Le Poisson qui rétrécit

Il y a mille ans, les colons norvégiens de ma ville de York mangeaient des morues qui pesaient parfois jusqu'à huit kilogrammes. Nous savons cela grâce aux archéologues et à leur fascination pour les tas de déchets médiévaux. Aujourd'hui pourtant, nous aurions bien de la chance si nous trouvions une morue qui pèse plus de deux kilogrammes. Qu'avons-nous fait à nos réserves de poisson pour entraîner de tels changements et cela a-t-il une grande importance ?

Les politiques de pêche sont conçues pour permettre aux petits poissons de grandir. Et ce, pour de bonnes raisons : le poisson attrapé quand il est trop petit ne sera que d'un trop petit rapport. De plus, le poisson n'a aucune chance de se reproduire, ce qui nuit au stock de poisson en général. Ainsi, l'intention avouée de la politique commune de pêche de l'Union européenne est de " protéger les ressources de pêche en régulant la quantité de poisson pêchée en mer, en permettant au jeune poisson de se reproduire et en assurant que ces mesures soient respectées. "

Au point où nous en sommes, cependant, nous avons épuisé nos réserves de poisson, au point qu'il ne reste que de faibles quantités de gros poissons adultes. Il suffit de considérer le cas de la morue de la Mer du Nord pour s'en apercevoir. Supposons que l'on ait dix mille poissons âgés d'un an, pour commencer. Si la mortalité naturelle est la seule à intervenir, un millier de ces poissons survivront jusqu'à atteindre l'âge de huit ans. Avec un niveau de pêche modéré, le nombre des survivants descend à environ une centaine d'individus. Toutefois, le niveau de mortalité due à la pêche tel que nous l'infligeons à la population des poissons ces vingt dernières années fait descendre le nombre de survivants à trois environ.

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