Summer Feeding Grounds Research Articles

Sex differences in site fidelity and migration of humpback whales (Megaptera novaeangliae) to the Hawaiian Islands

Humpback whales (Megaptera novaeangliae) perform extensive seasonal migrations between high-latitude summer feeding grounds and low-latitude winter reproductive grounds. To investigate gender-related site fidelity to the Hawaiian Islands, an important wintering area for North Pacific humpback whales, photographically based resight histories of 224 females and 416 males observed in Hawai'i from 1976 through 1991 were compiled. Results indicated that the mean number of years in which they were seen was higher for males than for females, that the probability of an individual being resighted across years was higher for males than for females, and that more males than females were seen in consecutive years. Potential sources of bias favoring the photographic capture of males were considered, but none were judged to be significant contributors to the results obtained. It was proposed instead that not all females undertake or complete the migration to the winter grounds each year. Because of the high energy costs of migration and reproduction, some females may overwinter in high latitudes, while others may become pregnant en route to the area traditionally associated with breeding and return to the feeding grounds before arriving at the terminal winter destination.

Genetic tagging of humpback whales.

The ability to recognize individual animals has substantially increased our knowledge of the biology and behaviour of many taxa. However, not all species lend themselves to this approach, either because of insufficient phenotypic variation or because tag attachment is not feasible. The use of genetic markers ('tags') represents a viable alternative to traditional methods of individual recognition, as they are permanent and exist in all individuals. We tested the use of genetic markers as the primary means of identifying individuals in a study of humpback whales in the North Atlantic Ocean. Analysis of six microsatellite loci among 3,060 skin samples collected throughout this ocean allowed the unequivocal identification of individuals. Analysis of 692 'recaptures', identified by their genotype, revealed individual local and migratory movements of up to 10,000 km, limited exchange among summer feeding grounds, and mixing in winter breeding areas, and also allowed the first estimates of animal abundance based solely on genotypic data. Our study demonstrates that genetic tagging is not only feasible, but generates data (for example, on sex) that can be valuable when interpreting the results of tagging experiments.

The social and reproductive biology of Humpback Whales: an ecological perspective

AbstractExisting knowledge of the social organization, mating system and reproduction of Humpback Whales (Megaptera novaeangliae) is reviewed to assess how our current understanding of this wide‐ranging marine mammal fits into the predictive framework developed from ecological studies of more accessible terrestrial taxa. The small unstable groups characteristic of this species on its summer feeding grounds appear to be a function of absence of predation and of the patchy, mobile nature of most prey; the absence of territoriality and the minimal importance of kinship in associations are also predictable consequences of the latter. The mating system is similar to both leks and to male dominance polygyny, in which males display (sing) or directly compete (perhaps sometimes in coalitions) for access to females. However, the rigid spatial structure characteristic of classic leks is absent. The mating system of this species is sufficiently different to merit a novel category, and ‘floating lek’ is proposed. The widespread distribution of females resulting from absence of both predation and resources during the breeding season preclude simultaneous monopolization by males of more than one potential mate. Furthermore, these factors, together with a male‐biased operational sex ratio, minimize the possibility of competition among females. The intensity of intrasexual competition among males conforms to predictions derived from information on testis size and from expectation of future reproductive success. Female choice and, to a lesser extent, differential allocation of competitive effort by males, appears likely. Lack of interpopulation variation in social and mating behaviour, and in general reproductive biology, is likely a response to similarity of marine environmental conditions. Year‐to‐year variation in reproductive rates may be linked to variations in the abundance of prey. The invariably uniparous nature of female Humpback Whales is assumed to be related to the energetic demands of lactation, and the lower ratio of available energy partitioned to reproduction that is characteristic of larger mammals. The reversed sexual size dimorphism of this species may reflect different selective pressures on males and females. Finally, there is now evidence that, as in some other taxa, offspring sex ratio is related to maternal condition.

Population characteristics of DNA fingerprints in humpback whales (Megaptera novaeangliae).

