Foraging ecology and niche overlap in pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales from waters of the U.S. mid‐Atlantic coast

A complementary approach of stomach content and stable isotope analyses was used to characterize the foraging ecology and evaluate niche overlap between pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales stranded on the U.S. mid‐Atlantic coast between 1998 and 2011. Food habits analysis demonstrated both species were primarily teuthophagous, with 35 species of cephalopods, and 2 species of mesopelagic fishes represented in their overall diets. Pianka's Index of niche overlap suggested high overlap between whale diets (O_n = 0.92), with squids from the families Histioteuthidae, Cranchidae, and Ommastrephidae serving as primary prey. Pygmy sperm whales consumed slightly larger prey sizes (mean mantle length [ML] = 10.8 cm) than dwarf sperm whales (mean ML = 7.8 cm). Mean prey sizes consumed by pygmy sperm whales increased with growth, but showed no trend in dwarf sperm whales. Significant differences were not detected in δ¹⁵N and δ¹³C values of muscle tissues from pygmy (10.8‰ ± 0.5‰, ?17.1‰ ± 0.6‰), and dwarf sperm whales (10.7‰ ± 0.5‰, ?17.0‰ ± 0.4‰), respectively. Isotopic niche widths also did not differ significantly and dietary overlap was high between the two species. Results suggest the feeding ecologies of the pygmy and dwarf sperm whales are similar and both species occupy equivalent trophic niches in the region.     

The diet of pygmy sperm whales, Kogia breviceps, stranded in New Zealand: implications for conservation

The stomach contents of 27 pygmy sperm whales, Kogia breviceps, stranded on New Zealand beaches between 1991 and 2003 are reported. These individuals comprise 16 males, 10 females, and one for which no sex information is available. The diet was found to include fish and crustaceans, but is comprised primarily of cephalopods, with 0–526 lower beaks, representing an estimated maximum of c. 60 kg of cephalopod prey consumed by any one whale. Cephalopod prey is attributed to 23 species from 13 families, and is dominated by juvenile individuals of the families Histioteuthididae and Cranchiidae (adults of which usually occur at depths exceeding 400 m). Perceived threats to this whale, particularly those affecting distribution and abundance of prey species, are also discussed. These are the first data reporting the diet of this whale species in New Zealand waters. A comparison of the diet of K. breviceps is made with that of the sperm whale, Physeter macrocephalus from New Zealand waters, and with the diet of Kogia known elsewhere.     

PYGMY SPERM WHALES KOGIA BREVICEPS IN THE NORTHEAST ATLANTIC: NEW INFORMATION ON STOMACH CONTENTS AND STRANDINGS

Little is known about the feeding ecology of pygmy sperm whales ( Kogia breviceps ) in the Northeast Atlantic. Results are presented on the stomach contents of five whales stranded on the Galician coast (NW Spain) between 1995 and 2002 and seven whales stranded on the French Atlantic coast between 1984 and 2001. These results are compared with those obtained from the stomach contents of two pygmy sperm whales (a pregnant female and her calf ) stranded on the Scottish (UK) coast in 1999, the first records of the species in Scotland. In 13 out of 14 cases, food remains consisted almost entirely of cephalopod beaks, although some crustacean and fish remains were also present. In all the Spanish specimens, the identified prey were oceanic species: the cephalopods Histioteuthis reversa , H. bonnellii , Todarodes sagittatus , the viperfish Chauliodus sloani , and the giant mysid Gnatophausia sp. The same cephalopod species were found in the stomachs of the whales stranded in Scotland, although both whales had also consumed neritic cephalopod species such as Rossia macrosoma and other sepiolids. In the French specimens, almost all prey identified were oceanic cephalopods ( H. reversa , Brachioteuthis riseii , T. sagittatus , Taonius pavo , etc. ), but remains of crustaceans and a neritic squid ( Loligo forbesi ) were also found. One whale from France had eaten mainly Henslow's swimming crab ( Polybius henslowi ). Results from the present study are consistent with those found by other authors in the Azores and the Canary Islands in that pygmy sperm whales appear to be mainly teuthophagous, with histioteuthid squids forming an important part of the diet. Strandings records suggest that occurrence of pygmy sperm whales in the NE Atlantic may be seasonal, with most strandings occurring in autumn and winter.     

