Fishery benefits from behavioural modification of fishes in periodically harvested fisheries closures

Periodically harvested fisheries closures are widely implemented across the South Pacific as a conservation and fisheries management tool. There is a lack of information on the mechanisms and effectiveness of this management system in meeting fisheries and ecosystem sustainability goals.A before-after-control-impact (BACI) pair design, was used to quantify flight initiation distance (FID), and biomass of two fishery-target (Acanthuridae and Scaridae) and one non-target (Chaetodontidae) families in two periodically harvested closures, two no-take marine reserves, and two open fished areas, prior to and after harvest of the periodically harvested closures. Creel surveys were used to quantify catch per unit effort (CPUE) in open fishing grounds, and during the periodic harvests.Before harvest, FID of targeted families was higher in fished areas than periodically harvested areas. After harvest, Acanthuridae FID in periodically harvested closures increased significantly to beyond the maximum effective range of spearguns. Total biomass of fishes was lower in fished areas than areas under either type of management. Acanthuridae biomass in the periodically harvested closures was similar to fished areas, and lower than in the no-take reserves. There was no difference post-harvest for either total or Acanthuridae biomass.CPUE was higher for fishing trips inside the periodically harvested closures than regular fishing activities. Fishes were generally larger in catches from periodically harvested closures, but this was not sufficient to account for the increase in CPUE, particularly of the Acanthuridae, which were significantly more abundant in the harvest catch.When fishes are protected temporarily from fishing, their wariness decreases, which makes them more easily catchable when fishing is reinstated. This study shows that fish behavioural change is an important and overlooked benefit of periodically harvested closures. However, differences in the magnitude of behavioural changes between fishery-target families may result in contrasting outcomes of periodically harvested management regimes.