Sea Lion Population Research Articles

Nitrogen transport from sea to land by a threatened and declining population of Australian sea lions (Neophoca cinerea) on Kangaroo Island, South Australia

Australian sea lions consume prey in highly productive foraging grounds and defaecate nutrients on land. The resident population of 1100 Australian sea lions contributes 3800 (±80) kg N year–1 into Seal Bay Conservation Park, Kangaroo Island, South Australia. If this population were to decline in abundance the nitrogen availability and coastal productivity of Kangaroo Island may be reduced.

Is management limiting the recovery of the New Zealand sea lion Phocarctos hookeri?

Pup production of the ‘nationally critical’ New Zealand sea lion Phocarctos hookeri has declined by 48 % since 1998, with fisheries bycatch playing a role in this decline. Current management of the sea lion population involves, amongst other measures, the setting of an annual bycatch limit based on Bayesian modelling of the sea lion population and fisheries information. Success of management scenarios is determined against two criteria, both of which involve keeping the sea lion population at or above 90 % of a modelled carrying capacity (6,987 mature individuals). Due to a lack of information on the pre-sealing abundance of the New Zealand sea lion, it is unclear whether the modelled carrying capacity represents a cap on sea lion recovery. Here, I use published estimates of genetic diversity based on microsatellite loci (expected heterozygosity, He) of the New Zealand sea lion and other otariid species to estimate historical effective population size (Ne). I then use existing knowledge of the ratio of Ne to census population size (NC) to determine a historical census population size of these species. Genetical estimates of historical Ne suggest that NZ sea lions were considerably more abundant (>68,000 individuals) historically than the current population estimate (11,855 animals). Importantly, the genetical estimate of historical population size suggests that the modelled carrying capacity (6,987 mature sea lions) is likely an underestimation of recovery potential of the species; hence, current management maybe limiting the recovery of the species.

The reproductive success of the Steller sea lion Eumetopias jubatus (Schreber, 1776) on Brat Chirpoev and Medny islands in 2001–2011

The reproductive success of the Steller sea lion was estimated based on monitoring the breeding performance of known-age branded females on Brat Chirpoev and Medny islands in 2001–2011. First pup birth occurred at 4 years of age, but the majority of females gave birth to their first pup at the age of 5 years on both islands. The period of the highest realization of female initial reproductive capacity on Medny Island was 4–5 years shorter compared to Brat Chirpoev Island. The differences were caused by a lower number of middle-aged females and a higher proportion of non-pregnant females on Medny Island. The low reproductive success of females is probably the main reason for the depression of the Steller sea lion population on Medny Island.

The recovery process of a population is not always the same: The case of Otaria flavescens

Populations of the South American sea lion (Otaria flavescens) were decimated throughout its range along the Atlantic coast. Responses to this decline have been different in different parts of the species' distribution range. Some stocks are still decreasing, some remain stable, and some are recovering slowly. In the Southwestern Atlantic, sea lion populations are now increasing. However, 50 years after the cessation of hunting these populations have not recovered to the levels they had before exploitation, with the recovery process occurring at the same time as increasing development of human coastal activities. The aims of this study were to present recent information on abundance and trends in the southern Patagonian population of sea lions and to test the hypothesis of population expansion with a particular recolonization process. Results showed that there was an increase in the number of sea lions in all colonies and a change in the social composition of nine colonies, but no new breeding colonies were found. The population trajectory of O. flavescens from southern Patagonia was similar to that observed in the rest of the South Atlantic populations, but the recovery and recolonization processes are still in progress. Here we discuss possible explanations of which factors could have delayed the recovery within the Southwestern Atlantic stocks.

Current bycatch levels in Auckland Islands trawl fisheries unlikely to be driving New Zealand sea lion (Phocarctos hookeri)population decline

