Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event

The occurrence of an unusual mortality event involving California sea lions (Zalophus californianus) along the central California coast in May 1998 was recently reported. The potent neurotoxin domoic acid (DA), produced naturally by the diatom Pseudo-nitzschia australis and transmitted to the sea lions via planktivorous northern anchovies (Engraulis mordax), was identified as the probable causative agent. Details of DA analyses for anchovy tissues and sea lion feces are described. Domoic acid levels were estimated in anchovy samples by HPLC-UV, and in sea lion feces using the same method as well as a microplate receptor binding assay, with absolute confirmation by tandem mass spectrometry. The highest DA concentrations in anchovies occurred in the viscera (223 +/- 5 microg DA g(-1)), exceeding values in the body tissues by seven-fold and suggesting minimal bioaccumulation of DA in anchovy tissue. HPLC values for DA in sea lion fecal material (ranging from 152 to 136.5 microg DA g(-1)) required correction for interference from an unidentified compound. Inter-laboratory comparisons of HPLC data showed close quantitative agreement. Fecal DA activity determined using the receptor binding assay corresponded with HPLC values to within a factor of two. Finally, our detection of P. australis frustules, via scanning electron microscopy, in both anchovy viscera and fecal material from sea lions exhibiting seizures provides corroborating evidence that this toxic algal species was involved in this unusual sea lion mortality event.     

Magnetic resonance imaging quality and volumes of brain structures from live and postmortem imaging of California sea lions with clinical signs of domoic acid toxicosis

Our goal in this study was to compare magnetic resonance images and volumes of brain structures obtained alive versus postmortem of California sea lions Zalophus californianus exhibiting clinical signs of domoic acid (DA) toxicosis and those exhibiting normal behavior. Proton density-(PD) and T2-weighted images of postmortem-intact brains, up to 48 h after death, provided similar quality to images acquired from live sea lions. Volumes of gray matter (GM) and white matter (WM) of the cerebral hemispheres were similar to volumes calculated from images acquired when the sea lions were alive. However, cerebrospinal fluid (CSF) volumes decreased due to leakage. Hippocampal volumes from postmortem-intact images were useful for diagnosing unilateral and bilateral atrophy, consequences of DA toxicosis. These volumes were similar to the volumes in the live sea lion studies, up to 48 h postmortem. Imaging formalin-fixed brains provided some information on brain structure; however, images of the hippocampus and surrounding structures were of poorer quality compared to the images acquired alive and postmortem-intact. Despite these issues, volumes of cerebral GM and WM, as well as the hippocampus, were similar to volumes calculated from images of live sea lions and sufficient to diagnose hippocampal atrophy. Thus, postmortem MRI scanning (either intact or formalin-fixed) with volumetric analysis can be used to investigate the acute, chronic and possible developmental effects of DA on the brain of California sea lions.     

Movement, dive behavior, and survival of California sea lions (Zalophus californianus) posttreatment for domoic acid toxicosis

Domoic acid (DA) is a neuroexcitatory toxin increasingly causing strandings and mortality of marine mammals. The hippocampus of mammalian brains, associated with learning, memory, and spatial navigation, is one of the predominant regions affected by DA exposure. California sea lions stranding from 2003 to 2006 as a result of DA toxicosis were classified as having acute ( n = 12) or chronic neurologic ( n = 22) clinical signs. Chronic neurologic cases were examined by magnetic resonance imaging to determine the extent of brain damage related to DA exposure. Brain damage included hippocampal and parahippocampal atrophy, temporal horn enlargement, and pathological T2 hyperintensity. Posttreatment, animals were fitted with satellite transmitters and their movement and dive behaviors compared with those of a control group. The only significant difference between acute and chronic animals was distance traveled per day. There were, however, significant differences between chronic neurologic cases and controls: chronic neurologic cases dove shallower for shorter durations, traveled further from shore, and spent less time hauled out and more time surface swimming than control animals. There was no relationship between severity of brain damage and behavioral patterns for chronic neurologic cases. Sea lions with chronic neurologic changes had a poor prognosis for survival following release.     

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

To 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.     

