We studied the buoyancy of 263 specimens of the sympatric sister species Notothenia coriiceps and... more We studied the buoyancy of 263 specimens of the sympatric sister species Notothenia coriiceps and N. rossii captured at King George Island. In these species without a swim bladder, we expressed measurements of buoyancy as percentage buoyancy (%B = weight in water/weight in air × 100), with smaller numbers reflecting more buoyant (i.e. less dense) species. Mean %B of N. coriiceps (4.34%) was significantly greater than that of N. rossii (3.82%), reflecting the lower density and more active swimming, migratory, and feeding behavior of N. rossii compared to N. coriiceps. Skeletal weight as a percentage of body weight was also significantly greater in N. coriiceps (2.46%) than N. rossii (1.65%). Paradoxically, the weight of the vertebral column as a percentage of skeletal weight was significantly greater in N. rossii (28.01%) than in N. coriiceps (24.29%); however, this is intelligible in light of the bone anatomy and histology. Our sample encompassed a wide size and age range, and trend lines for scatter plots of %B against standard length were curvilinear for both species, peaking at 140 to 160 mm, a phenomenon not previously seen in studies of notothenioid buoyancy. We conclude that the ontogenetic increase in %B (reduced buoyancy) in fingerlings/young juveniles and the ontogenetic decrease in %B (increased buoyancy) in older juveniles/immature adults reflects disproportionate growth of skeletal and visceral tissues, respectively, and is not causally related to concurrent pelagic-demersal habitat shifts.
A photographic seabed survey conducted off the Antarctic Peninsula region provided the opportunit... more A photographic seabed survey conducted off the Antarctic Peninsula region provided the opportunity to study spatial patterns, abundance and behaviour of the notothenioid benthic fish fauna. Overall, a total of 12,715 images taken with the Ocean Floor Observation System (OFOS) along 26 transects in three ecoregions (Joinville Island, Bransfield Strait and Drake Passage) were analysed. The fish fauna consisted of at least 34 species belonging to four families of both low-Antarctic and high-Antarctic origin. Nototheniids showed the highest relative abundance and species richness, followed by channichthyids, bathydraconids and artedidraconids. Direct in-situ observations in OFOS seabed images allowed descriptions of fish behaviour, such as aggregation of individuals (Notothenia coriiceps), specific body postures (Cygnodraco mawsoni and Cryodraco antarcticus) and parental care (Chaenodraco wilsoni, Chionodraco rastrospinosus, Pagetopsis macropterus and Trematomus hansoni). Fish density and species richness was primarily correlated with the occurrence of bryozoans, ascidians, and large cup-shaped sponges, providing a three-dimensional habitat suitable for fish settling, foraging, breeding and refuge from predators. Fish diversity was higher (a) off Joinville Island and in Bransfield Strait than in Drake Passage, where almost exclusively low-Antarctic species were recorded, and (b) between 100 and 600 m than at greater depths. Overall, the benthic fish fauna off the northern Antarctic Peninsula is zoogeographically composite and widespread, with well-structured spatial partitioning.
Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important ... more Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important mesopredators in the waters of the Antarctic continental shelf. They compete with each other for prey, yet the seals also prey upon toothfish. Such intraguild predation means that prevalence and respective demographic rates may be negatively correlated, but quantification is lacking. Following a review of their natural histories, we initiate an approach to address this deficiency by analysing scientific fishing catch per unit effort (CPUE; 1975-2011 plus sporadic effort to 2018) in conjunction with an annual index of seal abundance in McMurdo Sound, Ross Sea. We correlated annual variation in scientific CPUE to seal numbers over a 43 year period , complementing an earlier study in the same locality showing CPUE to be negatively correlated with spatial proximity to abundant seals. The observed relationship (more seals with lower CPUE, while controlling for annual trends in each) indicates the importance of toothfish as a dietary item to Weddell seals and highlights the probable importance of intra-and inter-specific competition as well as intraguild predation in seal-toothfish dynamics. Ultimately, it may be necessary to supplement fishery management with targeted ecosystem monitoring to prevent the fishery from having adverse effects on dependent species.
Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water dep... more Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m 2 , which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose family, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dolloidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepidorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni).
Although many notothenioid fishes are primarily carnivorous, some species consistently feed on ma... more Although many notothenioid fishes are primarily carnivorous, some species consistently feed on macroalgae and are therefore omnivorous. Among fish, the degree of herbivory is usually reflected in the morphology of the gastrointestinal system especially intestine length. We examined a large number of juvenile and adult specimens of nine sympatric notothenioid species collected sequentially over eight summer seasons at Potter Cove, South Shetland Islands. We provide relative intestine lengths (RIL), distinct proportions of algae and animal prey in the diets (W%), and numbers of pyloric caeca for all species. The sister species Notothenia coriiceps (NOC) and N. rossii (NOR) evidenced significantly different intestinal growth over ontogeny and ate distinctly different proportions of algae and animal prey. We establish a ranking of the degree of herbivory for the fish species in the local ecosystem, and this was found to be related to their distinct feeding types and strategies. There is a correspondence between intestine length/RILs and degree of herbivory in six of the nine species analysed but no clear association between the number of pyloric caeca and degree of omnivory or carnivory. Compared to other teleosts, our results, and those in the literature, indicate modest divergence in notothenioids that include a phylogenetic decrease in the number of pyloric caeca, from 6 to 7 in most nototheniids to 2-3 in channichthyids, and a 1.8-fold difference in average relative intestine lengths which are most frequently 50-70% of body length and never exceed body length. This is consistent with the unspecialized gastrointestinal morphology that reflects the dietary and ecological plasticity of many notothenioids, exemplified by the high degree of omnivory in species such as NOC and NOR.
The reproductive biology of the Tristan klip-fish, Bovichtus diacanthus, was investigated by macr... more The reproductive biology of the Tristan klip-fish, Bovichtus diacanthus, was investigated by macro-scopic and histological analyses of the gonads. Fish samples were collected in tide pools at Tristan da Cunha in July 2004. Most specimens of both sexes were developing, or sexually mature, with a gonadosomatic index (GSI) of 7.0–9.2 % in females and 0.2–0.6 % in males. Histologi-cally, testes showed a random distribution of spermatogo-nia along the lobules, a condition defined as the unrestricted spermatogonial type. Ripe males exhibited lobules with all spermatogenic stages of development from spermatogonia to spermatozoa. In mature females, the ovarian follicles consisted of three main cohorts of oocytes of different sizes; the smaller one represented by previ-tellogenic oocytes of 15–150 lm and the other two by yolked oocytes measuring, respectively, 300–1000 and 800–1500 lm. The overlap between the stock of advanced yolked oocytes and the early yolked oocytes was low, decreasing p...
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”.
Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important ... more Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important mesopredators in the waters of the Antarctic continental shelf. They compete with each other for prey, yet the seals also prey upon toothfish. Such intraguild predation means that prevalence and respective demographic rates may be negatively correlated, but quantification is lacking. Following a review of their natural histories, we initiate an approach to address this deficiency by analysing scientific fishing catch per unit effort (CPUE; 1975–2011 plus sporadic effort to 2018) in conjunction with an annual index of seal abundance in McMurdo Sound, Ross Sea. We correlated annual variation in scientific CPUE to seal numbers over a 43 year period (1975–2018), complementing an earlier study in the same locality showing CPUE to be negatively correlated with spatial proximity to abundant seals. The observed relationship (more seals with lower CPUE, while controlling for annual trends in each...
