Dramatic shifts in Hawaiian monk seal distribution predicted from divergent regional trends

Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this number is decreasing. Most monk seals reside in the remote Northwestern Hawaiian Islands (NWHI) where the decline is approximately 4%/yr, whereas relatively fewer seals currently occupy the main Hawaiian Islands (MHI). It is widely accepted that the MHI population is increasing, although there are no formal estimates of total abundance, population growth rate or vital rates. This lack of information has hampered efforts to anticipate future scenarios and plan conservation measures. We present the first estimates of MHI monk seal survival and age‐specific reproductive rates. Using these rates, a conservative estimate of current MHI abundance and a previously published stochastic simulation model, we estimate the MHI population growth rate and projected abundance trend. Analogous estimates for the NWHI are derived from a much richer data set. Estimated survival from weaning to age 1 yr is 77% in the MHI, much higher than recent NWHI estimates ranging from 42% to 57%. Moreover, MHI females begin reproducing at a younger age and attain higher birth rates than observed in the NWHI. The estimated MHI intrinsic rate of population growth is 1.07 compared to a 0.89–0.96 range in the NWHI. Assuming an initial abundance of 152 animals in the MHI, projections indicate that if current demographic trends continue, abundance in the NWHI and MHI will equalize in approximately 15 yr. These results underscore the imperative to mitigate the NWHI decline while devoting conservation efforts to foster population growth in the MHI, where documented threats including fishery interactions, direct killing, and disease could rapidly undo the current fragile positive trend.     

Survey for Selected Pathogens and Evaluation of Disease Risk Factors for Endangered Hawaiian Monk Seals in the Main Hawaiian Islands

A recently reestablished and increasing population of Hawaiian monk seals in the main Hawaiian Islands (MHI) is encouraging for this endangered species. However, seals in the MHI may be exposed to a broad range of human, pet, livestock, and feral animal pathogens. Our objective was to determine the movement and foraging habitats of Hawaiian monk seals in the MHI relative to the potential exposure of seals to infectious diseases in near-shore marine habitats. We captured 18 monk seals in the MHI between January 27, 2004 and November 29, 2005, tested them for various infectious diseases, and then monitored the foraging movements of 11 of them using satellite-linked radio transmitters for the next 32–167 days. All seals tested negative for canine adenovirus, calicivirus, four morbilliviruses, phocine herpes virus, Leptospira sp., and feline and canine heartworm antigen/antibody. Six of the seals tested positive on complement fixation for Chlamydophila abortus (formerly Chlamydia psittaci). Four seals demonstrated positive titers to Sarcocystis neurona, two to Neospora caninum, and two to Toxoplasma gondii. Fecal cultures showed approximately half (n = 6) positive for E. coli 0157, no Salmonella sp., and only one with Campylobacter sp. Satellite monitored seals spent considerable time foraging, traveling, and resting in neritic waters close to human population centers, agricultural activity, and livestock ranges, and sources of land-based water runoff and sewage dispersal. Consequently, Hawaiian monk seals in the MHI may be at risk of exposure to several infectious disease agents associated with terrestrial animals that can contaminate marine habitats from runoff along drainages and that are known to cause disease in marine mammals. Further, some seals overlapped substantially in their use of coastal habitats and several moved among islands while foraging and were seen on beaches near each other. This suggests that diseased seals could infect healthy conspecifics throughout the MHI.     

Seasonal diving behaviour in lactating subantarctic fur seals on Amsterdam Island

