Four species of dories (Family: Zeidae) and five species of oreos (Family: Oreosomatidae) are caught in the South East Fishery (SEF). John dory and mirror dory are included in the SEF quota sytem with Total Allowable Catches (TACs), in 1993, of 240 t and 800 t, respectively. Oreos, originally a by-catch of the orange roughy fishery, have become an increasing component of the deep-water trawl fishery with estimated landings in excess of 2000 t in 1992. Assessment of these species proved difficult because methods to age them needed to be developed: basic life history parameters such as longevity and growth were unknown. In this report methods to age dories and oreos are described and preliminary growth curves presented.

Three species of dories were considered; John dory (Zeus faber), mirror dory (Zenopsis nebulosus) and king dory (Cyttus traversi). The fourth species, silver dory (C. australis), is a low value by-catch species. Four oreo species were considered; smooth (Pseudocyttus maculatus), black (Allocyttus niger), warty (A. verrucosus), and spiky (Neocyttus rhomboidalis). The fifth species, ox-eye oreo (Oreosoma atlanticum) is rarely caught.

A total of about 3,500 readings were made from 1700 pairs of sagittal otoliths. Otoliths were examined whole, using a variation of the "broken and burnt" method and in section. Otolith growth, for each species, was determined from measuring otolith morphometrics and otolith weight. This was also used in the evaluation of age estimates and identification of errors. Intra- and inter reader variability were examined using Beamish and Fournier's Index of Average Percent Error and regressions of age estimates were used to determine whether there was bias between readers. Von Bertalanffy growth curves were fitted to individual observations using non-linear least squares.

For John and mirror dory, ages were estimated from counting annuli on the surface of whole otoliths. King dory otoliths were examined whole for fish less than 20cm and in section for larger fish. For the oreos, tranverse sectioning and subsequent grinding to a thickness of approximately 0.2mm revealed annuli which provided age estimates for a range of fish sizes.

Partial validation was possible for some species. Age estimates for juvenile John dory and king dory were consistent with the available length-frequency data. However, age estimates for adults of these species and for adult and juvenile mirror dory require validation. Our estimates for warty oreo gave similar results to radiometric analysis of whole otoliths. The maximum age from otolith sections was 130 years for a female fish of 36.5 cm TL compared to maximum ages of 130-170 for fish of length 34-35 cm from radiometric analyses. Because the morphology and incremental structure of oreo otoliths is similar between species, these results suggest our interpretation of the other species is also correct. The first 4 to 5 annuli seen in sectioned oreo otoliths are very broad after which there is distinct transition to much narrower annuli. This appears to be consistent with the change from a pelagic to demersal habitat previously reported for oreos.

Age estimates for each species were highly repeatable. Intra- and inter- reader variablity was low and there was no significant bias between readers. The growth of all species was adequately described by the von Bertalanffy growth curve (Table 1). Results for each species are summarised in Table 1. John dory and mirror dory appear to be relatively short-lived and fast growing while king dory are more slow growing. Our results indicate that oreos are extremely slow growing and long-lived. Similar results, for oreos, have been reported recently from studies in New Zealand.

In summary, the main objectives of the project have been met and our results will be of considerable use to future assessments of these species. For the oreos, they have important implications for management of the fishery.