Chelonia Limited

  Cetacean Monitoring Systems


Bycatch software

The following free-to-use programs can be used to model bycatch. The software is provided free with no liability for any errors or consequences. Comments to


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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.


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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.


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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.


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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).


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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.