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Estimating geo-referenced fishing effort is vital to develop advice for effective fisheries management. Many studies in recent decades have attempted to obtain complete, high-resolution effort data from vessel monitoring systems (VMSs). The main challenge in this regard is to develop a classification method for differentiating fishing activities (e.g., fishing days) from nonfishing activities in VMS data. This study developed a simple, novel classification criterion for a large-scale tuna longline (LTLL) fishery that has not been studied before. LTLL operations were first explored using observer data. Three approaches were designed for developing fishing-day classification criteria, using maximizing sum of sensitivity and specificity (SS) as the major performance measure and minimizing difference of SS as a reference. At least one VMS report with speed in the range of 2-5 kn (1 kn = 1.852 km x [h.sup.-1]) detected during the time-of-day period of 14:00-23:00 h was recommended as the criterion for defining a fishing day. Possible explanations for the differences between the estimated fishing days from VMS data and those reported on logbooks are discussed; most causes were related to specific features of the fishery. L'estimation de l'effort de peche georeference revet une importance vitale pour la formulation d'avis pour la gestion efficace des peches. De nombreuses etudes ces dernieres decennies ont tente d'obtenir des donnees exhaustives de haute resolution sur l'effort a l'aide du systeme de surveillance des navires (VMS). Le principal defi a cet egard consiste a etablir une methode de classification pour distinguer les activites de peche (p. ex. jours de peche) des autres activites dans les donnees du VMS. L'etude a etabli un critere de classification simple et novateur pour une peche au thon a la palangre a grande echelle (LTLL) n'ayant pas fait l'objet d'etudes anterieures. Les activites de LTLL ont d'abord ete examinees a l'aide de donnees d'observateurs. Trois approches ont ete mises au point pour etablir des criteres de classification des jours de peche, qui utilisent la maximisation de la somme de la sensibilite et de la specificite (SS) comme principale mesure du rendement et la minimisation de la difference de ces deux valeurs comme reference. Le critere recommande pour definir un jour de peche consiste en au moins un signalement du VMS associe a une vitesse de 2 kna 5 kn (1 kn = 1,852 km x [h.sup.-1]) detecte durant la periode du jour allant de 14:00-23:00 h. [Traduit par la Redaction], Introduction Estimating fishing effort is crucial to fisheries scientists, because it can provide information for calculating catch per unit effort (CPUE) to index stock abundance. While utilizing the effort data, [...]

Data from coastal fisheries are often incomplete, as these fisheries are usually small in scale, rendering them exempt from logbook submission requirements. The catch of Dolphinfish Coryphaena hippurus by Taiwanese fisheries once ranked second in the world but has dramatically declined to very low levels in recent years. To address this decline, assessment of a Dolphinfish abundance index was necessary. However, due to the small scale of the fisheries, logbook data were not available to calculate CPUE. This study aimed to estimate a statistically reliable index by (1) assigning effort matrices to landings data using coastal surveillance radar data; (2) standardizing the 2001–2015 CPUEs while using four approaches (classifying fishing tactics by multivariate techniques and principal components analysis) to differentiate the fisheries' effort toward catching Dolphinfish from the effort toward other target species; and (3) evaluating performance of the standardization models by using an R2 estimated by cross‐validation and bootstrap procedures. The approach that used a delta‐generalized additive model with a direct principal components procedure demonstrated the best fit. This study presents an example of deriving a statistically reliable abundance index from the data‐incomplete situations common for coastal fisheries, which allows for follow‐up population dynamics studies. The resulting index for Dolphinfish in the Taiwanese region showed two 7‐year cycles, with a prominent decline in 2015. Reasons for the fluctuation are unknown but may be due to environmental factors, the fast‐growing nature of the fish, and heavy exploitation of the stock by Taiwanese fisheries. [ABSTRACT FROM AUTHOR]