Humpback whales exhibit a remarkable social organization that is characterized by seasonal long-distance migration (> 10,000 km/year) between summer feeding grounds in high latitudes and winter calving and breeding grounds in tropical or near-tropical waters. All populations are currently considered endangered as a result of intensive commercial exploitation during the last 200 years. Using three hypervariable minisatellite DNA probes (33.15, 3'HVR, and M13) originally developed for studies of human genetic variation, we examined genetic variation within and among three regional subpopulations of humpback whales from the North Pacific and one from the North Atlantic oceans. Analysis of DNA extracted from skin tissues collected by biopsy darting from free-ranging whales revealed considerable variation in each subpopulation. The extent of this variation argues against a recent history of inbreeding among humpback whales as a result of nineteenth- and twentieth-century hunting. A canonical variate analysis suggested a relationship between scaled genetic distance, based on similarities of DNA fingerprints, and geographic distance (i.e., longitude of regional subpopulation). Significant categorical differences were found between the two oceanic populations using a multivariate analysis of variance (MANOVA) with a modification of the Mantel nonparametric permutation test. The relationship between DNA fingerprint similarities and geographic distance suggests that nuclear gene flow between regional subpopulations within the North Pacific is restricted by relatively low rates of migratory interchange between breeding grounds or assortative mating on common wintering grounds.

Resightings of Independent Fin Whales, Balaenoptera physalus, on Maternal Summer Ranges

Between 1981 and 1987 in Massachusetts Bay, 16 different fin whale ( Balaenoptera physalus ) calves were individually identified. Separation of mother and calf occurred after the 1st year in at least nine instances. Four calves were observed to return to the area in subsequent years, suggesting that, in at least some instances, fidelity to a summer feeding ground is determined matrilineally.

Influence of seasonal migration on geographic distribution of mitochondrial DNA haplotypes in humpback whales

Humpback whales (Megaptera novaeangliae) migrate nearly 10,000 km each year between summer feeding grounds in temperate or near-polar waters and winter breeding grounds in shallow tropical waters. Observations of marked individuals suggest that major oceanic populations of humpback whales are divided into a number of distinct seasonal subpopulations which are not separated by obvious geographic barriers. To test whether these observed patterns of distribution and migration are reflected in the genetic structure of populations, we looked for variation in the mitochondrial DNA of 84 individual humpback whales on different feeding and wintering grounds of the North Pacific and western North Atlantic oceans. On the basis of restriction-fragment analysis, we now report a marked segregation of mitochondrial DNA haplotypes among subpopulations as well as between the two oceans. We interpret this segregation to be the consequence of maternally directed fidelity to migratory destinations.

The energetics of migration by selective tidal stream transport: an analysis for plaice tracked in the southern North Sea

Adult plaice(Pleuronectes platessaL.) in the southern North Sea use selective tidal stream transport to migrate between their summer feeding grounds and winter spawning grounds. The fish come up into midwater when the tidal stream is flowing in one direction, but remain on the bottom when it is flowing in the opposite direction. This behaviour can theoretically save energy, which can be used for growth or reproduction. Alternatively, it may provide a transport system by means of which fish that have no ability to navigate over long distances can be conveyed reliably between their feeding grounds and spawning grounds.

NORTH PACIFIC HUMPBACK WHALE SONGS: A COMPARISON OF SOUTHEAST ALASKAN FEEDING GROUND SONGS WITH HAWAIIAN WINTERING GROUND SONGS

AbstractHumpback whales sing long, complex songs on their wintering grounds. On 25 August 1979 and 3 September 1981, we made recordings of humpback whale songs in southeastern Alaska, showing that humpback whales also sing on the summer feeding grounds. Both these Alaskan samples are songs in that they are repeating cyclical sound patterns and follow the known structure for humpback whale song. The Alaskan songs contain all the same material sung in the same order as that heard off Mexico and Hawaii in the surrounding wintering seasons. However, song, theme and some phrase durations are abbreviated in the Alaskan songs. The recording of these two songs represents the full sample of song recorded from 155 days over five years of attempting to record humpback whale song in Alaskan waters.

