Age estimation and validation for South Pacific albacore Thunnus alalunga

Area of Science:

• Fisheries Science
• Ichthyology
• Marine Biology

Background:

• Accurate age estimation is crucial for effective fisheries management.
• Albacore (Thunnus alalunga) are important commercial fish stocks in the South Pacific.
• Previous age estimation methods for tuna have shown variability and potential bias.

Purpose of the Study:

• To validate age estimation for albacore (Thunnus alalunga) in the South Pacific Ocean.
• To compare the accuracy of otoliths versus dorsal-fin spines for age determination.
• To recommend the most reliable method for age-based stock assessment and management.

Main Methods:

• Age estimation based on counting annual opaque growth zones in sectioned otoliths.
• Daily increment counts used to locate the first opaque zone relative to birthday.
• Marginal increment analysis and oxytetracycline mark-recapture experiment for periodicity validation.
• Direct comparison of age estimates from otoliths and dorsal-fin spines from the same individuals.

Main Results:

• Opaque zones in otoliths form during austral summer and complete by autumn/winter (April-August).
• Otolith-based age estimates are more accurate than those from dorsal-fin spines.
• Spines showed bias due to poor increment clarity and resorption of early growth zones.

Conclusions:

• Validated counts of annual growth zones from sectioned otoliths are the preferred method for albacore age estimation.
• This method provides more accurate age-based parameters for stock assessment and management advice.
• Findings align with studies on other tropical and temperate tuna species (Thunnini).