Abstract New Zealand sea lions are incidentally killed in trawl fisheries around the Auckland Islands with most mortality having been attributed to the Auckland Islands squid fishery. Fishery management measures include the establishment of a 12 nautical mile marine reserve around the Auckland Islands excluding all fishing within that range, the instigation of mortality limits that can trigger spatio‐temporal closures, and widespread use of a ‘Sea Lion Excluder Device’ (SLED) that allows sea lions to escape from a trawl net. Although there has been controversy regarding SLED efficacy, the evidence from numerous research trials and assessments is that SLEDs have contributed to reduced rates of sea lion bycatch in the Auckland Islands squid fishery. Population viability analysis (PVA) modelling, using VORTEX, of the Auckland Islands New Zealand sea lion population was undertaken to ascertain if the reported levels of bycatch of sea lions in trawl fisheries around the Auckland Islands are sustainable following substantial and effective mitigation to reduce bycatch, particularly in the Auckland Islands squid fishery. Modelling indicated slow population growth of the Auckland Islands New Zealand sea lion population with current bycatch estimates from all Auckland Islands trawl fisheries. Additional modelling seeking explanations for observed population declines over the last decade indicated that epizootic events that reduce pup production may have a greater impact on population growth, especially if these events are more frequent than previously assumed. Modelling results suggest that sea lion bycatch in the squid fishery and other trawl fisheries around the Auckland Islands is unlikely to be currently having a significant impact on the Auckland Islands New Zealand sea lion population. Therefore, resources should be directed towards other hypotheses for any continued sea lion population decline as well as continued refinement of mitigation techniques to reduce fisheries‐related mortality. Copyright © 2014 John Wiley & Sons, Ltd.

Competition influence in the segregation of the trophic niche of otariids: a case study using isotopic Bayesian mixing models in Galapagos pinnipeds.

The feeding success of predators is associated with the competition level for resources, and, thus, sympatric species are exposed to a potential trophic overlap. Isotopic Bayesian mixing models should provide a better understanding of the contribution of preys to the diet of predators and the feeding behavior of a species over time. The carbon and nitrogen isotopic signatures from pup hair samples of 93 Galapagos sea lions and 48 Galapagos fur seals collected between 2003 and 2009 in different regions (east and west) of the archipelago were analyzed. A PDZ Europa ANCA-GSL elemental analyzer interfaced with a PDZ Europa 20-20 continuous flow gas source mass spectrometer was employed. Bayesian models, SIAR and SIBER, were used to estimate the contribution of prey to the diet of predators, the niche breadth, and the trophic overlap level between the populations. Statistical differences in the isotopic values of both predators were observed over the time. The mixing model determined that Galapagos fur seals had a primarily teutophagous diet, whereas the Galapagos sea lions fed exclusively on fish in both regions of the archipelago. The SIBER analysis showed differences in the trophic niche between the two sea lion populations, with the western rookery of the Galapagos sea lion being the population with the largest trophic niche area. A trophic niche partitioning between Galapagos fur seals and Galapagos sea lions in the west of the archipelago is suggested by our results. At intraspecific level, the western population of the Galapagos sea lion (ZwW) showed higher trophic breadth than the eastern population, a strategy adopted by the ZwW to decrease the interspecific competition levels in the western region.

Giardia duodenalis and Cryptosporidium occurrence in Australian sea lions (Neophoca cinerea) exposed to varied levels of human interaction.

Giardia and Cryptosporidium are amongst the most common protozoan parasites identified as causing enteric disease in pinnipeds. A number of Giardia assemblages and Cryptosporidium species and genotypes are common in humans and terrestrial mammals and have also been identified in marine mammals. To investigate the occurrence of these parasites in an endangered marine mammal, the Australian sea lion (Neophoca cinerea), genomic DNA was extracted from faecal samples collected from wild populations (n = 271) in Southern and Western Australia and three Australian captive populations (n = 19). These were screened using PCR targeting the 18S rRNA of Giardia and Cryptosporidium. Giardia duodenalis was detected in 28 wild sea lions and in seven captive individuals. Successful sequencing of the 18S rRNA gene assigned 27 Giardia isolates to assemblage B and one to assemblage A, both assemblages commonly found in humans. Subsequent screening at the gdh and β-giardin loci resulted in amplification of only one of the 35 18S rRNA positive samples at the β-giardin locus. Sequencing at the β-giardin locus assigned the assemblage B 18S rRNA confirmed isolate to assemblage AI. The geographic distribution of sea lion populations sampled in relation to human settlements indicated that Giardia presence in sea lions was highest in populations less than 25 km from humans. Cryptosporidium was not detected by PCR screening in either wild colonies or captive sea lion populations. These data suggest that the presence of G. duodenalis in the endangered Australian sea lion is likely the result of dispersal from human sources. Multilocus molecular analyses are essential for the determination of G. duodenalis assemblages and subsequent inferences on transmission routes to endangered marine mammal populations.

PREVALENCE AND CHARACTERIZATION OFSALMONELLASHED BY CAPTIVE AND FREE-RANGE CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS) FROM A REHABILITATION CENTER AND THREE STATE RESERVES ALONG THE CALIFORNIA COAST

Salmonella is a genus of zoonotic bacteria that can infect a variety of animals, and may cause gastrointestinal disease in marine mammals. Many of the same Salmonella serotypes are shed by California sea lions (Zalophus californianus) and humans, which poses transmission questions and public health concerns. In this study, 454 fecal samples from three free-ranging California sea lion populations along the California coast and from animals undergoing rehabilitation at The Marine Mammal Center, Sausalito, California, were screened for the presence of Salmonella. In addition to fecal samples, 39 presumed vomitus samples were collected and processed. Of the 454 samples processed, 312 were from free-ranging sites and 142 were from rehabilitating California sea lions. A total of nine fecal samples were positive for Salmonella, yielding a 2.0% overall prevalence, as well as two presumed vomitus samples (5.1% prevalence). Salmonella shedding prevalence was 1.6% in samples collected from free-ranging animals, and 2.8% in rehabilitating animals. Four serotypes were found among the 11 positive samples, with Salmonella Enteritidis the most prevalent (64%). Antimicrobial resistance testing and pulsed-field gel electrophoresis were performed to further characterize isolates. Experiments were carried out to determine the minimal number of Salmonella required for detection by the methods used. It was determined that at least 10' colony-forming units per gram of feces was required for detection. The prevalence of Salmonella Enteritidis, and diversity of serotypes discovered is considerably different from those reported in previous studies. Overall, this study provides new insights into the epidemiology of Salmonella in California sea lions present in multi-use coastal ecosystems.

Examining the utility of fishery and survey data to detect prey removal effects on Steller sea lions (Eumetopias jubatus)

One focus of mitigation for Steller sea lion (Eumetopias jubatus) declines in Alaska has been to restrict commercial fishery activity around sea lion rookeries and haul-outs. However, a variety of statistical hypothesis tests have failed to relate sea lion population metrics to fish and fishing variables, prompting speculation that regulations may be unwarranted. In this study, we use simulation to show that standard hypothesis tests often have overstated power to detect a relationship between Steller sea lion vital rates and fish or fishing variables. The power and utility of hypothesis tests largely depend on choosing appropriate dependent and independent variables. In particular, pup counts were the most effective for diagnosing fecundity effects, and successive ratios of adult counts were the most effective for diagnosing survival effects. Fish relative abundance was the most effective independent variable, with other choices (e.g., fishery catch) often resulting in misleading inferences. We argue that Bayes factors are best suited for characterizing the relationship between fish abundance and Steller sea lion vital rates and that existing evidence does not preclude a strong relationship between sea lion fecundity and the availability of commercially harvested fish stocks.

Paleoindian pinniped exploitation in South America was driven by oceanic productivity

After centuries of pinniped exploitation, hunter-gatherers from the Atlantic coast of southern South America shifted in several occasions to other animal resources during the second half of the Holocene. The shift has been justified by the overexploitation of pinniped populations although changes in marine primary productivity may be an alternative explanation. This is a critical point, as currently large populations of sea lions and fur seals occur only in areas where marine productivity is high. This paper examines the zooarchaeological record to assess the intensity of pinniped exploitation and the stable isotope ratio of Nitrogen (δ15N) in mollusc shells collected from archaeological sites as a proxy of marine primary productivity in northern Patagonia and Tierra del Fuego during the second half of the Holocene. The results reveal major fluctuations of marine primary productivity and demonstrate that hunter-gatherers only relied intensely on pinnipeds when marine productivity was high. This finding suggests that the decline in pinniped abundance observed in the zooarchaeological record was caused by a bottom-up control of pinniped population and not by the overexploitation by hunter-gatherers.

Interannual variation in the at‐sea behavior of California sea lions (Zalophus californianus)

AbstractTo be successful, marine predators must alter their foraging behavior in response to changes in their environment. To understand the impact and severity of environmental change on a population it is necessary to first describe typical foraging patterns and identify the underlying variability that exists in foraging behavior. Therefore, we characterized the at‐sea behavior of adult female California sea lions (n = 32) over three years (2003, 2004, and 2005) using satellite transmitters and time‐depth recorders and examined how foraging behavior varied among years. In all years, sea lions traveled on average 84.7 ± 11.1 km from the rookery during foraging trips that were 3.2 ± 0.3 d. Sea lions spent 42.7% ± 1.9% of their time at sea diving and displayed short (2.2 ± 0.2 min), shallow dives (58.5 ± 8.5 m). Among individuals, there was significant variation in both dive behavior and movement patterns, which was found in all years. Among years, differences were found in trip durations, distances traveled, and some dive variables (e.g., dive duration and bottom time) as sea lions faced moderate variability in their foraging habitat (increased sea‐surface temperatures, decreased upwelling, and potential decreased prey abundance). The flexibility we found in the foraging behavior of California sea lions may be a mechanism to cope with environmental variability among years and could be linked to the continuing growth of sea lion populations.

No evidence of metabolic depression in Western Alaskan juvenile Steller sea lions (Eumetopias jubatus).

Steller sea lion (Eumetopias jubatus) populations have undergone precipitous declines through their western Alaskan range over the last four decades with the leading hypothesis to explain this decline centering around changing prey quality, quantity, or availability for this species (i.e., nutritional stress hypothesis). Under chronic conditions of reduced food intake sea lions would conserve energy by limiting energy expenditures through lowering of metabolic rate known as metabolic depression. To examine the potential for nutritional stress, resting metabolic rate (RMR) and body composition were measured in free-ranging juvenile Steller sea lions (N = 91) at three distinct geographical locations (Southeast Alaska, Prince William Sound, Central Aleutian Islands) using open-flow respirometry and deuterium isotope dilution, respectively. Average sea lion RMR ranged from 6.7 to 36.2 MJ d−1 and was influenced by body mass, total body lipid, and to a lesser extent, ambient air temperature and age. Sea lion pups captured in the Aleutian Islands (region of decline) had significantly greater body mass and total body lipid stores when compared to pups from Prince William Sound (region of decline) and Southeast Alaska (stable region). Along with evidence of robust body condition in Aleutian Island pups, no definitive differences were detected in RMR between sea lions sampled between eastern and western populations that could not be accounted for by higher percent total body lipid content, suggesting that that at the time of this study, Steller sea lions were not experiencing metabolic depression in the locations studied.

Estimation of Male Gene Flow from Measures of Nuclear and Female Genetic Differentiation

An approach is provided to estimate male gene flow and the ratio of male to female gene flow, given that there are estimates of diploid, nuclear gene flow and haploid, female gene flow. This approach can be applied to estimates of differentiation (F ST ) from biparentally and maternally inherited markers, assuming the equilibrium island model and equal effective numbers of males and females. Corrections to formulas used previously for California sea lions (González-Suárez M, Flatz R, Aurioles-Gamboa D, Hedrick PW, Gerber LR. 2009. Isolation by distance among California sea lion populations in Mexico: redefining management stocks. Mol Ecol. 18:1088-1099.) and American bison (Halbert ND, Gogan PJP, Hedrick PW, Wahl L, Derr JN. 2012. Genetic population substructure in bison in Yellowstone National Park. J Hered. 103:360-370.) are given and revised values for those species are calculated. The effect of unequal male and female effective population sizes, nonequilibrium conditions, and approximations of differentiation formulas are briefly discussed.

Macrobenthos and multi-molecular markers as indicators of environmental contamination in a South American port (Mar del Plata, Southwest Atlantic)

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.

Asymptomatic and chronic carriage of Leptospira interrogans serovar Pomona in California sea lions (Zalophus californianus)

Since 1970, periodic outbreaks of leptospirosis, caused by pathogenic spirochetes in the genus Leptospira, have caused morbidity and mortality of California sea lions (Zalophus californianus) along the Pacific coast of North America. Yearly seasonal epizootics of varying magnitude occur between the months of July and December, with major epizootics occurring every 3-5 years. Genetic and serological data suggest that Leptospira interrogans serovar Pomona is the infecting serovar and is enzootic in the California sea lion population, although the mechanism of persistence is unknown. We report asymptomatic carriage of Leptospira in 39% (33/85) of wild, free-ranging sea lions sampled during the epizootic season, and asymptomatic seroconversion with chronic asymptomatic carriage in a rehabilitated sea lion. This is the first report of asymptomatic carriage in wild, free-ranging California sea lions and the first example of seroconversion and asymptomatic chronic carriage in a sea lion. Detection of asymptomatic chronic carriage of Leptospira in California sea lions, a species known to suffer significant disease and mortality from the same Leptospira strain, goes against widely-held notions regarding leptospirosis in accidental versus maintenance host species. Further, chronic carriage could provide a mechanism for persistent circulation of Leptospira in the California sea lion population, particularly if these animals shed infectious leptospires for months to years.

