Structural correlates of forelimb function in fur seals and sea lions

Dissections, manipulation of ligamentary preparations, analysis of limb proportions, and quantitative aspects of forelimb myology are used to correlate forelimb morphology in fur seals and sea lions (sub-family Otariinae) with previously published data as to their locomotor function (English, '76a). Comparisons to structure and function in generalized fissiped carnivores are then used to elucidate locomotor adaptations in fur seals and sea lions. Unique features of forelimb function during swimming in these pinnipeds include the amounts of abduction-adduction and rotary movements used. Modifications of the size, attachments and fascicle architecture of the muscles and the structure and range of possible movement of the joints suggest that in fur seals and sea lions these movements (1) take place about the glenohumeral (shoulder) joints, (2) that the movements are probably finely controlled, and (3) that they contribute to the generation of massive forward thrust via the cooperative activity of muscles capable of generating large amounts of force throughout the range of movement. Recovery movements occur through a similarly large range, and modifications of forelimb anatomy either to minimize or overcome water resistance are noted. The adaptive significance of these modifications is interpreted as allowing fur seals and sea lions to swim at speeds necessary to feed on the fast swimming prey presumably abundant in their adaptive zone.     

Moving in two worlds: aquatic and terrestrial locomotion in sea snakes (Laticauda colubrina,Laticaudidae)

Yellow‐lipped sea kraits (Laticauda colubrina) are amphibious in their habits. We measured their locomotor speeds in water and on land to investigate two topics: (1) to what degree have adaptations to increase swimming speed (paddle‐like tail etc.) reduced terrestrial locomotor ability in sea kraits?; and (2) do a sea krait’s sex and body size influence its locomotor ability in these two habitats, as might be expected from the fact that different age and sex classes of sea kraits use the marine and terrestrial environments in different ways? To estimate ancestral states for locomotor performance, we measured speeds of three species of Australian terrestrial elapids that spend part of their time foraging in water. The evolutionary modifications of Laticauda for marine life have enhanced their swimming speeds by about 60%, but decreased their terrestrial locomotor speed by about 80%. Larger snakes moved faster than smaller individuals in absolute terms but were slower in terms of body lengths travelled per second, especially on land. Male sea kraits were faster than females (independent of the body‐size effect), especially on land. Prey items in the gut reduced locomotor speeds both on land and in water. Proteroglyphous snakes may offer exceptional opportunities to study phylogenetic shifts in locomotor ability, because (1) they display multiple independent evolutionary shifts from terrestrial to aquatic habits, and (2) one proteroglyph lineage (the laticaudids) displays considerable intraspecific and interspecific diversity in terms of the degree to which they use terrestrial vs. aquatic habitats.     

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.     

Comparative limb bone scaling in turtles: Phylogenetic transitions with changes in functional demands?

Several terrestrial vertebrate clades include lineages that have evolved nearly exclusive use of aquatic habitats. In many cases, such transitions are associated with the evolution of flattened limbs that are used to swim via dorsoventral flapping. Such changes in shape may have been facilitated by changes in limb bone loading in novel aquatic environments. Studies on limb bone loading in turtles found that torsion is high relative to bending loads on land, but reduced compared to bending during aquatic rowing. Release from torsion among rowers could have facilitated the evolution of hydrodynamically advantageous flattened limbs among aquatic species. Because rowing is regarded as an intermediate locomotor stage between walking and flapping, rowing species might show limb bone flattening intermediate between the tubular shapes of walkers and the flattened shapes of flappers. We collected measurements of humeri and femora from specimens representing four functionally divergent turtle clades: sea turtles (marine flappers), softshells (specialized freshwater rowers), emydids (generalist semiaquatic rowers), and tortoises (terrestrial walkers). Patterns of limb bone scaling with size were compared across lineages using phylogenetic comparative methods. Although rowing taxa did not show the intermediate scaling patterns we predicted, our data provide other functional insights. For example, flattening of sea turtle humeri was associated with positive allometry (relative to body mass) for the limb bone diameter perpendicular to the flexion-extension plane of the elbow. Moreover, softshell limb bones exhibit positive allometry of femoral diameters relative to body mass, potentially helping them maintain their typical benthic position in water by providing additional weight to compensate for shell reduction. Tortoise limb bones showed positive allometry of diameters, as well as long humeri, relative to body mass, potentially reflecting specializations for resisting loads associated with digging. Overall, scaling patterns of many turtle lineages appear to correlate with distinctive behaviors or locomotor habits.     

Hydrodynamic perception in true seals (Phocidae) and eared seals (Otariidae)

Pinnipeds, that is true seals (Phocidae), eared seals (Otariidae), and walruses (Odobenidae), possess highly developed vibrissal systems for mechanoreception. They can use their vibrissae to detect and discriminate objects by direct touch. At least in Phocidae and Otariidae, the vibrissae can also be used to detect and analyse water movements. Here, we review what is known about this ability, known as hydrodynamic perception, in pinnipeds. Hydrodynamic perception in pinnipeds developed convergently to the hydrodynamic perception with the lateral line system in fish and the sensory hairs in crustaceans. So far two species of pinnipeds, the harbour seal (Phoca vitulina) representing the Phocidae and the California sea lion (Zalophus californianus) representing the Otariidae, have been studied for their ability to detect local water movements (dipole stimuli) and to follow hydrodynamic trails, that is the water movements left behind by objects that have passed by at an earlier point in time. Both species are highly sensitive to dipole stimuli and can follow hydrodynamic trails accurately. In the individuals tested, California sea lions were clearly more sensitive to dipole stimuli than harbour seals, and harbour seals showed a superior trail following ability as compared to California sea lions. Harbour seals have also been shown to derive additional information from hydrodynamic trails, such as motion direction, size and shape of the object that caused the trail (California sea lions have not yet been tested). The peculiar undulated shape of the harbour seals’ vibrissae appears to play a crucial role in trail following, as it suppresses self-generated noise while the animal is swimming.     

Mirror image processing in three marine mammal species: killer whales (Orcinus orca), false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus)

Dolphins (Tursiops truncatus) and their relatives might be expected to show mirror-induced contingency checking, a prerequisite to self-recognition, because of their high brain development, their complex social life and their demonstrated abilities in bodily imitation. A study of killer whales'(Orcinus orca) behaviour in front of a mirror is presented, including a mark test. Shorter investigations of mirror behaviour are also described in false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus). Contingency checking was present in killer whales and possibly also in false killer whales, but no clear contingency checking was observed in sea lions. The mark test on killer whales suggested that the marked animal anticipated that its image would look different. This study shows that killer whales and false killer whales, like bottlenose dolphins, appear to possess the cognitive abilities required for self-recognition.     

Lateralised swimming behaviour in the California sea lion

Lateralised motor behaviour in the pinnipeds has been subject to little investigation. This study examined the swimming behaviour of seven zoo-housed California sea lions to determine whether they exhibited a directional bias in their motor behaviour. Data were collected on the direction of the animals' swimming patterns from the point of entering a pool of water from dry land. Each animal was studied for 100 episodes of swimming. All seven of the sea lions showed significant (P<0.001) bias in the direction of their swimming, although unidirectional bias was not observed at the level of the population. The direction of the sea lions' swimming patterns varied significantly according to the animals' sex. Males showed a preference at the level of the population for swimming in a clockwise direction, while females showed a population-level counterclockwise swimming preference. Overall, the findings appear to suggest that California sea lions, like other marine mammals, exhibit motor bias in the direction of their swimming patterns, although further work using larger sample sizes is needed before more firm conclusions regarding motor laterality in this species can be reached.     

Trial Implantation of Heart Rate Data Loggers in Pinnipeds

ABSTRACT Pinnipeds are major consumers in marine ecosystems, and understanding their energy budgets is essential to determining their role in food webs, particularly where there is competition with fisheries. Food consumption and energy expenditure have been evaluated in pinnipeds using different methods, but the use of heart rate to estimate energy expenditure is potentially a very powerful tool suited to the life history of these animals. We tested a procedure for the subcutaneous implantation of heart rate data loggers to determine whether heart rate could be recorded for ≥1 year in free-ranging pinnipeds, as it has been in birds. We implanted 3 captive California sea lions (Zalophus californianus) and 3 captive northern elephant seals (Mirounga angustirostris) with heart rate data loggers and monitored their recovery and behavior in a controlled environment. In both species, the implantation site allowed for excellent detection of the electrocardiogram, and we observed heart rate signatures characteristic of behaviors such as resting and diving. Although all 3 sea lions recovered well from the implantation surgery, all 3 elephant seals showed a substantial inflammatory response for unknown reasons, and we removed the implanted data loggers. Subcutaneous implantation of data loggers is a powerful technique to study physiology, energetics, and behavior in California sea lions, but more work is required to realize the potential of this technique in northern elephant seals.     

