Measuring the Length of a Pelagic Longline Set: Applications for Management

Recent U.S. federal fisheries management actions aimed at reducing bycatch have established or proposed limits on the length of a pelagic longline set. However, such management measures are unenforceable if the criteria for measuring the length of a pelagic longline set have not been defined. Differences in the physical gear and deployment strategies suggest high variability among the several methods that can be used to measure set length. This study uses a combination of scientifically monitored sets, fisheries observer data, and federal pelagic logbook data to compare four possible metrics of longline set length: the geographic track of the vessel while deploying the gear, a “folding ruler” approximation based on straight-line distance between ends of the sections of gear, the straight-line distance between the beginning and end of the gear, and a dead-reckoning distance based on vessel speed and the time duration of the gear deployment. Results indicate that while set lengths determined from self-reported data via logbook submissions are not significantly different from the other proposed methods, the inclusion of an ending location for each set within the logbook form could provide a basis for evaluation of the regulatory measure.