Isotopic evidence of connectivity between an inshore vegetated lagoon (nursery habitat) and coastal artificial reefs (adult habitats) for the reef fish Lethrinus lentjan on the Terengganu coast, Malaysia

Stable isotope analyses of muscle tissue (δ13Cmuscle and δ15Nmuscle) and otoliths (δ13Cotolith and δ18Ootolith) were used to retrospectively track habitat uses of Lethrinus lentjan, and to determine any association between Setiu Lagoon (nursery habitat) and coastal artificial reefs (CARs; adult habitats) on the Terengganu coast, Malaysia. Muscle stable isotopes exhibited a spatial change from inshore to offshore habitats associated with growth, possibly related to the reef-ward movement of the fish. Otolith stable isotopes of adult fish from CARs were measured in juvenile (from outside the core to the first opaque zone of otolith) and adult (the edge of otolith) portions and were compared with those of juveniles from Setiu Lagoon, suggesting that the adult fish may not primarily use the lagoon as a nursery before ontogenetically migrating to CARs. The effects of coastal currents between monsoonal seasons could reorientate offshore juvenile migration; hence, adult cohorts in CARs may be replenished from various nursery habitats along the coast. Additionally, similarities in the δ18Ootolith values of juvenile and adult sections suggested that some individuals may not spend their juvenile phases in shallow estuarine habitats. Based on the findings of this study, we recommend that coastal conservation strategies take into account multiple nursery habitats rather than a single one.

Timing of growth zone formations in otoliths of the snapper, Chrysophrys auratus, in subtropical and temperate waters differ and growth follows a parabolic relationship with latitude

Chrysophrys auratus was collected from one sub-tropical and two temperate regions spanning >2400 km along the coast of Western Australia (∼23.5–35.5° S). Marginal increment analysis demonstrated that, while a single opaque zone is formed in the otoliths of C. auratus each year, the period of deposition varies among regions. An opaque zone was formed in May to early September in the sub-tropical upper west coast, and thus when water temperatures were declining to their minima. In contrast, opaque zone formation occurred 3 months later in August to December in the temperate lower west and south coasts, when water temperatures were rising from their minima. The length and age distributions differed markedly among populations of C. auratus, with the strongest year classes varying among the three regions. Thus, it is likely that year class strength of C. auratus throughout its distribution along the coast of Western Australian is mostly related to local environmental conditions. Chrysophrys auratus grew far less rapidly and attained a smaller size in the warmer upper west coast than in the cooler temperate regions of the lower west and south coasts. A collation of data on C. auratus from ten populations in Australia and three in New Zealand showed that growth is greatest towards the mid-latitudes of its geographic range, i.e. at ∼31° S. Estimates of mean lengths at specified ages thus exhibit a parabolic relationship with latitude, with reduced growth (i.e. edge-of-range effects) occurring towards the latitudinal margins of the distribution of this sparid.

Validation of age determination using otoliths of the European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay

Validation of the age determination procedure using otoliths of European anchovy in the Bay of Biscay was achieved by monitoring very strong year-classes in successive spring catches and surveys, as well as the seasonal occurrence of edge types. Historical corroboration of the ageing method was obtained by cross-correlation between successive age groups by year-classes in catches and surveys (1987–2013). Summary annual growth in length is also presented. Yearly annuli consist of a hyaline zone (either single or composite) and a wide opaque zone, disrupted occasionally by some typical checks (mainly at age-0 and age-1 at peak spawning time). Age determination, given a date of capture, requires knowledge of the typical annual growth pattern of otoliths, their seasonal edge formation by ages and the most typical checks. Most opaque growth occurs in summer and is minimal (translucent) in winter. Opaque zone formation begins earlier in younger fish (in spring), and this helps distinguish age-1 from age-2+.

