abundances, in which case eliminating them was a good idea anyway, so the plot is
called a “Leslie plot”. Estimates of the original total stock are either the intercept on
the Ysum axis or the intercept on the CPUE axis, a, divided by q (which are
mathematically equal). It is the linearity of the series that implies the proportion of
CPUE to stock size. A similar test has been done for dredging of clams and scallops.
In one experiment (P. Rago, unpublished), a patch of bottom (11,613 m^2 ) with
substantial numbers of razor clams was repeatedly dredged, each track sieving about
1500 m^2 . The Leslie plot (Fig. 17.7b) of bushels (the unit in the fishery under study, 1
bushel ≈135 clams) captured vs. total clams was again quite linear. It was clearly very
difficult to get the last few clams. There are very few such results because a
requirement of depletion fishing can be devastation of the stock. But they do show
that in general CPUE can be a measure of stock. In most cases, however, there is no
way to estimate q, so Y/X must be used as a proxy for actual abundance numbers.
Fig. 17.7 Tests of CPUE by depletion fishing. (a) CPUE (number per line-hour)
plotted against cumulative catch for the snapper Etelis coruscans near western Samoa.
Fitted q was 0.0002 (fraction of stock caught per line-hour) for the fishing zone, or
0.0023 km−2.
(^) (After King 2007.)
(b) CPUE for razor clams vs. cumulative catch. q is 0.14 per haul.
(^) (Data from Paul Rago, NMFS.)