Electrona Antarctica Research Articles

The feeding strategies of the antarctic lanternfish electrona antarctica (pisces: myctophidae) in the amundsen and cosmonaut seas (southern ocean), assessed with a classification tree analysis

The feeding strategies of the antarctic lanternfish electrona antarctica (pisces: myctophidae) in the amundsen and cosmonaut seas (southern ocean), assessed with a classification tree analysis

Assessing the trophic ecology of Southern Ocean Myctophidae: the added value of DNA metabarcoding

Lanternfishes (Myctophidae) are key components of mesopelagic fish communities globally. In the Southern Ocean, incomplete information on myctophid diets limits our understanding of their energetics, interactions, and wider ecosystem impact. Traditional microscopic methods of diet analysis have relatively coarse prey resolution and possible taxonomic and observer biases. Deoxyribonucleic acid (DNA) metabarcode sequencing promises higher taxonomic and temporal resolution, but uncertainty remains in comparing this with microscopy-based analyses. Here, we applied 18S DNA metabarcode sequencing to stomach contents from 20 Electrona antarctica individuals that had previously been examined via microscopic analysis. Across all fish analysed, crustacean and gastropod taxa dominated the prey identified via both methods, with broad agreement between methods on the relative abundance of different prey items. DNA metabarcode sequencing recovered greater taxonomic diversity and resolution, particularly for soft-bodied prey items and small crustaceans. DNA sequencing results also more clearly differentiated diet between individuals collected from different environments. Overall, our findings illustrate how DNA-based methods are complementary to, and consistent with, traditional methods and can provide additional, high-resolution data on a range of trophic interactions.

Spatial Structure of Deep-Sea Pelagian Ichthiocenes in the Northern Weddell Sea (Powell Basin) and Brunsfield Strait in the Summer 2020 and 2022

A review of the composition and structure of deep-sea pelagic ichthyocenes in the Bransfield Strait and the northern part of the Weddell Sea (Powell Basin) in the Atlantic sector of the Southern Ocean is presented. The material was received in the summer of 2020 and 2022 at 26 stations at the layers from 120–0 to 2200–0 m. 901 specimens of juveniles and adult fishes belonging to 19 species from 10 families were collected. Statistical analysis made it possible to identify 4 significantly different regions, in which the dominant ichthyocenes were located in waters of different origin. These ichthyocenes are poor in the number of identified species, but often quite numerous. Relatively shallow-water representatives of the families Bathydraconidae, Channichthyidae, Liparidae, Nototheniidae, endemic to the shelf and slope of Antarctica, dominated in the area of the Antarctic Strait and on the shelf of the Antarctic Peninsula, while in the Bransfield Strait, the abyssal basin of the Powell Basin, as well as in the pelagic zone above deep-sea ridges and trenches, bordering it from the north are meso- and bathypelagic fish from the families Mycthophidae, Bathylagidae, Gonostomatidae, Paralepididae and Scopelarchidae. Near the northern boundary of the Powell Basin, the number of caught mesobatypelagic species and their average abundance were higher than in its central part (11 vs. 7 species and 63.5 vs. 84.1 ind./100 m2). In the central part of the basin, Bathylagus antarcticus dominated, with an average share of 40% in catches and 28.8 ind./100 m2, while in its northern part Electrona antarctica dominated, with an average share of 33% in – 27.4 ind./100 m2.

Phyto-detritus feeding by early-stage larvae of Electrona antarctica (Myctophidae) off Wilkes Land in the Southern Ocean, austral summer 2017

Phyto-detritus feeding by early-stage larvae of Electrona antarctica (Myctophidae) off Wilkes Land in the Southern Ocean, austral summer 2017

Macrozooplankton and micronekton community structure and diel vertical migration in the Heard Island Region, Central Kerguelen Plateau