Responses of wintering humpback whales (Megaptera novaeangliae) to playback of recordings of winter and summer vocalizations and of synthetic sound

Three natural sounds and one synthetic sound were played back to humpback whales during their 1985 and 1986 winter residency in Hawaiian waters. Playback was conducted from a vessel positioned within visual range of an elevated shorestation equipped with a high-precision surveyor's theodolite, used to determine the positions and movements of observed whale and of the playback vessel. A playback session consisted of 20 min of pretest observation with the vessel in place and underwater speaker deployed, followed by a 20-min test phase during which sound, or a blank tape control, was introduced. A total of 143 playback sessions, involving a total of 338 pods (a single whale or a group of whales), were completed over the two winter seasons. The major response observed during playback was a rapid approach to the playback vessel, characterized in some cases by velocities up to 9 km/h and approaches to within 50 m or less. Whales approaching were mainly singletons and, secondly, apparent adult pairs. No cow-calf pair ever approached. The approach was selective: 21.6% of targeted pods approached in response to a feeding sound recorded in summer feeding grounds in Alaska; 8.3% approached in response to social sounds recorded in the Hawaiian winter grounds in the presence of large surface-active pods; 3.4% responded to playback of winter song; and 4.1% responded to playback of synthetic sound. There were no approach responses to the blank tape control. Singing whales have been identified as males by many researchers. Data from Alaska suggested that the feeding sound was produced by a female; data from Hawaii suggests that the social sounds were produced by males. The different rates of response were attributed to the behavior of sexually active males seeking to affiliate with sexually mature females. Although a female may be present in pods producing social sounds, the presence of multiple males exhibiting aggression may inhibit the approach of other males. Song did not serve as an attractant for females, as measured by direct approach, but may still serve as a basis for female choice.

PHYSIOLOGICAL STRESS AND COLOR POLYMORPHISM IN THE INTERTIDAL SNAIL NUCELLA LAPILLUS.

The intertidal snail Nucella lapillus exhibits considerable variation in shell color both within and between populations differentially exposed to wave action. Populations from high-wave-energy shores tended to be highly polymorphic and were dominated by pigmented morphs (especially brown), while those at more sheltered locations exhibited less polymorphism and were predominantly white. Field and laboratory experiments were conducted to determine the role of physiological stress and selective predation in maintaining the observed distribution of color morphs. The results demonstrated that 1) physiological stress from high temperature and desiccation during periods of tidal emersion was greater on protected shores, 2) under similar natural conditions, brown morphs heated up faster, attained higher temperatures, desiccated more rapidly, and suffered greater mortality than did white morphs, and 3) when pairs of brown and white morphs were tethered intertidally there was virtually no mortality of either morph on the exposed shore or in shaded microhabitats on the protected shore, but brown morphs suffered much greater mortality in sunny microhabitats on the protected shore. These findings demonstrate that the interpopulation variation in shell color of N. lapillus is in part a response to a selective gradient in physiological stress. Selection for crypsis by visually hunting predators did not appear to play a prominent role; however, only adults were considered, and the predation experiments were conducted in the fall before shorebirds that prey on whelks had arrived from their summer feeding grounds. Further experimentation to quantify the effects of visual predators such as birds and fish, particularly on juvenile snails, is necessary to assess adequately the importance of predation.

Reproductive Biology of Pacific Herring (Clupea harengus pallasi)

