scholarly journals Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus

2019 ◽  
Vol 6 (10) ◽  
pp. 191369 ◽  
Author(s):  
S. P. Kirkman ◽  
D. P. Costa ◽  
A.-L. Harrison ◽  
P. G. H. Kotze ◽  
W. H. Oosthuizen ◽  
...  
Keyword(s):  
Prey Species ◽  
Foraging Ecology ◽  
Critical Role ◽  
Ecosystem Structure ◽  
Depth Range ◽  
Dive Behaviour ◽  
Top Predators ◽  
Fur Seals ◽  
Cape Fur Seal ◽  
Benthic Diving

While marine top predators can play a critical role in ecosystem structure and dynamics through their effects on prey populations, how the predators function in this role is often not well understood. In the Benguela region of southern Africa, the Cape fur seal ( Arctocephalus pusillus pusillus ) population constitutes the largest marine top predator biomass, but little is known of its foraging ecology other than its diet and some preliminary dive records. Dive information was obtained from 32 adult females instrumented with dive recorders at the Kleinsee colony (29°34.17′ S, 16°59.80′ E) in South Africa during 2006–2008. Most dives were in the depth range of epipelagic prey species (less than 50 m deep) and at night, reflecting the reliance of Cape fur seals on small, vertically migrating, schooling prey. However, most females also performed benthic dives, and benthic diving was prevalent in some individuals. Benthic diving was significantly associated with the frequency with which females exceeded their aerobic dive limit. The greater putative costs of benthic diving highlight the potential detrimental effects to Cape fur seals of well-documented changes in the availability of epipelagic prey species in the Benguela.

Trophic Cascades in Grasslands

2018 ◽  
Author(s):  
Brian J. Wilsey
Keyword(s):  
Indirect Effects ◽  
Prey Species ◽  
Trophic Levels ◽  
Herbaceous Plant ◽  
Direct Effects ◽  
Temperate Grasslands ◽  
Cascading Effect ◽  
Top Predators ◽  
Invertebrate Predators ◽  
Ecology Of Fear

Top predators have effects that can ‘cascade down’ on lower trophic levels. Because of this cascading effect, it matters how many trophic levels are present. Predators are either ‘sit and wait’ or ‘active’. Wolves are top predators in temperate grasslands and can alter species composition of smaller-sized predators, prey, and woody and herbaceous plant species, either through direct effects or indirect effects (‘Ecology of Fear’). In human derived grasslands, invertebrate predators fill a similar ecological role as wolves. Migrating populations of herbivores tend to be more limited by food than non-migratory populations. The phenology and synchrony of births vary among prey species in a way that is consistent with an adaptation to predation. Precocious species have highly synchronous birth dates to satiate predators. Non-precocious species (‘hiders’) have asynchronous births. Results from studies that manipulate both predators and food support the hypothesis that bottom-up and top-down effects interact.

Otolith chemistry is more accurate than otolith shape in identifying cod species (genus Pseudophycis) in the diet of Australian fur seals (Arctocephalus pusillus doriferus)

2011 ◽  
Vol 68 (10) ◽  
pp. 1732-1743 ◽  
Author(s):  
Jodie Kemp ◽  
Stephen E. Swearer ◽  
Gregory P. Jenkins ◽  
Simon Robertson
Keyword(s):  
Fourier Analysis ◽  
Significant Variation ◽  
Prey Species ◽  
Fine Scale ◽  
Accurate Identification ◽  
Fish Prey ◽  
Otolith Shape ◽  
Discriminant Model ◽  
Fur Seals ◽  
Otolith Core

Fine-scale shape variation and the added effect of partial digestion often limits accurate identification of different teleost prey species in marine diet studies using otoliths. We evaluated the use of fine-scale shape and trace element variation in digested otoliths to identify fish prey species from the diet of predators. Fourier analysis of otolith shape revealed significant variation between red cod ( Pseudophycis bachus ) and bearded rock cod ( Pseudophycis barbata ) otoliths. Incorporating otoliths that had been consumed by Australian fur seals ( Arctocephalus pusillus doriferus ) into a Fourier analysis discriminant model identified 73% of otoliths as those of red cod and 27% as those of bearded rock cod. However, in vitro digestion of red cod and bearded rock cod otoliths resulted in incorrect classification of both cod species otoliths to varying degrees when using Fourier analysis shape descriptors. There was significant variation between red cod and bearded rock cod otolith core chemistry. Incorporating otoliths consumed by the seals into an otolith core chemistry discriminant model identified all otoliths as those of red cod. Using otolith core chemistry to identify prey species was found to be successful, and there is great potential for this technique to have wider applications in investigating ecosystem trophic interactions.