Innervation patterns of mystacial vibrissae support active touch behaviors in California sea lions (Zalophus californianus)

Vibrissae or follicle-sinus complexes (F-SCs) are highly developed mammalian sensory structures. These blood-filled sinuses are richly innervated and possess novel mechanoreceptors. Although much is known regarding the function of F-SCs in terrestrial mammals, much less is known regarding marine carnivores such as pinnipeds. Pinnipeds possess the largest, most highly innervated vibrissae of any mammal. One such pinniped is the California sea lion, which are generalist marine predators that rely heavily upon tactile discrimination capabilities. Psychophysical studies demonstrate that haptic tactile discrimination using F-SCs is exceptionally sensitive. However, our knowledge of the structure and function of F-SCs in otariids is limited. Our objectives were to investigate the innervation and microstructure of F-SCs across the mystacial vibrissal field and infer function from haptic performance studies in California sea lions. Innervation and microstructure of vibrissae differed considerably compared to similar data available for phocids. Total innervation of mystacial vibrissae was estimated to be 86,042 axons. Investigations of innervation density and investment of microvibrissae versus macrovibrissae demonstrated a significantly increased axon density per F-SC in medial microvibrissal regions compared to lateral macrovibrissae, which supports psychophysical data and somatotopic organization of the central nervous system involved with tactile discrimination capability. Innervation increased from medial microvibrissae (705 ± 125 axons/F-SC) to lateral macrovibrissae (1,447 ± 154) as well as from dorsal (541 ± 60) to ventral (1,493 ± 327) vibrissal regions. These data provide a more complete picture of the sensory ecology of this important aquatic mammalian lineage; the specialization of peripheral sensory structures, central nervous structures with demonstrated enhanced haptic capabilities behaviorally has likely led to the ecological success of California sea lions.     

Risk factors for an outbreak of leptospirosis in California sea lions (Zalophus californianus) in California, 2004

Leptospirosis has been reported in California sea lions (Zalophus californianus) since 1970; however, the source of infection and mode of transmission remain unknown. To elucidate these features, demographic and environmental risk factors for leptospirosis were evaluated. California sea lion stranding records from northern California for 2004 were used to identify cases of leptospirosis (n = 316) and controls (n = 143). Demographic characteristics (age class, sex) and environmental factors, representing surrogates for exposure to dogs, cattle, rainfall, and freshwater sources, were compared between cases and controls with the use of a geographic information system (GIS) and logistic regression. Multivariate analyses revealed that summer and autumn seasons, juvenile age class, male sex, high dog-park density, and close proximity to dog parks were significantly associated with leptospirosis in sea lions, whereas county farmland cattle density, rainfall levels 30 days prior to stranding, human density, and proximity to freshwater sources were not associated. Thus, dogs and dog parks, or factors associated with them, might be further investigated to assess their relationship to leptospirosis in sea lions.     

