Aleuts: Ecosystem, Holocene History, and Siberian Origin

Observations of seabirds stealing food (kleptoparasitism) from marine mammals are rarely reported. During 67 h of observation at Seward, Alaska, where fishers frequently discard scraps of fish, we documented 16 incidents of gulls attempting to kleptoparasitize sea otters (Enhydra lutris) and seven incidents of gulls attempting to kleptoparasitize Steller sea lions (Eumetopias jubatus). An average of 3.5 ± 3.5 SD (range 1–13) glaucous-winged gulls (Larus glaucescens) and < 0.1 ± 0.3 SD (range 0–1) black-legged kittiwakes (Rissa tridactyla) attacked sea otters with discarded fish scraps, with a success rate of 53% per incident and 16% per individual gull. The gulls ignored sea otters with invertebrate prey. An average of 3.6 ± 1.7 SD (range 1–7) glaucous-winged gulls and 0.1 ± 0.4 SD (range 0–1) black-legged kittiwakes attacked sea lions with discarded fish scraps, with a success rate of 29% per incident and 8% per individual gull. Only glaucous-winged gulls succeeded in stealing food, usually comprising fragments of the original item floating on the surface after the victim dived, but twice food was stolen directly from sea otters. To avoid kleptoparasitism, sea otters used five evasive maneuvers (swimming away, diving, rolling, lunging toward gull, and pulling food from gull), whereas sea lions used only two (swimming away and diving). Kleptoparasitism of sea otters and sea lions by gulls is a previously overlooked behavior that merits further study of its potential benefits and costs.

Pinnipeds (e.g., seal, sea lion, walrus) are marine mammals that spend time both in and out of the water. All are able to vocalize in air using the pneumatically driven vocal fold vibrations, a mechanism common to terrestrial mammals. This is no surprise, as their ancestors were once terrestrial mammals. Pinnipeds, however, are also able to vocalize underwater. It is not known how they generate or transmit these sounds. This study explores pinniped laryngeal anatomy in: harbor seal (Phoca vitulina), gray seal (Halichoerus grypus), elephant seal (Mirounga angustirostris), California sea lion (Zalophus californianus), and walrus (Odobenus rosmarus). Comparisons were made with the laryngeal anatomy of several closely related terrestrial species including: dog (Canis familiaris) and black bear (Ursus americanus), and several semiaquatic species including: polar bear (Ursus maritimus), sea otter (Enhydra lutris), river otter (Lontra canadensis), beaver (Castor canadensis), muskrat (Ondatra zibethicus), and hippo (Hippopotamus amphibius). Comparisons were also made to fully aquatic mammals that can vocalize underwater including: manatee (Trichechus manatus), baleen whales (Caperea marginata, Balaena glacialis, Megaptera novaeangliae, Balaenoptera musculus, B. physalus, B. borealis, B. acutorostrata), and over 20 species of toothed whales (including sperm whales, beaked whales, dolphins, and porpoises). Results indicate that the harbor and gray seals have an unremarkable larynx that appears grossly similar to that of most other mammals. Elephant seal, sea lion, and walrus larynges, however, were unusual in having arytenoid cartilages that are extremely large and rounded on their rostral surface. The arytenoids form a valve across approximately half of the laryngeal lumen. Interestingly, this feature also occurs in sea otters. The corniculate and cuneiform cartilages are difficult to detect in the elephant seal, sea lion, and walrus. The epiglottic cartilage is very short in the sea lion and walrus, similar to the manatee, but robust in the elephant seal. The vestibular fold of the elephant seal is very prominent, and appears connected to the arytenoid cartilage. Harbor seal, gray seal, and walrus vocal folds are oriented perpendicular to airflow, as in other terrestrial mammals. Elephant seal and sea lion vocal folds are rotated, compared with other terrestrial mammals, with the ventral attachment located more rostrally. Their vocal folds are thus positioned near the ventral aspect of the larynx. This orientation is similar to those of the hippo, baleen whales, and toothed whales. None of the pinnipeds have vocal folds resembling the smooth sloped vocal folds of the manatee, or the thickened vocal folds of the polar bear. The unusual arytenoid size and vocal fold orientation in some pinnipeds may indicate evolutionary convergence with other underwater laryngeal vocalizers (e.g., hippo, baleen whales). It is unclear whether laryngeal morphologies of elephant seal, sea lion, and walrus are functional adaptations representing autapomorphies (uniquely derived features) of these species. Further work should be directed towards understanding whether laryngeal specializations may relate to variations in underwater sounds or in‐air vocalizations. More pinniped species need to be studied, particularly deep diving seals that are very vocal (e.g., Weddell seal) or fur seals (having external morphology and behaviors very similar to sea lions).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A High Price for Fish

