AMLR 2003 Weekly Report No. 12
1. The R/V Yuhzmorgeologiya is currently east-southeast of King George Island conducting a trawl survey of demersal finfish, net and acoustic based characterization of invertebrate fauna, and habitat classification within the 500 m isobath of the South Shetland Islands, Antarctica.
2. We have completed 67 stations to date. We are conducting the final station of our
South Shetlands Island Survey. As of 31
March, we have completed 36 stations in the lower
3. As of 31 March, a total of 6168 Kg of finfish (16,263 individuals) of 45 species have been caught and processed. The species with the greatest yield in weight as of 31 March has been Gobionotothen gibberifrons (1633 Kg), followed by Notothenia coriiceps (1365 Kg) and two species of icefish: Champsocephalus gunnari (880 kg) and Chaenocephalus aceratus (493). The largest catch by number has been C. gunnari (3770) followed by Gymnoscopelus nicholsi (3381).
in the lower
5. The reproductive state of the abundant
species showed several remarkable changes.
In C. gunnari
6. Diet studies conducted on 4,054 individuals from all species encountered confirmed observations from the previous two weeks and from the 2001 survey. C. gunneri preyed on more than 95% krill. Larger individuals fed occasionally on myctophids while smaller individuals (< 25 cm) took a small proportion of the euphausiids Thysanoessa macrura and Euphausia frigida and the hyperiid, Themisto gaudichaudii. Feeding intensity in C. aceratus and Cryodraco antarcticus was low. However, it is likely that the feeding intensity of these two species has been underestimated. An unknown proportion of stomach contents appears to be regurgitated. An accurate proportion of regurgitated stomachs is difficult to assess because stomach walls seem to be contracted fairly quickly after regurgitation. Only in a few cases does the stomach remain fully extended. Juveniles (< 30 cm) of the two species prey on mysids (Antarctomysis maxima) and krill while larger individuals rely primarily on fish and only to a small extent on krill. The change in diet is also clear from the load of endoparasitic nematode larvae (mostly Contracaecum sp.), because the number of heavily parasitized fish increases dramatically in fish larger than 28-30 cm. Chionodraco rastrospinosus had empty stomachs when still in prespawning condition and immediately after spawning. Later, when gonads are being resorbed, fish took krill and fish to a lesser extent. Gobionotothen gibberifrons fed on a variety of benthic organisms and occasionally salps and jellyfish. N. coriiceps took krill, fish, and to a lesser extent benthic invertebrates.
7. Studies of evolutionary phylogenetic relationships and variation of buoyancy between species benefited by the capture of two rare Antarctic species, Rakovitzia glacialis and Gerlarhea australis. Also, in the past week we had the opportunity to measure the buoyancy of nearly fifty specimens of the relatively rare species, Harpagifer antarcticus.
8. Blood and tissue samples were collected from
representatives of all notothenoid and non-notothenoiod (Zoarcids and eel
cods) species. Muscle tissue was
collected from all Dissostichus mawsoni (50),
specimens for future population biology studies since these species are also
present in large numbers at
9. All Antarctic fishes that possess blood antifreeze proteins also have them in their intestinal fluids. They are neither digested nor reabsorbed. Their synthetic origin is unknown but recently we have found a synthesis signal in the esophagus-stomach complex. Thus, intestinal tract tissue samples were collected in a manner that will allow isolation of antifreeze mRNA along their length beginning with the pharyngeal-esophagus to the pyloric sphincter. This will allow determination of the exact location where the digestive tract antifreeze glycoproteins are synthesized.
10. Krill abundance and dispersion is being
acoustically mapped at each trawl location and a mean Nautical Area Scattering
Coefficient (NASC) value is calculated for each station. NASC values may also be thought of as the
number of krill (m2) per 1 nm2 of sea surface. Stations
on the north shelf of
The Questar Tangent seabed classification system is
now functional as a new patch from the company has been sent to the ship and successfully
installed. Ground truthing of the acoustic seabed classification
catalogue continues with nightly video/still camera transects and sediment
grabs. To date, 9 sediment grabs, c. 2200 high resolution (2100 × 1700 pixel)
digital still images and > 21 hours of color video have been obtained from
the transects. We have also opportunistically
collected video and digital camera data from within the caldera at
A total of 26 CTD deployments have been made within the 500 m isobath of the
13. As we have progressed southwest along the
South Shetland Islands, the invertebrate bycatch has
continued to shift from the sponge dominated, high diversity, community found
off the northwestern tip of King George Island to an echinoderm (sea star)
dominated community with a relatively low total species count. A few shallow stations off
14. Although the contents of the Little BIT
continue to approximately parallel the composition of the fish trawl bycatch, it differs significantly in many respects. The most significant of these is in the sampling
of the ophiuroids (brittle stars). In some trawls, the bycatch
contains few, if any, of these important members of the benthic community. However, the Little BIT always brings up ophiuroids, often in large numbers. At station 57, about halfway down the
northwestern part of the
15. Various photographic field guides have been developed during AMLR 2003 with the objective of providing essential information for the identification of freshly collected material. None of these guides are complete and all are considered to be works in progress to be augmented and elaborated upon during future field seasons. These guides are briefly summarized.
and Nekton of the
c. Fish Maturity Stage Atlas. During the current fish stock assessment survey concerns were raised over the consistency of maturity stage identification. As a result, we collaborated in developing a photographic record of male and female gonadal development for as many species as possible. To date, at least one stage has been photographed for each of 16 species; most species are represented by at least 2 of 5 male and 2 of 5 female stages. Recognizing seasonal constraints, this work is intended to be more fully developed during future surveys.
Benthic Invertebrates of the
Atlas of Fish Otoliths. This final volume will
provide photographs of otoliths removed from fish
collected during the 2003 fish survey.
Together with line drawings obtained from Gon
and Haemstra's “Fishes of the Southern Ocean” these
are intended to help in predator diet studies at
C. Jones sends