Patterns and trends in the diet of long‐finned pilot whales (Globicephala melas) in the northeast Atlantic

There is little previous information on feeding habits of long‐finned pilot whales (Globicephala melas) in the northeast Atlantic. The present study analyzed stomach contents of pilot whales stranded in Portugal (n = 6), Galicia (northwest Spain) (n = 32), and Scotland (United Kingdom) (n = 10), from 1990 to 2011. These animals ranged from 213 to 555 cm in length (24 females, 19 males and 5 of unknown sex). The main prey identified were cephalopods of the families Octopodidae and Ommastrephidae, the former being numerically more important in Iberia (Portugal and Galicia) and the latter more important in Scotland, with Iberian whales also showing a more diverse diet. Multivariate analysis revealed evidence of geographical and seasonal variation in diet. Generalized Additive Modeling results indicated that more octopus (Eledone cirrhosa) were eaten in Iberia than in Scotland, more in the first half of the year, and more in larger whales. Numbers of ommastrephid squids in the stomach decreased over the study period and varied with season and whale length. This study confirms cephalopods as the main prey of pilot whales, as previously reported, although our results also suggest that, in the northeast Atlantic, ommastrephid squid are largely replaced as the main prey by octopods at lower latitudes.     

CETACEAN ABUNDANCE IN HAWAIIAN WATERS ESTIMATED FROM A SUMMER/FALL SURVEY IN 2002

Cetacean abundance is estimated for the U.S. Exclusive Economic Zone (EEZ) around the Hawaiian Islands based on a ship line‐transect survey from August to November, 2002. Sighting detection functions are estimated from this and other NOAA research surveys from 1986 to 2002 using a new, multiple‐covariate approach. Twenty‐four species were seen on this survey, including two species (Fraser's dolphin [Lagenodelphis hosei] and sei whale [Balaenoptera borealis]) that had not been previously documented to occur in Hawaiian waters. The most abundant large whales are sperm whales (Physeter macrocephalus) and Bryde's whales (Balaenoptera edeni). The most abundant delphinids are pilot whales (Globicephala macrorhynchus), rough‐toothed dolphins (Steno bredanensis), Fraser's dolphins, spotted dolphins (Stenella attenuata), and striped dolphins (Stenella coeruleoalba). Dwarf and pygmy sperm whales (Kogia sima and Kogia breviceps) and Cuvier's beaked whales (Ziphius cavirostris) are also estimated to be quite abundant. Some of the migratory baleen whales (fin whales [Balaenoptera physalus], sei whales, minke whales [B. acutorostrata], and humpback whales [Megaptera novaeangliae]) were seen only late in the survey. Abundance is estimated for 19 cetacean species. The overall density of cetaceans is low in the study area, especially for delphinids. The precision of density and abundance estimates is generally low for all species because of the low number of sightings.     

THE DIET OF GALÁPAGOS SPERM WHALES PHYSETER MACROCEPHALUS AS INDICATED BY FECAL SAMPLE ANALYSIS

Fecal samples were collected while following sperm whales ( Physeter macrocephalus ) off the Galápagos Islands, Ecuador. They contained 133 upper beaks and 164 lower beaks of cephalopods. Analysis of the lower beaks suggests that the sperm whales fed primarily on three genera of cephalopods; Histioteutbis (62%), Ancistrocbeirus (16%), and Octopoteutbis (7%). The beak dimensions indicate that the cephalopods ranged in mantle length from 5 to 54 cm and in mass from 12 to 650 g. Fecal samples varied significantly between five study years and over different parts of the study area, but the number of beaks collected per sample did not correlate significantly with defecation rate (a measure of feeding success). Using beak material from fecal samples gives a biased estimate of sperm whale diet, reducing the frequencies of very small and very large cephalopods. However, all other available methods of assessing sperm whale diet also possess biases.     