The Kerguelen Plateau is the largest topographic barrier to the eastward flowing Antarctic Circumpolar Current (ACC) in the Indian Sector of the Southern Ocean. The plateau is separated into a northern and southern plateau by the Fawn Trough. The northern plateau has a shallow bathymetry (<700 m) with two prominent island systems, the Kerguelen Islands on the northern end and Heard and McDonald Islands on the southern end. The interaction of the northern and southern branches of the Polar Front with the northern plateau results in a complex oceanographic environment, with potential for dynamic mixing of sub-Antarctic and Antarctic fauna. Furthermore, the High Nutrient Low Chlorophyll (HNLC) water that flows over the northern plateau is subject to natural iron fertilization from the shallow bathymetry (< 700 m), leading to extensive phytoplankton blooms each summer, particularly to the southeast of the Kerguelen Islands. The Heard Island region on the central plateau has been relatively underexplored. In January 2004, the Heard Island Predator-Prey Investigation and Ecosystem Study (HIPPIES) conducted macrozooplankton (RMT-8 trawl) and micronekton (IYGPT trawl) sampling in foraging areas used by top predators in the vicinity of the island. Macrozooplankton and micronekton were sampled day and night from three depth strata (0–100 m, 100–300 m and 300–600 m). In the area south and east of Heard Island, over bathymetry ≥1000 m depth, the water column had characteristics of the southern branch of the Polar Front (S-PF) and the macrozooplankton and micronekton were dominated by Antarctic Zone fauna (e.g., the euphausiids Euphausia triacantha and Euphausia frigida, and the myctophids Krefftichthys anderssoni, Electrona antarctica, Gymnoscopelus braueri and Gymnoscopelus nicholsi). Shallow slope and shelf stations were located north of the S-PF and the macrozooplankton assemblages were influenced by Polar Frontal Zone species (e.g., Euphausia vallentini), while the shelf micronekton were dominated by the bentho-pelagic channichthyids Champsocephalus gunnari and Channichthys rhinoceratus, together with G. nicholsi. Most macrozooplankton migrated from the deep epipelagic (100–300 m) into the surface epipelagic (<100 m) at night, although some macrozooplankton occurred at high densities in the surface epipelagic during the day (e.g., Rhincalanus gigas, Themisto gaudichaudii). Most micronekton species occurred in the mesopelagic layers (300–600 m) during the day, and migrated into the deep and surface epipelagic at night. Only the small but very abundant K. anderssoni utilized the top 300 m during the day. The vertical distributions of macrozooplankton and micronekton are discussed with respect to the foraging behavior and diets of top predators.

Oxidative stress, metabolic activity and mercury concentrations in Antarctic krill Euphausia superba and myctophid fish of the Southern Ocean

Indicators of oxidative stress and metabolic capacity are key factors in understanding the fitness of wild populations. In the present study, these factors were evaluated in the pelagic Southern Ocean taxa Antarctic krill (Euphausia superba) and myctophid fish (Electrona antarctica, Gymnoscopelus braueri and G. nicholsi) to establish a baseline record for future studies. Mercury (Hg) concentrations were also analysed to evaluate its potential impacts on species biochemical performance. E. superba had higher metabolic activity than most of the myctophid species, which may explain the comparatively lower energy reserves found in the former. The activity of antioxidant enzymes showed, generally, a lower level in E. superba than in the myctophid species. The lack of any relationship between Hg concentrations and organisms' antioxidant and biotransformation defence mechanisms indicate that levels of Hg accumulated in the studied species were not high enough to affect their biochemical processes adversely.

Comparative analysis of the diet of Arctocephalus gazella (Pinnipedia), at two localities of the South Shetland Islands, with emphasis on the fish component

ABSTRACT We studied the diet of non-breeding male Antarctic fur Seals Arctocephalus gazella (Peters, 1875) at two different localities of the South Shetland Islands: Stranger Point, King George Island/Isla 25 de Mayo and Duthoit Point, Nelson Island, by the analysis of 65 faecal samples collected in February 2012. Overall, Antarctic krill Euphausia superba (Dana, 1850) and fish were the main prey taxa followed by penguins and cephalopods. Myctophids were dominant among fish; Gymnoscopelus nicholsi (Gilbert, 1911) was the most important prey species at both sampling sites, followed by Electrona antarctica (Gunther, 1878) at Stranger Point and by the nototheniid Pleuragramma antarctica (Boulenger, 1902) at Duthoit Point. The relative similarity found in the dietary composition of fur seals from both locations suggest they might have been sharing common feeding areas. Our results were compared with those reported in the literature for different localities of the South Shetland Islands and the Scotia Sea region. The absence of formerly harvested demersal notothenioid species in the diet of fur seals may reflect the negative impact that commercial fisheries had on some fish populations and supports the importance of implementing long-term monitoring studies on the feeding habits of A. gazella in the area.

