Mackerel Icefish Champsocephalus Gunnari Research Articles

Fatty acid composition and energy allocation in muscle and gonad tissues indicate that the female mackerel icefish Champsocephalus gunnari is an income breeder.

The energy density and fatty acid composition profiles of the muscle and gonad tissues of female mackerel icefish Champsocephalus gunnari from the South Orkney Islands in Antarctica were investigated throughout ovarian development to better understand the reproductive allocation strategy and the role of specific fatty acids in the reproductive process. Energy density in gonads increased from resting to spawning stages as the ovaries developed (19.60-25.10 kJ g-1 dry mass [DM]). In contrast, energy density in muscles remained constant throughout ovarian development (20.13-22.87 kJ g-1 DM), suggesting that the spawning events of the C. gunnari rely on energy income from feeding rather than on the energy stored in body. In addition, the variation in fatty acid composition between muscle and gonad tissues may reflect the role of main FAs as energy source. These results suggest that C. gunnari may utilize an income breeding strategy.

Concentration and Distribution of Cu, Zn, Pb, and Cd in Mackerel Icefish (Champsocephalus gunnari) in South Georgia, Antarctic, During Winter.

Knowledge of the essential and nonessential elements distribution and behavior in Antarctic fish is important for understanding the essentiality and requirements of minerals in the diet of those species, as well as the bioavailability and storage of trace minerals in the tissues of fishes. In this study, the levels of zinc, copper, cadmium, and lead in muscle, intestine, liver, gill, and skin of mackerel icefish Champsocephalus gunnari (Lönnberg, 1905) in South Georgia were determined during winter. The following element concentration ranking was recorded: Zn > Cu > Cd > Pb in the muscle, Zn > Cu > Cd > Pb in the skin, Zn > Cu > Cd > Pb in the intestine, Zn > Cu > Pb > Cd in liver, and Zn > Cu > Cd > Pb in the gill. The concentration of Zn is higher by about two orders of magnitude than that of the other three elements for the tissues. Generally, apart from Cu levels in the liver and Cd levels in the intestine, the correlation of elements in tissues with both size and weight of C. gunnari is not observed. The levels of elements were compared to those reported for C. gunnari in the Kerguelen waters.

Incidental catch of marine organisms registered in the Chilean Antarctic krill fishery, years 2012-2016

Krill (Euphausia superba) catch is currently the most relevant fishery industry in Antarctic waters. This resource is a keystone species in the Antarctic food web, sustaining the contribution to the trophic ecology of many invertebrate and vertebrate species. To catch krill, part of the fleet in this fishery uses large mid-water nets that also retain a diversity of other organisms like plankton, meroplankton, and fish species as bycatch. Therefore, it is necessary to understand and evaluate the magnitude of this incidental catch, as well as the potential interactions between krill fishing gear with seabirds and mammals. To estimate the composition and extent of bycatch for this fishery included 784 samples of 25 kg and an equal number of 1 kg sub-samples obtained from Antarctic krill catches in Subarea 48, between years 2012 and 2016. A total of 15 fish species were identified along with the record of five other taxa and other unidentified specimens. The most relevant fish species bycaught by weight were mackerel icefish Champsocephalus gunnari, South Georgia icefish Pseudochaenichthys georgianus, and painted notie Lepidonotothen larseni. Additionally, 20 interactions with seabirds and nine interactions with Antarctic fur seals (Arctocephalus gazella) were registered. In the five years of operations, only three seabirds died, and only two individuals of A. gazelle caught by the net were killed.

Long-term trends in albatross diets in relation to prey availability and breeding success

Diet analyses can reveal important changes in seabird foraging ecology and, by inference, resource availability and predator–prey dynamics within the wider marine ecosystem. Here, we analysed stomach contents of 1544 grey-headed albatross Thalassarche chrysostoma (GHA) and black-browed albatross T. melanophris (BBA) chicks from Bird Island, South Georgia. We describe dietary shifts (1996–2017), and link those to annual prey availability indices and breeding success. Annual variability in diet was high, and long-term trends in the main components were broadly similar in both albatrosses. Fish consumption (by mass) generally increased over time. Mackerel icefish Champsocephalus gunnari occurrence increased in GHA diets, but was unrelated to local densities derived from fisheries/research cruises. Cephalopod consumption declined until the early 2000s, then plateaued, and the occurrence of the ommastrephid squid Martialia hyadesi declined over time in both albatrosses. In BBAs, Antarctic krill Euphausia superba consumption decreased over time. Conversely, Antarctic krill consumption by GHAs increased until the early 2000s, decreased until the mid-2010s, and increased again in 2017. Antarctic krill consumption was unrelated to local densities based on acoustic surveys, and did not correlate with breeding success. Remotely sensed chlorophyll-a within core foraging areas showed a positive relationship with Antarctic krill in GHA diets, but a negative relationship with M. hyadesi occurrence in both albatross diets. Dietary shifts had consequences for GHA breeding success, which was negatively related to the importance of the cranchiid Galiteuthis glacialis and positively related to M. hyadesi importance. These results highlight the complex mechanisms linking prey availability, diet and breeding success in albatrosses.