Diving behaviour was investigated in female subantarctic fur seals (Arctocephalus tropicalis) breeding on Amsterdam Island, Indian Ocean. Data were collected using electronic Time Depth Recorders on 19 seals during their first foraging trip after parturition in December, foraging trips later in summer, and during winter. Subantarctic fur seals at Amsterdam Island are nocturnal, shallow divers. Ninety-nine percent of recorded dives occurred at night. The diel dive pattern and changes in dive parameters throughout the night suggest that fur seals follow the nycthemeral migrations of their main prey. Seasonal changes in diving behaviour amounted to the fur seals performing progressively deeper and longer dives from their first foraging trip through winter. Dive depth and dive duration increased from the first trip after parturition (16.6 ± 0.5 m and 62.1 ± 1.6 s respectively, n=1000) to summer (19.0 ± 0.4 m and 65 ± 1 s, respectively, n=2000) through winter (29.0 ± 1.0 m and 91.2 ± 2.2 s, respectively, n=800). In summer, subantarctic fur seals increased the proportion of time spent at the bottom during dives of between 10 and 20 m, apparently searching for prey when descending to these depths, which corresponded to the oceanic mixed layer. In winter, fur seals behaved similarly when diving between 20 and 50 m, suggesting that the most profitable depths for feeding moved down during the study period. Most of the dives did not exceed the physiological limits of individuals. Although dive frequency did not vary (10 dives/h of night), the vertical travel distance and the time spent diving increased throughout the study period, while the post-dive interval decreased, indicating that subantarctic fur seals showed a greater diving effort in winter, compared to earlier seasons. Accepted: 1 August 1999     

Foraging behavior of lactating northern fur seals (<Emphasis Type="Italic">Callorhinus ursinus</Emphasis>) in the Commander Islands,Russia

We characterized the foraging behavior and habitat associations of lactating female northern fur seals (Callorhinus ursinus) from two of four rookeries comprising the stable population on the Commander Islands (CI). The CI females included in the study were from Severo-Zapadnoe rookery (SZR in 2008 and 2009) and Servernoe rookery (SR in 2009) which are 16 km apart on the northern tip of Bering Island (BI). We used satellite-linked tags and time–depth recorders to track the animals at sea and record dive behavior. For SZR females, the average foraging trip duration, mean dive depth, and maximum travel distance for both years were 3.4 ± 1.42 days, 16 ± 9.8 m, and 85 ± 59.6 km, respectively. The same measures for SR females were 4.4 ± 1.90 days, 20 ± 9.7 m, and 159 ± 70.8 km, respectively. The mean duration of foraging trips, mean number of bouts per trip and trip duration, mean direction of foraging trips, and size of foraging areas were significantly different between females from SR and SZR. Foraging trips of females from neither rookery were associated with high chl-a concentration. Overall, females on the CI appeared to expend less time and energy during foraging trips than females on the Pribilof Islands, and this may explain why the latter population is declining while the CI population is stable.     

VARIATION IN THE FORAGING LOCATION OF ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA) AND THE EFFECTS ON DIVING BEHAVIOR

This study investigated how female Antarctic fur seals adapt their foraging behavior, over time scales of days, to spatial unpredictability in the distribution of their food. Lactating Antarctic fur seals are central-place foragers that feed on highly patchy but spatially and temporally dynamic food. We measured the foraging distribution of 28 fur seals to test whether variation in foraging trip durations was reflected in variation in the location of foraging and the diving behavior of seals at sea. Based on the maximum distance travelled from the breeding beach, three categories of foraging trips were denned: those to the continental shelf area ( n = 12, median = 71 km), to oceanic water ( n = 11, median =164 km), and to farther offshore oceanic waters ( n = 5, median = 260 km). Trip duration and mean surface speed were positively correlated with the maximum distance travelled from the breeding beach. Seals on longer trips spent proportionally less of their time submerged, but there was no significant difference in the total number of dives or the total time spent foraging by seals in relation to trip duration. Evidence from this study and previous work investigating energy gain suggests that an animal on a longer foraging trip could potentially have a higher mean energy return per dive than a similar animal on a shorter foraging trip. Evidence presented suggests that the type of foraging trip (near or far) is not predetermined by the animal but may be a simple response to the stochastic distribution of the resources available.     

Habitat use and spatial fidelity of male South American sea lions during the nonbreeding period

Conditions experienced during the nonbreeding period have profound long‐term effects on individual fitness and survival. Therefore, knowledge of habitat use during the nonbreeding period can provide insights into processes that regulate populations. At the Falkland Islands, the habitat use of South American sea lions (Otaria flavescens) during the nonbreeding period is of particular interest because the population is yet to recover from a catastrophic decline between the mid‐1930s and 1965, and nonbreeding movements are poorly understood. Here, we assessed the habitat use of adult male (n = 13) and juvenile male (n = 6) South American sea lions at the Falkland Islands using satellite tags and stable isotope analysis of vibrissae. Male South American sea lions behaved like central place foragers. Foraging trips were restricted to the Patagonian Shelf and were typically short in distance and duration (127 ± 66 km and 4.1 ± 2.0 days, respectively). Individual male foraging trips were also typically characterized by a high degree of foraging site fidelity. However, the isotopic niche of adult males was smaller than juvenile males, which suggested that adult males were more consistent in their use of foraging habitats and prey over time. Our findings differ from male South American sea lions in Chile and Argentina, which undertake extended movements during the nonbreeding period. Hence, throughout their breeding range, male South American sea lions have diverse movement patterns during the nonbreeding period that intuitively reflects differences in the predictability or accessibility of preferred prey. Our findings challenge the long‐standing notion that South American sea lions undertake a winter migration away from the Falkland Islands. Therefore, impediments to South American sea lion population recovery likely originate locally and conservation measures at a national level are likely to be effective in addressing the decline and the failure of the population to recover.     

Krill-feeding behaviour of gentoo penguins as shown by animal-borne camera loggers

Animal-borne camera loggers were used to examine the patterns of prey encounter and feeding behaviour of gentoo penguins at King George Island, Antarctica. The still images from the camera loggers showed that the penguins encountered the swarms of krill for 25.5% (range: 8–38%) of their dives (>5 m) on average, during their foraging trips (mean duration of 5.4 h, n = 7 trips). They encountered krill swarms during the dives to 10–70 m depth, in pelagic as well as benthic habitats. In the benthic habitat, the penguins swam just above the sea floor and headed downward over a krill swarm, probably using the sea floor to assist them to feed on mobile swarms. The shallow coastal waters would be the important foraging habitat of gentoo penguins breeding in King George Island.     

Foraging and provisioning in Antarctic fur seals: interannual variability in time-energy budgets

This study examined three competing hypotheses to explain howlactating Antarctic fur seals (Arctocephalus gazella) respondto changes in the level of resource availability. Antarcticfur seals have episodic bouts of suckling (1-3 days), alternatingwith foraging trips (3-10 days). Foraging time budgets variedsignificantly (p <.001) among 8 consecutive years at BirdIsland, South Georgia. Foraging trip duration increased during periodsof relative food shortage. Time spent ashore was more consistentamong years than foraging trip duration but declined duringa year of particularly low food availability. In 4 of the 8years, there was a significant positive correlation betweentime spent ashore and foraging trip duration. In the other years,the relationship was close to statistical significance. Energydelivery to pups during suckling bouts followed an asymptoticpower function. Energy gain during foraging trips was estimatedfrom diving behavior, which suggested that the energy gain functionwas linear. Distance traveled during foraging trips was correlatedwith foraging trip duration, and long foraging trips were associatedwith reduced foraging intensity. There was support for the hypothesisthat lactating Antarctic fur seals compensate for reduced resources byincreasing the foraging trip duration rather than working harderand increasing their energy expenditure. However, there wasmost support for the hypothesis that lactating Antarctic furseals adjust time spent ashore as well as foraging trip duration,possibly to maximize the delivery of food to their offspring.Lactation appears to impose constraints on provisioning of offspringthat differ from those of seabirds foraging in the same environment andoften on the same prey.     