ARE PINNIPEDS FUNCTIONALLY DIFFERENT FROM FISSIPED CARNIVORES? THE IMPORTANCE OF PHYLOGENETIC COMPARATIVE ANALYSES

Abstract.— It is widely assumed that adaptations to an aquatic lifestyle are so profound as to produce only obvious differences between pinnipeds and the remaining, largely terrestrial carnivore species ("fissipeds"). Thus, comparative studies of the order Carnivora routinely examine these groups independently. This approach is invalid for two reasons. First, fissipeds are a paraphyletic assemblage, which raises the general issue of when it is appropriate to ignore monophyly as a criterion for inclusion in comparative studies. Second, the claim that most functional characters (beyond a few undoubted characteristic features) are different in pinnipeds and fissipeds has never been quantitatively examined, nor with phylogenetic comparative methods. We test for possible differences between these two groups in relation to 20 morphological, life-history, physiological, and ecological variables. Comparisons employed the method of independent contrasts based on a complete and dated species-level phylogeny of the extant Carnivora. Pinnipeds differ from fissipeds only through evolutionary grade shifts in a limited number of life-history traits: litter weight (vs. gestation length), birth weight, and age of eyes opening (both vs. size). Otherwise, pinnipeds display the same rate of evolution as phylogenetically equivalent fissiped taxa for all variables. Overall functional differences between pinnipeds and fissipeds appear to have been overstated and may be no greater than those among major fissiped groups. Recognition of this fact should lead to a more complete understanding of carnivore biology as a whole through more unified comparative tests. Comparative studies that do not include monophyletic groups for phylogenetically based comparative tests should be reconsidered.     

Molecular and morphometric evidence for separate species of Uncinaria (Nematoda: Ancylostomatidae) in California sea lions and northern fur seals: hypothesis testing supplants verification

California sea lions (Zalophus californianus) and northern fur seals (Callorhinus ursinus) are each believed to host distinct hookworm species (Uncinaria spp.). However, a recent morphometric analysis suggested that a single species parasitizes multiple pinniped hosts, and that the observed differences are host-induced. To explore the systematics of these hookworms and test these competing hypotheses, we obtained nucleotide sequences of nuclear ribosomal DNA (D2/D3 28S, D18/D19 28S, and internal transcribed spacer [ITS] regions) from 20 individual hookworms parasitizing California sea lion and northern fur seal pups where their breeding grounds are sympatric. Five individuals from an allopatric population of California sea lions were also sampled for ITS-1 and D18/D19 28S sequences. The 28S D2/D3 sequences showed no diagnostic differences among hookworms sampled from individual sea lions and fur seals, whereas the 28S D18/D19 sequences had one derived (apomorphic) character demarcating hookworms from northern fur seals. ITS sequences were variable for 7 characters, with 4 derived (apomorphic) states in ITS-1 demarcating hookworms from California sea lions. Multivariate analysis of morphometric data also revealed significant differences between nematodes representing these 2 host-associated lineages. These results indicate that these hookworms represent 2 species that are not distributed indiscriminately between these host species, but instead exhibit host fidelity, evolving independently with each respective host species. This evolutionary approach to analyzing sequence data for species delimitation is contrasted with similarity-based methods that have been applied to numerous diagnostic studies of nematode parasites.     

Primate limb bones and locomotor types in arboreal or terrestrial environments

Postcranial limb bones were compared among primates of different locomotor types. Seventy-one primate species, in which all families of primates were included, were grouped into nine locomotor types. Osteometrical data on long bones and data on the cross-sectional geometry of the humerus and the femur were studied by means of allometric analysis and principal component analysis. Relatively robust forelimb bones were observed in the primate group which adopted the relatively terrestrial locomotor type compared with the group that adopted the arboreal locomotor type. The difference resembled the previously reported comparison between terrestrial and arboreal groups among all quadrupedal mammals. The degree of arboreality in daily life is connected with the degree of hindlimb dominance, or the ratio of force applied to the fore- and hindlimb in positional behaviour and also with the shape, size and robusticity of limb bones.     

The development of the pulmonary surfactant system in California sea lions

Pulmonary surfactant has previously been shown to change during development, both in composition and function. Adult pinnipeds, unlike adult terrestrial mammals, have an altered lung physiology to cope with the high pressures associated with deep diving. Here, we investigated how surfactant composition and function develop in California sea lions (Zalophus californianus). Phosphatidylinositol was the major anionic phospholipid in the newborn, whereas phosphatidylglycerol was increased in the adult. This increase in phosphatidylglycerol occurred at the expense of phosphatidylinositol and phosphatidylserine. There was a shift from long chain and polyunsaturated phospholipid molecular species in the newborn to shorter chain and mono- and disaturated molecular species in the adult. Cholesterol and SP-B concentrations were also higher in the adult. Adult surfactant could reach a lower equilibrium surface tension, but newborn surfactant could reach a lower minimum surface tension. The composition and function of surfactant from newborn California sea lions suggest that this age group is similar to terrestrial newborn mammals, whereas the adult has a "diving mammal" surfactant that can aid the lung during deep dives. The onset of diving is probably a trigger for surfactant development in these animals.     

