Observations of cetaceans in the south-east Atlantic sector of the Southern Ocean,during summer 2008

Knowledge of cetacean species composition and their distribution in the south-east Atlantic sector of the Southern Ocean is scarce. During a survey in February–March 2008, systematic whale sightings were carried out along transect lines following the 5° and 15° E meridians between 35° and 67° S. In total, 67 toothed whales and 126 baleen whales were observed. Both fin whales (four animals) and Antarctic minke whales Balaenoptera bonaerenses (three animals) in addition to 16 individuals of unidentified species were among the observed baleen whales. The dominating baleen whale species in our study was humpback whales Megaptera novaeangliae with 108 individuals observed. They occurred single or in groups up to seven individuals (N _mean = 2.5 ind) and eight of the counts were of calves. The relationship between humpback whale occurrence and environmental variables including Antarctic krill (Euphausia superba) abundance from acoustic recordings, hydrography, bathymetry and production was tested using general additive models. Only temperature increased the predictive power of the model with whale occurrence increasing with the decreasing temperature in more southern areas.     

Stomach contents of long-finned pilot whales (Globicephala melas) from southern Chile

The widely distributed long-finned pilot whale (Globicephala melas) has been reported off the Chilean coast, from Iquique (20°12′S) south to Navarino Island (55°15′S; 67°30′W), but little is known about its biology or ecology in the region. Here, we report on the prey of this species, identified by stomach content analyses from animals stranded on Holget Islets, Beagle Channel, southern Chile in August 2006. The stomachs of seven individuals (six females and one male) contained cephalopod remains. The prey composition found in these southern Chilean pilot whales was similar to that described in other parts of the world and the Southern Ocean. This is the first report on the feeding habits of this species from Chile.     

Killer whale ecotypes: is there a global model?

Killer whales, Orcinus orca, are top predators occupying key ecological roles in a variety of ecosystems and are one of the most widely distributed mammals on the planet. In consequence, there has been significant interest in understanding their basic biology and ecology. Long‐term studies of Northern Hemisphere killer whales, particularly in the eastern North Pacific (ENP), have identified three ecologically distinct communities or ecotypes in that region. The success of these prominent ENP studies has led to similar efforts at clarifying the role of killer whale ecology in other regions, including Antarctica. In the Southern Hemisphere, killer whales present a range of behavioural, social and morphological characteristics to biologists, who often interpret this as evidence to categorize individuals or groups, and draw general ecological conclusions about these super‐predators. Morphologically distinct forms (Type A, B, C, and D) occur in the Southern Ocean and studies of these different forms are often presented in conjunction with evidence for specialised ecology and behaviours. Here we review current knowledge of killer whale ecology and ecotyping globally and present a synthesis of existing knowledge. In particular, we highlight the complexity of killer whale ecology in the Southern Hemisphere and examine this in the context of comparatively well‐studied Northern Hemisphere populations. We suggest that assigning erroneous or prefatory ecotypic status in the Southern Hemisphere could be detrimental to subsequent killer whale studies, because unsubstantiated characteristics may be assumed as a result of such classification. On this basis, we also recommend that ecotypic status classification for Southern Ocean killer whale morphotypes be reserved until more evidence‐based ecological and taxonomic data are obtained.     