A high price for fish

Completion of the analysis of the artifacts from Chaluka, the old village site at Nikolski, Umnak Island, has brought to light a number of new observations on the Aleutian core and blade industry, orginally described in American Antiquity, Vol. 17, No. 1, pp. 52-54. The use of lamellar flakes is part of the earliest Aleut culture and most of the flakes, four fifths, are found below the three meter level. This earliest Aleut culture was introduced by the paleo-Aleut people.These flakes were used mainly for scrapers and retouched on only one surface and along one or both edges. Quite a few of these are tanged, apparently for end-hafting. A number have well-worked points which, together with their general form, suggests their use as gravers. There are also two adze blades, two knives and at least one projectile point which appears to have been made from lamellar flakes.

To examine the marine habitat of the endangered western stock of the Steller's sea lion (Eumetopias jubatus), two interdisciplinary research cruises (June 2001 and May to June 2002) measured water properties in the eastern and central Aleutian Passes. Unimak, Akutan, Amukta, and Seguam Passes were sampled in both years, and three additional passes (Umnak, Samalga, and Tanaga) were sampled in 2002. In the North Pacific (and to a lesser extent in the Bering Sea), a strong front in water properties was observed near Samalga Pass in June of both years, with significantly warmer, fresher, and more nitrate‐poor water east of Samalga Pass than west of the pass. These water properties reflect differences in source waters (Alaska Coastal Current versus Alaskan Stream), mixing depth, and Bering Sea influence. Strong cross‐Aleutian gradients were also observed with warmer, fresher water on the North Pacific side of the archipelago. The nutrient content of the waters flowing through the passes, combined with the effects of mixing within the passes, influences the transport of nutrients into the Bering Sea. As water moves away from the strong mixing of the passes and becomes more stratified, phytoplankton can take advantage of the enhanced nutrient concentrations. Thus, the northern side of the Aleutian Islands (especially in the lee of the islands) appears to be more productive. Combined with evidence of coincident changes in many ecosystem parameters near Samalga Pass, it is hypothesized that Samalga Pass forms a physical and biogeographic boundary between the eastern and central Aleutian marine ecosystems.

In this study we examine the auditory capabilities of the sea otter (Enhydra lutris), an amphibious marine mammal that remains virtually unstudied with respect to its sensory biology. We trained an adult male sea otter to perform a psychophysical task in an acoustic chamber and at an underwater apparatus. Aerial and underwater audiograms were constructed from detection thresholds for narrowband signals measured in quiet conditions at frequencies from 0.125-40 kHz. Aerial hearing thresholds were also measured in the presence of octave-band masking noise centered at eight signal frequencies (0.25-22.6 kHz) so that critical ratios could be determined. The aerial audiogram of the sea otter resembled that of sea lions and showed a reduction in low-frequency sensitivity relative to terrestrial mustelids. Best sensitivity was -1 dB re 20 µPa at 8 kHz. Under water, hearing sensitivity was significantly reduced when compared to sea lions and other pinniped species, demonstrating that sea otter hearing is primarily adapted to receive airborne sounds. Critical ratios were more than 10 dB higher than those measured for pinnipeds, suggesting that sea otters are less efficient than other marine carnivores at extracting acoustic signals from background noise, especially at frequencies below 2 kHz.

