An anchovy ecosystem indicator of marine predator foraging and reproduction.

Forage fishes are key energy conduits that transfer primary and secondary productivity to higher trophic levels. As novel environmental conditions caused by climate change alter ecosystems and predator-prey dynamics, there is a critical need to understand how forage fish control bottom-up forcing of food web dynamics. In the northeast Pacific, northern anchovy (Engraulis mordax) is an important forage species with high interannual variability in population size that subsequently impacts the foraging and reproductive ecology of marine predators. Anchovy habitat suitability from a species distribution model (SDM) was assessed as an indicator of the diet, distribution and reproduction of four predator species. Across 22 years (1998-2019), this anchovy ecosystem indicator (AEI) was significantly positively correlated with diet composition of all species and the distribution of common murres (Uria aalge), Brandt's cormorants (Phalacrocorax penicillatus) and California sea lions (Zalophus californianus), but not rhinoceros auklets (Cerorhinca monocerata). The capacity for the AEI to explain variability in predator reproduction varied by species but was strongest with cormorants and sea lions. The AEI demonstrates the utility of forage SDMs in creating ecosystem indicators to guide ecosystem-based management.

Accuracy and precision of age determination using growth layer groups for California sea lions (Zalophus californianus) with known ages.

Age determination from counts of growth layer groups (GLGs) in tooth dentine is a common method for aging marine mammals. Using known-aged animals, we validated this method for acid etched teeth of California sea lions (CSLs), Zalophus californianus. Between 1991 and 2013, the upper left canine (n = 33) was collected opportunistically during necropsy from animals tagged or branded as pups that later died. Overall, 55%-61% of age estimates by GLG counting were within 1 yr of the known-age in the sample of 1-30-yr-old CSLs. Accuracy of age estimates was found to be dependent on age of the CSLs, however. 71%-79% of age estimates were within 1 yr of the known-age in CSLs <10 yr old. These findings support the validity of counting GLGs to estimate age for CSLs <10 yr old to within 1 yr of accuracy.

Detecting signals of chronic shedding to explain pathogen persistence: Leptospira interrogans in California sea lions.

Identifying mechanisms driving pathogen persistence is a vital component of wildlife disease ecology and control. Asymptomatic, chronically infected individuals are an oft-cited potential reservoir of infection, but demonstrations of the importance of chronic shedding to pathogen persistence at the population-level remain scarce. Studying chronic shedding using commonly collected disease data is hampered by numerous challenges, including short-term surveillance that focuses on single epidemics and acutely ill individuals, the subtle dynamical influence of chronic shedding relative to more obvious epidemic drivers, and poor ability to differentiate between the effects of population prevalence of chronic shedding vs. intensity and duration of chronic shedding in individuals. We use chronic shedding of Leptospira interrogans serovar Pomona in California sea lions (Zalophus californianus) as a case study to illustrate how these challenges can be addressed. Using leptospirosis-induced strands as a measure of disease incidence, we fit models with and without chronic shedding, and with different seasonal drivers, to determine the time-scale over which chronic shedding is detectable and the interactions between chronic shedding and seasonal drivers needed to explain persistence and outbreak patterns. Chronic shedding can enable persistence of L. interrogans within the sea lion population. However, the importance of chronic shedding was only apparent when surveillance data included at least two outbreaks and the intervening inter-epidemic trough during which fadeout of transmission was most likely. Seasonal transmission, as opposed to seasonal recruitment of susceptibles, was the dominant driver of seasonality in this system, and both seasonal factors had limited impact on long-term pathogen persistence. We show that the temporal extent of surveillance data can have a dramatic impact on inferences about population processes, where the failure to identify both short- and long-term ecological drivers can have cascading impacts on understanding higher order ecological phenomena, such as pathogen persistence.

Effects of Age, Colony, and Sex on Mercury Concentrations in California Sea Lions.

