Primary Feeding Grounds Research Articles

Migration and foraging strategies at varying spatial scales in western North Atlantic right whales: a review of hypotheses

Western North Atlantic right whales (Eubalaena glacialis) utilise several important foraging habitats off the northeastern United States andeastern Canada, where they feed on dense patches of zooplankton. At a fundamental level, a right whale’s optimal strategy should be tolocate and exploit the prey patches with the highest net energetic return from foraging. There remain many questions, however, concerningtheir migration and foraging strategies and the environmental cues and sensory modalities involved in migration and foraging, all of whichare likely to vary at different spatial scales. For example, a right whale most likely uses different mechanisms and strategies for locationof primary feeding grounds than those used for detection of optimum prey patches within a feeding area. This paper proposes a multi-scaled,hierarchical, conceptual model of right whale migratory and foraging strategies and presents a variety of hypotheses concerning themechanisms involved. Right whales may return to the general area of their feeding grounds based on prior experience. The locations ofsuccessful foraging in the immediately preceding years are likely to be re-visited, as are habitats to which an animal was exposed whileaccompanying its mother during its first year of life. It is also possible that the whales utilise large- or medium-scale environmental cues,such as currents, temperature discontinuities, or salinity signals indicating coastal plumes, to locate likely areas of high zooplankton patchdensity. Whilst on their feeding grounds, right whales tend to be aggregated, but there are usually outliers which may represent occasionalexcursions in search of other prey patches, though there is currently no evidence to address whether they communicate information aboutprey to other individuals. Their behaviour whilst actively feeding indicates that they can detect differences in patch density and adjust theirbehaviour accordingly. A likely sensory mechanism for quantification of patch density and triggering of feeding behaviour would be thevibrissae around the anterior opening of the mouth.

Critically endangered western gray whales migrate to the eastern North Pacific.

Western North Pacific gray whales (WGWs), once considered extinct, are critically endangered with unknown migratory routes and reproductive areas. We attached satellite-monitored tags to seven WGWs on their primary feeding ground off Sakhalin Island, Russia, three of which subsequently migrated to regions occupied by non-endangered eastern gray whales (EGWs). A female with the longest-lasting tag visited all three major EGW reproductive areas off Baja California, Mexico, before returning to Sakhalin Island the following spring. Her 22 511 km round-trip is the longest documented mammal migration and strongly suggests that some presumed WGWs are actually EGWs foraging in areas historically attributed to WGWs. The observed migration routes provide evidence of navigational skills across open water that break the near-shore north-south migratory paradigm of EGWs. Despite evidence of genetic differentiation, these tagging data indicate that the population identity of whales off Sakhalin Island needs further evaluation.

Remote Antarctic feeding ground important for east Australian humpback whales

Understanding the dynamics of population recovery is particularly complex when an organism has multiple, remote breeding and feeding grounds separated by one of the longest known migration routes. This study reports on the most comprehensive assessment of humpback whale (Megaptera novaeangliae) movements between remote Antarctic waters south of New Zealand and east Australia (EA), and the migratory corridors and breeding grounds of Australia and Oceania. A total of 112 individual whales were identified; 57 from microsatellites and 61 by fluke with 23 % (n = 26) matched to sites outside Antarctica. Despite large datasets from other southern regions being included in the comparison, the whales were predominantly linked to EA (n = 24). Only two matches to the Oceania catalogues directly north was surprising; therefore the primary feeding grounds of these endangered whales still remain unknown. The confirmation of the Balleny Islands as an important feeding ground for EA whales could provide an insight into reasons behind the rapid recovery of this population. Determining the feeding grounds of Oceania’s whales may explain whether prey energetics or migration length are limiting factors to their recovery and will allow an understanding of future ecosystem changes in these whales.

Erratum to: Immature Pacific bluefin tuna, Thunnus orientalis, utilizes cold waters in the Subarctic Frontal Zone for trans-Pacific migration

The habitat and movements of a Pacific bluefin tuna were investigated by reanalyzing archival tag data with sea surface temperature data. During its trans-Pacific migration to the eastern Pacific, the fish took a direct path and primarily utilized waters, in the Subarctic Frontal Zone (SFZ). Mean ambient temperature during the trans-Pacific migration was 14.5 ± 2.9 (°C ± SD), which is significantly colder than the waters typically inhabited by bluefin tuna in their primary feeding grounds in the western and eastern Pacific (17.6 ± 2.1). The fish moved rapidly through the colder water, and the heat produced during swimming and the thermoconservation ability of bluefin tuna likely enabled it to migrate through the cold waters of the SFZ.

