Validation of age and growth in a long-lived temperate reef fish using otolith structure, oxytetracycline and bomb radiocarbon methods

Abstract

Generating age estimates for long-lived fish requires particular attention to validation because they are usually difficult to age owing to narrow increment structure. A robust validation of the accuracy and precision of banded morwong, Cheilodactylus spectabilis, sampled from Tasmanian waters, was undertaken. Age at the first enumerated increment was established from analysis of juvenile cohorts, and the timing and periodicity of increment formation was established using a quantitative model from oxytetracycline (OTC) mark-recaptures at liberty for periods of up to 8 years. The accuracy of age estimates was examined independently by comparing radiocarbon values in the otolith region corresponding to the first year of growth against the south-western Pacific calibration curve. C. spectabilis is very long-lived, with males and females living to over 90 years of age. Growth modelling revealed a fast initial growth phase, terminating in an abrupt plateau near the asymptotic length. This species displays substantial sexual dimorphism in growth, with males growing to larger sizes than females.

Life cycle characteristics of the Blue Morwong Nemadactylus valenciennesi, compared with those of other species of Cheilodactylidae

“…Conversely, there would be no obvious advantage for maturity to be delayed in N. macropterus and C. spectabilis because the growth curves of these species exhibit a marked tendency to level off very early in life (Fig. 9, Jordan 2001a;Ewing et al 2007) and thus any such delay would not result in a sufficient increase in reproductive output throughout the remainder of life to offset mortality.…”

“…4), it is helpful to consider the early and similar pattern of growth of the cheilodactylids N. macropterus and C. spectabilis, for both of which there were more extensive data (Jordan 2001a;Ewing et al 2007). Those studies showed that, by 1 year of age, N. macropterus and C. spectabilis had attained fork lengths of 145 and 132 mm, respectively.…”

“…L ∞ is the asymptotic fork length (mm), k is the growth coefficient (year -1 ), t 0 is the hypothetical age (years) at which fish would have zero length, s refers to south coast and w to lower west coast in south-western Australia. Data for N. macropterus and C. fuscus were taken from Jordan (1998;2001a) and 800 Lowry (2003), respectively, while those for C. spectabilis were from Murphy and Lyle (1999) and Ewing et al (2007). …”

“…n s , n r , and n g ; number of fish caught by spear fishing, recreational line fishing and gill netting, respectively. Cheilodactylus fuscus, Ewing et al (2007) used the Schnute growth curve for C. spectabilis because it provided a better fit than the von Bertalanffy growth curve. L ∞ is the asymptotic fork length (mm), k is the growth coefficient (year -1 ), t 0 is the hypothetical age (years) at which fish would have zero length, s refers to south coast and w to lower west coast in south-western Australia.…”

Growth Models and Analysis of Crustacean Growth Data

“…Due to its flexibility, not only can the model detect the high growth rate of longtail tuna and long-lived temperate reef fish (Ewing et al, 2007) during an early phase, but it can also discover the low growth rate of large temperate pelagic fish (Stewart et al, 2004). The five-parameter Schnute-Richards model (Schnute & Richards, 1990) can be expressed as…”