The deeper the rounder: body shape variation in lice parasitizing diving hosts.

Seal lice, unique among insects, show remarkable adaptability to the extreme conditions of the deep sea. Evolving with their seal and sea lion hosts, they have managed to tolerate hypoxia, high salinity, low temperature, and elevated hydrostatic pressure. Given the diving capabilities of their mammalian hosts, which can reach depths of hundreds to thousands of meters, our study examines the morphological variation among closely related seal lice species infesting hosts with different maximum diving depths. In particular, our research reveals a significant morphological difference between lice associated with regular and deep-diving hosts, where lice from deep-diving hosts tend to be rounder. This could be an adaptation to withstand the high hydrostatic pressures found in the deep ocean. The rounded shape optimizes the louse's ability to withstand external pressure by redistributing it over a larger ventral/dorsal plane. This in turn minimizes the internal energy required to support body deformations, thereby increasing the louse's resilience in the deep sea environment.

Regional variations and drivers of essential and non-essential elements in Steller sea lion pups from the Aleutian Islands, Alaska.

Exposure and resulting tissue concentrations of various elements from natural and anthropogenic sources are influenced by multiple factors, such as geographic location, age, diet, and metabolic rate, that can influence wildlife health. Essential and non-essential elements were assessed in lanugo and whole blood collected in 2019 from 102 Steller sea lion (Eumetopias jubatus) pups from two rookeries from the western and central Aleutian Islands: Agattu (WAI, n = 54) and Ulak Islands (CAI, n = 48). Rookery, sex, dorsal standard length, and trophic ecology (ẟ15N, ẟ13C values) effects on element concentration were evaluated. Significant differences in element concentrations of lanugo were exhibited across rookeries (p < 0.05), except for zinc (Zn). For example, higher mercury (Hg) and selenium (Se) concentrations were observed in WAI than CAI, while other elements were lower in WAI. Whole blood showed higher sulfur (S) and Se concentrations in CAI compared to WAI, while WAI had elevated strontium (Sr) and Hg concentrations relative to CAI. Trophic ecology significantly influenced most element concentrations, possibly due to regional variations in adult female feeding and food web dynamics. Interactions between elements were found in lanugo across both rookeries, with varying strengths. Whole blood displayed less pronounced yet consistent associations, with variable intensities. Essential elements sodium (Na), potassium (K), and calcium (Ca) formed a distinct group whose interaction is crucial for nervous system function and muscle contraction. Another group comprised zinc (Zn), iron (Fe), manganese (Mn), magnesium (Mg), phosphorous (P), S, and Se, which are known for indirectly interacting with enzyme function and metabolic pathways. Hg and Se formed a distinct group probably due to their known chemical interactions and physiological protective interactions.

Unveiling mercury levels: Trophic habits influence on bioaccumulation in two Otariid species.

Mercury, a toxic metal released by various human activities, exerts environmental stress through its bioaccumulation and biomagnification, particularly in marine habitats. South American fur seals (Arctocephalus australis) and sea lions (Otaria flavescens) reproduce on the Atlantic coast of Uruguay. As top predators, they can accumulate toxic levels of mercury and are often used as sentinel species for monitoring ecosystem health. Fur seals prey on pelagic species, such as fish and squid, while sea lions consume coastal-benthic prey. We analyzed the total mercury concentration (THg) in hair and the trophic habits (δ13C and δ15N) of females from both species. The average THg concentration in adult female sea lions (30.5 ± 9.3 µg/g dry weight) was significantly higher than in fur seals (6.3 ± 2.5 µg/g dry weight). Additionally, the mean δ15N and δ13C values were significantly higher in sea lion (δ15N: 19.2 ± 0.6‰, δ13C: -13.8 ± 0.2‰) compared to fur seals (δ15N: 16.5 ± 0.5‰, δ13C: -15.5 ± 0.6‰). Our results suggest that different trophic levels and feedings areas affect the THg concentration in Uruguayan Otariids. Notably, at the intraspecific level, the THg concentration in sea lions increased with δ13C values, suggesting a link to coastal feeding habits. This indicates that coastal feeding behaviors, compared to feeding in pelagic environments, enhance mercury bioaccumulation in Otariids along the Uruguayan coast, with the discharge of freshwater from the Río de la Plata (one of the largest estuaries in South America) basin identified as a potential mercury source. THg concentrations found in female sea lion hair are the highest reported in Otariids globally. Mercury levels exceeded toxic thresholds observed in other mammals and could pose significant health risks. Our findings may explain why sea lions were particularly affected by the avian influenza outbreak in Uruguay compared to fur seals. Monitoring the declining sea lion population is crucial, making our results significant for integrated conservation and management strategies.