Modelo espacial para la detección de sitios potenciales para la alimentación de aves playeras migratorias en el noroeste de México

La mayoría de las aves playeras migratorias hacen uso de los humedales principalmente como zonas de alimentación; estos sitios están sujetos a diversas amenazas debido a que en ellos convergen varios intereses humanos. El noroeste de México es una región que presenta gran abundancia de aves playeras y forma parte del corredor migratorio del Pacífico; sin embargo, aún no se cuenta con información sistemática que proporcione las bases para identificar y priorizar los hábitats aptos para la alimentación de estas aves y que brinde herramientas para desarrollar estrategias de manejo. Debido a la extensión y complejidad de estos hábitats, las imágenes de satélite son una herramienta útil para ubicarlos y caracterizarlos. En este trabajo, describimos un marco metodológico para desarrollar modelos espaciales como herramienta para identificar humedales potenciales para la alimentación de aves playeras migratorias mediante el análisis de imágenes satelitales Landsat TM, sistemas de información geográfica y métricas de paisaje. Nuestros resultados muestran diferencias consistentes en la configuración espacial de los sitios identificados en la Península de Baja California y el macizo continental. Asimismo, muestran que los sitios continentales presentan una mayor conectividad y extensión, mientras que los sitios peninsulares presentan menor extensión y mayor aislamiento. Discutimos que los aspectos que contribuyen al grado de importancia de un sitio como zona de alimentación para estas aves son su extensión, el grado de agrupamiento de los parches de sustrato húmedo dentro en cada zona y la distancia entre zonas.

What Happened to Gray Whales during the Pleistocene? The Ecological Impact of Sea-Level Change on Benthic Feeding Areas in the North Pacific Ocean

BackgroundGray whales (Eschrichtius robustus) undertake long migrations, from Baja California to Alaska, to feed on seasonally productive benthos of the Bering and Chukchi seas. The invertebrates that form their primary prey are restricted to shallow water environments, but global sea-level changes during the Pleistocene eliminated or reduced this critical habitat multiple times. Because the fossil record of gray whales is coincident with the onset of Northern Hemisphere glaciation, gray whales survived these massive changes to their feeding habitat, but it is unclear how.Methodology/Principal FindingsWe reconstructed gray whale carrying capacity fluctuations during the past 120,000 years by quantifying gray whale feeding habitat availability using bathymetric data for the North Pacific Ocean, constrained by their maximum diving depth. We calculated carrying capacity based on modern estimates of metabolic demand, prey availability, and feeding duration; we also constrained our estimates to reflect current population size and account for glaciated and non-glaciated areas in the North Pacific. Our results show that key feeding areas eliminated by sea-level lowstands were not replaced by commensurate areas. Our reconstructions show that such reductions affected carrying capacity, and harmonic means of these fluctuations do not differ dramatically from genetic estimates of carrying capacity.Conclusions/SignificanceAssuming current carrying capacity estimates, Pleistocene glacial maxima may have created multiple, weak genetic bottlenecks, although the current temporal resolution of genetic datasets does not test for such signals. Our results do not, however, falsify molecular estimates of pre-whaling population size because those abundances would have been sufficient to survive the loss of major benthic feeding areas (i.e., the majority of the Bering Shelf) during glacial maxima. We propose that gray whales survived the disappearance of their primary feeding ground by employing generalist filter-feeding modes, similar to the resident gray whales found between northern Washington State and Vancouver Island.

