CONSEQUENCES OF ALTERNATIVE FUNCTIONAL RESPONSE FORMULATIONS IN MODELS EXPLORING WHALE-FISHERY INTERACTIONS

We evaluated the utility of Ecosim for exploring interactions between cetacean predators, their prey, and fisheries. We formulated six Ecosim parameterizations, representing alternative hypotheses of feeding interactions (functional response) between cetaceans and their main fish prey, and examined differences in the predicted responses to simulated harvesting regimes for minke whales and their prey. Regardless of the type of function response formulated, intense fishing on the main fish prey of minke whales had a longer-lasting negative impact on minke whales than when minke whale biomass was removed directly by harvesting. Consumption rate, biomass, feeding time and mortality of minke whales were all sensitive to the type of functional response specified. Inclusion of "handling time" limited minke whales consumption at high prey densities and predicted higher consumption at low prey densities; features characteristic of a type II functional response. Predicted decline and recovery rates of minke whales were slower than when consumption rates were not limited. Addition of "foraging time" adjustments resulted in more conservative estimates of decline and recovery. However, when "other mortality" was linked to time spent foraging, exposure to higher mortality at low prey densities, and reduced mortality at high prey densities resulted in dramatic differences in predicted biomass trajectory. Sensitivity to the "other mortality" assumption is important for cetaceans whose predation mortality is only a small proportion of total mortality. Differences in the feeding and biomass dynamics were also observed when prey availability to predators was represented by changes in prey vulnerability, confirming earlier reports that Ecosim predictions are sensitive to this parameter.     

Future recovery of baleen whales is imperiled by climate change

Historical harvesting pushed many whale species to the brink of extinction. Although most Southern Hemisphere populations are slowly recovering, the influence of future climate change on their recovery remains unknown. We investigate the impacts of two anthropogenic pressures—historical commercial whaling and future climate change—on populations of baleen whales (blue, fin, humpback, Antarctic minke, southern right) and their prey (krill and copepods) in the Southern Ocean. We use a climate–biological coupled “Model of Intermediate Complexity for Ecosystem Assessments” (MICE) that links krill and whale population dynamics with climate change drivers, including changes in ocean temperature, primary productivity and sea ice. Models predict negative future impacts of climate change on krill and all whale species, although the magnitude of impacts on whales differs among populations. Despite initial recovery from historical whaling, models predict concerning declines under climate change, even local extinctions by 2100, for Pacific populations of blue, fin and southern right whales, and Atlantic/Indian fin and humpback whales. Predicted declines were a consequence of reduced prey (copepods/krill) from warming and increasing interspecific competition between whale species. We model whale population recovery under an alternative scenario whereby whales adapt their migratory patterns to accommodate changing sea ice in the Antarctic and a shifting prey base. Plasticity in range size and migration was predicted to improve recovery for ice‐associated blue and minke whales. Our study highlights the need for ongoing protection to help depleted whale populations recover, as well as local management to ensure the krill prey base remains viable, but this may have limited success without immediate action to reduce emissions.     

Fatty acids in common minke whale (Balaenoptera acutorostrata) blubber reflect the feeding area and food selection,but also high endogenous metabolism

The fatty acid (FA) composition has been analysed in the blubber of 56 minke whales caught during the Norwegian commercial whaling period in 2009–2011. Minke whales from four regions were sampled: the North Sea, Vesterålen, Spitsbergen/Bear Island and Finnmark. The FA profiles of the whale blubber have been compared with FA profiles of potential prey species to investigate if FA analysis can be used to predict the diet of minke whales and how the FA profiles of the blubber reflect the regional ecosystem in which the whales were caught. Clear differences in blubber FA profiles were found between minke whales from different areas, and the results of the present study show that FA analysis of the blubber can be used to indicate the whale's diet, but there appears to be a strong impact from metabolism on several FAs. The whale blubber FAs are separate from those of the prey by having relatively high levels of FAs likely to originate from endogenous metabolism, such as 18:1n9 (Δ9-desaturation of 18:0); chain shortening products of 22:1(n-11); 20:1(n-11) and 18:1(n-11); as well as 22:5(n-3), which is an elongation product of 20:5(n-3). High metabolic activity in the adipose tissue was also evident by the clear stratification of FA profiles found throughout the blubber layer. It is remarkable that the whale blubber has much lower levels of the long-chain PUFAs 20:5(n-3) and 22:6(n-3) than found in the prey organisms. It is likely that this results from selective partitioning of diet FAs between the storage lipids and membrane lipids.     

