Age validation, growth, mortality, and additional population parameters of the goldband snapper (Pristipomoides multidens) off the Kimberley coast of northwestern Australia

摘要

Goldband snapper (Pristipomoides multidens) collected from commercial trap and line fishermen off the Kimberley coast of northwestern Australia were aged by examination of sectioned otoliths (sagittae). A total of 3833 R multidens, 80-701 mm fork length (98-805 mm total length), were examined from commercial catches from 1995 to 1999. The oldest fish was estimated to be age 30+ years. Validation of age estimates was achieved with marginal increment analysis. The opaque and translucent zones were each formed once per year and are considered valid annual growth increments (the translucent zone was formed once per year between January and May). A strong link between water temperature and translucent zone formation was evident in R multidens. The von Bertalanffy growth function was used to describe growth from length-at-age data derived from sectioned otoliths. No significant differences in length-at-age were found between sexes and growth parameters were L-infinity = 598 mm, K = 0.187/yr, t(0) = -0.173 (r(2)=0.76). Regression models of estimated age as a function of otolith and fish measurements indicated a significant relationship between estimated age and otolith weight (r(2)=0.94). Total instantaneous mortality (Z) estimates generated from catch-at-age data of R multidens from the northern demersal scalefish fishery (NDSF) were 0.65 for 1995-96, 0.87 for 1996-97, and 0.71 for 1997-98. Estimates of the annual instantaneous rate of natural mortality (M) were 0.10-0.14. The NDSF population of R multidens is considered to be exploited above optimum levels on the basis of these mortality estimates. The protracted longevity, moderately slow growth and low natural mortality rates of R multidens predisposes this species as one vulnerable to overfishing, thus cautious management strategies will be required. Furthermore, capture of R multidens from depths of 60 meters or greater results in a high mortality of fish because the physoclistous ruptures causing internal hemorrhaging and hence there is a low probability of survival of any fish returned to the sea. Thus traditional harvest strategies involving size limits will be inappropriate for these fish. Conversely, harvest strategies that include appropriately targeted spatial fishery closures may provide a useful additional means of preserving the spawning stock biomass of these fish and protect against recruitment overfishing.