QUANTIFICATION OF TERRESTRIAL HAUL-OUT AND ROOKERY CHARACTERISTICS OF STELLER SEA LIONS

Steller sea lions ( Eumetopias jubatus ) are known to have occupied the same terrestrial haul-out and rookery sites across the North Pacific Rim for centuries, but it is not known why they choose and stay at these locations, or what defines their preferred habitat. Classifying and comparing the shoreline type of haul-outs and rookeries against sites not used by Steller sea lions showed that they preferentially locate their haul-outs and rookeries on exposed rocky shorelines and wave-cut platforms. However, no preference was found for selecting rookeries on sheltered shore types. Shoreline types used less frequently by sea lions included fine-to-medium-grained sand beaches, mixed sand and gravel beaches, gravel beaches, and sheltered rocky shores. Quantifying the shoreline types used by sea lions confirms anecdotal reports of habitat preferences and may prove useful in identifying and protecting sea lion terrestrial habitat, or in forecasting how climate change might affect the distribution of sea lions.     

Terrestriality constrains salamander limb diversification: Implications for the evolution of pentadactyly

Patterns of phenotypic evolution can abruptly shift as species move between adaptive zones. Extant salamanders display three distinct life cycle strategies that range from aquatic to terrestrial (biphasic), to fully aquatic (paedomorphic) and to fully terrestrial (direct development). Life cycle variation is associated with changes in body form such as loss of digits, limb reduction or body elongation. However, the relationships among these traits and life cycle strategy remain unresolved. Here, we use a Bayesian modelling approach to test whether life cycle transitions by salamanders have influenced rates, optima and integration of primary locomotory structures (limbs and trunk). We show that paedomorphic salamanders have elevated rates of limb evolution with optima shifted towards smaller size and fewer digits compared to all other salamanders. Rate of hindlimb digit evolution is shown to decrease in a gradient as life cycles become more terrestrial. Paedomorphs have a higher correlation between hindlimb digit loss and increases in vertebral number, as well as reduced correlations between limb lengths. Our results support the idea that terrestrial plantigrade locomotion constrains limb evolution and, when lifted, leads to higher rates of trait diversification and shifts in optima and integration. The basic tetrapod body form of most salamanders and the independent losses of terrestrial life stages provide an important framework for understanding the evolutionary and developmental mechanisms behind major shifts in ecological zones as seen among early tetrapods during their transition from water to land.     

Terrestrial locomotion in sea snakes: the effects of sex and species on cliff-climbing ability in sea kraits (Serpentes, Elapidae, Laticauda)

Ecomorphological theory predicts a match between an organism's environment and its locomotor abilities, such that animals function most effectively under the conditions they experience in nature. However, amphibious species must simultaneously optimize performance in two different habitats posing incompatible demands on locomotor morphology and physiology. This situation may generate a mismatch between environment and locomotor function, with performance optimized only for the more important habitat type; alternatively, selection may fine-tune locomotor abilities for both types of challenges. Two species of sea kraits in New Caledonia offer an opportunity to examine this question: Laticauda laticaudata is more highly aquatic than L. colubrina , and males are more terrestrial than females within each taxon. We examined an aspect of locomotor performance that is critical to coming ashore on steep-walled rocky islets: the ability to climb steep cliffs. We also measured the muscular strength of these animals, a character that is likely critical to climbing performance. Laticauda colubrina was heavier-bodied and stronger (even relative to its body mass) than the more aquatic L. laticaudata ; and within each species, males were heavier-bodied and stronger than females. The same patterns were evident in cliff-climbing ability. Thus, the ability of different species and sexes of sea kraits to climb steep cliffs correlates with their body shape even though these primarily aquatic animals use terrestrial habitats only rarely.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 433–441.     