MORPHOLOGICAL,TOXICOLOGICAL, AND GENETIC DIFFERENCES AMONG PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE) SPECIES IN INLAND EMBAYMENTS AND OUTER COASTAL WATERS OF WASHINGTON STATE,USA1

Plankton samples from three inland embayments and several outer coastal sites of Washington State were collected from 1997 through 1999 and were examined for the presence of diatoms of the genus Pseudo‐nitzschia and levels of the toxin, domoic acid (DA). Seven species were observed, including Pseudo‐nitzschia pungens (Grunow ex Cleve) Hasle, P. multiseries (Hasle) Hasle, P. australis Frenguelli, P. fraudulenta (Cleve) Hasle, P. cf. heimii Manguim, P. pseudodelicatissima (Hasle) Hasle, and P. delicatissima (Cleve) Heiden. The coastal Pseudo‐nitzschia species assemblages differed significantly from those observed within embayments. The dominant species observed at coastal sites were P. pseudodelicatissima and P. cf. heimii. Pseudo‐nitzschia assemblages found in embayments included one or more of the following species: P. pungens, P. multiseries, P. australis, P. pseudodelicatissima, and P. fraudulenta. The nuclear large subunit rRNA gene was sequenced for six of the seven species identified. This sequence revealed that P. multiseries, P. pungens, P. australis, and P. heimii were genetically similar to those found in California, whereas P. delicatissima and P. pseudodelicatissima were distinct from the California isolates. Although the concentrations of DA in razor clams along Washington State coasts have exceeded regulatory limits several times since 1991, levels of DA in shellfish from Washington State embayments have not yet exceeded regulatory limits. The widespread presence of toxin‐producing Pseudo‐nitzschia species suggests, however, that toxic blooms are likely to occur within embayments in the future. In conjunction with the monitoring of environmental conditions conducive to toxic bloom formation, the development of species‐specific probes for rapid and accurate detection of potentially toxic Pseudo‐nitzschia species in this region would enable the forecasting of a toxic event before DA accumulates in shellfish, thereby reducing the impacts to coastal communities.     

加州Santa Monica海湾鳍足类的生态学

研究了加州Santa Monica海湾鳍足类的生态学.从1997-2007年乘船调查了277次,发现海狮(Zalophus californianus)是最常见的动物(89%,见到的次数为1393次),其次是港海豹(Phoca vitulina richardsi,8%,n=131)和北象海豹(Mirounga angustirostris,1%,n=15).在29%的遇见次数(观察到瓶海豚205次)中,发现海狮(偶尔也发现港海豹)与瓶鼻海豚集群(Tursiops truncatus);短喙真海豚(Delphinus delphis)与长喙真海豚(D.capensis)在53% 的遇见次数(遇见真海豚次数n=155)中,发现短喙真海豚(Delphinus delphis)与长喙真海豚(D.capensis)集群;一般在沿岸水域(离岸边距离<500 m)见到海狮和港海豹,但在整个海湾也能见到,表现出这两个物种对海底峡谷的偏爱.北象海豹仅见于近海,主要在海底峡谷附近. 经常看到海狮、港海豹和北象海豹游动(50%,n=728)、进行热调节(14%,n=205)、以及取食(3.2%,n=47),但几乎见不到有社会性活动(0.21%,n=3).     

Taxonomical diversity of Pseudo‐nitzschia from the Central Adriatic Sea

The aim of our research was to study the composition of Pseudo‐nitzschia species during a period when neurotoxin domoic acid (DA) was present in shellfish. Sampling was conducted in Ka?tela Bay (Central Adriatic Sea), between November 2015 and January 2016. Concentrations of DA analyzed in various shellfish species were low, below the regulatory limit, while the highest abundance of Pseudo‐nitzschia spp. reached 1.85 × 10⁵ cells L^?1 in the surface layer, at the beginning of November. Within the temperature and salinity range recorded during the investigated period, a positive correlation of Pseudo‐nitzschia spp. abundance was recorded with temperature. Morphological analyses by scanning electron microscopy revealed the presence of five Pseudo‐nitzschia species that had already been reported in the Adriatic Sea – P. calliantha, P. delicatissima, P. fraudulenta, P. pseudodelicatissima /P. cuspidata and P. subfraudulenta – as well as an unknown Pseudo‐nitzschia sp. The composition of the Pseudo‐nitzschia assemblage changed over the investigated period. The species P. pseudodelicatissima/P.cuspidata was found throughout the entire period and the highest diversity was noticed in January, when all six observed species were recorded. These results represent the first taxonomical investigation of the genus Pseudo‐nitzschia in Ka?tela Bay, as well as the first report of DA in shellfish from this area.     

