Capture Based Aquaculture (CAP)


INDICATOR BACKGROUND AND RATIONAL FOR INCLUSION

Some aquaculture production systems, known as capture-based aquaculture (CBA), depend on the capture of wild fish either as a source of broodstock (mature fish used for breeding) or as farm stock that are raised to commercialsize (i.e., ranching). The life stage of the species may range from larvae to adult at the time of capture (Lovatelli and Holthus 2008). The capture of wild fish for use in aquaculture results in the same set of pressures as a conventional fishery. Specific impacts associated with ongoing CBA fisheries are the reduction of (wild) genetic biodiversity, stock depletion or collapse from low recruitment, habitat degradation from capture methods, and localised or wide-scale population disturbances (Ottolenghi et al. 2004).

INDICATOR FORMULA

Formula

CAP = ∑(Amount from Wild Capture (kg) x Sustainability Score)

Sustainability Score = (harvest performance) x (Stock Status) x (Management Score)

Units: kg x Sustainability Score

Sample Calculation

Sample Normalised Calculation: Flathead Grey Mullet from Egypt, 2007

This indicator is a measure of the sustainability of capture-based aquaculture. If the performer does not rely on the capture of wild fish to sustain its production, it receives a perfect score (100) for this indicator.

Amount of Wild Capture (kilograms)

Within the CAP formula, the amount of wild capture measures the loss in future biomass of seed fish resulting from capture-based aquaculture. It is calculated accordingly:

Amount of Wild Capture = Total Weight Removed from Wild − (Total Weight
                                              Removed from Wild × Natural Mortality)

This calculation measures the total volume of fish removed from the wild ecosystem, but it adjusts for natural mortality to account for the fact that not all fish removed from the wild would have survived if left in the wild. This avoids any overestimation of the impact of wild fish removed. Once the volume of fish removed from the wild is calculated, it is multiplied by the Sustainability Score to obtain a measure of the total seed removed from the wild that is unsustainably fished and/or poorly managed.

Sustainability Score Calculation

The Sustainability Score of the fishery supplying the seed for an aquaculture system is the product of three factors: harvest performance, stock status, and an assessment of the management regime for that particular fishery. These three measures are multiplied so that the final Sustainability Score most effectively differentiates between high and low performers. (See the FAQ for more detailed information on calculating the Sustainability Score)

 

ADDRESSING DATA GAPS

GAPI employed the following decision rules to treat gaps in Capture Based Aquaculture data: