Aerial surveys for Antarctic minke whales (Balaenoptera bonaerensis) reveal sea ice dependent distribution patterns

This study investigates the distribution of Antarctic minke whales (AMW) in relation to sea ice concentration and variations therein. Information on AMW densities in the sea ice‐covered parts of the Southern Ocean is required to contextualize abundance estimates obtained from circumpolar shipboard surveys in open waters, suggesting a 30% decline in AMW abundance. Conventional line‐transect shipboard surveys for density estimation are impossible in ice‐covered regions, therefore we used icebreaker‐supported helicopter surveys to obtain information on AMW densities along gradients of 0%–100% of ice concentration. We conducted five helicopter surveys in the Southern Ocean, between 2006 and 2013. Distance sampling data, satellite‐derived sea‐ice data, and bathymetric parameters were used in generalized additive models (GAMs) to produce predictions on how the density of AMWs varied over space and time, and with environmental covariates. Ice concentration, distance to the ice edge and distance from the shelf break were found to describe the distribution of AMWs. Highest densities were predicted at the ice edge and through to medium ice concentrations. Medium densities were found up to 500 km into the ice edge in all concentrations of ice. Very low numbers of AMWs were found in the ice‐free waters of the West Antarctic Peninsula (WAP). A consistent relationship between AMW distribution and sea ice concentration weakens the support for the hypothesis that varying numbers of AMWs in ice‐covered waters were responsible for observed changes in estimated abundance. The potential decline in AMW abundance stresses the need for conservation measures and further studies into the AMW population status. Very low numbers of AMWs recorded in the ice‐free waters along the WAP support the hypothesis that this species is strongly dependent on sea ice and that forecasted sea ice changes have the potential of heavily impacting AMWs.     

Current and future patterns of global marine mammal biodiversity

Quantifying the spatial distribution of taxa is an important prerequisite for the preservation of biodiversity, and can provide a baseline against which to measure the impacts of climate change. Here we analyse patterns of marine mammal species richness based on predictions of global distributional ranges for 115 species, including all extant pinnipeds and cetaceans. We used an environmental suitability model specifically designed to address the paucity of distributional data for many marine mammal species. We generated richness patterns by overlaying predicted distributions for all species; these were then validated against sightings data from dedicated long-term surveys in the Eastern Tropical Pacific, the Northeast Atlantic and the Southern Ocean. Model outputs correlated well with empirically observed patterns of biodiversity in all three survey regions. Marine mammal richness was predicted to be highest in temperate waters of both hemispheres with distinct hotspots around New Zealand, Japan, Baja California, the Galapagos Islands, the Southeast Pacific, and the Southern Ocean. We then applied our model to explore potential changes in biodiversity under future perturbations of environmental conditions. Forward projections of biodiversity using an intermediate Intergovernmental Panel for Climate Change (IPCC) temperature scenario predicted that projected ocean warming and changes in sea ice cover until 2050 may have moderate effects on the spatial patterns of marine mammal richness. Increases in cetacean richness were predicted above 40° latitude in both hemispheres, while decreases in both pinniped and cetacean richness were expected at lower latitudes. Our results show how species distribution models can be applied to explore broad patterns of marine biodiversity worldwide for taxa for which limited distributional data are available.     

SPATIOTEMPORAL PREDICTION MODELS OF CETACEAN HABITATS IN THE MID-WESTERN NORTH ATLANTIC OCEAN (FROM CAPE HATTERAS, NORTH CAROLINA, U.S.A. TO NOVA SCOTIA, CANADA)

Habitat prediction models were developed for 13 cetacean species of the mid-western North Atlantic Ocean: beaked whale, fin whale, humpback whale, minke whale, pilot whale, sperm whale, bottlenose dolphin, common dolphin, Risso's dolphin, spotted dolphin, whitesided dolphin, and harbor porpoise. Using the multiple logistic regression, sightings of cetaceans during the 1990–1996 summer (June-September) surveys were modeled with oceanographic (sea surface temperature, monthly probability of front occurrence) and topographic (depth, slope) variables for the same period. Predicted habitat maps for June and August were created for each species using a Geographical Information System. The predicted habitat locations matched with current and historic cetacean sighting locations. The model also predicted habitat shifts for some species associated with oceanographic changes. The correct classification rate of the prediction models with 1997–1998 summer survey data ranged from 44% to 70%, of which most of the misclassifications were caused by false positives ( i.e. , absence of sightings at locations where the models predicted).     

Two new dimorphic soft-coral species (Anthozoa: Octocorallia) from Antarctica

Sphaeralcyon shackletonisp. nov. and Sphaeralcyon scottisp. nov. are described and illustrated from material collected at the Scotia Sea and Weddell Sea on the Polarstern cruises ANT XIX/3 (ANDEEP-I), ANT XIX/5 (LAMPOS), and ANT XXI/2 (BENDEX). With the discovery of Sphaeralcyon shackletoni and S. scotti, three species are now known in the genus Sphaeralcyon, all them reported from the Southern Ocean. The diagnosis of the genus has been slightly modified to accommodate some of the characters of the new species.     

The Contributions of Sea Ice Algae to Antarctic Marine Primary Production

The seasonally ice-covered regions of the Southern Ocean havedistinctive ecological systems due to the growth of microalgaein sea ice. Although sea ice microalgal production is exceededby phytoplankton production on an annual basis in most offshoreregions of the Southern Ocean, blooms of sea ice algae differconsiderably from the phytoplankton in terms of timing and distribution.Thus sea ice algae provide food resources for higher trophiclevel organisms in seasons and regions where water column biologicalproduction is low or negligible. A flux of biogenic materialfrom sea ice to the water column and benthos follows ice melt,and some of the algal species are known to occur in ensuingphytoplankton blooms. A review of algal species in pack iceand offshore plankton showed that dominance is common for threespecies: Phaeocystis antarctica, Fragilariopsis cylindrus andFragilariopsis curta. The degree to which dominance by thesespecies is a product of successional processes in sea ice communitiescould be an important in determining their biogeochemical contributionto the Southern Ocean and their ability to seed blooms in marginalice zones.     

Cetacean sightings near South Georgia islands,South Atlantic Ocean

The information about cetacean occurrence around the Island of South Georgia is scarce. With the main goal of gathering information on a feeding ground of humpback whales (Megaptera novaeangliae) that winter in Brazilian waters, we conducted an expedition to South Georgia. We present here the information regarding cetacean sightings during the expedition. From 28 January to 2 March, 2006 we carried out 13 research cruises, covering 700 nautical miles and 110 h of observation. We registered 10 sightings, in 7 h of ad libitum observations, of the following species: Megaptera novaeangliae, Eubalaena australis, Balaenoptera physalus, Mesoplodon layardii, Orcinus orca and Lagenorhynchus cruciger. We present data on location, depth, group size, structure, and behavior for this geographical area of essential importance for cetacean conservation.     

Habitat use of hourglass dolphins near the South Shetland Islands,Antarctica

The hourglass dolphin Lagenorhynchus cruciger is the only regularly occurring small delphinid found south of the Antarctic Polar Front, yet little is known about its ecology and habitat use. This study uses 8 years (14 cruises) of standardized shipboard surveys during January–March (2003–2011) in southern Drake Passage near the South Shetland Islands to summarize the spatial distribution of hourglass dolphin sightings and quantify habitat use. Sighting data are linked to bathymetry (depth, slope) and distance to the average location of oceanographic features. A generalized linear model is used to examine the relationships between sightings and habitat features. Hourglass dolphins were sighted on 50% of surveys (n = 29); sightings were concentrated in February. Group size tended to be 2–6 individuals; there were only 2 sightings of larger groups, of 15 and 25 individuals. Sightings were distributed entirely within the deep pelagic waters north of the South Shetland Islands in southern Drake Passage and were closely associated with the southern boundary of the Antarctic Circumpolar Current. Information on occurrence and distribution reported in this study may be useful for refining habitat associations for hourglass dolphins at regional scales in the Southern Ocean.     