Most British Columbia herring begin sexual maturation in the late summer and become sexually mature in the subsequent March or April. As they mature, most stocks migrate from summer feeding grounds to overwintering areas and then to shallow nearshore spawning areas. Also, newly recruited, sexually maturing fish join the adult spawning stocks, either on the summer or winter grounds. These events occur in an unpredictable environment. Consequently, reproduction in Pacific herring (Clupea harengus pallasi) may be viewed as a biological problem of maintaining synchrony and precision: specifically the synchronous maturation of (1) males and females and (2) the recruit spawners with the adult fish that have spawned in previous years. Biological precision is required to ensure that gametes are released at the correct place at the correct time. Further precision is required to achieve an appropriate balance between egg number and egg size, and then to control the density of eggs deposited on the bottom. The annual temperature regime is a vital regulator of these processes. Generally, the warmer the temperature, or lower the latitude, the earlier the maturation and spawning time. There are some notable exceptions that indicate local adaptation to other environmental cues. Also, experimental work indicates that food supply can affect the maturation rate. Intensities of egg depositions are generally similar among Pacific North American stocks, and indeed for many documented herring spawnings from Asian and European stocks. It has been shown that eggs in the middle of very thick spawns have lower survival so there is a selective advantage for biological mechanisms that ensure more even and lighter egg densities. This paper suggests that egg density in Pacific herring is controlled by a biological feedback mechanism involving milt concentration and hydrographic factors. Earlier spawners tend to be larger and there is a positive relationship between female size and egg size, a tendency consistent with other herring stocks and species. Size-adjusted fecundity, when compared among different regions and years, is strikingly uniform within British Columbia. On a broad geographic scale (California to Alaska), size-specific fecundity declines with latitude. Recent experimental work reveals that total egg number is higher at early stages of maturation and decreases as spawning time approaches. Presumably, this decrease reflects selective resorption of some developing oocytes, and probably occurs in response to available body energy. The duration and geographical variation in spawning time is relevant to questions concerning the evolutionary and taxonomic relationships between Pacific herring and Atlantic herring (Clupea harengus harengus). Other aspects of reproductive biology have important management implications, particularly for (1) predicting recruitment, (2) deriving stock estimates from spawn surveys, and (3) managing fisheries.

Compatibility of ships and whales in Glacier Bay, Alaska

Glacier Bay, southeast Alaska, normally a summer feeding ground for humpback whales, was abruptly abandoned in midsummer 1978, prompting charges by environmentalists that increased vessel traffic had driven them out. Subsequent research focused on whale-prey relationships, vessel effects on whales, and the overall acoustic environment of Glacier Bay compared to nearby areas where whales continue to feed in undiminished numbers. Prey studies showed a high correlation between whale distribution and prey abundance; in 1982 a group of whales chose to spend most of the summer feeding in the busiest, noisiest part of the Bay. Behavior studies showed whales are affected by vessels up to 3-km away, but reactions were of short duration, and meaning in terms of possible physiological stress and cumulative effect is unknown. Acoustic studies revealed minor differences between the Bay and comparison areas (e.g., “white sound” from effervescence of melting glacier ice, and sporadic seismic noise), which presumably are longstanding phenomena that do not explain the recent reduction of whales. Humpbacks are gradually reoccupying the Bay, possibly the result of current traffic regulations and restrictions on numbers of vessels allowed entrance. However, a “crash” of whale prey stocks in 1978 still cannot be discounted. [Work supported by National Park Service, National Marine Fisheries Service, and Alaska cruise ship industry.]

Observations on the Perch Population of Ullswater

Differences in the population dynamics of a fish species are often observed when widely differing places and environments are compared. The present investigation was undertaken to explore the reasons for known differences between the populations of perch (Perca fluviatilis L.) in Ullswater and Windermere which are two limnologically similar lakes only 16 km (10 miles) apart in the English Lake District. Windermere is the largest of the fifteen major lakes in the district and Ullswater the second with a total area of 8-9 kM2, a length of 11 -8 km and mean breadth of 869 m (Mill 1895). The average depth is 25-3 m, maximum depth 62-5 m and total drainage area 230-5 km2. The area of shallow water less than 7-5 m, i.e. the area of spawning and summer feeding ground available to the perch, is 3-82 km2 or 43 % of the total, compared to Windermere where the area of shallow water is 4-82 km2 or 33% of the total. The present water level is 145 m above sea level. Pearsall (1949) classifies the English lakes as a series from those that have rocky shores and are unproductive to those with shores more or less silt-covered that are relatively productive. Ullswater and Windermere are both towards the middle of this series, but Ullswater is a little less productive than the north basin of Windermere; in neither lake is the hypolimnion deoxygenated in summer. Apart from the perch, the fish species known to be present in Ullswater are salmon (Salmo salar L.), small numbers of which come up to spawn from the River Eden, trout (S. trutta L.), schelly (Coregonus wartmanni Dottrens), eel (Anguilla anguilla L.), minnow (Phoxinus phoxinus L.), stickleback (Gasterosteus aculeatus L.), bullhead (Cottus gobio L.), loach (Nemachilus barbatula L.) and lampreys (Lampetra planeri Bloch and L. fluviatilis L.). The trout occur in large numbers but are small in size (Swynnerton & Worthington 1939). Certain owners used to exercise netting rights on Ullswater, and Bush (letter of 7 April 1948) has given details of the fish caught during the previous 50 years by his family. An annual average of 113 kg of trout of an approximate mean weight of 170 g were seined and gill netted, and no change in average size was noted over the period. In mid-June each yearthe catches of trout declined and perch began to be caughtsometimes as many as 100 per night. The size of perch selected by such a gill net would not normally be less than 20 cm (Kipling 1963) and would therefore be comparable to the size of adult perch caught in Ullswater today. Char (Salvelinus sp.) originally occurred ii Ullswater but from about 1820 became rare (Watson 1899), and are now extinct, perhaps owing to the partial destruction and pollution of their spawning ground by washings from lead mines at Glenridding on one of the afferent becks. The main difference in fish fauna between Ullswater and most other lakes in the district including Windermere is the absence of pike (Esox lucius L.). In Windermere pike are numerous and appear to be important as predators on the perch (Frost 1954). This provides one of the main possible causes for differences between the population dynamics of perch in the two lakes and was a stimulant to the investigation.