Otolith chemistry of Electrona antarctica suggests a potential population marker distinguishing the southern Kerguelen Plateau from the eastward‐flowing Antarctic Circumpolar Current

AbstractLarge submarine plateaus impede the eastward flow of the deep‐reaching Antarctic Circumpolar Current (ACC), and at the southern Kerguelen Plateau (SKP), the ACC flow is steered north through the Fawn Trough and south through the Princess Elizabeth Trough. During the Kerguelen Axis study, a regional‐scale ecosystem survey, oceanographic sampling showed the ACC water properties west of the SKP to be distinct from those over the SKP. Electrona antarctica, a dominant mesopelagic fish species, is associated with Circumpolar Deep Water transported by the ACC, and modified versions that occur over and downstream from the SKP including along the Antarctic continental slope. Here, otolith chemistry from samples of E. antarctica collected during the survey were used to test a biophysical hypothesis predicting structuring and movement between populations along zonal flow in the ACC. In chemistry deposited during early life in the otolith nuclei, the relationship between MgCa−1 and SrCa−1 showed complete separation between fish collected over the SKP and within the ACC proper, indicating population differentiation. Chemistry from the otolith edges, deposited during the period leading up to capture, showed significantly higher concentrations of MgCa−1 over the SKP, likely related to differences in feeding and reproduction. Fish with nucleus chemistry characteristic of the SKP were also found in samples caught further east, suggesting they were transported along the ACC downstream, and southward toward the Antarctic continent within the Australian–Antarctic Gyre.

Main drivers of mercury levels in Southern Ocean lantern fish Myctophidae

Myctophids are the most abundant fish group in the Southern Ocean pelagic ecosystem and are an important link in the Antarctic marine food web. Due to their major ecological role, evaluating the level of mercury (Hg) contamination in myctophids is important as a step towards understanding the trophic pathway of this contaminant. The concentrations of total Hg were determined in muscle, gill, heart and liver tissue of 9 myctophid species to quantify tissue partitioning variability between species. Organic Hg concentration and proportion in muscle was also determined. Hg concentrations were higher in the liver and heart than in muscle and gills, but the proportion of organic Hg was almost 100% in muscle, indicating that the main uptake route for Hg is through the diet. Most of the species analysed have similar vertical and horizontal distributions, and similar feeding modes and prey. Geographical and temporal variability of Hg concentrations was examined using samples from 3 different sampling cruise (2007/08, 2015/16 and 2016/17) and 2 locations (South Georgia and South Orkneys Islands). Our results appear to indicate a decreasing trend in Hg contamination over the last decade, particularly gill tissue, which is in agreement with a previous study on squid from the same region. There was no significant variability in Hg concentration between the different sampling locations. Hg levels were consistent with values reported previously for myctophids around the world, indicating low global-scale geographic variability. A positive relationship between fish size and Hg concentration was found for most species, with the exception of Electrona antarctica females, which may be explained through Hg elimination by egg laying. We estimate that myctophids collectively comprise a Southern Ocean mercury ‘reserve’ of ≈1.82 metric tonnes.

Determination and precision of otolith growth zone estimates of Electrona antarctica in the Southern Kerguelen Plateau region in the Indian sector of the Southern Ocean