DIVING BEHAVIOR OF THE PACIFIC HARBOR SEAL (PHOCA VITULINA RICHARDII) IN MONTEREY BAY, CALIFORNIA

Physical environment and physiological characteristics of marine mammals potentially affect the duration and depth of diving. Härkönen (1987b) proposed a hypothesis that the harbor seal would gain maximum energy by foraging at intermediate depths. To investigate this hypothesis, we studied diving behavior of the Pacific harbor seal (Phoca vitulina ricbardii) during 1995 through 1997 in Monterey Bay, California. Dive depths (n = 13,063 dives) were recorded via time‐depth recorders. Approximately 80% of recorded dives were classified as square dives (type I), which typically were associated with foraging in pinnipeds. Approximately 11% of dives were V dives (type II; 1,402 dives), and the remainder (1,225 dives) were skewed dives (type III and IV). The deepest recorded dive was 481 m, while the greatest duration was 35.25 min. Body mass explained the variability of durations of long dives for females (95th percentile; D₉₅♂=‐5.47 + 0.18 × (mass♀), r²= 0.91, 95% CI for slope = [0.08, 0.28], n= 5) and for males (D₉₅♂=‐5.86 + 0.18 × (mass♀), r²= 0.83, 95% CI for slope = [0.12, 0.24], n= 11). The large proportion of variability in deep dives, however, was explained by body mass only for males (95th percentile; Z₉₅♂=‐363.9 + 6.05 × (mass♀), r²= 0.83, 95% CI for slope = [3.93, 8.17], n= 11) and not for females (Z₉₅,♂=?148.1 +3.11 × (mass♀), r²= 0.58, 95% CI for slope = [‐1.7, 7.9], n= 5, 95% CI for slope= [?1.7, 7.9]). Median depths of presumed foraging dives of harbor seals in the Monterey Bay area were between 5 and 100 m, which were within the range of the previously reported depths for other areas (< 100 m). Our findings generally supported Härkönen's hypothesis that harbor seals forage in the intermediate depth in their environment.     

SUMMER DIVING BEHAVIOR OF MALE WALRUSES IN BRISTOL BAY, ALASKA

Pacific walruses ( Odobenus rosmarus divergens ) make trips from ice or land haul-out sites to forage for benthic prey. We describe dive and trip characteristics from time-depth-recorder data collected over a one-month period during summer from four male Pacific walruses in Bristol Bay, Alaska. Dives were classified into four types. Shallow (4 m), short (2.7 min), square-shaped dives accounted for 11% of trip time, and many were probably associated with traveling. Shallow (2 m) and very short (0.5 min) dives composed only 1% of trip time. Deep (41 m), long (7.2 min), square-shaped dives accounted for 46% of trip time and were undoubtedly associated with benthic foraging. V-shaped dives ranged widely in depth, were of moderate duration (4.7 min), and composed 3% of trip time. These dives may have been associated with navigation or exploration of the seafloor for potential prey habitat. Surface intervals between dives were similar among dive types, and generally lasted 1–2 min. Total foraging time was strongly correlated with trip duration and there was no apparent diel pattern of diving in any dive type among animals. We found no correlation between dive duration and postdive surface interval within dive types, suggesting that diving occurred within aerobic dive limits. Trip duration varied considerably within and among walruses (0.3–9.4 d), and there was evidence that some of the very short trips were unrelated to foraging. Overall, walruses were in the water for 76.6% of the time, of which 60.3% was spent diving.     

False killer whales and fisheries interactions in Hawaiian waters: Evidence for sex bias and variation among populations and social groups

We assessed scarring patterns as evidence of fisheries interactions for three populations of false killer whales in Hawai‘i. Bycatch of the pelagic population in the tuna longline fishery exceeds their Potential Biological Removal level. Scarring was assessed by seven evaluators as consistent, possibly consistent, or not consistent with fisheries interactions, and average scores computed. Scores were highest for scarred main Hawaiian Island (MHI) false killer whales, followed by pelagic and Northwestern Hawaiian Island (NWHI) individuals. Considering only whales for which the majority of evaluators scored scarring as consistent revealed significant differences among populations in the percentage of individuals scarred; MHI: 7.5%, pelagic: 0%, NWHI: 0%. Assessment by social cluster for the MHI population showed that 4.2% of Cluster 1, 7.1% of Cluster 2, and 12.8% of Cluster 3 individuals had such scarring, although differences between clusters were not statistically significant. There was a significant sex bias; all sexed individuals (n = 7) with injuries consistent with fisheries interactions were female. The higher proportion of MHI individuals with fisheries‐related scarring suggests that fisheries interactions are occurring at a higher rate in this population. The bias towards females suggests that fisheries‐related mortality has a disproportionate impact on population dynamics.     

