Repetitive fishing, local depletion, and fishing efficiencies in the Kerguelen Islands fisheries

Commercial catch per unit effort (cpue) recorded by observers on board trawlers operating in the French EEZ around the Kerguelen Islands (south Indian Ocean) are used to analyse the impact of repetitive fishing on cpues and to estimate local fishing efficiencies. Series of cpues from the same fishing locations and no more than two days apart are first built, and then the mean depletion effect of repetitive fishing (between 4% and 10% for Patagonian toothfish and around 20% for icefish and marbled notothen) is quantified. Random fluctuations of cpues around an exponential decrease (i.e. the reference model when fishing efficiencies are constant) lead to modelling fishing efficiency as a random variable. Based on the observations of the ratio between two consecutive catches, a method is developed to estimate the probability density function of fishing efficiencies. The significant decrease of average fishing efficiency between the start of the fishery and its full exploitation phase is explained by a change in regulations (from global to individual quotas).