The distribution of four species of the genus Macrourus (Gadiformes: Macrouridae) from the Southern Ocean based on samples from the toothfish longline fishery

The known distribution of Macrourus caml is extended to the Ob and Lena Banks area, and southwest of Heard and McDonald Islands. Macrourus holotrachys was recorded from Prince Edward Islands and the Ob and Lena Banks. Macrourus carinatus specimens examined were all from Prince Edward Islands, the type locality. Macrourus whitsoni specimens examined were all from the southeast Atlantic Ocean at about 69˚S, close to the Antarctic continent (off Maud Land), consistent with a previous study which reported the species from 64–77˚S. A revised identification key is provided.

Photographic survey of benthos provides insights into the Antarctic fish fauna from the Marguerite Bay slope and the Amundsen Sea

We reviewed photographic images of fishes from depths of 381–2282 m in Marguerite Bay and 405–2007 m in the Amundsen Sea. Marguerite Bay fishes were 33% notothenioids and 67% non-notothenioids. Channichthyids (47%) and nototheniids (44%) were the most abundant notothenioids. The deep-living channichthyidChionobathyscus dewitti(74%) and the nototheniid genusTrematomus(66%) were the most abundant taxa within these two families. The most abundant non-notothenioids were the macrouridMacrourus whitsoni(72%) and zoarcids (18%). Amundsen Sea fishes were 87% notothenioids and 13% non-notothenioids, the latter exclusivelyMacrourus whitsoni. Bathydraconids (38%) and artedidraconids (30%) were the most abundant notothenioids. We observed thatMacrourus whitsoniwas benthopelagic and benthic and infested by large ectoparasitic copepods. Juvenile (42 cm)Dissostichus mawsoniwas not neutrally buoyant and resided on the substrate at 1277 m.Lepidonotothen squamifronswas seen near and on nests of eggs in early December. APogonophrynesp. from 2127 m was not a member of the deep-living unspottedP. albipinnagroup.Chionobathyscus dewittiinhabited the water column as well as the substrate. The pelagic zoarcidMelanostigma gelatinosumwas documented in the water column a few metres above the substrate. The zoogeographic character of the Marguerite Bay fauna was West Antarctic or low-Antarctic and the Amundsen Sea was East Antarctic or high-Antarctic.

Mercury concentrations of two toothfish and three of its prey species from the Pacific sector of the Antarctic

Muscle tissue samples were collected from Antarctic toothfish (Dissostichus mawsoni Norman) and Patagonian toothfish (D. eleginoides Smitt) in 1998 and from D. mawsoni and three of its prey species - Whitson's grenadier (Macrourus whitsoni (Regan)), ice fish (Chionobathyscus dewitti Andriashev & Neyelov), and blue antimora (Antimora rostrata (Günther)) - in 2006 to determine their mercury. Mercury levels were highly variable both within and between the five species studied but were positively correlated with fish length in four of the species. Once the factors length and year had been accounted for, the mercury levels in D. eleginoides were more than four times greater than in D. mawsoni. The low levels of mercury in D. mawsoni relative to its prey species and the four-fold difference in mercury concentrations between it and D. eleginoides were unexpected. Reasons for these different levels of bioaccumulation were explored including differences in diet, growth and longevity, and location. Differences in bioaccumulation between the two toothfish species could be explained partly through differences in their geographic distribution and differences in trophic position. However, the low levels of mercury in D. mawsoni relative to its prey species can only be explained by a lower rate of mercury assimilation and/or a higher rate of mercury elimination by D. mawsoni.

Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

<em>Abstract</em>.—An exploratory longline fishery for toothfish (<em>Dissostichus </em>spp.) in the Ross Sea, Antarctica has been carried out since 1997. The main bycatch species in this fishery is the grenadier, <em>Macrourus whitsoni. </em>No assessments have been carried out of the impact of the fishery on grenadiers, although they have life history characteristics that make them vulnerable to overexploitation. The aims of this research were two-fold; firstly, to characterize the bycatch fishery and to determine factors affecting bycatch rates; and secondly to examine potential methods of monitoring its abundance. A standardized CPUE analysis was used to determine factors affecting bycatch rates of grenadiers in the fishery. The analysis was based on fine-scale haul-by-haul data from all vessels in the fishery from 1999 to 2005. The major factors influencing grenadier bycatch were vessel, area, and depth. Catch rates of grenadiers were highest along the continental slope of the Ross Sea in depths from 600 to 1000 m, and there was an order of magnitude difference in grenadier catch rates between different vessels. Examination of vessel characteristics showed that catch rates of grenadiers were significantly lower with the Spanish line system than with the autoline system. There are several plausible reasons for this difference, including hook location with respect to the seabed, bait type, and differences in levels of reporting of bycatch between vessels. Various approaches to monitoring and assessing grenadiers in the Ross Sea fishery were explored. We conclude that the year effect from the standardized CPUE analysis is unlikely to be monitoring abundance but instead probably reflect changes in gear characteristics, fisher behavior, and targeting of effort. Trends in the length composition of the catch are confounded with depth, and are also of limited value at present. We consider that the best approach to obtaining abundance estimates for grenadiers in the Ross Sea would be to carry out a random bottom trawl survey of the continental slope.

Helminths of Antarctic fishes: Life cycle biology, specificity and geographical distribution

Bony fishes (Teleostei) play an important role in the completion of life cycles of helminth parasites in the Antarctica. These fishes may be definitive, second intermediate or paratenic hosts of the helminths. The most species-rich taxon is Digenea. Virtually all of these digeneans use teleosts as definitive hosts. Only one species, Otodistomum cestoides, occurs as the adult stage in skates (Chondrichthyes), with teleosts as its second intermediate host. Among 14 cestode species maturing in fishes only one, Parabothriocephalus johnstoni, occurs in a bony fish, Macrourus whitsoni, whereas the others are parasites of Chondrichthyes (cartilaginous fishes). Antarctic Chondrichthyes are not infected with nematode and acanthocephalan species. Specificity to the intermediate and/or paratenic hosts of the majority of Antarctic helminths is wide, whereas that for definitive hosts is often narrower, restricted to one order or sometimes even to one or two host species. Almost all of 73 helminth species maturing in Antarctic fishes are endemics. Only 4 digenean and one nematode species are cosmopolitan or bipolar.