ABUNDANCE OF CETACEANS IN THE OCEANIC NORTHERN GULF OF MEXICO, 1996–2001

The Gulf of Mexico is a subtropical marginal sea of the western North Atlantic Ocean with a diverse cetacean community. Ship-based, line-transect abundance surveys were conducted in oceanic waters (>200 m deep) of the northern Gulf within U. S. waters (380,432 km²) during spring from 1996 to 1997 and from 1999 to 2001. Data from these five surveys were pooled and minimum abundance estimates were based on 12,162 km of effort and 512 sightings of at least 19 species. The most commonly sighted species (number of groups) were pantropical spotted dolphin, Stenella attenuata (164); sperm whale, Physeter macrocephalus (67); dwarf/pygmy sperm whale, Kogia simalbreviceps (58); Risso's dolphin, Grampus griseus (38); and bottlenose dolphin, Tursiops truncatus (24). The most abundant species (number of individuals; coefficient of variation) were S. attenuata (91,321; 0.16); Clymene dolphin, S. clymene (17,355; 0.65); spinner dolphin, S. longirostris (11,971; 0.71); and striped dolphin, S. coeruleoalba (6,505; 0.43). The only large whales sighted were P. macrocephalus (1,349; 0.23) and Bryde's whale, Balaenopteraedeni (40; 0.61). Abundances for other species or genera ranged from 95 to 2,388 animals. Cetaceans were sighted throughout the oceanic northern Gulf and, whereas many species were widely distributed, some had more regional distributions.     

The influence of historical climate changes on Southern Ocean marine predator populations: a comparative analysis

The Southern Ocean ecosystem is undergoing rapid physical and biological changes that are likely to have profound implications for higher‐order predators. Here, we compare the long‐term, historical responses of Southern Ocean predators to climate change. We examine palaeoecological evidence for changes in the abundance and distribution of seabirds and marine mammals, and place these into context with palaeoclimate records in order to identify key environmental drivers associated with population changes. Our synthesis revealed two key factors underlying Southern Ocean predator population changes; (i) the availability of ice‐free ground for breeding and (ii) access to productive foraging grounds. The processes of glaciation and sea ice fluctuation were key; the distributions and abundances of elephant seals, snow petrels, gentoo, chinstrap and Adélie penguins all responded strongly to the emergence of new breeding habitat coincident with deglaciation and reductions in sea ice. Access to productive foraging grounds was another limiting factor, with snow petrels, king and emperor penguins all affected by reduced prey availability in the past. Several species were isolated in glacial refugia and there is evidence that refuge populations were supported by polynyas. While the underlying drivers of population change were similar across most Southern Ocean predators, the individual responses of species to environmental change varied because of species specific factors such as dispersal ability and environmental sensitivity. Such interspecific differences are likely to affect the future climate change responses of Southern Ocean marine predators and should be considered in conservation plans. Comparative palaeoecological studies are a valuable source of long‐term data on species’ responses to environmental change that can provide important insights into future climate change responses. This synthesis highlights the importance of protecting productive foraging grounds proximate to breeding locations, as well as the potential role of polynyas as future Southern Ocean refugia.     

Integrated abundance and biomass of sympagic meiofauna in Arctic and Antarctic pack ice

The abundance and biomass of sympagic meiofauna were studied during three cruises to the Antarctic and one summer expedition to the central Arctic Ocean. Ice samples were collected by ice coring and algal pigment concentrations and meiofauna abundances were determined for entire cores. Median meiofauna abundances for the expeditions ranged from 4.4 to 139.5 × 10³ organisms m⁻² in Antarctic sea ice and accounted for 40.6 × 10³ organisms m⁻² in Arctic multi-year sea ice. While most taxa (ciliates, foraminifers, turbellarians, crustaceans) were common in both Arctic and Antarctic sea ice, nematodes and rotifers occurred only in the Arctic. Based on the calculated biomass, the potential meiofauna ingestion rates were determined by applying an allometric model. For both hemispheres, daily and yearly potential ingestion rates were below the production values of the ice algal communities, pointing towards non-limited feeding conditions for ice meiofauna year-round. Accepted: 29 March 1999     

