Spatio-temporal and interspecific variation in otolith trace-elemental fingerprints in a temperate estuarine fish assemblage

We tested whether estuarine fishes have site-specific differences in the concentrations of trace elements in their otoliths that can be used as ‘fingerprints’ to identify them to their estuary of origin. To evaluate the robustness of this approach, we tested whether elemental fingerprints were consistent among individuals of five species that were collected in 1996 from three temperate estuaries in southern California. We also tested whether elemental fingerprints were consistent between spring and autumn 1996 for three species in one of the sites, Carpinteria Marsh. The species evaluated comprised a mid-water-dwelling smelt (Atherinops affinis), two benthic gobies (Clevelandia ios and Ilypnus gilberti), and two flatfish (Paralichthys californicus and Hypsopsetta guttulata). The concentrations of six elements (Mn, Cu, Zn, Sr, Ba, and Pb) were determined in the otoliths using inductively coupled plasma-mass spectrometry (ICP-MS). Within estuaries, the five species exhibited strong variation in elemental concentration, indicating substantial interspecific differences in otolith environmental history. When the five fish species were considered separately, multivariate (MANOVA) and univariate (ANOVA) analyses of variance indicated that the elemental composition of otoliths differed significantly among the estuaries in four of the five species. Based on linear discriminant function analyses (DFA), differences were strong enough that trace element composition could be used to accurately assign fish to their site of origin [mean (range): 93.5% (74–100%)]. However, elemental signatures within Carpinteria Marsh were not consistent between spring and autumn 1996, and this was reflected in a substantial reduction in the accuracy of assigning fish to their true site of origin. When we compared site differences between fish species (site×species interactions), the elemental fingerprints were most similar between closely related species (e.g. the two gobies and the two flatfish) and most dissimilar between distantly related species, both phylogenetically and ecologically. Among the six elements analyzed, Sr and Ba exhibited the most inconsistent pattern among species, with significant differences in 80 and 70% of the pairwise species comparisons, respectively. The remaining four elements showed ≥70% consistency in the pattern of variation among sites for the different species. Thus, while otolith elemental fingerprinting can be a useful tool for inferring estuarine residency, such fingerprints may be temporally variable and species specific.     

Spatial variation in otolith chemistry of Lutjanus apodus at Turneffe Atoll, Belize

Lutjanus apodus (Schoolmaster) were collected from several mangroves and coral reefs at Turneffe Atoll, Belize, in order to investigate whether elemental concentrations from the otolith edge could be used as a means to identify the habitat (mangrove or coral reef) and site (9 mangrove sites and 6 reef sites) from which they were collected. Results of a two factor nested MANOVA (sites nested within habitat) indicated significant differences in elemental concentrations between habitats (i.e., mangrove versus reef) as well as among sites. When separate Linear Discriminant Function Analyses (LDFA) were used to assess whether the spatial variability in otolith chemistry was sufficient to differentiate individuals to their respective habitats or sites, the results indicated that fish were classified (jackknife procedure) with a moderate to poor degree of accuracy (i.e., on average, 67% and 40% of the individuals were correctly classified to the habitat and site from which they were collected, respectively). Using a partial Mantel test we did not find a significant correlation between the differences in otolith elemental concentrations between sites and the distance between sites, while controlling the effect of habitat type (mangrove or reef). This suggests that for mangrove and reef sites at Turneffe Atoll, Belize, the overlap in terms of L. apodus otolith elemental concentrations is too high for investigations of fish movement. Finally, by comparing previously published Haemulon flavolineatum otolith chemistry to that of L. apodus we assessed whether these species showed similar habitat and/or site specific patterns in their otolith chemistry. Although both species were collected from the same sites our results indicated little similarity in their elemental concentrations, thus suggesting that habitat and site elemental signatures are species specific.     

Validation of growth zone deposition rate in otoliths and scales of flathead mullet Mugil cephalus and freshwater mullet Myxus capensis from fish of known age

Flathead mullet Mugil cephalus and freshwater mullet Myxus capensis are important components in South African estuarine fish communities and fisheries, but there is little information on their age and growth or age validation. This study validated the periodicity of growth zone formation in sectioned sagittal otoliths and scales of fish of known age that had been at liberty for 10 years. For both M. cephalus and M. capensis, the number of growth zones counted on otolith sections did not differ significantly from the known age of the fish. There were significantly fewer growth zones on scales than the known age of both M. cephalus and M. capensis. Growth zone deposition rate could therefore be validated as annual for otoliths but not for scales of the two species. It is recommended that future ageing studies focus on otoliths rather than scales.     

