New records of orange roughy Hoplostethus atlanticus juveniles in Chile

Orange roughy Hoplostethus atlanticus juveniles <24 cm fork length (L_F) (10–17 years old) were recorded for the first time in Chile, when 10 specimens were collected on the continental slope and seamount JF2 in Juan Fernandez Archipelago. The L_F, total mass, anatomical and parasitological information are reported. Relevance to current life‐cycle hypotheses is discussed.     

Diets of deepwater oreos (Oreosomatidae) and orange roughy Hoplostethus atlanticus

The diets of black oreo Allocyttus niger, smooth oreo Pseudocyttus maculatus, spiky oreo Neocyttus rhomboidalis and orange roughy Hoplostethus atlanticus were determined from examination of contents of 240, 311, 76 and 415 non‐empty stomachs, from fishes sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand. Hoplostethus atlanticus had an opportunistic predatory strategy with a broad diet dominated by prawns and mesopelagic teleosts, but with substantial components of mysids and cephalopods. Pseudocyttus maculatus was strongly specialized on gelatinous zooplankton (jellyfish and salps). Allocyttus niger consumed mainly salps and hyperiid amphipods, and to a lesser extent fishes, prawns, mysids and copepods. Neocyttus rhomboidalis primarily consumed salps, along with mysids, euphausiids and fishes. Only P. maculatus did not exhibit significant ontogenetic variation in diet. The diets were also influenced by year and bottom depth. Differences in the distributions and diets of the four species probably reduce conflicts in resource use.     

Nine new microsatellite loci for the orange roughy (Hoplostethus atlanticus)

We isolated nine new dinucleotide microsatellites for the deep-sea fish Hoplostethus atlanticus. These loci are generally highly polymorphic, with allele number ranging from 3 to 31 and observed heterozygosity ranging from 0.067 to 0.933. In conjuction with previously published loci, these markers will be useful for fine-scale analysis of population structure in this commercially important and threatened species.     

K-selection characteristics of orange roughy (Hoplostethus atlanticus) stocks in New Zealand waters

The distributions of length frequencies subdivided by age of orange roughy (Hoplostethus atlanticus: Trachichthyidae) had the modal characteristics of K-selected populations. Oceanographic data showed that the depth strata occupied by orange roughy have boundary characteristics which could lead to the development of non-equilibrium dissipative thermodynamic structures and which would account for the K-selection configuration of orange roughy stocks.     

Morphometric analysis of orange roughy (Hoplostethus atlanticus) off the continental slope of southern Australia

Morphometric variation was used to examine the stock structure, in southern Australian waters, of the deepwater marine teleost Hoplostethus atlanticus , orange roughy. Seven samples were collected from non-spawning aggregations in 1989–1990. Three samples were also collected in the winter of 1992, two from the main spawning site off the eastern coast of Tasmania (St Helens), and the third from the other main fishing ground south of Tasmania. The 38 morphometric measurements taken from each of over 1300 fish were size-standardized by an allometric formula and analysed by univariate and multivariate statistics. The results indicate significant variation in the morphology of orange roughy caught from geographically distinct aggregations. They further suggest that the main spawning aggregation may consist of fish from different groups at different times of the spawning period. There appear to be at least seven morphologically distinguishable stocks of orange roughy in southern Australian waters, despite genetic data indicating appreciable levels of gene flow between them.     

The food and feeding relationships of black oreo, Allocyttus niger, smooth oreo, Pseudocyttus maculatus, and eight other fish species from the continental slope of the south-west Chatham Rise, New Zealand

The food and feeding habits of black oreo and smooth oreo sampled at depths of 600–1200 m from the south-west Chatham Rise in 1983 are described, with notes on prey of eight other fish species. All these fish species fed benthopelagically. Black oreo preyed on hyperiid amphipods, salps and natant decapod crustaceans; smooth oreo on salps and amphipods. Dietary composition of both species changed with size of fish. Aspects of feeding relationships between the fish species were examined including dietary similarity and prey-size selection. Findings are compared with results of research on other New Zealand deepwater fish species.     