Diving pattern and performance in relation to foraging ecology in the gentoo penguin, Pygoscelis papua

We present data on diving pattern and performance (dive depth, duration, frequency and organization during the foraging trip) in gentoo penguins Pygoscelis papua , obtained using time-depth recorders ( n = 9 birds, 99 foraging trips). These data are used to estimate various parameters of foraging activity, e.g. foraging range, prey capture rates, and are compared in relation to breeding chronology. Foraging trip duration was 6 h and 10 h, and trip frequency 1.0/day and 0.96/day, during the brooding and creche periods, respectively. Birds spent on average 52%of each foraging trip diving. Dive depth and duration were highly bimodal: shallow dives (< 21 m) averaged 4 m and 0.23 min, and deep dives (> 30 m) 80 m and 2.5 min, respectively. Birds spent on average 71%and 25%of total diving time in deep and shallow dives, respectively. For deep dives, dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals 2–3 times dive duration. We suggest that most shallow dives are searching/exploratory dives and most deep dives are feeding dives. Deep dives showed clear diel patterns averaging 40 m at dawn and dusk and 80–90 m at midday. Estimated foraging ranges were 2.3 km and 4.1 km during the brood and creche period, respectively. Foraging trip duration increased by 4 h between the brood and creche periods but total time spent in deep dives (i.e. time spent feeding) was the same (3 h). Of 99 foraging trips, 56%consisted of only one dive bout and 44%of 2–4 bouts delimited by extended surface intervals > 10 min. We suggest that this pattern of diving activity reflects variation in spatial distribution of prey rather than the effect of physiological constraints on diving ability.     

Familial social structure and socially driven genetic differentiation in Hawaiian short‐finned pilot whales

Social structure can have a significant impact on divergence and evolution within species, especially in the marine environment, which has few environmental boundaries to dispersal. On the other hand, genetic structure can affect social structure in many species, through an individual preference towards associating with relatives. One social species, the short‐finned pilot whale (Globicephala macrorhynchus), has been shown to live in stable social groups for periods of at least a decade. Using mitochondrial control sequences from 242 individuals and single nucleotide polymorphisms from 106 individuals, we examine population structure among geographic and social groups of short‐finned pilot whales in the Hawaiian Islands, and test for links between social and genetic structure. Our results show that there are at least two geographic populations in the Hawaiian Islands: a Main Hawaiian Islands (MHI) population and a Northwestern Hawaiian Islands/Pelagic population (F_ST and Φ_ST p < .001), as well as an eastern MHI community and a western MHI community (F_ST p = .009). We find genetically driven social structure, or high relatedness among social units and clusters (p < .001), and a positive relationship between relatedness and association between individuals (p < .0001). Further, socially organized clusters are genetically distinct, indicating that social structure drives genetic divergence within the population, likely through restricted mate selection (F_ST p = .05). This genetic divergence among social groups can make the species less resilient to anthropogenic or ecological disturbance. Conservation of this species therefore depends on understanding links among social structure, genetic structure and ecological variability within the species.     

Testing assumptions of central place foraging theory: a study of Adélie penguins Pygoscelis adeliae in the Ross Sea

We investigated central place foraging (CPF) in the context of optimal foraging theory in Adélie penguins Pygoscelis adeliae of the southern Ross Sea by using satellite tracking and time‐depth recorders to explore foraging at two spatio‐temporal scales: within the day‐to‐day (sub‐mesoscale: single foraging trip, 10s of km²) and the entire breeding season (mesoscale: trips by multiple individuals across the collective foraging area, 100s of km²). Specifically, we examine whether three basic assumptions of the Orians–Pearson CPF model, shown to occur in other CPF species, are met: 1) within a patch, the rate of prey acquisition declines with time spent in that patch; 2) food is distributed in discrete patches and is not available between those patches; and 3) CPF species have knowledge of the potential (or average, at least) feeding rate within their universe of patches, and use this knowledge to determine their foraging strategy when planning or engaging in a foraging trip. We found that prey consumption rates did not decline with time spent in patches, and penguins foraged to some degree most of the time when at sea. Food availability, as measured by foraging dive rate, appeared to be predictable within the same day at the same location, but predictability broke down after 2 d at distances > 10 km away. We conclude that the assumptions of the Orians–Pearson CPF model are not a good fit to the circumstances of Ross Sea penguins, which clearly are central place foragers.     

