Otaria Research Articles

Stable isotope analysis reveals pelagic foraging by the Southern sea lion in central Chile

The diet of Southern sea lion Otaria flavescens is poorly known along the coast of central Chile (32°–39°S), where a population of about 17,300 individuals occurs, in an ecosystem that sustains one of the world's most important fishing industries. The primary objective of this study was to reconstruct the diet and estimate Trophic Positions (TPs) of sea lions and their prey off central Chile using stable isotopes ( δ 13C and δ 15N). Our results showed that the diet of sea lions is primarily composed of pelagic prey, with the jack mackerel Trachurus murphyi as the principal prey item in the diet of sea lion (1–99th percentile: 20–66%), while demersal prey accounted for only 0–2.8%. We also found regional differences on the relative contribution of prey to the diet of sea lions. Animals that were sampled close to major fishing areas showed an increase in the relative contribution of jack mackerel to the diet as opposed to animals sampled away from these areas that displayed a relatively more heterogeneous diet. Trophic Positions (TPs) of sea lions prey items ranged between 3.39 for jack mackerel and 4.48 for pink cusk-eel ( Genypterus blacodes). The TP for sea lions was 4.57. Hence, our results showed a community composed by at least 5 trophic levels, with sea lion as the top predator. In summary, our study demonstrates that the Southern sea lion is displaying pelagic foraging off central Chile. We highlight the necessity of conducting further research on the trophic ecology and diving behavior of Southern sea lion to obtain a better understanding of their role as top predator.

Intra-sexual female agonistic behaviour of the South American sea lion (Otaria flavescens) in two colonies with different breeding substrates

Female agonistic behaviour during pregnancy and lactation is common in several pinnipeds and has been associated to pup or territory defence. Previous studies on female agonistic behaviour in pinniped breeding groups have not usually considered the number of females per breeding group, which could influence the degree of aggressiveness. We compared female agonistic behaviour (open-mouth displays and bites) within two colonies with different breeding substrates (homogeneous, Punta Norte; heterogeneous, Piramide) of South American sea lions using two methods: weighted means and general linear models. We found that both aggressive interaction rates were significantly affected by female density, which accounted for a greater proportion on the variability in bite rates than in open-mouth rates. Controlling for the number of females, we found with both methods that open-mouth rates were higher than bite rates within the Piramide colony; however, no differences were found within the Punta Norte colony. In Piramide, open-mouth rates could be used more often as threats to minimise the chances of more severe aggressions. The conclusion is that females vary their use of agonistic interactions in relation to their density in the colony with heterogeneous substrate, which may be related to the presence of limited numbers of tide pools that heightens competition for thermoregulatory resources.

Massive death of pinnipeds 1200 years ago: Taphonomic history of the “Lobos site” (Golfo Nuevo, Patagonia, Argentina)

The Lobos site was discovered in October 2000, as a result of the exposure of a stratified set of pinniped bone remains. These remains correspond to the Otaria flavescens species and were found on the walls of a ravine. Research included several samplings; an excavation according to archaeological methodology, and taphonomic, biological, archaeological, geological, and forensic studies. These studies indicate the occurrence of a massive natural death of a pinniped colony 1200 years 14C BP. Associated pupal cases remains suggest that the episode took place in summer and that the pinniped bodies were buried by mass wasting events a month later. Some of the bones were afterwards redeposited by water.

Operational interaction between South American sea lions Otaria flavescens and artisanal (small-scale) fishing in Chile: Results from interview surveys and on-board observations

A longstanding competition for fishery resources has existed in Chile between the South American sea lion ( Otaria flavescens) and artisanal (small-scale) fisheries. This competition is viewed as a conflict by the fishermen because sea lions prey on fish caught in their fishing gear, often causing its damage. The objective of the study was to describe the interaction between sea lions and fishermen, and to evaluate the effects of operational interference caused by sea lions on their artisanal fishery. Descriptions of the interactions cited were made during 69 observational trips on fishing vessels plus interviews of 384 fishermen. Evaluation of the interactions was based on minimum and maximum scenarios. Almost all the artisanal fishermen complained of frequent problems with sea lions, however, such interactions were observed in 14.5% of the observer trips on fishing vessels. The results showed that loss of catch due to sea lions, varied between 1.83 and 21.1% of the CPUE (under minimal) and from 1.98 to 33.8% (under maximal) interactive scenarios. Although proportions of interactive fishing events and number of sea lions were different between the locations studied, CPUE per fishing gear did not differ significantly between interactive and non-interactive fishing trips among the areas. Also, no significant relation was found between the numbers of sea lions interacting during the fishing trip and the CPUE. Our results suggest that sea lions do not produce a significant effect on variations in the CPUE obtained by artisanal fishermen. Nevertheless, these findings must be confirmed with more intensive monitoring. A cooperative design of a co-management plan, which considers biological, social, and economical features will contribute to make consensus within the stakeholders looking for management options with the aim of reducing the conflicts.