长江口刀鲚幼鱼耳石碳、氧同位素特征初报

为了解长江口刀鲚(Coilia nasus)耳石中碳、氧稳定同位素的特征及其可能反映出的生态学意义,作者利用稳定同位素质谱分析技术,首次对长江口刀鲚幼鱼的耳石进行碳、氧稳定同位素的初步研究。结果显示,δ13C和δ18O分别为–12.1±1.8(‰VPDB)和–7.9±1.2(‰VPDB),总体上δ13C波动较大,而δ18O波动较小。基于个体的δ13C和δ18O散点分布可将本研究中的刀鲚归为两个组,可能起源于长江中两个不同孵化场水域的群体,其中δ18O显示出两组刀鲚所经历环境积温上的差异,反映出两者起源水域温度环境的不同;而δ13C的差异说明两组刀鲚在饵料组成上的有所差异。     

Early scale growth characteristics of the New Zealand snapper,chrysophrys auratus (Forster), with reference to selection of a scale‐sampling site

Scales from 17 body areas of juvenile snapper, Chrysophyrs auratus (Forster), were examined to determine scale growth characteristics, with the aim of denning the most suitable body site for routine scale‐sampling. Least‐square regressions of fish length on scale measurement from 0+ fish were calculated for several body areas, and back‐calculations were made to fish length at first annulus (L₁) from a sample of 1+ fish, using both the “uncorrected” and “corrected” formulae.

The overall fish/scale relationship is curvilinear, but high correlation coefficients show that fish/scale regressions from 0+ snapper may be taken as essentially linear. Such regressions give hypothetical fish lengths at scale formation of 8–23 mm. Mid‐body scales form at 10–14 mm, caudal scales earlier, head scales later.

Back‐calculated L₁ values from each area were compared with the mean for the whole body. Using the uncorrected formula there is a general trend for them to be lower than the mean at the head and higher at the tail, while the mid‐body region shows minimum variation from the mean. These variations are caused at least partly by differences in time of scale formation. The corrected formula gives smaller L₁ variations and a mean back‐calculated L₁almost identical to an observed L₁ from independent length frequency data.

The observed variations in scale structure and growth suggest that the “pectoral area”, bounded by the lateral line and the ventral edge of the pectoral fin, is the most suitable site for scale sampling.     

The geopotential topography of the Ocean surface around New Zealand

Present knowledge of the geopotential topography of the ocean surface around New Zealand with respect to the 1,000 decibar isobaric surface is summarised and its relation to the geostrophic circulation of surface waters is discussed.     

Validated aging methodology using otoliths,and growth parameters for hoki (Macruronus novaezelandiae) in New Zealand waters

The age of hoki was determined by counting bands in otolith cross‐sections. The technique was validated using the progression of length modes in length‐frequency distributions (for age classes 0+ to 4+) and the progression of strong and weak year classes in age‐frequency distributions from commercial catches sampled off the west coast of the South Island, New Zealand, from 1988 to 1994. Von Bertalanffy growth parameters for the west coast and Cook Strait spawning populations are significantly different, providing further support for a two‐stock hypothesis. In both areas female hoki have a growth rate significantly faster than males, and also a greater life expectancy.     

X射线断层扫描技术在鲤鱼耳石对环境响应研究中的应用初探

作为生命矿物文石和球文石的载体,鱼耳石(fish otoliths)记载了鱼体生长过程中大量的环境信息。近30年来,其研究取得了很多成果,但利用医学技术的研究尚未见报道。文中尝试应用医学X射线断层扫描技术(CT)对取自河北白洋淀和北京密云水库的野生鲤鱼耳石进行分析研究。结果表明:白洋淀鲤鱼的星耳石和微耳石CT值均大于密云水库鲤鱼耳石相应的CT值,与白洋淀水体中的重金属元素含量明显高于密云水库水体中的重金属含量存在较好的相关性;同一水域星耳石与微耳石的CT值也存在明显差异,分析认为这种差异可能与元素的亲和性及占位方式有关。