We measured total mercury (THg) concentrations in California sea lions (Zalophus californianus) and examined how concentrations varied with age class, colony, and sex. Because Hg exposure is primarily via diet, we used nitrogen (δ (15)N) and carbon (δ (13)C) stable isotopes to determine if intraspecific differences in THg concentrations could be explained by feeding ecology. Blood and hair were collected from 21 adult females and 57 juveniles from three colonies in central and southern California (San Nicolas, San Miguel, and Año Nuevo Islands). Total Hg concentrations ranged from 0.01 to 0.31 µg g(-1) wet weight (ww) in blood and 0.74 to 21.00 µg g(-1) dry weight (dw) in hair. Adult females had greater mean THg concentrations than juveniles in blood (0.15 vs. 0.03 µg(-1) ww) and hair (10.10 vs. 3.25 µg(-1) dw). Age class differences in THg concentrations did not appear to be driven by trophic level or habitat type because there were no differences in δ (15)N or δ (13)C values between adults and juveniles. Total Hg concentrations in adult females were 54 % (blood) and 24 % (hair) greater in females from San Miguel than females from San Nicolas Island, which may have been because sea lions from the two islands foraged in different areas. For juveniles, we detected some differences in THg concentrations with colony and sex, although these were likely due to sampling effects and not ecological differences. Overall, THg concentrations in California sea lions were within the range documented for other marine mammals and were generally below toxicity benchmarks for fish-eating wildlife.

Review of research on hookworms (Uncinaria lucasi Stiles, 1901) in northern fur seals (Callorhinus ursinus Linnaeus, 1758).

The objective of this article is to review knowledge on the hookworm Uncinaria lucasi Stiles, 1901 in northern fur seals, Callorhinus ursinus Linnaeus, 1758. Emphasis is placed on research on this host-parasite system in the Pribilof Islands, AK, USA where the bulk of the studies has been performed.

Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals.

Assessing the physiological impact of stressors in pinnipeds is logistically challenging, and many hormones are altered by capture and handling, limiting the utility of metabolically active tissues. Hair is increasingly being used to investigate stress-related and reproductive hormones in wildlife populations due to less-invasive collection methods, being metabolically inert once grown and containing multiple biomarkers of ecological interest. We validated enzyme immunoassays for measuring aldosterone, cortisol, corticosterone, and testosterone in lanugo (natal hair grown in utero) samples collected from Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus). We applied laboratory validation methods including recovery of added mass, parallelism and dilution linearity. We found no effects due to differences in alcohol- versus detergent-based cleaning methods. Further, there were no significant differences in hormone concentrations in hair samples collected immediately after the molt and the subsequent samples collected over 1 year, indicating steroid hormones are stable once deposited into pinniped hair. We found no sex differences in any hormone concentrations, likely due to the lanugo being grown in utero and influenced by maternal hormone concentrations. For Steller sea lion and California sea lion pups, we found hormone concentrations significantly differed between rookeries, which warrants future research. Hair provides a novel tissue to explore the intrinsic or extrinsic drivers behind hormone measurements in otariids, which can be paired with multiple health-related metrics to further investigate possible drivers of physiological stress.

Migratory strategies of juvenile northern fur seals (Callorhinus ursinus): bridging the gap between pups and adults.

In species exhibiting differential migration by sex and age, understanding what differences exist, and the adaptive reasons for these differences is critical for determining how demographic groups will respond to environmental variability and anthropogenic perturbations. We used satellite-telemetered movement and diving data to investigate differential migration and its ontogeny in a highly migratory North Pacific Ocean predator, the northern fur seal (Callorhinus ursinus; NFS), with a focus on understudied juvenile (1- to 2-year-old) animals. We instrumented 71 juvenile NFS in two years (2006-07 and 2007-08) at three major North American breeding sites and compared their migratory strategies with pups and adults. Although sexual dimorphism is strong in adult NFS, only weak differences in body mass between sexes were found in juveniles, which had similar body mass to pups (~3-4 months). However, unlike widely-dispersed pups, juvenile male and female NFS dispersed in different directions, and used different habitats characterized by distinct hydrography and prey assemblages during migration, similar to breeding adults. Juvenile diving behavior differed only modestly among habitats and between sexes, consistent with weak differences in body mass. Evidence of habitat sexual segregation by juvenile NFS contradicts previous hypotheses that physiological differences predominantly drive the ontogeny of differential migration.

The energetic consequences of behavioral variation in a marine carnivore.

