable booms and busts that can precede systematic declines in stock levels.

1 comentário:

Thiago P. Nunes disse...

... se não te falo no email, entao te pego aqui... Muito legal o assunto que colocas. Sempre. Distingues os três possíveis comportamentos de peixes frente a redução de indivíduos em suas específicas populações. Foco no ponto 2, quando sugere que o corpo, tamanho e a dinâmica do animal diminui. No decorrer do tempo e por causa da pressão pescatória, isso é mesmo uma tendência? Então se recuarmos no tempo veremos indivíduos mais robustos? E esta mudança anatômica pode ser vista como adaptação ou mutação?
Obrigado mestre meu.
thiago p.n.