Mackerel icefish size and age differences and long‐term change at South Georgia and Shag Rocks

This study analysed the total length (LT)‐frequency distribution of mackerel icefish Champsocephalus gunnari at South Georgia and Shag Rocks from nine bottom trawl surveys at South Georgia and eight at Shag Rocks between 1987 and 2002. The estimated mean LT of age‐classes 1+, 2+, 3+ and 4+ years during January were, respectively, 14·7, 23·5, 29·8 and 35·1 cm at South Georgia. Age‐classes 1+, 2+ and 3+ years were 18·3, 26·2 and 33·8 cm at Shag Rocks. The derived Bertalanffy growth parameters for South Georgia were: L∞ = 51·7 cm, k = 0·27 and t0 = −0·26. The mean LT of each age‐class of C. gunnari at Shag Rocks was significantly larger than at South Georgia, equivalent to c. 5 months growth, although the annual growth in LT was similar. This is further evidence that C. gunnari hatched earlier at Shag Rocks. At South Georgia, the mean LT of age‐classes 1+ and 3+ years were correlated, and significantly decreased between 1987 and 2002, and were smaller following warmer summers. This decrease in the size of C. gunnari may be the result of reduced food availability linked to climate warming.

Mackerel icefish Champsocephalus gunnari in the diet of upper trophic level predators at South Georgia: implications for fisheries management

The mackerel icefish Champsocephalus gunnari Lonnberg is an important component of the ecosystem at South Georgia. Its diet is dominated by Antarctic krill Euphausia superba; in turn, it is also an important prey of a number of upper trophic level predators, as well as being the target of commercial fisheries. Data on the frequency and size structure of mackerel icefish in the diet of Antarctic fur seals Arctocephalus gazella and gentoo penguins Pygoscelis papua from 1991 to 2002 were used to examine trophic interactions involving this species and to evaluate the potential impact of predators on its population. Mackerel icefish occurred in 10 to 20% of scats from Antarctic fur seals and comprised 48% of the diet by mass of gentoo penguins. The contribution of mackerel icefish to the diet of predators was in inverse proportion to the contribution of Antarctic krill. The length- frequency distributions of mackerel icefish indicated a dominant mode at 130 to 180 mm total length (the 1+ age class), with apparent strong cohorts entering the population in 1993, 1996, 1999 and 2001. Extrapolation of diet data to produce a consumption estimate for the South Georgia population of Antarctic fur seals and gentoo penguins suggests that scientific trawl surveys may underestimate the standing stock of mackerel icefish by 1 order of magnitude. Changes in the South Georgia ecosystem over the past 2 decades may have increased the level of consumption of mackerel icefish by predators, providing a potential ecosystem-based explanation for the lack of a recovery to the pre- exploitation population size.

Antarctic fur seals foraging in the Polar Frontal Zone: inter-annual shifts in diet as shown from fecal and fatty acid analyses

We studied the dietary preferences of Antarctic fur seals Arctocephalus gazella from Cap Noir, Iles Kerguelen, foraging in the Antarctic Polar Frontal Zone (PFZ) in February of 1998, 1999 and 2000. Scats were collected and analyzed for remaining prey hard parts in each of the 3 years, and in 1999 and 2000, the fatty acid (FA) composition of fur seal milk samples was also examined for longer- term dietary preferences. Scat analyses revealed that seals foraged primarily on fish and some squid in all 3 years with 25 species of fish being taken during the study. Myctophid fish accounted for an aver- age of 94% by number of all fish consumed with 3 species, Gymnoscopelus nicholsi, G. piabilis and Electrona subaspera, forming the core diet. Inter-annual differences in dietary species composition were apparent, however, with the presence of the mackerel icefish Champsocephalus gunnari in 1998 and the myctophid Protomyctophum tenisoni in 1999 accounting primarily for the differences ob- served between years. While reconstituted prey biomass per scat was similar between years, scats from 1998 represented less energy per gram than those from 1999 and 2000. This study highlights the usefulness of using FA signature analysis to confirm longer-term shifts in dietary intake of fur seals us- ing milk samples. Polyunsaturated fatty acids (PUFAs) were significantly more prevalent in the 1999 milk samples, which were also lower in overall lipid content (43% vs 53%). G. nicholsi, a particularly oily fish, occurred in higher proportions in the diet in 2000, perhaps explaining the higher incidence of monounsaturated fatty acids (MUFAs) in this year and the generally higher lipid levels present in milk samples. The inter-annual variation in the diet of Antarctic fur seals confirmed by these 2 techniques lends support to the hypothesis that previously identified variations in oceanographic conditions surrounding Iles Kerguelen in 1998, 1999 and 2000 affect the availability of fur seal prey resources.

Inter‐annual variation in the gonad cycle of the mackerel icefish

Spawning by Antarctic fish is generally considered to be seasonal and restricted to a brief period during the autumn and winter. Arising from this it has been assumed that the gonadal maturation cycle is also closely associated with the time of year. The gonad maturation cycle of the mackerel icefish Champsocephalus gunnari was investigated using data collected during research surveys and from sampling the commercial fishery. Spawning appears to occur at the same time each year, but the timing of gonadal development is subject to a considerable inter‐annual variation. The implications of this variation are discussed with respect to feeding conditions.