Antarctic lanternfish (Electrona antarctica) is the dominant mesopelagic fish species in the Southern Ocean. It is the most common myctophid occurring south of the Antarctic Polar Front, and an important component of Southern Ocean food webs, both as a zooplankton predator and as a major prey item for higher predators. Despite its importance, there are major gaps in current understanding of the life history of E. antarctica, with previous ageing studies having produced inconclusive results, hampering our understanding of the population structure in this species and its role in marine ecosystems. This is particularly relevant around the Kerguelen Plateau, a highly productive region in the Indian sector of the Southern Ocean, where E. antarctica is a key mid-trophic level species. The present study took advantage of mesopelagic sampling efforts in the southern Kerguelen Plateau region on the 2015–2016 Kerguelen Axis study, and enumerated growth zones in the otoliths of a sample of 100 E. antarctica collected during the voyage. Growth zones were counted using both sectioned and whole otoliths and the precision of estimates was estimated by repeat counts. The estimated number of growth zones in the sectioned otoliths of E. antarctica (standard length 53–97 mm) ranging from 2 to 9. The average coefficient of variation (CV) and average percentage error (APE) for the estimated growth zones were 6.78% and 4.51%, respectively based on counts of sectioned otoliths. The number of growth zones in sectioned otoliths is positively related to weight of otolith and standard length of fish. The results presented here can inform future work on age structure and life history of E antarctica in the Southern Ocean as understanding of the nature of growth rings improves.

Estimates of density of mesopelagic fish in the Southern Ocean derived from bulk acoustic data collected by ships of opportunity

The demand for information on mid-trophic level (MTL) organisms in open-ocean marine ecosystems has led to initiatives to collect acoustic data opportunistically in different regions around the world. Although, bulk acoustic data can provide information on the distribution patterns and dynamics of MTL organisms, it is necessary to convert acoustic-derived indices into biologically relevant quantities for parameterising and validating ecosystem and trophic models. A 7-year time series of acoustic data collected by ships of opportunity (SOOP) in the New Zealand sector of the Southern Ocean, information on species’ distribution derived from trawl samples collected in research voyages, and target strength (TS) estimates obtained using a resonance-scattering model and literature TS–length relationships, were used to obtain the first estimates of density of mesopelagic fish in this region. Estimates of mesopelagic fish density decreased from north to south reflecting changes in species composition and scattering properties across three latitudinal regions (Northern, Central and Southern). Density estimates ranged from 16.4–40.1 in the north to 4.4–13.4 g m−2 in the south. Catches revealed that the Northern region was dominated by Lampanyctodes hectoris and Protomyctophum sp. (Myctophidae) and Maurolicus australis (Sternoptychidae); the Central and Southern regions were dominated by the myctophids Electrona antarctica and Protomyctophum sp. and the Antarctic krill, Euphausia superba. Information on species composition was the main source of uncertainty in the density estimates, highlighting the need for more biological sampling. This study demonstrates that it is possible to integrate acoustic data collected opportunistically with auxiliary information from research voyages and literature to provide estimates of mesopelagic fish biomass in remote areas.

Stomach content analysis of mesopelagic fish from the southern Kerguelen Axis

Mesopelagic fish represent an important trophic link between zooplankton and higher order predators in Southern Ocean food webs. Information on their feeding habits is still sparse, representing a key area of uncertainty in efforts to understand and model Southern Ocean food web dynamics. We used visual assessment of stomach contents to characterise the diets of three myctophids (Electrona antarctica, Gymnoscopelus braueri, Krefftichthys anderssoni) and one bathylagid (Bathylagus antarcticus) over the southern extension of the Kerguelen Plateau (‘southern Kerguelen Axis’), a highly productive area of both biological and economic importance in the Indian sector of the Southern Ocean. Diets of all four species were dominated by euphausiids, amphipods, copepods and fish. Bathylagus antarcticus also preyed upon a high proportion of soft-bodied organisms. There was strong evidence for dietary variability both within and between species, and this variability was driven by latitudinal variation in zooplankton assemblages. Size-based shifts in diet were apparent, with larger individuals of myctophid and bathylagid species consuming larger prey. Linear mixed effects models also demonstrated that the weight of prey consumed increased in relation to predator weight. Dietary information presented here advances our understanding of the mesopelagic components of Southern Ocean food webs, which will improve the development of food web models for the region.

Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 610:149-162 (2019) - DOI: https://doi.org/10.3354/meps12861 Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean Anna Belcher*, Ryan A. Saunders, Geraint A. Tarling British Antarctic Survey, Natural Environment Research Council, Cambridge, CB3 0ET, UK *Corresponding author: annbel@bas.ac.uk ABSTRACT: Mesopelagic fish have recently been highlighted as an important, but poorly studied component of marine ecosystems, particularly regarding their role in the marine pelagic food webs and biogeochemical cycles. Myctophids (Family Myctophidae) are one of the most biomass-dominant groups of mesopelagic fishes, and their large vertical migrations provide means of rapid transfer of carbon to the deep ocean where it can be sequestered for centuries or more. In this study, we develop a simple regression for the respiration rate of myctophid fish using literature-based wet mass and habitat temperature data. We apply this regression to net haul data collected across the Scotia-Weddell sector of the Southern Ocean to estimate respiration rates of the biomass-dominant myctophid species. Electrona carlsbergi, Electrona antarctica, and Gymnoscopelus braueri made a high contribution (up to 85%) to total myctophid respiration. Despite the lower temperatures of the southern Scotia Sea (-1.46 to 0.95°C), total respiration here was as high (reaching 1.1 mg C m-2 d-1) as in the warmer waters of the mid and northern Scotia Sea. The maximum respiratory carbon flux of the vertically migrating community was 0.05 to 0.28 mg C m-2 d-1, equivalent to up to 47% of the gravitational particulate organic carbon flux in some parts of the Scotia-Weddell region. Our study provides the first baseline estimates of respiration rates and carbon flux of myctophids in the Southern Ocean. However, direct measurements of myctophid respiration, and of mesopelagic fish generally, are needed to constrain these estimates further and incorporate these fluxes into carbon budgets. KEY WORDS: Myctophid · Respiration · Lantern fish · Carbon · Active flux · Southern Ocean Full text in pdf format Supplementary materialCorrigendum PreviousNextCite this article as: Belcher A, Saunders RA, Tarling GA (2019) Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean. Mar Ecol Prog Ser 610:149-162. https://doi.org/10.3354/meps12861 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 610. Online publication date: February 01, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Diet overlap among top predators at the South Orkney Islands, Antarctica

In order to understand interspecific trophic relationships between top predators, we analyzed diet information for nine bird and two seal species collected in the austral summer from 1996 to 2000 at South Orkney Islands. Overall, the diet of most of the predators was mainly composed of krill and fish. The percentage of re-occurrence of prey among predators ranged from 25.3 to 36.7, and fish, krill and squid re-occurred most frequently. The re-occurrence of fish among predator pairs ranged from 8.1 to 28.1. The species that re-occurred most frequently were the nototheniid fishes Gobionotothen gibberifrons, Nototheniops nudifrons and Nototheniops nybelini, and the myctophid Electrona antarctica. Prey overlap was greatest between Chinstrap (Pygoscelis antarctica) and Adelie (Pygoscelis adeliae) Penguins. Most predator pairs had high overlap of fish prey species. Predators that could forage on demersal and water column prey had yearly variable diets. This variability may be explained by fluctuations in krill availability. In years when krill is scarce (e.g. 2000), these predators diversify their diet by increasing the consumption of fish, which increases the re-occurrence of these preys in the diets. Our samples suggest the recovery of G. gibberifrons stocks around the South Orkney Islands and draw attention to the potential increase of interspecific food competition between predators under scenarios of decreasing krill availability. This information can be used to identify the ecological consequences of fluctuations in krill availability and aid in the management of krill fisheries.

Seasonal variation in the predatory impact of myctophids on zooplankton in the Scotia Sea (Southern Ocean)

