Fish communities, distribution and production Maj Wetjen 1 , Kai Wätjen 1 , Chiara Papetti 1,2 ,

Masimiliano Babbucci², Emilio Riginella², Nils Koschnick¹, Rainer Knust¹

not on board: Tina Sandersfeld¹ Grant No: AWI_PS82_03

1AWI

2Uni-Padova

Objectives

The fish fauna of the Antarctic waters is, with respect to other marine systems of lower latitudes, predominantly populated by demersal organisms while the pelagic zone is only sparsely inhabited. The Antarctic fish fauna is dominated by a single perciform suborder, the Notothenioidei. Over 90 % of the species of this suborder are endemic in the Southern Ocean and mainly represented by 5 families which account for more than 50 % of the species and more than 90 % of the fish biomass on the Antarctic shelf. The Notothenioidei, comprising more than 100 closely related species, include a wide range of ecotypes from sluggish demersal benthos feeders to herring-like pelagic shoaling species and large piscivorous predators.

Despite the low diversity on higher taxonomic levels, the diversity of species within demersal communities on the high Antarctic shelf is extraordinarily high.

On the eastern Weddell Sea shelf, the fish fauna is closely associated to the benthic sponge communities and adapted to the year-round cold water temperature of about -1,8 °C. On the deeper slope (>600 m) in warmer waters deep sea species like eelpouts (e.g. Pachycara brachycephalum) and snailfishes (Liparidae) occur and species diversity is much lower. From the southern Weddell Sea and Filchner area only a few data on fish distribution are available from expeditions in the early 1980s. Based on the results of these expeditions, the differences between the fish fauna of southern Weddell Sea in comparison to the eastern Weddell Sea seems to be minor in terms of species number and species composition (Schwarzbach 1988), but seems to be most evident in respect of fish biomass and production (Hubold 1992). Biomass of demersal fish species on the southern shelf is low and the estimated production is only one-fourths of the production on the eastern shelf.

Pelagic fish biomass, in contrast, is distinctly higher on the southern shelf. The main objectives of this project were to investigate the spatial distribution, species composition, biomass and production of demersal and pelagic fish fauna in the Filchner area. These data will form the basis for further analysis of the relationship between abiotic parameters, such as Water temperature, ice cover and the spatial and temporal development of biodiversity in the Filchner area.

Work at sea

Species composition, biomass and size distribution of the demersal and pelagic fish fauna were determined from both, bottom trawl and Agassiz trawl catches on all study sites. Trawling took place at water depths between 213.5 m and 1,749.5 m. Fish were sorted by species, and the total length (TL) and standard length (SL) measurements were rounded down to the nearest whole centimeter.

Fish weights were recorded to within an accuracy of 1 g. During weighing, a distinction was made between the total weight and the gutted weight of the fish. In addition, individuals were sexed and the gonad weight was taken. In

3.3.4 Antarctic fishes

juveniles, it was not possible to sex every individual. In this case, individuals were only documented as juveniles (J). Trawling distance was computed via the GPS positions of each trawl. The trawling area was calculated over the distance and the width of the trawl. All biomass and abundance data were converted to an area of 1,000 m², which allows a direct comparison of the data from each haul of the single stations. The aim was, despite to get an idea of the biomass, abundance and distribution of Antarctic fish in the Filchner area, to take different samples needed for the single integrated projects within our working group. The main objectives were to catch some alive fish, to get environmental samples of different specimens (e.g. gonads, otoliths, stomachs) and also muscle or fin tissues for population genetics and phylogenetics. During the cruise PS82, an aquarium container system and a backup system container were installed to host alive fish. Sampling of alive fish was mainly done by bottom trawls. With the baited fish trap, which was only used once, four individuals of the genus Trematomus could be collected additionally to the bottom trawl catches. Only alive fish in a good condition were taken out of the catches and were immediately taken into an antibiotic bath, where they were kept for a few hours to maintain their health.

Afterwards, fish were conveyed into the aquarium container where they are kept at 0 °C water temperature.

Preliminary (expected) results

In total 23 bottom trawls and 17 Agassiz trawls could be realized at different study sites during the cruise PS82 (Fig. 3.3.4.1.1). Dead fish from the trawls were directly

Fig. 3.3.4.1.1:

Overview of all bottom trawls and

Agassiz trawls realised during the

cruise PS82

processed after the trawl. All individuals were identified, measured (total length and standard length), weighted (total weight and gutted weight), and sexed.

Over 2,000 samples were taken from different Antarctic fish species, hence building a sufficient basis for further ecological, physiological, molecular, and genetic analyses. These data will provide information about the growth, reproduction, and population genetics of fish in the Filchner area. So far, the biomass (Fig. 3.3.4.1.2) and abundance (Fig. 3.3.4.1.3) of all species from the bottom trawls could be calculated for the different stations. Besides Pleuragramma antarcticum, species from the genus Chionodraco and Trematomus constitute a relatively great portion of the total biomass observed at the single investigated stations. Comparing the single investigated stations, total biomass per haul was obviously lower in the southern trench (PS82/078-1, PS82/084-1, PS82/088-1). Highest mean biomass could be observed in the eastern shelf areas. This is also true for the abundance;

highest number of individuals could be detected at station PS82/306-1 whereas the lowest were found at station PS82/088-1.

Fig. 3.3.4.1.2: Biomass (g/1,000 m²) of the single species or genus caught by bottom trawls during the cruise PS82

3.3.4 Antarctic fishes

Fig. 3.3.4.1.3: Abundance (N/1,000 m²) of the single species or genus caught by bottom trawls during the cruise PS82

Data management

All samples taken during this expedition will be analysed in the laboratories at the AWI in Bremerhaven and the University Padova in Italy. Tissue samples will be analysed for stable isotopes and population genetics, stomach contents will be investigated to get a better insight in the prey taxa, gonads will be inspected for the reproductive status and otoliths will be analysed to determine the age and growth of Antarctic fish in the Filchner area. After data analyses, all results generated from this expedition will be published in the AWI data base PANGAEA Data Publisher for Earth & Environmental Science (http://www.pangaea.de/).

References

Hubold G (1992) Ecology of Weddell Sea fishes. Reports on Polar Research, 103, 157pp.

Schwarzbach W (1988) The demersal fish fauna of the eastern and southern Weddell Sea:

geographical distribution, feeding of fishes and their trophic position in the food web.

Reports on Polar Research, 54, 94pp.

3.3.4.2 The role of the Antarctic silverfish Pleuragramma antarcticum