Oceanographic factors influencing the distribution of South American fur seal, Arctocephalus australis around the Falkland Islands before the breeding season

2009 ◽  
Vol 89 (8) ◽  
pp. 1597-1600 ◽  
Author(s):  
Vladimir Laptikhovsky
Keyword(s):  
Prey Species ◽  
Falkland Islands ◽  
South American ◽  
Important Food ◽  
Factors Influencing ◽  
South West ◽  
Fur Seals ◽  
Fur Seal ◽  
Important Food Source ◽  
Productive Zone

Distribution of fur seals Arctocephalus australis has been studied in October 2007 on the western, southern and eastern Falkland shelves during the survey of spawning grounds of the red cod, Salilota australis. Fur seals presence/absence, numbers and sex were recorded at every oceanographic station. Animals were found foraging on the shelf edge south-west of the islands, in a productive zone with quasi-stationary eddies at a periphery of upwelling. It was also the zone of maximum abundance of lobster-krill, Munida spp.—an important food source of fur seals and aggregations of both red cod and blue whiting, Micromesistius australis. No fur seals were found in waters of the relative cold and saline Falkland Current as well as in the relatively warm, fresh and oxygen-rich waters of Argentine Drift. It allows supposing that position and extension of the foraging grounds are caused by oceanographic features determining distribution of prey species.

scholarly journals Foraging segregation of two congeneric diving seabird species breeding on St. George Island, Bering Sea

2016 ◽  
Vol 13 (8) ◽  
pp. 2579-2591 ◽  
Author(s):  
Nobuo Kokubun ◽  
Takashi Yamamoto ◽  
Nobuhiko Sato ◽  
Yutaka Watanuki ◽  
Alexis Will ◽  
...  
Keyword(s):  
Bering Sea ◽  
Environmental Changes ◽  
Foraging Ecology ◽  
Stress Hormones ◽  
Food Resource ◽  
Dive Depth ◽  
Bottom Phase ◽  
Seabird Species ◽  
Top Predators ◽  
The Bering Sea

Abstract. Subarctic environmental changes are expected to affect the foraging ecology of marine top predators, but the response to such changes may vary among species if they use food resources differently. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabird: common (Uria aalge: hereafter COMUs) and thick-billed (U. lomvia: hereafter TBMUs) murres breeding on St. George Island, located in the seasonal sea-ice region of the Bering Sea. We investigated their foraging trip and flight durations, diel patterns of dive depth, and underwater wing strokes, along with wing morphology and blood stable isotope signatures and stress hormones. Acceleration–temperature–depth loggers were attached to chick-guarding birds, and data were obtained from 7 COMUs and 12 TBMUs. Both species showed similar mean trip duration (13.2 h for COMUs and 10.5 h for TBMUs) and similar diurnal patterns of diving (frequent dives to various depths in the daytime and less frequent dives to shallow depths in the nighttime). During the daytime, the dive depths of COMUs had two peaks in shallow (18.1 m) and deep (74.2 m) depths, while those of TBMUs were 20.2 m and 59.7 m. COMUs showed more frequent wing strokes during the bottom phase of dives (1.90 s−1) than TBMUs (1.66 s−1). Fish occurred more frequently in the bill loads of COMUs (85 %) than those of TBMUs (56 %). The δ15N value of blood was significantly higher in COMUs (14.5 ‰) than in TBMUs (13.1 ‰). The relatively small wing area (0.053 m2) of COMUs compared to TBMUs (0.067 m2) may facilitate their increased agility while foraging and allow them to capture more mobile prey such as larger fishes that inhabit deeper depths. These differences in food resource use may lead to the differential responses of the two murre species to marine environmental changes in the Bering Sea.

scholarly journals Impact of aragonite saturation state changes on migratory pteropods

