Seasonal and Geographic Variation of Southern Blue Whale Subspecies in the Indian Ocean

Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four “acoustic populations” occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.     

Circumpolar diversity and geographic differentiation of mtDNA in the critically endangered Antarctic blue whale (Balaenoptera musculus intermedia)

The Antarctic blue whale (Balaenoptera musculus intermedia) was hunted to near extinction between 1904 and 1972, declining from an estimated initial abundance of more than 250,000 to fewer than 400. Here, we describe mtDNA control region diversity and geographic differentiation in the surviving population of the Antarctic blue whale, using 218 biopsy samples collected under the auspices of the International Whaling Commission (IWC) during research cruises from 1990–2009. Microsatellite genotypes and mtDNA sequences identified 166 individuals among the 218 samples and documented movement of a small number of individuals, including a female that traveled at least 6,650 km or 131° longitude over four years. mtDNA sequences from the 166 individuals were aligned with published sequences from 17 additional individuals, resolving 52 unique haplotypes from a consensus length of 410 bp. From this minimum census, a rarefaction analysis predicted that only 72 haplotypes (95% CL, 64, 86) have survived in the contemporary population of Antarctic blue whales. However, haplotype diversity was relatively high (0.968±0.004), perhaps as a result of the longevity of blue whales and the relatively recent timing of the bottleneck. Despite the potential for circumpolar dispersal, we found significant differentiation in mtDNA diversity (F_ST = 0.032, p<0.005) and microsatellite alleles (F_ST = 0.005, p<0.05) among the six Antarctic Areas historically used by the IWC for management of blue whales.     

Genetic Variation at Exon 2 of the MHC Class II DQB Locus in Blue Whale (Balaenoptera musculus) from the Gulf of California

The genes of the Major Histocompatibility Complex (MHC) play an important role in the vertebrate immune response and are among the most polymorphic genes known in vertebrates. In some marine mammals, MHC genes have been shown to be characterized by low levels of polymorphism compared to terrestrial taxa; this reduction in variation is often explained as a result of lower pathogen pressures in marine habitats. To determine if this same reduction in variation applies to the migratory population of blue whales (Balaenoptera musculus) that occurs in the Gulf of California, we genotyped a 172 bp fragment of exon 2 of the MHC Class II DQB locus for 80 members of this population. Twenty-two putatively functional DQB allotypes were identified, all of which were homologous with DQB sequences from other cetacean species. Up to 5 putative alleles per individual were identified, suggesting that gene duplication has occurred at this locus. Rates of non-synonymous to synonymous substitutions (ω) and maximum likelihood analyses of models of nucleotide variation provided potential evidence of ongoing positive selection at this exon. Phylogenetic analyses of DQB alleles from B. musculus and 16 other species of cetaceans revealed trans-specific conservation of MHC variants, suggesting that selection has acted on this locus over prolonged periods of time. Collectively our findings reveal that immunogenic variation in blue whales is comparable to that in terrestrial mammals, thereby providing no evidence that marine taxa are subject to reduced pathogen-induced selective pressures.     

Decline in energy storage in the Antarctic minke whale (<Emphasis Type=Italic>Balaenoptera bonaerensis</Emphasis>) in the Southern Ocean

The annual trend in energy storage in the Antarctic minke whale was examined using catch data from all 18 survey years in the Japanese Whale Research Program (JARPA). Regression analyses clearly showed that blubber thickness, girth and fat weight have been decreasing for nearly 2 decades. The decrease per year is estimated at approximately 0.02 cm for mid-lateral blubber thickness and 17 kg for fat weight, corresponding to 9% for both measurements over the 18-year period. Furthermore, “date”, “extent of diatom adhesion”, “sex”, “body length”, “fetus length”, “latitude”, “age” and “longitude” were all identified as partially independent predictors of blubber thickness. The direct interpretation of this substantial decline in energy storage in terms of food availability is difficult, since no long-term krill abundance series is available. However, an increase in the abundance of krill feeders other than minke whales and a resulting decrease in the krill population must be considered as a likely explanation.     

Red Shift,Blue Shift: Investigating Doppler Shifts,Blubber Thickness,and Migration as Explanations of Seasonal Variation in the Tonality of Antarctic Blue Whale Song

The song of Antarctic blue whales (Balaenoptera musculus intermedia) comprises repeated, stereotyped, low-frequency calls. Measurements of these calls from recordings spanning many years have revealed a long-term linear decline as well as an intra-annual pattern in tonal frequency. While a number of hypotheses for this long-term decline have been investigated, including changes in population structure, changes in the physical environment, and changes in the behaviour of the whales, there have been relatively few attempts to explain the intra-annual pattern. An additional hypothesis that has not yet been investigated is that differences in the observed frequency from each call are due to the Doppler effect. The assumptions and implications of the Doppler effect on whale song are investigated using 1) vessel-based acoustic recordings of Antarctic blue whales with simultaneous observation of whale movement and 2) long-term acoustic recordings from both the subtropics and Antarctic. Results from vessel-based recordings of Antarctic blue whales indicate that variation in peak-frequency between calls produced by an individual whale was greater than would be expected by the movement of the whale alone. Furthermore, analysis of intra-annual frequency shift at Antarctic recording stations indicates that the Doppler effect is unlikely to fully explain the observations of intra-annual pattern in the frequency of Antarctic blue whale song. However, data do show cyclical changes in frequency in conjunction with season, thus suggesting that there might be a relationship among tonal frequency, body condition, and migration to and from Antarctic feeding grounds.     

Freezing avoidance of the Antarctic icefishes (Channichthyidae) across thermal gradients in the Southern Ocean

Biogeographic studies separate the Antarctic Notothenioid fish fauna into high- and low-latitude species. Past studies indicate that some species found in the high-latitude freezing waters of the High-Antarctic Zone have low-serum hysteresis freezing points, while other species restricted to the low-latitude seasonal pack ice zone have higher serum hysteresis freezing points above the freezing point of seawater (−1.9°C), but the relationship has not been systematically investigated. Freeze avoidance was quantified in 11 species of Antarctic icefishes by determining the hysteresis freezing points of their blood serum, in addition, the freezing point depression from serum osmolytes, the antifreeze activity from serum antifreeze glycoproteins (AFGPs), and the antifreeze activity from serum antifreeze potentiating protein were measured for each species. Serum hysteresis freezing point, a proxy for organismal freeze avoidance, decreased as species were distributed at increasing latitude (linear regression r ² 0.66, slope −0.046°C °latitude⁻¹), which appeared largely independent of phylogenetic influences. Greater freeze avoidance at high latitudes was largely a result of higher levels of antifreeze activity from serum AFGPs relative to those in species inhabiting the low-latitude waters. The icefish fauna could be separated into a circum High-Antarctic Group of eight species that maintained serum hysteresis freezing points below −1.9°C even when sampled from less severe habitats. The remaining three species with low-latitude ranges restricted to the waters of the northern part of the west Antarctic Peninsula and Scotia Arc Islands had serum hysteresis freezing points at or above −1.9°C due to significantly lower combined activity from all of their serum antifreeze proteins than found in the High-Antarctic Zone icefish.     

A new species of Vanbenedenia Malm, 1860 (Copepoda: Lernaeopodidae) from the Southern Indian Ocean

A rare find of the elusive genus Vanbenedenia off the south-eastern coast of South Africa on a Hydrolagus sp. proved to be an as yet undescribed species. Vanbenedenia hydrolagae n. sp. differs from the three other species of the genus by virtue of the relative length of the second maxillae, the absence of multiple setae on the exopod of the first maxilla and the bifid nature of the sclerotised hook and sub-terminal seta of the maxilliped. SEM micrographs provided information on the mouth-cone.     

Seasonal variation of phytoplankton community structure and nitrogen uptake regime in the Indian Sector of the Southern Ocean

This study investigates the dynamics of phytoplankton communities and nitrogen uptake in the Indian sector of the Southern Ocean during spring and summer. The study area is oligotrophic (Chl a stocks <50 mg m⁻²); nevertheless, a large spatial variation of phytoplankton biomass and community structure was observed. During both seasons the phytoplankton community in the seasonal ice zone showed higher biomasses and was mainly composed of large diatom cells. However, in the permanently open ocean zone the community had low biomass and was chiefly composed of nano- and picoflagellates. In the polar front zone, although biomass was higher, the community structure was similar to the open ocean zone. The results suggest that the variation in phytoplankton community structure on a larger scale resonates with gradients in water column stability and nutrient distribution. However, significant changes in biomass and nutrient stocks but little change in community structure were observed. Absolute nitrogen uptake rates were generally low, but their seasonal variations were highly significant. During spring the communities displayed high specific nitrate uptake (mean rate = 0.0048 h⁻¹), and diatoms (in the seasonal ice zone) as well as nano- and picoflagellates (in the permanently open ocean zone and polar front zone) were mainly based on new production (mean ƒ-ratio = 0.69). The transition to summer was accompanied by a significant reduction in nitrate uptake rate (0.0048 h⁻¹ → 0.0011 h⁻¹) and a shift from predominantly new to regenerated production (ƒ-ratio 0.69 → 0.39). Ammonium played a major role in the seasonal dynamics of phytoplankton nutrition. The results emphasize that, despite a large contrast in community structure, the seasonal dynamics of the nitrogen uptake regime and phytoplankton community structure in all three subsystems were similar. Additionally, this study supports our previous conclusion that the seasonal shift in nitrogen uptake regime can occur with, as well as without, marked changes in community structure. Received: 2 December 1997 / Accepted: 20 April 1998     

