Seasonal Changes in Energy Requirements of Harp Seals (original) (raw)
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Polar Research, 1991
We have employed a model for the energy balance of seals to estimate the energy consumption and energy expenditure of ringed seals throughout the year, using biological and physical parameters as input. Data on growth and seasonal changes in body mass and fat content “drives” the seasonal dynamics of the model output. The energy requirements for lactation and activity are based on data from earlier published studies. The analysis suggests that the food intake of ringed seals is highly seasonal. In adult males it is low during the periods of territory defense, mating and moulting from March to June. During this period the seals lose body mass, mainly as fat. The model predicts that lactating females increase their food intake to some extent during the approximately six-week lactation period. After the ice breakup, food intake increases in both sexes, partly as a result of increasing maintenance energy requirements, and partly because the body fat stores are rebuilt in late summer and autumn. The over-all energy requirements of the ringed seal appear to be basically similar to those of terrestrial mammals.
Seasonal energetics of northern phocid seals
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2009
The metabolic rate of harp (Pagophilus groenlandicus), harbor (Phoca vitulina), and ringed seals (Pusa hispida) was measured at various temperatures in air and water to estimate basal metabolic rates (BMRs) in these species. The basal rate and body composition of three harp seals were also measured throughout the year to examine the extent to which they vary seasonally. Marine mammalian carnivores generally have BMRs that are over three times the rates expected from body mass in mammals generally, both as a response to a coldwater distribution and to carnivorous food habits with the basal rates of terrestrial carnivores averaging about 1.8 times the mean of mammals. Phocid seals, however, have basal rates of metabolism that are 30% lower than other marine carnivores. Captive seals undergo profound changes in body mass and food consumption throughout the year, and after accounting for changes in body mass, the lowest rate of food intake occurs in summer. Contrary to earlier observations, harp seals also have lower basal rates during summer than during winter, but the variation in BMR, relative to mass expectations, was not associated with changes in the size of fat deposits. The summer reduction in energy expenditure and food consumption correlated with a reduction in BMR. That is, changes in BMR account for a significant portion of the seasonal variation in energy expenditure in the harp seal. Changes in body mass of harp seals throughout the year were due not only to changes in the size of body fat deposits, but also to changes in lean body mass. These results suggest that bioenergetics models used to predict prey consumption by seals should include timevariant energy requirements.
Journal of Experimental Marine Biology and Ecology, 2014
Northern fur seal Callorhinus ursinus numbers on the Pribilof Islands have been in decline over the past two decades while numbers have increased at other sites, such as in the Kuril Islands in Russia and at Bogoslof Island in the Aleutian Islands. Although these divergent abundance trends remain unexplained, the potential influence of food limitations could be studied by examining the time-energy budgets of individual lactating fur seals. Our goal was to find suitable proxies for food intake and energy expenditure of lactating seals so that we might provide time and energy budgets of an increasing population on Lovushki Island, Russia that could be compared with the declining Pribilof fur seal population. Between 2005 and 2008, we outfitted 13 lactating fur seals with instruments that collected data on depth, external temperature, stomach temperature, GPS location, and acceleration. With these data we investigated proxies for 1) food intake, including time spent at sea, time spent diving, vertical travel distance (VTD), wiggle behavior, and changes in stomach temperature; 2) involuntary costs, including indices of basal metabolism (BMCI), thermal exposure, and instrument hydrodynamic drag (TAG); and 3) locomotive costs, including overall dynamic body acceleration (ODBA), horizontal travel distance, and flipper strokes. We also considered an index of work (WORK) calculated using horizontal distance, ODBA, and seal mass. Multimodel inference was used to determine which proxies best described changes in seal mass at sea when considering two sets of candidate models that differed by excluding or including locomotive costs (n = 13 and n = 7, respectively). Seal mass changes were positively associated with VTD and TAG and negatively associated with BMCI (p b 0.001, adjusted R 2 = 0.84) when locomotive proxies were excluded. With locomotive proxies considered, models were improved and mass changes were best described by being positively related to VTD and negatively associated with WORK (p b 0.001, adjusted R 2 = 0.95). We suggest that relative energy budgets for individual lactating northern fur seals could be compared using proxies for energetics that are easily monitored with standard data logging instruments.