2011 ◽  
Vol 279 (1729) ◽  
pp. 732-738 ◽  
Author(s):  
Steeve Comeau ◽  
Jean-Pierre Gattuso ◽  
Anne-Marin Nisumaa ◽  
James Orr
Keyword(s):  
Critical Role ◽  
The Arctic ◽  
Depth Range ◽  
High Latitudes ◽  
Empirical Relationships ◽  
Saturation State ◽  
Aragonite Saturation ◽  
Ecological Changes ◽  
State Changes ◽  
Ipcc Sres

Thecosome pteropods play a key role in the food web of various marine ecosystems and they calcify, secreting the unstable CaCO 3 mineral aragonite to form their shell material. Here, we have estimated the effect of ocean acidification on pteropod calcification by exploiting empirical relationships between their gross calcification rates (CaCO 3 precipitation) and aragonite saturation state Ω a , combined with model projections of future Ω a . These were corrected for modern model-data bias and taken over the depth range where pteropods are observed to migrate vertically. Results indicate large reductions in gross calcification at temperate and high latitudes. Over much of the Arctic, the pteropod Limacina helicina will become unable to precipitate CaCO 3 by the end of the century under the IPCC SRES A2 scenario. These results emphasize concerns over the future of shelled pteropods, particularly L. helicina in high latitudes. Shell-less L. helicina are not known to have ever existed nor would we expect them to survive. Declines of pteropod populations could drive dramatic ecological changes in the various pelagic ecosystems in which they play a critical role.

Seasonal dive behaviour of lactating New Zealand fur seals (Arctocephalus forsteri)

1998 ◽  
Vol 76 (2) ◽  
pp. 350-360 ◽  
Author(s):  
R H Mattlin ◽  
N J Gales ◽  
D P Costa
Keyword(s):  
New Zealand ◽  
Dive Depth ◽  
Dive Duration ◽  
Early Summer ◽  
Late Winter ◽  
Individual Values ◽  
Dive Behaviour ◽  
Fur Seals ◽  
Fur Seal ◽  
Bay Islands

The dive behaviour of 18 female New Zealand fur seals (Arctocephalus forsteri) from Taumaka, Open Bay Islands, New Zealand (43°52'S, 168°53'E), was recorded during early (summer; December-February), mid (autumn; March-May), and late (winter; June-August) lactation. Mean dive depth, dive duration, and bottom time for dives >=6 m in depth increased from summer through winter. Variation in individual seal dive behaviour within a season accounted for approximately 11, 9, and 11% of the observed difference between seasons in dive depth, dive duration, and bottom time, respectively. Seasonal dive data (mean ± 1 SD) were as follows: summer: dive depth 30 ± 37 m, dive duration 1.4 ± 1.1 min, and bottom time 0.5 ± 0.6 min; autumn: dive depth 54 ± 47 m, dive duration 2.4 ± 1.3 min, and bottom time 1.0 ± 0.8 min; winter: dive depth 74 ± 64 m, dive duration 2.9 ± 1.5 min, and bottom time 1.2 ± 1.1 min. Maximum recorded dive depth was 274 m for a 5.67-min dive in autumn. Maximum duration was 11.17 min for a dive to 237+ m in winter. New Zealand fur seals are the deepest diving fur seal species reported thus far. The estimated theoretical aerobic dive limit was exceeded on 18.4% of dives (range of individual values 0.2-57.8%). Females (n = 12) were ashore about 1.8 days at a time during February through November, and this increased to about 4.3 days during December and January. Average time spent away from the rookery ranged from 3 to 15 days.

scholarly journals Puma (Puma concolor) predation on tapir (Tapirus terrestris)

2016 ◽  
Vol 16 (1) ◽  
Author(s):  
Fernando Cesar Cascelli Azevedo ◽  
Vagner Canuto ◽  
Fernanda Souza ◽  
Cynthia Elisa Widmer
Keyword(s):  
Forest Fragmentation ◽  
Atlantic Forest ◽  
Prey Species ◽  
Puma Concolor ◽  
Anthropogenic Habitats ◽  
First Report ◽  
Top Predators ◽  
Tapirus Terrestris ◽  
Generalist Diet ◽  
Different Levels

