Age structure affects population productivity in an exploited fish species

Area of Science:

• Marine biology
• Fisheries science
• Population dynamics

Background:

• Long-term changes in animal population age and size structure are documented but their impact on productivity is unclear.
• Fisheries and climate change can alter fish demographic structures, affecting populations.
• Northeast Arctic (NEA) cod, a major commercial stock, has undergone significant age-size structure changes due to fishing.

Purpose of the Study:

• To investigate the impact of spawner age structure on NEA cod population productivity over 75 years.
• To determine if shifts toward younger spawners negatively affect recruitment success.
• To assess the influence of maternal effects and female size on reproductive output.

Main Methods:

• Analysis of NEA cod population data spanning 75 years.
• Modeling to assess the relationship between spawner age structure and productivity (recruits per spawning stock biomass).
• Inclusion of environmental factors like temperature and cannibalism in the model.

Main Results:

• A shift in age structure toward younger spawners negatively impacts population productivity.
• Older spawning individuals are linked to higher recruitment success, likely due to maternal effects.
• A threefold difference in productivity was observed between the youngest and oldest spawning stocks since the 1950s.

Conclusions:

• Population age structure is crucial for fish population productivity.
• Harvest-induced demographic changes can negatively feedback on fisheries by creating younger spawning stocks.
• Integrating demographic data into harvest strategies is essential for sustainable fishery management.