| Theodolite surveys, acoustic recordings, and behavioral sampling were conducted from January to May for 4 consecutive years 1997--2000 to assess temporal and spatial overlap of whale-watching activities and gray whales, Eschrichtius robustus, that are present seasonally in Bahia Magdalena, Mexico. Data on occurrence and movements of whales and boats were collected with a Sokkisha DT20E theodolite from Magdalena Island (24.32°N, 112.03°W) and from San Carlos Pier (24.47°N, 112.07°W). A total of 691 scans were analyzed with Aardvark 1.2.4 and Pythagoras 1.2.1 computer software. Acoustic data were collected with an 8104 B&K hydrophone and 2635 B&K preamplifier connected to a Marantz 430 recorder aboard a research skiff. A total of 2884 minutes of field recordings from the skiff were analyzed with Canary 1.2 computer software and 906 minutes of behavioral data were collected concurrently.; While boat traffic did not affect overall number of whales, pod speed, linearity and reorientation movements of whales were different, and the speed of travel for individual whales was slower during boat presence than absence. Ambient noise throughout Bahia Magdalena varied as a function of bottom depth and boat traffic. Whale vocalizations changed in response to ambient noise levels, which increased due to boats. Eleven distinct gray whale call types were identified and coded BMC1 through BMC11, and specific characteristics in each signal type, such as central frequency, bandwidth, duration, and high and low frequencies, were contrasted in the presence and absence of boats. Whale behavioral responses varied with type of approach by boats. Approaches that were fast or close (direct) resulted in more fluke down dives, rolling, and change in heading. Approaches that were slow or far (indirect) resulted in more head raises and fluke and flipper swishes. In summary, although acoustic and behavioral response of whales varied with location, pod size and composition, activity, and age, short-term effects of boat traffic are evident. Because of this, continued assessment of the cumulative effects of increased boat traffic in the Bahia Magdalena Complex is recommended. Changes to the present whale-watching regulations are suggested. |
