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increased catch per trip (per gear) might simply reflect the fact that the fishers are active for longer<br />
each day and therefore are likely to catch more, i.e. their catch per trip will be higher. If CPUE were<br />
based on catch per gear-hour the actual trip length would be already accounted for and therefore<br />
that any seasonal increase in CPUE would result from some other feature of the fishery, perhaps<br />
related to abundance, fishing grounds targeted or the catchability of the gear.<br />
The relatively tight confidence intervals around the early data points (under the 1 st protocol) are<br />
also noteworthy, when compared to those generated by the 2 nd and 3 rd protocol. The data indicate<br />
that the range of CPUE one is likely to record from any one trip is smaller during, for example in<br />
1996 that in 2003. In August 2003 the data show that one could predict (with 90% confidence) that<br />
an ngalawa fisherman using mishipi would catch between 1.46 and 2.59 kg/trip for each handline<br />
used, with an average catch of 2.02 kg/gr/trip. In August 1999, the fisher would on average catch<br />
between 1.50 and 1.88 kg/gr/trip with a mean of 1.69 kg/gr/trip. The mean catch is higher in 2003<br />
but the range of catch he could expect is also higher about that mean. Tight confidence intervals<br />
indicate a low variance between individual samples and this can be an indication that the data were<br />
perhaps not collected in a proper fashion.<br />
Figure 13 presents data for ngalawa vessels using mishipi gear for the period August 2001 to July<br />
2004, using kg/gr/hr as the unit of catch-rate. In other words it doesn’t matter if the fishers spend all<br />
day or just 1 hour fishing, nor how many gears they are using. The CPUE should reflect either an<br />
increase in abundance, an increase in catchability or some spatial movement that allows them to<br />
fish in grounds where resources are more abundant or individually larger (assuming no significant<br />
change in handling time is associated with landing larger fish). There is no apparent significant<br />
increase or decrease in CPUE over the period of these data.<br />
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