Geographic distribution and diversity of mitochondrial DNA haplotypes in South American sea lions ( Otaria flavescens) and fur seals ( Arctocephalus australis)

Genetic diversity and population structure of two species of South American pinnipeds, Otaria flavescens and Arctocephalus australis, from colonies located along the south-eastern coast of South America, were analysed using mitochondrial DNA haplotypes and compared with two populations of these species from the Pacific coast. A 445 base-pair segment, that included the tRNA-Glu gene (31 bp) and the adjacent cytochrome b gene (414 bp), was amplified using the polymerase chain reaction and sequenced directly. O. flavescens and A. australis showed six and seven haplotypes with 12 and 20 polymorphic sites, respectively. In the Atlantic Ocean there was an individual of A. australis that showed an haplotype that was highly divergent from the others. If this haplotype is excluded, the pattern of haplotype differentiation obtained for both species indicated a possible bottleneck that would have occurred 110,000 years ago, which also affected other pinnipeds. Colonies of the Atlantic and the Pacific did not share haplotypes. This result, based on a limited number of samples for the comparisons between oceans, suggests that populations from both oceans correspond to different evolutionarily significant units. O. flavescens on the Atlantic coast shows two clusters of breeding colonies in Uruguay and Patagonia, separated by a thousand kilometres. Colonies within clusters did not show significant differences in haplotype frequencies, but the difference between the clusters was significant, suggesting that they correspond to different conservation stocks.

Sex-specific foraging strategies and resource partitioning in the southern elephant seal (Mirounga leonina)

The evolution of resource specializations is poorly understood, especially in marine systems. The southern elephant seal (Mirounga leonina) is the largest of the phocid seals, sexually dimorphic, and thought to prey predominantly on fish and squid. We collected vibrissae from male and female southern elephant seals, and assessed stable C and N isotope ratios along the length of the vibrissae. Given that whiskers grow slowly, this sampling strategy reflects any variation in feeding behaviour over a period of time. We found that isotopic variation among females was relatively small, and that the apparent prey choice and trophic level of females was different from that for males. Further, males showed a very broad range of trophic/prey choice positions, grouped into several clusters, and this included isotopic values too low to match a broad range of potential fish and cephalopod prey tested. One of these clusters overlapped with data for South American sea lions (Otaria flavescens), which were measured for comparison. Both male southern elephant seals and southern sea lions forage over the continental shelf, providing the potential for competition. We discuss the possibility that individual southern elephant seals are pursuing specialist foraging strategies to avoid competition, both with one another, and with the South American sea lions that breed nearby.

Changes in diet and maternal attendance of South American sea lions indicate changes in the marine environment and prey abundance

Behavioural observations were made of South American sea lions Otaria flavescens in Peru to determine whether changes in their diet and maternal attendance patterns reflected physical changes in the marine environment and alterations in the abundance and distribution of prey. The study was conducted during the breeding season between 1998 and 2002, which was a period that encompassed a strong El Nino (1997 to 1998) and a moderate La Nina (1999 to 2001). Observations revealed strong linkages between maternal attendance patterns and the abundance of prey and oceanographic features close to the rookeries. Acute prey shortage during El Nino resulted in females increasing the length of their foraging trips and decreasing the time they spent onshore with their pups. In contrast, shorter times at sea and longer times onshore were observed during the favourable conditions of La Nina when preferred prey (anchovy and squat lobster) were more abun- dant near the rookeries. Pup mortalities increased when females spent more time at sea searching for prey and did not return frequently enough to nurse their pups. A larger diversity of prey species (particularly of demersal fishes) was consumed during El Nino when anchovy and lobster were less available. Females appeared to adjust their diets and maternal attendance patterns in response to annual changes in the abundance and distribution of prey. These observations suggested that diet and maternal responses reflect interannual fluctuations of the unpredictable Peruvian upwelling ecosystem, and implied that South American sea lions may be good indicators of relative changes in the distribution and abundance of marine resources.

