Publisher :
Place of publication :
Publication year : 2008
Thematic : Fisheries
Language : English
Note
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.
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Keywords : Rattus arrogans
Encoded by : Pauline Carmel Joy Eje
