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Assessing Northern Elephant Seal feeding habits by stomach lavage
Abstract
A bstract
Stomach lavaging was used to study the feeding habits of northern elephant seals ( Mirounga angustirostris ) found on San Miguel Island, California, during the spring of 1984. Fifty‐nine elephant seals were chemically immobilized with an intramuscular injection of ketamine hydrochloride. Once immobilized, an animal's stomach was intubated, filled with 3–4 liters of water to create a slurry of the undigested food items, and evacuated into a collection device. The stomachs of 57 (96.6%) of the animals lavaged contained identifiable parts of prey. Twenty‐nine different food items were identified, 12 of which have not been previously reported as prey of the northern elephant seal: two teleost fish, Coryphaenoides acrolepis (Pacific rattail) and another unidentified macrourid; two crustaceans, Pasiphaea pacifica (glass shrimp) and Euphausia sp.; six squid, Abraliopsis felis, Gonatus berryi, Histioteuthis dofleini, Cranchia scabra, Taonius pavo, and Galiteuthis sp. and two octopi, Octopus dofleini and Octopus rubescens.
... Marine mammal diet has been studied by various techniques, such as stomach content analysis, scat content or scat DNA analysis, stable isotopes and fatty acid analyses (reviewed in Tollit et al., 2010). Stomach content analysis allows the direct assessment of prey that was consumed by marine mammals (Antonelis et al., 1987Field et al., 2007). However, this method has inherent biases toward prey with hard parts and recently consumed items (Harvey and Antonelis, 1994). ...
... However, relatively few studies have examined the diet of northern elephant seals while they are at sea. Previous studies using stomach content analysis (Antonelis et al., 1987 suggested that seals fed more on squid than on fish. Yet, more recently, Naito et al. (2013Naito et al. ( , 2017 proposed that northern elephant seals feed on myctophids and ragfish in the mesopelagic zone, based on several images and videos obtained from animal-borne still and video cameras. ...
... Our results indicate that fish largely dominate the diet of postbreeding female northern elephant seals (Fig. 2). Our data offer a contrasting view to previous studies that, based on stomach contents, reported a higher occurrence of cephalopods than fish (cephalopods and teleosts found in 112 and 75 out of 193 stomach contents, respectively; Antonelis et al., 1987Antonelis et al., , 1994. Stomach contents analysis has an inherent bias toward hard parts such as squid beaks that tend to be retained in the stomach, which likely explains the discrepancy (Harvey and Antonelis, 1994). ...
Knowledge of the diet of marine mammals is fundamental to understanding their role in marine ecosystems and response to environmental change. Recently, animal-borne video cameras have revealed the diet of marine mammals that make short foraging trips. However, novel approaches that allocate video time to target prey capture events is required to obtain diet information for species that make long foraging trips over great distances. We combined satellite telemetry and depth recorders with newly developed date/time-, depth-, and acceleration-triggered animal-borne video cameras to examine the diet of female northern elephant seals during their foraging migrations across the eastern North Pacific. We obtained 48.2 hours of underwater video, from cameras mounted on the head (n=12) and jaw (n=3) of seals. Fish dominated the diet (78% of 697 prey items recorded) across all foraging locations (range: 37-55°N, 122-150°W), diving depths (range: 238-1167 m) and water temperatures (range: 3.2-7.4 °C), while squid comprised only 7% of the diet. Identified prey included fishes such as myctophids, Merluccius sp., and Icosteus aenigmaticus, and squids such as Histioteuthis sp., Octopoteuthis sp., and Taningia danae. Our results corroborate fatty acid analysis, which also found that fish are more important in the diet and contrasts to stomach content analyses that found cephalopods to be the most important component of the diet. Our work shows that in-situ video observation is a useful method for studying the at-sea diet of long-ranging marine predators.
... Understanding the diet of mesopelagic predators like the northern elephant seal (Mirounga angustirostris) can provide valuable insights into the deep ocean food web (Benoit-Bird and Lawson, 2016;. Yet, obtaining dietary information on these elusive predators is notoriously difficult, limiting our knowledge to that gained from stomach contents (from dead seals or stomach lavage) and fecal studies (from enemas or scat) (Antonelis et al., 1987;Staniland et al., 2003). Further, samples obtained from elephant seals on shore are biased toward hard parts that resist digestion and toward their last meal, as these animals may have been fasting for days or weeks since leaving their primary foraging areas. ...
... Northern elephant seals utilize the entire eastern North Pacific Ocean, foraging for 9-10 months of the year and diving continuously into the mesopelagic zone (LeBoeuf et al., 2000;Robinson et al., 2012), where they feed almost exclusively below 400 m (Naito et al., 2013). Stomach content analyses have suggested that adult elephant seal diet is dominated by pelagic squids (Huey, 1930;Condit and Le Boeuf, 1984;Antonelis et al., 1987Antonelis et al., , 1994. In contrast, juvenile elephant seals appear to have a more diverse diet, mostly feeding over the continental shelf on a range of intertidal and neritic organisms (Sinclair, 1994). ...
... Since we had more prey in the library (n = 51) than dietary FAs (n = 43), we needed either to select one of these approaches or find an alternate method to decrease the number of prey types prior to modeling. All the squids in our library, except for B. anonychus, were previously documented in seal stomach contents (Condit and Le Boeuf, 1984;Antonelis et al., 1987Antonelis et al., , 1994 and were retained in the prey library, but we had no previous elephant seal diet data to justify excluding any mesopelagic fish species. The a priori pooling approach was a viable option, since it would avoid the problem of non-unique diet estimates. ...
Understanding the diet of deep-diving predators can provide essential insight to the trophic structure of the mesopelagic ecosystem. Comprehensive population-level diet estimates are exceptionally difficult to obtain for elusive marine predators due to the logistical challenges involved in observing their feeding behavior and collecting samples for traditional stomach content or fecal analyses. We used quantitative fatty acid signature analysis (QFASA) to estimate the diet composition of a wide-ranging mesopelagic predator, the northern elephant seal (Mirounga angustirostris), across five years. To implement QFASA, we first compiled a library of prey fatty acid (FA) profiles from the mesopelagic eastern North Pacific. Given the scarcity of a priori diet data for northern elephant seals, our prey library was necessarily large to encompass the range of potential prey in their foraging habitat. However, statistical constraints limit the number of prey species that can be included in the prey library to the number of dietary FAs in the analysis. Exceeding that limit could produce non-unique diet estimates (i.e., multiple diet estimates fit the data equally well). Consequently, we developed a novel ad-hoc method to identify which prey were unlikely to contribute to diet and could, therefore, be excluded from the final QFASA model. The model results suggest that seals predominantly consumed small mesopelagic fishes, including myctophids (lanternfishes) and bathylagids (deep sea smelts), while non-migrating mesopelagic squids comprised a third of their diet, substantially less than suggested by previous studies. Our results revealed that mesopelagic fishes, particularly energy-rich myctophids, were a critical prey resource, refuting the long-held view that elephant seals are squid specialists.
... Subsequent investigations revealed that female northern elephant seals are wide-ranging pelagic predators, foraging at great depths (Le Boeuf et al. 2000). During the 2 to 3 mo foraging period following lactation, females range across a wide area of the northeastern Pacific -from 38 to 58°N, and from near the coast of the continent at 125°W to as far west as 173°E -diving nearly continuously to mean depths in the range of 400 to 700 m. Adult female elephant seals feed predominantly on cephalopod prey that inhabits epi-, meso-, or bathypelagic oceanic zones (Antonelis et al. 1987(Antonelis et al. , 1994. Given their deep diving pattern, wide spatial distribution and long foraging periods, we would expect El Niño events to have lesser impacts on female northern elephant seals than on coastal pinnipeds. ...
... Northern elephant seals feed primarily on mesopelagic squid, elasmobrachs, and myctophid fish (Antonelis et al. 1987). As foraging difficulties in the present study did not appear to be associated with foraging location, explanations based on reduced prey availability would imply reductions in squid abun-dance throughout the northeast Pacific Ocean. ...
Our aim was to examine the foraging behavior of northern elephant seals Mirounga angustirostris during the 1997-98 El Nino and compare it to foraging in others years. Given their deep diving and spatial distribution, their immediate response to a severe El Nino was expected to give insight into the timing, scale and magnitude of El Nino Southern Oscillation impacts on a large marine predator. Time-depth records and Argos-linked satellite tracks were obtained from adult females departing on post-breeding foraging migrations from 1990 to 1999, including females foraging during the 1998 El Nino. Rates of mass gain and trip duration were recorded for females from 1983 to 1999. Movement tracks of females in 1998 were similar to those observed in non-El Nino years. Rate of mass gain at sea was 0.29 +/- 0.36 kg d(-1) in 1998, the lowest measured since 1983. Marked declines in the mass gain rate of females were noted in severe El Nino years, but not in moderate El Nino years. Females increase spring foraging trip duration to compensate for decreases in foraging success. In 1998, the frequency distribution and temporal pattern of dive shapes suggested reduced residence time in prey patches and increased travel time between patches and these parameters showed a strong relationship with rates of mass gain. Our data confirm that the immediate ecological impact of the 1997-98 El Nino was not limited to the near-shore coastal margin, but extended far out into the North Pacific Ocean.
... Scat samples were collected on land or ice, which did not require capture or disturbance of the seals; however, it is not possible to assign scats to specific individual or even to specific subgroups of a population (i.e., adults or juveniles). To obtain dietary information from individuals, stomach lavage (Antonelis et al., 1987;Ferreira & Bester, 1999) and an enema technique (Staniland et al., 2003) can be applied to live pennipeds captured on land or ice. As scat samples collected on land retain dietary information of recent foraging, these methods were only applicable to those species that feed near the landing sites or to the later stages of foraging trips as those foraging further from the colony for extended times will undoubtedly defecate at sea (Naya et al., 2002). ...