Size at maturity of Mediterranean marine fishes

In this review we collected data on the length at maturity (L_m) and maximum reported total length (L_max) of 565 Mediterranean marine fish stocks, representing 150 species, 68 families, 24 orders and 3 classes. Overall, L_m ranged from 2 cm, for the males of the toothcarp Aphanius fasciatus, to 350 cm, for the females of the bluntnose sixgill shark Hexanchus griseus. L_m was positively linearly related with L_max for Actinopterygii (logL_m = ?0.123 + 0.92 × logL_max; r ² = 0.87, n = 471, P < 0.001) and Elasmobranchii (logL_m = ?0.008 + 0.922 × logL_max; r ² = 0.90, n = 92, P < 0.001) with the two slopes being significantly different (ANCOVA: F = 2,904, P < 0.001). The reproductive load (L_m/L_max) ranged between 0.23 (sand steenbras Lithognathus mormyrus) and 0.94 (angular roughshark Oxynotus centrina and thornback ray Raja clavata). The mean L_m/L_max was significantly (ANOVA, F = 34.14, P < 0.001) lower for Actinopterygii (mean = 0.59, SD = 0.122, n = 471) compared to Elasmobranchii (mean = 0.70, SD = 0.132, n = 92) and Holocephali (mean = 0.77, SD = 0.077, n = 2). The L_m/L_max was significantly (ANOVA, F = 43.80, P < 0.001) higher for species providing some form of parental care, i.e. guarders, bearers, nesters (mean L_m/L_max ± SD = 0.68 ± 0.141, n = 111) compared to non-guarders (mean L_m/L_max ± SD = 0.59 ± 0.123, n = 454). The mean L_m/L_max displayed a remarkable constancy with longitude (northern and southern Mediterranean coastline: ANOVA, F = 0.01, P = 0.93), latitude (western, central and eastern regions: ANOVA, F = 1.25, P = 0.29) and habitat (ANOVA, F = 0.85, P = 0.51).     

Decreased binding capacity (B max) of muscarinic acetylcholine receptors in fibroblasts from boys with attention-deficit/hyperactivity disorder (ADHD)

Monoaminergic dysregulation is implicated in attention-deficit/hyperactivity disorder (ADHD), and methylphenidate and amphetamines are the most frequently prescribed pharmacological agents for treating ADHD. However, it has recently been proposed that the core symptoms of the disorder might be due to an imbalance between monoaminergic and cholinergic systems. In this study, we used fibroblast cell homogenates from boys with and without ADHD as an extraneural cell model to examine the cholinergic receptor density, that is, muscarinic acetylcholine receptors (mAChRs). We found that the binding capacity (B _max) of [³H] Quinuclidinyl benzilate (³H-QNB) to mAChRs was decreased by almost 50 % in the children with ADHD (mean = 30.6 fmol/mg protein, SD = 25.6) in comparison with controls [mean = 63.1 fmol/mg protein, SD = 20.5, p ≤ 0.01 (Student’s unpaired t test)]. The decreased B _max indicates a reduced cholinergic receptor density, which might constitute a biomarker for ADHD. However, these preliminary findings need to be replicated in larger ADHD and comparison cohorts.     

Macromolecular production of phytoplankton in the northern Bering Sea, 2007

Photosynthetic carbon allocations into different macromolecular classes provide important clues regarding physiological conditions of phytoplankton and the nutritional status of potential grazers. The productivity experiments for photosynthetic carbon allocations were conducted at three light depths (100, 30, and 1 %) for nine different stations in the northern Bering Sea as an important gateway into the western Arctic Ocean, using the ¹³C isotope tracer technique to determine the major controlling factors and physiological conditions of phytoplankton. The photosynthetic carbon allocations into different macromolecular classes [Low molecular weight metabolites (LMWM), lipids, proteins, and polysaccharides] of primary producers were determined based on the productivity experiments. LMWM and polysaccharides had similar vertical patterns whereas lipids and proteins had reverse vertical patterns at all the stations, which is consistent with other results under different light depths. The overall average allocations were 37.9 (SD = ± 18.8 %), 26.6 (SD = ± 17.4 %), 26.5 (SD = ± 20.7 %), and 9.1 % (SD = ± 7.8 %), for LMWM, lipids, proteins, and polysaccharides, respectively. Based on a general pattern of macromolecular production in the northern Bering Sea, phytoplankton was in a physiologically transitional phase from an unlimited status to a nitrogen-deficient condition during our cruise period, 2007. However, more in situ field measurements for macromolecular production under a variety of environmental conditions will improve the understanding of the physiological responses of phytoplankton to the ongoing environmental changes in the Arctic Ocean.     

