Swimming velocities and breathing rates were measured for migrating gray whales ( Eschrichtius robustus (Lilljeborg, 1861)) at Costa Azul, Baja California, to compare swimming effort of southbound whales, northbound whales without calves, and northbound mothers and calves. From December 2004 to May 2005, whales were followed using a theodolite to determine swimming velocity. Binoculars were used to count whale blows and their timings were recorded to determine breathing rates. Individual whale breathing rates (BR) were divided by their swimming velocity (V) to derive a comparative index of swimming effort in units of breaths per kilometre. There were significant differences in mean BR, V, and swimming effort among the three migrating groups (p < 0.05). Southbound migrating whales averaged a swimming effort of 7.4 breaths·km^–1(V = 1.9 m·s^–1, BR = 0.8 breaths·min^–1). Northbound whales without calves showed the lowest swimming effort of the three migrating groups (4.7 breaths·km^–1, V = 1.8 m·s^–1, BR = 0.5 breaths·min^–1). Northbound mothers and calves had the same swimming velocity (V = 1.2 m·s^–1), but BR and swimming effort were calculated separately yielding a swimming effort of 7.6 breaths·km^–1(BR = 0.5 breaths·min^–1) for mothers and 10.1 breaths·km^–1(BR = 0.7 breaths·min^–1) for calves. Cost of transport was calculated for northbound calves, yielding a range based on 1.5% and 3% tidal volumes of 0.25–0.34 and 0.51–0.58 J·kg^–1·m^–1, respectively.

The exceptional growth of whalewatching in Baja California Sur (BCS) and other parts of Mexico during the last 10 years motivated the design and implementation of a Mexican whalewatching law based on experiences in BCS. However, recent research in the Ensenada whalewatching area confirms that this law is insufficient in this area because whalewatching boats and other fishing, cruising, or drifting boats influence the behavior (swimming direction and velocity) of migrating gray whales. In the long term, the migration corridor might be displaced offshore, and whalewatching may become infeasible. This study proposes a management planning process to adapt regulations to this area, to promote adherence to regulations by encouraging self-regulation and strengthening law enforcement, and to enhance the tourist service on board. The actors involved were identified.