... The factors suggested the erosion (e.g., Arim & Naya, 2003;Bowen, 2000;Orr & Harvey, 2001) and passage restriction (Yonezaki et al., 2003) in prey hard items. Therefore, to obtain accurate dietary information, stomach contents should be obtained using the stomach lavage technique (e.g., Antonelis et al., 1987;Ferreira & Bester, 1999). ...
An enema technique was developed to obtain dietary information on northern fur seals (Callorhinus ursinus) at sea. The enema apparatus consisted of a hand pump and a soft PVC tube connected to a plastic tank filled with seawater. The tube was inserted into the fur seal's anus, and fecal samples flushed out into a polyethylene bag enveloping the posterior of the fur seal. The efficacy of the enema sampling was tested on 23 fur seals captured and killed off the Pacific coast of northern Japan in April 1998. Twenty of 23 enema samples contained hard prey items such as fish otoliths and squid beaks. The average number (+ SD) of hard prey items retrieved from the whole large intestine was 26.9 + 33.0% for fish otoliths, 37.3 + 38.5% for squid upper beaks, and 43.3 + 40.9% for squid lower beaks. Size distributions of these prey items retrieved from the enema samples were similar to that remaining in the large intestines. These results indicated that the enema technique could provide dietary information that is comparable to intestinal contents and scat analysis. Combination of the enema technique with a pelagic live capture method using gillnets could provide a nondestruc-tive way to investigate the feeding ecology of individual fur seals migrating offshore.
... 230 m) to catch prey on or near the seafloor (e.g. sharks, cephalopods, fish; [38,39]). Conversely, females travel throughout vast swathes of the North Pacific Ocean and feed in open ocean habitats. ...
Sex-specific phenotypic differences are widespread throughout the animal kingdom. Reproductive advantages provided by trait differences come at a cost. Here, we link sex-specific foraging strategies to trade-offs between foraging reward and mortality risk in sexually dimorphic northern elephant seals ( Mirounga angustirostris ). We analyse a decadal dataset on movement patterns, dive behaviour, foraging success and mortality rates. Females are deep-diving predators in open ocean habitats. Males are shallow-diving benthic predators in continental shelf habitats. Males gain six times more mass and acquire energy 4.1 times faster than females. High foraging success comes with a high mortality rate. Males are six times more likely to die than females. These foraging strategies and trade-offs are related to different energy demands and life-history strategies. Males use a foraging strategy with a high mortality risk to attain large body sizes necessary to compete for females, as only a fraction of the largest males ever mate. Females use a foraging strategy with a lower mortality risk, maximizing reproductive success by pupping annually over a long lifespan. Our results highlight how sex-specific traits can drive disparity in mortality rates and expand species' niche space. Further, trade-offs between foraging rewards and mortality risk can differentially affect each sex's ability to maximize fitness.
... Similar to bearded seals and walruses, northern elephant seals are hypothesized to be suction feeders (Antonelis et al., 1987;Kienle & Berta, 2016;Naito et al., 2013); therefore, the increased size of the facial expression muscles may aid in suction feeding. ...
Secondarily aquatic tetrapods have many unique morphologic adaptations for life underwater compared with their terrestrial counterparts. A key innovation during the land-to-water transition was feeding. Pinnipeds, a clade of air-breathing marine carnivorans that include seals, sea lions, and walruses, have evolved multiple strategies for aquatic feeding (e.g., biting, suction feeding). Numerous studies have examined the pinniped skull and dental specializations for underwater feeding. However, data on the pinniped craniofacial musculoskeletal system and its role in aquatic feeding are rare. Therefore, the objectives of this study were to conduct a comparative analysis of pinniped craniofacial musculature and examine the function of the craniofacial musculature in facilitating different aquatic feeding strategies. We performed anatomic dissections of 35 specimens across six pinniped species. We describe 32 pinniped craniofacial muscles—including facial expression, mastication, tongue, hyoid, and soft palate muscles. Pinnipeds broadly conform to mammalian patterns of craniofacial muscle morphology. Pinnipeds also exhibit unique musculoskeletal morphologies—in muscle position, attachments, and size—that likely represent adaptations for different aquatic feeding strategies. Suction feeding specialists (bearded and northern elephant seals) have a significantly larger masseter than biters. Further, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other pinniped species. These morphologic changes likely help generate and withstand suction pressures necessary for drawing water and prey into the mouth. In contrast, biting taxa (California sea lions, harbor, ringed, and Weddell seals) do not exhibit consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders. Generally, we discover that all pinnipeds have well-developed and robust craniofacial musculature. Pinniped head musculature plays an important role in facilitating different aquatic feeding strategies. Together with behavioral and kinematic studies, our data suggest that pinnipeds’ robust facial morphology allows animals to switch feeding strategies depending on the environmental context—a critical skill in a heterogeneous and rapidly changing underwater habitat.
... While it may be relatively easy to observe, identify, and quantify foraging in large mammals, birds, and reptiles that kill large prey, it can be more difficult to observe invertebrates foraging in situ because their behavior tends to be cryptic, nocturnal, and concealed in leaf litter or subterranean (Symondson 2002;Nordberg et al. 2018a). Classifying and quantifying invertebrate diet are also acutely challenging because most invertebrates are fluid feeders such that ingested prey cannot easily be identified using traditional methods, such as gastric dissection (Shine 1977), gastric lavage (Antonelis et al. 1987) or pellet/ fecal sampling (Southern 1954;Nordberg et al. 2018b). Moreover, laboratory simulations are unlikely to replicate conditions that produce natural behavior in both predator and prey (Symondson 2002). ...
On isolated islands, large arthropods can play an important functional role in ecosystem dynamics. On the Norfolk Islands group, South Pacific, we monitored the diet and foraging activity of an endemic chilopod, the Phillip Island centipede (Cormocephalus coynei), and used a stable isotope mixing model to estimate dietary proportions. Phillip Island centipede diet is represented by vertebrate animals (48%) and invertebrates (52%), with 30.5% consisting of squamates, including the Lord Howe Island skink (Oligosoma lichenigera) and Günther's island gecko (Christinus guentheri); 7.9% consisting of black-winged petrel (Pterodroma nigripennis) nestlings; and 9.6% consisting of marine fishes scavenged from regurgitated seabird meals. Centipede predation was the principal source of petrel nestling mortality, with annual rates of predation varying between 11.1% and 19.6% of nestlings. This means that 2,109-3,724 black-winged petrel nestlings may be predated by centipedes annually. Petrels produce a single offspring per year; therefore, predation of nestlings by centipedes represents total breeding failure for a pair in a given year. Our work demonstrates that arthropods can play a leading role in influencing vertebrate reproductive output and modifying trophic structures and nutrient flow in island ecosystems.
... Elephant seals do not chew food but instead swallow prey (Antonelis et al. 1987;Abbott and Verstraete 2005); therefore, it is likely that they use suction to feed on small prey of <15 cm length and/or < 70 g weight (Naito et al. 2013;Adachi et al. 2019). The diet of the northern elephant seal is not well understood, but diving patterns and isotopic data suggest that there are sexual differences both in feeding strategies and in the type of prey. ...
... Elephant seals do not chew food but instead swallow prey (Antonelis et al. 1987;Abbott and Verstraete 2005); therefore, it is likely that they use suction to feed on small prey of <15 cm length and/or < 70 g weight (Naito et al. 2013;Adachi et al. 2019). The diet of the northern elephant seal is not well understood, but diving patterns and isotopic data suggest that there are sexual differences both in feeding strategies and in the type of prey. ...
Pinnipeds are marine mammals that include eared seals, true seals, and walruses. This book presents detailed reviews on the ecology and conservation of 10 pinniped species along the coasts and islands in Latin America, from Mexico to Chile and Argentina. Topics covered include their population dynamics, trophic ecology, reproduction, and behavior. In addition, the book addresses major conservation issues regarding climate change, interaction with fisheries, ecotourism, and other human activities.
... Elephant seals do not chew food but instead swallow prey (Antonelis et al. 1987;Abbott and Verstraete 2005); therefore, it is likely that they use suction to feed on small prey of <15 cm length and/or < 70 g weight (Naito et al. 2013;Adachi et al. 2019). The diet of the northern elephant seal is not well understood, but diving patterns and isotopic data suggest that there are sexual differences both in feeding strategies and in the type of prey. ...
Among the five seal species inhabiting the southern hemisphere and distributed around and south of the Antarctic Convergence, the southern elephant seal (Mirounga leonina, Pinnipedia, Phocidae) has the northernmost distribution, reaching sites surrounded by temperate waters. During the annual cycle, seals spend most of their time at sea, alternating with two highly synchronized shore-based haul-out periods for breeding and molting. On land, the distribution area is restricted to locations on islands or mainland, while at sea they travel distances of thousands of km². In the global distribution, there are four genetically identified stocks; two are settled in Latin America (Georgias del Sur-South Georgia and Península Valdés). In this chapter, we focus on the colonies of Argentina, Chile, and the Antarctic Peninsula that have resident animals for breeding and molting and from where tagged seal migration covers a wide latitudinal range from the equator to Antarctica. Long-term and systematic studies at the Península Valdés colony facilitated the comparison with other colonies further south. Annual cycle, demographic, and foraging aspects are described in this chapter emphasizing migrations at sea and distribution. The chapter closes with a consideration of conservation status and threats.
... Elephant seals do not chew food but instead swallow prey (Antonelis et al. 1987;Abbott and Verstraete 2005); therefore, it is likely that they use suction to feed on small prey of <15 cm length and/or < 70 g weight (Naito et al. 2013;Adachi et al. 2019). The diet of the northern elephant seal is not well understood, but diving patterns and isotopic data suggest that there are sexual differences both in feeding strategies and in the type of prey. ...
