Changes in growth and reproductive traits of dragonet Callionymus valenciennei in Tokyo Bay, concurrent with decrease...

Area of Science:

• Marine Biology
• Fisheries Science
• Ecology

Background:

• Dragonet (Callionymus valenciennei) stock size in Tokyo Bay drastically decreased by 86% from the early 1990s to the mid-2000s.
• Declining fish stocks often trigger adaptive changes in life history traits.

Purpose of the Study:

• To investigate the changes in growth and reproductive traits of dragonet concurrent with stock size decrease.
• To understand the implications of these trait changes for population resilience.

Main Methods:

• Comparative analysis of dragonet standard length at maturation and spawning timing between the 1990s and 2000s.
• Assessment of growth rates post-maturation for both sexes across the two decades.
• Evaluation of potential environmental factors, such as hypoxia, affecting larval survival.

Main Results:

• The minimum standard length for gonadal maturation decreased from 6.0 cm in the 1990s to 4.8 cm in the 2000s.
• Spawning onset shifted earlier, from summer in the 1990s to spring in the 2000s.
• Post-maturation somatic growth significantly decreased in the 2000s compared to the 1990s.

Conclusions:

• Life history adjustments, including earlier maturation and reduced somatic growth, likely represent an energy trade-off to enhance reproductive success under resource limitation.
• Despite these adaptations, population recovery was hindered by negative impacts of hypoxia on larval settlement during the altered spring spawning season.