Mortality in sea lions is associated with the introduction of the H5N1 clade 2.3.4.4b virus in Brazil October 2023: whole genome sequencing and phylogenetic analysis.

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 virus was detected in the South American sea lions found dead in Santa Catarina, Brazil, in October 2023. Whole genome sequencing and comparative phylogenetic analysis were conducted to investigate the origin, genetic diversity, and zoonotic potentials of the H5N1 viruses. The H5N1 viruses belonged to the genotype B3.2 of clade 2.3.4.4b H5N1 virus, which was identified in North America and disseminated to South America. They have acquired new amino acid substitutions related to mammalian host affinity. Our study provides insights into the genetic landscape of HPAI H5N1 viruses in Brazil, highlighting the continuous evolutionary processes contributing to their possible adaptation to mammalian hosts.

Unraveling the gut microbiota of Mexican pinnipeds: the dominance of life histories over phylogeny.

Studying how phylogeny influences the composition and functions of microbiotas within animal hosts is essential for gaining insights into the connection between genetics, ecology, and health in the animal kingdom. However, due to limited comprehensive studies, this influence remains unclear for many wild mammals, including Mexican pinnipeds. We employed 16S rRNA gene deep-sequencing to investigate the impact of phylogeny on the gut microbiota of four pinniped species inhabiting Mexican shores: the Pacific harbor seal (Phoca vitulina richardii), the northern elephant seal (Mirounga angustirostris), the California sea lion (Zalophus californianus), and the Guadalupe fur seal (Arctocephalus philippii townsendi). Our results indicated that factors such as diets and shared life histories exerted more influence on microbiota composition than phylogeny alone. Notably, otariid species sharing similar life histories displayed greater microbiota similarity than phocids, which have distinct life histories and fewer microbiota similarities. Furthermore, harbor seals have more microbial similarities with the two otariid species than with elephant seals. Of particular concern, we observed a higher abundance of potentially pathogenic bacteria (e.g., Photobacterium damselae and Clostridium perfringens) in harbor seals and Guadalupe fur seals compared to other pinnipeds. This finding could pose health threats to these species and nearby human populations.IMPORTANCEPinnipeds in Mexico host microbial communities that remain understudied. While several factors can influence microbiota composition, the role of phylogenetic relationships among these pinnipeds remains unclear due to limited knowledge of the microbiota in certain species. This study aimed to fill this gap by characterizing the composition and function of the gut microbiota in the four pinniped species that occur in Mexico. Our analysis reveals that shared diets and life histories contribute to similarities in the composition of gut microbial communities. This study also highlights the potential differences in the metabolic capabilities and adaptations within the gut microbiota of pinnipeds. Understanding how phylogeny impacts microbial communities enhances our insights into the evolutionary dynamics of marine mammals.

Pacific and Atlantic sea lion mortality caused by highly pathogenic Avian Influenza A(H5N1) in South America.

We describe the evolution of the outbreak of Highly Pathogenic Avian Influenza (HPAI) A(H5N1) in sea lions (Otaria flavescens) of South America. At least 24,000 sea lions died in Peru, Chile, Argentina, Uruguay, and Brazil between January-October 2023. The most plausible route of infection is cohabiting with or foraging on infected birds. However, we urge a detailed evaluation of the sea lions actual source of infection given that the concomitant massive wild bird mortalities registered in the Pacific Ocean did not occur in the Atlantic Ocean.

Otariid gammaherpesvirus 1 in South American fur seals (Arctocephalus australis) and a novel related herpesvirus in free-ranging South American sea lions (Otaria byronia): Prevalence and effects of age, sex, and sample type.