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.     

A missing piece in the Arctic food web puzzle? Stomach contents of Greenland sharks sampled in Svalbard, Norway

Harbour seals in Svalbard have short longevity, despite being protected from human hunting and having limited terrestrial predation at their haulout sites, low contaminant burdens and no fishery by-catch issues. This led us to explore the diet of Greenland sharks (Somniosus microcephalus) in this region as a potential seal predator. We examined gastrointestinal tracts (GITs) from 45 Greenland sharks in this study. These sharks ranged from 229 to 381?cm in fork length and 136–700?kg in body mass; all were sexually immature. Seal and whale tissues were found in 36.4 and 18.2%, respectively, of the GITs that had contents (n?=?33). Based on genetic analyses, the dominant seal prey species was the ringed seal (Pusa hispida); bearded seal (Erignathus barbatus) and hooded seal (Cystophora cristata) tissues were each found in a single shark. The sharks had eaten ringed seal pups and adults based on the presence of lanugo-covered prey (pups) and age determinations based on growth rings on claws (≤1?year and adults). All of the whale tissue was from minke whale (Balenoptera acutorostrata) offal, from animals that had been harvested in the whale fishery near Svalbard. Fish dominated the sharks’ diet, with Atlantic cod (Gadus morhua), Atlantic wolffish (Anarhichas lupus) and haddock (Melanogrammus aeglefinus) being the most important fish species. Circumstantial evidence suggests that these sharks actively prey on seals and fishes, in addition to eating carrion such as the whale tissue. Our study suggests that Greenland sharks may play a significant predatory role in Arctic food webs.     

Associations between seabirds and cetaceans: a review

(1) Seabird-cetacean associations involve many genera.
(2) Some seabirds/cetaceans associate with more species than others, e.g. minke and pilot whales, Common dolphins and porpoises amongst cetaceans, and gannet & kittiwake amongst seabirds. Killer whale, sperm whale, shag and cormorant have not been recorded in associations, in the N.E. Atlantic.
(3) All observed associations would be predicted on the basis of the diets of the associated species.
(4) Most associations are probably opportunistic or incidental, as a result of concentration of shared prey.
(5) Some species, however, may associate more regularly, e.g. minke & pilot whales, Common dolphin and porpoise amongst cetaceans and gannet amongst seabirds. It is not possible to say which derives benefit from the association, but on theoretical grounds it is most likely to be the seabird.
(6) Minke and pilot whales may drive towards the surface food normally out of reach of seabirds, particularly Procellariformes. Common dolphins feed by herding fast-moving fish shoals into tight groups which will be a more concentrated food source for diving sea-birds, such as gannets, and make food more accessible to other species. Porpoises may achieve the same result with inshore shoals of sprats and sand eels, particularly for auks and kittiwakes, and terns.     

Rorqual whale (Balaenopteridae) surface lunge‐feeding behaviors: Standardized classification,repertoire diversity,and evolutionary analyses

Rorqual whales (Family: Balaenopteridae) are the world's largest predators and sometimes feed near or at the sea surface on small schooling prey. Most rorquals capture prey using a behavioral process known as lunge‐feeding that, when occurring at the surface, often exposes the mouth and head above the water. New technology has recently improved historical misconceptions about the natural variation in rorqual lunge‐feeding behavior yet missing from the literature is a dedicated study of the identification, use, and evolution of these behaviors when used to capture prey at the surface. Here we present results from a long‐term investigation of three rorqual whale species (minke whale, Balaenoptera acutorostrata; fin whale, B. physalus; and blue whale, B. musculus) that helped us develop a standardized classification system of surface lunge‐feeding (SLF) behaviors. We then tested for differences in frequency of these behaviors among the three species and across all rorqual species. Our results: (1) propose a unified classification system of six homologous SLF behaviors used by all living rorqual whale species; (2) demonstrate statistically significant differences in the frequency of each behavior by minke, fin, and blue whales; and (3) provide new information regarding the evolution of lunge‐feeding behaviors among rorqual whales.     