The process of forest fragmentation affects mostly top predators, which are more prone to first disappear. Pumas, Puma concolor, are known to have a generalist diet that includes a wide variety of wild and domestic prey species. The capacity of adapting their diet to consuming prey in anthropogenic habitats may be the reason for this species' success in incorporating anthropogenic areas with different levels of fragmentation as part of its habitat. Here we report a case of puma consumption of a large wild prey species, the tapir, Tapirus terrestris. From March 2012 to October 2013 we collected 85 puma's scats opportunistically inside fragments of the Atlantic Forest in the Parana state, Brazil. In one of the scats we found hairs and some hooves of a tapir, as well as puma hairs. We propose two hypotheses that may explain the occurrence of tapir in a pumás scat: (1) an event of scavenging or (2) an event of predation on a juvenile tapir. The most likely explanation for this event may be the predation of a juvenile in response to a possible abundant presence of tapirs in the study area. This event adds to our understanding of the great plasticity of this species to adapt to an altered landscape. To our knowledge, this is the first report of a puma scavenging or predation event on a tapir.

scholarly journals Sharks shape the geometry of a selfish seal herd: experimental evidence from seal decoys

2009 ◽  
Vol 6 (1) ◽  
pp. 48-50 ◽  
Author(s):  
Alta De Vos ◽  
M. Justin O'Riain
Keyword(s):  
Experimental Evidence ◽  
Predation Risk ◽  
Prey Species ◽  
Group Formation ◽  
Predator Prey ◽  
Selfish Herd ◽  
Fur Seal ◽  
Cape Fur Seal ◽  
Shark Attacks ◽  
Proportional Reduction

Many animals respond to predation risk by forming groups. Evolutionary explanations for group formation in previously ungrouped, but loosely associated prey have typically evoked the selfish herd hypothesis. However, despite over 600 studies across a diverse array of taxa, the critical assumptions of this hypothesis have remained collectively untested, owing to several confounding problems in real predator–prey systems. To solve this, we manipulated the domains of danger of Cape fur seal ( Arctocephalus pusillus pusillus ) decoys to provide evidence that a selfish reduction in a seals' domain of danger results in a proportional reduction in its predation risk from ambush shark attacks. This behaviour confers a survival advantage to individual seals within a group and explains the evolution of selfish herds in a prey species. These findings empirically elevate Hamilton's selfish herd hypothesis to more than a ‘theoretical curiosity’.

scholarly journals Exploring the origins of the indentation size effect at submicron scales

2021 ◽  
Vol 118 (30) ◽  
pp. e2025657118
Author(s):  
Xiaolong Ma ◽  
Wesley Higgins ◽  
Zhiyuan Liang ◽  
Dexin Zhao ◽  
George M. Pharr ◽  
...  
Keyword(s):  
Size Effect ◽  
Indentation Size Effect ◽  
Critical Role ◽  
Small Scale ◽  
Structural Development ◽  
Depth Range ◽  
Indentation Size ◽  
Dislocation Source ◽  
Dislocation Interaction ◽  
Submicron Scale

The origin of the indentation size effect has been extensively researched over the last three decades, following the establishment of nanoindentation as a broadly used small-scale mechanical testing technique that enables hardness measurements at submicrometer scales. However, a mechanistic understanding of the indentation size effect based on direct experimental observations at the dislocation level remains limited due to difficulties in observing and quantifying the dislocation structures that form underneath indents using conventional microscopy techniques. Here, we employ precession electron beam diffraction microscopy to “look beneath the surface,” revealing the dislocation characteristics (e.g., distribution and total length) as a function of indentation depth for a single crystal of nickel. At smaller depths, individual dislocation lines can be resolved, and the dislocation distribution is quite diffuse. The indentation size effect deviates from the Nix–Gao model and is controlled by dislocation source starvation, as the dislocations are very mobile and glide away from the indented zone, leaving behind a relatively low dislocation density in the plastically deformed volume. At larger depths, dislocations become highly entangled and self-arrange to form subgrain boundaries. In this depth range, the Nix–Gao model provides a rational description because the entanglements and subgrain boundaries effectively confine dislocation movement to a small hemispherical volume beneath the contact impression, leading to dislocation interaction hardening. The work highlights the critical role of dislocation structural development in the small-scale mechanistic transition in indentation size effect and its importance in understanding the plastic deformation of materials at the submicron scale.

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