Working Group 2

Improving estimates of stock reproductive potential: Standardising sampling procedures and methods across North Atlantic

Specific types of data are required to estimate stock reproductive potential. The extensiveness of data sets for this purpose varies widely among fish species and stocks. Improvement of stock assessment methodology necessitates a better understanding of variability in recruitment as function of stock reproductive potential. Evaluating the reproductive potential of fish stocks requires understanding of stock-specific reproductive characteristics and the underlying mechanisms. These include spawner biomass, sex ratio, growth, condition, maturation, potential and realized fecundity, egg viability, and hatching success. Studying reproductive characteristics involves a number of protocols, techniques and methodologies that need to be standardised across the different research institutes or universities. Correspondingly, there is a need for concise sampling and analyses procedures across institutions, as well representative area coverage across the distribution of a population. At present considerable differences exist in applied procedures within a species and between closely related researchers. As a consequence, obtained results are inconsistent; in North Sea herring for example, Denmark, Norway and Scotland have very different estimates of the maturity ogives. Thus, the overall objective of WG 2 is to develop guidelines for the design of long-term collection schedules and internationally agreed protocols that improve the capacity to routinely and regularly estimate reproductive potential.

WG2 has the following deliverables:

  1. List of variables needed to be considered in order to estimate Stock Reproductive Potential including importance and difficulty of those variables.
  2. International Coordinated Protocols detailing the sampling procedures depending on the reproductive strategies for growth, maturity, fecundity.
  3. Evaluation of the frequency and intensity of sampling for the variables described.
  4. Workshop on histological and stereological methods in studies on fish reproduction
  5. Workshop on identification and classification of reproductive strategies.
  6. Workshop on fecundity and atresia estimation including male spermatozoa production.

At least three methodological workshops will be developed within this WG to discuss the following issues:

  • Workshop on histology and stereology or alternative methods for quantification will specifically address questions related to gametogenesis patterns in males and females; comparison of macroscopic vs. histology assessment and linking macroscopic images and histological descriptions of maturity status; criteria to interpret follicle stages in whole mounts; rates of follicle growth and regression and identification of females that skip spawning using Postovulatory follicles and ovary Tunica diameter. Further stereological and alternative methods for quantification of oocytes will be compared (e.g., auto diametric and Disector methods).
  • Main focus of the workshop on identification and classification of reproductive strategies will be a comparison of female and male gametogenesis across a wide range of species and reproduction strategies. Further, different aspects classifying the reproductive strategy of teleosts will be considered. Discussions of methodology needed to assess reproductive strategies will be stimulated. This includes the usefulness of protocols for staining various cells components and structures. Guidelines for an illustrated atlas on reproductive strategies and comparative gametogenesis will be elaborated. Differences in reproductive strategies normally are related to life span (short versus long lived species) and habitat, (demersal versus pelagic), but the most obvious differences occur between cold and temperate-warm species. Methodologies for stock reproductive potential have to be developed differently for cold vs. warm-temperate species. In this sense the workshop will promote a stronger connection among researchers and methodologies.
  • The workshop on fecundity and atresia estimation will elaborate differences in fecundity estimation procedures between determinate and indeterminate teleosts. Examples of different fecundity types will serve as basis for discussions. Different fecundity measures, e.g., realised vs. potential fecundity, relative vs. total fecundity, will be compared for their suitability as indicators of reproductive potential for different species. Special emphasis will be given to the role of atresia in the determination of realised fecundity. The applicability of different stereological methods to estimate atresia will be tested. Guidelines for fecundity studies on species with different fecundity types will be developed. Further, methods to determine male spermatozoa production and fertilization capacity will be discussed.