VARIABILIDAD DE PERFILES DE ÁCIDOS GRASOS DE BALLENA AZUL, musculus, EN EL GOLFO DE CALIFORNIA

Blue whales from the Northeast Pacific population migrate to the Gulf of California during winter and spring. This area is the only known nursing ground of the Northeast Pacific population, where nursing females-calves pairs, young, adults females and males individuals occur. In this zone, the whales continue to feed on the most abundant euphausiid in the area, Nyctiphanes simplex, which constitutes its principal prey. Previous work based upon fatty acid profiles have led to inferences about the diet, and/or differentiate between populations or distributional areas of some marine mammals. In this study, using the dart biopsies of the subcutaneous blubber of Gulf of California blue whales, it is proved the hypothesis that the fatty acid profiles of storage lipids are more associated to the nutritional source, while those of structural lipids are associated with differences in cellular membranes. Based upon 50 biopsies of blue whales including calves, lactating females, females and males taken between 2003 and 2005 the fatty acids profiles were determined using a gas chromatography coupled to a selective detector of masses (GC-MS). Histological analysis of the blubber showed that the triglycerides (70%), and phospholipids (30%) are embedded throughout the biopsy, with no evidence of stratification, which confirmed that biopsies can be used for obtaining both storage and structural fatty acids. There were 34 structural fatty acids identified and quantified, 30 of them occurred at concentrations higher than 0.1% and 11 revealed significant differences (p<0.05) between calves, lactating females, females and males.The use of the structural fatty acids allowed for the classification of 100% of the calves and lactating females, but only 94% and 78% of the remaining females and males, respectively, probably because of the inclusion of immature and old individuals. As for the storage fatty acids, there were 52 fatty acids identified and quantified, 39 of them at concentrations higher than 0.1% and 22 presented significant differences (p<0.05) between categories. The storage fatty acids showed a clear separation between calves, lactating females, females and males. The classification percentages for all the categories were of 100% showing that these fatty acids class is an excellent indicator of sex, lactating state and calves. Some of the fatty acids important for distinguishing categories were dominant, essential, or with a biological importance such as 16:1n-7, 20:5n-3 and 22:1n-11. The storage fatty acid profiles of all the categories of blue whales were compared to the storage fatty acids of Nyctiphanes simplex (undifferentiated juveniles, female juveniles, spent females, male juveniles and male adults) resulting in a high correlation between all categories of blue whales and the euphausiids (R Canónica = 0.912. Ji(20) = 145.73, p<0.05). This study leads to the conclusion that the storage and structural fatty acid profiles of blue whales vary as a function of category and sex. Physiological conditions, such as lactation in the case of nursing females, and the particular metabolism of each category, are determinant factors in the differentiation of blue whale groups based upon fatty acid profiles.