DIETS OF BAIRD'S BEAKED WHALES, BERARDIUS BAIRDII, IN THE SOUTHERN SEA OF OKHOTSK AND OFF THE PACIFIC COAST OF HONSHU, JAPAN

Stomach contents were analyzed from 127 Baird's beaked whales, Berardius bairdii , taken in coastal waters of Japan. During late July-August of 1985–1987, 1989, and 1991, 107 samples were collected from off the Pacific coast of Honshu. An additional 20 samples were collected from whales taken in the southern Sea of Okhotsk during late August—September of 1988 and 1989. Prey identification using fish otoliths and cephalopod beaks revealed the whales fed primarily on deep-water gadiform fishes and cephalopods in both regions. Prey species diversity and the percentage of cephalopods and fish differed between the two regions. Off the Pacific coast of Honshu the whales fed primarily on benthopelagic fishes (81.8%) and only 18.0% on cephalopods. Eight species of fish representing two families, the codlings (Moridae) and the grenadiers (Macrouridae), collectively made up 81.3% of rhe rotal. Thirty species of cephalopods representing 14 families made up 12.7%. In the southern Sea of Okhotsk, cephalopods accounted for 87.1% of stomach contents. The families Gonatidae and Cranchiidae were the predominant cephalopod prey, accounting for 86.7% of the diet. Gadiform fish accounted for only 12.9% of the diet. Longfin codling, Laemonema longipes , was the dominant fish prey in both regions. Depth distribution of the two commonly consumed fish off the Pacific coast of Honshu indicate the whales in this region fed primarily at depths ranging from 800 to 1,200 m.     

Isotopic niche width differentiation between common bottlenose dolphin ecotypes and sperm whales in the Gulf of California

World populations or stock distinction of Tursiops truncatus has been difficult to assess, because of large variations in morphology, habitat, feeding habits, and social structure among areas, which may reflect phylogenetic segregation or ecological plasticity. In the Gulf of California, Mexico, two common bottlenose dolphin ecotypes (inshore and offshore) have been reported. The offshore ecotype is frequently observed in association with sperm whales (Physeter macrocephalus) but the reason for this is still unknown. To explore the degree of resource partitioning/overlap between these species and stocks, we used skin stable isotope values (δ¹³C, δ¹⁵N) to estimate quantitative metrics of isotopic niche width (Bayesian standard ellipse areas, SEA_B) and estimated their diet composition using Bayesian isotopic mixing models. The inshore ecotype in different regions (north, central, and south) of the Gulf of California exhibited distinct δ¹⁵N values and SEA_B, suggesting a latitudinal gradient in nitrogen sources of coastal localities. The SEA_B of inshore and offshore bottlenose dolphin ecotypes was completely distinct, indicating resource partitioning. Associated offshore ecotype and sperm whales had overlapping SEA_B. The isotopic mixing model indicates that a considerable proportion of both species’ diet is large Humbolt squid. Our results suggest that resource partitioning and species association are two strategies that bottlenose dolphin ecotypes use in this zone.     

Feeding habits of the blue shark, Prionace glauca, and salmon shark, Lamna ditropis, in the transition region of the Western North Pacific

We describe the feeding habits of 70 blue sharks (Prionace glauca) and 39 salmon sharks (Lamna ditropis) caught at 0–7 m depth at night by research drift gillnets in the transition region of the western North Pacific during April–May of 1999 and 2000. Blue sharks of 50–175 cm total length fed on a large variety of prey species, consisting of 24 species of cephalopods and 16 species of fishes. Salmon sharks of 69–157 cm total length fed on a few prey species, consisting of 10 species of cephalopods and one species of fish. Important prey for the blue sharks were large, non-active, gelatinous, meso- to bathypelagic cephalopods (e.g., Chiroteuthis calyx, Haliphron atlanticus, Histioteuthis dofleini and Belonella borealis) and small myctophid fishes. Important prey for the salmon sharks were mid-sized, active, muscular, epi- to mesopelagic squids (e.g. Gonatopsis borealis, Onychoteuthis borealijaponica and Berryteuthis anonychus). Our results suggest that blue sharks feed on cephalopods mainly during the daytime when they descend to deep water. Salmon sharks may feed opportunistically with no apparent diurnal feeding period. Blue sharks and salmon sharks have sympatric distribution in the transition region in spring; they have different feeding habits and strategies that reduce competition for food resources.     

