Population histories of right whales (Cetacea: Eubalaena) Inferred from Mitochondrial Sequence Diversities and Divergences of Their Whale Lice (Amphipoda: Cyamus)

Right whales carry large populations of three ‘whale lice’ (Cyamus ovalis, Cyamus gracilis, Cyamus erraticus) that have no other hosts. We used sequence variation in the mitochondrial COI gene to ask (i) whether cyamid population structures might reveal associations among right whale individuals and subpopulations, (ii) whether the divergences of the three nominally conspecific cyamid species on North Atlantic, North Pacific, and southern right whales (Eubalaena glacialis, Eubalaena japonica, Eubalaena australis) might indicate their times of separation, and (iii) whether the shapes of cyamid gene trees might contain information about changes in the population sizes of right whales. We found high levels of nucleotide diversity but almost no population structure within oceans, indicating large effective population sizes and high rates of transfer between whales and subpopulations. North Atlantic and Southern Ocean populations of all three species are reciprocally monophyletic, and North Pacific C. erraticus is well separated from North Atlantic and southern C. erraticus. Mitochondrial clock calibrations suggest that these divergences occurred around 6 million years ago (Ma), and that the Eubalaena mitochondrial clock is very slow. North Pacific C. ovalis forms a clade inside the southern C. ovalis gene tree, implying that at least one right whale has crossed the equator in the Pacific Ocean within the last 1–2 million years (Myr). Low-frequency polymorphisms are more common than expected under neutrality for populations of constant size, but there is no obvious signal of rapid, interspecifically congruent expansion of the kind that would be expected if North Atlantic or southern right whales had experienced a prolonged population bottleneck within the last 0.5 Myr.

Pinniped Populations at Islas ae Guadalupe, San Benito, Cedros, and Natividad, Baja California, in 1968

In April and June 1968, the Pacific Ocean Biological Survey Program (POBSP) of the Smithsonian Institution conducted surveys on breeding marine birds and pinnipeds on various Mexican islands. Between 18 to 26 April and 21 to 29 June, pinniped populations were surveyed at Islas de Guadalupe, San Benito, Cedros, and Natividad off Baja California. Species observed were the California sea lion, Zalophus californianus, Guadalupe fur seal, Arctocephalus townsendi, harbor seal, Phoca vitulina, and northern elephant seal, Mirounga angustirostris

Baleen Whales: Conservation Issues and The Status Of The Most Endangered Populations

Most species of baleen whales were subject to intensive overexploitation by commercial whaling in this and previous centuries, and many populations were reduced to small fractions of their original sizes. Here, we review the status of baleen whale stocks, with an emphasis on those that are known or thought to be critically endangered. Current data suggest that, of the various threats potentially affecting baleen whales, only entanglement in fishing gear and ship strikes may be significant at the population level, and then only in those populations which are already at critically low abundance. The impact of some problems (vessel harassment, and commercial or aboriginal whaling) is at present probably minor. For others (contaminants, habitat degradation, disease), existing data either indicate no immediate cause for concern, or are insufficient to permit an assessment. While the prospect for many baleen whales appears good, there are notable exceptions; populations that are of greatest concern are those suffering from low abundance and associated problems, including (in some cases) anthropogenic mortality. These include: all Northern Right Whales Eubalaena glacialis, Bowhead Whales Balaena mysticetus of the Okhotsk Sea and various eastern Arctic populations, western Gray Whales Eschrichtius robustus, and probably many Blue Whale Balaenoptera musculus populations. We review the status of these populations and, where known, the issues potentially affecting their recovery. Although Humpback Whales Megaptera novaeangliae and Southern Right Whales Eubalaena australis were also heavily exploited by whaling, existing data indicate strong recovery in most studied populations of these species.

Monitoring the Prey-Field of Marine Predators: Combining Digital Imaging With Datalogging Tags

There is increasing interest in the diving behavior of marine mammals. However, identifying foraging among recorded dives often requires several assumptions. The simultaneous acquisition of images of the prey encountered, together with records of diving behavior will allow researchers to more fully investigate the nature of subsurface behavior. We tested a novel digital camera linked to a time-depth recorder on Antarctic fur seals (Arctocephalus gazella). During the austral summer 2000-2001, this system was deployed on six lactating female fur seals at Bird Island, South Georgia, each for a single foraging trip. The camera was triggered at depths greater than 10 m. Five deployments recorded still images (640 x 480 pixels) at 3-sec intervals (total 8,288 images), the other recorded movie images at 0.2-sec intervals (total 7,598 frames). Memory limitation (64 MB) restricted sampling to approximately 1.5 d of 5-7 d foraging trips. An average of 8.5% of still pictures (2.4%-11.6%) showed krill (Euphausia superba) distinctly, while at least half the images in each deployment were empty, the remainder containing blurred or indistinct prey. In one deployment krill images were recorded within 2.5 h (16 km, assuming 1.8 m/sec travel speed) of leaving the beach. Five of the six deployments also showed other fur seals foraging in conjunction with the study animal. This system is likely to generate exciting new avenues for interpretation of diving behavior.