Patterns of introduction and diversification of Vanilla planifolia (Orchidaceae) in Reunion Island (Indian Ocean)

The cultivated species Vanilla planifolia is a typical example of a crop introduced from its area of origin (America) to new regions where natural pollinators are absent. Although the Vanilla cultivars are exclusively vegetatively propagated, a high degree of phenotypic variation is observed among the cultivars in their introduction areas such as Reunion Island. To test several hypotheses explaining this variation-different introduction events, somatic mutations and sexual reproduction (through manual pollination)-we used AFLP markers to elucidate the patterns of introduction of V. planifolia. Most of the accessions cultivated in the world were derived from a single accession, possibly the Mexican cultivar Mansa. The patterns of diversification of this cultivated species were also studied and compared with other cultivated (V. tahitensis) and wild (V. pompona and V. bahiana) species. Except for one particular phenotype ('Aiguille'), which may come from sexual reproduction, cultivated accessions exhibit very low levels of genetic diversity. They have evolved by the accumulation of point mutations through vegetative multiplication. The genetic diversity revealed could not explain the phenotypic diversity, which may be related to epigenetics or polyploidy. This new understanding of the basis of genetic diversity of vanilla may assist to improve management of genetic resources.     

Phytoplankton species composition and abundance in the Indian sector of the Antarctic Ocean

Summary Water samples collected in the southwestern Indian Ocean between Africa and Antarctica in March 1980 were analyzed quantitatively for phytoplankton. Diatoms dominate the phytoplankton in this region and their numbers generally increase southward with peaks of abundance in both the northern Antarctic Zone and south of the Antarctic Divergence. Average cell numbers (i.e., 6.1×10⁵ diatoms l^-1 in the Antarctic Zone) are comparable to maximum numbers previously reported for the Southern Ocean. Dinoflagellates, flagellates and monads occur in highest concentrations north of the Polar Front. Their numbers are somewhat reduced south of the Antarctic Divergence, and are lowest in the Antarctic Zone. Various diatom assemblages are characteristic of different latitudinal zones. Waters north of and in the vicinity of the Polar Front are rich in the Nitzschia, Pseudonitzschia group of species. In the Antarctic Zone, Nitzschia nana and Dactyliosolen tenuijunctus dominate. Nitzschia species of the Fragilariopsis group are most numerous at stations south of the Antarctic Divergence. Striking differences are noted between the species compositions of quantitative and net-haul samples. A few nanoplanktonic diatoms (e.g. Nitzschia nana and single cells of Chaetoceros spp.) and the weakly silicified Dactyliosolen tenuijunctus, which are dominant in the quantitative samples, are either entirely absent or present only as solitary cells in the net collections.     

Diet of the Antarctic starry skate Amblyraja georgiana (Rajidae, Chondrichthyes) at South Georgia (Southern Ocean)

Stomach contents were identified from 206 Antarctic starry skate (Amblyraja georgiana) that were collected during three groundfish surveys (September 2007, April 2008 and January 2009) at South Georgia, Southern Ocean. The diet of A. georgiana varied with skate size and between years. Preferred prey included fish (particularly for larger individuals) and Antarctic krill, Euphausia superba, as well as amphipods, polychaetes and other benthic fauna. The skate A. georgiana appears to be an opportunistic predator, and the clear presence of Antarctic krill in this demersal predator’s diet may indicate a benthic habit of this euphausiid species, which has hitherto mainly been considered as occupying a purely pelagic niche.     

