OCS Study MMS 88-0056 LGL Rep. TA 833-1 of COMPARISON OF
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OCS Study MMS 88-0056 LGL Rep. TA 833-1 COMPARISON OF BEHAVIOR OF BOWREAD WHALES OF TEE DAVIS STRAIT AND BERING/BEAUFORT STOCKS W. John Richardson and Kerwin J. Finley LGL Limited, environmental research associates 22 Fisher St., P.O.B. 280 King City, Ontario LOG lKO Canada for U.S. Minerals Management Service Procurement and General Services Division 1110 Herndon Parkway, Room 319 Herndon, VA 22070 March 1989 Contract No. 14-12-0001-30390 This study was funded by the Alaska Outer Continental Shelf Region of the Minerals Management Service, U.S. Dept. of the Interior, Anchorage, AK, under contract 14-12-0001-30390 The opinions, findings, conclusions, or recommendations expressed in this report are those of the authors and do not necessarily reflect the views of the U.S. Dept. of the Interior, nor does mention of trade names or commercial products constitute endorsement or recommendation for use by the Federal Government. Abstract ii ABSTRACT This report describes statistical and other comparisons between the behavior of two stocks of bowhead whales that have been studied in late summer and autumn: the Eastern Arctic or ‘Davis Strait - Baffin Bay’ stock and the Western Arctic or ‘Bering - Chukchi - Beaufort’ stock. The comparisons are based on data collected in several previous studies, including previously-unanalyzed eastern arctic data. The behavioral repertoires of bowhead whales in the two regions were qualitatively similar in most respects. However, the comparisons revealed statistically significant quantitative differences in behavior. Such differences were evident for all three categories of whales that were compared: feeding in deep water, socializing in shallow waterj and migrating. Multivariate and other analyses indicated that some but not all of these differences could be ascribed to regional differences in environmental conditions or whale activities. The report discusses possible reasons for behavioral differences that were not attributable to differences in environmental conditions or whale activities. Sexual interactions were observed much more often at Isabella Bay in the eastern arctic than observed at any location in the western arctic during late summer or autumn. The difference was partly but not fully understandable on the basis of age segregation within the two populations. The reasons for the greater amount of sexual activity observed in autumn in the eastern arctic are not fully understood. This difference is potentially important with regard to the dynamics of the two populations. Executive Summary iii EXECUTIVE SUMMARY Introduction Bowhead whales in the western arctic (Bering-Chukchi-Beaufort stock) are exposed to a variety of types of human activities in several parts of their annual range. These bowheads exhibit short-term behavioral reactions to disturbance by various human activities. However$ it is not known whether such disturbances lead to any long-term changes in behavior, or to any deleterious effects on the bowhead population. Extensive data have been collected in recent years on the behavior of western arctic bowheads under presumably undisturbed as well as potentially disturbed conditions. Bowhead whales in the eastern arctic (Davis Strait-Baffin Bay stock) are not exposed to nearly as much human activity, given the absence of bowhead hunting there and the much lower level of offshore oil exploration. Data on the behavior of eastern arctic bowheads have been collected in recent years during studies along the east coast of Baffin Island. These data had not been analyzed in any detail before the present project. MMS suggested that the eastern arctic population might serve as a virtually undisturbed ~control! population in order to assess whether the behavior of western arctic bowheads has been altered by the cumulative effects of various human activities. This overall objective has been formulated by MMS as a test of the following null hypothesis: I-lo : There are no significant differences in normal behavior between bowhead whales of the Western Arctic and Davis Strait stocks. To test this hypothesis and interpret the results, it is necessary to (1) analyze the existing but previously-unanalyzed data on the behavior of the Eastern Arctic bowheads, (2) compare their behavior with that of the Western Arctic stock, (3) quantify the relative amounts of human activity to which the two stocks have been exposed in recent years$ and (4) evaluate whether any observed differences in behavior are attributable to differences in human activities. The study was planned as a two-phase project. In Phase 1, the behavior of the two stocks of bowheads was to be compared (items 1 and 2 from the above list). In Phase 2, the relative exposure of the two stocks to human activity is to be determined, and behavioral similarities and differences between stocks are to be evaluated in relation to differences in human activities (items 3 and 4). The present report presents the results from Phase 1. Data Sources and Methods The western arctic data used for these analyses came from three studies funded by BLM/MMS or the oil industry and conducted by LGL in the 1980-86 period, plus a study conducted for MMS by the Naval Ocean Systems Center (NOSC) in 1983: 1. The LGL/MMS study of behavior and disturbance responses by bowheads summering in the Canadian Beaufort Sea in 1980-84 (Richardson [cd.] 1985). Executive Summary iv 2. The LGL/MMS study of bowheads feeding in the eastern Alaskan Beaufort Sea during September of 1985 and 1986 (Richardson et al, 1987b). 