(^) While CPUE is useful in some fisheries, it must be kept in mind that these measures
are sensitive to even small shifts in fishing technique. For example, North Pacific
halibut (Hippoglossus stenolepis) are captured by laying out lines of baited hooks
across the bottom, leaving them for 12–24 hours, then reeling in the line and, on most
days, fish. Up until 1982–1983, the fishers used “J-hooks”, then switched to circle
hooks (Fig. 17.8). The capture rate per hook fished rose by a factor of two to three,
depending upon fish size (IPHC 1998). An apparently simple change in hook shape
raised the hooking rate and reduced escapes dramatically. Sometimes subtle changes
in technique occur in a fishery without managers being aware. Since fishers are
intensely aware of their own CPUE, these can be improvements in gear, search
efficiency, communication among fishers, focusing fishing at the most productive
times, and simply more experience in the work. Changes of CPUE caused by
technique modification can appear to managers to be increases in stock size.
Whenever stock condition warrants it, managers like to (or legally must) provide
fishers higher quotas or longer seasons, so misinterpreted upward CPUE shifts can
readily result in over-fishing.
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