Validation of age and growth estimates using thin otolith sections from the purple wrasse, Notolabrus fucicola

Abstract

The age of Notolabrus fucicola from the east and southeast coasts of Tasmania was estimated from counts of opaque (transmitted light) growth zones in thin transverse sections of sagittal otoliths. The position of the first annulus was validated through the otolith radii of known-age juveniles. Marginal increment analysis was performed by examining the growing edge of otoliths over 2 years. This showed that opaque zones were formed annually and were consistently deposited from late September to early December (spring season), which is coincident with annual increases in somatic growth and water temperature during this season. A criterion was developed to ensure accurate age estimation for individuals sampled during the time of year when deposition of opaque material was incomplete or not apparent. The maximum age estimated was 20 years and the relationship between fork length and age was described by the von Bertalanffy growth function (L∞ = 368 mm, K = 0.116 and t0 = –1.87 for males and L∞ = 385.7 mm, K = 0.109 and t0 = –1.96 for females). The clarity of increment structure and rigorous validation protocol that was adopted minimised the risks associated with using marginal increment analysis to validate the periodicity of increment formation and it provided robust age and growth estimates for N. fucicola in Tasmanian waters.

Fishing constrains phenotypic responses of marine fish to climate variability

“…They inhabit the shallow (<25 m) coastal waters of south‐east Australia and New Zealand (Russell & Gomon, ), displaying fidelity to the reef on which they settle (Barrett, ). Individuals can reach 600 mm in length and live ≥25 years (Denny & Schiel, ), with a maximum age of 20 observed in the study region (Ewing, Welsford, Jordan, & Buxton, ). Peak growth occurs during the austral spring and summer (Welsford & Lyle, ).…”

“…All reefs have been subjected to commercial fishing since 1990 (Figure c). Fish were caught using baited fish traps and sampled when total length was >130 mm (see Ewing et al, for additional sampling details). The formation of annual growth increments in purple wrasse otoliths has been validated (Ewing et al, ), and ageing precision (calculated using average percentage error (APE), Beamish & Fournier, ) is high (0.8% within readers, 2.6% among readers; Ewing et al, ).…”

“…Extrinsic variables included site (PB, EHN, HCR), average annual southern oscillation index ( SOI ), average annual sea surface temperature (SST) over the fish growth year ( annualSST , 1 October to 30 September), average warm period SST ( warmSST , 1 October to 31 March), and the presence or absence of commercial fishing operations ( fishery ). Sex was not considered due to uncertainty around when fish sex‐changed to males and evidence from von Bertalanffy growth models indicating minimal sex‐specific differences in growth (Ewing et al, ).…”

“…Individuals can reach 600 mm in length and live ≥25 years (Denny & Schiel, 2002), with a maximum age of 20 observed in the study region (Ewing, Welsford, Jordan, & Buxton, 2003). Peak growth occurs during the austral spring and summer (Welsford & Lyle, 2005).…”

Otoliths as individual indicators: a reappraisal of the link between fish physiology and otolith characteristics

“…There is no doubt that temperature overall plays an important role with regard to the cyclic pattern of otolith opacity and several studies have explored the role of seasonal temperature variations in generating translucent and opaque growth zones (Ewing et al 2003;Newman and Dunk 2003;Pilling et al 2007;Borthagaray et al 2011;Gjøsaeter and Danielssen 2011). This has primarily been through studies of seasonality of marginal increment opacity from which temperature and seasonal effects have been inferred.…”