A randomised cluster design was used successfully to sample otoliths from targetted individuals taken by individual longlines in the fishery for Dissostichus eleginoides. The line was divided into constituent baskets of line; we used the line as the sampling frame, and baskets as the primary sampling units. The design allows representative samples to be taken while a line is being hauled; it offers the potential of little disruption to commercial activities and reductions in observer effort needed to achieve known levels of confidence.
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Abstract:
A shore-based design used to sample sports fisheries was adapted to sample otoliths from targetted individuals caught in the artisanal longline fishery for Dissostichus eleginoides off northern Chile. Observers were stationed dockside and at a processing factory. A 14-day sampling frame was used, divided into primary sampling units of days/area and secondary sampling units of three- and eight-hour periods. Compared to shipboard sampling, the design allowed more flexibility in allocation of observer effort and cut time wasted during poor fishing or travel to fishing grounds. However, data on catch date, location, and depth cannot be independently verified, nor data taken on by-catch or incidental mortality of higher predators.