Occurrence of dwarf minke whales (Balaenoptera acutorostrata subsp.) around the Antarctic Peninsula

The occurrence of dwarf minke whales (Balaenoptera acutorostrata subsp.) around the Antarctic Peninsula was examined based on 406 sightings of minke whales recorded during the Chilean Antarctic Scientific Expeditions and other opportunistic cetacean surveys. Identification of the species was made only for the whales sighted in the proximity of the vessels when the specific diagnostic characters could be confirmed. Of the 406 sightings, 296 were assigned to Antarctic (519 individuals), nine (11 individuals) to dwarf and 101 to unidentified minke whales (149 individuals). Dwarf minke whales were identified by the reported external diagnostic characters for this species. Seven animals occurred around the South Shetland Island and four in the Gerlache Strait. In addition, another two animals were identified as dwarf minke whales in the Bellinghausen Sea in winter 1993, being these the most southern records for this species. These results confirm the occurrence of dwarf minke whales around the Antarctic Peninsula during the summer seasons, as well as in the Bellinghausen Sea in winter. The geographical range of these sightings was comprised between 61°03′ and 69°25′S and between 55°29′ and 86°53′W. These results also suggest that some dwarf minke whales remain in the Antarctic during the austral winter.     

Sighting frequency and relative abundance of bottlenose dolphins (Tursiops truncatus) along the northeast coast of Margarita Island and Los Frailes Archipelago, Venezuela

The study of local cetaceans in Venezuela has a very recent history, and few efforts have been made in the assessment of coastal populations based on field research. The occurrence of whales and dolphins along the northeast coast of Venezuela has been documented through sightings and stranding records. Given the underwater topographical features and the influence of upwelling processes, this area is considered a very productive coastal ecosystem. Our objective was to establish the sighting frequency and relative abundance of bottlenose dolphins in the area. Sighting records were gathered on bottlenose dolphins and other cetacean species occurring along the northeast coast of Margarita Island and Los Frailes Archipelago through direct observation during land-based (6 surveys, 48 hours of observation) and boat-based surveys (24 surveys, 121 hours of observation, 1295 km covered). A sighting frequency was calculated using two methodologies and then compared, considering: 1) a mean effective observation time (4.27 hours), and 2) distance covered with cetacean sightings (1108 kin). A third method is proposed relating a mean effective distance covered with cetacean sightings and expressed as a percentage. The abundance index was calculated using the mean effective observation time. The sighting frequency of Tursiops truncattus in the study area was 3 - 4 sightings per day of 4.27 observation hours, or by 185 kilometers covered. The relative abundance was calculated as 35 dolphins in the study area, so a total population of less than 60 dolphins could inhabit the proposed range. Tursiops truncatus is the dominant species in the northeast coast of Margarita Island and Los Frailes Archipelago with 70% of all the sightings, so this locality could be termed as the distribution range of a possible local population of bottlenose dolphins.     

Results of a short study of interactions of cetaceans and longline fisheries in Atlantic waters: environmental correlates of catches and depredation events

In the Atlantic, economic losses have been reported from shark, swordfish and tuna longline fisheries due to depredation by cetaceans. We examined interactions of odontocete cetaceans with commercial longliners operating in waters off Brazil and the Azores archipelago during 2006–2007, analysing relationships between catches, depredation on hooked fish, cetacean sightings, acoustic records of cetacean presence and environmental variables. Data were provided by skippers of six vessels and by on-board observers for two vessels. The percentage of longline sets depredated by cetaceans was low (ranging from 1% to 9% of total sets per ship) but the proportion of fish damaged was high (up to 100%) when depredation occurred. Catches were related to the phase of the moon, cloud cover, sea surface temperature and water depth whereas cetacean sightings were primarily related to catches. In particular there was a positive association between Delphinus delphis sightings and catches of swordfish, and between Stenella frontalis sightings and mako catches. Acoustic detection was low when depredation by false killer whales occurred although high rates of clicks were detected when delphinids were sighted and false killer whales were by-caught. This may indicate that false killer whales are not echolocating when feeding on fish hooked on a longline. Guest editor: V. D. Valavanis Essential Fish Habitat Mapping in the Mediterranean     