Hunting and social behaviour of leopard seals (Hydrurga leptonyx) at Seal Island, South Shetland Islands, Antarctica

The hunting behavior of leopard seals Hydrurga leptonyx was monitored opportunistically at Seal Island, South Shetland Islands, during the austral summers from 1986/87 to 1994/95. Leopard seals used several methods to catch Antarctic fur seal pups Arctocephalus gazella and chinstrap penguins Pygoscelis antarctica, and individuals showed different hunting styles and hunting success. One to two leopard seals per year were responsible for an average of 60% of observed captures of fur seal pups. Leopard seals preyed on penguins throughout the summer, but preyed on fur seal pups only between late December and mid-February. Hunting behavior differed significantly between different locations on the island; fur seals were hunted only at one colony, and penguins were hunted in several areas. The relative abundance of prey types, size of prey in relation to predator, and specialization of individual leopard seals to hunt fur seal prey probably influence individual prey preferences among leopard seals. On five occasions, two leopard seals were seen together on Seal Island. Possible interpretations of the relationship between the interacting leopard seals included a mother-offspring relationship, a consorting male-female pair, and an adult leopard seal followed by an unrelated juvenile. In two incidents at Seal Island, two leopard seals were observed interacting while hunting: one seal captured fur seal pups and appeared to release them to the other seal. Observations of leopard seals interacting during hunting sessions were difficult to confirm as co-operative hunting, but they strongly implied that the two seals were not agonistic toward one another. The hunting success of individual leopard seals pursuing penguins or fur seals is probably high enough for co-operative hunting not to become a common hunting strategy; however, it may occur infrequently when it increases the hunting productivity of the seals.

Population Growth of Antarctic Fur Seals: Limitation by a Top Predator, The Leopard Seal?

Antarctic fur seals (Arctocephalus gazella) in the South Shetland Islands are recovering from 19th-century exploitation more slowly than the main population at South Georgia. To document demographic changes associated with the recovery in the South Shetlands, we monitored fur seal abundance and reproduction in the vicinity of Elephant Island during austral summers from 1986/1987 through 1994/1995. Total births, mean and variance of birth dates, and average daily mortality rates were estimated from daily live pup counts at North Cove (NC) and North Annex (NA) colonies on Seal Island. Sightings of leopard seals (Hydrurga leptonyx) and incidents of leopard seal predation on fur seal pups were recorded opportunistically during daily fur seal research at both sites. High mortality of fur seal pups, attributed to predation by leopard seals frequently observed at NC, caused pup numbers to decline rapidly between January and March (i.e., prior to weaning) each year and probably caused a long-term decline in the size of that colony. The NA colony, where leopard seals were never observed, increased in size during the study. Pup mortality from causes other than leopard seal predation appeared to be similar at the two sites. The number of pups counted at four locations in the Elephant Island vicinity increased slowly, at an annual rate of 3.8%, compared to rates as high as 11% at other locations in the South Shetland Islands. Several lines of circumstantial evidence are consistent with the hypothesis that leopard seal predators limit the growth of the fur seal population in the Elephant Island area and perhaps in the broader population in the South Shetland Islands. The sustained growth of this fur seal population over many decades rules out certain predator–prey models, allowing inference about the interaction between leopard seals and fur seals even though it is less thoroughly studied than predator–prey systems of terrestrial vertebrates of the northern hemisphere. Top-down forces should be included in hypotheses for future research on the factors shaping the recovery of the fur seal population in the South Shetland Islands.

Intraspecific Comparison of Population Structure, Genetic Diversity, and Dispersal Among Three Subspecies of Townsend’s Big-Eared Bats, Corynorhinus townsendii townsendii, C. t. pallescens, and the Endangered C. t. birginianus

Townsend’s big-eared bat, Corynorhinus townsendii, is distributed broadly across western North America and in two isolated, endangered populations in central and eastern United States. There are five subspecies of C. townsendii; C. t. pallescens, C. t. australis, C. t. townsendii, C. t. ingens, and C. t. virginianus with varying degrees of concern over the conservation status of each. The aim of this study was to use mitochondrial and microsatellite DNA data to examine genetic diversity, population differentiation, and dispersal of three C. townsendii subspecies. C. t. virginianus is found in isolated populations in the eastern United States and was listed as endangered under the Endangered Species Act in 1979. Concern also exists about declining populations of two western subspecies, C. t. pallescens and C. t. townsendii. Using a comparative approach, estimates of the genetic diversity within populations of the endangered subspecies, C. t. virginianus, were found to be significantly lower than within populations of the two western subspecies. Further, both classes of molecular markers revealed significant differentiation among regional populations of C. t. virginianus with most genetic diversity distributed among populations. Genetic diversity was not significantly different between C. t. townsendii and C. t. pallescens. Some populations of C. t. townsendii are not genetically differentiated from populations of C. t. pallescens in areas of sympatry. For the western subspecies gene flow appears to occur primarily through male dispersal. Finally, geographic regions representing significantly differentiated and genetically unique populations of C. townsendii virginianus are recognized as distinct evolutionary significant units.