WP 2: Impact of exogenous processes on recruitment dynamics

Description of work

Background

A prerequisite for recovery of fish populations is the survival of sufficient quantities of offspring to maturity. This task will examine the biological and oceanographic basis for the production and survival of spawned eggs, larvae and early juveniles. As reported in the literature, recruitment varies widely from year to year and depends partly on environmental influences on both individuals and the population. Changes in the frequency of production of strong year classes result in multi-annual periods of exceptionally high or low recruitment. These periods can coincide with periods of high or low fishing mortality, resulting in population declines and recoveries now evident for several European fish stocks. As a result, recovery of depleted fish stocks can be slow even under optimal management and compliance if conditions for recruitment deteriorate relative to long-term historical averages or those present when the stock supported high fishing intensity.
Estimated recovery rates therefore depend on assumptions about future environmental conditions and population response at typical time scales of 5-10 years (i.e., some to several generations for the species of interest). However predictions of environmental variability at these time scales have low confidence. Thus this task will use an approach that develops the understanding of causes of past declines in order to estimate via scenario modelling the likely duration and uncertainty of recovery periods for situations of variable environmental forcing. The most likely multi-decadal environmental change in the future is a general warming of the earth's climate, and there is oceanographic and biological evidence (e.g., warmer sea temperatures in northeast Atlantic ecosystems and more northerly distributions of fish species) that this change is already underway.

The work will be conducted in four inter-related tasks. Hypotheses to be addressed will include those related to ecosystem effects (e.g., abiotic conditions for survival of eggs and larvae, food and predator abundances, ocean circulation) on growth and survival of early life history stages, and how changes in spawner biomass and size/age composition affect recruitment probability via changes in the timing and location of egg production and the abundance, distribution and survival of larvae and young-of-the-year juveniles.

Tasks

  • 2.1 Identification of Critical Life stages and Processes
  • 2.2 Develop Process Understanding and Models
  • 2.3 Implement Process Knowledge in Biological-Physical Individual-based Oceanographic models
  • 2.4 Scenario Modelling Variations in Biological and Physical Forcing to Develop Predictive Capacities with Respect to Stock Recovery.

Read more: Description of WP 2 tasks

To top