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Feeding Aggregations (feeding + aggregation)
Selected AbstractsDistribution and abundance of West Greenland humpback whales (Megaptera novaeangliae)JOURNAL OF ZOOLOGY, Issue 4 2004Finn Larsen Abstract Photo-identification surveys of humpback whales Megaptera novaeangliae were conducted at West Greenland during 1988,93, the last 2 years of which were part of the internationally coordinated humpback whale research programme YoNAH, with the primary aim of estimating abundance for the West Greenland feeding aggregation. The area studied stretched from the coast out to the offshore margin of the banks, determined approximately by the 200 m depth contours, between c. 61°70,N and c. 66°N. The surveys were conducted between early July and mid-August and 993 h were expended on searching effort. A total of 670 groups of humpback whales was encountered leading to the identification of 348 individual animals. Three areas of concentration were identified: an area off Nuuk; an area at c. 63°30,N; and an area off Frederikshåb. Sequential Petersen capture,recapture estimates of abundance were calculated for five pairs of years at 357 (1988,89), 355 (1989,90), 566 (1990,91), 376 (1991,92), and 348 (1992,93). Excluding the anomalously high estimate in 1990,91, the simple mean is 359 (se= 27.3, CV = 0.076) and the inverse CV-squared weighted mean is 356 animals (se= 24.9, CV = 0.070). These calculations lead us to conclude that between 1988 and 1993 there were 360 humpbacks (CV = 0.07) in the West Greenland feeding aggregation. Using the Cormack,Jolly,Seber model framework non-calf survival rate was estimated at 0.957 (se= 0.028). Our data have low power (P < 0.3) to detect a trend of 3.1%, assuming the probability of a type I error was 0.05. [source] The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the ,Merry-Go-Round' hypothesisJOURNAL OF FISH BIOLOGY, Issue 3 2010M. J. Dadswell One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62° N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62° N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high-seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium-137 (137Cs) levels in S. salar returning to a Quebec river suggested 62·3% had fed at or east of Iceland, whereas levels in 1 sea-winter (SW) Atlantic Canada returnees indicated 24·7% had fed east of the Faroes. Lower levels of 137Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open-ocean migrations of epipelagic fishes. [source] Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian OceanMAMMAL REVIEW, Issue 2 2007T. A. BRANCH ABSTRACT 1Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of ,8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings. 2Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually consisted of solitary whales (65.2%) or pairs (24.6%); larger feeding aggregations of unassociated individuals were only rarely observed. Sighting rates (groups per 1000 km from many platform types) varied by four orders of magnitude and were lowest in the waters of Brazil, South Africa, the eastern tropical Pacific, Antarctica and South Georgia; higher in the Subantarctic and Peru; and highest around Indonesia, Sri Lanka, Chile, southern Australia and south of Madagascar. 3Blue whales avoid the oligotrophic central gyres of the Indian, Pacific and Atlantic Oceans, but are more common where phytoplankton densities are high, and where there are dynamic oceanographic processes like upwelling and frontal meandering. 4Compared with historical catches, the Antarctic (,true') subspecies is exceedingly rare and usually concentrated closer to the summer pack ice. In summer they are found throughout the Antarctic; in winter they migrate to southern Africa (although recent sightings there are rare) and to other northerly locations (based on acoustics), although some overwinter in the Antarctic. 5Pygmy blue whales are found around the Indian Ocean and from southern Australia to New Zealand. At least four groupings are evident: northern Indian Ocean, from Madagascar to the Subantarctic, Indonesia to western and southern Australia, and from New Zealand northwards to the equator. Sighting rates are typically much higher than for Antarctic blue whales. 6South-east Pacific blue whales have a discrete distribution and high sighting rates compared with the Antarctic. Further work is needed to clarify their subspecific status given their distinctive genetics, acoustics and length frequencies. 7Antarctic blue whales numbered 1700 (95% Bayesian interval 860,2900) in 1996 (less than 1% of original levels), but are increasing at 7.3% per annum (95% Bayesian interval 1.4,11.6%). The status of other populations in the Southern Hemisphere and northern Indian Ocean is unknown because few abundance estimates are available, but higher recent sighting rates suggest that they are less depleted than Antarctic blue whales. [source] Extension of ideal free resource use to breeding populations and metapopulationsOIKOS, Issue 1 2000C. Patrick Doncaster The concept of an ideal and free use of limiting resources is commonly invoked in behavioural ecology as a null model for predicting the distribution of foraging consumers across heterogeneous habitat. In its original conception, however, its predictions were applied to the longer timescales of habitat selection by breeding birds. Here I present a general model of ideal free resource use, which encompasses classical deterministic models for the dynamics in continuous time of feeding aggregations, breeding populations and metapopulations. I illustrate its key predictions using the consumer functional response given by Holling's disc equation. The predictions are all consistent with classical population dynamics, but at least two of them are not usually recognised as pertaining across all scales. At the fine scale of feeding aggregations, the steady state of an equal intake for all ideal free consumers may be intrinsically unstable, if patches are efficiently exploited by individuals with a non-negligible handling time of resources. At coarser scales, classical models of population and metapopulation dynamics assume exploitation of a homogeneous environment, yet they can yield testable predictions for heterogeneous environments too under the assumption of ideal free resource use. [source] Phenological resistance of grapes to the green June beetle, an obligate fruit-eating scarabANNALS OF APPLIED BIOLOGY, Issue 2 2010D.L. Hammons Changes in fruit characteristics associated with ripening increase the vulnerability of crops to insect depredation, making it difficult for growers to protect cultivated fruits from pest injury close to harvest. This study evaluated phenological resistance, the use of cultivars that ripen before or after peak pest activity, for reducing injury to grapes (Vitis spp.) by the green June beetle (GJB) (Cotinis nitida), an obligate feeder on soft, ripe fruits. Accumulation of sugars, softening of berry skins and recruitment of GJB feeding aggregations were monitored on replicated vines of early-, mid- and late-season ripening cultivars that require from 85 to 125 growing days from bloom to harvest. GJB flight peaked in late July and early August coinciding with later stages of veraison of early-season ripening cultivars which recruited numerous GJB feeding aggregations resulting in >95% crop loss. Small (1,2 weeks) phenological differences between mid-season ripening cultivars and peak GJB flight translated to marked differences in injury, whereas cultivars that ripened in mid-August or later, after GJB flight had waned, sustained little or no damage. Trapping experiments confirmed that the tougher berries and low sugar content of less-ripe fruit clusters inhibited beetle feeding and induction of yeast-mediated volatiles responsible for GJB host-location. Implications of these findings for sustainable or organic management of GJB and other near-harvest fruit pests are discussed. [source] | ||||||||||