No abstract

Oceanographic processes have been shown to play a pivotal role in the control of recruitment variability in some commercial, northern temperate fish populations. This study investigates the link between inter-annual changes in larval supply and wind stress for unexploited reef fish populations at Lizard Island, northern Great Barrier Reef. For the first time, this relationship is analysed separately for front-reef and back-reef habitats and results for 3 major reef fish familes (Pomacentridae, Apogorudae, Blenniidae) reveal that the link between wind stress and larval supply appears to be habitat-dependent, In the back-reef habitat, there appears to be a positive correlation between interannual changes in the frequency of onshore winds and the level of larval supply. This phenomenon is associated with large-scale changes in weather systems, suggesting that the relationship may be predictable at a region-wide scale. Results for the front-reef habitat suggest that the effect of wind stress on inter-annual levels of larval supply is less important. Survival and advection of earlier larval stages may be more influential in determining fluctuations in the magnitude of replenishment to this habitat. Although not helpful in predicting inter-annual changes In larval supply, a local retention mechanism may keep larval supply lnto thls habitat elevated above that of the back-reef side. Comparison of these results with a non-reef mixed-age group of schooling pelagic fishes suggests that these patterns are a unique feature of the replenishment process.

Duration of presettlement phase was examined for the temperate reef fish Parika scaber. Information was also collected on seasonality, growth, development, and diet before settlement. Presettlement P. scaber associated with drift algae offshore of rocky reefs were of sizes 7 to 35 mm standard length (SL); highest abundances were found between November and January. Fish just prior to settlement were collected from algae tethered seaward of reefs. Fish associated with drift algae and fish captured around tethered algae had similar size-frequency relationships. Fish that associated with drift and tethered algae and settled on reefs were between 22 and 66 d old. Despite this wide range of ages and sizes, at any one time a large proportion of P. scaber around drift and tethered algae were of a similar size and age. However, among sampling times the mean value for these relations vaned.Hence, P. scaber have the capacity to settle at a variety of ages and sizes. Presettlement P. scaber (described from 3.5 mm) have a full adult fin-ray complement and a similar colouration to fish on the reef at 8 to 9 mm length. Development to the adult form correlated with a change from allometric to isometric growth. Reared and tetracycline-treated fish demonstrated that increments were deposited daily, after hatching, in the sagittal and lapillus otoliths. Assuming that the spacing of increments relates to the growth of fish, a growth curve was determined: After an initial period of slow growth there was a rapid acceleration in growth to 7 mm; growth remained relatively conztant in h g e : fish. Thc spacificj of inclements suggested that development rate vaned among samples of fish captured at different times. Growth rates, determined from age-size relations, showed a similar variation. T h~s is discussed in relation to the conditions fish may have experienced in the pelagic enviroment.

Otolith increment widths in a temperate reef fish, Parika scaber (Pisces:Monacanthidae), have been shown to vary in different months and to correlate with changes in somatic growth rate. This results in the persistence of a constant otolith-size/fish-size relationship. In the present study, the response of otolith growth to laboratory-induced changes in body growth was determined over a 10-day period in December 1985. Juveniles were subjected to two ranges of temperature (19-21�C and 24-26�C) and three feeding levels (fully fed, partially fed, and starved) of a diet consisting of larvae of Opifex fuscus, an endemic mosquito. Fish were individually tagged to ensure that changes in growth rate and any associated changes in otolith microstructure could be accurately determined for any individual. Fully fed fish grew more slowly during treatment than they did prior to treatment, and starved fish did not grow at all. Partially fed fish exhibited a size-hierarchy effect, with larger fish increasing in body size at the expense of smaller individuals. No temperature effect on growth rate was recorded. In contrast to the results from an associated field study, otoliths of fully fed fish continued to increase at the same daily width despite the induced alteration in growth rate. Thus, otoliths were disproportionately large compared with estimates from the field. However, otoliths of starved fish were not as large as predicted from a continual production of daily rings at a constant width. Daily ring deposition may have ceased at different times during the experiment for the starved fish, depending on body size. Alternatively, deposition may have continued, but at a spacing that was not detectable by light microscopy. We conclude that adequate validation of response of otolith growth to changes in somatic growth is necessary before individual growth histories can be back-calculated. This is true even where strong evidence from the field suggests that back-calculation is possible.