Otariid gammaherpesvirus 1 (OtGHV1) is associated with high rates of urogenital carcinoma in free-ranging California sea lions (Zalophus californianus; CSL), and until recently was reported only in the Northern Hemisphere. The objective of this study was to survey free-ranging South American sea lions (Otaria byronia; SASL) and South American fur seals (Arctocephalus australis: SAFS) in Punta San Juan, Peru for OtGHV1 and to determine prevalence characteristics. Twenty-one percent (14/67) of urogenital swabs collected over three years (2011, 2014, 2015) from live pinnipeds of both species tested positive with a pan-herpesvirus conventional PCR. Sequencing of SAFS amplicons revealed 100% homology to OtGHV1 at the DNA polymerase, glycoprotein B, and viral bcl2-like genes. Sequencing of SASL amplicons revealed a novel related virus, herein called Otariid gammaherpesvirus 8 (OtGHV8). For comparison of sample sites, urogenital, conjunctival, and oropharyngeal swabs collected from 136 live pinnipeds of both species at Punta San Juan between 2011-2018 were then assayed using quantitative PCR for a segment of the OtGHV1/8 DNA polymerase gene using a qPCR assay now determined to cross-react between the two viruses. In total, across both species, 38.6% (51/132) of urogenital swabs, 5.6% (4/71) of conjunctival swabs, and 1.1% (1/90) of oropharyngeal swabs were positive for OtGHV1/8, with SASL only positive on urogenital swabs. Results from SASL were complicated by the finding of OtGHV8, necessitating further study to determine prevalence of OtGHV1 versus OtGHV8 using an alternate assay. Results from SAFS suggest a potential relationship between OtGHV1 in SAFS and CSL. Though necropsy surveillance in SAFS is very limited, geographic patterns of OtGHV1-associated urogenital carcinoma in CSL and the tendency of herpesviruses to cause more detrimental disease in aberrant hosts suggests that it is possible that SAFS may be the definitive host of OtGHV1, which gives further insight into the diversity and phyogeography of this clade of related gammaherpesviruses.

Cardiorespiratory patterns of male South American sea lions (Otaria flavescens) resting on land.

The goal of this study was to characterize the cardiorespiratory patterns of male South American sea lions (SASLs, Otaria flavescens) resting on land. We recorded respiratory and heart rate (n = 360 individuals studied) by observing the nostrils, chest movements and the impact of the heart on the thoracic wall. The sea lions breathe apneustically with a pause on inspiration, representing 74% of the respiratory cycle. The mean breathing frequency was 3.2 ± 1.0 breaths min-1, with a breathing cycle presenting periods of bradypneas, tachypneas, and long-term post-inspiratory pauses. The normal heart rate (nHR) was 73.4 ± 14.5 beats min-1 and no significant differences were observed between age classes. All animals showed variability in HR in relation to respiratory phases (Inspiration: 101.2 ± 18.4 beats min-1; post-inspiratory pause: 73.4 ± 14.5 beats min-1; expiration: 64.6 ± 17.7 beats min-1), consistent with respiratory sinus arrhythmia (RSA). The mean HR (measured during all respiratory phases) was 79.9 ± 22.7 beats min-1, and was significantly different between age classes. The total duration of respiratory cycle, and duration of both inspiration and expiration, decreased with an increment in ambient temperature, with no variation in the pause duration. Heart rate during pause and expiration was significantly higher during high temperatures. Similar changes in cardiorespiratory patterns have been reported in other pinnipeds. Our results showed ontogenetic differences in development and typical variations with environmental and behavioral variables.

Mercury and selenium concentrations in lanugo of free-ranging California sea lions in the southern Gulf of California, Mexico.

Total mercury ([THg]) and selenium ([TSe]) concentrations were determined in California sea lion (Zalophus californianus) lanugo from the Gulf of California in 2021 and 2022. Relationships with sex, morphometrics, and year were evaluated. Following toxicological thresholds of concern for piscivorous mammals, most pups had a [THg] < 10 ppm, one pup (2021) had a [THg] > 20 ppm, no pups had a [THg] > 30 ppm. Females had significantly higher [TSe] than males; sex did not influence [THg]. [THg] and [TSe] in 2022 were significantly higher in the general population and male cohorts compared to 2021. Significant negative correlations were observed between [THg], [TSe], and morphometrics (2021). These results indicate that, compared to other pinniped species, regional California sea lions may have a decreased likelihood of experiencing Hg-related adverse health effects. Year-related changes in element concentrations suggest continued monitoring of this population to assess pinniped, environmental, and potentially, human health.

