Dianne M. Tracey

Lead-radium dating of orange roughy (Hoplostethus atlanticus): validation of a centenarian life span

Life-span estimates for orange roughy (Hoplostethus atlanticus) range from ~20 years to well over 100 years. In this study, an improved lead-radium dating technique provided independent age estimates from sagittal otoliths. This tech- nique used the known properties of radioactivity for lead-210 and radium-226 to determine the validity of fish age esti- mates. An improvement to lead-radium dating using mass spectrometry allowed the use of smaller samples than previously possible; therefore, an application was made to otolith cores, the first few years of otolith growth. This ap- proach circumvented the use of whole otoliths and alleviated many of the assumptions that were necessary in previous lead-radium dating applications. Hence, it was possible to critically evaluate lead-radium dating as a tool in fish age vali- dation. The measurement of lead-radium ratios for a series of age groups that consisted of otolith cores, grouped based on growth-zone counts from thin sections, showed a high degree of correlation to the expected lead-radium ingrowth curve. This finding provided support for age estimation procedures using thin otolith sectioning. As independent estimates of age, the results indicated that fish in the oldest age group were at least 93 years old, providing robust support for a centenarian life span.

Background and review of ageing orange roughy (Hoplostethus atlanticus, Trachichthyidae) from New Zealand and elsewhere

Abstract Studies on New Zealand orange roughy (Hoplostethus atlanticus) otoliths, and of orange roughy ageing conducted in New Zealand and elsewhere are described. Ageing studies have concentrated on three aspects: the interpretation of daily growth increments, the interpretation of annual growth increments, and radiometric analyses. All the methods suffer from problems relating to validation. Daily growth zones have not been validated, annual zones have been validated for juvenile fish only, and assumptions necessary for the application of radio‐metric techniques may be flawed. However, the weight of current evidence indicates that orange roughy are a slow‐growing, long‐lived species. A review of otolith morphology and microstructure studies, and a summary of the productivity parameters used in stock assessments of orange roughy, are also presented. Standard protocols used to prepare and interpret otoliths in current investigations are described. This review highlights the complexities of ageing long‐liv...

Fish species composition on seamounts and adjacent slope in New Zealand waters

Abstract Datasets from deep‐water fisheries abundance surveys on the commercially important species—orange roughy (Hoplostethus atlanticus), smooth oreo (Pseudocyttus maculatus), and black oreo (Allocyttus niger) —were used to compare fish fauna between seamounts in 10 different parts of the New Zealand region. For five of these areas, fauna was also compared between the seamounts and nearby areas of the relatively flat slope. Dominant species were listed for each area. Diversity was compared between seamount complexes, and between seamount and slope areas. Differences between the species taken in different seamount areas were investigated using similarity analysis. Total species richness was similar in all seamount regions, but mean species richness was found to be much higher in southern areas. Species richness was consistently higher on the relatively flat slope than on seamounts. Five seamount areas south of 41°S were found to have similar fish fauna, as compared with three seamount areas north of 41°S which were different from the southern areas and from each other.

Mitochondrial genome rearrangements in the Scleractinia / Corallimorpharia complex: implications for coral phylogeny

Corallimorpharia is a small Order of skeleton-less animals that is closely related to the reef-building corals (Scleractinia) and of fundamental interest in the context of understanding the potential impacts of climate change in the future on coral reefs. The relationship between the nominal Orders Corallimorpharia and Scleractinia is controversial—the former is either the closest outgroup to the Scleractinia or alternatively is derived from corals via skeleton loss. This latter scenario, the “naked coral” hypothesis, is strongly supported by analyses based on mitochondrial (mt) protein sequences, whereas the former is equally strongly supported by analyses of mt nucleotide sequences. The “naked coral” hypothesis seeks to link skeleton loss in the putative ancestor of corallimorpharians with a period of elevated oceanic CO2 during the Cretaceous, leading to the idea that these skeleton-less animals may be harbingers for the fate of coral reefs under global climate change. In an attempt to better understand their evolutionary relationships, we examined mt genome organization in a representative range (12 species, representing 3 of the 4 extant families) of corallimorpharians and compared these patterns with other Hexacorallia. The most surprising finding was that mt genome organization in Corallimorphus profundus, a deep-water species that is the most scleractinian-like of all corallimorpharians on the basis of morphology, was much more similar to the common scleractinian pattern than to those of other corallimorpharians. This finding is consistent with the idea that C. profundus represents a key position in the coral <-> corallimorpharian transition.

Fecundity of orange roughy (Hoplostethus atlanticus) in New Zealand waters

Abstract Fecundity estimates were made from late‐vitellogenic ovaries of orange roughy sampled from five spawning grounds in New Zealand waters: Challenger Plateau (1987, 1988, 1989, 1990), Cook Canyon (1988, 1989), Chatham Rise (1990), Ritchie Banks (1990), and Puysegur Bank (1991). Total fecundity of fish from the different areas ranged from 11 000 to 180 000 eggs per fish, with mean relative fecundity ranging between 26 000 and 49 000 eggs per kg body weight. Total fecundity was positively related to length in all samples except from the Ritchie Banks. Comparisons of size‐fecundity relationships were made between years from Challenger Plateau samples, and between Challenger Plateau, Cook Canyon, Chatham Rise, and Puysegur Bank samples. There was no apparent trend in fecundity over time on the Challenger Plateau. There were significant differences revealed by analysis of covariance between areas, with fecundity of orange roughy from the Puysegur Bank being greater than on the Chatham Rise, which was in ...