Migratory movements and surfacing rates of humpback whales (Megaptera novaeangliae) satellite tagged at Socorro Island, Mexico

AbstractHumpback whales wintering in the Revillagigedo Archipelago, Mexico, have been considered a different subpopulation from those found off mainland Mexico and Baja California. The primary feeding grounds for Revillagigedo humpbacks remain unknown. In February 2003, we deployed 11 Argos satellite‐monitored radio tags to track movements and surfacings of humpback whales (five adults without calves, five mothers with calves, one calf) off Socorro Island in the Revillagigedo Archipelago. Tracking ranged from 222 to 10,481 km over 4.9–149.1 d. Eight whales left Socorro Island: five visited other Mexican wintering destinations, seven moved north of these areas. Migration routes were primarily offshore (average 444 km). Two whales were tracked to feeding grounds: one to British Columbia (46 d migration), and one to Alaska (49 d migration). Mean travel speeds were 1.2 km/h in wintering areas, 4.0 km/h during migration, and 2.2 km/h in feeding areas. Overall surfacing rates ranged from 21 to 88 surfacings/h. Surfacing rates differed between the calf and all other whales, and between feeding areas and migratory/wintering areas for the calf and an adult without a calf. The calf also showed diel variation in surfacing rates. The offshore habits of tagged whales may explain scarce resightings of Revillagigedo humpbacks outside the Revillagigedo Archipelago.

GRAY WHALE OCCURRENCE AND FORAGE SOUTHEAST OF KODIAK, ISLAND, ALASKA

Although the Bering and Chukchi seas are commonly cited as the principal summer feeding grounds of Eastern North Pacific (ENP) gray whales (e.g., Highsmith et al. in press, Swartz et al. 2006), records indicate that this population actually feeds opportunistically throughout its range from the lagoons of Baja California, Mexico, to Alaskan waters (Nerini 1984). Specifically, recent reports suggest that whales may routinely feed in the Gulf of California (Sanchez-Pacheco et al. 2001) and Bahia Magdalena, Baja California Sur (Caraveo-Patino and Soto 2005), whereas Clapham et al. (1997) noted that feeding gray whales occurred offshore California even in the 1920s when population numbers were very low. The dynamic nature of foraging in this population is best described from coastal study sites along the southeastern shore of Vancouver Island, Canada, where whales shift among pelagic, epi-benthic, and benthic prey within and between years (Darling et al. 1998; Dunham and Duffus 2001, 2002). In the 1980s the southern Chukchi Sea and the Chirikov Basin in the northern Bering Sea were considered the primary feeding grounds for ENP gray whales, based on reported high densities of both whales (Braham 1984, Kim and Oliver 1989, Moore et al. 2000) and their ampelicid amphipod prey (Grebmeier et al. 1989, Highsmith and Coyle 1990). However, by 2002, benthic productivity in the Chirikov Basin had declined precipitously, due to either whale foraging (Highsmith et al. 2006), ecosystem change (Grebmeier et al. 2006), or both, and only the southern Chukchi Sea supported dense aggregations of gray whales (Moore et al. 2003). Indeed, the

Insights on Habitat Selection and Behavioural Patterns of Peale's Dolphins (<I>Lagenorhynchus australis</I>) in the Strait of Magellan, Southern Chile

During the austral summer/autumn of 2001, habitat selection of Peale’s dolphins (Lagenorhynchus australis) was assessed through a five-month land-based survey in two sectors on the central west coast of the Strait of Magellan, Punta Arenas, Chile. The main objective of this study was to evaluate habitat selection of Peale’s dolphins in relation to kelp beds and the behavioural patterns determining dolphins habitat use. In 191 h of observation effort, habitat use of Peale’s dolphins displayed a significant concentration in only a small part of the study area, which was strongly associated with kelp beds. Feeding was the most frequent behaviour observed, followed by traveling. The former behavioural state was observed principally inside and on the border of kelp beds, while traveling was observed mainly outside the beds. Peale’s dolphins’ preference for kelp beds, which seemed to be their primary feeding ground, was evident throughout this study. Kelp forests appear to be a fundamental habitat for Peale’s dolphins in coastal ecosystems, and their protection might be crucial for the conservation of Peale’s dolphin populations.

