This is a program to carry
out power analysis of proposed bycatch reduction trials. This program uses any available data set from
previous observation of the fishery, or an estimated
mean rate and variance, and allows the user to set
bycatch reduction rates. The program re-samples
actual data entered, or generates a distribution
from the mean entered.
Uses the same re-sampling process as ByTrial to show the effects on trial
power of having an uneven split between 'active' and
'control' gear. In general, power is increased
slightly by having more than half the gear active,
and is diminished sharply if less than half the gear
is active.
Population
models for harbour porpoises. These book-keeping type
models track each individual female in a virtual
population and allocate outcomes (death or giving
birth) randomly with defined probabilities for each
year class. Mortality from bycatch can be entered as
a separate cause of mortality. Percentage of all
mortality that is due to bycatch is also shown.
Initial setting files are provided.
This is a
turtle bycatch model in which a turtle swims in the locality of a
drift net. Swimming speed, diving time, escape
probability and direction changing parameters are
entered and bycatch rates are generated. A large
part of the effect of the input parameters for
direction change and speed can be approximated to
'distance made good' in a day (see Tdmg.exe below).
Generates 'distance made good'
values. The
work needed to investigate the implications of these
models has not be carried out - the models could be used to derive approximate
turtle densities from drift net bycatch data in the
NE Atlantic and elsewhere using available data on
turtle speed, depths of dives and 'distance made
good' in a day. Versions of these
programs that export the results of large numbers of
trials are also available free - please
contact us for more information.