The Guadalupe fur seal (Arctocephalus philippii townsendi or A. townsendi) was at the brink of extinction due to overhunting during the eighteenth and nineteenth centuries. Today, the Guadalupe fur seal remains classified as an Endangered species by Mexican law and as Threatened under the US Endangered Species Act of 1973. Currently, the entire population is estimated at around 40,000 individuals, with a single well-established breeding site on Guadalupe Island. Around 20 years ago, it was discovered that Guadalupe fur seals had recolonized San Benito Archipelago, which is 260 km southeast of Guadalupe Island. However, breeding activity at this site continues to be negligible with <1% of pups born here each year. It is likely that recovery of the Guadalupe fur seal depends on prey availability, which is influenced by oceanographic factors in the California Current Ecosystem (CCE). In this regard, differences in foraging habits have been found between the two colonies (Guadalupe and San Benito) in recent years and within the Guadalupe colony across decades. The population recovery rate has been lower than that observed for other pinnipeds that inhabit the CCE. Additionally, there are recent records of unusual mortality events along the US west coast; higher neonatal mortality due to starvation at Guadalupe Island; and marked reduction of the colony size at San Benito, which are all related to anomalous warm water events. These threats are intensified and more frequent because of climate change, which is the most significant threat to the species, especially given that over 99% of Guadalupe fur seals breed at one island, making it more vulnerable to this impact.
... Elephant seals do not chew food but instead swallow prey (Antonelis et al. 1987;Abbott and Verstraete 2005); therefore, it is likely that they use suction to feed on small prey of <15 cm length and/or < 70 g weight (Naito et al. 2013;Adachi et al. 2019). The diet of the northern elephant seal is not well understood, but diving patterns and isotopic data suggest that there are sexual differences both in feeding strategies and in the type of prey. ...
The purpose of this book is to present reviews on the ecology and conservationConservation of pinnipeds that occur in the waters and on the coasts and islands of Latin AmericaLatin America, a vast region extending from MexicoMexico in the north to ArgentinaArgentina and ChileChile in the south. The aspects covered for each species include the following: general characteristics, Latin American and worldwide (if applicable) distributionDistribution and abundanceAbundance, annual cycleForagingcycle (e.g., puppingPupping/moltingMolting phenology), migrationMigration or movementsMovements, reproductive biology, behaviorForagingbehavior (social organization, foraging strategies, and breeding strategies), foraging/dietDiet, conservation statusConservation status (IUCN red listIUCN Red List and national lists), and threatsThreats (e.g., huntingHunting, fisheries interactionsFisheries interactions, and climate changeClimate change, among others). In this introduction, we present basic concepts and generalized information about pinniped species distributed in Latin AmericaLatin America (Fig. 1.1).
... Diet.-We do not know what elephant seals eat during most of the time that they are at sea and especially, what they eat while on focal foraging areas. Most of what is known about the diet of northern elephant seals comes from prey remains in dead animals and lavaged stomachs of animals returning to rookeries (Condit and Le Boeuf 1984, Antonelis et al. 1987, DeLong and Stewart 1991. These methods, unfortunately, reflect only prey consumed during the last few days of transit (Helm 1984, Harvey et al. 1989. ...
... Lavage or stomach flushing is a common approach applied to dietary studies(Karnovsky et al., 2012), in-turn allowing for non-lethal sampling of plastic ingestion. Lavage has been applied across animal groups to assess the ingestion of debris in turtles(Seminoff et al., 2002), seabirds(Lavers et al., 2018) and some marine mammals (mostly pinnipeds;Antonelis Jr et al., 1987). Lavage is somewhat limited in application as only certain parts of the digestive system are flushed and not all ingested debris is recovered(Hutton et al., 2008). ...
Studies documenting plastic ingestion in animals have increased in recent years. Many do not describe the less conspicuous, sub-lethal impacts of plastic ingestion, such as reduced body condition or physiological changes. This means the severity of this global problem may have been underestimated. We conducted a critical review on the sub-lethal impacts of plastic ingestion on marine vertebrates (excluding fish). We found 34 papers which tried to measure plastics' impact using a variety of tools, and less than half of these detected any impact. The most common tools used were visual observations and body condition indices. Tools that explore animal physiology, such as histopathology, are a promising future approach to uncover the sub-lethal impacts of plastic ingestion in vertebrates. We encourage exploring impacts on species beyond the marine environment, using multiple tools or approaches, and continued research to discern the hidden impacts of plastic on global wildlife.
... For example, diet studies on northern elephant seals Mirounga angustirostris by stomach lavage revealed the recurrent occurrence of bioluminescent pyrosomes among other food items, in both sub-adult males and adult females (Antonelis et al., 1987). It is thus possible to assume that these bioluminescent organisms have been ingested in lieu of mesopelagic lantern-fishes, which are also bioluminescent and consumed by this predator (e.g. ...
There is growing evidence that gelatinous zooplanktonic organisms ("gelata") are regular prey for marine endotherms. Yet the consumption of gelata is intriguing in terms of the energy reward, because endotherms have a high energy demand and the consumption of gelata provides little energy return. In this paper, we take advantage of recent advances in diet analysis methods, notably animal-borne video loggers and DNA analysis in seabirds, to examine our current understanding of this interaction. We suggest that several hypotheses commonly raised to explain predation on gelata (including increased biomass, reduced prey availability, and secondary ingestion) have already been tested and many lack strong support. We emphasize that gelata are widely consumed by endotherms (121 cases reported across 82 species of seabirds, marine mammals, and endothermic fishes) from the Arctic to the Antarctic but noticeably less in the tropics. We propose that in line with research from terrestrial ecosystems atypical food items might be beneficial to the consumers in a non-energetic context, encompassing self-medication, and responding to homeostatic challenges. Changing the "last resort" context for a "functional response" framework may improve our understanding of widespread predation on gelata. Further biochemical analyses are needed to formally examine this perspective.
... Consequently, pup mass at birth or weaning reflects the success of maternal foraging during the 8 months prior to giving birth. Females feed primarily on mesopelagic squid, elasmobranchs, and myctophid fishes (Antonelis et al. 1987). ...
Lifetime reproductive success of individuals in a natural population provides an estimate of Darwinian fitness. We calculated lifetime reproductive success in a colony of female northern elephant seals (Mirounga angustirostris (Gill, 1866)) by monitoring annual breeding throughout life of 7735 female weanlings marked individually at Año Nuevo, California, USA, from 1963 to 2005. Great variation in lifetime reproductive success was evident in three aspects of life history: (1) 75% of the females died before reaching breeding age and produced no pups; (2) nearly half of the survivors bred for only a few years before dying, and young females had low weaning success; (3) less than 1% of the females in the sample were exceptionally successful producing up to 20 pups in life. Many females that bred early, while still growing, had decreased lifespan, low weaning success, and lower lifetime reproductive success than females that postponed first breeding. Exceptional reproductive success was associated with giving birth annually, living long (up to age 23), and weaning large pups that were more likely to survive and breed. We conclude that there is strong selection for increased lifespan and multiparous supermoms that contribute significantly to pup production in the next generation.
... Northern elephant seals eat a variety of mesopelagic fish and squid species, 31,41,42 and while their diet has not been well characterized, Goetsch 43 documented that seals foraging in the North Central Pacific ate more fish (and less squid) than seals foraging in the Subarctic Pacific during the post-molt foraging trip. In addition to these broad-scale patterns, we were also able to capture more localized variation in foraging behavior, as evidenced by the increase in δ 13 C and δ 15 (B) Isotope ratios of whisker segments that were grown in each ecoregion with the mean and 95% confidence intervals. ...
... The other explanation is the different digestion rates for crustacean species. The much longer digestion times needed for hard shells often result in biased evaluation of the importance of prey items (Antonelis et al., 1987;Olson & Boggs, 1986). Remains of exoskeletons of crustaceans may exaggerate their importance as prey items for D. mawsoni. ...
Stomach contents of the Antarctic toothfish, Dissostichus mawsoni , collected from subareas 58.4 and 88.3, were analyzed using next generation sequencing (NGS) technology. After processing the raw reads generated by the MiSeq platform, a total of 131,233 contigs (130 operational taxonomic units [OTUs]) were obtained from 163 individuals in subarea 58.4, and 75,961 contigs (105 OTUs) from 164 fish in subarea 88.3. At 98% sequence identity, species names were assigned to most OTUs in this study, indicating the quality of the DNA barcode database for the Antarctic Ocean was sufficient for molecular analysis, especially for fish species. A total of 19 species was identified from the stomach of D. mawsoni in this study, which included 14 fish species and five mollusks. More than 90% of contigs belonged to fish species, supporting the postulate that the major prey of D. mawsoni are fish. Two fish species, Macrourus whitsoni and Chionobathyscus dewitti , were the most important prey items (a finding similar to that of previous studies). We also obtained genotypes of prey items by NGS analysis, identifying an additional 17 representative haplotypes in this study. Comparison with three previous morphological studies and the NGS-based molecular identification in this study extended our knowledge regarding the prey of D. mawsoni , which previously was not possible. These results suggested that NGS-based diet studies are possible, if several current technical limitations, including the quality of the barcode database or the development of precise molecular quantification techniques to link them with morphological values, are overcome. To achieve this, additional studies should be conducted on various marine organisms.
... Elephant seals undergo biannual foraging trips, ranging upwards of 5000 or 10000 km depending on the season, within several open-ocean and near-coastal hydrographic ecoregions, including the Subarctic Gyre, the North Pacific Polar Front, and the California Current (Le Boeuf et al., 2000;Robinson et al., 2012;Springer et al., 1999). The northern elephant seal is the only pinniped species in the North Pacific that forages almost entirely on fish and squid in the mesopelagic zone (Antonelis et al., 1987;Le Boeuf et al., 2000;Naito et al., 2013). Biannual foraging trips ( Fig. 1) are interspersed with extensive fasting periods on land, at which time individuals lose up to 40% of their body mass (Costa et al., 1986;Worthy et al., 1992). ...
