Gray whales accomplish an annual migration which spans as much as 50° of latitude in the northeast Pacific Ocean. This migration links their summer high latitude feeding grounds with winter calving and breeding areas. The purpose of this study was to determine how adult females apportion their stored lipid reserves while away from their principal feeding areas to accommodate their own maintenance and locomotory needs while developing a fetus and transferring energy through lactation to support growth and maintenance of their calves. Major components of this study included examinations of migratory swimming speeds and costs of transport, of calf growth and mortality rates, of metabolic and heat loss rates, of summer distribution patterns, and of the magnitudes and utilization rates of maternal lipid reserves. The results of this study support the conclusions of other investigations that calf heat losses are similar to minimum observed metabolic rates, and that maintenance and lactation costs can be accommodated without winter feeding by all but the small adult females. It is suggested that present oceanographic conditions in the North Pacific Ocean support a larger gray whale population and allow very different gray whale feeding and migrating patterns than existed during the last glacial maximum. / Graduation date: 1986

Thesis (M.S.)--Queen's University, 2000. / Includes bibliographical references (leaves 91-101).

Thesis (Ph. D.)--University of Washington, 1981. / Vita. Bibliography: leaves [241]-251.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 88-95). Also available on the World Wide Web.

Thesis (M.A.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 49-54). Also available via Humboldt Digital Scholar.

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Gray whales (Eschrichtius robustus), while engaged in underwater signalling, circumvent noise in the acoustical channel by the structure and timing of their calls. Data yielding this conclusion were collected during an acoustical study on gray whales and their habitats (1981-1984). Sonographic analyses of tape recordings were used to quantify the acoustical repertoire, the ambient noise characteristics of the area, and the relationship between the animals' calls and the environment. The acoustical responses of whales to artificially increased levels of noise were documented during playback experimentation in Mexico. Nine sound parameters were inspected and compared between control and experimental conditions: calling rates, call types, frequency range of signals (Hz), emphasized frequencies (Hz), received levels of sounds (dB re 1 μPa), call duration (sec), percentage of calls exhibiting frequency modulation, number of pulses per series, and repetition rates of signals. The observed surface behavior of gray whales in response to noise (i.e., dive durations, movements and abundance) was also investigated. Analyses yielded: a description of gray whale call types; a characterization of the acoustical habitats occupied by this species, including a list of sources contributing to the ambient noise and a profile of the propagation characteristics of the study area; a determination of the relationship between whale calls and their habitats; and the acoustical capabilities and strategies of whales in response to noise. The plasticity observed in the overall behavior of this whale is of adaptive significance when considering the dynamic nature of noise in the environment. Typically, the multiple strategies employed by the whales when faced with various noise situations enable them to minimize the detrimental effect that noise has on their underwater signalling. Gray whale responses varied with the sound source and may also differ relative to the geographical range and/or general behavior of the animal. It is concluded that ambient noise (both natural and man-made) has a profound effect on the behavior of this coastal species and that acoustical calling is modified to optimize signal transmission and reception. / Science, Faculty of / Zoology, Department of / Graduate

The growing industry of whale-watching is allowing increasing numbers of people access to whales in their natural environment, and constitutes a non-consumptive use of the whales compared to whaling. At the same time, questions are often raised about the hidden effects of whale-watching on the whales. A population of gray whales (Eschrichtius robustus) which spends the summer feeding in Clayoquot Sound, on the West Coast of Vancouver Island, is regularly observed by whale-watchers from the nearby tourist centre of Tofino. Concern among whale-watching business operators and tourists about the possible effects of whale-watching on the feeding whales was heightened in the years preceding this study by an apparent northward movement of the whales, taking them farther from the Tofino, the point of departure for whale-watching tours. This study attempts to explain this apparent trend by finding out whether the whales' short-term behaviour is affected by the presence of whale-watching vessels, and by examining their short and long-term behaviour in the wider context of some of the features of their environment. Whales were observed from a small research vessel for three feeding seasons, in five locations within the area known as Clayoquot Sound. The whales' ventilations were recorded continuously and their location and the number of whale-watching vessels present was recorded at regular intervals. The whales' benthic prey was sampled in all three seasons and their planktonic prey in 1995. A series of variables were calculated from the ventilation data and compared to the number of vessels. The whales' dive behaviour was correlated much more strongly with feeding location than with vessel number. Even with these two factors taken into account, much of the variation in their behaviour remains unaccounted for. Because of this, although the behavioural change in the presence of vessels is statistically significant, there is reason to doubt whether it is biologically significant. The effects of feeding location are probably a composite of the effects of depth, prey type and other factors which are difficult to measure. Of the two main components, prey type appears to have a greater effect than depth on gray whale behaviour. Interaction exists between the effects of site and those of whale-watch vessels, meaning that the effects of vessels are different at different sites. The general pattern is that the effects of vessel presence are more pronounced in shallow sites than in deep, although there are some exceptions to this trend. Gray whale prey shows considerable variation in location, density and composition from year to year. The long-term patterns of gray whale habitat use more closely resemble a prey-selection-driven pattern than a pattern of avoidance of whale-watch vessels. The relatively small influence of vessel numbers on gray whale feeding behaviour suggests that the current guidelines in place for whale-watching vessels are effective in limiting disturbance of the whales. The variable nature of their prey supply suggests that gray whales use all the sites in Clayoquot Sound, and that the availability of a diverse selection of prey is necessary for their success in the tertiary feeding grounds. / Graduate

While direct measurements of energetic demands are nearly impossible to collect on large cetaceans, comprehensive bioenergetic models can give insights on such parameters by combining physiological and ecological knowledge. This model was developed to estimate necessary food intake of gray whales, Eschrichtius robustus, of the Eastern North Pacific stock. Field Metabolic Rates (FMR) for gray whales were first estimated based on various assumptions (e.g. volumetric representation of gray whales, extent of their feeding season, and blubber depth distribution) using morphometric data, energetic costs, and food assimilation according to age and gender specific requirements. Food intake rates for gray whales of varying maturity and gender were then estimated based on FMR and caloric value of prey and compared to food intake rates of previous studies. Monte Carlo simulations and sensitivity analysis were performed to assess the model's predictions compared to observed field data from previous studies. Predicted average food intakes for adult male, pregnant/ lactating female, and immature whales were 475 ± 300, 525 ± 300 and 600 ± 300 kg d-1, respectively. Estimated blubber depths resulting from these food intakes were comparable to field data obtained from whaling data. Sensitivity analysis indicated food intake, from all parameters, as having the highest impact on the percent change in ending mass from a simulation. These food intake estimates are similar to those found in a previous study and fall within the range of food intake per body mass observed in other species of cetaceans. Though thermoregulation can be a factor in some cetaceans, it appears not to be an additional cost for gray whales as the present model's predicted lower critical temperatures for the whales (TLC) were below ambient temperatures. With temperatures increasing in the Bering Sea, the main prey of gray whales, ampeliscid amphipods, could be adversely affected, possibly resulting in increased food shortages leading to a surge in gray whale strandings.

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