The apps can be used to model bycatch. The apps
are provided free
with no liability for any errors or consequences. Comments to nick.tregenza@chelonia.co.uk.
ByTrial.exe |
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. |
BySymm.exe |
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. |
HPpop.exe |
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. |
Tbycatch.exe |
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). |
Tdmg.exe |
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. |
