Age determination of orange roughy,Hoplostethus atlanticus (Pisces: Trachichthyidae) using210Pb:226Ra disequilibria

Abstract

Abstract. Natural levels of 21°pb:226Ra in otoliths of orange roughy, Hoplostethus atlanticus, from south-east Australian waters, were measured to determine fish ages radiometrically. Up to maturity, radiometric age estimates were consistent with a single constant otolith growth rate. Radiometric ages for juveniles were comparable with, but greater than, those obtained in a recent, validated New Zealand study which employed counts of annuli on the surface of otoliths. Beyond maturity, radiometric ages were obtained by modelling with an otolith growth rate set at 45% of the juvenile rate. Radiometric ageing confirms that orange roughy is very slow-growing, with an age at maturity (32 cm standard length, SL) of ,-~ 32 yr, and is very long-lived, with fish 38 to 40 cm being 77 to 149 yr old. These results have important implications for the management of the fishery.

Diet and food consumption of a deep-sea fish orange roughy Hoplostethus atlanticus (Pisces Trachichthyidae), off southeastern Australia

“…1979, Childress et al 1980). Orange roughy, on the other hand, grows exceptionally slowly, maturing a t -20 yr at -30 cm, and achieves a standard length of 45 to 50 cm at 50 to l00 + yr (Mace et al 1990, Fenton et al 1991. The relatively high rate of food consumption and low growth rate of orange roughy have clear implications for estimates of the species' metabolism and growth efficiency.…”

“…Bathypelagic organisms generally consume less food than shallower species, possibly because their metabolism is lower rather than due to decreased growth rate (Torres et al 1979, Childress et al 1980, Mauchline 1988. However, orange roughy grows very slowly: validated otolith-based and radiometric aging studies indicate that orange roughy matures at about 20 yr at -30 cm, and grows only 15 to 20 cm further over a life-span of 50 to 100+ yr (Mace et al 1990, Fenton et al 1991. It might be expected, therefore, that orange roughy has a particularly low rate of food consumption, if its metabolism is similar to that of other non-migratory deepwater species.…”

<sup>210</sup>Pb-<sup>226</sup>Ra chronology reveals rapid growth rate of <i>Madrepora oculata</i> and <i>Lophelia pertusa</i> on world's largest cold-water coral reef

“…Another method based on 210 Pb ingrowth from the 226 Ra allows dating of recent carbonates such as near-shore mollusc shells (Baskaran et al, 2005), fish otoliths (Fenton et al, 1991) and whale bones (Schuller et al, 2004). This 210 Pb ingrowth method requires either that the initial 210 Pb incorporated is negligible compared to the radiogenic 210 Pb produced by the decay of 226 Ra, or that its initial activity can be estimated.…”

Chemistry and composition of fish otoliths:pathways, mechanisms and applications

“…Nevertheless, there is compelling empirical evidence in support of a closed system: if ' "Rn is lost during decay, age estimates based on daughter:parent isotope ratios should be skewed towards lower ratios, and hence younger ages. Yet all published 210Pb:226Ra ratios to date have resulted in extremely old age estimates, some of which have exceeded 100 yr (Carnpana et al 1990, Fenton et al 1991, Francis 1995. Therefore, if Rn emanation is occurring in these otoliths, it must be occurring at very low levels.…”

“…Current discriminatory power is on the order of 5 yr for 2'0Pb:226~a and 1 to 2 yr for 228Th:'28Ra, over age ranges of 0 to 50 and 0 to 3 yr, respectively. Therefore, this approach is best suited to species where the candidate age interpretations are widely divergent, such as in Sebastes or Hoplostethus (Campana et al 1990, Fenton et al 1991.…”