WP 1: Mechanisms of changes in stock structure and reproductive potential

Description of work

Background

One prerequisite for the recovery of depleted fish populations is that their realized reproductive potential provides sufficient viable offspring for the population to expand.  It is apparent that the use of a simple measure, Spawning Stock Biomass, is an insufficient indicator of reproductive potential.  As reported in the literature, egg production and viability of offspring varies in response to changes in abundance, size composition and condition of spawning females. Therefore, it is necessary to provide better estimates of the reproductive potential of a stock due to structuring by fishing effort in a variable environment. The changing environment, in combination with varying fishing mortality, causes significant changes in growth, reproduction, and population genetics by affecting habitats, prey availability, predation, stock size, as well as characteristics of surviving offspring and adults. Consequently both short- and long-term changes in environmental conditions and fisheries can result in changes in the productivity of ecosystems and reproductive potential of fish stocks. This WP will examine the biological, ecological and climatic basis of stock reproductive potential to provide reliable metrics that can be used to evaluate stock reproductive status and recovery strategies.  In this context a key output will be an evaluation of the influence of changes in stock size, structure and distribution, depensatory and density-dependent mechanisms, and population genetics including longer term, evolutionary based variation on the ability and time needed for stocks to recover after depletion.

A series of hypotheses to be examined include:

  1. The ability of a stock to sustain itself, and potentially expand, is a function of the reproductive status of the stock and the prevailing environmental conditions.
  2. The reproductive potential of the stock is a function of stock size and structure.
  3. Stock size and structure influence the quantity and quality of offspring produced and thus the robustness of the stock to further exploitation or the ability to recover from over-exploitation.
  4. Exploitation of a stock will effectively reduce and alter the gene pool and ultimately determine the ability of the stock to recover from over-exploitation.
  5. Exploitation causes predictable adaptive evolutionary changes in a stock's genetic composition, which will affect the reproductive potential and production capacity of the stock.
  6. Exploitation will influence the dynamics of the biology of a species in a predictable manner that will influence the overall productivity of a stock.
  7. Exploitation and changes in stock size influence the distribution of a stock.
  8. Changes in stock size will affect distribution and migration patterns and the ability of a stock to expand during a 'recovery' period.

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 The work will be divided into four tasks to specifically address the hypotheses:

(to read more, click on the task below)

1.1 Estimation of changes in stock reproductive potential

1.2 Resolution of changes in genetic composition of stocks

1.3 Evaluation of fisheries induced evolution

1.4 Determination of changes in stock distributions and migrations

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