Stomach contents of mass-stranded short-finned pilot whales (Globicephala macrorhynchus) from North Carolina

We examined the stomach contents of 27 short‐finned pilot whales (Globicephala macrorhynchus) that mass stranded on the North Carolina coast on 15 January 2005. Eleven whales had prey parts in their forestomachs. We used frequency of occurrence and numerical abundance to assess the relative importance of prey. Brachioteuthis riisei (numerical abundance 28%), an oceanic species, was the most important cephalopod prey, but Taonius pavo (12%) and Histioteuthis reversa (9%) also represented a substantial part of the diet. A large number of otoliths belonging to the fish Scopelogadus beanii were present (25%). These results differ from reports of the stomach contents of short‐finned pilot whales from the Pacific coast in which neritic species dominate the diet. Our findings also suggest that there is a considerable difference between the diet of short‐ and long‐finned pilot whales (Globicephala melas) in the western North Atlantic. The latter feed predominantly on the long‐finned squid (Loligo pealei) whereas the former feed on deep‐water species. Our results indicate the whales fed primarily off the continental shelf prior to stranding.     

THREE MASS STRANDINGS OF SPERM WHALES (PHYSETER MACROCEPHALUS) IN SOUTHERN AUSTRALIAN WATERS

One hundred and fifteen sperm whales (97 female, 15 male, 3 unknown sex) were involved in three mass stranding events during the month of February 1998 along the west and northwest coastlines of Tasmania, Australia. Sixty-six of these whales stranded at Ocean Beach, Strahan; 35 at Greens Beach, Marrawah; and 11 at Black River Beach, Stanley. The remaining whales stranded singly along the coastline. Three mass strandings of this species in such close temporal proximity have not been reported in this area before, and this is the first time that data have been comprehensively collected from complete or near-complete groups of sperm whales from Tasmanian waters. Adult females dominated the three stranding groups. Total lengths ranged from 417 to 1,200 cm and ages ranged from 0.75 to 64 yr. Four females were lactating and four fetuses were found amongst the groups. Stomach contents were dominated by pelagic cephalopods.     

Spatial and temporal analysis of killer whale (Orcinus orca) strandings in the North Pacific Ocean and the benefits of a coordinated stranding response protocol

Killer whales (Orcinus orca) are widely distributed throughout the world's oceans, yet little has been documented about their stranding patterns. Knowledge of stranding patterns improves our ability to examine and sample carcasses and provides a foundation for understanding killer whale natural history, diet, reproduction, anthropogenic stressors, emerging diseases, and patterns of unusual mortality. We compiled published and unpublished killer whale stranding data to describe stranding patterns in the North Pacific Ocean. Between 1925 and 2011, 371 stranded killer whales were reported in Japan (20.4%), Russia (3.5%), Alaska (32.0%), British Columbia (27.4%), Washington (4.0%), Oregon (2.7%), California (5.1%), Mexico (3.8%), and Hawaii (0.8%). Strandings occurred at all times of year, but regionally specific seasonal differences were observed. Mortality and annual census data from Northern and Southern Resident populations were extrapolated to estimate that across the North Pacific, an average of 48 killer whales die annually. However, over the last two decades, an average of only 10 killer whale carcasses were recovered annually in this ocean, making each event a rare opportunity for study. Publication of a standardized killer whale necropsy protocol and dedicated funding facilitated the number of complete postmortem necropsies performed on stranded killer whales from 1.6% to 32.2% annually.     