First reports of Pseudo‐nitzschia micropora and P. hasleana (Bacillariaceae) from the Southern Hemisphere: Morphological,molecular and toxicological characterization

Pseudo‐nitzschia H. Peragallo is a marine diatom genus found worldwide in polar, temperate, subtropical and tropical waters. It includes toxigenic representatives that produce domoic acid (DA), a neurotoxin responsible for Amnesic Shellfish Poisoning. In this study we characterized two species of Pseudo‐nitzschia collected from Port Stephens and the Hawkesbury River (south eastern Australia) previously unreported from Australian waters. Clonal isolates were sub‐sampled for (i) light and transmission electron microscopy; (ii) DNA sequencing, based on the nuclear‐encoded partial large subunit ribosomal RNA gene and internal transcribed spacer (ITS)‐ITS1, 5.8S and ITS2 rDNA regions and, (iii) DA production as measured by liquid chromatography‐mass spectrometry. Morphological and molecular data unambiguously revealed the species to be Pseudo‐nitzschia micropora Priisholm, Moestrup & Lundholm (Port Stephens) and Pseudo‐nitzschia hasleana Lundholm (Hawkesbury River). This is the first report of the occurrence of these species from the Southern Hemisphere and the first report of P. micropora in warm‐temperate waters. Cultures of P. micropora, tested for DA production for the first time, proved to be non‐toxic. Similarly, no detectable toxin concentrations were observed for P. hasleana. Species resolution and knowledge on the toxicity of local Pseudo‐nitzschia species has important implications for harmful algal bloom monitoring and management.     

The fecal viral flora of California sea lions

California sea lions are one of the major marine mammal species along the Pacific coast of North America. Sea lions are susceptible to a wide variety of viruses, some of which can be transmitted to or from terrestrial mammals. Using an unbiased viral metagenomic approach, we surveyed the fecal virome in California sea lions of different ages and health statuses. Averages of 1.6 and 2.5 distinct mammalian viral species were shed by pups and juvenile sea lions, respectively. Previously undescribed mammalian viruses from four RNA virus families (Astroviridae, Picornaviridae, Caliciviridae, and Reoviridae) and one DNA virus family (Parvoviridae) were characterized. The first complete or partial genomes of sapeloviruses, sapoviruses, noroviruses, and bocavirus in marine mammals are reported. Astroviruses and bocaviruses showed the highest prevalence and abundance in California sea lion feces. The diversity of bacteriophages was higher in unweaned sea lion pups than in juveniles and animals in rehabilitation, where the phage community consisted largely of phages related to the family Microviridae. This study increases our understanding of the viral diversity in marine mammals, highlights the high rate of enteric viral infections in these highly social carnivores, and may be used as a baseline viral survey for comparison with samples from California sea lions during unexplained disease outbreaks.     

ACCUMULATION OF DOMOIC ACID BY THE COASTAL DIATOM PSEUDO‐NITZSCHIA MULTISERIES: A POSSIBLE COPPER COMPLEXATION STRATEGY

Domoic acid (DA) is a neurotoxic amino acid produced by several members of the diatom genus Pseudo‐nitzschia. Trophic transfer of DA up the food chain has been implicated in the deaths of 100's of marine birds and marine mammals along the central California Coast. The physiological function of DA in Pseudo‐nitzschia spp. has not been defined, although some evidence indicates that elevated metal concentrations can induce DA accumulation (Subba RAO et al., 1998, P.S.Z.N. Mar. Ecol. 19:31). Although California coastal waters have experienced a decline in several heavy metals from 1977–1990, copper concentrations have increased by as much as 25% (Stephenson, M. D. & Leonard, G. H., 1994, Mar. Poll. Bull. 28:148). Many algae produce chelators, including amino acids, in response to toxic [Cu²+] (Wu et al. 1998, J. Phycol. 34: 113). Domoic acid, a tricarboxylic acid, has 4 functional groups that may readily form chelation complexes with transition metals like copper. Copper enrichment experiments indicate that while Cu²+ is toxic to Pseudo‐nitzschia multiseries at total [Cu] greater than 16.1μM (pCu 6.0), intracellular DA accumulation increases up to this point with no decline in growth rates relative to cultures grown in standard enriched seawater. These data suggest that DA may be accumulated by P. multiseries to mitigate the toxicity of elevated [Cu²+]. Chemiluminescence will be used to quantify the binding affinity (expressed as conditional stability constants, Kc) of DA for Cu²+. Defining the Cu‐DA dose response relationship in Pseudo‐nitzschia can facilitate prediction of future toxic bloom events.     