High apex predator biomass on remote Pacific islands

On coral reefs in Palmyra—a central Pacific atoll with limited fishing pressure—total fish biomass was 428 and 299% greater than on reefs in nearby Christmas and Fanning Islands. Large apex predators, groupers, sharks, snappers, and jacks larger than 50 cm in length, accounted for 56% of total fish biomass in Palmyra on average, but only 7 and 3% on Christmas and Fanning. These biomass proportions are remarkably similar to those previously reported for the remote and uninhabited Northwest Hawaiian Islands (NWHI) and densely populated Main Hawaiian Islands (MHI), although Palmyra’s reefs are dominated in biomass by sharks (44% of the total), whereas the NWHI by jacks (39%). Herbivorous fish biomass was also greater on Palmyra than on Christmas and Fanning (343 and 207%, respectively). These results and previous findings indicate that remote, uninhabited islands support high levels of consumers, and highlight the importance of healthy coral reef ecosystems as reference points for assessment of human impacts and establishment of restoration goals.     

Daily activity and minimum food requirements during winter for gentoo penguins (Pygoscelis papua) in the South Shetland Islands, Antarctica

Estimates of daily activity and consequent demand for food during winter are scarce for many polar seabirds, yet essential for assessing constraints on foraging effort, demand for food, and potential competition with local fisheries. We affixed archival temperature tags to gentoo penguins (Pygoscelis papua) from two colonies in the South Shetland Islands to measure the frequency, timing, and duration of foraging trips and to estimate minimum food requirements during winter. Foraging trip frequencies ranged from 0.85 to 1.0 trips day⁻¹ and were positively correlated with day length. Early winter foraging trips more closely matched day length than late winter foraging trips. The data suggest that individuals maximize foraging time during the early winter period, likely to recover body mass following the breeding season and molt. The more attenuated response of foraging trip durations to increasing day length in late winter may be related to differences in local resource availability or individual behaviors prior to the upcoming breeding season. Minimum food requirements also exhibited a seasonal cycle with a mid-winter minimum. On average, minimum food requirements were estimated at 0.70 ± 0.12 kg day⁻¹. Extrapolated to the regional population of gentoo penguins, winter food requirements by gentoo penguins were equivalent to roughly 33% of annual krill catches by commercial fisheries in the South Shetland Island region over the past decade. Current expansion of the gentoo population and the krill fishery in the southern Scotia Sea warrants continued monitoring of gentoo penguins during winter.     

Overnight foraging trips by chick‐rearing Nazca Boobies Sula granti and the risk of attack by predatory fish

Most tropical booby species complete breeding foraging trips within daylight hours, thus avoiding nights at sea. Nazca Boobies Sula granti are unusual in this respect, frequently spending one or more nights away from the nest. We used GPS dataloggers, time‐depth recorders, and changes in body weight to characterize foraging trips and to evaluate potential influences on the decisions of 64 adult Nazca Boobies to spend a night at sea, or to return to their chicks on Isla Española, Galápagos, in daylight hours. The tagged birds foraged east of Isla Española, undertaking both single‐day (2–15 h, 67% of trips) and overnight trips (28 h–7.2 days, 33%), and executing 1–19 foraging plunge‐dives per single‐day trip. Birds might forage longer if they are in nutritional stress when they depart, but body weight at departure was not correlated with trip length. Birds might be expected to return from longer trips with more prey for young, but they returned from single‐day and overnight trips with similar body weights, consistent with previous indications that Nazca Boobies forage until accumulating a target value of prey weight. Birds with a lower dive frequency during the first 5 h of a trip were more likely to spend the night at sea, suggesting that they might choose to spend the night at sea if prey capture success was low. At night, birds almost never dived and spent most of their time resting on the water’s surface (11.8–12.1 h, > 99% of the time between civil sunset and civil dawn). Thus, the night is an unproductive time spent among subsurface predators under low illumination. The birds’ webbed feet provided evidence of this risk: 24% of birds were missing > 25% of their foot tissue, probably due to attacks by predatory fish, and the amount of foot tissue lost increased with age, consistent with a cumulative risk across the lifespan. In contrast, other tropical boobies (Blue‐footed Sula nebouxii and Brown Boobies Sula leucogaster), which do not spend the night on the water, showed no such damage. These results suggest that chick‐rearing Nazca Boobies accept nocturnal predation risk on occasions of low prey encounter during a foraging trip’s first day.     

