Modelling the spatio-temporal distribution of age-1 Bay of Biscay anchovy (<i>Engraulis encrasicolus</i>) at spawning time

Abstract

SUMMARY: To efficiently manage and maintain fish stock abundance and age structure, it is necessary to understand variability in its spatial distribution. The main objective of this study was to describe the demographic structure of the Bay of Biscay anchovy during the main spawning period based on adult samples from 15 daily egg production method surveys. The proportion of age-1 individuals was modelled using generalized additive models with a binomial distribution and a logit link in relation to geographical and environmental covariates. The possibility of obtaining different models depending on the average age-1 proportion (low or high) was also explored. In general, age-1 individuals were found in shallow waters close to the coast, especially associated with the Gironde and Adour river plumes, whereas older individuals were prevalent on the shelf break and in oceanic waters. However, in years with a high age-1 proportion the younger individuals were also dominant in oceanic waters. These results could be used for management purposes, such as defining protected areas for particular age groups.Keywords: spatial age composition, anchovy, Bay of Biscay, daily egg production method, generalized additive model, environmental effects.RESUMEN: Distribución espacio-temporal de la edad 1 de anchoa del golfo de Bizkaia (Engraulis Encrasicolus) en el momento de puesta. -Con el fin de gestionar eficientemente la abundancia y la estructura espacial de un stock es necesario entender su distribución espacial. El objetivo principal de este trabajo es describir la estructura demográfica de la anchoa del golfo de Bizkaia durante el periodo de desove a partir de las muestras de adultos recogidas en 15 campañas del método de producción diaria de huevos. La proporción de individuos de edad 1 se modeló en función de variables geográficas y ambientales por medio de un modelo aditivo generalizado con distribución binomial y función enlace logit. Además se estudió la posibilidad de obtener diferentes modelos dependiendo de si la proporción de edad 1 promedio es baja o alta. En general, los individuos de edad 1 se encontraron en aguas poco profundas cerca de la costa, especialmente en las plumas de los ríos Garona y Adur, mientras que los individuos de mayor edad prevalecieron en el cantil y en aguas oceánicas. Sin embargo, los años con una alta proporción de edad 1, los individuos jóvenes fueron también predominantes en aguas oceánicas. Estos resultados podrían utilizarse para fines relacionados con la gestión, tales como la definición de áreas protegidas para determinados grupos de edad.Palabras clave: composición de edad espacial, anchoa, golfo de Bizkaia, método de producción diaria de huevos, modelo aditivo generalizado, efectos ambientales.

Validation of age determination using otoliths of the European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay

“…The reason for these differences is related to the spatial pattern of the Spanish fishery because it operates in regions of deep water rather close to the Spanish coast where the bigger anchovies are found Ibaibarriaga et al 2013). In contrast, the surveys systematically cover all areas occupied by the population, with the major part of the population often placed around the northern coastal shelf close to the mouth of the Gironde River where age-1 predominates and the mean lengths at ages are smaller than in the remaining areas Vaz et al 2002;Ibaibarriaga et al 2013).…”

“…It provided the foundations for several studies on spatial distribution of adults at spawning time Vaz et al 2002;Ibaibarriaga et al 2013) and on the modelling of otolith shape (Gonzalez-Salas and Lenfant 2007) and growth (Hernández et al 2009, Pecquerie et al 2009. Beyond this, recent studies on otolith micro-increment formation of this anchovy have enabled the daily rhythm of deposition to be established in larvae (Aldanondo et al 2008), as well as in juveniles and adults (Cermeño et al 2003), and the method for otolith daily increment examination (Cermeño et al 2008).…”

Genetic population structure of anchovy (Engraulis encrasicolus) in North-western Europe and variability in the seasonal distribution of the stocks

“…Distributions of anchovies inhabiting the Bay of Biscay and the North Sea had a similar seasonal pattern, with a clear contraction during the spawning season and a spreading over a much larger area for overwintering. With aggregated abundance data over multiple years and climatologies for environment covariates, our objective was not to model precisely anchovy habitat as it was done already for the spawning season (Ibaibarriaga et al, 2013;Petitgas et al, 2014;Planque et al, 2007). Our objective was rather to explain the pattern of variability in anchovy distribution between seasons.…”