The information below represents a brief history of the ageing of groundfish species at the Alaska Fisheries Science Center. The coefficient of variation provides a very rough indication of the difficulty age readers have in producing precise ages. However, it should be kept in mind that the experience level of the age readers will also have a significant influence on the precision of the ages being generated.
The history categories themselves provides a combination of our overall experience in ageing a particular species as it relates to volume, corroborative information, and difficulties that have been encountered. The history category does not express the actual difficulty of the different species but instead provides a crude history summary that can be compared across species.
History Categories of Aged Species
- H1: Species which are production aged with age validation through known age fish or OTC marks. Also ages are corroborated through experience and strong year-classes. No major ageing problems are apparent.
- H2: Species which are production aged and corroborated with a weaker validation such as radiometric Pb-210/Ra-226 or C14. Year classes make sense, and no major ageing problems are apparent.
- H3: Species which are production aged and are corroborated through experience: marginal increment analysis and/or strong year-classes. No major ageing problems are apparent.
- H4: Species for which we have only very limited ageing experience. However, no major ageing problems are apparent from the specimens examined.
- H5: Species for which we have substantial experience, but where a significant number of specimens may be very difficult to age. Research, however, indicates ages are reasonably correct and should provide good statistics on average age and longevity.
- H6: Species for which we have had little experience, but will require more research to obtain usable age data. Ageing may require special techniques and ages are only approximate.
- Known age: otoliths from species of known age.
- OTC: otoliths from fish tagged with oxytetracycline.
- Pb-210/Ra-226: radiometric age validation.
- C14: radiocarbon age validation.
- MIA: marginal increment analysis.
- Tags: recoveries or otoliths from tagged fish.