From the Eye of the Albatrosses: A Bird-Borne Camera Shows an Association between Albatrosses and a Killer Whale in the Southern Ocean

Albatrosses fly many hundreds of kilometers across the open ocean to find and feed upon their prey. Despite the growing number of studies concerning their foraging behaviour, relatively little is known about how albatrosses actually locate their prey. Here, we present our results from the first deployments of a combined animal-borne camera and depth data logger on free-ranging black-browed albatrosses (Thalassarche melanophrys). The still images recorded from these cameras showed that some albatrosses actively followed a killer whale (Orcinus orca), possibly to feed on food scraps left by this diving predator. The camera images together with the depth profiles showed that the birds dived only occasionally, but that they actively dived when other birds or the killer whale were present. This association with diving predators or other birds may partially explain how albatrosses find their prey more efficiently in the apparently ‘featureless’ ocean, with a minimal requirement for energetically costly diving or landing activities.     

Contribution of spermatozoal centrosomes to the microtubule-organizing centre in Antarctic minke whale ( Balaenoptera bonaerensis )

Using an interspecies microinsemination assay with bovine oocytes, it was examined whether centrosomes of Antarctic minke whale spermatozoa function as the microtubule-organizing centre (MTOC). Bull and rat spermatozoa were used as positive and negative controls, respectively. Vitrified-warmed bovine mature oocytes were subjected to immunostaining against alpha-tubulin 4-6 h after intracytoplasmic injection (ICSI) of 5 mM dithiothreitol-treated spermatozoa. Aster formation occurred from whale spermatozoa (33%) and bull spermatozoa (33%), but very little from rat spermatozoa (3%). Activation treatment for the microinseminated oocytes with 7% ethanol + 2 mM 6-dimethylaminopurine resulted in a similar proportion of oocytes forming a whale sperm aster (35% vs 27% in the non-treated group; 4 h after ICSI) but a significantly larger aster (ratio of aster diameter to oocyte diameter, 0.57 vs 0.30 in the non-treated group). These results indicate that the centrosome introduced into bovine oocytes by whale spermatozoa contributes to the MTOC and that assembly of the microtubule network is promoted by oocyte activation.     

Biology and population dynamics of Notothenia rossii rossii from the Kerguelen Islands (Indian sector of Southern Ocean)

Summary Recent cruises on board research vessels and trawlers have followed the adult fishes of the Notothenia rossii rossii Richardson, 1844 population from the Kerguelen Islands. The food of this Nototheniidae being mainly planktonic, the movements of shoals are connected with the high productivity areas. In the Southern Ocean these areas are localized around the Antarctic Convergence. At the Kerguelen Islands the irregular configuration of the shelf and seasonal variations in water masses change the positions of the productive areas. For this reason the adult population can be to the north or south off the archipelago. Spawning only gathers the mature fishes in the southeast of Kerguelen during winter. At that time this species is very vulnerable to fishing efforts. The population dynamics of this Antarctic fish is studied with fishery statistics and biological data. A decline of the average length and catches per unit effort are observed from one year to the next.

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Resumé De récentes missions à bord de navires de recherche et de chalutiers ont permis de suivre la population adulte de Notothenia rossii rossii Richardson, 1844 des îles Kerguelen. Le régime alimentaire de ce Nototheniidae étant principalement de nature planctonique, les mouvements des bancs de poissons sont liés aux zones de haute productivité. Dans l'océan austral ces zones sont localisées au niveau de la convergence antarctique. Aux îles Kerguelen la topographie du plateau continental et les variations saisonnières de l'hydrologie modifient continuellement la position des zones de productivité. Pour cette raison la population adulte peut se trouver soit au nord soit au sud de l'archipel. Seule la ponte réunit les poissons matures dans le sud-est des îles Kerguelen pendant l'hiver. A cette période l'espèce est très vulnérable à un effort de pêche. La dynamique de la population de ce poisson antarctique est étudiée à partir des statistiques de pêche et des données biologiques. Une baisse de la longueur moyenne de la population ainsi qu'une diminution des valeurs de la prise par unité d'effort sont observées pendant la période considérée.

     

Patterns of horizontal distribution of the larvae of southern bluefin (Thunnus maccoyii) and other tuna in the Indian Ocean

The fine- to coarse-scale distribution patterns of tuna larvaein the east Indian Ocean were investigated by a combinationof continuous transect sampling using surface tows and randomsampling using double oblique tows. Thunnus maccoyii was themost abundant species, reaching densities near patch centresof 22 m^–1 in surface tows, which is 25 times greater thanthe highest previous records for tuna larvae. Patches of T.maccoyiilarvae in areas of high abundance appeared to 5.2 for T.maccoyii.There was no change in the index when tow distance was doubledto 1200 m, older larvae. Lloyd's index of patchiness was consistentlyhigh for all tuna species, ranging from 3.0 to 5.2 for T.maccoyyii.There was no change in the index when tow distance was doubledto 1200 m, which suggests that the dominant patch size was somewhatlarger than the larger sampling interval. Sampling larvae atthe same site 4 days apart resulted in estimates of abundancethat differed by an order of magnitude. Abundance estimatedfrom a single station would depend largely on what day the stationwas occupied and where the sample was taken in relation to apatch. ¹Present address: Victoria Institute of Marine Sciences andDepartment of Zoology, University of Melbourne, Parkville, Victoria3052, Australia     