Purification and characterization of chitinases from Clostridium sp. E-16 isolated from the intestinal tract of the South American sea lion (Otaria flavescens)

This study was undertaken to examine the properties of chitinases purified from Clostridium sp. E-16, an intestinal bacterium of the South American sea lion (Otaria flavescens). We also elucidated the taxonomic status of this bacterium to better understand the role of intestinal anaerobic bacteria in marine animals. Two chitinases were purified with ammonium sulfate precipitation, affinity chromatography and preparative electrophoresis from culture supernatant fluid from Clostridium sp. E-16. Molecular mass was estimated to be 77 kDa for chitinase 1 and 98 kDa for chitinase 2 by SDS-PAGE. Optimum pH of both purified chitinases was between 5.0 and 7.0. Chitinase 1 was inhibited with Cu(2+), Fe(2+), Hg(2+) and Zn(2+), while chitinase 2 was inhibited with Fe(2+). Phylogenetic analysis using 16S ribosomal DNA (rDNA) sequences and phenotypic characterization revealed that Clostridium sp. E-16 was closely related to Clostridium baratii. It is likely that chitinases from C. baratii or a C. baratii-like bacterium play an important role in degradation of chitin in the intestinal tract of the South American sea lion and in marine environments. This is the first report of chitinase purification and characterization from a marine Clostridium strain.

Morphologic, Histochemical, and Immunohistochemical Characterization of Tracheobronchial Respiratory Glands in South American Sea Lion Otaria flavescens (Pinnipedia, Mammalia)

Tracheobronchial airways from Otaria flavescens routinely were processed for histological, histochemical, and immunohistochemical methods to study individual mucusproducing cells (IMPC and submucosaI glands. The IMPCs were interspersed in the epithelium of the trachea. They showed neutral and weakly acidic and carboxylated glycoconjugates. Only IMPCs in the trachea secrete sialylated glycoconjugates. Submucosal glands were formed by 1) collecting duct lined by a ciliated pseudostratified to simple columnar epithelium without cilias. They showed neutral and carboxylic glycoconjugates. 2) Glandular sinus, a branched secretory unit in which the lining epithelium showed two possible secretory mechanisms: merocrine type of neutral glycoconjugates and apocrine type of sialylated and sulphated or carboxylated glycoconjugates, with positive reaction for proteins. 3) Glandular branched tubules emerging from glandular sinuses were lined by columnar cells with an apical cytoplasm containing neutral and carboxylated glycoconjugates. Myoepithelial cells surrounded both glandular sinuses and tubules. Cytokeratin 7 was specific for glandular sinus and for a few ciliated cells of the trachea, whereas cytokeratin 19 was observed in glandular sinuses, glandular tubules, and in some tracheal cells. These results showed that the secretory cells of glandular sinuses and tubular glands are well differentiated and that a possible common origin may be inferred. (The J Histotechnol 29:29, 2006)Submitted February 16, 2005; accepted with revisions August 12, 2005

SPECTRAL SENSITIVITY IN TWO SPECIES OF PINNIPEDS (PHOCA VITULINA AND OTARIA FLAVESCENS)

AbstractSpectral sensitivity was measured in air in the light adapted state in two harbor seals and a South American sea lion using a behavioral training technique. Increment thresholds were determined in a spectral range from 390 nm to 670 nm in a simultaneous two‐choice discrimination task. The spectral sensitivity curves show two maxima in sensitivity, one main peak with a maximum around 500 nm in the harbor seal and around 550 nm in the South American sea lion, and a second, smaller peak with a maximum in the range of 410 nm in both species. The broad shape and the position of the maximum of the spectral sensitivity curve of the harbor seals suggests that even under photopic conditions both rods and cones are contributing to the measurements since harbor seals possess only one cone type. The maximum sensitivity in the green part of the spectrum may indicate an adaptation to a specific underwater environment.

Antipredator defenses in birds and mammals

In nature, the ability to defend against predators is fundamental to an animal's survival. From the giraffes that rely on their spotted coats to blend into the patchy light of their woodland habitats to the South American sea lions that pile themselves in heaps to ward off the killer whales that prey on them in the shallow surf, defense strategies in the animal kingdom are seemingly innumerable. In Antipredator Defenses in Birds and Mammals, Tim Caro ambitiously synthesizes predator defenses in birds and mammals and integrates all functional and evolutionary perspectives on antipredator defenses that have developed over the last century. Structured chronologically along a hypothetical sequence of predation - Caro evokes a gazelle fawn desperate to survive a cheetah attack to illustrate the continuum of the evolution of antipredator defenses - Antipredator Defenses in Birds and Mammals considers the defenses that prey use to avoid detection by predators; the benefits of living in groups; morphological and behavioral defenses in individuals and groups; and, finally, flight and adaptations of last resort. Antipredator Defenses in Birds and Mammals will be of interest to both specialists and general readers interested in ecological issues.