Spawning dynamics of orange roughy,Hoplostethus atlanticus,in mid-slope waters of New Zealand

Synopsis The social and reproductive biology of the sand tilefish,Malacanthus plumieri (Malacanthidae), was studied at Glover's Reef, Belize, where this species occurs in colonies over sand-rubble flats. Individuals each occupy a home burrow refuge and a surrounding home range. Home range overlap among adjacent fish of the same sex is low, and individuals defend exclusive use of much of their home range against all conspecifics except mates (i.e., territoriality). Areas defended by males overlap the territories of up to 6 females; and male territory area is positively related to the number of female residents. Males maintain dominance over females within their territories by aggression, including intervention into some female disputes. Females spawn pelagically-dispersed eggs as frequently as every day. Each female spawns near her burrow, almost exclusively with the male whose defended area encompasses her territory (harem polygyny). Tilefish colonies therefore consist of a mosaic of female territories over which adjacent male territories are superimposed. Histological evidence and observation of behavioral sex change in one female revealed thatM. plumieri is capable of protogynous sex reversal. Females did not change sex in response to removal of one male. Occurrence of small transitional fish indicates that the onset of sex change is controlled by factors other than size-related social hierarchies within harems or colonies.     

Fecundity and its variability in orange roughy: effects of population density, condition, egg size, and senescence

Fecundity of orange roughy in 1987–1989 adjusted for standard length (S.L.) varied significantly between New South Wales (42 787 eggs female⁻¹) South Australia (35 339 eggs female⁻¹) and east Tasmania (31 085 eggs female⁻¹). Only 10-17% of the variability in fecundity of eastern Tasmania orange roughy was explained by s.l . in any year from 1987–1992. However, liver condition and age of the fish, in combination with s.l ., explained 27% of the variation in fecundity. Fecundity declined in fish over 60 years old. It was also significantly correlated with lipid levels in the ovary, in particular, with triacylglycerol as a proportion of the total lipid fraction. Significant interannual changes in fecundity appeared to be related to the impact of fishing. From 1987–1992, the orange roughy stock off east Tasmania was reduced by 50% by the fishery, and mean fecundity increased 20% over that period. This compensatory increase in individual fecundity, combined with an apparent increase in the proportion of females spawning annually from 54 to 71%, limited the decline in the population's egg production over this period to approximately 15%.     

Hypotheses of spatial stock structure in orange roughy Hoplostethus atlanticus inferred from diet, feeding, condition, and reproductive activity

We evaluate hypotheses for meso-scale spatial structure in an orange roughy (Hoplostethus atlanticus) stock using samples collected during research trawl surveys off the east coast of New Zealand. Distance-based linear models and generalised additive models were used to identify the most significant biological, environmental, and temporal predictors of variability in diet, proportion of stomachs containing prey, standardised weight of prey, fish somatic weight, fish total weight, and reproductive activity. The diet was similar to that observed elsewhere, and varied with ontogeny, depth, and surface water temperature. Smaller sized and female orange roughy in warmer bottom water were most likely to contain food. Fish condition and reproductive activity were highest at distances more than 20 km from the summit of the hills. Trawl survey catches indicated greater orange roughy densities in hill strata, suggesting hill habitat was favoured. However, analyses of feeding, condition, and reproductive activity indicated hill fish were not superior, despite fish densities on hills being reduced by fishing which, in principle, should have reduced intra-specific competition for food and other resources. Hypotheses for this result include: (1) fish in relatively poor condition visit hills to feed and regain condition and then leave, or (2) commercial fishing has disturbed feeding aggregations and/or caused habitat damage, making fished hills less productive. Mature orange roughy were observed on both flat and hill habitat during periods outside of spawning, and if this spatial structure was persistent then a proportion of the total spawning stock biomass would remain unavailable to fisheries targeting hills. Orange roughy stock assessments informed only by data from hills may well be misleading.     

Seasonal and environmental codes in the chemistry of the scales of the hoki Macruronus novaezelandiae

Hoki (Macruronus novaezelandiae: Merluccidae) scales do not have conventional annual (annuli) marks, but when observed by transmitted light showed light and dark bands of the type produced by intra-annual variation in the growth rate of the internal lamellae of the scale. The calcium, fluorine, strontium and zinc content of the hoki scale was measured with a proton microprobe and showed cycles in elemental composition that could be interpreted as seasonal.     