Occurrence of hourglass dolphin (Lagenorhynchus cruciger) and habitat characteristics along the Patagonian Shelf and the Atlantic Ocean sector of the Southern Ocean

The hourglass dolphin, Lagenorhynchus cruciger, is one of the smallest cetaceans found in Antarctic waters. Although frequently observed, this is one of the least studied species of dolphin. In this study, we investigate the occurrence of hourglass dolphin in the South-West Atlantic and Southern Ocean from 42°S to 63°S and characterize the oceanographic and environmental features associated with their occurrence. Sighting data were collected during two scientific cruises in December 2009 and January and February 2011 and integrated into a geographical information system with environmental variables such as sea surface temperature, ocean colour, depth, distance to oceanographic fronts and distance from shore. We used a principal component analysis (PCA) to identify patterns in data and a non-hierarchic cluster analysis (K means) to classify observations into groups. A total of 19 sightings (96 individuals) were recorded. Group size ranged from one to twelve dolphins (mean 5.05). We could differentiate two groups in relation to the environmental conditions where animals were found, one group occurring in shallow coastal waters and the other occurring in deeper and colder waters further offshore. The present study contributes novel information on environmental measures associated with hourglass dolphin distribution in the South-West Atlantic and Southern Oceans. Additionally, it includes relatively high sighting clusters of this species in two highly productive and biodiverse areas (Burdwood Bank/Isla de los Estados and the South Shetland Islands).     

On the distribution of sympagic macro-fauna in the seasonally ice covered Barents Sea

Summary The sympagic fauna (= sea ice fauna) of the Barents Sea was investigated on nine (2–5 weeks) cruises in the period 1983–1988. The amphipods Apherusa glacialis, Onisimus sp. and Gammarus wilkitzkii were the most conspicuous and abundant invertebrate species associated with the ice. Mean biomass-values ranged from 0 to about 2 g/m², and were less than 0.001 g/m² in five of the nine cruises. Apherusa glacialis, Onisimus sp. and Gammarus wilkitzkii are regarded as autochthonous sympagic species, and as such dependent upon a permanent ice cover. Allochthonous sympagic species were few and without significant importance. The variations in species abundance and biomass were believed to be closely connected to the age and drift-history of the ice. The density of the sympagic fauna increases as a result of increasing influx of ice into the Barents Sea from the Arctic Ocean. Density of the sympagic fauna were believed to increase with decreasing distance to the multiyear/first-year ice boundary. A. glacialis was found further away from the spreading centers and in higher numbers than the other sympagic species due to its greater motility. No day-night variations in the occurrences of the sympagic fauna were recorded.     

Phenotypic Plasticity of Southern Ocean Diatoms: Key to Success in the Sea Ice Habitat?

Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species’ known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem.     

Modeling the relationship of Antarctic minke whales to major ocean boundaries

The population size of Antarctic minke whales Balaenoptera bonaerensis has been changing simultaneously with profound changes in the physics, i.e., mesopredator habitat features, of the Southern Ocean. Although the two trends may not be related, distinguishing among the factors responsible requires a better understanding of minke whale habitat preferences. For the first time at a large geographic scale, i.e., between 140° E and 35° W, we use data not constrained by vessels needing to avoid sea ice to model the habitat affinities of this pagophilic mesopredator. Using Maxent, we modeled minke whale proximity to the Antarctic Shelf Break Front (ASBF) and the southern boundary of Antarctic Circumpolar Current (sbACC), as well as association with sea ice, given that global climate change is altering the positions or intensity of these features. We also included water depth and chlorophyll (proxy for productivity) as variables. Minke whale presence data were gathered using strip and line census on 55 cruises on board icebreakers during late spring and summer, 1976–2005. The most important variable was distance to ASBF, followed by water depth and sea-ice concentration. That is, found principally in waters south of the sbACC during summer, minke whales were most abundant near the outer edge of the continental shelf (shallow depth), including areas heavily covered by sea ice. We propose that as the sbACC moves south and sea ice disappears, as projected by global climate models, minke whale habitat will shrink, and likely intra- and inter-specific competition will increase.     