On detection of pseudo-nitzschia (bacillariophyceae) species using whole cell hybridization: sample fixation and stability

Some species within the genus Pseudo‐nitzschia H. Peragallo are associated with production of domoic acid, the agent responsible for amnesic shellfish poisoning (ASP). Identification and enumeration of particular Pseudo‐nitzschia in natural populations is often difficult and time consuming because of the need for detailed morphological observations, which often require scanning or transmission electron microscopy. In earlier publications we described the development of large subunit ribosomal RNA (LSU rRNA)‐targeted fluorescent DNA probes for discriminating among a variety of Pseudo‐nitzschia species collected from Monterey Bay, California. Probes are applied using whole cell hybridization and a custom filtration manifold, enabling rapid identification and quantification of target species in cultured as well as field samples. In this work we compared a variety of preservation techniques and assessed the stability of stored samples with respect to their reactivity towards the probes. Of the preservatives tested, a saline ethanol‐based treatment gave the best results in terms of probes yielding a bright and uniform cell label. Culture samples treated with this fixative continued to react well with the probes for at least 6 weeks post‐fixation whether stored in the preservative or dried post‐preservation, with samples being kept at either room temperature or ?20° C. Likewise, field samples containing a variety of diatoms and dinoflagellate species stored in the saline ethanol solution at room temperature were also stable for at least 4–6 weeks, reacting brilliantly towards a positive control probe. After prolonged storage, however, cell reactivity towards the probes diminished dramatically. Post‐hybridization, samples stored at 4° C were found to retain their fluorescence for at least 1 week. These results indicate a wider window of opportunity for Pseudo‐nitzschia analysis using whole cell hybridization than previously reported. Sample collection, preservation, and probing protocols optimized for Pseudo‐nitzschia are also applicable to a wide range of phytoplankton species. The time required to execute the whole cell hybridization protocol was reduced by premixing probe with hybridization buffer. The premixed probe solutions as well as fixative and wash solutions are all stable at room temperature for at least 6 weeks. Application of two different species‐specific probes, each labeled with a different fluorochrome, allowed detection of two species on a single filter. The latter could be adopted in the future to increase the rate of sample processing and decrease the cost of sample analysis.     

Demographics and spatio‐temporal signature of the biotoxin domoic acid in California sea lion (Zalophus californianus) stranding records

California sea lions (Zalophus californianus) in otherwise good nutritional condition have been consistently affected by the marine biotoxin domoic acid since the late 1990s. In this study we evaluated the temporal and spatial stranding patterns of suspected and confirmed cases of domoic acid intoxicated sea lions from 1998 to 2006, using records of strandings along the California coast obtained from members of the California Marine Mammal Stranding Network. The majority of domoic acid cases were adult females (47%–82% of the total annual domoic acid cases), a contrast to strandings that were not related to domoic acid, which were generally dominated by juveniles and pups. Exposure to this biotoxin led to a 6.67‐fold increase in adult female strandings in 2000, and a 5.44‐fold increase in adult female deaths in 2006, relative to strandings and deaths of adult female not affected by domoic acid. Domoic acid cases have occurred annually since 1998 (except for 1999) between April and August, with clusters centered primarily at Pismo Beach (San Luis Obispo County), as well as at other beaches in San Luis Obispo, Monterey, Santa Cruz, Santa Barbara, Orange, and San Diego counties. The larger ecological and population level implications of increased domoic acid strandings and deaths, particularly among adult female sea lions, warrant further attention and need to be investigated.     

Trophic level and overlap of sea lions (Zalophus californianus) in the Gulf of California, Mexico

Stable isotope and scat analyses were used in concert to determine trophic level and dietary overlap among California sea lions from different rookeries in the Gulf of California. Isotopic analysis of the fur of sea lion pups revealed differences in δ¹⁵N and δ¹³C values among rookeries during the breeding season. Mean δ¹⁵N and δ¹³C values varied from 20.2‰ to 22.4‰ and from −15.4‰ to −14.0‰, respectively. The pattern of differences among rookeries was similar between years in most cases. Isotopic variations among rookeries were associated with differences in prey consumption. There was a significant correlation between δ¹⁵N value and trophic level, as determined by scat analysis. Joint application of isotopic and scat analyses allowed us to identify how the feeding habits of sea lions vary with location. Our results suggest the presence of spatial structure in available prey as well as the localized use of prey by sea lions across the Gulf of California.     

