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The evolution of spawning migrations: state dependence and fishing-induced changes
Christian Jørgensen1, Erin S Dunlop, Anders Frugard Opdal
1Department of Biology, University of Bergen, Box 7803, N-5020 Bergen, Norway. christian.jorgensen@bio.uib.no
Ecology
|January 14, 2009
Summary
Atlantic cod (Gadus morhua) migration distance is influenced by individual state and environmental factors. Fishing pressure reduces migration extent and impacts spawning grounds, especially for homing cod.
Area of Science:
- Ecology
- Evolutionary Biology
- Fisheries Science
Background:
- Marine species migration is crucial for growth, survival, and reproduction, driven by environmental heterogeneities.
- Atlantic cod exhibit diverse migratory behaviors, from sedentary to long-distance annual migrations.
- The Northeast Arctic cod stock undertakes southward spawning migrations.
Purpose of the Study:
- To investigate the evolution of migration distance in Atlantic cod using a bioenergetics model.
- To understand how individual states (length, age, condition, food availability) influence migration strategies.
- To compare migration patterns under historical and contemporary fishing regimes for both homing and roaming cod.
Main Methods:
- Developed a state-dependent bioenergetics optimization model.
- Assumed a linear relationship between migration distance and offspring survival, influenced by environmental factors like water temperature.
- Modeled two behaviors: homing (site fidelity) and roaming (no constraints).
Main Results:
- Larger, healthier cod migrated farther and tended to mature later.
- Roaming cod exhibited greater southward spread with increased size and age.
- Homing cod showed more restricted spawning ranges.
- Contemporary fishing led to earlier maturation, shorter migrations, contracted spawning areas, and poorer body condition, particularly impacting homing behavior.
Conclusions:
- Individual state and environmental conditions are key drivers of cod migration distance and strategy.
- Fishing pressure significantly alters cod life history, reducing migration and impacting population distribution.
- Conservation and management strategies must consider the differential impacts of fishing on migratory behaviors like homing.
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