Otolith "spawning zones" across multiple Atlantic cod populations: Do they accurately record maturity and spawning?

Area of Science:

• Ichthyology
• Fish Biology
• Otolith Microchemistry

Background:

• Spawning zones in cod otoliths are traditionally linked to spawning events.
• Recent studies question the direct relationship between otolith spawning zones and actual spawning.
• Otolith spawning zones are not widely recorded outside Norway, limiting comparative studies.

Purpose of the Study:

• To determine if otolith spawning zones are a general characteristic of Atlantic cod across diverse populations.
• To investigate temporal changes in the occurrence of spawning zones.
• To correlate otolith-derived maturity at age with gonad maturity stages.

Main Methods:

• Examination of otolith macrostructure from multiple Atlantic cod populations.
• Analysis of a large archival collection of cod otoliths.
• Comparison of otolith-derived maturity with gonad maturity stages.

Main Results:

• Spawning zones appear to be a universal trait in Atlantic cod, irrespective of environment or migratory behavior.
• Maturity at age derived from otolith spawning zones aligns with gonad maturity data.
• A one- to two-year lag was observed between spawning zone formation and sexual maturity.

Conclusions:

• Otolith spawning zones are a reliable, widespread indicator of spawning history in Atlantic cod.
• The observed lag suggests a physiological adjustment period post-first spawning.
• Spawning zones offer a valuable tool for assessing maturity in data-limited fish populations.