Mercury (Hg) biomonitoring and toxicological risk assessments for marine mammals commonly sample different tissues, making comparisons to toxicity benchmarks and among species and regions difficult. Few studies have examined how life history events, such as fasting, influence the relationship between total Hg (THg) concentrations in different tissues. We evaluated the relationships between THg concentrations in blood, muscle, and hair of female and male northern elephant seals (Mirounga angustirostris) at the start and end of the breeding and molting fasts. The relationships between tissues varied among tissue pairs and differed by sampling period and sex. Blood and muscle were generally related at all time periods; however, hair, an inert tissue, did not strongly represent the metabolically active tissues (blood and muscle) at all times of year. The strongest relationships between THg concentrations in hair and those in blood or muscle were observed during periods of active hair growth (end of the molting period) or during time periods when internal body conditions were similar to those when the hair was grown (end of the breeding fast). Our results indicate that THg concentrations in blood or muscle can be translated to the other tissue type using the equations we developed, but that THg concentrations in hair were generally a poor index of internal THg concentrations except during the end of fasting periods. This article is protected by copyright. All rights reserved.
... The only prey item that was not from a mammal or seabird was a single squid beak, which may well have originated in the stomach of a northern elephant seal, the remains of which were found in the same whale. Squid are known to be an important prey of this pinniped (Antonelis et al. 1987 Fig. 1), identification (ID) number of the individual if known and its sex, prey species and evidence used for identification, and the minimum number of individuals of each prey species represented in the carcass. * Identified as resident whales belonging to the southern community from mtDNA analysis of tissue samples (L.G. ...
Two forms of killer whale (Orcinus orca), resident and transient, occur sympatrically in coastal waters of British Columbia, Washington State, and southeastern Alaska. The two forms do not mix, and differ in seasonal distribution, social structure, and behaviour. These distinctions have been attributed to apparent differences in diet, although no comprehensive comparative analysis of the diets of the two forms had been undertaken. Here we present such an analysis, based on field observations of predation and on the stomach contents of stranded killer whales collected over a 20-year period. In total, 22 species of fish and 1 species of squid were documented in the diet of resident-type killer whales; 12 of these are previously unrecorded as prey of O. orca. Despite the diversity of fish species taken, resident whales have a clear preference for salmon prey. In field observations of feeding, 96% of fish taken were salmonids. Six species of salmonids were identified from prey fragments, with chinook salmon (Oncorhynchus tshawytscha ) being the most common. The stomach contents of stranded residents also indicated a preference for chinook salmon. On rare occasions, resident whales were seen to harass marine mammals, but no kills were confirmed and no mammalian remains were found in the stomachs of stranded residents. Transient killer whales were observed to prey only on pinnipeds, cetaceans, and seabirds. Six mammal species were taken, with over half of observed attacks involving harbour seals (Phoca vitulina). Seabirds do not appear to represent a significant prey resource. This study thus reveals the existence of strikingly divergent prey preferences of resident and transient killer whales, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations. 1471
... hake), and crustaceans (e.g. red pelagic crab) (Antonelis et al., 1987(Antonelis et al., , 1994. It is difficult to assess the elephant seal diet using traditional methods like scat analysis or stomach lavage because they feed at sea for long periods of time and fast when they are on land to breed or moult (Condit & Le Boeuf, 1984). ...
Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only phocid species found in Mexico. There is evidence that harbour seals at other latitudes exhibit non-migratory behaviour; however, there is lack of knowledge regarding this species' movements in Mexico. In contrast, elephant seal migrations to high latitudes are documented. In order to analyse this behaviour in harbour seals, hair samples (N = 19) were collected from weaned, or nearly weaned, pups on Natividad Island, Baja California (BC), during the 2013 breeding season (February). Lanugo samples (N = 20) were also collected from elephant seal pups on the San Benito Archipelago (60 km north of Natividad) during the same season, providing information on maternal foraging during the last 4–5 months before sampling. Of the two species, BC harbour seals had higher isotope values, reflecting their non-migratory behaviour. These differences may be due to the depleted base values in the higher latitude foraging areas used by northern elephant seals relative to the areas around Natividad frequented by harbour seals. A lower trophic position by elephant seals was considered but taken as an unlikely explanation for this variation. Bayesian analysis confirmed the distinction, with a low overlap value (0.4) and different isotopic spaces (Phoca: 0.5, Mirounga: 1.6). Building upon previous studies of the trophic ecology of the two phocids that inhabit the region, we provide new information by comparing the two species during the same season using the same tissue type sampled from individuals of similar age classes.
... In addition, diet composition studies have demonstrated that the diet of northern and southern elephant seals is primarily composed of cephalopods and soft-bodied fish (Green & Williams, 1986;Antonelis et al. 1987;Green & Burton, 1993;Le Boeuf & Laws, 1994;Naito et al. 2013). These soft-bodied prey items are the prey of other known suction feeders, including beaked whales (Heyning & Mead, 1996), dwarf and pygmy sperm whales (Bloodworth & Marshall, 2005) and long-finned pilot whales (Werth, 2000). ...
One adaptation crucial to the survival of mammalian lineages that secondarily transitioned from land to water environments was the ability to capture and consume prey underwater. Phocid seals have evolved diverse feeding strategies to feed in the marine environment, and the objectives of this study were to document the specialized feeding morphologies and identify feeding strategies used by extant phocids. This study used principal component analysis (PCA) to determine the major axes of diversification in the skull for all extant phocid taxa and the recently extinct Caribbean monk seal (n = 19). Prey data gathered from the literature and musculoskeletal data from dissections were included to provide a comprehensive description of each feeding strategy. Random Forest analysis was used to determine the morphological, ecological and phylogenetic variables that best described each feeding strategy. There is morphological evidence for four feeding strategies in phocids: filter; grip and tear; suction; and pierce feeding. These feeding strategies are supported by quantitative cranial and mandibular characters, dietary information, musculoskeletal data and, for some species, behavioral observations. Most phocid species are pierce feeders, using a combination of biting and suction to opportunistically catch prey. Grip and tear and filter feeding are specialized strategies with specific morphological adaptations. These unique adaptations have allowed leopard seals (Hydrurga leptonyx) and crabeater seals (Lobodon carcinophaga) to exploit novel ecological niches and prey types. This study provides the first cranial and mandibular morphological evidence for the use of specialized suction feeding in hooded seals (Cystophora cristata), northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina). The most important variables in determining the feeding strategy of a given phocid species were cranial and mandibular shape, diet, and phylogeny. These results provide a framework for understanding the evolution and adaptability of feeding strategies employed by extant phocid species, and these findings can be applied to other pinniped lineages and extinct taxa.
... Gastric lavage, or stomach flushing, is an easy diet sampling method that requires minimal equipment (Bangley et al. 2013) as it involves the pumping of water into the stomach via a tube until food items are expelled via the mouth (Barnett et al. 2010). Gastric lavage has been performed on a variety of animals, including marine mammals (Antonelis et al. 1987), turtles (Eckert et al. 1999), teleost fishes (Hartleb and Moring 1995) and, to a much lesser extent, elasmobranchs. To the authors' knowledge, there have been only two studies that have used gastric lavage on members of the Myliobatiformes (stingrays) in the natural environment, being those of Vaudo and Heithaus (2011) and Ajemian et al. (2012). ...
Understanding the trophic interactions of ecologically important mesopredators such as Myliobatiformes (stingrays) is vital, but, given their susceptibility to overexploitation, the collection of stomach contents for dietary analysis necessitates the use of non-lethal methods. We provide a detailed method of using gastric lavage to collect stomach contents from the ‘Vulnerable’ porcupine ray Urogymnus asperrimus at the St Joseph Atoll of the Amirantes Group, Seychelles. Rays were captured by hand, inverted and restrained while a plastic hose, connected to a bilge pump, was inserted into the stomach to flush out the contents. A high percentage (94.5%) of gastric lavage attempts resulted in the collection of stomach contents. There was no visual evidence of stress or short-term, post-release mortality and, given the success and relative ease of this technique, we conclude that the described method of gastric lavage is an effective, non-lethal means of obtaining stomach contents from stingrays.
... A decrease in parasites could be due to a shift in diet. The diet of the female NES is comprised mainly of mesopelagic squid and fish (Antonelis et al. 1987), which carry diverse groups of helminth parasites which vary with food web structure (Marcogliese 2002). The strong negative association of serum cortisol with IgE at the return from foraging suggests that immune responses to parasites may be influenced by variation in plasma cortisol during foraging. ...
Mounting an immune response requires substantial energy. Ecological immunology theory predicts allocation trade‐offs between reproductive effort and immune responses under conditions of energy limitation. Little is known about the impact of capital breeding strategies on energy allocation to immune function in mammals.
Northern elephant seals ( NES ) forage in the marine environment, breed in dense terrestrial colonies and exhibit high rates of energy expenditure for lactation while fasting. Body reserves strongly influence reproductive effort and lactation requires elevation of plasma cortisol for energy mobilization.
We characterized immune response by measuring a suite of immune markers including cytokines, an acute phase protein, and immunoglobulins early and late in breeding and moult haul‐outs in 197 samples from 129 female NES . We explored potential impacts of breeding, body condition and plasma cortisol on immune function.
Immune responses were greater and more varied during breeding. Adiposity had positive associations with innate immune responses across all life‐history stages. Body mass had positive associations with both adaptive and innate immune responses early in fasts. Females with lower fat reserves showed reduced innate immune responses at the end of lactation. Immunoglobulin E , a marker of immune response to parasitic infection, exhibited a significant negative association with cortisol across all life‐history stages.
These data suggest that breeding carries an immune cost and provide evidence for allocation trade‐offs between immune function and breeding effort. These trade‐offs may reflect a compromise between immune costs inherent in colonial breeding and energetic limitations that arise in use of capital breeding strategies. Variation in evidence for immunosuppressive effects of cortisol suggests that decoupling of these effects may be limited to specific aspects of the immune response during terrestrial fasting. Immune responses that are required for survival may be modulated relative to the energetic demands required for successful reproduction.
... Elephant seals undergo biannual foraging trips, ranging upwards of 5000 or 10000 km depending on the season, within several open-ocean and near-coastal hydrographic ecoregions, including the Subarctic Gyre, the North Pacific Polar Front, and the California Current (Le Boeuf et al., 2000;Robinson et al., 2012;Springer et al., 1999). The northern elephant seal is the only pinniped species in the North Pacific that forages almost entirely on fish and squid in the mesopelagic zone (Antonelis et al., 1987;Le Boeuf et al., 2000;Naito et al., 2013). Biannual foraging trips ( Fig. 1) are interspersed with extensive fasting periods on land, at which time individuals lose up to 40% of their body mass (Costa et al., 1986;Worthy et al., 1992). ...
... Octopus tehuelchus beaks were collected from fresh scats of the South American sea lion (Otaria flavescens) from the rookery at Punta Bermeja, Rio Negro Province, Argentina (418S 638W) (Bustos et al., 2014) in November 2005. Alluroteuthis antarcticus beaks were collected from the stomach contents of adult wandering albatrosses (subjected to stomach lavage) at Bird Island in 2009 (Xavier et al., 2003b) and from the stomach contents of Southern elephant seals (Mirounga leonina) (immobilized by injection of ketamine hydrochloride and subjected to stomach lavage following Antonelis et al., 1987) at Stranger Point, Isla 25 de Mayo/King George Island, South Shetlands (628S 588W) during the moulting season of 1995/96 (Daneri et al., 2000). ...
The diets of marine predators are a potential source of information about range shifts in their prey. For example, the short-finned squid Illex argentinus, a commercially fished species on the Patagonian Shelf in the South Atlantic, has been reported in the diet of grey-headed, Thalassarche chrysostoma; black-browed, T. melanophris; and wandering, Diomedea exulans, albatrosses breeding at Bird Island, South Georgia (54°S 28°W) in the Southern Ocean. Tracking data suggest that these birds may feed on
I. argentinus while foraging in Southern Ocean waters during their breeding season. This led to the hypothesis that I. argentinus may occur south of the Antarctic Polar Front. To test this hypothesis, we used stable isotope analyses to assess the origin of I. argentinus . We compared I. argentinus
beaks from the diets of the three albatross species with beaks of cephalopod species endemic to the Patagonian Shelf and others from the Southern Ocean. Our results show that I. argentinus from the diet of albatrosses at Bird Island have δ13C values in the range −18.77 to −15.28‰. This is consistent with δ
13C values for Octopus tehuelchus, a typical species from the Patagonian Shelf. In contrast, Alluroteuthis antarcticus, a Southern Ocean squid, has typically Antarctic δ13C in the range −25.46 to −18.61‰. This suggests that I. argentinus originated from warmer waters of the Patagonian Shelf region. It is more likely that the albatross species obtained I. argentinus by foraging in the Patagonian Shelf region than that I. argentinus naturally occurs south of the Antarctic Polar Front.
... Bottlenose dolphin stomach contents analysis could be done from necropsies and stomach lavage (Antonelis et al. 1987;Iverson et al. 2004;Barnett et al. 2010;McCabe et al. 2010). ...
Bottlenose dolphins (Tursiops truncatus) are understudied in the Lower St. Johns River Jacksonville, Northeast Florida, USA. Aerial surveys were used to assess the distribution of bottlenose dolphins between 1999 and 2012. Sighting aggregation areas of 15 or greater bottlenose dolphins occurred at Jacksonville University, Dames Point Bridge, Sisters Creek, and Mayport. These areas were analyzed to understand what abiotic and biotic factors influenced bottlenose dolphin aggregations. Salinity and tide were significant factors at the three sites. Principal components analysis revealed that dissolved oxygen and water temperature explained 68-70% variance at each site and were inversely correlated with each other. Prey species of bottlenose dolphins were not found to be significantly different between aggregations areas and non-aggregations areas.
This study represents the first exploratory analysis comparing fish abundance and aerial survey bottlenose dolphin sighting data. It serves as a baseline for future studies involving determination of economies related to normal dolphin habitat and potential prey preferences. This study also benefits conservation actions as it illuminates important aggregation sites and probable important feeding habitats for bottlenose dolphins in the St. Johns River. Establishing bottlenose dolphin aggregations in the SJR may be used to understand any changes in dolphin behavior and distribution that may result from changes in the environment such as Harmful Algae Blooms (HABs), fish kills, surface water supply use policy, and marine construction activities like dredging.
Keywords: Aggregations, Aerial Surveys, Bottlenose Dolphins (Tursiops truncatus), Estuary, Fisheries monitoring, Foraging, St. Johns River
... There are several different methods of analyzing prey consumption in seals. Some rely on the analysis of stomach contents for determining seal diets, whether through stomach lavage as used by Antonelis Jr. et. Al, (1987) in which a tube is inserted through the mouth to allow for stomach contents to be pumped out, or through evisceration (Bowen et al., 1993;Hauksson and Bogason, 1997;Lundström et al., 2007 andNilssen et al., 1995;Víkingsson et al., 2003;and Weslawski et al., 1994). Others have taken a less intrusive method, relying on the identification ...
... Although trials with animals in captivity are clearly useful, researchers need to be aware of their drawbacks. An alternative, albeit an onerous one, might be to equip free-living animals with IMASENs for foraging trips and undertake stomach sampling (Antonelis et al., 1987;Boness et al., 1994) immediately after they return to the colony. The most recently-ingested prey will presumably be the least digested and it might be possible to work back through time in both prey swallowed and the IMASEN signals. ...
... Northern elephant seals are long-lived, mesopelagic, high-trophic level predators. Based on diving behavior [34,35], jaw-motion recorders paired with cameras [36], and stomach content analysis [37], northern elephant seals are hypothesized to consume mesopelagic fish and squid. However, little is conclusively known about their diet, since they return from their foraging migrations with nearly all prey completely digested. ...
Persistent organic pollutants, including polychlorinated biphenyls (PCBs), are widely distributed and detectable far from anthropogenic sources. Northern elephant seals (Mirounga angustirostris) biannually travel thousands of kilometers to forage in coastal and open-ocean regions of the northeast Pacific Ocean and then return to land where they fast while breeding and molting. Our study examined potential effects of age, adipose percent, and the difference between the breeding and molting fasts on PCB concentrations and congener profiles in blubber and serum of northern elephant seal females. Between 2005 and 2007, we sampled blubber and blood from 58 seals before and after a foraging trip, which were then analyzed for PCBs. Age did not significantly affect total PCB concentrations; however, the proportion of PCB congeners with different numbers of chlorine atoms was significantly affected by age, especially in the outer blubber. Younger adult females had a significantly greater proportion of low-chlorinated PCBs (tri-, tetra-, and penta-CBs) than older females, with the opposite trend observed for hepta-CBs, indicating that an age-associated process such as parity (birth) may significantly affect congener profiles. The percent of adipose tissue had a significant relationship with inner blubber PCB concentrations, with the highest mean concentrations observed at the end of the molting fast. These results highlight the importance of sampling across the entire blubber layer when assessing contaminant levels in phocid seals and taking into account the adipose stores and reproductive status of an animal when conducting contaminant research.
... Alternatively, while some stomach content analyses of male and female Indo-Pacific bottlenose dolphins indicated no significant differences in prey preferences (Amir et al., 2005;Walton et al. 2007), others have found sex-specific differences in prey choice Ross, 1990a, 1990b). Historically, research into the feeding ecology of marine mammals has been approached in a variety of ways, including anecdotal observations (e.g., Shane, 1990), fecal analysis of hard remains (e.g., Sinclair and Zeppelin, 2002), DNA analysis of feces (e.g., Dunshea et al., 2013;Meekan et al., 2009), examination of stomach contents of dead stranded animals (e.g., Barros and Wells, 1998;Barros et al., 2000;Dunshea et al., 2013), and stomach lavage (Antonelis et al., 1987;Dunshea et al., 2013;Gibbs et al., 2011). While all are useful techniques, each has limitations. ...
... Based on results from this and a previous study by Fiscus et al. (1989), these prey species likely represented a significant portion of the dominant oceanic cephalopods in the California Current System approximately 30 yr ago. Several of these species also were found in the stomach contents of other marine mammals sampled around this time period, including a shortfinned pilot whale (Globicephala macrorhynchus), Hubbs' beaked whales (Mesoplodon carlhubbsi), and several pinniped species (Fiscus 1982, Mead et al. 1982, Seagars and Henderson 1985, Antonelis et al. 1987, Hanni et al. 1997. Their historical presence in the diet of sperm whales and other marine predators, coupled with a more recent study on the diet of sharks in this region (Preti et al. 2012; data for marine mammals are lacking), indicate these cephalopod species still are important prey species for large marine predators in the California Current System. ...
On 16 June 1979, a herd of 41 sperm whales stranded near the mouth of the Siuslaw River in Florence, Oregon. The stomach contents from 32 whales were collected, identified to the lowest taxonomic level possible, enumerated, and measured. A total of 20,247 cephalopod lower beaks that represented 24 species from 14 different families were recovered. The most numerous species were Histioteuthis hoylei (25.9%), Taonius borealis (12.9%), Galiteuthis phyllura (11.2%), Gonatopsis/Berryteuthis type (10.9%), and Moroteuthis robusta (10.7%). Reconstructed estimates of mass indicated that M. robusta contributed almost 50% of the total mass of cephalopods consumed, followed by H. hoylei (19.3%), and T. borealis (7.0%). The most important species in the diet of stranded whales were M. robusta, H. hoylei, T. borealis, G. phyllura, Octopoteuthis deletron, and Gonatopsis/Berryteuthis type. There were significant differences in the diet of males and females, but no differences between sperm whales of different age groups. Overall, sperm whales primarily consumed small cephalopods that were likely eaten south of 45ºN in or near the California Current System. This study provides new estimates of the food habits of sperm whales in the northeast Pacific from one of the largest strandings of this species.
... Because a thorough analysis of gastrointestinal contents generally requires the sacrifice of an animal, intact gastrointestinal specimens are no longer typically used in diet analyses. Lavage and enema procedures are also not widely used to describe the diet of the population because sample sizes are often small and animals may require chemical immobilization, thereby increasing the risk of injury or fatality (Antonelis et al., 1987;Harvey and Antonelis, 1994). ...
Examination of hard parts recovered from scats (feces) is currently the most common method for determining the diet of pinnipeds. However, large or sharp prey remains may be spewed (regurgitated) biasing prey composition and size estimations in diet studies based on scats. Percent frequency of occurrence (FO%) and age or size of selected prey remains recovered from northern fur seal (Callorhinus ursinus) scat (n=3444) and spew samples (n=267) collected from rookeries on St. George Island and St. Paul Island, Alaska, between 1990 and 2000 were compared to determine if a bias in prey composition and age or size estimations existed between scats and spews.
Overall prey composition was similar between sample type and location, but the relative FO% of primary prey (≥5%) varied by sample type and location. Age or size estimates of walleye pollock (Theragra chalcogramma) and of two species of gonatid squids (Gonatopsis borealis and Berryteuthis magister) were significantly larger in spews than in scats. Observed differences in FO% and estimated age or size of prey species whose remains were found in scats and spews likely result from size-selective digestion of prey remains. Scats were biased toward smaller prey remains, whereas spews were biased toward larger prey remains and cephalopod beaks. The percent overlap between age classes of walleye pollock caught by the commercial trawl fishery and age classes of walleye pollock consumed by northern fur seals varied noticeably between sample types for both islands (scats: St. George=15. 5%; St. Paul=4.1%; spews: St. George=94.6%; St. Paul=89.6%). These results demonstrate that the inclusion of multiple sampling methods allows for a more accurate assessment of northern fur seal prey occurrence and prey age and size.
... Octopus sp. Todaropsis eblanae Todarodes angolensis Ocythoe tuberculata Northern elephant seal Mirounga angustirostris Abraliopsis felis, Architeuthis japonica, Antonelis et al. (1987, 1994 ...
The Guadalupe fur seal (Arctocephalus townsendi) is a specialist predator
feeding on prey present in one trophic level. Data related to the diet of the
Guadalupe fur seal are few. It is still unknown where most of the individuals
forage or the composition of their diet. On Isla Guadalupe, the San Benito
Archipelago and the Farallon Islands, fur seals primarily feed on pelagic and
coastal squids. However, differences between colonies were found probably
caused by differences in diversity and abundance of prey species over the
continental shelf and the pelagic environment, and maybe due to the plasticity
of the species in their foraging behavior. Diet composition of the Guadalupe
fur seal might reflect adaptations to local and temporal environmental conditions.
The aim of this work was to consider historical information, add new
information, identify main prey species, and determine where in the marine
regions the Guadalupe fur seals feed.
... Lavaging, emetics and enemas have been used in a few studies, but all, as do the above methods, involve seal capture, and although a successful method for elephant seals (Antonelis et al. 1987), it has been shown to be an unproductive method for grey seals (Hammond & Fedak 1994a). ...
... Twenty five recently hauled out southern elephant seals (1 1 males and 14 females) were immobilised by injection of ketaminehydrochloride at StrangerPoint(62" 14'S, 58"40'W), King George Islandand subjectedto stomach lavage (Antonelis et al. 1987). Stomach contents were washed through a 1 mm mesh and stored in 70% ethanol. ...
In the summer of 1995/96, 25 southern elephant seals, Miroungaleonina, were stomach lavaged at Stranger Point, King George Island, South Shetland Islands. Cephalopod remains were present in 72% of the individuals sampled (n = 18). Seven species of squid and three of octopus were identified. The squid Psychroteuthisglacialis was the most important prey in terms of numbers (77%), biomass (80.8%) and frequency of occurrence (94.4%). Next in importance in terms of mass was the squid Alluroteuthisantarcticus (7.8%) in the diet of females and the octopodid Pareledone?charcoti in the diet of males (13.2%). Females preyed on a wider variety of squid taxa than males (7 vs 3) but octopodids occurred only in stomach contents from males. The predominance of P.glacialis in the prey of the South Shetland Islands elephant seals can be explained by the southerly location of the foraging areas of this population compared to South Georgia, Heard and Macquarie islands, where the diet of southern elephant seals has previously been analysed. Psychroteuthisglacialis is the predominant squid in waters close to the Antarctic continent.
The different two-dimensional shapes of dives of reveal much about the foraging ecology of elephant seals (Mirounga spp.). We give a brief history of dive typing, instrument development that improved and validated the process, and address what dive types reveal about foraging strategies, foraging success, and foraging location. Dive types were initially classified by visual inspection and later with Principal Component Analysis and Clustering, or machine-learning algorithms. Time-depth recorders, with the additional measure of swim speed, yield four major dive types: pelagic foraging, benthic foraging, transit, and drift dives. Geolocation, 3D measures, and other sensors confirm the principal dive types and add additional relevant information about diving and the environment. Dive types have revealed that females forage pelagically over deep water in the open ocean on prey in the deep scattering layer, whereas males forage benthically near continental slopes. Transit dives are used to get to and from foraging sites. Passive drift dives may serve the funtions of digestion, rest, and sleep. The direction of drifting reflects buoyancy, which changes as the seal feeds, thus giving a measure of foraging success. Sex-specific differences in dive types indicative of foraging begin to appear at two years of age. Dive typing has also been used to describe the foraging ecology of other pinnipeds as well as cetaceans.
How did the elephant seal survive being driven to the brink of extinction in the nineteenth century? What variables determine the lifetime reproductive success of individual seals? How have elephant seals adapted to tolerate remarkable physiological extremes of nutrition, temperature, asphyxia, and pressure? Answering these questions and many more, this book is the result of the author's 50-year study of elephant seals. The chapters cover a broad range of topics including diving, feeding, migration and reproductive behavior, yielding fundamental information on general biological principles, the operation of natural selection, the evolution of social behavior, the formation of vocal dialects, colony development, and population changes over time. The book will be a valuable resource for graduate students and researchers of marine mammal behavior and reproductive life history as well as for amateur naturalists interested in these fascinating animals.
How did the elephant seal survive being driven to the brink of extinction in the nineteenth century? What variables determine the lifetime reproductive success of individual seals? How have elephant seals adapted to tolerate remarkable physiological extremes of nutrition, temperature, asphyxia, and pressure? Answering these questions and many more, this book is the result of the author's 50-year study of elephant seals. The chapters cover a broad range of topics including diving, feeding, migration and reproductive behavior, yielding fundamental information on general biological principles, the operation of natural selection, the evolution of social behavior, the formation of vocal dialects, colony development, and population changes over time. The book will be a valuable resource for graduate students and researchers of marine mammal behavior and reproductive life history as well as for amateur naturalists interested in these fascinating animals.
The northern elephant seal (Mirounga angustirostris) is the largest carnivore in the Northern Hemisphere. They are sexually dimorphic with adult males weighing up to 2000 kg and measuring up to 4.5 m and adult females weighing up to 700 kg and measuring up to 3 m. In addition to the differences in weight and length, adult males have a facial proboscis, which gives the common name “elephant.” It is a deep-diving marine mammal that can dive to depths over 1500 m. The species forages within the cold waters of the North Pacific Ocean. Breeding sites are located mainly on sandy beaches of temperate islands and a few mainland coastal areas of California, USA, and Baja California, Mexico. Despite being nearly driven to extinction due to the intense commercial harvesting in the nineteenth century, the northern elephant seal has recolonized its historical range and as of 2010 had an estimated population size of 201,000 individuals. However, due to low genetic diversity, a consequence of the population bottleneck, the main threats to the species appear to be disease outbreaks and environmental changes.
Meeressäuger haben ein breites, regional stark divergierendes Beutespektrum. Die Verdaulichkeit dieser Nahrung ist in der Regel sehr hoch. Zum Grund- und Energieumsatz in freier Wildbahn liegen nur wenige empirische Daten vor. Diese weisen eher daurauf hin, dass sie sich nicht wesentlich von Werten terrestrischer Carnivore unterscheiden. Gleiches gilt für die Futteraufnahme. Kennzeichnend für viele Meeressäuger ist eine ausgeprägte Saisonalität mit Fastenperioden, während denen jedoch häufig ein enormer Energiebedarf besteht. Dieser wird durch spezielles Depot-Fettgewebe gewährleistet. Der Flüssigkeitsbedarf wird direkt über die Nahrung sowie mittels Aufnahme von Meerwasser gedeckt. Die Dünndärme sind bei allen Meeressäugern verhältnismässig lang, was eventuell auf die Tauchgänge während des Beuteerwerbes zurückzuführen ist. Der Magen-Darm-Trakt der Pinnipedia entspricht weitestgehend dem typischen Bild der Fleischfresser. Der Magen der Cetaceen ist bei allen Spezies mehrkammerig und wurde wiederholt mit dem Wiederkäuer-Magen verglichen. Eine bakterielle Fermentation im Vormagen ist bei Bartenwalen vorhanden, allerdings ist der Beitrag zur Energiedeckung eher gering. Es scheint, dass sich die Vormagenfermentation an die jeweilige Nahrung anpassen kann. Daneben übernimmt das Vormagensystem vermutlich die Funktion einer mechanischen Futter-Zerkleinerung, einer partiellen Vorverdauung sowie eines Speicherorgans. SUMMARY Marine mammals have a wide range of diet and the digestibility of their food is very high. There are only few empiric data about metabolism of marine mammals in the wild. The data suggest that they are similar to terrestrial carnivores. The same applies for food intake. Characteristic for the nutrition of a large number of marine mammals is a distinct seasonal demand with extensive fasting periods, during which, furthermore, frequently a high energy requirement exists. This is provided by a special fat tissue. The fluid balance occurs with the food, but also via mariposia. The small intestines of marine mammals are comparatively long. This could result from the dives during forage. The gastrointestinal tract of pinnipeds is most likely equates to that of other carnivores. The stomach of all cetacean species is multi-chambered similar to the ruminants with up to 15 compartments and has been often compared with that. A bacterial fermentation in the forestomach exists for baleen whales, but contribution for energy needs is low. It seems that the microbial flora can adapt to different preys. In addition, the forestomach takes other features like mechanical disintegration of food, partial pre-digestion, and the function of a storage organ.
Intersexual foraging variation is a strategy thatis usually adopted by sexually dimorphic species. Thenorthern elephant seal (Mirounga angustirostris) exhibits one of the most pronounced examples of sexual dimorphismin pinnipeds and segregation in this species’ migration toward foraging grounds in the North Paciic is well documented for colonies in California; however, we lackcomparable data from colonies in Mexico. The aim of this study was to use stable isotope analysis (δ13C and δ15N)to evaluate diet variation between adult males and femalesfrom a Mexican colony. Fur was collected from adult males(N = 15) and pups (N = 42) on the San Benito Archipelagoduring the 2012 molting season (summer) and the 2013breeding season (winter). Values for adult females were inferred from their pups, based on previous studies. The resulting δ13C and δ15N values were signiicantly lower than those of their male counterparts. This diference may be due to the higher trophic position and a probable consumption of benthic prey (δ15N) by males, and the use of mostly oceanic habitats (δ13C) by adult females; the latter also had a larger isotopic niche than that of the former, as a probable consequence of more variable foraging grounds. Although our results are not the relection of a simultaneous segregation, we obtained solid evidence on intersexual variation, which is common among dimorphic pinnipeds, particularly in terms of trophic position and habitat use, which tend to be the result of a marked diference in body mass and diferent energetic requirements.
Le capsule ovigere possono assumere importanza fondamentale nella determi- nazione indiretta della specie di appartenenza. A tal fine è stata impostata una chiave dicotomica per il loro riconoscimento specifico. Viene descritto inoltre il ciclo biologico dei condroitti, in particolare il processo che porta alla formazione della capsula da parte della ghiandola nidamentale. Delle capsule sono forniti i particolari morfologici e le varie misure da acquisire allo scopo di procedere a un’analisi in grado di separarle automaticamente tramite l’impiego di un sempli- ce programma in excel. Per ogni specie è stata redatta una scheda che riporta le principali caratteristiche, la descrizione della capsula e la distribuzione nel ba- cino mediterraneo. Infine, poiché i gusci rilasciati nell’ambiente possono essere predati tramite un foro realizzato sulla loro superficie da parte di vari predatori, quali echinodermi, molluschi gasteropodi, ecc., è stato fatto un tentativo di met- tere in relazione la forma dei buchi con l’organismo che li ha prodotti.
The Antarctic and Sub-Antarctic fur seals co-exist at Marion Island. We investigated the suitability of stomach lavaging as a method to determine the diet of these two species. Intramuscular injections of ketamine hydrochloride and xylazine hydrochloride through an unbarbed Telinject-dart resulted in variable degrees of immobilization. Stomach lavaging following immobilization and physical restraint produced low retrieval of stomach contents (7 out of 29 seals). We conclude that the use of these methods to determine otariid diets is limited.
Mercury contamination of oceans is prevalent worldwide and methylmercury concentrations in the mesopelagic zone (200-1000 m) are increasing more rapidly than in surface waters. Yet mercury bioaccumulation in mesopelagic predators has been understudied. Northern elephant seals (Mirounga angustirostris) biannually travel thousands of kilometres to forage within coastal and open-ocean regions of the northeast Pacific Ocean. We coupled satellite telemetry, diving behaviour and stable isotopes (carbon and nitrogen) from 77 adult females, and showed that variability among individuals in foraging location, diving depth and δ(13)C values were correlated with mercury concentrations in blood and muscle. We identified three clusters of foraging strategies, and these resulted in substantially different mercury concentrations: (i) deeper-diving and offshore-foraging seals had the greatest mercury concentrations, (ii) shallower-diving and offshore-foraging seals had intermediate levels, and (iii) coastal and more northerly foraging seals had the lowest mercury concentrations. Additionally, mercury concentrations were lower at the end of the seven-month-long foraging trip (n = 31) than after the two-month- long post-breeding trip (n = 46). Our results indicate that foraging behaviour influences mercury exposure and mesopelagic predators foraging in the northeast Pacific Ocean may be at high risk for mercury bioaccumulation.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
Halichoerus grypus faeces were collected from Donna Nook, Lincolnshire; otoliths were identified and measured to estimate the size of the fish ingested. For the whole year, sandeels Ammodytidae, cod Gadus morhua and Dover sole Solea solea accounted for 56.2% of the diet by weight. Other flatfish (dab Limanda limanda, flounder Platichthys flesus and plaice Pleuronectes platessa) contributed a further 21.6% by weight. Cod, sandeels and other roundfish dominated the diet at the beginning of the year. Flatfish took over in the spring to be succeeded by sandeels during the summer. Cod returned to the diet in October and the year ended with the diet divided between flatfish and roundfish, excluding sandeels. -from Authors
For 31 of the 33 extant species of pinnipeds it is either known or
suspected that they include cephalopods in their diet. The two
exceptions are the Baikal Seal and the Caspian Seal, which inhabit
freshwater where cephalopods do not occur. The available evidence
indicates that no species of seal specializes entirely on cephalopods
and only few regularly eat appreciable quantities of this prey, although
for several they appear to be seasonally important prey. For most
pinnipeds only rudimentary prey identifications have been published. The
most common taxa of cephalopods reported to be consumed by seals are
members of the neritic Loliginidae, the oceanic Ommastrephidae,
Onychoteuthidae and Gonatidae, as well as benthic octopods. Too few
quantitative diet analyses on enough pinnipeds have been done to
quantify the consumption of cephalopods by seals globally with any
precision.
Seasonal variation in harbour Seal diet in the south-western North Sea was investigated from faeces collected monthly, over a 2 yr period, from a high-water haulout site in the Wash on the east coast of England. A total of 12 444 fish otoliths from 31 species was recovered from 708 faeces; otolith measurements were corrected for partial digestion and used to estimate the proportion, by weight, of each species in the diet. Overall, the diet was dominated by whiting (24 %), sole (15%), dragonet (13 %) and sand goby (11%). Other flatfish (dab, flounder, plaice: 12%), other gadoids (bib, cod: 11%), bullrout (7 %) and sandeels (3 %) were also consumed. A strong seasonality in diet was apparent which can be summarised as: whiting, bib and bullrout dominated from late autumn through early spring; sand goby peaked during winter and early spring; dragonet, sandeels and flatfish (except sole) dominated from late spring to early autumn; and sole peaked in spring. Harbour seal diet composition in general, and seasonal changes in diet in particular, appeared mainly to be linked to availability (in terms of prey distribution and abundance, feeding or spawning activity and, perhaps, prey size) but this was not always the case. In a few species (whiting, dab and plaice), seasonal changes in consumption appeared to be related to the availability of other species. Differences in harbour seal and grey seal diets in the same area were consistent with the 2 species feeding in different areas, but there was also evidence of a maximum preferred prey size for harbour seals.
A bstract
The Hawaiian monk seal ( Monachus schauinslandi ) is thought to be a foraging generalist, preying on numerous species in diverse habitats of the subtropical Northwestern Hawaiian Islands. At the atoll of French Frigate Shoals, recent evidence of emaciation and low survival in monk seals prompted a search for their specific prey communities and foraging habitat.
A video camera (National Geographic Television's CRITTERCAM) fitted to 24 adult male seals documented benthic and demersal foraging on the deep slopes (50‐80 m) of the atoll and neighboring banks. The number of bottom searches for prey was compared by year, time of day, type of bottom, individual seal, and length of bottom time. Analysis of variance identified a significant interaction of seal and bottom type, explaining 65% of the total variance. Seals fed on communities of cryptic fauna (fish and large invertebrates) in transitional “ecotone” regions of low relief where consolidated substrate, rubble, and talus bordered areas of sand. Independent areal surveys of bottom types throughout the atoll and neighboring banks suggest that the type of bottom selected as foraging habitat represents a relatively small percentage of the total benthic area available.
Frequency of occurrence for the four most commonly identified prey species was 48.7% Pacific whiting Merluccius productus; 46.7% market squid Loligo opalescens; 35.9% rockfish Sebastes spp.; and 20.0% northern anchovy Engraulis mordax. California sea lions feed opportunistically on seasonally abundant schooling fishes and squids. -from AuthorsPacific whiting Merluccius productus market squid Loligo opalescens rockfish Sebastes northern anchovy Engraulis mordax
Male-male competition and reproductive success of northern elephant seals, Mirounga augustirostris, was studied for six consecutive breeding seasons at Año Nuevo Island, California. The conclusions were as follows: (i) Less than one third of the males in residence copulate during a breeding season. A few males are responsible for the majority of copulations, (ii) The number and age of males copulating varies with: (a) harem location and topography, (b) the number of estrous females in the harem, and (c) the number of males competing for females, (iii) Copulation frequency is related directly to success in male-male competition, i.e., social rank. (iv) The same individuals may dominate breeding for three consecutive breeding seasons. (v) Successful males die within a year or two after their reproductive peak. (vi) The reproductive success of most males is nil or low because many die before reaching breeding age and some of those that reach maturity are prevented from mating by the highest ranking males. (vii) Individual strategies have important consequences for reproductive success, (viii) Male-male competition is a major cause of pup mortality prior to weaning.
The potential reproductive success of males is much greater than that of females. Changes in colony number and composition affect the reproductive success of males as well as females.
Phocid seals were immobilized safely and repeatedly, using a combination of ketamine and diazepam at mean IM or IV dosages of 1.5 mg/kg and 0.05 mg/kg, respectively. Induction and recovery were smoother than with ketamine used alone. Experimentally induced pneumonia did not alter the effects of the drugs, thus attesting to the safety of the ketamine-diazepam combination.