Isotopic and genetic evidence for culturally inherited site fidelity to feeding grounds in southern right whales (Eubalaena australis)

Ocean warming will undoubtedly affect the migratory patterns of many marine species, but specific changes can be predicted only where behavioural mechanisms guiding migration are understood. Southern right whales show maternally inherited site fidelity to near-shore winter nursery grounds, but exactly where they feed in summer (collectively and individually) remains mysterious. They consume huge quantities of copepods and krill, and their reproductive rates respond to fluctuations in krill abundance linked to El Niño Southern Oscillation (ENSO). Here we show that genetic and isotopic signatures, analysed together, indicate maternally directed site fidelity to diverse summer feeding grounds for female right whales calving at Península Valdés, Argentina. Isotopic values from 131 skin samples span a broad range (–23.1 to –17.2‰δ¹³C, 6.0 to 13.8‰δ¹⁵N) and are more similar than expected among individuals sharing the same mitochondrial haplotype. This pattern indicates that calves learn summer feeding locations from their mothers, and that the timescale of culturally inherited site fidelity to feeding grounds is at least several generations. Such conservatism would be expected to limit the exploration of new feeding opportunities, and may explain why this population shows increased rates of reproductive failure in years following elevated sea-surface temperature anomalies off South Georgia, the richest known feeding ground for baleen whales in the South Atlantic.     

Isotopic niche differs between seal and fish‐eating killer whales (Orcinus orca) in northern Norway

Ecological diversity has been reported for killer whales (Orcinus orca) throughout the North Atlantic but patterns of prey specialization have remained poorly understood. We quantify interindividual dietary variations in killer whales (n = 38) sampled throughout the year in 2017–2018 in northern Norway using stable isotopic nitrogen (δ¹⁵N: ¹⁵N/¹⁴N) and carbon (δ¹³C: ¹³C/¹²C) ratios. A Gaussian mixture model assigned sampled individuals to three differentiated clusters, characterized by disparate nonoverlapping isotopic niches, that were consistent with predatory field observations: seal‐eaters, herring‐eaters, and lumpfish‐eaters. Seal‐eaters showed higher δ¹⁵N values (mean ± SD: 12.6 ± 0.3‰, range = 12.3–13.2‰, n = 10) compared to herring‐eaters (mean ± SD: 11.7 ± 0.2‰, range = 11.4–11.9‰, n = 19) and lumpfish‐eaters (mean ± SD: 11.6 ± 0.2‰, range = 11.3–11.9, n = 9). Elevated δ¹⁵N values for seal‐eaters, regardless of sampling season, confirmed feeding at high trophic levels throughout the year. However, a wide isotopic niche and low measured δ¹⁵N values in the seal‐eaters, compared to that of whales that would eat solely seals (δ_N‐measured = 12.6 vs. δ_N‐expected = 15.5), indicated a diverse diet that includes both fish and mammal prey. A narrow niche for killer whales sampled at herring and lumpfish seasonal grounds supported seasonal prey specialization reflective of local peaks in prey abundance for the two fish‐eating groups. Our results, thus, show differences in prey specialization within this killer whale population in Norway and that the episodic observations of killer whales feeding on prey other than fish are a consistent behavior, as reflected in different isotopic niches between seal and fish‐eating individuals.     

Interactions between Cetacean and Fisheries in the Southern Ocean

Soon after longlining on Patagonian toothfish (Dissostichus eleginoides) started in the Southern Ocean in the second half of the 1980s, interactions of cetaceans with these fisheries became apparent. The two species primarily involved were orcas (killer whales) (Orcinus orca) and male sperm whales (Physeter macrocephalus). Both species took substantial number of fish from the line primarily during day light hours. Catch rates of longliners declined to less than 50% when orcas occurred close to longline vessels while the loss to sperm whales was much less obvious. They were seen diving close to the line down to 400 m where they apparently took fish. Their impact on catch rates was much less notable. Sperm whales became frequently entangled in the line and part of the line was lost in a number of cases. Other cetaceans were rarely seen in the vicinity of longline vessels. They became entangled in the line only occasionally and one whale (presumably a minke whale) died.     

Population Structure of Humpback Whales from Their Breeding Grounds in the South Atlantic and Indian Oceans

Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.     