Fish prey of southern elephant seals, <Emphasis Type="Italic">Mirounga leonina</Emphasis>, at King George Island

Between November and February in the years 1993/1994 to 1999/2000, 153 southern elephant seals, Mirounga leonina, were stomach lavaged at King George Island. Fish occurred in 16 of 108 stomachs containing food items. Myctophids were the dominant fish prey, contributing 76.6% of the 145 sagittal otoliths found. The most important prey species was Gymnoscopelus nicholsi, which constituted 69% of the otoliths and occurred in 75% of stomach samples. Next in importance was the nototheniid Pleuragramma antarcticum, which occurred in 31.3% of samples and represented 11.7% in numbers. We suggest that while myctophids may be the dominant fish prey of elephant seals in areas close to King George Island, they are probably replaced by P. antarcticum as seals migrate towards higher latitudes where this fish is extremely abundant.     

Gill raker structure and selective predation on zooplankton by particulate feeding fish

The relationship between the gill raker structure of planktivorous fish (number, distance between gill rakers and length) and selective feeding on different species and size classes of zooplankton was studied. Gill raker structure was measured for brown trout Salmo trutta , Arctic charr Salvelinus alpinus , whitefish Coregonus lavaretus , roach Rutilus rutilus , bleak Alburnus alburnus , and three-spined stickleback Gasterosteus aculeatus . All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structure was studied by comparing prey found in fish stomachs with the availability of zooplankton from several lakes. Gill raker length and distance were significantly correlated with fish length. Although gill raker structure differed among species, all fish species selected the larger zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despite great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predators. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularly in salmonids and roach, is rejected.     

Diets of sympatric flatfishes, Hippoglossoides platessoides, Pleuronectes ferrugineus, Pleuronectes americanus, from Sable Island Bank, Canada

Prey exploitation was documented for Hippoglossoides platessoides, Pleuronectes ferrugineus , and P. americanus collected from southeast Sable Island Bank in February and June 1989. Diets varied significantly by sample and with fish species and length. Of 239 species consumed by flatfishes, 66 were determined to be principal prey. Crustaceans, particularly amphipods, were the most frequently exploited prey of all three flatfish species. Small H. platessoides fed on suprabenthic fauna, while larger fish exploited epifauna and hyperiid suprafauna. P. ferrugineus exploited epibenthic fauna, consuming crustaceans and tunicates when small and polychaetes when larger. P. americanus preyed on epifauna; smaller fish exploited polychaetes while larger fish usually consumed crustaceans associated with ectoproct colonies. Feeding intensity was dramatically lower in February, food being found in stomachs of only 36% of H. platessoides and 49% of P. ferrugineus , and lacking in the stomachs of P. americanus . In June, stomachs of 86% of H. platessoides , 94% of P. ferrugineus and 96% of P. americanus contained food. Results indicate that prey resources for the three flatfish species are partitioned by specific habitat and prey type preferences.     