3. The LGL/Shell Western study of bowheads migrating past drillsites in the Alaskan Beaufort Sea during the autumn of 1986 (Koski and Johnson 1987). 4. The NOSC/MMS study of bowheads near seismic vessels in the Alaskan Beaufort Sea during the autumn of 1983 (Ljungblad et al. 1984b). Heavy ice conditions prevented most seismic exploration in 1983. The data considered here were those collected when no significant source of man-made underwater noise was present. All data collected in the four western arctic studies were collected by aerial observers using a standardized observation method. The aircraft circled at an altitude of at least 1500 ft (457 m) during all observation sessions considered here. This has been shown to be high enough to avoid significant disturbance by the observation aircraft. The eastern arctic data were collected during two LGL shore-based studies along the east coast of Baffin Island: 1. A study of bowheads migrating south past Cape Adair in the autumn of 1979. Limited additional data were available from 1978 (Koski and Davis 1979, 1980). 2. A study of bowheads summering at Isabella Bay in the late summer - early autumn periods of 1984-86. Limited additional data were available from 1983 and 1987 (Finley et al. 1986; Finley 1987, unpubl. ). In both studies, most data came from a theodolite deployed on a coastal hill or cliff. The theodolite was about 209 m above sea level at Cape Adair and 136 m above sea level at Isabella Bay--high enough to allow observations and tracking of whales several kilometers away. Aerial surveys provided supplementary data in 1978-79. At Isabella Bay, data on zooplankton and underwater sounds were acquired occasionally from boats, and whale sizes were determined in 1986 by aerial photogrammetry. LGL’s western arctic data were already available in a standardized computer-readable format prior to the present study. At the start of this project, they were converted into an improved format incorporating some additional variables. LGL’s eastern arctic data, which had not previously been analyzed in detail, plus NOSC’S 1983 western arctic data, were coded in the new format, entered into a computer, and validated. The first major step of the analysis was to identify comparable subsets of the eastern and western arctic data. Preliminary analyses indicated that three categories of whale activity occurred commonly in both regions: feeding in deep (>50 m) water, socializing in shallow (<50 m) water, and migrating. A fourth category, local travel, was commonly rec~gnized only at Isabella Bay. Separate analyses were performed for each of these four categories of whale activities. Several other categories of activity were recognized in the Executive Summary v western arctic, e.g. near-bottom, water-column and near-surface feeding in shallow water; socializing in deep water. The behavior of western arctic bowheads engaged in these latter activities has been reported previously, and was not analyzed further in this study because of the absence of corresponding eastern arctic data. Bowheads Feeding in Deep Water Most feeding activity at Isabella Bay occurred in deep water over glacial-remnant troughs several kilometers offshore. Essentially all feeding was of the type recognized in the western arctic as ‘water column feeding’. There was little evidence of coordinated feeding behavior between different individual whales. However, surfacing-dive sequences of some ‘paired’ whales were synchronous. Near-surface feeding apparently was rare, and near-bottom feeding was not detected. Whales feeding in a trough >200 m deep several kilometers northeast of the observation site on Cape Raper moved back and forth through the area from one surfacing to the next. When at the surface, bowheads often defecated, and fecal samples (n = 2) contained remnants of large copepods. Limited zooplankton sampling indicated that concentrations of large copepods occurred at depths >100 m. Bowheads feeding in deep water off Isabella Bay exhibited long dives and surfacings~ with many respirations per surfacing. An average surfacing - respiration - dive cycle consisted of a 15.8 min dive followed by a 4.7 min surfacing during which the whale respired 17 times. This behavior is consistent with diving to great depths. The interval between successive blows within a surfacing averaged 16.9 s. Within this category of whales, surfacing - respiration - diving behavior was correlated with few of the environmental variables that we considered.