Assessing the impact of toothed whale depredation on socio-ecosystems and fishery management in wide-ranging subantarctic fisheries

Marine predators feeding on fisheries catches directly on the fishing gear, a behaviour termed “depredation”, has emerged as a major human-wildlife conflict globally, often resulting in substantial socio-economic and ecological impacts. This study investigated the extent of this conflict in commercial Patagonian toothfish (Dissostichus eleginoides) fisheries across subantarctic waters where both killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) feed on toothfish caught on longline hooks. Using long-term datasets from six major fishing areas, from southern Chile to the Indian Ocean sector of the Southern Ocean, statistical models were developed to quantify the catch removals due to whale depredation interactions. The results indicated that these removals were large, totalling more than 6600 t of toothfish between 2009 and 2016 with an annual mean of 837 t [95% CI 480–1195 t], comprised of 317 t [232–403 t] and 518 t [247–790 t] removed by killer whales and sperm whales, respectively. Catch removals greatly varied between areas, with the largest estimates found at Crozet, where on average 279 t [179–379 t] of toothfish per year, equivalent to 30% [21–37%] of the total catches. Together, these findings provide metrics to assess the impacts of depredation interactions on the fishing industry, whale populations, fish stocks and associated ecosystems. With an estimated $15 M USD worth of fish depredated every year, this study highlights the large geographic scale and economic significance of the depredation issue and its potential to compromise the viability of some toothfish fisheries which are the primary socio-economic activity in subantarctic regions.

     

Occurrence of false killer whales (Pseudorca crassidens) and their association with common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand

On a global scale, false killer whales (Pseudorca crassidens) remain one of the lesser‐known delphinids. The occurrence, site fidelity, association patterns, and presence/absence of foraging in waters off northeastern New Zealand are examined from records collected between 1995 and 2012. The species was rarely encountered; however, of the 61 distinctive, photo‐identified individuals, 88.5% were resighted, with resightings up to 7 yr after initial identification, and movements as far as 650 km documented. Group sizes ranged from 20 to ca. 150. Results indicate that all individuals are linked in a single social network. Most observations were recorded in shallow (<100 m) nearshore waters. Occurrence in these continental shelf waters is likely seasonal, coinciding with the shoreward flooding of a warm current. During 91.5% of encounters, close interspecific associations with common bottlenose dolphins (Tursiops truncatus) were observed. Photo‐identification reveals repeat inter‐ and intraspecific associations among individuals with 34.2% of common bottlenose dolphins resighted together with false killer whales over 1,832 d. While foraging was observed during 39.5% of mixed‐species encounters, results suggest that social and antipredatory factors may also play a role in the formation of these mixed‐species groups.     

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.     

Behavioral context of echolocation and prey-handling sounds produced by killer whales (Orcinus orca) during pursuit and capture of Pacific salmon (Oncorhynchus spp.)

Availability of preferred salmonid prey and a sufficiently quiet acoustic environment in which to forage are critical to the survival of resident killer whales (Orcinus orca) in the northeastern Pacific. Although piscivorous killer whales rely on echolocation to locate and track prey, the relationship between echolocation, movement, and prey capture during foraging by wild individuals is poorly understood. We used acoustic biologging tags to relate echolocation behavior to prey pursuit and capture during successful feeding dives by fish-eating killer whales in coastal British Columbia, Canada. The significantly higher incidence and rate of echolocation prior to fish captures compared to afterward confirms its importance in prey detection and tracking. Extremely rapid click sequences (buzzes) were produced before or concurrent with captures of salmon at depths typically exceeding 50 m, and were likely used by killer whales for close-range prey targeting, as in other odontocetes. Distinctive crunching and tearing sounds indicative of prey-handling behavior occurred at relatively shallow depths following fish captures, matching concurrent observations that whales surfaced with fish prior to consumption and often shared prey. Buzzes and prey-handling sounds are potentially useful acoustic signals for estimating foraging efficiency and determining if resident killer whales are meeting their energetic requirements.     

Morphometric analysis of Chilean blue whales and implications for their taxonomy

In the Southern Hemisphere, blue whales are currently divided into two subspecies, Antarctic blue whales (Balaenoptera musculus intermedia) and pygmy blue whales (B. m. brevicauda), but there is some debate about whether Chilean blue whales should also be considered as a separate subspecies. Here, we provide novel morphometric data to directly address this taxonomic question from a biological survey of 60 blue whales taken during the 1965/1966 Chilean whaling season. The data show that maximum body length and mean body length of both sexually mature females and males for Chilean blue whales are intermediate between pygmy and Antarctic blue whales; and that fluke-anus lengths of Chilean blue whales are significantly different from pygmy blue whales, but not necessarily from Antarctic blue whales. There is also some support from the data that snout-eye measurements are different among all three groups. These data provide further confirmation that Chilean blue whales are a distinct population requiring separate management from other blue whale populations, and are also consistent with suggestions that Chilean blue whales are not the same subspecies as pygmy blue whales.     