Resource seasonality and fish diets in an Illinois stream

Synopsis The purpose of this study was to evaluate the intensity of competition for food among 9 species of stream fishes that primarily eat aquatic invertebrates. The taxonomic and size composition, and numerical abundance of aquatic invertebrates were monitored for one year using drift and benthic samples. Diet data were obtained from stomachs of fishes captured at the same time and place that invertebrate sampling was done. Diet characteristics examined included taxonomic and size composition, number of prey per fish, and diet breadth. Drifting invertebrates were more abundant early in the year (March–June) than later (July–January). The summer-early fall scarcity of invertebrates was especially notable among those>3.6 mm long, which comprised the bulk of prey found in fish stomachs. Average prey size eaten by a fish species was positively correlated with fish mouth size, but interspecific overlap in prey size was extensive. Cyprinids as a group (5 species) ate proportionally fewer small (< 3.6 mm long) prey from July to January than did the centrarchids and stonecat. Taxonomic compositions of available invertebrates and fish diets varied markedly among sampling dates, but the use of prey taxa by fishes was not correlated with the availability of those taxa. Use of aquatic prey taxa was generally similar among fish species, but cyprinids as a group ate proportionally more terrestrial prey from July to January than did the centrarchids and stonecat. Diet breadths for all species increased as food levels declined, indicating that these fishes experienced resource depression. Food scarcity was evidently more severe for cyprinids since their stomachs contained few prey through the summer and fall relative to the centrarchids and stonecat. Though the fish species studied probably compete for food in the summer and fall, this competition did not account for the community structure observed.     

Fish eggs and larvae in the diet of herring Clupea harengus membras Linnaeus, 1758 and the sprat Sprattus sprattus balticus (Schneider, 1904) (Clupeidae) in the Southeastern Baltic Sea

The qualitative and quantitative composition of fish eggs and larvae in the stomach contents of Baltic herring and sprat was examined. The occurrence of fish eggs and larvae in the diet of herring was markedly higher, compared to sprat. Eggs of four and larvae of nine fish species were found in the herring stomachs. The prey species composition of the herring and sprat diets was related to the ichthyoplankton composition and to the degree of overlapping of the prey and predator distributions. Sprat eggs were the predominant prey in the herring diet in May and sprat larvae prevailed in August. The daily ration estimates indicate that the sprat larvae consumption by herring in August exceeded the sprat egg consumption in May by many times. Cod eggs in the herring stomachs were only found at the optimal oxygen content and salinity for the cod eggs in the near-bottom water layer.     

Assessing changes in numbers and distribution of large whale entanglements in Newfoundland and Labrador,Canada1

Entanglements of large whales in commercial fisheries in Newfoundland and Labrador, Canada, have been consistently recorded since 1979, as part of a program aimed at releasing captured animals and reducing costs to fishermen. This data set represented an opportunity to identify fisheries posing particular entanglement risks to local whale populations. Data were assessed over the periods 1979–1992 and 1993–2008, corresponding to distinct phases in fisheries distribution and intensity. Between 1979 and 2008, 1,209 large whale entanglements were recorded in Newfoundland and Labrador. These were mostly humpback whales (Megaptera novaeangliae; 80%) and minke whales (Balaenoptera acutorostrata; 15%). Dramatic declines in reported inshore whale entanglement rates were observed following the 1992 moratorium on Atlantic cod (Gadus morhua) fisheries. Recently, more entanglements have been reported further offshore, largely due to expansion of fisheries targeting snow crab (Chionoecetes opilio). For all whale species, entanglement rates and associated mortality rates varied considerably in different fishing gear. Fractions of humpback and minke whales found dead in different fishing gear differed substantially, with minke whales far more likely to be found dead than humpback whales.     

Molecular genetic identification of whale and dolphin products from commercial markets in Korea and Japan