Time-calibrated phylogeny and full mitogenome sequence of the Galapagos sea lion (Zalophus wollebaeki) from scat DNA.

Background: The Galapagos sea lion, Zalophus wollebaeki, is an endemic and endangered otariid, which is considered as a sentinel species of ecosystem dynamics in the Galapagos archipelago. Mitochondrial DNA is an important tool in phylogenetic and population genetic inference. In this work we use Illumina sequencing to complement the mitogenomic resources for Zalophus genus-the other two species employed Sanger sequencing-by a complete mitochondrial genome and a molecular clock of this species, which is not present in any case. Materials and Methods: We used DNA obtained from a fresh scat sample of a Galapagos sea lion and shotgun-sequenced it on the Illumina NextSeq platform. The obtained raw reads were processed using the GetOrganelle software to filter the mitochondrial Zalophus DNA reads (∼16% survive the filtration), assemble them, and set up a molecular clock. Results: From the obtained 3,511,116 raw reads, we were able to assemble a full mitogenome of a length of 16,676 bp, consisting of 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNA), and two ribosomal RNAs (rRNA). A time-calibrated phylogeny confirmed the phylogenetic position of Z. wollebaeki in a clade with Z. californianus, and Z. japonicus, and sister to Z. californianus; as well as establishing the divergence time for Z. wollebaeki 0.65 million years ago. Our study illustrates the possibility of seamlessly sequencing full mitochondrial genomes from fresh scat samples of marine mammals.

Mass mortality event in South American sea lions (Otaria flavescens) correlated to highly pathogenic avian influenza (HPAI) H5N1 outbreak in Chile.

In Chile, since January 2023, a sudden and pronounced increase in strandings and mortality has been observed among South American (SA) sea lions (Otaria flavescens), prompting significant concern. Simultaneously, an outbreak of highly pathogenic avian influenza H5N1 (HPAIV H5N1) in avian species has emerged since December 2022. To investigate the cause of this unexpected mortality, we conducted a comprehensive epidemiological and pathologic study. One hundred sixty-nine SA sea lions were sampled to ascertain their HPAIV H5N1 status, and long-term stranding trends from 2009 to 2023 were analyzed. In addition, two animals were necropsied. Remarkably, a significant surge in SA sea lion strandings was observed initiating in January 2023 and peaking in June 2023, with a count of 4,545 stranded and deceased animals. Notably, this surge in mortality correlates geographically with HPAIV outbreaks affecting wild birds. Among 168 sampled SA sea lions, 34 (20%) tested positive for Influenza A virus, and 21 confirmed for HPAIV H5N1 2.3.4.4b clade in tracheal/rectal swab pools. Clinical and pathological evaluations of the two necropsied stranded sea lions revealed prevalent neurological and respiratory signs, including disorientation, tremors, ataxia, and paralysis, as well as acute dyspnea, tachypnea, profuse nasal secretion, and abdominal breathing. The lesions identified in necropsied animals aligned with observed clinical signs. Detection of the virus via immunohistochemistry (IHC) and real-time PCR in the brain and lungs affirmed the findings. The findings provide evidence between the mass mortality occurrences in SA sea lions and HPAIV, strongly indicating a causal relationship. Further studies are needed to better understand the pathogenesis and transmission.

Metal-specific biomagnification and trophic dilution in the coastal foodweb of the California sea lion (Zalophus californianus) off Bahía Magdalena, Mexico: The role of the benthic-pelagic foodweb in the trophic transfer of trace and toxic metals.

Trace metals concentrations along with stable isotopes ratios were measured in marine algae, sea grass, sponges, echinoderms, mollusks, crustaceans, fishes, and the California sea lion, to assess the bioaccumulation potential and detect potential risks for top predators off Bahia Magdalena, Mexico. We assessed the trophic magnification factor (TMF) to determine the potential for biomagnification of 11 trace metals. The concentrations of Fe and Zn were one order of magnitude higher than all other metals. Concentrations of As, Cu, Cd, Co, Cr, Fe, Mn and Ni correlated negatively with trophic level, supporting trophic dilution (TMF < 1, p > 0.05), while Zn and Hg had significant trophic magnification (TMF > 1, p < 0.05) when assessing only the benthic-pelagic foodweb. This research provides a baseline concentration of metals in multiple species, metal-specific foodweb bioaccumulation and biomagnification of mercury, underscoring the key role of the macrobenthic community as biovectors for trophic transfer of Hg through the foodweb to the California sea lion.