Trace elements in tissues of white-chinned petrels (Procellaria aequinoctialis) from Kerguelen waters,Southern Indian Ocean

The use of seabirds to assess marine contamination by trace elements in areas remote from pollutant emission points has already been done at various latitudes. Nevertheless, little information is available concerning the Southern Indian Ocean. Determining the contaminants levels, there appears necessary not only due to several deleterious effects reported in literature, but also as previous studies have highlighted elevated concentrations of cadmium (Cd) and mercury (Hg) in mollusks, crustaceans and fish. Within this context, the white-chinned petrel appears as a key species due to its lifespan, diet and trophic position. Thirty-three accidentally killed (collision with lights/bycatch in longline vessels) individuals collected in Kerguelen waters were analysed for Cd, copper (Cu), Hg, selenium (Se) and zinc (Zn) in liver, kidney, pectoral muscle, feathers and for mature males, testis. Elevated Hg concentrations (average 58.4 μg g^?1 dw in liver) are likely due to the presence of mesopelagic prey in the diet of Procellaria aequinoctialis. Cd concentrations (average of 65.7 μg g^?1 dw in kidney) can be attributed to a high level of fisheries offal consumption, as well as crustacean and squid ingestion. Correlation of Hg with Se indicates its detoxification by co-precipitation, and correlation of Cd with Zn suggests its displacement by Cd on metallothioneins binding sites. This work also indirectly confirms ecological data (range and diet composition) from the wintering period of the species, which is rather scarce. Seasonal diet change and moulting accounted more for the obtained results than sex of the birds.     

The pteridophytes of Mauritius (Indian Ocean): ecology and distribution

A survey of the pteridophytes of Mauritius is presented, including a summary of their habitats, ecology, and phytogeographical affinities. Of the 186 infrageneric taxa recorded from the island, 8 are adventive or naturalized, and 27 are presumed rare or extinct. Major ecological groupings are presented and species are listed for both indigenous and secondary plant communities.     

Patterns of Vocalization Use by Female Red-winged Blackbirds (Aves: Emberizidae,Icterinae): Variation and Context

Variation within communication systems can be examined at several levels: variation among individual notes, variation in the arrangement of notes, and variation in delivery. Here, variation in the arrangement and delivery of notes used in female red-winged-blackbird vocalizations is described, and this variation is examined for correlations with the context in which the vocalizations were given. Within a vocalization, notes were normally arranged in a series of similar notes. Of the 75 different note arrangements recorded from the population, 12 arrangements accounted for 84 % of vocalizations. Provisional results indicate that the arrangement of notes was influence by the following contexts: 1. The stage of the breeding season; 2. The individual female; 3. The breeding status of the female; 4. Certain female behaviour patterns; 5. Other red-winged-blackbird vocalizations; and 6. The presence or absence of a female's mate in the territory. Variation in delivery was measured by the number of notes within a vocalization; delivery was influenced by the stage of the breeding season, the individual female, and the breeding status of a female. Most note arrangements were used in a wide variety of contexts and did not appear to be functionally distinct.     

Influence of the frontal zones on ichthyoplankton and mesopelagic fish assemblages in the Crozet Basin (Indian sector of the Southern Ocean)

One of the aims of oceanographic campaign MD 68/SUZIL, carried out in austral autumn 1991 in the Indian sector of the Southern Ocean and its adjacent subtropical waters, was to investigate the influence of hydrography on the ichthyoplankton and mesopelagic fish assemblages in the Crozet Basin. It appears that, in contrast to other sectors of the Southern Ocean, the main biogeographical barriers are the Subantarctic Front and the Agulhas Front which appear to be vertical convergence fronts. The importance of the Antarctic Polar Front and the Subtropical Front as barriers to fish seems to be minimized in this area because of its particular hydrological features, such as the lack of a subantarctic zone, the maximum current intensity of the Subantarctic Front between these fronts, and their structures — they are horizontal convergence fronts.