Aerial hearing thresholds and detection of hearing loss in male California sea lions (Zalophus californianus) using auditory evoked potentials

Auditory evoked potential (AEP) measurements are useful for describing the variability of hearing among individuals in marine mammal populations, an important consideration in terms of basic biology and the design of noise mitigation criteria. In this study, hearing thresholds were measured for 16 male California sea lions at frequencies ranging from 0.5 to 32 kHz using the auditory steady state‐response (ASSR), a frequency‐specific AEP. Audiograms for most sea lions were grossly similar to previously reported psychophysical data in that hearing sensitivity increased with increasing frequency up to a steep reduction in sensitivity between 16 and 32 kHz. Average thresholds were not different from AEP thresholds previously reported for male and female California sea lions. Two sea lions from the current study exhibited abnormal audiograms: a 26‐yr‐old sea lion had impaired hearing with a high‐frequency hearing limit (HFHL) between 8 and 16 kHz, and an 8‐yr‐old sea lion displayed elevated thresholds across most tested frequencies. The auditory brainstem responses (ABRs) for these two individuals and an additional 26‐yr‐old sea lion were aberrant compared to those of other sea lions. Hearing loss may have fitness implications for sea lions that rely on sound during foraging and reproductive activities.     

First report of the potentially toxic marine diatom Pseudo‐nitzschia simulans (Bacillariophyceae) from the East Australian Current

Certain species of the marine diatom genus Pseudo‐nitzschia are responsible for the production of the domoic acid (DA), a neurotoxin that can bioaccumulate in the food chain and cause amnesic shellfish poisoning (ASP) in animals and humans. This study extends our knowledge by reporting on the first observation of the potentially toxic species Pseudo‐nitzschia simulans from this region. One clonal strain of P. simulans was isolated from the East Australian Current and characterized using light and transmission electron microscopy, and phylogenetic analyses based on regions of the internal transcribed spacer (ITS) and the D1–D3 region of the large subunit (LSU) of the nuclear‐encoded ribosomal deoxyribonucleic acid (rDNA), as well as examined for DA production as measured by liquid chromatography–mass spectrometry. Although this strain was non‐toxic under the defined growth conditions, the results unambiguously confirmed that this isolate is the potentially toxic species P. simulans – the first report of this species from the Southern Hemisphere.     

IDENTIFICATION AND ASSESSMENT OF DOMOIC ACID PRODUCTION IN OCEANIC PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE) FROM IRON‐LIMITED WATERS IN THE NORTHEAST SUBARCTIC PACIFIC1

We identified and investigated the potential toxicity of oceanic Pseudo‐nitzschia species from Ocean Station Papa (OSP), located in a high‐nitrate, low‐chlorophyll (HNLC) region of the northeast (NE) subarctic Pacific Ocean. Despite their relatively low abundances in the indigenous phytoplankton assemblage, Pseudo‐nitzschia species richness is high. The morphometric characteristics of five oceanic Pseudo‐nitzschia isolates from at least four species are described using SEM and TEM. The species identified are Pseudo‐nitzschia dolorosa Lundholm et Moestrup, P. granii Hasle, P. heimii Manguin, and P. cf. turgidula (Hust.) Hasle. Additional support for the taxonomic classifications based on frustule morphology is provided through the sequencing of the internal transcribed spacer 1 (ITS1) rDNA. Pseudo‐nitzschia species identification was also assessed by the construction of ITS1 clone libraries and using automated ribosomal intergenic spacer analysis (ARISA) for environmental samples collected during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES), conducted in close proximity to OSP in July of 2002. Based on ITS1 sequences, the presence of P. granii, P. heimii, P. cf. turgidula, and at least five other putative, unidentified Pseudo‐nitzschia ITS1 variants was confirmed within iron‐enriched phytoplankton assemblages at OSP. None of the oceanic isolates produced detectable levels of particulate domoic acid (DA) when in prolonged stationary phase due to silicic acid starvation. The lack of detectable concentrations of DA suggests that either these strains produce very little or no toxin, or that the physiological conditions required to promote particulate DA production were not met and thus differ from their coastal, toxigenic congeners.     

