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Male Agonistic Behavior on Atlantic Cod Spawning Grounds
J E Skjæraasen1, P Arechavala-Lopez2, Ø Karlsen1
1Institute of Marine Research Bergen Norway.
Ecology and Evolution
|April 27, 2026
Summary
Male Atlantic cod exhibit higher activity levels than females during spawning, particularly at depths below 20m. This suggests male-male agonistic interactions, consistent with a lek mating system, occur in natural spawning grounds.
Area of Science:
- Marine Biology
- Animal Behavior
- Ecology
Background:
- The mating system of Atlantic cod (Gadus morhua) is debated, with some evidence suggesting a lek system requiring male-male competition.
- Direct observation of agonistic behaviors in marine environments is challenging.
- Previous studies relied on confined conditions, potentially inflating observed male interactions.
Purpose of the Study:
- To investigate male-male agonistic interactions in Atlantic cod on natural spawning grounds using advanced telemetry.
- To compare activity levels between male and female cod in both natural and confined settings.
- To determine the influence of depth on cod activity patterns during the spawning season.
Main Methods:
- Deployed acoustic transmitters with accelerometers and depth sensors on 154 mature Atlantic cod.
- Collected ~1.5 million accelerometer detections from field and net-pen studies in Western Norway (2019-2024).
- Analyzed activity levels in relation to sex, depth, and study environment (field vs. confinement).
Main Results:
- Male cod exhibited significantly higher activity than females in net-pen studies and in the field during spawning.
- Males were more active than females at depths greater than 20m in natural environments; no sex difference was observed above 20m.
- Activity levels were generally lower in the field compared to confinement, but sex differences persisted during spawning.
Conclusions:
- Inferred male-male agonistic interactions occur on natural Atlantic cod spawning grounds, supporting the lek mating system hypothesis.
- Heightened male activity at deeper spawning grounds is linked to their distribution and potential territorial/agonistic behaviors.
- Activity levels and inferred interactions are reduced in natural settings compared to confined conditions.
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