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.     

Distribution,feeding habits and morphology of killer whales Orcinus orca in the Caribbean Sea

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Linking killer whale survival and prey abundance: food limitation in the oceans' apex predator?

Killer whales (Orcinus orca) are large predators that occupy the top trophic position in the world''s oceans and as such may have important roles in marine ecosystem dynamics. Although the possible top-down effects of killer whale predation on populations of their prey have received much recent attention, little is known of how the abundance of these predators may be limited by bottom-up processes. Here we show, using 25 years of demographic data from two populations of fish-eating killer whales in the northeastern Pacific Ocean, that population trends are driven largely by changes in survival, and that survival rates are strongly correlated with the availability of their principal prey species, Chinook salmon (Oncorhynchus tshawytscha). Our results suggest that, although these killer whales may consume a variety of fish species, they are highly specialized and dependent on this single salmonid species to an extent that it is a limiting factor in their population dynamics. Other ecologically specialized killer whale populations may be similarly constrained to a narrow range of prey species by culturally inherited foraging strategies, and thus are limited in their ability to adapt rapidly to changing prey availability.     

Spatial and temporal analysis of killer whale (Orcinus orca) strandings in the North Pacific Ocean and the benefits of a coordinated stranding response protocol

Killer whales (Orcinus orca) are widely distributed throughout the world's oceans, yet little has been documented about their stranding patterns. Knowledge of stranding patterns improves our ability to examine and sample carcasses and provides a foundation for understanding killer whale natural history, diet, reproduction, anthropogenic stressors, emerging diseases, and patterns of unusual mortality. We compiled published and unpublished killer whale stranding data to describe stranding patterns in the North Pacific Ocean. Between 1925 and 2011, 371 stranded killer whales were reported in Japan (20.4%), Russia (3.5%), Alaska (32.0%), British Columbia (27.4%), Washington (4.0%), Oregon (2.7%), California (5.1%), Mexico (3.8%), and Hawaii (0.8%). Strandings occurred at all times of year, but regionally specific seasonal differences were observed. Mortality and annual census data from Northern and Southern Resident populations were extrapolated to estimate that across the North Pacific, an average of 48 killer whales die annually. However, over the last two decades, an average of only 10 killer whale carcasses were recovered annually in this ocean, making each event a rare opportunity for study. Publication of a standardized killer whale necropsy protocol and dedicated funding facilitated the number of complete postmortem necropsies performed on stranded killer whales from 1.6% to 32.2% annually.     

The occurrence of two bill morphs of prions Pachyptila vittata on Gough Island

Prions Pachyptila are abundant seabirds in the Southern Ocean that have been used to infer environmental change, but this relies on an understanding of their morphological diversity. Species limits among prions are largely defined by the size and structure of their bills. The broad-billed prion P. vittata, which breeds at temperate islands in the central South Atlantic Ocean and around New Zealand, is the largest species with adult bill widths averaging 21–22 mm. We report local differences in bill sizes on Gough Island, with typical adults breeding in some areas and narrower-billed birds in other areas (average bill width 18–19 mm, although at one site there was a second mode at bill widths of 16–17 mm). The narrow-billed birds have slightly shorter bills, heads and wings (averaging 1–2 % smaller than typical adult broad-billed prions), but the difference in bill width is much more marked (15 %). The small-billed birds differ from typical broad-billed prions in having blue colouration in the upper mandible and are similar in size to MacGillivray’s prion P. [salvini/vittata] macgillivrayi from Amsterdam and St Paul islands in the temperate Indian Ocean. The occurrence of two prion morphs on Gough Island raises intriguing questions about their ecology and systematics. Small-billed birds breed 3 months later than large-billed birds, suggesting that they are a separate species, not an example of bill polymorphism.