Molecular tools for understanding population structure in Antarctic species

During the last decade, methods for detecting DNA polymorphisms have proliferated at a bewildering pace. Today the investigator must choose among various types of genetic markers as well as between a variety of methods for discovering and screening polymorphisms. Polymorphisms useful for the analysis of population structure are found in both mitochondrial and nuclear genomes. Marker development may proceed along two routes: 1) discovery of species–specific markers, and 2) application of universal methods. Species-specific markers are based on sequence data from the target species or close relatives, whereas universal markers are based on the use of polymerase chain reaction (PCR) primers targeted to regions highly conserved across diverse taxa. Markers commonly employed include mitochondrial DNA polymorphisms, microsatellites, anonymous nuclear loci and known genes (both coding and noncoding regions). Methods for detecting polymorphisms range from technically simple (RFLP analysis) to more sophisticated mutation scanning methods. We review the application of these approaches to several key Antarctic species (the Patagonian toothfish Dissostichus eleginoides, the mackerel icefish Champsocephalus gunnari, and the squid Martialia hyadesi Rochebrune & Mabille, 1889) and present preliminary data on genetic polymorphisms in toothfish and icefish.

Variation in standing stock of the mackerel icefish Champsocephalus gunnari at South Georgia

Summary 1. Bottom trawl surveys on the South Georgia shelf indicate episodic declines in the abundance of the mackerel icefish Champsocephalus gunnari that, since 1990, are not directly attributable to commercial fishing. 2. The greatest effect has been observed in years when krill are known to have been scarce on the South Georgia shelf. 3. It is thought that C. gunnari survivorship is closely related to, but indirectly influenced by, krill availability. 4. Examination of food chain relationships indicates that predation by fur seals is likely to play a major role in the observed changes in C. gunnari abundance. 5. Periodic shifts in food chain relationships, involving krill, C. gunnari and fur seals, are postulated that could explain the episodic declines in the abundance of C. gunnari in the absence of fishing. 6. The study demonstrates how a key predator can have an over‐riding impact on a commercial fish species, highlighting the importance of the ecosystem approach to fisheries management.

Interannual variation in condition of the mackerel icefish

Mackerel icefish Champsocephalus gunnari are widespread on the South Georgia (54° S, 36° W) shelf. Analysis of condition indicated a strong interannual variation. High condition indices, indicative of good feeding conditions, were present when krill were abundant in the region. Years when krill were scarce and condition index was consequently low, were consistent with years when indices from land-based krill predators also indicated that krill were scarce.

Interannual variation in condition of the mackerel icefish

Mackerel icefish Champsocephalus gunnari are widespread on the South Georgia (54° S, 36° W) shelf. Analysis of condition indicated a strong interannual variation. High condition indices, indicative of good feeding conditions, were present when krill were abundant in the region. Years when krill were scarce and condition index was consequently low, were consistent with years when indices from land-based krill predators also indicated that krill were scarce.

A combined acoustic and trawl survey for efficiently estimating fish abundance

When fish are patchily distributed, unstratified trawl surveys give highly variable abundance estimates. If the patches are small and mobile, it is impractical to use pre-stratified or multi-stage adaptive designs to reduce variability. Based on recent trawl surveys for mackerel icefish Champsocephalus gunnari, we have modified the survey design and analysis to reduce estimation variance at minimal cost, using concomitant qualitative acoustic data. We have also developed new confidence interval procedures that should be accurate even for small samples. In computer simulations, the new method substantially outperformed a standard trawl survey.

Variations in the diet composition and feeding intensity of mackerel icefish Champsocephalus gunnari at South Georgia (Antarctic)

The diet composition and feeding intensity of mackerel icefish Champsocephalus gunnari around Shag Rocks and the mainland of South Georgia was analyzed from ca 8700 stomachs collected in January/February 1985, January/February 1991 and January 1992. Main prey items were krill Euphausia superba, the amphipod hyperiid Themisto gaudichaudii, mysids (primarily Antarctomysis maxima), and in 1985 also Thysanoessa species. The proportion of krill and T gaudichaudii in the diet varied considerably among the 3 years, whereas the proportion of mysids in the diet remained fairly constant, Krill appears to be the preferred food. In years of krill shortage, such as in 1991, krill was replaced by T gaudichaudii. The occurrence of krill in the diet in 1991 was among the lowest within a 28 yr period of investigation. Variation in food composition among sampling sites was high. This high variation appears to be primarily associated with differences in prey availability, but much less with prey size selectivity. Feeding intensity varied considerably among seasons. It was highest in 1992. The proportion of empty stomachs was uncommonly high and stomach content weight was uncommonly low in January 1991, a period when energy-rich food was needed for the final maturation of gonads. At the same time, an unusually high proportion of sexually mature fish showed no signs of the gonad development necessary for spawning in that season. It was hypothesized that as in some other non-Antarctic fish species the shortage of suitable food may have forced the fish to sacrifice gonad maturation in order to maintain body size.