Intraspecific variability in foraging behavior has been documented across a range of taxonomic groups, yet the energetic consequences of this variation are not well understood for many species. Understanding the effect of behavioral variation on energy expenditure and acquisition is particularly crucial for mammalian carnivores because they have high energy requirements that place considerable pressure on prey populations. To determine the influence of behavior on energy expenditure and balance, we combined simultaneous measurements of at-sea field metabolic rate (FMR) and foraging behavior in a marine carnivore that exhibits intraspecific behavioral variation, the California sea lion (Zalophus californianus). Sea lions exhibited variability in at-sea FMR, with some individuals expending energy at a maximum of twice the rate of others. This variation was in part attributable to differences in diving behavior that may have been reflective of diet; however, this was only true for sea lions using a foraging strategy consisting of epipelagic (<200 m within the water column) and benthic dives. In contrast, sea lions that used a deep-diving foraging strategy all had similar values of at-sea FMR that were unrelated to diving behavior. Energy intake did not differ between foraging strategies and was unrelated to energy expenditure. Our findings suggest that energy expenditure in California sea lions may be influenced by interactions between diet and oxygen conservation strategies. There were no apparent energetic trade-offs between foraging strategies, although there was preliminary evidence that foraging strategies may differ in their variability in energy balance. The energetic consequences of behavioral variation may influence the reproductive success of female sea lions and result in differential impacts of individuals on prey populations. These findings highlight the importance of quantifying the relationships between energy expenditure and foraging behavior in other carnivores for studies addressing fundamental and applied physiological and ecological questions.

Age-prevalence of Otarine Herpesvirus-1, a tumor-associated virus, and possibility of its sexual transmission in California sea lions.

Otarine Herpesvirus-1 (OtHV-1) is a gammaherpesvirus routinely detected in urogenital tumor tissues of adult sea lions dying during rehabilitation, To investigate the epidemiology of this virus and guide the development of a mathematical model of its role in the multifactorial etiology of cancer in California sea lions, polymerase chain reaction (PCR) amplification of an OtHV-1 specific fragment of the DNA polymerase gene was used to look for evidence of OtHV-1 infection in urogenital and pharyngeal swabs and peripheral blood mononuclear cells (PBMC) of sea lions of different ages. Samples were also examined from pregnant females and their late term in utero or aborted fetuses to investigate potential for vertical transmission. Prevalence of infection in 72 adult females was 22%, whereas it was 46% in 52 adult males, and was significantly lower in 120 juvenile animals (6%). OtHV-1 DNA was most often detected in the lower reproductive tract of the adult animals, especially the males, and rarely in the pharynx or urogenital tract of juvenile animals. These data suggest sexual transmission may an important route of transmission. Additional studies are required to confirm this mode of transmission. Additionally, the virus was detected in a single prematurely born pup, suggesting the possibility of perinatal transmission. No indication of a PBMC associated viremia was evident in adults using standard PCR or in juveniles using standard and real time PCR.

Hookworm enteritis with bacteremia in California sea lion pups on San Miguel Island.

Large breeding populations of California sea lions (Zalophus californianus) are located on San Miguel and San Nicolas Islands in the Southern California Bight. In 2001, there was a substantial increase in pup mortality in late summer and fall. From June 2002 to January 2003, 208 freshly dead pups were examined on San Miguel Island, the most western of the Channel Islands off the coast of southern California. Tissues from 186 of these pups were examined histologically. The primary lesions in 133 (72%) of the pups were an enteritis associated with hookworms and infections in major organs. Emaciation/starvation in 43 pups (26%) was the second most important cause of death.

Extreme weather events influence dispersal of naive northern fur seals.