SUMMARYWe quantitatively assessed ocular vascular patterns of six Antarctic notothenioid fishes t... more SUMMARYWe quantitatively assessed ocular vascular patterns of six Antarctic notothenioid fishes that vary in their expression of the circulating oxygen-binding protein, hemoglobin (Hb). Digital image analyses revealed marked differences in vessel morphometries among notothenioid species. Hemoglobinless (–Hb) icefishes display mean vessel length densities that are greater (Chaenocephalus aceratus, 5.51±0.32 mm mm–2; Champsocephalus gunnari, 5.15±0.50 mm mm–2) than those observed in red-blooded (+Hb) species(Gymnodraco acuticeps, 5.20±0.46 mm mm–2; Parachaenichthyes charcoti, 4.40±0.30 mm mm–2; Trematomus hansoni, 3.94±0.08 mm mm–2; Notothenia coriiceps, 2.48±0.21 mm mm–2). –Hb fishes also have mean vessel diameters that are ∼1.5 times greater than vessel diameters of +Hb species (–Hb,0.193±0.006 mm; +Hb, 0.125±0.005 mm). Vascular density index(VDI), a stereological index that is affected by both vessel number and length, is greatest in –Hb C. aceratus (3.51±0.20) and lowest in +Hb N....
The endemic Antarctic teleosts of the suborder Notothenioidei are bottom dwellers. They lack swim... more The endemic Antarctic teleosts of the suborder Notothenioidei are bottom dwellers. They lack swim bladders, are heavier than seawater, and feed on or near the bottom. The midwaters surrounding the Antarctic continent are productive and underutilized by fishes. There is an evolutionary trend toward pelagism in some notothenioids. We discovered that the largest Antarctic fish, Dissostichus mawsoni, was neutrally buoyant. Attainment of neutral buoyancy was associated with specializations of the skeletal, integumentary, muscular, and digestive systems. The skeleton had a low mineral content and contained considerable cartilage. Scales were also incompletely mineralized. Static lift was obtained from extensive lipid (mostly triglyceride) deposits. A 2–8 mm subcutaneous lipid layer accounted for 4.7% of the body weight. White muscle also contained much lipid–23% on a dry weight basis, or 4.8% of the body weight. Microscopic examination suggested that the liver was active in lipid metaboli...
The scaleless notothenioid Gymnodraco acuticeps is a bottom dweller beneath the sea ice of McMurd... more The scaleless notothenioid Gymnodraco acuticeps is a bottom dweller beneath the sea ice of McMurdo Sound, Antarctica. Gymnodraco experience unusual environmental conditions, including highly oxygenated subzero water. Skin morphology is evaluated with reference to its potential as a barrier to ice propagation and as a surface for cutaneous respiration. Light and electron microscopy and histochemistry reveal skin structure that is generally similar to that of other teleosts. In the epidermis, epithelial cells are arranged in nine to fifteen layers, and two types of mucous cells are also present. Large mucous cells are most common on external epidermal surfaces, whereas small cells are more frequent on internal epithelial surfaces. Epithelial cell junctions have extensive areas of desmosomes as well as interdigitations of the cell membranes, especially in the basal and midepidermis. The dermis consists of an exceptionally dense stratum compactum. The skin is thicker than that of Bovich...
Eelpouts of the family Zoarcidae comprise a monophyletic group of marine fishes with a worldwide ... more Eelpouts of the family Zoarcidae comprise a monophyletic group of marine fishes with a worldwide distribution. Centers of high zoarcid diversity occur in the North Atlantic and North Pacific, with important radiations into the Arctic, along southern South America, and into the Southern Ocean around Antarctica. Along with snailfishes (Liparidae), zoarcids form an important component of the non-notothenioid fauna in the subzero shelf waters of Antarctica. We document the anatomy and histology of the brains, cranial nerves, olfactory apparatus, cephalic lateral lines, taste buds, and retinas of three Antarctic zoarcid species, living at depths of 310 -939 m, representing three of the nine genera from this region. The primary emphasis is on Ophthalmolycus amberensis, and we provide a detailed drawing of the brain and cranial nerves of this species. Although this brain reflects general perciform neural morphology, it exhibits a reduction of the (optic) tecta and the eminentia granulares and crista cerebellares of the lateral line system. Interspecific differences among the three species are slight. The olfactory rosette consists of three to four lamellae and the nasal sac, contrary to the claim of Fanta et al. ([2001] Antarct Rec, Natl Inst Polar Res, Tokyo 45:27-42), is not in communication with the cephalic lateral line system. Primary olfactory neurons are abundant and converge on branches of the olfactory nerve. Numerous taste buds are located in the lips. All three species lack an ocular choroid rete and have relatively thin retinas with a low cell density and a single bank of rods as the only type of photoreceptor. Neural diversification among Antarctic zoarcids has not involved the evolution of sensory specialists; brain and sensory organ morphologies do not approach the condition seen in primary deep-sea fishes, or even that of some sympatric non-perciform secondary deep-sea fishes, including liparids and muraenolepidids (eel cods). There may be phylogenetic constraints on brain morphology in perciforms such that we do not see extreme specialization in sensory and neural systems for deep habitats. We suggest that the brains and sensory organs of Antarctic zoarcids reflect habitation of 500 -2,000-m depths and likely reflect morphologies seen in zoarcids living on continental slopes elsewhere in the world. This balance among the sensory modalities makes zoarcids relatively generalized among secondary deep-sea fishes and may be one of the reasons this opportunistic and adaptable group has been successful in colonizing a variety of emergent and ephemeral habitats.