Detection and characterization of diverse coccidian protozoa shed by California sea lions

Large body size, carnivory, and endothermic costs lead to exceptionally high caloric demands in many mammalian predators. The potential impact on prey resources may be marked but is difficult to demonstrate because of the mobility, sparseness, and cryptic nature of these animals. In this study, we developed a method based on comparative bioenergetics and demographic modeling to evaluate predator effects and then used this approach to assess the potential impact of killer whales on sea otter and Steller sea lion populations in the Aleutian Islands. Daily caloric requirements of killer whales determined from allometric regressions for field metabolic rate show that an adult killer whale requires 51–59 kcal·kg−1·d−1 (2.5–2.9 W/kg). Caloric values of prey items determined by bomb calorimetry ranged from 41 630 kcal for an adult female sea otter to sequentially higher values for male otters, sea lion pups, and adult Steller sea lions. Integrating these results with demographic changes in marine mammal populations show that fewer than 40 killer whales could have caused the recent Steller sea lion decline in the Aleutian archipelago; a pod of five individuals could account for the decline in sea otters and the continued suppression of sea lions. The collapse of the historical prey base of killer whales due to human whaling may have contributed to a sequential dietary switch from high to low caloric value prey, thereby initiating these declines. This study demonstrates that a combined physiological–demographic approach increases our ability to critically evaluate the potential impact of a predator on community structure and enables us to define underlying mechanisms that drive or constrain top-down forcing in dynamic ecosystems.

The importance of food availability (bottom-up control) vs. predation (top-down control) in affecting population dynamics of individual species and the structure of marine communities and ecosystems is in most cases poorly known, but vigorously debated. This debate has recently focused on the dramatic declines of populations of four species of marine mammals in Alaska (Estes et al. 1998, Springer et al. 2003, 2008; Williams et al. 2004, Fritz and Hinckley 2005, Trites et al. 2007, Wade et al. 2007). Between the early 1970s and late 1990s, the abundance of harbor seals (Phoca vitulina), Steller sea lions (Eumetopias jubatus), and sea otters (Enhydra lutris) collapsed sequentially by 80%–90% throughout southwest Alaska—the Aleutian Islands, Bering Sea, and western Gulf of Alaska. The major portion of each collapse occurred over short intervals of about 10 yr. Harbor seals have since begun a slow recovery in at least a part of this range (Small et al. 2003); sea lions have variously increased somewhat, remained stable, or continued to decline (NMFS 2007); and sea otters were still declining in most areas through the early 2000s (Doroff et al. 2003, Estes et al. 2005, J. Estes1). Across that entire span of years, a fourth species, the northern fur seal (Callorhinus ursinus) on the Pribilof Islands in the Bering Sea, has experienced a less precipitous, but continuing, and now concerning, decline—for example, pup production, the index of total abundance, has fallen by 26% since 2002 and their abundance is just 24% of the peak in 1955 (Trites and Larkin 1989, Towell and Fowler 2006). Three principal hypotheses have been proposed to explain these collapses and the lack of significant recovery: direct mortality from human activities, nutritional limitation, and predation. Direct mortality of sea lions was caused primarily by commercial harvests, bycatch in commercial fisheries, and legal and illegal shooting (Atkinson et al. 2008): direct mortality has not been invoked as a cause of the declines of any of the other species in the region since the mid 1970s or earlier. The cause of purported nutritional limitation of pinnipeds is thought to be climate change or commercial fisheries, or both, which altered the availability of various species of