Using DNA barcoding to link cystacanths and adults of the acanthocephalan Corynosoma australe of the Southeastern Pacific Ocean (off Peru coast).

The objective of this study is to use DNA barcoding to link cystacanths and adults belonging to the acanthocephalans Corynosoma australe found in the Southeastern Pacific Ocean off the coast central from Peru. We sampled three species of commercial fish (Paralichthys adspersus (Steindachner), Paralabrax humeralis (Valenciennes), and Cheilodactylus variegatus (Valenciennes)) and two South American sea lions, Otaria byronia, stranded on the beaches of the city of Huacho and Barranca, Lima province. A total of 509 acanthocephalan larvae were found in the body cavity of 95 fish (prevalence 54.28%, total mean intensity 8.64). A total of 127 adult worms were found in the large intestine from two South American sea lions (P= 100%, MI= 63.5). A total of 203 larvae from P. humeralis were isolates (P=65.71%; MI= 8.83; MA=5.8), 235 (P=54.29%; MI= 12.37; MA= 6.71) from C. variegatus, and 71 (P=42.86%; MI= 4.73; MA= 2.03) from P. adspersus. All adult and larval specimens were morphologically identified as C. australe. They were generated cytochrome c oxidase subunit 1 (cox1) gene sequences of specimens and were compared with available data from GenBank. Molecular phylogenetic analysis supported our morphological identification, where the Peruvian isolates formed a clade with other isolates of C. australe from other countries of the American continent. Of the sequences obtained, two haplotypes were detected and were not identical with previous reports. Based on both DNA barcoding and morphological analyses, our finding represents the first molecular data of C. australe from Peru and the report of Cheilodactylus variegatus as a new paratenic host on the central coast, extending the knowledge and distribution range of this acanthocephalan in Southeastern Pacific Ocean.

Bacterial dysbiosis and epithelial status of the California sea lion (Zalophus californianus) in the Gulf of California.

Despite the high incidence of urogenital carcinoma (UGC) in California sea lions stranded along California, no UGC has been reported in other areas of their distribution; however, cell morphologies typical of premalignant states have been found. Risk factors for UGC include high of organochlorines and infection with a gammaherpesvirus, OtHV-1, but the importance of the bacteriome for epithelial status remains unknown. We characterized the genital bacteriome of adult female California sea lions along their distribution in the Gulf of California and examined whether the diversity and abundance of the bacteriome varied spatially, whether there were detectable differences in the bacteriome between healthy and altered epithelia, and whether the bacteriome was different in California sea lions infected with OtHV-1 or papillomavirus. We detected 2270 ASVs in the genital samples, of which 35 met the criteria for inclusion in the core bacteriome. Fusobacteriia and Clostridia were present in all samples, at high abundances, and Actinobacteria, Alphaproteobacteria, and Campylobacteria were also well-represented. Alpha diversity and abundance of the California sea lion genital bacteriome varied geographically. The abundance of bacterial ASVs varied depending on the genital epithelial status and inflammation, with differences driven by classes Fusobacteriia, Clostridia, Campylobacteria and Alphaproteobacteria. Alpha diversity and abundance were lowest in samples in which OtHV-1 was detected, and highest those with papillomavirus. Our study is the first investigation of how the bacteriome is related to epithelial status in a wild marine species prone to developing cancer.

Agreement Study between Total Leukocyte Count Methodologies in South American Sea Lions (Otaria byronia) and Peruvian Fur Seals (Arctocephalus australis).

