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In the Southern Ocean, myctophids (family Myctophidae) are speciose, dominate the mesopelagic fish biomass, and are important in the diets of many fishes, squids, seabirds, and marine mammals. Consequently, they play a key role in carbon export and energy transfer from primary consumers to top predators. However, they are delicate and rarely found intact in predator stomachs, which makes them difficult to identify to species. Fortunately, their otoliths (sagittae) are mostly distinctive and therefore useful for species identification. Previous studies describing Southern Ocean myctophid otoliths were often limited by small sample sizes or focused on only a few species. To facilitate myctophid identifications in diet studies, we provide scanning electron microscope images of otoliths with brief descriptions for 37 species of Southern Ocean myctophids. The identities of problematic taxa were confirmed with DNA. Most species were found to have distinctive otoliths, which can be used to identify them to the species level. Large Gymnoscopelus piabilis otoliths comprised two types, which may represent different species. In addition, allometric equations are provided for 32 species to enable back calculation of fish size. [ABSTRACT FROM AUTHOR]

Fisheries ecosystem-based management is an important tool for sustainable harvesting of fisheries worldwide. Knowledge of trophic interactions is crucial since changes in trophic balances can induce severe changes in the structure of marine communities. While advocated for deep-sea fisheries, a lack of studies in the benthopelagic area persist. The Antarctic toothfish, Dissostichus mawsoni, is a top predator inhabiting the Southern Ocean deep-sea and a high-value species in a fishery managed by CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources). Previous studies suggested a geographical variability in its diet, but never studying it in the same year. We analysed stomach contents and stable isotopes of δ15N and δ13C in the muscle of D. mawsoni captured in three fishing areas from the Amundsen and Dumont D'Urville Seas, during the 2016/17 fishing season. Although significant spatial differences were found, five taxa were found in all sites, Antimora rostrata, Macrourus spp., Muraenolepis spp., Moroteuthopsis longimana and Psychroteuthis glacialis. High diversity of prey confirms D. mawsoni as a generalist feeder. Values of δ15N showed similar trophic position across areas, in contrast to the differences found in δ13C values. GLM showed that δ15N and δ13C values varied with otolith length, latitude and the opposite isotope, i.e. δ13C and δ15N respectively. Implications for D. mawsoni fisheries management are discussed considering different predation release scenarios. [ABSTRACT FROM AUTHOR]

The giant Antarctic Octopus Megaleledone setebos is the largest Southern Ocean octopod whose ecology is poorly known. Here, we study ontogenetic shifts of habitat and trophic ecology of M. setebos throughout its life cycle by stable isotopic analysis of δ13C and δ15N on its beaks collected from the diet of Antarctic toothfish in Amundsen and Ross Seas (Antarctica). Values of δ13C (from − 24.3 to − 19.4‰) differed between beaks of individuals from different capture locations, thus reflecting the ability of M. setebos living in different habitats. Despite sequential sampling along beaks showed a small (< 2.3‰), but significant variation in lower beak's δ13C values, a relation with δ15N values suggests that such differences are related to changes in the diet with M. setebos inhabiting the same area its entire life. Values of δ15N differed between beaks of individuals from different capture locations, suggesting that different habitats of M. setebos are associated with different diets. Serial sampling along the beaks (from + 4.2 to + 10.7‰) suggests an ontogenetic change of, at least, one trophic level from juvenile to adult. We also report a capture of two large intact specimens from Dumont D'Urville Sea (Antarctica): a male with 1150 mm of total length and 18,300 g of mass and a female with 1030 mm of total length and 10,061 g of mass. The beaks of these both specimens, confirmed to be of M. setebos through genetic analysis, were also used to confirm the identification of M. setebos collected from Antarctic toothfish stomachs. [ABSTRACT FROM AUTHOR]

The Antarctic toothfish (Dissostichus mawsoni Norman 1937) is the largest notothenioid inhabiting high-latitude Antarctic waters, where it is an important fishery resource and plays a key ecological role at a high trophic level. Despite the considerable amount of data on D. mawsoni biology and distribution developed since the fishery began in 1997, crucial aspects of the life cycle, including spawning and early life history, remain undescribed. During the first winter longline survey to the northern Ross Sea region in 2016, ripe male and female D. mawsoni were collected for the first time, and in vitro fertilisation of eggs was performed. Here, we report on the first characterisation of D. mawsoni egg structure and initial embryonic development. The duration of the egg cleavage period was similar to that of other nototheniid species releasing pelagic eggs. The structural features of fertilised eggs, including chorion thickness and structure, support the hypothesis that eggs of D. mawsoni are pelagic. The data presented here contribute to the description of the potential habitat of the eggs of this species, and provide the first diagnostic information to recognise the eggs of D. mawsoni. [ABSTRACT FROM AUTHOR]

We respond to comments made in the opinion paper by Ainley et al. (Hydrobiologia, 10.1007/s10750-015-2607-4, ) regarding our recent publication on the biology, ecology and life history of Antarctic toothfish ( Dissostichus mawsoni) in the Ross Sea region. We focus in particular on the spatial and temporal extent of data collected from the fishery; results of research to date on changes in abundance and size of Antarctic toothfish at McMurdo Sound; and the subject of neutral buoyancy and inferences about vertical distribution. We conclude by re-iterating the need for well-designed, standardised research programmes to address remaining uncertainties in its life history. [ABSTRACT FROM AUTHOR]

The Antarctic toothfish ( Dissostichus mawsoni, Norman) is a large notothenioid fish that supports valuable fisheries around the Antarctic continent. The Ross Sea fishery, which started in 1997, is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Whilst a large amount of research into the biology of this species has been carried out over the past decade, much of this work has been presented in CCAMLR working group papers and has not been published in the primary literature. In this paper, we bring together and summarise the extensive published and unpublished literature on the biology and ecology of Antarctic toothfish in the Ross Sea region including distribution, stock structure, reproduction, age and growth, and trophic ecology in a single document for the first time. We also review and further develop testable hypotheses surrounding its life cycle and identify gaps in our knowledge including spawning behaviour and early life history which need to be addressed. [ABSTRACT FROM AUTHOR]

Feeding habits of the four most abundant deep-sea demersal trawl-caught macrourids on Chatham Rise, New Zealand, were examined from stomach contents. Two species were predominantly benthic foragers: Coelorinchus bollonsi on infaunal and epifaunal polychaetes, and C. aspercephalus on epifaunal crustaceans; and two species were predominantly mesopelagic foragers; C. oliverianus on calanoid copepods, and Lepidorhynchus denticulatus on mesopelagic crustaceans. The most important predictors of diet variability were identified using distance-based linear models and included areal predictors in all four species, fish size in C. aspercephalus, C. bollonsi and L. denticulatus, and sample year in C. bollonsi. Cluster analyses showed that the diets of C. aspercephalus and C. bollonsi were most distinct. There was a greater interspecific similarity in diet in the spatial and fish size subgroups of C. oliverianus and L. denticulatus, than at the species level. Failing to account for areal, temporal, and ontogenetic variability in diets may bias evaluations of resource competition. [ABSTRACT FROM AUTHOR]

A correction to the article "The Antarctic toothfish (Dissostichus mawsoni): biology, ecology, and life history in the Ross Sea region" that was published in the previous issue is presented.