Age-based demography and reproduction of hapuku, Polyprion oxygeneios, from the south coast of Western Australia: implications for management

Wakefield, C. B., Newman, S. J., and Molony, B. W. 2010. Age-based demography and reproduction of hapuku, Polyprion oxygeneios, from the south coast of Western Australia: implications for management. – ICES Journal of Marine Science, 67: 1164–1174. The hapuku, Polyprion oxygeneios, inhabits deep (>100 m) continental slope waters of Western Australia. In all, 1352 P. oxygeneios were collected from the waters along the south coast of Western Australia (ca. 35°S) from 2004 to 2008. The species is gonochoristic, and spawns during the austral winter (May–September). Ages were estimated from counts of opaque zones from thin-sectioned sagittal otoliths. Classification analysis of the outer margin of sectioned otoliths indicated that a single opaque zone is deposited annually. Female P. oxygeneios (n = 630; 535–1114 mm total length, TL) ranged in age from 2 to 35 years and males (n = 691; 521–1004 mm TL) from 2 to 52 years. von Bertalanffy growth models for male and female P. oxygeneios were statistically, but not biologically, different (<5% difference in mean and estimated lengths-at-age). Estimates of the lengths and ages at which 50% of the females and males in the population reached sexual maturity were 760 and 702 mm TL and 7.1 and 6.8 years. The instantaneous rate of natural mortality (M) was estimated to be 0.09. Estimates of the instantaneous rate of fishing mortality (F) were low (0.01–0.05). Harvest rates in 2005 and 2006 were close to estimated sustainable levels. Monitoring of any future increases in catch and effort in continental slope waters in both State- and Commonwealth-managed fisheries is required in order to assess impacts to stock sustainability. Sustainable management would also benefit from improved understanding of possible pan-oceanic recruitment of the species among southern hemisphere populations.

Age and growth of coney (Cephalopholis fulva), from the central coast of Brazil

Coney (Cephalopholis fulva) otoliths were collected from 1997 to 1999 off the central coast of Brazil. Analysis of the edges of otoliths sections suggests that one translucent and one opaque zone are formed once a year. Coney age and size-ranges were 2–25 years and 172–428 mm total length (TL) respectively. The von Bertalanffy growth equation was TLt=316(1−e−0.138(t+5.301)). The maximum age observed in this study is well above that previously reported for coney.

Age and growth of two endemic flatfish (Colistium guntheri and C. nudipinnis) in central New Zealand waters

Brill (Colistium guntheri) and turbot (C. nudipinnis) were aged by counting opaque growth zones in whole and sectioned otoliths. Zones counts from whole otoliths under-estimated age compared with counts from thin otolith sections. Other species of flatfish that have previously been aged from whole otoliths should be re-examined for evidence of age under-estimation, which may be common in species with thick otoliths. Marginal analysis of thin sections supported the hypothesis that one translucent and one opaque zone are formed each year in brill aged 5–10-years old. Marginal analyses for brill greater than 10 years of age, and for turbot, were inconclusive. However, 2+ and 3+ captive-reared turbot deposited the expected number of opaque zones from hatching. Both species grow rapidly for the first three years of life before growth slows appreciably. Turbot grow faster and larger than brill, and females grow faster and larger than males in both species. Growth is minimal in fish older than five years. Maximum observed ages were 21 years for brill and 16 years for turbot.

Formation and annual periodicity of opaque zones in sagittal otoliths of Mugil cephalus (Pisces: Mugilidae)

The present study used a variety of methods to validate the annual periodicity and to determine the timing of formation of opaque and translucent zones in the sagittal otoliths of sea mullet (Mugil cephalus) from south-eastern Australia. Otoliths of captive juvenile fish were sampled regularly to determine timing of formation of the first opaque zone and ‘marginal increment analysis’ was used to infer timing of formation of subsequent zones. Otoliths of tagged (oxytetracycline injected) and recaptured fish also provided direct observations about the timing and periodicity of otolith zone formation. An ‘increment’ was defined as a translucent zone followed by an opaque zone. The first opaque zone was typically completed in February–March, at an age of 22–23 months. Subsequent opaque zones were completed between November and March, but typically in December. Opaque zones were associated with periods of slow otolith growth during winter and spring. Otoliths of fish aged between 0 and 11 years were examined during the study. Otoliths were sampled from two locations on the south-eastern Australian coast, separated by 5.5° latitude. The transition between opaque and translucent zones appeared more distinct in otoliths from the higher latitude, resulting in greater precision of age estimates at this location. Precision of age estimation was also found to vary with time of year. It is recommended that sampling of otoliths for age determination of Mugil cephalus in south-eastern Australia occur from April to October. Sampling at these times would avoid months in which otolith increments are most difficult to interpret and when the stage of completion of increments is most variable.