We report the analyses of a dataset spanning 39 years of near‐annual fishing for Dissostichus maw... more We report the analyses of a dataset spanning 39 years of near‐annual fishing for Dissostichus mawsoni in McMurdo Sound, Antarctica, 1972–2011. Data on total length, condition and catch per unit effort (CPUE) were derived from the > 5500 fish caught, the large majority of which were measured, tagged and released. Contrary to expectation, the length frequency of the McMurdo Sound catch was dominated by fish in the upper two‐thirds of the overall distribution exhibited in the industrial catch for the Ross Sea shelf. Fish length and condition increased from the early 1970s to the early 1990s and then decreased. Fish length positively correlated with Ross Sea ice extent in early spring, a relationship possibly caused by more ice encouraging larger fish to move farther south over the shelf and into the study area. Fish condition positively correlated with the amount of open water in the Ross Sea during the previous summer (Feb), perhaps reflecting greater availability of prey with the ...
An isolated partial right dentary (BAS D.515.2) collected by the British Antarctic Survey prompte... more An isolated partial right dentary (BAS D.515.2) collected by the British Antarctic Survey prompted a re-evaluation of gadiform remains from the La Meseta Formation (conventionally middle Eocene) of Isla Marambio (Seymour Island), Antarctic Peninsula. Modern gadiforms (hakes and cods) range from the Arctic to Antarctic, inhabiting deep sea benthic, shore, estuarine, and freshwater environments. Based on a fossil record primarily composed of otoliths, they are known to extend back to the Eocene and Oligocene. The new specimen was recovered from the fossil penguin locality D.515. It is characterized by a single row of sharp, ankylosed teeth set upon robust bony pedestals. The surface anterior to the mental foramen exhibits ascending and descending ridges with slightly rugose texture. The ascending ridge is fractured, but partially covers the lateral aspect of the tooth row. BAS D.515.2 is unlike the dentary of macrourid gadiforms, also recovered from the Eocene of Antarctica. BAS D.515...
The Antarctic plunderfishes Artedidraco lönnbergi and A. skottsbergi are small, bottom dwelling s... more The Antarctic plunderfishes Artedidraco lönnbergi and A. skottsbergi are small, bottom dwelling species inhabiting the continental shelf of the High Antarctic Zone. During cruise 97-9 of the US RV Nathaniel Palmer during the summer in the south-western Ross Sea, samples of both species were collected by means of bottom trawling. On the basis of macroscopic and histological analysis, we present the first data on the reproductive characteristics of these two plunderfishes, including gametogenesis, spawning period and absolute fecundity. Histologically, we found immature (stage I and II) and mature (stage V) females in both species, whereas developing females (stage III) were found only in A. skottsbergi. All examined male specimens of A. skottsbergi were in the final stage of spermatogenesis (stage III), whereas male A. lönnbergi were immature (stage I), mature (stage IV) and post-reproductive (stage V) individuals. In both species, spawning takes place in summer during December and January. Absolute fecundity was very low, with less than 100 and 200 oocytes in A. lönnbergi and A. skottsbergi, respectively. These data are compared with those reported in literature for other artedidraconids.
