Whales as Indicators of Historical and Current Changes in the Marine Ecosystem of the Indo-Pacific Sector of the Antarctic

We review the scientific information on whales that could be indicative of historical and current changes in the ecosystem in the Indo-Pacific sector of the Antarctic. The increased krill availability in the middle of the past century as a result of the heavy harvesting of the larger baleen whale species could have been translated into better nutritional conditions for the Antarctic minke whale, resulting in a decreasing trend in the age at sexual maturity and an increasing trend in recruitment rate and hence total population size between approximately 1940 and 1970. This nutritional condition has deteriorated more recently, as revealed by a decrease in energy storage and stomach content weight since the 1980’s; these changes coincide with appreciable increases in the abundances of humpback and fin whales, which were heavily harvested in the first half of the past century. The historical demographic changes observed in the Antarctic minke whale are consistent with the pattern to be expected under the krill surplus hypothesis, with minke whales now again competing with other (recovering) baleen whale species for krill. However, these minke whales could also be using alternative feeding areas (e.g. polynias within the pack-ice) in response to the increase in abundance and geographical expansion of these other large whale species. This could provide an alternative explanation for indications from sighting surveys and population models of a decrease and then re-stabilisation of minke whale abundance in open water areas since the 1970s

Investigating Population Genetic Structure in a Highly Mobile Marine Organism: The Minke Whale Balaenoptera acutorostrata acutorostrata in the North East Atlantic

Inferring the number of genetically distinct populations and their levels of connectivity is of key importance for the sustainable management and conservation of wildlife. This represents an extra challenge in the marine environment where there are few physical barriers to gene-flow, and populations may overlap in time and space. Several studies have investigated the population genetic structure within the North Atlantic minke whale with contrasting results. In order to address this issue, we analyzed ten microsatellite loci and 331 bp of the mitochondrial D-loop on 2990 whales sampled in the North East Atlantic in the period 2004 and 2007–2011. The primary findings were: (1) No spatial or temporal genetic differentiations were observed for either class of genetic marker. (2) mtDNA identified three distinct mitochondrial lineages without any underlying geographical pattern. (3) Nuclear markers showed evidence of a single panmictic population in the NE Atlantic according STRUCTURE's highest average likelihood found at K = 1. (4) When K = 2 was accepted, based on the Evanno's test, whales were divided into two more or less equally sized groups that showed significant genetic differentiation between them but without any sign of underlying geographic pattern. However, mtDNA for these individuals did not corroborate the differentiation. (5) In order to further evaluate the potential for cryptic structuring, a set of 100 in silico generated panmictic populations was examined using the same procedures as above showing genetic differentiation between two artificially divided groups, similar to the aforementioned observations. This demonstrates that clustering methods may spuriously reveal cryptic genetic structure. Based upon these data, we find no evidence to support the existence of spatial or cryptic population genetic structure of minke whales within the NE Atlantic. However, in order to conclusively evaluate population structure within this highly mobile species, more markers will be required

Filopatría de la ballena jorobada (Megaptera novaeangliae Borowski, 1781), al área de alimentación del estrecho de Magallanes

La ballena jorobada migra entre las áreas de alimentación en las altas latitudes y las áreas de reproducción en las bajas latitudes, exhibiendo un marcado grado de filopatría hacia sus destinos migratorios. La ballena jorobada del Pacífico suroriental migra entre el área de reproducción, principalmente en las aguas de Ecuador y Colombia, y el área de alimentación alrededor de la península Antártica. Estudios previos han sugerido una segunda área de alimentación para esta población, localizada en las aguas del estrecho de Magallanes. El presente estudio evalúa la filopatría de la ballena jorobada esta segunda área de alimentación en el estrecho de Magallanes, usando datos de foto-identificación obtenidos durante 10 cruceros de avistamiento realizados en tres veranos australes consecutivos (2002-2003 a 2004-2005). Si el estrecho de Magallanes constituye una segunda área de alimentación para una parte de los animales de la población del Pacífico suroriental, entonces se debería esperar un alta proporción de retorno de esos animales foto-identificados a esta área, en diferentes veranos australes. La filopatría de los ejemplares foto-identificados a esta segunda área de alimentación en el estrecho de Magallanes muestra ser alto (promedio=78,9%). Además, la filopatría de los ejemplares no mostró ser significativamente diferentes entre sexos ni entre categorías de clase/edad. Finalmente, la alta tasa de retorno de los ejemplares foto-identificados en los diferentes veranos australes, indica que el estrecho de Magallanes constituye otra zona de alimentación para, al menos, una parte de la población de ballena jorobada del Pacífico suroriental

