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Comparative swimming effort of migrating gray whales (Eschrichtius robustus) and calf cost of transport along Costa Azul, Baja California, Mexico

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Abstract:

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.

Nous avons mesuré les vitesses de nage et les taux de respiration chez des baleines grises (Eschrichtius robustus (Lilleborg, 1861)) en migration à Costa Azul, Basse-Californie, afin de comparer les efforts de nage de baleines en direction sud, de baleines sans petits en direction nord et de mères et de petits en direction nord. De décembre 2004 à mai 2005, nous avons suivi les baleines et mesuré leur vitesse de nage à l’aide d’un théodolite. Nous avons déterminé le nombre et le moment des souffles à la jumelle afin de calculer les taux de respiration. Les taux de respiration des baleines individuelles (BR) divisés par leur vitesse de nage (V) donnent un indice comparatif de l’effort de nage en nombre de respirations à kilometre. Il y a des différences significatives de BR moyen, de V et d’effort de nage entre les trois groupes de migrateurs (p < 0,05). Les baleines en migration vers le sud fournissent un effort de nage moyen de 7,4 respirations·km-1 (V = 1,9 m·s-1, BR = 0,8 respirations·min-1). Les baleines migratrices vers le nord non accompagnées de petits font l’effort de nage le plus faible des trois groupes de migrateurs, soit 4,7 respirations·km-1 (V = 1,8 m·s-1, BR = 0,5 respirations·min-1). Les mères et les petits en migration vers le nord maintiennent la même vitesse de nage (V = 1,2 m·s-1), mais leur effort de nage et leur BR, calculés séparément, sont respectivement de 7,6 respirations·km-1 (BR = 0,5 respirations·min-1) chez les mères et de 10,1 respirations·km-1 (BR = 0,7 respirations·min-1) chez les petits. Le coût du transport a pu être calculé pour les petits migrant en direction nord et il s’étend de 0,25-0,34 à 0,51-0,58 J·kg-1·m-1 pour des volumes courants respectifs de 1,5 % et de 3,0 %.

Document Type: Research Article

Publication date: April 1, 2008

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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