Ms. L. (Laure) Pecquerie

Address:	Ifremer, Dept Ecologie & Modèles pour l'Halieutique, Rue de l'Ile d'Yeu BP 21105, 44311 Nantes Cedex 3
Phone:	+33 (0)2 40 37 41 23
Email:	laure.pecquerie@ifremer.fr
	Curriculum vitae
Specialization:	Fishery Science
Project:	Growth and reproduction of bay of Biscay anchovy
Publications:

Introduction

Anchovy, Engraulis encrasicolus, is an important target of coastal fisheries, and the present stocks are rapidly declining. The species is also prey for a large number of marine predators. Little is known about details of the dynamics of its food, food intake, migration, and energetics. An increase of knowledge of its energetics could help in developing responsible fisheries management for this species. The purpose of the project is to contribute to this knowledge by application of the DEB theory to anchovy data. More in particular the aims are to

connect anchovy dynamics to spatially explicit models for lower trophic levels
spatialise life cycle energetics
predict location and timing of spawning

Spatial distribution of the population

During May or June surveys (spawning season), the population is mostly distributed in the south of the Bay of Biscay, with the small and big individuals distributed in- and offshore respectively. The age classes are intermingled. The explanation is possibly because swimming speeds depends on size, not on age, and food density has a spatial structure.

There is some evidence from the spatial distribution of the French pelagic fishery catches that the population is distributed in the north of the Bay of Biscay at the end of summer and in autumn. There is one study of the size of the fishes in the catches in the North in July-September 2000, and there is also a distribution of the fishes according to their size, with the big ones being more in the north.

Autumn surveys (2003 and 2005) showed that big Age 0 individuals (juveniles) are integrated in the schools of the adults.

Description of the growth data

Otoliths show opaque regions that indicate growth conditions and hyaline ones that correspond to growth arrest. Otoliths from juvenile even show a daily ring pattern. The location of these rings has information about the growth of the individuals. Growth generally ceases during the low food densities in winter times. During spawning the otolith tends to grow without aragonit deposits and for some individuals, a spawning ring is identifiable (false winter ring). In a similar way as for estimating annual growth, it was possible to estimate the growth before and after spawning on those individuals that showed a spawning ring: growth before spawning was that measured between the previous winter ring and the spawning ring and the growth after spawning was that measured between the spawning ring and the next winter ring. Large individuals suffer from intensive harvesting by fisheries, and are rare. Otolith data indicate:

All individuals have at least one annulus on their otoliths : seasonal growth, age of the fishes older than on year
There is a linear relationship between growth between the first and second winter and the growth before the first winter
Age 1: All individuals have an otolith with an opaque border in May: growth has resumed before the catch of the individual
Age 2: All individuals have an otolith with a hyalin border in May: growth has not resumed
Age 3: All individuals present an annual growth during age 2: as Age 2 individuals have not resumed growth in May, they resume growth after May but before the following winter because we observed a third winter ring
8 and 50 % of age 2 individuals typically have a spawning ring. Petitgas and Grellier (2003) mention individuals that have a spawning ring between the first and the second winter ring. It indicates that their growth rate decreased significantly sometimes between two winters.

Understanding anchovy growth & reproduction pattern

It turns out to be possible to find a set of parameters of the standard DEB model that reproduces the mean length at age of the population. For this purpose available data for anchovy had to be supplemented with energetics studies on other fish species, such as flatfish. With appropriate rules for the handling of the reproduction buffer a realistic reproduction (i.e. spawning) pattern can be found: Hatching occurs during spring and summer in 10-20 batches. Juveniles grow until the next spring. At the end of winter (they are Age 1 fishes), they still allocate energy to growth.

The fact that equally sized Age 1 fish resume growth before spawning, while Age 2 and 3 fish do not, is more difficult to understand in the context of the DEB theory. One possibility is that allocation to reproduction varies with size and/or age. Such a tradeoff between growth and reproduction is, however, inconsistent with the DEB theory, in which allocation to growth competes with that to somatic maintenance, not with reproduction. Another possibility is the variation of parameter values among individuals. The capacity to grow reduces with the size of the individual relative to its maximum size, and so with age. A scatter in maximum sizes might explain why size ranges of first and second year individual overlap. Body size scaling arguments link covariation of several parameters, which needs to be studied on their applicability to anchovy. A third possibility is that first and other year individuals experience different food densities, for instance by choosing different food items, or being in different locations.

In terms of newly developed methodology to analyse energetics data in the context of DEB theory, we developed a model for the growth and the colour of otoliths with the aim to translate otolith data into trajectories of temperature and food densities as experienced by that individual fish. To this end we separate out the various contributions of assimilation, dissipation and body growth to otolith growth and otolith chemical composition (i.e. colour). This methodology has a much wider field of application, even in archeology and paleontology. Secondly we took the changes in shape into account in the early juvenile stage. By assuming that this stage behaves as a V1-morph, we extended the standard DEB model with a single parameter. This extended version can capture the sigmoid length-to-age curves that are typical for a wider class of fish data.

The further analysis of the various possibilities to interpret size differences and growth potentials and the necessity to provide estimates for realistic food density and temperature trajectories involves a link with hydrodynamics models that include site-specific primary (and secondary) production. We use the Mars 3D-model for this purpose and constructed environmental forcing scenarios that lead to new interpretations of fish growth data in the context of DEB theory.

This is the symposium that closed my project

Go to projects' entry