Phylogeny and Population Genetic Structure of Minke Whales Worldwide: A Review of Recent Studies

In 1998, two species of minke whales were recognized based on the review of the morphological and genetic information available at that time: the Antarctic minke whale (Balaenoptera bonaerensis), which is restricted to the Southern Hemisphere, and the cosmopolitan common minke whale (Balaenoptera acutorostrata). Furthermore, three sub-species of the common minke whale were recognized: the North Atlantic (B. a. acutorostrata), North Pacific (B. a. scammoni) and Southern Hemisphere (B. a. subsp.). This chapter reviews the genetic studies on minke whales conducted after 1998. The review is organized by topic, e.g., those studies focused on phylogeny and other matters most relevant for taxonomy, and those focused on population genetic structure within oceanic basins most relevant for conservation and management. On the former topic, the new genetic information, whilst strongly supporting the minke whale taxonomic classification recognized in 1998, also reveals substantial genetic differentiation within the Southern Hemisphere common minke whales, with subsequent taxonomic implications. On the latter topic, results from different analytical procedures have provided information on population identification and structure in the Indo-Pacific sector of the Antarctic and western North Pacific, but they have failed to identify unequivocally any population within the North Atlantic common minke whales

Surface feeding behavior of humpback whales in the Magellan Strait

Surface feeding behavior of 37 identified humpback whales in the Magellan Strait are reported with the aim of describing feeding behavior and investigating whether differences in prey type determine the feeding strategy in this area. A total of three lunging and one bubbling behaviors are reported, of which two ('single straight-line bubble curtain' and 'sub-surface skimming') are novel behaviors for this species and each feeding behavior tended to be consistent in regards to the prey species available at a given time. However, our data set did not contain a sufficient sample size to fully interpret this association with the available prey species

Plasma and urine levels of electrolytes, urea and steroid hormones involved in osmoregulation of cetaceans

Cetaceans are well adapted to their hyperosmotic environment by properly developed osmoregulatory ability. A question here is how they regulate water and mineral balances in marine habitats. In the present study, we determined blood and urine levels of various chemicals involved in osmoregulation, compared them with those in artiodactyls, and characterized the values in the whales. Blood and urine samples obtained from baleen whales of common minke (Balaenoptera acutorostrata), sei (B. borealis), and Bryde's whales (B. brydei), and toothed whales of sperm whales (Physeter macrocephalus) were analyzed for osmolality, major electrolytes, urea, steroid hormones and glucose. The urine osmolality and Na+ concentrations in the cetaceans were much higher than those in the cattle. Furthermore, the cetaceans had 5 to 11-fold urea in plasma than the cattle, and 2 to 4-fold urea in urine. There were no significant difference in the plasma concentrations of corticosteroids between the cetaceans and the cattle. The present results indicate that the osmoregulatory parameters seem to be not affected by the reproductive stage and sex steroid hormones. The concentrations of urea in plasma and urine of the baleen whales were higher than those of the sperm whales, indicating a possibility that their osmoregulatory mechanisms may be correlated to their feeding habits. The present results suggest that cetaceans have unique osmoregulatory mechanisms by which they excrete strongly hypertonic urine to maintain fluid homeostasis in marine habitats

Hybrids between common and Antarctic minke whales are fertile and can back-cross

Background: Minke whales are separated into two genetically distinct species: the Antarctic minke whale found in the southern hemisphere, and the common minke whale which is cosmopolitan. The common minke whale is further divided into three allopatric sub-species found in the North Pacific, southern hemisphere, and the North Atlantic. Here, we aimed to identify the genetic ancestry of a pregnant female minke whale captured in the North Atlantic in 2010, and her fetus, using data from the mtDNA control region, 11 microsatellite loci and a sex determining marker. Results: All statistical parameters demonstrated that the mother was a hybrid displaying maternal and paternal contribution from North Atlantic common and Antarctic minke whales respectively. Her female fetus displayed greater genetic similarity to North Atlantic common minke whales than herself, strongly suggesting that the hybrid mother had paired with a North Atlantic common minke whale. Conclusion: This study clearly demonstrates, for the first time, that hybrids between minke whale species may be fertile, and that they can back-cross. Whether contact between these species represents a contemporary event linked with documented recent changes in the Antarctic ecosystem, or has occurred at a low frequency over many years, remains open