Trematomus eulepidotus and T. loennbergii are two of the most common epibenthic fish in the water... more Trematomus eulepidotus and T. loennbergii are two of the most common epibenthic fish in the waters of the High Antarctic continental shelf. Since the reproductive biology of these species has not been studied in the Ross Sea, we provide a macroscopic and histological analysis of the reproductive effort and gonadal development in both sexes. Most samples were collected during benthic trawl surveys in the south-western Ross Sea in the 1996 and 1997 summer seasons. The aim of the study was to define the reproductive characteristics of these two sympatric species and to examine the hypothesis that different reproductive strategies mitigate interspecific competition. We found that, in common with most Antarctic notothenioids, both species possess a suite of similar reproductive strategies including delayed sexual maturity, prolonged gametogenesis, group-synchronous oocyte maturation, a single spawning event per year and iteroparity. Both species show a comparable reproductive effort in t...
Trematomus newnesi inhabited inshore (<20 m) subzero waters in McMurdo Sound where it fed in t... more Trematomus newnesi inhabited inshore (<20 m) subzero waters in McMurdo Sound where it fed in the water column on Euphausia crystallorophias and fishes. This sample included the largest reported specimens of this species. The length–weight relationship was Weight = 3.17 × 10−6 (Standard Length)3.34, n = 67, r2 = 0.95. The population was phenotypically plastic, with two distinct morphs easily separated by visual inspection – the typical morph and a large mouth/broad headed morph comprising 28% of the sample. The large mouth morph had a wider and blunter head, longer upper jaw, wider gape, more heavily ossified jaws and darker colouration. To document this morphology, four views of the head are illustrated. Inference from morphology and measurements suggested that the large mouth morph was more benthic than the typical semipelagic morph. Museum specimens from Cape Adare confirmed the presence of the large mouth morph 700 km north of McMurdo Sound. This is the first clear example of ...
We analysed histological characteristics of gonads and reproductive effort of the small deep-livi... more We analysed histological characteristics of gonads and reproductive effort of the small deep-living dragonfishes Akarotaxis nudiceps (Waite) and Bathydraco marri Norman collected in the south-western Ross Sea. From a macroscopic point of view, most specimens of B. marri were juveniles in early stages of gonad maturity, except for a maturing female. Conversely, the sample of A. nudiceps was composed of both immature and adult fish in different stages of maturity. A single A. nudiceps female was mature with a gonadosomatic index of 9.8%. Its absolute and relative fecundity was 260 oocytes and 31.5 oocytes g−1 TW, respectively, with a mean size of ripe oocytes of 1.9 mm. Gametogenesis in both species closely resembled that observed in other notothenioids, with females possessing two well-defined groups of oocytes. One group consisted of previtellogenic oocytes as a reserve stock while the other group was maturing oocytes to be ovulated in the current spawning season. A distinctive feat...
Antarctica is a continental island and the waters of its shelf and upper slope are an insular evo... more Antarctica is a continental island and the waters of its shelf and upper slope are an insular evolutionary site. The shelf waters resemble a closed basin in the Southern Ocean, separated from other continents by distance, current patterns and subzero temperatures. The benthic fish fauna of the shelf and upper slope of the Antarctic Region includes 213 species with higher taxonomic diversity confined to 18 families. Ninety-six notothenioids, 67 liparids and 23 zoarcids comprise 45%, 32% and 11% of the fauna, a combined total of 88%. In high latitude (71–78°S) shelf areas notothenioids dominate abundance and biomass at levels of 90–95%. Notothenioids are also morphologically and ecologically diverse. Although they lack a swim bladder, the hallmark of the notothenioid radiation has been repeated diversification into water column habitats. There are pelagic, semipelagic, cryopelagic and epibenthic species. Notothenioids exhibit the disproportionate speciosity and high endemism character...
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Papers by Joseph Eastman