Conservation and management of humpback dolphins: the South African perspective

AbstractPopulation biology and socio-ecology of Indo-Pacific humpback dolphins Sousa chinensis were investigated during a 3-year study period in the Algoa Bay region, South Africa. The dolphins inhabit a narrow strip of coastal waters, mostly less than 15 m deep. Groups are small (mean = 7 animals) and their daily activities concentrate around shallow rocky reefs—the primary feeding grounds. Dependence on these restricted, shallow-water habitats is evident throughout the year. Site fidelity is generally weak and is subject to seasonal migration, although female site fidelity seems to be related to reproductive stage. Births occur predominantly in summer. The social system is highly fluid, structured to some degree by sex and age, ‘matesearching’ behaviour being the most likely male reproductive strategy. The dolphins inhabiting Algoa Bay are part of a substantially larger population that uses a considerable length of the coastal zone. Estimated population parameters are generally low, as are modelled population growth rates, and an increase in the population size seems unlikely. Humpback dolphins appear to be vulnerable to negative environmental pressure and the alteration/destruction of inshore habitats is probably among the greatest threats to them. Conservation of this species should be given high priority and be seen as an important part of integrated coastal zone management. Establishment of multiple-use management areas with controlled ecotourism and several priority sites declared as strict reserves seems to be the most effective conservation approach. In order to be successful, conservation and management policies need to recognize the needs and lifestyles of the local inhabitants.

Conservation and management of humpback dolphins: the South African perspective*

Population biology and socio-ecology of Indo-Pacific humpback dolphins Sousa chinensis were investigated during a 3-year study period in the Algoa Bay region, South Africa. The dolphins inhabit a narrow strip of coastal waters, mostly less than 15 m deep. Groups are small (mean = 7 animals) and their daily activities concentrate around shallow rocky reefs—the primary feeding grounds. Dependence on these restricted, shallow-water habitats is evident throughout the year. Site fidelity is generally weak and is subject to seasonal migration, although female site fidelity seems to be related to reproductive stage. Births occur predominantly in summer. The social system is highly fluid, structured to some degree by sex and age, ‘matesearching’ behaviour being the most likely male reproductive strategy. The dolphins inhabiting Algoa Bay are part of a substantially larger population that uses a considerable length of the coastal zone. Estimated population parameters are generally low, as are modelled population growth rates, and an increase in the population size seems unlikely. Humpback dolphins appear to be vulnerable to negative environmental pressure and the alteration/destruction of inshore habitats is probably among the greatest threats to them. Conservation of this species should be given high priority and be seen as an important part of integrated coastal zone management. Establishment of multiple-use management areas with controlled ecotourism and several priority sites declared as strict reserves seems to be the most effective conservation approach. In order to be successful, conservation and management policies need to recognize the needs and lifestyles of the local inhabitants.

HABITAT USE AND PREFERENCES OF INDO‐PACIFIC HUMPBACK DOLPHINS SOUSA CHINENSIS IN ALGOA BAY, SOUTH AFRICA

AbstractThis paper examines environmental and behavioral determinants of the habitat use and preferences of Indo‐Pacific humpback dolphins inhabiting the Algoa Bay region on the south Eastern Cape coast of South Africa. In order to quantify the habitat use and preference, two indices were used, the Coefficient of Area Use (AU) and the Activity Index (AI). The dolphins inhabit a narrow strip of shallow, inshore waters of Algoa Bay and remain mostly within 400 m of the shore, in water less than 15 m deep, with no apparent preference for clear or turbid water. Water depth is probably the main factor limiting their inshore distribution, and the 25‐m isobath seems to represent the critical depth. Within this confined, inshore distribution, dolphin activities concentrate in the vicinity of rocky reefs‐their primary feeding grounds. Dolphin dependence on these shallow‐water habitats is evident throughout the year and, consequently, the inshore shallow reefs are identified as the “key habitat” which is of primary importance for humpback dolphins in Eastern Cape waters. The dolphins' dependence on this restricted type of habitat within an already restricted inshore distribution makes them particularly vulnerable to alteration or loss of this habitat.