Over the last twenty-five years, archaeologists have compiled a substantial zooarchaeological record of pinnipeds on the Washington, Oregon, and California coasts. Archaeological studies have also shown that patterns of pinniped species abundance and distribution in the late twentieth century do not necessarily reflect conditions in the ancient past, while recent biological studies demonstrate range expansion of some species subsequent to the Marine Mammal Protection Act of 1972. Archaeologists disagree over what the zooarchaeological record reveals about Native American hunting during pre-contact times. Did pinnipeds regularly use mainland breeding areas prior to human use? Did Native Americans club pinnipeds on their terrestrial breeding areas or use watercraft and specialized technologies to hunt at sea? Did Native American hunting cause changes in pinniped or sea otter behavior and migration patterns? This chapter explores Native American use of seals, sea lions, and sea otters in the estuaries of northern Oregon and southern Washington.

Marine Wildlife Rescue and Rehabilitation Centers (MWRRCs) are crucial for the rehabilitation of endangered marine species, such as penguins, sea turtles, sea lions, and/or sea otters. In Chile, rescue of marine fauna is coordinated by the National Fisheries and Aquaculture Service (SERNAPESCA). This organization is responsible for assisting stranded animals and transporting them to 6 of the 13 MWRRCs that exist throughout the 6,435 km coastline of the country. Stranding events were analyzed for two species of pinnipeds (Otaria flavescens and Arctocephalus australis), two species of penguins (Spheniscus humboldti and Spheniscus magellanicus), two species of chelonians (Chelonia mydas and Lepidochelys olivacea), and one species of sea otter (Lontra felina) found stranded at the coast of Chile during 2009-2019 period. Success in post-rehabilitation release of individuals was also examined. A total of 2,818 stranding events were recorded with a total of 3,198 stranded animals, corresponding to O. flavescens (52.9%), S. humboldti (20.4%), S. magellanicus (17.9%) and L. olivacea (4.3%). Of the 3,198 stranded animals, 721 specimens were referred to MWRRC, and only 136 were released post-rehabilitation. This shows an18.8% success rate in the release of marine fauna species post-rehabilitated in rescue centers after their stranding. It is necessary to improve coordination between SERNAPESCA and MWRRCs in Chile to improve the release rate and to increase the number of MWRRCs to recover endangered marine species that strand along the country’s coast.

Review of Human Impacts on Seals, Sea Lions, and Sea Otters: Integrating Archaeology and Ecology of the Northeast Pacific. Todd J. Braje and Torben C. Rick, editors. 2011. University of California Press, Berkeley. Pp. 328. $65.00 (hardcover). ISBN 9780520267268.

Sea otters off the Alaskan coast play a pivotal role in marine ecosystems: By dining on sea urchins, the animals help preserve kelp forests that feed a range of species, from barnacles to bald eagles. Now, on page 473, a team of ecologists has documented a 90% crash in sea otter populations in western Alaska9s Aleutian Islands since 1990, with devastating effects on kelp forests. The reason for the crash, the researchers believe, is that killer whales, never before known to eat sea otters, appear to be snacking on the creatures, apparently because their usual food source--seals and sea lions--is declining.

Harmful algal blooms (HABs), commonly known as “red tides,” are documented in almost every coastal region of the world. Over the past decade, these toxic blooms appear to have increased in number, magnitude, and seasonal duration, potentially due to the spread of toxic algal species to new areas, eutrophication caused by human development of coastal areas, and global climate change Some of the microscopic, single-celled algae that constitute the base of the marine food chain produce the potent toxins found in these harmful blooms. These toxins can accumulate in fish, shellfish, and other marine organisms, and move through the food chain, at times affecting the highest consumers, including marine mammals and humans. Humans are usually well-protected by federal and state monitoring programs that detect the toxins at an early stage and restrict the harvest or sale of the toxic seafood. However, marine mammal health is not protected by the same routine monitoring programs. Recent evidence has indicated that mass mortalities and strandings of whales, dolphins, sea lions, manatees, and sea otters, in some cases, may be caused by their exposure to marine biotoxins.