We report the methods and results of molecular genetic identification of the species and, in some cases, geographical origins of whale and dolphin products purchased from retail markets and restaurants in Japan and South Korea. As reported previously (Baker & Palumbi 1994), we used the polymerase chain reaction (PCR) and a portable laboratory to amplify, purify and later sequence a portion of the mitochondrial DNA control region from 16 commercial products purchased in Japan. This ‘spot check’ revealed a surprising variety of species for sale, including minke, fin and humpback whales and one or two species of dolphins sold as ‘kujira’ or whale. In the Korean survey, DNA amplifications were conducted by two of us (C.S.B. and F.C.) working with independent equipment and reagents. The two sets of DNA amplifications were returned to our respective laboratories and sequenced independently for cross-validation. Among the total of 17 species-specific sequences we found a dolphin, a beaked whale, 13 Northern Hemisphere minke whales (representing at least seven distinct individuals) and two whales which are closely related to the recognized sei and Bryde's whales but could not be identified as either using available type sequences. We suggest that these two specimens represent a currently unrecognized species or subspecies of Bryde's whale, possibly the so-called ‘small-form’ reported from the tropical waters of the Indo-Pacific. We conclude that molecular systematic analyses of DNA sequences have tremendous utility for the identification of whale and dolphin products. However, there are certain constraints on the application of these techniques for monitoring whaling or trade in whale products. First, PCR and DNA sequencing can generate misleading artefacts. These can generally be recognized or eliminated through experimental controls. Second, phylogenetic reconstructions of DNA sequences can be misinterpreted if the database of type sequences is inadequate or the taxonomy of the group is incomplete. This constraint is, at present, a more serious obstacle to molecular monitoring of whaling. Our results highlight uncertainties about the taxonomic status of oceanic populations and morphological forms of two species (or species complexes) targeted by legal and illegal hunting, the minke and Bryde's whales. Despite these uncertainties, it is difficult to reconcile some of the species available in Japanese and Korean commercial markets with recent catch records made available to the International Whaling Commission. It is particularly disturbing that two specimens of an unrecognized species or subspecies of baleen whale were for sale in a restaurant in South Korea in October, 1994, 8 years after the acceptance of an international moratorium on commercial whaling.     

Evidence of resource partitioning between humpback and minke whales around the western Antarctic Peninsula

For closely related sympatric species to coexist, they must differ to some degree in their ecological requirements or niches ( e.g. , diets) to avoid interspecific competition. Baleen whales in the Antarctic feed primarily on krill, and the large sympatric prewhaling community suggests resource partitioning among these species or a nonlimiting prey resource. In order to examine ecological differences between sympatric humpback and minke whales around the Western Antarctic Peninsula, we made measurements of the physical environment, observations of whale distribution, and concurrent acoustic measurements of krill aggregations. Mantel's tests and classification and regression tree models indicate both similarities and differences in the spatial associations between humpback and minke whales, environmental features, and prey. The data suggest (1) similarities (proximity to shore) and differences (prey abundance versus deep water temperatures) in horizontal spatial distribution patterns, (2) unambiguous vertical resource partitioning with minke whales associating with deeper krill aggregations across a range of spatial scales, and (3) that interference competition between these two species is unlikely. These results add to the paucity of ecological knowledge relating baleen whales and their prey in the Antarctic and should be considered in conservation and management efforts for Southern Ocean cetaceans and ecosystems.     

Cetacean mitochondrial DNA control region: sequences of all extant baleen whales and two sperm whale species

The sequence of the mitochondrial control region was determined in all 10 extant species commonly assigned to the suborder Mysticeti (baleen or whalebone whales) and to two odontocete (toothed whale) species (the sperm and the pygmy sperm whale). In the mysticetes, both the length and the sequence of the control region were very similar, with differences occurring primarily in the first approximately 160 bp of the 5' end of the L-strand of the region. There were marked differences between the mysticete and sperm whale sequences and also between the two sperm whales. The control region, less its variable portion, was used in a comparison including the 10 mysticete sequences plus the same region of an Antarctic minke whale specimen and the two sperm whales. The difference between the minke whales from the North Atlantic and the Antarctic was greater than that between any acknowledged species belonging to the same genus (Balaenoptera). The difference was similar to that between the families Balaenopteridae (rorquals) and Eschrichtiidae (gray whales). The findings suggest that the Antarctic minke whale should have a full species status, B. bonaerensis. Parsimony analysis separated the bowhead and the right whale (family Balaenidae) from all remaining mysticetes, including the pygmy right whale. The pygmy right whale is usually included in family Balaenidae. The analysis revealed a close relationship between the gray whale (family Eschrichtiidae) sequence and those of the rorquals (family Balaenopteridae). The gray whale was included in a clade together with the sei, Bryde's, fin, blue, and humpback whales. This clade was separated from the two minke whale types, which branched together.      