Myctophids are the biomass-dominant mesopelagic fishes in the Southern Ocean, but their trophic role within the pelagic food web south of the Antarctic Polar Front is poorly resolved from a seasonal perspective at the ocean-basin scale. In this study, the predatory impact of the predominant Southern Ocean myctophid community (Electrona antarctica, Electrona carlsbergi, Gymnoscopelus braueri, Gymnoscopelus fraseri, Gymnoscopelus nicholsi, Protomyctophum bolini, Protomyctophum tenisoni, Protomyctophum choriodon, Krefftichthys anderssoni and Nannobrachium achirus) on their zooplankton prey was examined during austral spring, summer and autumn in the Scotia Sea, one of the most productive regions of the Southern Ocean. Seasonal variations in diet and predation rates were apparent for all species. Based on the percentage index of relative importance, myctophids had high overlap in their diets, with all species mostly consuming copepods, small euphausiids and amphipods. Myctophid size was a key determinant of diet in the region, with larger species and intra-specific size classes consuming larger prey. Cluster analyses revealed myctophid feeding guilds that appeared to change seasonally, although there was little evidence of dietary specialisation. Myctophid predation on the daily productivity of most copepod species was relatively low across seasons (<7%), except for Calanus simillimus that was predated upon highly in summer (∼26%). From the macrozooplankton component of the prey field, the myctophid community consumed substantial proportions of the euphausiid Thysanoessa spp. in each season (∼7 to 76% daily productivity), particularly in summer. Relatively high proportions of the daily Antarctic krill (Euphausia superba) productivity (∼8–58%) were also consumed by the larger myctophid species, particularly in summer by Electrona antarctica, suggesting increased competition for krill resources during the higher predator breeding season and possible reductions in food web stability during periods of reduced krill availability at this time. The amphipod Themisto gaudichaudii formed an important part of the larger myctophid species’ diet in all seasons, with between 10 and 38% of its daily productivity being consumed. Myctophid predation on the daily productivity of salps was up to 4%, whilst their impact on ostracods and pteropods was negligible (<0.1% of daily productivity) in all seasons. This study demonstrates that Southern Ocean myctophids link secondary productivity to higher predators through both krill-independent and krill-dependent trophic pathways across seasons, with myctophids comprising a more krill-dependent pathway during austral summer.

Otolith nucleus chemistry distinguishes Electrona antarctica in the westward-flowing Antarctic Slope Current and eastward-flowing Antarctic Circumpolar Current off East Antarctica

Eastward transport in the Southern Ocean is concentrated in jets associated with fronts in the Antarctic Circumpolar Current (ACC), whereas flow along the Antarctic continental slope is strongly westward in the Antarctic Slope Current (ASC). The dominant mesopelagic fish endemic to the Southern Ocean, Electrona antarctica (Günther, 1878), has been linked to Circumpolar Deep Water (CDW) transported by the ACC, and a modified version of CDW associated with the ASC. In conjunction with a regional-scale hydrographic survey south of the Kerguelen Plateau, we sampled fish from the ACC and ASC across Princess Elizabeth Trough off East Antarctica, and examined their otolith chemistry. Material laid down in the nucleus during early life showed heterogeneity, arguing against a single homogeneous population. Instead, it suggested exposure to different environments after hatching, consistent with separate transport pathways along the ACC and ASC. Despite clear differences between stations documented in the survey, material laid down along the edge did not show heterogeneity, suggesting instead exposure to similar environments. Seasonal movement northward by ASC fish into the ACC may explain both these results, and potential physical mechanisms include circulation in the Australian-Antarctic Gyre; northward movement of slope waters along the eastern margin of Princess Elizabeth Trough; and seasonal extension of sea-ice into the ACC. Such meridional movement would expose fish to zonal flow, eastward in the ACC during winter and westward in the ASC during summer, promoting regional retention as well as creating opportunities for mixing with fish transported along the ACC.

Developmental intervals during the larval and juvenile stages of the Antarctic myctophid fish Electrona antarctica in relation to changes in feeding and swimming functions

The Antarctic myctophid fish species Electrona antarctica is believed to play a key role in the Southern Ocean food web, but there have been few studies on its early life history. This study examined the developmental changes in the external morphology and osteology of E. antarctica from the early larva to juvenile stages through the transformation phase and inferred changes in its behaviour and feeding mode. Once the larvae reached 12–13 mm body length (BL), they adopted a primordial suction feeding mode along with the acquisition of early swimming capabilities. Thereafter, both swimming and feeding functions were enhanced through fin development and ossification and acquisition of elements of the jaw and suspensorium. These processes indicate that larvae transition from the planktonic to nektonic phase upon reaching 12–13 mm BL when they enhance their both swimming and feeding abilities with growth. Transformation occurred when larvae reached 19–21 mm BL with changes such as discontinuous increases in eye diameter and upper jaw length and the appearance of photophores and dense body pigmentation. Osteological development of swimming- and feeding-related structures were mostly complete after transformation. Rapid changes in external morphology and osteology during the transformation stage are most likely related to ontogenetic vertical migration into deep waters.

