Definition of a directed fishing effort in a mixed-species trawl fishery, and its impact on stock assessments

Abstract

Catch-per-unit effort (CPUE) has frequently been used as an index of abundance and more specifically to calibrate virtual population analysis (VPA). In multi-species fisheries, CPUE calculated from fishing trips targeting the species seems to be more effective for calibration than the classical ratio total landings/total effort. Target species are determined from an analysis of the composition of catches (landings) of each fishing trip, each trip being categorised as to whether it targets the given species or not. It is obvious that existing but not reported discards would affect these results. Classification of trips can be achieved on a single-species basis, each species being considered successively and each trip possibly being relevant for more than one species. Using a more general approach, classification can be achieved by metiers, each of these being determined by one or a group of target species and each trip being categorised into one and only one metier. This method of categorising trips is based on thresholds of target species contribution to the catch and on an overall explanatory level. For the main species of the French demersal fishery off the west coast of Scotland and in the Celtic Sea, CPUEs are calculated using different methods to define the trips used to calculate fishing effort and associated landings. Besides important differences in actual values, CPUEs may also differ in their trends depending on the delinition of directed effort. Tuned VPA, carried out for some species, shows that large variations in population estimates, fishing mortality or short-term predictions could occur when using directed effort, while the catchability model fits the data better. 0 Ifremer/Elsevier, Paris Multi-species fisheries / directed effort / target species / metier / tuned virtual population analysis / stock assessment / NE Atlantic Resume -Definition d'un effort de p&he dirige dans une p&herie pluri-specitique, et son impact sur I'evaluation des stocks. Les captures par unite d'effort de p&he (CPUE) sont frequemment utilisees comme indice d'abondance et servent notamment a la calibration des analyses de cohortes (VPA). Plutot que le simple rapport entre la production et l'effort total developpe sur une zone de p&he, les CPUE calculees a partir de (< mar&es D ciblant l'espece consideree semblent plus pertinentes. A partir de l'analyse de la composition des debarquements de chaque G make N, il est possible de determiner des especes cibles et de classer les << makes >> selon que le pecheur recherche ou non ces especes. Cette classification des makes peut se faire soit en considerant chaque espece successivement, une maree pouvant &tre pertinente pour plusieurs d'entre elles, soit plus globalement, en reference a des metiers, chacun ttant defini par des seuils d'une ou plusieurs especes cibles, chaque mar&e &ant alors dediee a un metier et un seul. Cette etude pmsente la methode utilisee, baste sur des seuils d'especes cibles et un niveau global d'explication. Pour les pecheries francaises de l'ouest de 1'Ec...

Caracterizacion de las tacticas de pesca en la pesqueria multiespecifica de crustaceos demersales en Chile

“…La información de captura (en algunos casos desembarques) ha sido utilizada extensivamente en la literatura para definir tácticas de pesca (He et al, 1997;Pelletier & Ferraris 2000;Ulrich & Andersen, 2004;Marchal, 2008), que junto a otros elementos operacionales y logísticos de la flota (Biseau, 1998) permiten identificar cuando la composición de captura debe ser empleada para la clasificación de pesquerías multiespecíficas. En este sentido, el análisis estadístico de la composición de captura entrega herramientas objetivas en el análisis de pesquerías multiespecíficas, en comparación con el juicio experto.…”

“…> 50%), (2) curvas de Biseau (Biseau, 1998), donde se analiza gráfi-camente el porcentaje acumulado de cierta especie en las capturas, y dependiendo de la forma de la gráfica se asigna el lance a una táctica de pesca particular y (3) mediante análisis multivariado de la composición de captura, donde regularmente se combina análisis de componentes principales con análisis jerárquico de agrupación (dendrogramas). Las tres técnicas descritas poseen algún grado de subjetividad en el análisis.…”

Characterisation and standardisation of a red shrimp <i>Aristeus antennatus</i>, (Risso, 1816) fishery off the Alicante gulf (SE Spain)

“…Since the resulting classes of vessels by PCA are based on catches of the most discriminant species, which do not necessarily include the targeted one, the CPUEs calculated within each group of vessels cannot be considered as actual directed CPUEs (Biseau, 1998). Consequently, it was considered better not to use these results to group vessels into an "activity group" for calculating red shrimp CPUEs, but rather to consider that the PCA results provided a clear description of the fishery.…”

“…In a multi-species fishery, the target species of each group must be identified as a first step. Subsequent identification can then be undertaken by Principal Components Analysis (Biseau and Gondeaux, 1988;Laurec et al, 1989) or by the analysis of the catch composition in relation to the relative fishing effort applied (Biseau, 1998), thereby obtaining a small number of groups composed of vessels that fish in a similar way, according to the species fished.…”

Only two fisheries? Characteristics of the industrial bottom gillnet fisheries in southeastern and southern Brazil and their implications for management

“…whether it may be considered a true target or only an accessory species, for example. Classification criteria used in the present paper, as adapted from Biseau (1998) is presented in Table 1. Species not subject to directed effort but retained due to its commercial value.…”