INTRASPECIFIC GENETIC DIFFERENTIATION IN CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS) FROM SOUTHERN CALIFORNIA AND THE GULF OF CALIFORNIA

Intraspecific patterns of mitochondrial DNA sequence variation were determined among California sea lions ( Zalophus califomianus californianus ) from three colonies along the Pacific coast of southern and Baja California and one colony in the Gulf of California. We found no variation in 368 base pairs (bp) of cytochrome b sequence among 40 sea lions from these localities, but analysis of 360 base pairs of control region revealed eleven genotypes. The four genotypes found in the Gulf of California population were unique and phylogenetically distinct from those found in sea lions along the Pacific coast. The average sequence divergence between Gulf and Southern California genotypes was 4.3%, suggesting a relatively long period of isolation. However, colonies along the Pacific coast, which are less than 200 km apart, shared mtDNA genotypes, indicating that recent genetic exchange has occurred between them. Therefore, we suggest that regional female philopatry exists in California sea lions. Regional boundaries may be related to oceanic currents or patchiness in the distribution of resources. Further research is needed to better understand the underlying causes of genetic differentiation in the California sea lion.     

Pseudo‐nitzschia blooms,domoic acid,and related California sea lion strandings in Monterey Bay,California

Blooms of the toxin‐producing diatom Pseudo‐nitzschia commonly occur in Monterey Bay, California, resulting in sea lion mortality events. The links between strandings of California sea lions suffering from domoic acid (DA) toxicity, toxic cell numbers, and their associated DA concentration in Monterey Bay and in sea lion feces were examined from 2004 to 2007. While Pseudo‐nitzschia toxic cells and DA concentrations were detectable in the water column most of the time, they were often at low levels. A total of 82 California sea lions were found stranded in the Bay between 2004 and 2007 with acute or chronic signs associated with DA poisoning. The highest number with detectable DA in feces occurred in April 2007 and corresponded with the presence of a highly toxic bloom in the Bay. Higher DA levels occurred in feces from sea lions stranding with acute toxicosis and lower concentrations in feces of sea lions exhibiting signs of chronic DA poisoning or not exhibiting any neurologic signs. Results indicated that sea lions are likely exposed to varying levels of DA through their prey throughout the year, often at sublethal doses that may contribute to a continued increase in the development of chronic neurologic sequelae.     

Linking seasonal distribution patterns with prey availability in a central-place forager, the Steller sea lion

Aim We used a novel approach to infer foraging areas of a central‐place forager, the Steller sea lion (Eumetopias jubatus), by assessing changes in the temporal and spatial distribution patterns of sea lions at terrestrial sites. Specifically, our objectives were (1) to classify seasonal distribution patterns of Steller sea lions and (2) to determine to what extent the seasonal distribution of Steller sea lions is explained by seasonal concentrations of prey. Location Southeast Alaska, USA. Methods Steller sea lions of all age classes were counted monthly (2001–04) by aerial surveys at 28 terrestrial sites. Hierarchical cluster analysis and principal components analysis were used to classify seasonal distribution patterns of Steller sea lions at these terrestrial sites. We estimated the proportion of sea lions in the study area that were associated with each seasonal distribution pattern. Results Multivariate ordination techniques revealed four distinct seasonal distributional patterns. During December, 55% of the sea lions in the study area were found at Type 1 sites, located near over‐wintering herring aggregations. During May, 56% of sea lions were found at Type 2 sites, near aggregations of spring‐spawning forage fish. In July, 78% of sea lions were found at Type 3 sites, near summer migratory corridors of salmon. During September, 44% of sea lions were found at Type 4 sites, near autumn migratory corridors of salmon. Main conclusions Seasonal attendance patterns of sea lions were commonly associated with the seasonal availability of prey species near terrestrial sites and reflected seasonal foraging patterns of Steller sea lions in Southeast Alaska. A reasonable annual foraging strategy for Steller sea lions is to forage on herring (Clupea pallasii) aggregations in winter, spawning aggregations of forage fish in spring, salmon (Oncorhynchus spp.) in summer and autumn, and pollock (Theragra chalcogramma) and Pacific hake (Merluccius productus) throughout the year. The seasonal use of haulouts by sea lions and ultimately haulout‐specific foraging patterns of Steller sea lions depend in part upon seasonally available prey species in each region.