Rapid selection effects in a short-lived semelparous squid species exposed to exploitation: inferences from the optimisation of life-history functions |
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Authors: | EJ Murphy PG Rodhouse |
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Institution: | (1) British Antarctic Survey, Natural Environment Research Council, Cambridge, UK |
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Abstract: | The short life span of cephalopods suggests a potential for high sensitivity to the artificial selective effects of human
exploitation. To explore the effects of such selection life-history optimisation was applied using data for a semelparous
squid, Illex argentinus with a life span of one year. Survival and fecundity functions were combined to generate a life time reproductive potential
function. The maximum reproductive potential identified the optimum age for the squid to mature. In a situation of a constant
mortality rate the maximum reproductive potential was achieved at an earlier age of maturation as mortality rate increased.
The exact age when the optimum maturation occurs is sensitive to the rate of mortality and the form of the assumed growth
curve but covers the age range when maturation is known to occur in this species. A more realistic seasonal fishing mortality
function produced a more complex fitness curve with a temporally more restricted optimal age of maturity. The selection effects
will be stronger in a seasonal fishery suggesting potentially very rapid evolutionary rates. Developing analyses specifically
considering frequency-dependence and environmental-feedbacks will be valuable to clarify the potential of squid to show rapid
evolutionary responses to selection. Strong selection for early age of maturation could affect the yield from the fishery
but more importantly, could also make the migratory strategy, on which the fishery is based, an unviable option, resulting
in collapse of the fishery that exploits the migratory component of the species.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Illex argentinus life-history optimisation selection squid |
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