Mercury levels in some New Zealand sea fishes

Abstract Twenty‐seven deep‐water fish species from a number of locations around New Zealand were sampled between 1976 and 1980 to determine their flesh mercury levels. Twenty‐four species (1300 specimens) had mean mercury levels below 0.5 mg.kg‐1, the maximum permitted by the New Zealand Food and Drug Regulations (1973). The overall range was 0.02–2.40 mg. kg‐1. Mercury levels and fish length were positively correlated in 13 species. Locality effects were also detected; in ling (Genypterus blacodes), mercury levels in individuals from all but 2 of the 5 areas investigated were significantly different. Water temperature was considered to be an important factor because fast‐growing ling in warm waters generally had more mercury in their flesh than those from cooler regions.

Concentration and distribution of mercury in flesh of orange roughy (Hoplostethus atlanticus)

Abstract Orange roughy (Hoplostethus atlanticus) occurs in commercially fishable concentrations along the northern Chatham Rise, east of New Zealand. In preliminary analyses for mercury, the mean level in the flesh coincided exactly with the maximum permissible level of 0.5 mg/kg set by the New Zealand Department of Health for fish sold on the local market. Because of its export potential, more detailed studies followed. Flesh samples of orange roughy were collected at sea and from a number of fish factories around New Zealand. Samples were taken at 2 depths below the skin to determine whether mercury was associated with the waxy subcutaneous layer. No significant difference was detected, but the variability in mercury levels between 2 of the sampled groups was found to be significant and was attributed to fish from different size ranges being analysed. The lower figure (0.35 mg/kg) was obtained from fish with lengths representative of the commercial catch. It is recommended that this value be officially ...

Diel variation in spawning orange roughy (Hoplostethus atlanticus, Trachichthyidae) abundance over a seamount feature on the north‐west Chatham Rise

Abstract The diel variation in abundance of an orange roughy (Hoplostethus atlanticus Collett) spawning aggregation on a deepsea seamount on the Chatham Rise known as “Graveyard” was studied using acoustics. A 4‐day survey was carried out using a Latin cube statistical design. The acoustic data was echo‐integrated and analysis of variance was carried out to estimate the effects of day, time of day, and transect path. The estimated biomass of the spawning aggregation did not display any significant diel variation. We conclude that this result validates the current practice of acoustically surveying orange roughy on this seamount without considering diel effects. The aggregation fluctuated in abundance over the survey period, suggesting that turnover offish was occurring. Differences in roughy biomass with transect orientation indicate the importance of randomised radial transects for these surveys.

The Antarctic Circumpolar Current as a diversification trigger for deep-sea octocorals

BackgroundAntarctica is surrounded by the Antarctic Circumpolar Current (ACC), the largest and strongest current in the world. Despite its potential importance for shaping biogeographical patterns, the distribution and connectivity of deep-sea populations across the ACC remain poorly understood. In this study we conducted the first assessment of phylogeographical patterns in deep-sea octocorals in the South Pacific and Southern Ocean, specifically a group of closely related bottlebrush octocorals (Primnoidae: Tokoprymno and Thourella), as a test case to study the effect of the ACC on the population structure of brooding species. We assessed the degree to which the ACC constitutes a barrier to gene flow between northern and southern populations and whether the onset of diversification of these corals coincides with the origin of the ACC (Oligocene-Miocene boundary).ResultsBased on DNA sequences of two nuclear genes from 80 individuals and a combination of phylogeographic model-testing approaches we found a phylogenetic break corresponding to the spatial occurrence of the ACC. We also found significant genetic structure among our four regional populations. However, we uncovered shared haplotypes among certain population pairs, suggesting long-distance, asymmetrical migration. Our divergence time analyses indicated that the separation of amphi-ACC populations took place during the Middle Miocene around 12.6 million years ago, i.e., after the formation of the ACC.ConclusionWe suggest that the ACC constitutes a semi-permeable barrier to these deep-sea octocorals capable of separating and structuring populations, while allowing short periods of gene flow. The fluctuations in latitudinal positioning of the ACC during the Miocene likely contributed to the diversification of these octocorals. Additionally, we provide evidence that the populations from each of our four sampling regions could actually constitute different species.

Deep-Sea Fish Distribution Varies between Seamounts: Results from a Seamount Complex off New Zealand

Fish species data from a complex of seamounts off New Zealand termed the “Graveyard Seamount Complex’ were analysed to investigate whether fish species composition varied between seamounts. Five seamount features were included in the study, with summit depths ranging from 748–891 m and elevation from 189–352 m. Measures of fish species dominance, rarity, richness, diversity, and similarity were examined. A number of factors were explored to explain variation in species composition, including latitude, water temperature, summit depth, depth at base, elevation, area, slope, and fishing effort. Depth at base and slope relationships were significant with shallow seamounts having high total species richness, and seamounts with a more gradual slope had high mean species richness. Species similarity was modelled and showed that the explanatory variables were driven primarily by summit depth, as well as by the intensity of fishing effort and elevation. The study showed that fish assemblages on seamounts can vary over very small spatial scales, in the order of several km. However, patterns of species similarity and abundance were inconsistent across the seamounts examined, and these results add to a growing literature suggesting that faunal communities on seamounts may be populated from a broad regional species pool, yet show considerable variation on individual seamounts.