Predicting interactions between recolonising marine mammals and fisheries: defining precautionary management

AbstractInteractions between fisheries and marine mammals have created costly and unresolved issues throughout the world. This study examines the spatial and resource overlaps between recolonising New Zealand sea lions, Phocarctos hookeri (Grey) (using satellite tracking) and local fisheries (using spatio‐temporal catch database) on the Otago coast, New Zealand. Around Otago, spatial and resource overlaps existed year‐round and it is predicted that incidental deaths in fishing gear and resource competition may arise as the sea lion population increases. Preventive management methods (e.g. marine protected areas) and monitoring studies (e.g. fish stock assessments) are proposed. The use of precautionary management could ensure sustainable profitable fisheries and successful recolonisation by sea lions around Otago, and it could be used as a case study for other areas with recovering marine mammal populations that interact with fisheries.

Comment on sea lion population viability analysis

Comment on sea lion population viability analysis

Survival estimates for the Australian sea lion: Negative correlation of sea surface temperature with cohort survival to weaning

AbstractThe Australian sea lion (Neophoca cinerea) population at Seal Bay Conservation Park, South Australia, is estimated to be declining at a rate of 1.14% per breeding season. To better understand the potential causes of this decline, survival rates were examined to 14 yr of age for eight cohorts marked as pups (aged 0.17 yr) between 1991 and 2002. Apparent yearly survival rates (Φ) varied by cohort for pups from marking to weaning at 1.5 yr (Φ= 0.30–0.67). Postweaning juvenile survival (1.5–3 yr) was 0.89 and survival from 3 to 14 yr was constant (Φ female:male = 0.96:0.89). Φ of pup cohorts was negatively correlated to local sea surface temperature where the sea lions forage (SST) and was especially low for cohort 7 in 2000 (0.30). It is possible that periods of unusually warm oceanographic conditions may be limiting primary production and inhibiting maternal provisioning to pups. Pup survival to weaning is relatively low compared to other otariid species, is likely to limit recruitment, and may be contributing to the decline in pup abundance observed in the colony.

Prepartum and postpartum trophic segregation between sympatrically breeding femaleArctocephalus australisandOtaria flavescens

Abstract In Uruguay, the South American fur seal population (Arctocephalus australis) is increasing, whereas the South American sea lion (Otaria flavescens) population is declining. Previous research using fecal analysis suggested a high degree of trophic overlap between these species. In this study we used stable isotope analysis to assess whether trophic overlap occurs between female fur seals and sea lions during the breeding season. We measured δ15N and δ13C values in serum and skin from pups of both species (n = 47) to reflect pre- and postpartum maternal feeding habits, respectively. Our results suggested a lack of trophic overlap between lactating females; both serum and skin samples from sea lion pups had significantly greater δ13C and δ15N values than samples from fur seal pups, suggesting that lactating sea lions forage near shore, whereas lactating fur seals forage offshore. The pre- to postpartum diet shift in fur seals would be mainly caused by a reduction in the diversity of the exploited ...

Using life‐history traits of New Zealand sea lions, Auckland Islands to clarify potential causes of decline

AbstractAnnual censuses of New Zealand (NZ) sea lions Phocarctos hookeri at the subantarctic Auckland Islands have indicated a decline in pup production of over 40% during the first decade of the 2000s. With this significant decline and likely decline in the population as a whole, population ecology theory hypothesizes that life‐history traits such as reproduction rate, survival or growth should improve, particularly if density‐dependency is playing a significant role in the population. This research examined whether changes in NZ sea lion pup production were associated with changes in adult abundance or population life‐history traits in an attempt to clarify potential causes of decline. Since 1998/1999, daily surveys of Sandy Bay, Enderby Island, were undertaken during the NZ sea lion breeding season (December–February). These surveys confirm that the number of adults at the breeding area has significantly declined during the period of pup production decline. There was no difference between years in mean pup birth date, but the ratio of pups to females ashore during peak pupping varied significantly. The sex ratio of pups at birth also varied from year to year, but with no significant variation overall. Pup mortality varied significantly only during years of epizootic events (1997/1998, 2001/2002 and 2002/2003). Pup birth mass showed little variation between 2000/2001 and 2006/2007, increasing slightly in the last 3 years of study. Pup mass at 3 weeks, although highly variable, showed no trend during the period of decline. Despite the significant decrease in pup production and breeding animals, not all life‐history traits relating to pup mass and survival or female fecundity improved. Research suggests that indirect fishing‐related pressures may influence some of these traits and that the NZ sea lion population was unlikely to have been influenced by density‐dependent factors or to have been at or near carrying capacity before the decline.