Biomass estimation of orange roughy: a summary and evaluation of techniques for measuring stock size of a deep-water fish species in New Zealand

A number of techniques have been employed to measure biomass of orange roughy in New Zealand. Time series of stratified random trawl surveys in a number of areas over periods of 5–10 years have given relative abundance indices, which have been used in stock reduction analyses to estimate true biomass. This has given confident results for the Chatham Rise stock, and surveys have also shown strong trends in other regions. Acoustic surveys have been carried out on three grounds. They can give relative indices of orange roughy abundance in areas of fiat or medium sloping bottom, and have the potential for estimation of absolute biomass from a single survey. Egg production surveys have been employed on two grounds on the east coast of the North Island, where conditions of tight spawning aggregations and steep bottom topography have limited the success of other methods. Both daily fecundity reduction and annual egg production methods have been used. These have given estimates of true biomass from one-off surveys, although results are imprecise. Both unstandardized and standardized analyses of commercial catch-per-unit-effort data have given relative indices of abundance, which have formed an important part of stock assessment for several fisheries. No single technique used to measure the size of orange roughy stocks has proven ideal or appropriate in all New Zealand situations. All have advantages and disadvantages, depending on the characteristics of the fishing area and fish behaviour. For two areas, a combination of methods have been applied, which has given more confident results than those from a single technique.     

Spatial variation in reproduction, and occurrence of non-reproductive adults, in orange roughy, Hoplostethus atlanticus Collett (Trachichthyidae), from south-eastern Australia

This study was designed to determine whether orange roughy reproduce throughout their distribution in Australian waters, and if so, whether commencement of spawning and length at maturity vary within the region. We found that females from four widely separated sampling areas reproduced in 1988, but that the onset of spawning and length at maturity were not the same in all the areas. In New South Wales, ovulation was finished by mid-June, and 50% of females were mature at 28 cm standard length (S.L.). On the other hand, females from eastern and western Tasmania and South Australia did not spawn until mid-July, and 50% of females from Tasmania were not mature until 32 cm S.L. Females from all areas had oocytes with yolk granules at least 5 months before ovulation. However, in the few months before spawning, some adult females from all areas had not undergone vitellogenesis or were resorbing all yolky oocytes. The best estimates of the proportion of these non-reproductive females were made in March and April, when the single batch of eggs to be spawned was clearly distinguishable, and before spawning aggregations had formed. In 1990 in eastern Tasmania, at the site of a major spawning aggregation, the best estimate of the proportion of non-reproductive fish was 45%. We suggest that scarcity of food, coupled with the cost of joining a spawning aggregation, may result in intermittent spawning in this long-lived species.     

Preliminary estimates of the age and growth of immature smooth oreo Pseudocyttus maculatus Gilchrist 1906 (Oreosomatidae) in the Falkland Islands region of the South Atlantic

Sectioned otoliths were used to estimate the age of 29 specimens of the smooth oreo (Pseudocyttus maculatus Gilchrist 1906) from the Falkland Islands region of the South Atlantic. This represents the first ageing study of this species in this region of the world. All specimens were immature (sub-adults), the largest having a maximum total length of 347 mm. Growth increments were observed in sectioned otoliths and assumed to be annual in periodicity. The maximum age estimate of individuals in this study was 20 years and the form of somatic growth was similar to previous research on this species from Australian waters. The otolith microstructure consisted of an inner, mostly opaque zone with wide increments followed by an outer, mostly translucent zone with narrower increments. It is suggested that these zones correspond to the two growth phases in the life history of this species, namely the pelagic juvenile phase (opaque zone) and the demersal sub-adult/adult phase (translucent zone). Received: 27 May 1997 / Accepted: 31 October 1997     

Historic trawl data and recent information infers temporal change in the occurrence of squid in the diet of orange roughy (Hoplostethus atlanticus Collett) in New Zealand

A review of historical trawl data for orange roughy on Chatham Rise and Challenger Plateau, New Zealand, between the years 1984 and 1996 infers a shift in this species’ diet, with a progressive decline in the percentage occurrence of squid being apparent. On Chatham Rise, this decline in the percentage occurrence of squid appears to be compensated for by increases in the percentage occurrence of fish and crustaceans in orange roughy diet, whereas on Challenger Plateau, decreases in all of squid, fish and crustaceans are apparent. New orange roughy dietary data for 2004 from Chatham Rise is consistent with earlier data series, with further declines in the percentage occurrence of squid apparent. Declines in the occurrence of squid in the diet of orange roughy could be attributed to declines in the abundance of squid as a consequence of fisheries activity.