Age-reading of lumpsucker (Cyclopterus lumpus) otoliths: dissection, interpretation and comparison with length composition

Summary

This paper describes the use of lumpsucker (Cyclopteruslumpus) otoliths for age determination, with focus on methods that were found practical, the precision achieved in the first documented age-reading workshop of this species, and comparisons with length composition of the stock. The otoliths are very small and special training is necessary to locate them. The zonation pattern is relatively distinct and it was usually easy to establish a set of rings assumed to be annuli. The precision of age estimates was reasonably high for ages 1–4, although no formal verification was available at the time of reading. After the workshop, the resulting age–length relationship was compared to new estimates of length composition of juvenile lumpsucker prior to and after the migration from the coast. This supported the applied reading method. The age estimates together with length frequencies from the spawning ground suggest that males may spawn for the first time at age 2–3, and females at age 3–4. This is at least 1–2 years less than all previous estimates of age at maturity. However, further verification (e.g., by tracing the edge properties throughout the year) should be done before age-structured data are used in assessments of this species.