INCREASED FOOD AND ENERGY CONSUMPTION OF 



LACTATING NORTHERN FUR SEALS, 



CALLORHINUS URSINUS 



Michael A. Perez and Elizabeth E. Mooney 1 



ABSTRACT 



Data from pelagic northern fur seals, Callorhinus ursinus, taken during 1958-74 by the United States 

 and Canada in the eastern Bering Sea were analyzed to determine relative feeding rates of lactating 

 and nonlactating females. Estimates of the quantity of food and energy consumed by these seals during 

 July-September were evaluated. The average daily feeding rate (adjusted for percentage of time feeding 

 at sea) for lactating seals is 1.6 times that for nonlactating seals. During July-September, the total popula- 

 tion of lactating and nonlactating females were estimated to consume 146.5 x 10 3 1 (204.5 x 10 9 kcal) 

 and 43.1 x 10 3 1 (60.2 x 10 9 kcal) of food respectively. Fish accounted for 66.4% of food biomass (69.4% 

 of total energy consumption); squid, the remainder. 



The energetics of reproduction, especially during 

 lactation, are poorly documented for free-ranging 

 animals. The various reproductive states of domestic 

 mammals, e.g., cattle, sheep, etc., have been exten- 

 sively studied; and there has also been considerable 

 research on rodents, e.g., mice, voles, etc., under 

 both laboratory and field conditions. As a result of 

 these studies it is widely accepted that most nursing 

 females require considerably more energy than do 

 nonnursing females of the same species, age, and 

 size. Brody (1945) also noted that the maintenance 

 requirements of lactating animals are elevated 

 relative to nonlactating animals. 



In some mammalian species, food intake during 

 lactation may be up to 5 times greater than that 

 observed in nonpregnant, nonlactating adult 

 females, and lactating animals often convert con- 

 siderable body substance to support the lactation 

 process (Baldwin 1978). Previous studies on ter- 

 restrial mammals have specifically shown increased 

 energy consumption by lactating females relative 

 to nonlactating females. For example, captive deer 

 mice, Peromyscus maniculatus, have a 96% to a 

 194% increase (Stebbins 1977); and ewes have a 

 116% increase (Engels and Malan 1979). The bat, 

 Myotis thysanodes, which undergoes thermoregula- 

 tory physiological changes during reproductive 

 stages, also has higher energy requirements for lac- 

 tating females (Studier et al. 1973). Lactating 

 humans are recommended to increase food con- 



sumption by at least 25% (Eagles and Randall 1980); 

 however, some lactating humans in Guatemala meet 

 their additional lactation energy costs by fat loss 

 (Schutz et al. 1980). 



There are few studies on the energetics and con- 

 sumption of food during lactation by marine mam- 

 mals. Lactation appears to drain the energy reserves 

 of large baleen whales; the blubber of lactating 

 females (e.g., blue, Balaenoptera musculus, and fin, 

 Balaenoptera physalus, whales) is lean and 

 emaciated compared with nonlactating females 

 (Lockyer 1978, 1981a). Lockyer (1981b) estimated 

 that adult female sperm whales, Physeter macro- 

 cephalus, need to increase their food intake by about 

 32-63% during lactation, meaning that they would 

 need to feed 4 or 5 times daily to meet higher energy 

 requirements. Lockyer (1981b) also estimated that 

 minke, Balaenoptera acutorostrata, and fin whales 

 increase their food intake by 75 and 86%, respec- 

 tively. Spotte and Babus (1980) did not find a 

 significantly increased mean feeding rate for one 

 captive, pregnant bottlenosed dolphin, Tursiops 

 truncatus, but standard deviations were consistently 

 greater. In addition, during the first 3V2 mo of 

 lactation, a captive mother bottlenosed dolphin con- 

 sumed 170% more food than she did while not lac- 

 tating the following year (Mooney 2 ). Costa and Gen- 

 try (in press) derived metabolic rates for lactating 

 female northern fur seals from measurements of 

 water flux and discussed the components of the 



'Northwest and Alaska Fisheries Center National Marine Mam- 

 mal Laboratory, National Marine Fisheries Service, NOAA, 7600 

 Sand Point Way, N.E., Seattle, WA 98115. 



2 Mooney, E.E. 1981. Unpubl. data. Northwest and Alaska 

 Fish. Cent. Natl. Mar. Mammal Lab., Natl. Mar. Fish. Serv., 

 NOAA, 7600 Sand Point Way NE, Seattle, WA 98115. 



Manuscript accepted August 1985. 



FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



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