Body condition influences ontogeny of foraging behavior in juvenile southern elephant seals

Ontogeny of diving and foraging behavior in marine top predators is poorly understood despite its importance in population recruitment. This lack of knowledge is partly due to the difficulties of monitoring juveniles in the wild, which is linked to high mortality early in life. Pinnipeds are good models for studying the development of foraging behaviors because juveniles are large enough to robustly carry tracking devices for many months. Moreover, parental assistance is absent after a juvenile departs for its first foraging trip, minimizing confounding effects of parental input on the development of foraging skills. In this study, we tracked 20 newly weaned juvenile southern elephant seals from Kerguelen Islands for up to 338 days during their first trip at sea following weaning. We used a new generation of satellite relay tags, which allow for the transmission of dive, accelerometer, and location data. We also monitored, at the same time, nine adult females from the colony during their post‐breeding trips, in order to compare diving and foraging behaviors. Juveniles showed a gradual improvement through time in their foraging skills. Like adults females, they remarkably adjusted their swimming effort according to temporal changes in buoyancy (i.e., a proxy of their body condition). They also did not appear to exceed their aerobic physiological diving limits, although dives were constrained by their smaller size compared to adults. Changes in buoyancy appeared to also influence their decision to either keep foraging or return to land, alongside the duration of their haul outs and choice of foraging habitat (oceanic vs. plateau). Further studies are thus needed to better understand how patterns in juveniles survival, and therefore elephant seal populations, might be affected by their changes in foraging skills and changes in their environmental conditions.     

Foraging behaviour and feeding locations of Rock Shags Phalacrocorax magellanicus from a colony in Patagonia, Argentina

During 1996 and 1997, foraging Rock Shags Phalacrocorax magellanicus were studied at Punta Loma, Argentina using radio-transmitters deployed on ten adult shags during the chick-rearing period. Rock Shags undertook 2.6 ± 0.6 sd trips per day. The mean duration of a feeding trip was 2.6 ± 0.7 hours. A bird spent 36% of daylight hours away from the colony on feeding trips, diving for 92% of the foraging trip, and made a mean of 106 dives per foraging trip. Foraging trip duration was strongly correlated with the total number of dives made in one foraging trip. Rock Shags fed mainly in water less than 10m deep with a gravelly sand bottom and within 5 km of shore. Mean foraging range was 3.8 ± 2.6 km and 2.6 ± 2.3 km for 1996 and 1997, respectively. These results suggest a high foraging effort (diving time per foraging trip) for Rock Shags, presumably associated with poor food conditions close to the colony. Comparison is made with other Phalacrocorax species.     

Patterns of energy acquisition by a central place forager: benefits of alternating short and long foraging trips

In some seabirds, foraging trips have been defined as eitherlong or short, with the length of time spent traveling to theforaging area apparently a critical feature in determining foragingtrip length. Using logger technology, together with complimentarydata from published studies, we investigated traveling and foragingtimes in 18 free-living Adélie Penguins Pygoscelis adeliae,which were foraging for chicks. Most deep, foraging dives weredistributed around the center of the foraging trip. This centraltendency was particularly apparent if the cumulative amountof undulations in the depth profile (indicative of prey capture)was considered during deep dives; values started to increasebefore 20.9% and ceased after 67.2% of the dives had occurred.This concentration of the feeding activity in the middle ofthe foraging trip indicates that birds traveled to and froma prey patch whose location varied little over the birds' trips.These data form the basis for a simple model that uses travelingand foraging times together with projected rates of prey ingestionand chick and adult gastric emptying to determine that thereare occasions when, to optimize rates of prey ingestion whileat sea for both adults and chicks, birds should conduct foragingtrips of bimodal lengths.