The pelagic icefish Chamsocephalus gunnari was the main prey, in terms of numbers (55%) and weight (76%) of fish consumed. Other species taken include the lantern fish Gymnoscopelus nicholsi, the nototheniids Notothenia rossii, N. gibberifrons and Patagonotothen larseni and Pseudochaenichthys georgianus. The estimated mean weight of the C. gunnari specimens was 160 g (range 45-560 g) and most were young adults aged 3-5 yr; individuals of other species were mainly much smaller. Individual scat samples contained remains which represented a weight of 80-2000 g of fish, and in all but one case a single species accounted for >80% of this. Fish formed a very small portion of the fur seals' diet in summer. The fish taken were mainly epipelagic, krill-feeding species. This is in line with the diet and diving patterns of A. gazella which feeds principally on krill in the upper water layer, and it is likely that the seals take fish from shoals associated with krill.-from Authors
Harbor seal abundance at Tillamook Bay peaked during pupping (May-June) and molting (August) periods, while peak abundance at Netarts Bay coincided with the annual return (October-November) of chum salmon Oncorhynchus keta. Observations of seals preying on adult salmon resulted in estimated losses of 6.1, 7.2, and 1.5% of the total chum returns for 1978, 1979 and 1980, respectively, due to seal predation in the Whiskey Creek area. Pacific sand lance Ammodytes hexapterus was the most frequently identified prey item. Ten species of flatfish (Order Pleuronectiformes) were identified as harbor seal prey with Parophrys vetulus, Glyptocephalus zachirus, Citharichthys sordidus, Microstomus pacificus and Lyopsetta exilis ranking among the 7 most frequently occurring food items. In general, benthic and epibenthic fish appeared to be important in the harbor seal diet. Tagged harbor seals frequented at least 4 different estuaries and one coastal haul-out area, ranging from 25-550 km from the tagging area. -from Authors
ABSTRAC'r-Prey species consumed by northern elephant seals were identified from the stom- ach and throat contents of dead seals and from observations of prey captured. Their diet is catholic, consisting of a variety of pelagic, deep water squid, Pacific hake, sharks, rays, and ratfish. Feeding grounds of elephant seals were inferred from sightings of tagged elephant seals at non-rookery locations. Feeding areas extended from northern Baja California to northern Vancouver Island. Juveniles of both sexes and adult males moved north from their haul out sites in search of food, travelling furthest north during the summer. A few sightings suggested that adult females remain in the vicinity of the rookeries where they breed.
There are six species of pinnipeds-California sea lion, Zalophus californianus; northern sea lion, Eume- topias jubatus; northern fur seal, Callorhinus ursinus; Guadalupe fur seal, Arctocephalus townsendi; harbor seal, Phoca uitulina richardsi; and northern elephant seal, Mirounga angustirostris-that inhabit the study area of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). The numbers of animals in each population are given; the size, distribution, and seasonal movements are de- scribed. The known prey species of the pinnipeds are listed for each species. The otariids, with certain excep- tions, consume the same kinds of prey, although in slight- ly different amounts. In general they feed most commonly on the smaller schooling fishes and squids of the epi- pelagic zone, and the two sea lion species enter nearshore and estuarine waters to prey on small schooling and anadromous fish. The two phocids, again with certain exceptions, prey on different species. The elephant seal apparently feeds in deeper water than the harbor seal on benthic and demersal species and the harbor seal on near- shore demersal and neretic species, occasionally enter- ingestuarine and river waters to prey on anadromous fish and such small schooling fishes that regularly enter these waters. RESUMEN Existen seis especies de pinipedos - el lobo marino de California, Zalophus californianus; el lobo marino del norte, Eumetopias jubatus; el os0 marino austral del norte, Callorhinus ursinus; el os0 marino austral de Guadalupe, Arctocephalus townsendi; la foca peluda, Phoca vitulina richardsi; y el elefante marino del norte, Mirounga angustirostris - 10s cuales habitan el area de estudio de California Cooperative Oceanic Fisheries Investigations (CalCOFI). Se da el numero de animales de cada poblacion; se describe el tamaiio, la distribucion, y sus desplazamientos con la estacion. Se ha hecho una lista de las especies que se consideran son presas de cada especie de pinipedo. Los otariidos, con ciertas excepciones, consumen 10s mismos tips de presas, aunque en cantidades ligeramente diferentes. En general se alimentan de 10s peces mas pequeiios en 10s cardiunenes y de calamares de la zona epipelagica, y las dos especies de lobo marino entran en la zona cerca de la costa y las aguas estuarinas y engullen 10s pequenos peces en 10s cardumenes y peces ana- dromos. Los dos focidos, otra vez con ciertas excep- ciones, predan especies diferentes. Aparentemente, el elefante marino se alimenta en aguas mas profundas que la foca peluda, alimentindose de especies demersales y benticas, y la foca peluda se alimenta de especiesdemer- sales costeras y neriticas, entrando ocasionalmente en rios y aguas estuarinas haciendo presa de 10s peces anadromos y otros pequeiios peces que entran regularmente en estas aguas.
CHEMICAL IMMOBILIZATION OF GRAY SEALS
1. Ketamine hydrochloride was used intravenously for immobilization of young harp seals, Phoca groenlandica.2. Induction and recovery were very rapid, with good control of dose strength over duration and degree of immobilization.3. An effective range of 0.5–7.5 mg/kg total body weight is suggested.
The probability of weaning a healthy pup increases with age in female northern elephant seals, Mirounga angustirostris. On Año Nuevo Island, California, weaning success among ‘prime’ females, those 6 years of age or older, was more than double that of ‘young’ females, those 3 to 5 years old. Prime females were better mothers than young females because of superior size, higher social dominance, and greater maternal experience; they were more likely to mate with high-ranking males and gave birth at an optimal time and place, circumstances that maximized the probability that their pups would survive, develop, and reproduce. The competitive advantage of prime-age mothers over younger ones was greatest when female and pup density was high. Young females improved their chances of reproducing successfully by emigrating from crowded harems and establishing new colonies.
Seasonal and annual dynamics of California sea lion feeding on Pacific hake were examined in relation to prey availability using otoliths found in spewings and scats. Sea lions fed most heavily on 2- to 4-year-old hake in spring and summer (ca. 90% of the diet is hake). When hake moved offshore in the spawning season, sea lions fed more on other species (30–50% of the diet is hake). The strong 1973 year class of hake had a great impact on the size and species composition of the prey consumed because sea lions fed heavily on the juveniles of this year class. When 2- to 3-year-old hake were not abundant due to year class failures, sea lions fed more on larger hake and on other species, mostly rockfish. It is estimated that California sea lions annually consume from about 100 000 to 250 000 tons of Pacific hake. An empirical model is used as an aid to discuss the effects of prey density, availability of alternative prey and predator switching behavior on the intensity of sea lion feeding on hake.
Nine free-ranging Galápagos sea lions were immobilised for marking, using a combination of ketamine (3 to 5 mg per kg) and xylazine (0.5 to 1.0 mg per kg). The degree of effect depended largely on the animals' behavioural and physiological state before immobilisation (after parturition, high arousal, subject to aggression, etc.) All nine animals survived. Overheating in the immobilised state may quickly result in heart and circulatory failures.
Ketamine was used as an immobilizing agent to obtain biological specimens from northern elephant seals in their natural habitat. Effective immobilization was achieved with dosages of 1.4 to 6.9 mg/kg of body weight.
Carfentanil was used to anaesthetise 46 adult grey seals (Halichoerus grypus) on 78 occasions during two breeding seasons. The mean dose was 9.92 micrograms/kg bodyweight during the first season and 10.22 micrograms/kg during the second. Naloxone hydrochloride was used as the antagonist, averaging 0.53 mg/kg and 1.73 mg/kg over the two periods although the latter is probably unnecessarily high. Ketamine and xylazine at a ratio of 5:1 were also used during the same two seasons, 57 seals being anaesthetised on 104 occasions. The average dose of ketamine was 4.96 mg/kg and 5.15 mg/kg with xylazine in proportion. Complications arose on a number of occasions and these are discussed.
Ketamine, given intramuscularly (I.M.) at dosages of 4.5 to 11 mg/kg of body weight, was used effectively to immobilize and anesthetize seals and sea lions under field and laboratory conditions. The results of temperature and cardiac monitoring and of behavioral observations indicated that the drug meets most of the requirements for use under field conditions. It is equally desirable for use in healthy captive seals, but is contraindicated in seals that are in poor condition.
Northern elephant seals (Mirounga angustirostris) were hunted to near extinction in the 19th century. Protection has allowed them to recolonize former habitat on islands off
California, where the population is increasing more than 14 percent per year. Immigration of young pregnant females from Baja
California initiated the California rookeries but is responsible for only a small part of recent population growth. Almost
25,000 northern elephant seal pups were born in the species' range in Mexico and the United States in 1982 in comparison with
only six known births in 1911.
The elephant seal (Mirounga angustirostris) in Oregon An appraisal of ketamine as an immobilizing agent in wild and captive pinnipeds
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Egg‐cases of some elasmobranchs and a cyclostome from California waters
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Population growth and censuses of the northern elephant seal, Mirounga angustirostris, on the California Channel Islands
- G A Antonelis
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ANTONELIS, G. A., JR., S. LEATHERWOOD AND D. K. ODELL. 1981. Population growth and censuses of the northern elephant seal, Mirounga angustirostris, on the California Channel Islands, 1958-78. Fishery Bulletin 79:562-567.
Southwest Fisheries Center, Administri ': Report LJ-85-OlC Capture of an elephant seal c -an Diego, California, with notes on stomach contents
- L M Huey
National Marine Fisheries Service, Southwest Fisheries Center, Administri ': Report LJ-85-OlC. 57 pp. HUEY, L. M. 1930. Capture of an elephant seal c -an Diego, California, with notes on stomach contents. Journal of Mammalogy 11:229-231.
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Stomach content analysis of short-finned pilot whales (Globicephala macrorhyncus) and northern elephant seals (Mirounga angustirostris) from the south-ern California Bight. National Marine Fisheries Service, Southwest Fisheries Center Administrative Report LJ-Sb-OSC
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Guide to the coastal marine fishes of California. California Department of Fish and Game, Fish Bulletin 157 Contents of the stomach of an elephant seal
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Stomach contents of porpoise, Stenella spp. and yellowfin mna. TbhrrnnuJ aibarareJ. in mixed-species aggregations Stomach contents and feces as indicators of harbor seal, Pbora vitulina. foods in the Gulf of Alaska
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