Epizootic vesicular disease in captive California sea lions

An epizootic of vesicular disease occurred in a group of semi-domesticated California sea lions (Zalophus californianus) during the months of April and May 1997. Ten castrated mature male sea lions, ages 12 to 19 yr, were housed in three adjacent open-ocean net enclosures in San Diego Bay (California, USA). Four animals (40%) developed oral and extremity vesicles, anorexia, and were reluctant to perform learned behaviors. One animal developed vesicles but maintained a normal appetite and behavior. The remaining animals showed no clinical signs of infection. Virus (designated FADDL 7005) was isolated from four of the five animals that developed vesicles. Serum antibody titers to FADDL 7005, a previously untyped calicivirus, were demonstrated in animals that showed any combination of clinical signs and in two animals that did not show any clinical signs. No virus was isolated from five fecal samples collected from four of the group animals. Clinical signs lasted 4 to 20 days in affected animals. All affected animals recovered from infection. An experimental swine was inoculated with FADDL 7005 and developed vesicular disease, which was transmitted to another experimental swine upon contact. It is proposed that FADDL 7005 is a new San Miguel sea lion virus.     

Characterizing habitat suitability for a central‐place forager in a dynamic marine environment

Characterizing habitat suitability for a marine predator requires an understanding of the environmental heterogeneity and variability over the range in which a population moves during a particular life cycle. Female California sea lions (Zalophus californianus) are central‐place foragers and are particularly constrained while provisioning their young. During this time, habitat selection is a function of prey availability and proximity to the rookery, which has important implications for reproductive and population success. We explore how lactating females may select habitat and respond to environmental variability over broad spatial and temporal scales within the California Current System. We combine near‐real‐time remotely sensed satellite oceanography, animal tracking data (n = 72) from November to February over multiple years (2003–2009) and Generalized Additive Mixed Models (GAMMs) to determine the probability of sea lion occurrence based on environmental covariates. Results indicate that sea lion presence is associated with cool ( <14°C ), productive waters, shallow depths, increased eddy activity, and positive sea‐level anomalies. Predictive habitat maps generated from these biophysical associations suggest winter foraging areas are spatially consistent in the nearshore and offshore environments, except during the 2004–2005 winter, which coincided with an El Niño event. Here, we show how a species distribution model can provide broadscale information on the distribution of female California sea lions during an important life history stage and its implications for population dynamics and spatial management.     

Age‐ and sex‐specific survival of California sea lions (Zalophus californianus) at San Miguel Island,California

We conducted a mark‐recapture study of California sea lions (Zalophus californianus) using pups branded on San Miguel Island, California, from 1987 to 2014, and annual resightings from 1990 to 2015. We used the Burnham model (Burnham 1993), an extension of the Cormack‐Jolly‐Seber mark‐recapture model, which includes recoveries of dead animals, to analyze age, sex, and annual patterns in survival. Generally, females had higher survival than males. For female pups, the average annual survival was 0.600 and for male pups it was 0.574. Yearling survival was 0.758 and 0.757 for females and males, respectively. Peak annual survival was at age 5 and was 0.952 for females and 0.931 for males. Pups with larger mass at branding had higher survival as pups and yearlings, but the effect was relative within each cohort because of large between‐cohort variability in survival. Annual variability in sea surface temperature (SST) affected survival. For each 1°C increase in SST, the odds of survival decreased by nearly 50% for pups and yearlings; negative SST anomalies yielded higher survival. Annual variation in male survival was partly explained by leptospirosis outbreaks. Our study provides a unique view of one demographic parameter that contributed to the successful recovery of the California sea lion population.     

Diet estimation in California sea lions,Zalophus californianus

We performed a captive feeding experiment using California sea lions to assess biases associated with estimating pinniped diet using scats and spews. Sea lions were fed nine of their natural prey species: anchovy, sardine, Pacific mackerel, jack mackerel, hake, steelhead smolts, shortbelly rockfish, pink salmon, and market squid. Recovery percentages varied among prey species using otoliths and were improved for adult salmon and sardine using the all‐structure method. Numerical and graded length correction factors provided better estimates of number and size of prey consumed. Four models used to determine the proportions of prey species consumed by a sea lion population were tested. The all‐structure method and variable biomass reconstruction model, in conjunction with numerical and graded length correction factors, provided more accurate estimates than without. We provide numerical correction factors for all prey species, including correction factors for specific salmon bones: vertebrae, branchials, radials, teeth, gill rakers, and hypurals.