Recruitment studies: Manual on precision and accuracy of tools

This manual is one of the results of the project Precision and Accuracy of Tools in Recruitment Studies (PARS), financed by the EU (FAIR-CT96–1371). The project PARS is concerned with improving the methodologies used in investigations and the monitoring of the early life stages of fish larvae, especially herring and sardine. These are important in both stock assessments and strategic research intended to improve predictive capability. The project deals with precision and accuracy issues in two categories of measurements, which together encompass most of the data that are routinely required from samples of early life stages of fish:

• the growth and condition of individuals;

• the origin of individuals.

Quantitative evaluation of the growth rate and condition of larvae in relation to environmental conditions at the time of capture is an essential prerequisite for predictive assessment of survival potential. In particular, the identification of starving or sub-optimally growing larvae in the population is a powerful method for evaluating survival probability. Both biochemical and otolith microstructure methodologies offer the prospect of identifying individuals at risk. However, the understanding of the underlying physiology of somatic and otolith growth and development is not sufficiently advanced; therefore, it does not allow a high degree of accuracy. In particular, decoupling of otolith and somatic growth under some circumstances is recognized but not understood.

Determining the origin of early life stages is important for a number of applications. Origin in this context refers to the time and location at which a specimen was hatched, and the history of an individual’s growth rate and the environment between hatching and capture. A combination of otolith microstructure and chemical analyses provides the tools necessary for this study. The project evaluates the discriminatory power of these methods using controlled mesocosm and laboratory experiments and tests their precision by reference to field-caught material.

This manual is an important step for standardizing techniques used in recruitment studies and will be beneficial to anyone working in the field of fish recruitment in order to increase the nowledge of fish stocks and their management.