Distribution and partial characterization of ice-active molecules associated with sea-ice diatoms

Macromolecular ice-active substances (IASs) that cause pitting of ice-crystal surfaces were previously shown to be associated with two species of Antarctic sea-ice diatom. Here it is shown that IASs are associated with many, if not all, sea-ice diatoms of McMurdo Sound, Antarctica, are present in the bottom layer of sea ice in rough proportion to the density of cells, and exist in winter-grown, algae-containing sea ice in different parts of the Southern Ocean and in at least one location in the Arctic. The IASs are retained to varying degrees by dialysis tubing with 50-, 100- and 300-kDa molecular weight cut-offs, suggesting a large molecular weight range, and have a solute requirement (∼≥200 mOsm/kg) for activity. The IASs occur as smears on both native and denaturing electrophoretic gels, which further suggests a heterogeneous nature. One apparently pure sample contained carbohydrate and protein (at an approximate 3:2 ratio on a weight basis), suggesting that the IASs are glycoproteins. The IASs preferentially bind to ice crystals, as they are concentrated in the ice phase of partially frozen solutions. Accepted: 25 April 2000     

Spatiotemporal patterns of marine mammal distribution in coastal waters of Galicia, NW Spain

The spatial and seasonal distribution of cetaceans and possible links with environmental conditions were studied at the Galician continental shelf. Data were collected between February–August 2001 and June–September 2003 during opportunistic surveys onboard fishing boats. Seven species of cetaceans were identified from 250 sightings of 6,846 individuals. The common dolphin (Delphinus delphis) was by far the most frequently sighted and the most widely distributed species. Spatiotemporal trends in cetacean distribution and abundance, and their relationships with environmental parameters (sea depth, SST and chlorophyll-a) were quantified using generalised additive models (GAMs). Results for all cetaceans were essentially the same as for common dolphins alone. Modelling results indicated that the number of common dolphin sightings per unit effort was higher further south. The number of individual common dolphins seen per sighting of this species (i.e. group size) was however higher in the north and west of the study area, higher later in the year and higher in 2001 than in 2003. In contrast, the number of common dolphin calves seen (per sighting of this species) was higher in the south. Models including environmental variables indicated larger common dolphin group sizes in deeper waters and at higher chlorophyll concentrations (i.e. in more productive areas). There was also a positive relationship between survey effort and group size, which is probably an artefact of the tendency of the survey platforms (fishing boats) to spend most time in areas of high fish abundance. Numbers of common dolphin calves per sighting were found to be higher in shallower waters. The results are consistent with common dolphins foraging mainly in deeper waters of the Galician continental shelf, while more southern inshore waters may represent a nursery area.     

Cumulative solar irradiance and potential large-scale sea ice algae distribution off East Antarctica (30°E–150°E)

We present a computational model of the large-scale cumulative light exposure of sea ice in the Southern Ocean off East Antarctica (30°E–150°E). The model uses remotely sensed or modelled sea ice concentration, snow depth over sea ice, and solar irradiance data, and tracks sea ice motion over the season of interest in order to calculate the cumulative exposure of the ice field to photosynthetically active radiation (PAR). Light is the limiting factor to sea ice algal growth over winter and early spring, and so the results have implications for the estimation of algal biomass in East Antarctica. The model results indicate that highly light-exposed ice is restricted to within a few degrees of the coast in the eastern part of the study region, but extends much further north in the 30°E–100°E sector. The relative influences of sea ice motion, solar flux, and snow depth variations on interannual variations in model predictions were evaluated. The model estimates of cumulative PAR were found to correlate with satellite estimates of subsequent open-water chlorophyll-a concentration, consistent with the notion that sea ice algae can provide inocula for phytoplankton blooms.