Migration of Antarctic minke whales to the Arctic

The Antarctic minke whale (Balaenoptera bonaerensis), and the common minke whale found in the North Atlantic (Balaenoptera acutorostrata acutorostrata), undertake synchronized seasonal migrations to feeding areas at their respective poles during spring, and to the tropics in the autumn where they overwinter. Differences in the timing of seasons between hemispheres prevent these species from mixing. Here, based upon analysis of mitochondrial and microsatellite DNA profiles, we report the observation of a single B. bonaerensis in 1996, and a hybrid with maternal contribution from B. bonaerensis in 2007, in the Arctic Northeast Atlantic. Paternal contribution was not conclusively resolved. This is the first documentation of B. bonaerensis north of the tropics, and, the first documentation of hybridization between minke whale species.     

DIET OF WEDDELL SEALS LEPTONYCHOTES WEDDELLII AT VESTKAPP, EASTERN WEDDELL SEA (ANTARCTICA), IN RELATION TO LOCAL FOOD SUPPLY

Thirteen Weddell seals ( Leptonychotes weddellii ) were collected at Vestkapp, eastern Weddell Sea coast, in austral spring 1986. All stomachs contained partially digested food. The mean wet weight of stomach contents was 7.5 kg, 3.3% of the. mean body weight of the collected seals. Twelve fish species and three cephalopod species were identified from 372 left otoliths and 25 lower beaks, representing 58.4% of 679 total prey items obtained. Composition by number of total prey was: Chionodraco myersi (15.8%), Trematomus eulepidotus (10.0%), Pagetopsis maculatus (9.7%), Racovitzia glacialis (9.6%) and Cryodraco antarcticus (4.1%). Otoliths of the seven other fish species and beaks of the three cephalopod species together represented 9.1% of total prey numbers. The pooled wet weights calculated from 13 prey species (regressions for two octopod species were not available) amounted to 43.5 kg food mass and represented 44.7% of the combined food mass in all stomachs. Composition by mass was: C. myersi (44.5%), T. eulepidotus (19.8%), squid Psychroteuthis glacialis (8.5%), P. maculates (7.9%), C. antarcticus (7.1%) and R. glacialis (6.2%). The remaining 7 fish species together represented 5.8% by mass. Temporal variation in food availability was apparent. Midwater fish Pleuragramma antarcticum was the staple food of Weddell seals from the same area during the 1985 summer, whereas it was absent in the samples taken in spring 1986. Estimates of fish biomass from net hauls demonstrate a highly variable availability of pelagic food resources for top predators in the Vestkapp area.     

The diet of Antarctic fur seals, Arctocephalus gazella, at King George Island, during the summer–autumn period

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, by scat analysis from February to April 1996. Overall, krill and fish were the most frequent prey, occurring in an average of 97% and 69% of samples (n=128), followed by cephalopods (12%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill-feeding species suggesting that seals foraged primarily on krill and opportunistically on fish species associated with krill swarms. A seasonal change observed in the relative proportions of the different fish prey taxa indicates that fur seals spent more time foraging over the shelf in summer and off the shelf in autumn. During the study period, commercial fishing in the area was not based upon any of the fish identified in this study.     

The food of Atlantic salmon, Salmo salar L., caught by long–line in northern Norwegian waters

A total of 1145 stomachs from Atlantic salmon caught over the shelf off Helgeland/Trøndelag, and in the oceanic waters off Andenes, northern Norway during late winter–spring, 1969–1972 were examined. Food was found in 52.9% of the stomachs examined. The most important food items found in fish caught in the Helgeland/Trøndelag area were euphausids and hyperid amphipods while the myctophid Benthosema glaciale , the squid Gonatus fabricil and euphausids were found most frequently in the salmon caught off Andenes. Most salmon had preyed upon only one species, and few stomachs contained three or more prey species. The type of food did not appear to be related to the length of the fish. It is suggested that some mesopelagic feeding occurred.