Working Group 1

Identifying the causes and consequences of variation in stock reproductive potential

In the standard assessments of many fish stocks, several key components of reproductive potential (growth, condition, maturation rates, sex ratios, relative fecundity) are assumed to be constant over broad scales in space and time. As a result, indices of reproductive potential that are used to formulate scientific advice under-represent the true magnitude of variation in stock reproductive potential. This makes the advice less sensitive to the variety of biotic and abiotic factors that influence reproductive potential. Working Group 1 will evaluate the degree to which assumptions about growth and reproduction are violated using a combination of laboratory, field, and stock-level evidence. The Working Group will identify biotic and abiotic drivers that have contributed to temporal and spatial variation in different components of reproductive potential. Using this process-based understanding of how variability in stock reproductive potential has been generated in the past, methodology for forecasting future stock reproductive potential for a variety of environmental, ecological and fishing scenarios will be developed. In combination with WG3 the potential effects of refining stock-level estimates of stock reproductive potential on management advice in light of changing environmental conditions and varying management strategies will be addressed

WG1 has the following deliverables:

  1. Document detailing the magnitude by which standard indices of stock representation under- or misrepresent indices compared to indices that have higher degree of biological, temporal and (or) spatial resolution.
  2. Document identifying the biotic and or abiotic drivers contributing to variation in stock reproductive potential for several stocks.
  3. Models to illustrate how information about the causes of variation in stock reproductive potential can be used to forecast the consequences of this variation for future development of the stock.

At least three workshops will be held in association with this Working Group, with the goals of:

  • Estimating key components of stock reproductive potential. This kick-off workshop will be organized to assist researchers in developing more refined estimates of stock reproductive potential by combining historical databases with new knowledge about reproductive potential of individuals. The possibility that estimates can be further refined by including age- or size-specific variability in egg quality will also be explored. Time series for a range of stocks representing alternative metrics of stock reproductive potential, such as female-only spawner biomass and total egg production will be compiled.
  •  Develop time series describing trends in both stock reproductive potential and relevant environmental, ecological and fishing-related factors. Discussion will focus on identifying and quantifying potential drivers of variation in stock reproductive potential. To do this, sensitivity analysis will be undertaken in order to establish which demographic and reproductive traits have the greatest effect on the variability in stock reproductive potential for a range fish stocks. Once these highly influential factors have been established, then possible environmental, ecological and fishing-related factors will be identified for each stock separately.
  • Evaluation of statistical models relating temporal variation in stock reproductive potential to different drivers. Discussion will focus on how information can be used to address strategic “what if” questions related to the relative importance of different factors to future values of stock reproductive potential. For example, if the reduction in old fish was found to be highly influential determinant of stock reproductive potential then strategic questions related to conserving/over-exploiting large fish could be explored. This Workshop will also illustrate the implementation of the data and statistical models developed by WG in a modelling framework that is being widely used to assess different management options (see http://www.flr-project.org/). This will permit the effects of alternative indices of stock reproductive potential on management to be quantified objectively.