South American sea lions (Otaria byronia) and Peruvian fur seals (Arctocephalus australis) are sympatric species inhabiting the coastal Peruvian marine ecosystem. Declining abundance has prompted population health monitoring programs, including temporal monitoring of blood parameters. Several methods exist to determine total leukocyte count, yet no studies have evaluated agreement between methods in pinnipeds. We assessed agreement between total leukocyte counts determined by blood film estimate, Leuko-TIC, HemoCue, and UNOPETTE methods by using archival results from pinnipeds at Punta San Juan, Peru. Blood film estimates were prospectively performed, and resulting data were compared with retrospective leukocyte counts obtained from both species between 2009 and 2019 by using the other methodologies. Agreement in hematologic counts between methods was evaluated using Passing-Bablok regression and Bland-Altman plots (α=0.05). In total, 295 individuals (201 A. australis and 94 O. byronia) were included in the analysis. The blood film estimate method resulted in the highest leukocyte values (P<0.0001). Leuko-TIC counts were significantly higher than HemoCue counts (P<0.0001). Constant and proportional error was present in the agreement between the blood film estimate method and the other methods. Given the variation demonstrated between the different methodologies, additional research is needed to further evaluate agreement between these methodologies. The results underscore the importance of maintaining consistency in leukocyte count methodology for monitoring trends in population health over time. Method consistency may be the more important clinical consideration for assessing changes in leucocyte count over time and avoiding apparent changes depending on the methodology used.

California sea lions interfere with striped marlin hunting behaviour in multi-species predator aggregations.

The open ocean offers a suite of ecological conditions promoting the occurrence of multi-species predator aggregations. These mixed predator aggregations typically hunt large groups of relatively small and highly cohesive prey. However, the mechanisms and functions of these mixed predator aggregations are largely unknown. Even basic knowledge of whether the predator species' interactions are mutualistic, commensal or parasitic is typically missing. Moreover, recordings of attack and capture rates of marine multi-species predator aggregations, which are critical in understanding how and why these interactions have evolved, are almost completely non-existent owing to logistical challenges. Using underwater video, we quantified the attack and capture rates of two high-trophic level marine predators, California sea lions (Zalophus californianus) and striped marlin (Kajikia audax) attacking schools of fishes in the Southern California Current System, offshore the Baja California Peninsula. Recording over 5000 individual attacks across 13 fish schools, which varied in species, size and predator composition, we found that sea lions kleptoparasitized striped marlin hunts and reduced the frequency of marlin attacks and captures via interference competition. We discuss our results in the context of the phenotypic differences between the predator species and implications for a better understanding of multi-species predator aggregations. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity.

The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding.

Detection of microplastic particles in scats from different colonies of California sea lions (Zalophus californianus) in the Gulf of California, Mexico: A preliminary study.

Microplastics (MPs, < 5 mm in size) are highly bioavailable to many taxa within the marine ecosystem, either ingested directly or indirectly through trophic transfer from polluted prey. The ingestion analysis of these MPs from top predators, such as pinnipeds in Mexico, is relatively unexplored. Forty-eight scats from California sea lions were collected on six rookeries along the Gulf of California. From these scat samples, 294 suspected MPs particles were classified and chemically analyzed; 34% were synthetic and semi-synthetic, and 66% were non-synthetic. Blue-colored polyethylene terephthalate fibers were the most common type of MP registered. During laboratory work, multiple contamination control measures were implemented. Although the ingestion pathway is still unknown, our results support the other authors that suggest the potential trophic transfer of MPs to top predators and incidental ingestion while foraging. The particles documented here provide important baseline information for future MP research in the Gulf of California.

Doppler echocardiography in a healthy, non-sedated Southern Sea Lion (Otaria flavescens) - a preliminary approach about the feasibility and clinical utility.

Echocardiography is commonly used in veterinary clinical practice for many species but is not as easily applied in non-sedated marine mammals. Additionally, Doppler echocardiography provides further information on hemodynamics, estimation of cardiac output, characterization of flow patterns, and diastolic function. However, its applications in marine mammals have not been as widely explored either. The present report aimed to characterize the left ventricle structure and function of the Southern Sea Lion (Otaria flavescens) through a Doppler echocardiography study. Data were obtained from a healthy animal trained for different veterinary examination routines. This communication constitutes the first report of Doppler echocardiography with stroke volume, and cardiac output measurement in pinnipeds, and the first report of measurement of myocardial performance index in aquatic mammals. This data brought initial information about in vivo structure and function of the heart of the Southern Sea Lion that can be safely and effectively evaluated with the use of transthoracic Doppler echocardiography. Our data have both clinical and research implications for future studies evaluating diseases of the cardiopulmonary system in pinnipeds, and cardiovascular physiology investigation in diving mammals.