Composition and seasonal variation in the diet of the South American sea lion (<i>Otaria flavescens</i>) from Quequén, Argentina

Diet seasonality in South American sea lions, Otaria flavescens , was studied using 252 scats from a male-exclusive haul-out site located in Puerto Quequen (38°37'S, 58°50'W) Argentina during 2001. Prey species were identified from hard remains and their relative importance was assessed considering frequency of occurrence, abundance and biomass. The main prey consumed by sea lions were teleost fish (20 species), followed by cephalopods (four species) and crustaceans. The raneya, Raneya fluminensis , was the most frequent prey year-round, and the most abundant in autumn and winter. The Argentine anchovy, Engraulis anchoita , and the stripped weakfish, Cynoscion guatucupa , were the most abundant prey in spring and summer, respectively. Seasonal differences in the sizes consumed were only found for C. guatucupa . The sea lions from Puerto Quequen showed a diverse diet, mainly feeding on demersal and pelagic prey. Our study fills a geographical gap on the seasonal variation of the diet of South American sea lions. Two main patterns emerged from studies conducted along the geographic range of the species: (1) O. flavescens is a generalist and opportunist feeder, preying on a wide range of species; mainly those of pelagic and demersal habits, (2) South American sea lions change the frequency and/or specific composition of their diet seasonally, possibly as a result of changes in the relative availability of each species in the environment.

Interactions between South American sea lions Otaria flavescens (Shaw) and salmon farms in southern Chile

By means of surveys in 48 salmon farms in Chile, and the analysis of fish mortality in 23, the results showed that attacks by the South American sea lion, Otaria flavescens, were periodical at a daily and seasonal scale, and because of their natural nocturnal feeding behaviour, were more frequent at night and in fall–winter seasons. The attacks varied markedly between the farms studied. No relation was found between the intensity of attacks, the distance to the nearest colony of sea lions and the population in the colony. Differences found between farms could be because of the different protective devices used, namely anti-predator nets, acoustic harassment devices (AHDs) and fibreglass models of killer whales, and the way in which they were used. Of these devices, only the anti-predator net achieved a permanent reduction in sea lion attacks. Both AHDs and fibreglass killer whales were inefficient in the short term.

Multispecies modelling of some components of the marine community of northern and central Patagonia, Argentina

Using a bioenergetic and allometric approach, we developed multispecies trophodynamic models of the marine community of northern and central Patagonia in the southwestern South Atlantic Ocean that included hake (Merluccius hubbsi), squid (Illex argentinus), anchovy (Engraulis anchoita), and South American sea lions (Otaria flavescens). We used these to explore the effects of model structure and parameter uncertainty on predictions of the effects of different management regimes using continuation and bifurcation analysis. We considered five different functional responses and used the Akaike Information Criterion for model selection. The best models involved laissez-faire Holling Type III-shaped functional responses and the worst one corresponded to the Ecosim form. These models showed many similar behaviours but also showed marked differences in some exploitation scenarios. This suggests that using a single model structure as the basis for managing these stocks could lead to misleading, and potentially dangerous, conclusions.

Generalized linear models applied to stranding data of South American sea lions (Otaria flavescens) and South American fur seals (Arctocephalus australis) in southern Brazil

Monthly strandings of South American sea lions, Otaria flavescens, and South American fur seals, Arctocephalus australis, collected between 1993 and 2002 along the coastline of Rio Grande do Sul, Brazil, are analyzed with generalized linear models (GLM) to describe spatial and temporal stranding patterns and to estimate the annual number of stranded animals by species. Results indicate a strong seasonal pattern for both species with maximum average number of strandings in September and minimum in January. While year effects are not significant, differences between regions (north or south of the Patos Lagoon mouth) are. Estimated numbers of stranded sea lions and seals in a typical year are 115, with 95% confidence interval (76; 160) and 95, with 95% confidence interval (48; 180), respectively. GLMs proved to be a very useful tool to examine the influence of time and space on strandings in a statistically rigorous framework.

Foraging patterns of breeding Dolphin GullsLarus scoresbiiat Punta Tombo, Argentina