GRAY WHALES (ESCHRICHTIUS ROBUSTUS) OFF SAKHALIN ISLAND, RUSSIA: SEASONAL AND ANNUAL PATTERNS OF OCCURRENCE1

AbstractThe annual return, seasonal occurrence, and site fidelity of Korean‐Okhotsk or western gray whales on their feeding grounds off northeastern Sakhalin Island, Russia, were assessed by boat‐based photo‐identification studies in 1994‐1998. A total of 262 pods were observed, ranging in size from 1 to 9 whales with an overall mean of 2.0. Sixty‐nine whales were individually identified, and a majority of all whales (71.0%) were observed in multiple years. Annual sighting frequencies ranged from 1 to 18 d, with a mean of 5. 4 d. The percentage of whales reidentified from previous years showed a continuous annual increase, reaching 87.0% by the end of the study. Time between first and last sighting of identified individuals within a given year was 1‐85 d, with an overall mean of 40.6 d. Annual calf proportions ranged from 4.3% (1997) to 13.2% (1998), and mother‐calf separations generally occurred between July and September. The seasonal site fidelity and annual return of whales to this part of the Okhotsk Sea emphasize its importance as a primary feeding ground for this endangered population.

Distribution of heavy metals in muscle, liver and kidney of northern fur seal ( Callorhinus ursinus) caught off Sanriku, Japan and from the Pribilof Islands, Alaska

The concentrations of iron, manganese, zinc, copper, cadmium, and mercury were determined in muscle, liver and kidney of 67 northern fur seals ( Callorhinus ursinus) collected off Sanriku, Japan, and from the Pribilof Islands, Alaska. Almost all the elements except cadmium were highest in liver. Cadmium levels in kidney were higher than those in liver and muscle for all animals analyzed. Concentrations of mercury increased significantly with age in muscle, liver and kidney, as did iron levels in muscle and liver and cadmium levels in muscle, while manganese concentrations decreased with age in muscle and kidney. The kidney also showed decreased copper concentration with age. Cadmium concentrations of the northern fur seals in this study were higher than the other otariids, reflecting a predominantly squid diet. Concentrations of manganese and mercury were found to be higher in the fur seals caught off Sanriku than in animals from the Pribilof Islands, while those of zinc and cadmium were found to be lower. Variable concentrations of cadmium might have been attributed to those in seawaters. Discriminant analysis of heavy metal concentrations was used to identify habitat. Sixty-three of 67 animals (94%) were correctly classified using this technique. Heavy-metal concentrations in tissues may provide a useful method to elucidate the primary feeding grounds of fur seals.

Swarming benthic crustaceans in the Bering and Chukchi seas and their relation to geographic patterns in gray whale feeding

Swarming benthic crustaceans were widespread in the Chukchi and Bering seas. Swarms differed in their geographic extent, local biomass, and life stages of swarming individuals and thus in their availability to feeding gray whales (Eschrichtius robustus). Immature amphipods apparently swarmed for dispersal, whereas cumaceans probably swarmed for mating. All life stages of the hyperbenthic mysids occurred above the sea floor. Although the geographic spread of mysid swarms and shrimp communities was much greater than for the amphipod and cumacean swarms, the latter swarmed in denser patches to produce higher local biomass. Crustacean swarms are important in describing the geographic patterns of gray whale feeding from the Chukchi Sea to Baja California, including the primary, secondary, and tertiary feeding grounds. The primary feeding ground is in the southern Chukchi Sea and especially the northern Bering Sea, where gray whales suck infaunal amphipods from fine sand, producing an extensive record of feeding excavations. The primary feeding ground is divided into a relatively deep zone (> 20 m), where tube-dwelling ampeliscid amphipods are the major prey, and a shallow zone (< 20 m), where burrowing pontoporeid amphipods dominate. The secondary feeding ground is in the southern Bering Sea along the eastern Alaska Peninsula and adjacent Alaskan mainland where shrimp and mysids are the major prey. The tertiary feeding ground is at the periphery of the primary and secondary feeding grounds in Alaskan waters and south of the Bering Sea where there is a general decrease in the availability of prey and their use by gray whales from Canada to Baja California. The tertiary prey communities include swarms of amphipods, cumaceans, and mysids as well as infaunal polychaete worms, but mysids are used the most by whales. The primary gray whale feeding ground was much smaller during low sea levels when the extensive Beringian Platform was exposed to air. This shallow shelf is a unique habitat that presently harbors the largest ampeliscid amphipod community in the world. At low sea level, swarming crustaceans like those sampled in the present study may have been equally or more important to gray whales than infaunal prey. These historical changes in prey availability may account for the catholic diet of the gray whale.

