Threshold foraging by gray whales in response to fine scale variations in mysid density

The gray whale (Eschrichtius robustus) is a coastal species whose nearshore summer foraging grounds off the coast of British Columbia offer an opportunity to study the fine scale foraging response of baleen whales. We explore the relationship between prey density and gray whale foraging starting with regional scale (10 km) assessments of whale density (per square kilometer) and foraging effort as a response to regional mysid density (per cubic meter), between 2006 and 2007. In addition we measure prey density at a local scale (100 m), while following foraging whales during focal surveys. We found regional mysid density had a significant positive relationship with both gray whale density and foraging effort. We identify a threshold response to regional mysid density for both whale density and foraging effort. In 2008 the lowest average local prey density measured beside a foraging whale was 2,300 mysids/m³. This level was maintained even when regional prey density was found to be substantially lower. Similar to other baleen whales, the foraging behavior of gray whales suggests a threshold response to prey density and a complex appreciation of prey availability across fine scales.     

Separating pygmy and Antarctic blue whales using long-forgotten ovarian data

Pygmy blue whales ( Balaenoptera musculus brevicauda ) are ≤24.1 m and are generally found north of 52°S in summer, whereas the more southerly Antarctic blue whales ( B. m. intermedia ) may exceed 30 m. Previous assessments have assumed that catches and recent surveys south of 60°S recorded Antarctic blue whales, but these may have included pygmy blue whales. Here, we use ovarian corpora, which accumulate with ovulations and hence with length, to separate these subspecies. The resulting Bayesian mixture model, applied to 1,380 Northern Region (north of 52°S and 35°–180°E) and 3,844 Southern Ocean (south of 52°S) blue whales, estimated that only 0.1% (95% credibility intervals 0.0%–0.4%) of the Antarctic region blue whales were pygmy blue whales and, unexpectedly, found significantly lower lifetime ovulation counts for pygmy blue whales than for Antarctic blue whales (7.6 vs . 13.6). Over four decades, despite substantial depletion of Antarctic blue whales, there was no trend in the estimated proportion of pygmy blue whales in the Antarctic. Several lines of investigation found no evidence for sizeable numbers of pygmy blue whales in ovarian corpora data collected in the 1930s, as was previously hypothesized.     

REEXAMINING THE RELATIONSHIP BETWEEN BODY SIZE AND TONAL SIGNALS FREQUENCY IN WHALES: A COMPARATIVE APPROACH USING A NOVEL PHYLOGENY

A negative relationship between cetacean body size and tonal sound minimum and maximum frequencies has been demonstrated in several studies using standard statistical approaches where species are considered independent data points. Such studies, however, fail to account for known dependencies among related species—shared similarity due to common ancestry. Here we test these hypotheses by generating the most complete species level cetacean phylogeny to date, which we then use to reconstruct the evolutionary history of body size and standard tonal sounds parameters (minimum, maximum, and center frequency). Our results show that when phylogenetic relationships are considered the correlation between body size (length or mass) and minimum frequency is corroborated with approximately 27% of the variation in tonal sound frequency being explained by body size compared to 86% to 93% explained when phylogenetic relationships are not considered. Central frequency also correlates with body size in toothed whales, but for other tonal sound frequency parameters, including maximum frequency, this hypothesized correlation disappears. Therefore, constraints imposed by body size seem to have played a role in the evolution of minimum frequency but alternative hypotheses are required to explain variation in maximum frequency.     

The origins and character of 'aboriginal subsistence' whaling: a global review

The International Whaling Commission (IWC) recognizes aboriginal subsistence whaling to be distinct from commercial whaling, and these two broad categories of whaling are subject to different management approaches. This paper describes recent, ongoing and likely future whale hunts that qualify, or may qualify, for aboriginal subsistence status within the IWC’s management framework. To ensure conservation of the whale populations, a forthright exposition of the origins, development and character of these hunts is needed in addition to stock assessment, a risk‐averse catch limit algorithm and appropriate mechanisms within the whaling communities to ensure compliance. The hunts for Bowhead Whales (Balaena mysticetus) and Gray Whales (Eschrichtius robustus) in the Arctic and North Pacific, respectively, and Sperm Whales (Physeter macrocephalus) in Indonesia have long histories and local origins. Those for Humpback Whales (Megaptera novaeangliae) in the Lesser Antilles and at Tonga in the South Pacific were introduced by foreign commercial whalers. Whale hunting in the Philippines appears to have originated both locally and as a result of foreign influence. The relatively recent initiation of whaling for Fin Whales (Balaenoptera physalus) and Minke Whales (Balaenoptera acutorostrata) in Greenland required introduced technology but can be viewed as a modern adaptation of an ancient tradition. Consensus in deciding how to classify and manage non‐industrial whaling has been, and will remain, elusive. Even with common definitions of key terms such as ‘subsistence’, ‘commercial’ and ‘aboriginal’, interpretations will depend on whether one’s priorities are whale‐centred or human‐centred.     

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.     

Allele-sharing methods for estimation of population size

Genetic data are becoming increasingly important in ecology and conservation biology. This article presents a novel method for estimating population size from DNA profiles obtained from a random sample of individuals. The underlying idea is that the degree of biological relationship between individuals in the sample reflects the size of the population and that DNA profiles provide information about relatedness. A pseudolikelihood approach is taken, involving pairwise comparison of individuals. The main field of applications is seen to be catch data, and as an example, the method is applied to DNA profiles (10 microsatellite loci) from 334 North Atlantic minke whales. It is concluded that the sample size is too small for the method to give useful results. The question about the required sample size is investigated by simulation.     

New approaches for field studies of mammals: experiences with marine mammals

The constraints imposed by studying a mammal in an aquatic environment and by the nerd to use benign methods have made it necessary to develop novel approaches in order to investigate the biology of marine mammals. The approaches have been made possible by recent technological advances and by the willingness of granting agencies to fund expensive, high–risk projects in marine science.
We review new trchniques which have been developed for estimating the population size of marine mammals, for investigating the relationsip between individuals and populations, for studying the behaviour and energetics of animals in the open sea, and for the management of small and endangered populations. We also indicate how these techniques may be applied to a variety of terrestrial mammals.