The Dolphin GullLarus scoresbiiis a little‐known, rare species endemic to southern South America. Knowledge of its feeding ecology is essential for development of management and conservation strategies. To obtain information on their use of food resources and on the frequency and duration of their foraging trips, we followed seven individuals by radiotelemetry during the breeding season of 2002 at the Punta Tombo Reserve, Argentina. In 99% of mapped locations (n = 4069) the Gulls were within 2.4 km of their colony. Dolphin Gulls foraged mostly at the colonies of three other species, feeding on Magellanic PenguinSpheniscus magellanicusand Imperial CormorantPhalacrocorax atricepsregurgitates and on Southern Sea LionOtaria flavescensfaeces. The sea lion colony was the most frequently visited foraging area, accounting for 64% of the total (n = 260 trips). A similar trend was observed during both the incubation (60%,n = 38 trips) and the chick (64%,n = 40 trips) stages. The mean number of trips per day was 3.8 (range = 3–5), with a mean duration of 123 min (sd = ±27). Trip duration differed between foraging areas, being significantly longer at the sea lion than at the penguin and cormorant colonies. The small foraging range given by its particular feeding strategy suggests that Dolphin Gulls, in contrast to most other seabirds that range over large expanses of ocean in search of food, may be effectively conserved within protected areas during the breeding season.

A new shot at a release mechanism for devices attached to free-living animals

Detailed studies of the behavior and location of free-ranging animals can be considerably enhanced with the use of animal-mounted devices. A few devices, such as data loggers, have to be recovered to access the data, whereas satellite tags or radiocollars often are left on the animal after the study period. Recovery of devices, which usually necessitates animal recapture, can be problematic, especially in larger species. This paper presents a new, non-electronic release mechanism, requiring no power source on the animal, that was successfully tested on South American sea lions (Otaria flavescens) in Argentina during the 2003–2004 austral summer. The system has potential for many larger terrestrial or aquatic animals.

The effects of prey availability on pup mortality and the timing of birth of South American sea lions (Otaria flavescens) in Peru

AbstractPup mortality and the timing of birth of South American sea lions Otaria flavescens were investigated to determine the possible relationship between fluctuations in prey availability in the Peruvian upwelling ecosystem and current and future reproductive success of sea lions during six consecutive breeding seasons. Our study from 1997 to 2002 encompassed the strongest El Niño on record and one La Niña event. Pup mortality ranged from 13% before El Niño to 100% during El Niño, and was negatively correlated with prey availability. Abortions were also more frequent when prey availability was low. However, pup mortality remained high following El Niño due to the punctuated short‐term effects it had on population dynamics and subsequent maternal behaviour. Births occurred later in the season after years of low food availability and earlier following years of high food availability. The peak of pupping occurred around the peak of mortality in all years, and may have been the product of intensive competition between bulls at the peak of the breeding season. The stronger and more frequent El Niños that appear to be occurring along the Peruvian coast may produce significant stochastic changes in future births and pup mortality, which may place the vulnerable South American sea lion population in Peru at greater risk.

Recovery of the South American sea lion (Otaria flavescens) population in northern Patagonia

The size of and trend in the South American sea lion (Otaria flavescens) population located in northern Patagonia were estimated and changes in the distribution, size, and structure of individual sites were analyzed during the period 1983–2002. Total counts were made during the reproductive season. Regression models were used to analyze the trend. Pups represented around 40% of the animals counted. The annual rates of change for pups and nonpups were not significantly different (p > 0.05, n = 7), although some rookeries showed higher rates of change for pups than for nonpups. Pup numbers have been increasing at the rate of 3.4% per year at the oldest rookeries, but the rate of increase was higher at new rookeries. Using Bayes' methods, the precision of the estimates and the contribution to the abundance of each rookery produced an alternative estimate of the trend in pup numbers in 5.7%. The key in the recovery of this population includes higher survival rates of juveniles combined with increased available habitat for newly reproducing individuals. This process led to the occupancy of new areas for hauling out and breeding. This hypothesis could explain the higher rates of increase in pups in peripheral areas while reproductive rates remain unchanged.

Uncinaria hamiltoni (Nematoda: Ancylostomatidae) in South American sea lions, Otaria flavescens, from northern Patagonia, Argentina.

Thirty-one South American sea lion pups (Otaria flavescens) found dead in Punta León, Argentina, during the summer of 2002, were examined for hookworms (Uncinaria hamiltoni). Parasite parameters were analyzed in 2 locations of the rookery, i.e., a traditional, well-structured breeding area and an expanding area with juveniles and a lax social structure. Prevalence of hookworms was 50% in both localities, and no difference was observed in prevalence between pup sexes (P > 0.05). Hookworms were concentrated in the small intestine. Transmammary transmission is assumed because only adult hookworms were found in the pups. The mean intensity of hookworms per pup was 135; the mean intensity in females (92.78) was significantly different (P < 0.05) from that of males (230.25). No difference (P > 0.05) in intensity was found between the 2 breeding areas, although prevalence was higher in the traditional breeding area than in the other area. Location was the only factor affecting hookworm prevalence (P log-linear model: 0.9552; chi2: 1.5629). No apparent trend between body condition and intensity of hookworms was observed.