Destruction and Opportunity on the Sea Floor: Effects of Gray Whale Feeding

Gray whales (Eschrichtius robustus) are highly disruptive bottom feeders that remove infaunal invertebrate prey and sediments by suction. The response of the benthos to gray whale feeding was examined in the primary feeding grounds of the Bering Sea and in an ecological analog of these prey communities along the west coast of Vancouver Island. Prey communities were dominated by ampeliscid and other amphipod crustaceans that formed dense tube mats. Large feeding excavations (often 2—20 m2) were rapidly colonized by scavenging lysianassid amphipods, especially Anonyx spp., that attacked injured and dislodged infauna. Many of the attacked animals were small crustaceans (<1 cm long) and polychaete worms. Anonyx xpp. was 20—30 times more abundant inside fresh excavations than in the surrounding tube mat, where they dispersed within hours after the initial feeding disturbance. A smaller species of lysianassid, Orchomene minuta, invades less rapidly and remained much longer in excavations than the larger, Anonyx spp. Natural scavenging events outside feeding excavations revealed that lysianassids commonly fed on relatively small crustacean carcasses (<3 cm long). Within days and weeks, gray whale feeding excavations trapped organic debris. Most invading species were much more abundant in debris patches compared to debris—free areas of the same excavations. The numbers of some colonists remained elevated in disturbed areas for >2 mo. Early colonists were characterized by much greater abundances inside excavations relative to the adjacent tube mat. Two numerically dominant groups of tube—dwelling amphipods were not characterized by a large pulse of abundance inside excavations. Ampelisca and Protomedeia gradually colonized pits. They also swam less frequently than the early colonists, and probably had more infaunal habits. Gray whale feeding clearly has a dramatic impact on the structure of benthic communities, and also may enhance the population size of several secondary prey.

Gray whale feeding on dense ampeliscid amphipod communities near Bamfield, British Columbia

Gray whales fed on dense populations of ampeliscid amphipods while summering along the west coast of Vancouver Island. These amphipod crustacean communities are ecological analogs of the primary feeding grounds of gray whales in the northern Bering Sea. The same major genera of amphipods dominated the Alaskan and Canadian feeding grounds, including Ampelisca, Photis, Protomedeia, Anonyx, and Orchomene, and comprised 67 to 90% of the number of infaunal crustaceans at the two locations. This is the first documented report of gray whale feeding on benthic infauna south of the Bering Sea. Feeding gray whales observed in Pachena Bay produced an extensive record of feeding excavations in bottom sediments. Excavation patterns suggest that: (i) whales used suction to extract infaunal prey and sediments; (ii) a maximum of six excavations was made in one feeding dive; (iii) excavation size was related to whale size; (iv) small and large whales fed in different parts of the bay; and (v) whales effectively located and worked the densest patches of benthic prey. We estimate that a 6-m whale consumed 116 kg of infaunal prey per 12-h day, and that a 12-m whale consumed 552 kg per 12-h day. Scavenging lysianassid amphipods were attracted to feeding disturbances within seconds and preyed on injured and dislodged infauna. Individual feeding excavations were large, deep valleys in a tube-mat plateau. In addition to the lysianassids, many other infauna undoubtedly colonize these highly modified habitats, resulting in important effects on the structure of benthic communities.

Ecology and breeding behavior of a cichlid fish, Cyrtocara eucinostomus, on a large lek in Lake Malawi, Africa

Cyrtocara eucinostomus, a mouthbrooding cichlid, breeds on a 4 km long breeding arena between 3–9 m depth in the Cape Maclear region of Lake Malawi. At times over 50,000 males display there, making this breeding arena the largest ever reported. The form and function of the arena and the behavior of the fish on the arena are analogous to bird leks. This arena serves only as a mating ground. All parental care is provided by the females, which leave the arena with the eggs. Courtship takes place in the morning and most of the males leave in the afternoon to forage on zooplankton in deeper water. They return at dusk. The few males that remain on the arena switch their behavior from courting to foraging on zooplankton. Comparisons of this fish arena are made with bird leks and it is concluded that the mating system of this fish can be defined as a lek in the avian sense. 1) There is no male parental care and an absence of monogamous pair bonding. 2) Males and females are sexually dimorphic and there are males present which mimic females to gain entrance into the arena. 3) The arena is traditional with a lack of environmental constraints and is away from the primary feeding grounds.