Notes on New Zealand mammals 6. Second report on the stomach contents of long‐finned pilot whales,Globicephala melas

Abstract

We report data on the stomach contents of the long‐finned pilot whale, Globicephala melas, recovered from a group of whales stranded on Ruakaka Beach, northeastern New Zealand, in November 2006. In nine whales for which identifiable stomach contents were recovered (three that stranded on 10 November and six that stranded on 11 November) prey remains comprised exclusively cephalopod beaks attributed to five squid species. The stomachs of a further two whales contained unidentifiable upper beaks only, while the stomachs of five whales were completely empty. No whale appeared to have been satiated immediately before stranding, given that the maximum biomass of prey recently consumed by any one whale was calculated to be <5 kg. All squids ingested represented oceanic species, found from 50 to 1000 m but more common towards the deeper end of this range. These data both complement and contrast with the only other dietary information available for this species in New Zealand waters, reported from stomach contents of whales stranded on Farewell Spit, South Island in December 2005.     

Fine‐scale spatial differences in humpback whale diet composition near Kodiak,Alaska

On the North Pacific feeding grounds, humpback whales (Megaptera novaeangliae) are recovering from commercial whaling at a rapid rate (6.8%). The potential effect that this recovery will have on trophic dynamics involving these predators is currently unknown. To better elucidate complex trophic dynamics, variability in diet composition of apex predators on their respective feeding grounds needs to be understood. Thus, we explored the diet composition of two defined subaggregations of humpback whales of the Kodiak Archipelago population (“North,” “South”) using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin and regional prey samples in Bayesian dietary mixing models. Humpback whales in the “North” region consumed proportionally more fish, dominated by capelin (Mallotus villosus), whereas, whales in the “South” region consumed predominantly krill. The difference in diet composition appears to reflect regional differences in prey availability. Thus, regional variability in diet composition by humpback whales may have disproportionate impacts on prey resources of sympatric predators depending on available prey biomass. As a result, we suggest fine‐scale studies of apex predator diets are needed to better model trophic dynamics with accuracy.     

Statolith microstructure and age of early life stages of planktonic squids Galiteuthis phyllura and Belonella borealis (Oegopsida, Cranchiidae) from the northern North Pacific

Statolith morphology and microstructure were studied in twocommon species of panktonic cranchiid squids, Belonella borealis[four juveniles with mantle length (ML) 375–450 mm] andGaliteuthis phyllura (13 paralarvae and juveniles, ML 9–235mm),caught near the bottom and in pelagic layers over the continentalslope of Siberia in the northwest Bering Sea. The total numberof growth increments within the statoliths ranged from 277 to294 in B.borealis and from 10 to 209 in G.phyllura. Assumingthat these increments were produced daily, both species growrapidly in length (daily growth rate = 1.13mm day^–1 duringthe first 8–10 months of their juvenile phase in the mesopelagiclayers, prior to migration into deeper waters for maturation.     

First report on the stomach contents of long‐finned pilot whales,Globicephala melas,stranded in New Zealand

Abstract

Stomach contents of the long‐finned pilot whale, Globicephala melas, are reported for the first time from New Zealand waters. Analyses based on two male and three female whales (2.5–5.3 m in length) that stranded on Farewell Spit, Golden Bay, South Island in December 2005 revealed a diet comprised exclusively of cephalopods (2-33 lower cephalopod beaks per stomach). Two genera of cephalopod from two orders; arrow squid, Nototodarus spp. (Teuthoidea: Ommastrephidae), and common octopus, Pinnoctopus cordiformis (Octopoda: Octopodidae) were represented. A further five pilot whale stomachs were examined and found to be empty.     

Prey preferences of sympatric fin (Balaenoptera physalus) and humpback (Megaptera novaeangliae) whales revealed by stable isotope mixing models

Over‐exploitation of top predators and fish stocks has altered ecosystems towards less productive systems with fewer trophic levels. In the Celtic Sea (CS), discards and bycatch levels have prompted concern about some fisheries, while fin and humpback whales are recovering from centuries of over‐exploitation. A lack of empirical evidence on the preferred diet of some predators such as whales in the CS has hindered the implementation of effective conservation measures using an ecosystem‐based approach to fisheries management. Using a Bayesian framework (SIAR), stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope mixing models were used to assign proportionate diet solutions to fin and humpback whales (skin biopsies) and putative prey items: herring (Clupea harengus), sprat (Sprattus sprattus), and krill (Meganyctiphanes norvegica and Nyctiphanes couchii) in the CS. Krill was the single most important prey item in the diet of fin whales, but one of the least important for humpback whales (albeit based on a small sample of humpback whale samples). Age 0 sprat and herring comprised a large proportion of the diet of both species, followed by older sprat (age 1–2) and older herring (age 2–4). An ecosystem based approach to fisheries management will be required in the CS if we seek effective conservation of both fin and humpback whales, and sustainable fisheries.     