Since 1975, northern fur seal (Callorhinus ursinus) numbers at the Pribilof Islands (PI) in the Bering Sea have declined rapidly for unknown reasons. Migratory dispersal and habitat choice may affect first-year survivorship, thereby contributing to this decline. We compared migratory behaviour of 166 naive pups during 2 years from islands with disparate population trends (increasing: Bogoslof and San Miguel Islands; declining: PI), hypothesizing that climatic conditions at weaning may differentially affect dispersal and survival. Atmospheric conditions (Bering Sea) in autumn 2005-2006 were anomalously cold, while 2006-2007 was considerably warmer and less stormy. In 2005, pups departed earlier at all sites, and the majority of PI pups (68-85%) departed within 1 day of Arctic storms and dispersed quickly, travelling southwards through the Aleutian Islands. Tailwinds enabled faster rates of travel than headwinds, a trend not previously shown for marine mammals. Weather effects were less pronounced at Bogoslof Island (approx. 400 km further south), and, at San Miguel Island, (California) departures were more gradual, and only influenced by wind and air pressure in 2005. We suggest that increasingly variable climatic conditions at weaning, particularly timing, frequency and intensity of autumnal storms in the Bering Sea, may alter timing, direction of dispersal and potentially survival of pups.

Contrasting effects of heterozygosity on survival and hookworm resistance in California sea lion pups.

Low genetic heterozygosity is associated with loss of fitness in many natural populations. However, it remains unclear whether the mechanism is related to general (i.e. inbreeding) or local effects, in particular from a subset of loci lying close to genes under balancing selection. Here we analyse involving heterozygosity-fitness correlations on neonatal survival of California sea lions and on susceptibility to hookworm (Uncinaria spp.) infection, the single most important cause of pup mortality. We show that regardless of differences in hookworm burden, homozygosity is a key predictor of hookworm-related lesions, with no single locus contributing disproportionately. Conversely, the subsequent occurrence of anaemia due to blood loss in infected pups is overwhelmingly associated with homozygosity at one particular locus, all other loci showing no pattern. Our results suggest contrasting genetic mechanisms underlying two pathologies related to the same pathogen. First, relatively inbred pups are less able to expel hookworms and prevent their attachment to the intestinal mucosa, possibly due to a weakened immune response. In contrast, infected pups that are homozygous for a gene near to microsatellite Hg4.2 are strongly predisposed to anaemia. As yet, this gene is unknown, but could plausibly be involved in the blood-coagulation cascade. Taken together, these results suggest that pathogenic burden alone may not be the main factor regulating pathogen-related mortality in natural populations. Our study could have important implications for the conservation of small, isolated or threatened populations, particularly when they are at a risk of facing pathogenic challenges.

An immunogenetic basis for the high prevalence of urogenital cancer in a free-ranging population of California sea lions (Zalophus californianus).

In response to an unprecedented prevalence of cancer recently identified in free-ranging populations of California sea lions [(CSL) (Zalophus californianus], we examined the role of the immunologically important major histocompatibility (MHC) genes in this disease epidemic. Associations between MHC genes and cancer have been well established in humans, but have never before been investigated in wildlife. Using a previously developed technique employing sequence-specific primer-based PCR with intercalating dye technology, MHC genotypes were examined from 27 cancer-positive and 22 cancer-negative CSL stranded along the California coastline. Analyses elucidated an underlying immunogenetic component to the high prevalence of urogenital cancer in sea lions. Furthermore, these results demonstrate the functional relevance of CSL class II MHC by revealing a non-random nature of cancer susceptibility associated with the presence of specific genes.

Class II multiformity generated by variable MHC- DRB region configurations in the California sea lion ( Zalophus californianus).

In light of the immunological importance of molecules encoded within the major histocompatibility complex ( MHC), there are numerous studies examining the variability of these genes in wildlife populations. An underlying assumption in many of these studies is that MHC diversity invariably arises from a high level of allelic variation at a single gene locus, leading to widespread descriptions of thriving species with apparently limited MHC polymorphism. Indeed, in a previous study we failed to find sequence features compatible with traditionally diverse peptide-binding functions in MHC class II ( DQA and DQB) genes in California sea lions and therefore expanded the search for polymorphism to the DRA and DRB genes. Our results show that, in contrast to Zaca-DQA, -DQB, and - DRA, Zaca-DRB has sequence features compatible with antigen binding and presentation. In fact Zaca-DRB constitutes a gene family, comprising at least seven loci, each of which exhibits limited variability, and which are present in variable configurations between individuals. This unusual mechanism for generating MHC DRB diversity is similar to that observed in the rhesus macaque, but has not been reported in any other species. The identification of a novel system of class II MHC variability in the California sea lion justifies new studies into the organizational basis of immunogenetic diversity in other marine species, and its role in infectious disease susceptibility.