Ecological Notes on the Bat Pipistrellus subflavus

Ecological notes on Pipistrellus subflavus were obtained during the summers of 1949 through 1957 in West Virginia and Indiana. The center of abundance of this species is the Ohio River valley; Pipistrellus prefers watercourses at forest edges. Daylight hours are probably spent in trees. Myotis lucifugus and Pipistrellus are rarely found together on summer feeding grounds, but other bats, particularly Lasiurus borealis and Eptesicus fuscus, commonly feed with pipistrelles. Although considerable data have been published on the behavior and ecology of bats in their daytime roosts and hibernating quarters, there has been little study of their choice of feeding grounds and their behavior thereon. We present here observations on these aspects of the life history of the eastern pipistrelle (Pipistrellus subflavus) made during the summers of 1949 through 1957, in West Virginia and Indiana.

Migration and Feeding of the Gray Whale (Eschrichtius gibbosus)

Observations of gray whales from the coasts of British Columbia, Washington, and Alaska are compared with published accounts in order to re-assess knowledge of migration and feeding of the American herd. Source of material is mainly from lighthouses and lightships.The American herd of gray whales retains close contact with the shore during migration south of Alaska. Off Washington and British Columbia the northward migration begins in February, ends in May, and is at a peak during the first two weeks in April; the southward migration occurs in December and January, and is at a peak in late December. Northward migrants stop occasionally to rest or feed; southward migrants are travelling faster and appear not to stop to rest or feed during December and January. Gray whales seen off British Columbia, sometimes in inside protected waters, from June through October, probably remain in this area throughout the summer and fall months.Available evidence suggests that gray whales retain contact with the coast while circumscribing the Gulf of Alaska, enter the Bering Sea through eastern passages of the Aleutian chain, and approach St. Lawrence Island by way of the shallow eastern part of the Bering Sea. Arriving off the coast of St. Lawrence Island in May and June the herd splits with some parts dispersing along the Koryak coast and some parts continuing northward as the ice retreats through Bering Strait. Gray whales feed in the waters of the Chukchi Sea along the Siberian and Alaskan coasts in July, August and September. Advance of the ice through Bering Strait in October initiates the southern migration for most of the herd. In summering areas, in northern latitudes, gray whales feed in shallow waters on benthic and near-benthic organisms, mostly amphipods.There is no evidence to indicate that gray whales utilize ocean currents or follow the same routes as other baleen whales in their migrations. Visual contact with coastal landmarks appear to aid gray whales in successfully accomplishing the 5000-mile migration between summer feeding grounds in the Bering and Chukchi Seas and winter breeding grounds in Mexico.Reconstruction of the migration from all available data shows that most of the American herd breeds and calves in January and February, migrates northward in March, April and May, feeds from June through October, and migrates southward in November and December.