Stable isotopes document the trophic structure of a deep-sea cephalopod assemblage including giant octopod and giant squid

Although deep-sea cephalopods are key marine organims, their feeding ecology remains essentially unknown. Here, we report for the first time the trophic structure of an assemblage of these animals (19 species) by measuring the isotopic signature of wings of their lower beaks, which accumulated in stomachs of stranded sperm whales. Overall, the species encompassed a narrow range in δ¹³C values (1.7‰), indicating that they lived in closely related and overlapping habitats. δ¹³C values can be interpreted in terms of distribution with the more ¹³C-depleted species (e.g. Stigmatoteuthis arcturi, Vampyroteuthis infernalis) having a more pelagic habitat than the more ¹³C-enriched, bathyal species (e.g. Todarodes sagittatus and the giant squid Architeuthis dux). The cephalopods sampled had δ¹⁵N values ranging 4.6‰, which is consistent with the species spanning approximately 1.5 trophic levels. Neither the giant octopod (Haliphron atlanticus) nor the giant squid reached the highest trophic position. Species δ¹⁵N was independent of body size, with large squids having both the highest (Taningia danae) and lowest (Lepidoteuthis grimaldii) δ¹⁵N values. Their trophic position indicates that some species share the top of the food web, together with other megacarnivores such as the sperm whale.     

The diet of common eiders wintering in Nuuk,Southwest Greenland

Southwest Greenland provides wintering grounds for 70% (∼460,000) of the northern common eider (Somateria mollissima borealis) population. From 241 gullet samples (esophagus and proventriculus content) collected over three winters (1999–2002) near Nuuk, we identified 39 species consumed by the eiders. In contrast to studies elsewhere, fresh mass of the diet was dominated by soft-bottom species: the bivalve Mya eideri (32.8%) and the polychaete Pectinaria spp. (24.2%). The hard-bottom blue mussel (Mytilus edulis), usually the dominant prey of common eiders, was only the fourth most important diet species (7.5%). Overall, bivalves accounted for 56% of the diet. Twenty-seven prey species were minor foods with aggregate fresh mass of only 5.5%. Diets of males and females were similar, whereas juveniles consumed greater mass of crustaceans and less of bivalves. Diet diversity was higher in mid-winter than late winter, and higher in coastal habitats than in fjords. Within one important wintering area the results indicate that optimal size of blue mussels may be depleted over winter.     

Stable isotope records of sei whale baleens from Chilean Patagonia as archives for feeding and migration behavior

Carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope variations in baleen plates of sei whales (Balaenoptera borealis) stranded after a mass mortality event in Chilean Patagonia were investigated to assess potential dietary and migratory patterns. Carbon and nitrogen isotope ratios of seven baleens from six individuals were analyzed. The δ¹³C values ranged from ? 19.1 to ? 15.9‰ and the δ¹⁵N values from 8.7 to 15.4‰. Variations of up to 2.9‰ for δ¹³C and 5.3‰ for δ¹⁵N were observed within one baleen. Carbon and nitrogen isotope records of each baleen were significantly correlated and showed recurring oscillations confirmed by wavelet analyses. Oscillations slightly differed in periodicity indicating variable baleen growth rates between 10.0 and 16.5 cm/year. Food sources of the whales are discussed in terms of available isotope data for potential prey taxa and potential migratory behavior on the basis of latitudinal isotope gradients of particulate organic matter. Cyclicity could be explained by regular migrations of the sei whales from subtropical calving areas to high‐latitude foraging grounds. δ¹⁵N records of baleens differed between individuals eventually pointing to diverse feeding and migratory preferences among sei whale individuals.