Distributions of larval and juvenile/adult stages of the Antarctic myctophid fish, Electrona antarctica, off Wilkes Land in East Antarctica

Myctophid fish are an important component of the Southern Ocean food web because of their very high biomass. This study investigated the spatial distributions of larval and juvenile/adult stages of the Antarctic myctophid Electrona antarctica. Fish were sampled in January 2011 and 2012 on a transect along 140°E and in January 2013 along 110°E using two different opening/closing net systems. In total, 1075 specimens of E. antarctica were collected: 948 larvae, 127 juveniles/adults, and 2 in the transformation stage. Most larvae were collected at 5–200 m depth, with diel vertical migration (DVM) not apparent. Larvae were mainly distributed in the Modified Circumpolar Deep Water (−1.5 °C–2.0 °C). By contrast, an analysis of the echogram at 38 kHz and discrete depth samples implied that juveniles/adults undertook DVM except in the continental slope area (65.5°S). As the distribution of krill is limited to the cold water mass (<–1.5 °C) along the continental slope, E. antarctica and krill populations are spatially separated off Wilkes Land during summer. According to the previously estimated larval period of 30–47 days, E. antarctica may spawn in late November to December in the marginal ice zone or near the sea ice edge. This study suggests that the environment related to sea ice provides a nursery ground for early stage larvae of E. antarctica.

Seasonal variation in the diet of Antarctic fur seals, Arctocephalus gazella, at 25 de Mayo/King George Island, South Shetland Islands, Antarctica

Assessing the trophic ecology of fur seals is essential for defining their roles as a top predator in Antarctic marine ecosystems. To this end, we examined the diet of Antarctic fur seals, Arctocephalus gazella, in the South Shetlands. While previous studies have considered the diet of this species at this location in summer, to the best of our knowledge, this is the first study to report on the diet of this population in winter, thus adding essential information on the extent of seasonal variation. A total of 224 scats were collected in the winter 2004 (n = 118) and summer 2004/2005 (n = 106) on the coasts of Stranger Point, Isla 25 de Mayo/King George. For the total study period krill (Euphausia superba) was the main prey taxon, followed by fish, cephalopods and penguins. During winter Pleuragramma antarcticum was dominant, while myctophids were almost absent. Conversely, in summer Electrona antarctica and Gymnoscopelus nicholsi, followed by P. antarcticum, dominated the fish diet. It is concluded that fur seals centred their foraging activity on a krill community and fish associated with krill aggregations.

The diet of the Antarctic fur seal Arctocephalus gazella at the South Orkney Islands in ten consecutive years

To improve the knowledge on the Antarctic fur seal foraging behavior, evaluate whether changes in its diet are associated with changes in prey availability, and evaluate whether fisheries had negative impacts on Antarctic fur seal populations, a total of 1359 scats of non-breeding males were collected in ten consecutive sampling periods between 1994 and 2003 at Laurie Island, South Orkney Islands. Antarctic krill was the most numerous prey throughout the sampling period followed in importance by fish prey. Antarctic krill also predominated by reconstructed mass, except during 1994 and 1998 when penguins were the most important prey, and during 1995 when fish dominated. Among fish, demersal-benthic species (mainly Gobionotothen gibberifrons, Chaenocephalus aceratus and Chionodraco rastrospinosus) dominated the diet except in 1997, 1998, 1999 and 2002 when myctophids (mainly Gymnoscopelus nicholsi and Electrona antarctica) were the most important fish prey. In seasons when fish dominated the diet, the diet was primarily comprised of demersal species. Although our results are in overall agreement with previous studies, the contribution to the diet of the main preys changed throughout the sampling period, probably in parallel with changes in prey abundance. According to historical results on fish consumption, the fisheries carried out in the past have had negative impacts on seal populations from the South Orkney Islands.