Seasonal Changes in Food Intake of Harp Seals (Phoca Groenlandica) at 69°N
Marine Mammal Science, 1994
Food intake (PI), body mass (BM), and compartmental growth were recorded for 12 mo in four captive 2–4‐yr‐old male harp seals (Phoca groenlandica), exposed to an artificial light regime that closely resembled natural day length at 69°. In early May before molting, both FZ and BM decreased in all four animals. Total body fat (TBF) declined from 51% of BM in March (n = 4) to 30% in August (n = 2), while total body water (TBW) concomitantly increased from 37% to 51% and total body protein (TBP) from 11% to 17%. In July FI started to increase, while BM started to increase in August. TBF increased while TBW and TBP decreased from August, all three parameters reaching a stable level in October at 47%, 39%, and 12%, respectively. Thereafter, body composition was maintained rather constant until May. Between October and March/April FI fluctuated for all animals, while BM showed a fairly steady increase. Average daily amount of capelin consumed was 2.67 kg·d−1, equivalent to 25,600 kJ·d−1, o...
Marine Ecology Progress Series, 2002
Pinnipeds have marked seasonal changes in body condition, accumulating energy reserves prior to the reproduction period, and depleting these reserves during the breeding and molting periods. This cycle is not well described in male harp seals Phoca groenlandica. We obtained morphometric measurements for 3167 Northwest Atlantic male harp seals sampled between 1979 and 1995. The part of the yearly cycle covered in this study (November to May) was divided into short blocks around median dates called 'periods'. For each period, a growth curve was calculated for body mass, sculp mass, core mass and standard length. These sequential growth curves were used to calculate changes in size-at-age between periods. In addition, seasonal changes in 3 condition indices (general, sculp and core condition), in blubber thickness and in the ratio of sculp to total mass were analyzed using locally weighted regressions. Male harp seals returned from their high-latitude feeding grounds heavier, in better condition, and with a thicker blubber layer than when they left the area in the spring. However, maxima in length, mass, condition and blubber thickness were not observed until the February 22 period (February 12 to March 4), or in the case of seals younger than 5 yr, sometime in March. Mass losses associated with the rut began between the periods February 22 and March 15 (March 5 to 25) and were most pronounced in seals older than 10 yr. About 66% of the losses in mass came from the core during this period. We estimated that males lost 39.4 kg during the rut (1.16 kg d-1 or 0.78% of initial mass d-1 , 44% from sculp and 56% from core) and incurred energy expenditures of 840 MJ (24.7 MJ d-1). This corresponds to twice the standard metabolic rate (SMR), and suggests that males are feeding during the rut. All males lost mass in April, and again in May. They began to molt April 19 period (April 16 to 22). Fewer than half the seals had completed the shedding of old hair when the study ended, in the May 10 period. Rates of mass loss during the molt varied from 1 to 1.8 kg d-1 , depending on the age of the seals. Minima of length, mass, condition and blubber thickness were observed in May. Molting appears to be a period of high energy expenditures (3 to 5 SMR) despite the low levels of activity observed at this time. This study revealed that length also changes seasonally: fat seals in February were longer than lean seals of the same age in late April.
Canadian Journal of Zoology, 2015
Seasonal changes in daily energy expenditure (DEE) and its key underlying components (costs of resting metabolic rate (RMR), thermoregulation, activity, and growth) were measured to determine seasonal energy requirements, bioenergetic priorities, and potential times of year when unpredicted episodes of nutritional stress would have their greatest effect on female northern fur seals (Callorhinus ursinus (L., 1758)). The mean (±SD) DEE of six captive juvenile female fur seals was 527.8 ± 65.7 kJ·kg−1·d−1 and fluctuated seasonally (lower during summer and winter, and up to 20% greater in spring and fall). RMR also changed significantly with season and was higher in the fall (potentially due to moulting or anticipated migratory activity). However, changes in RMR did not follow the same seasonal trend as those of DEE. The largest component of DEE was RMR (∼80%, on average), followed by the cost of activity (which may have driven some of the seasonal variations in DEE). In contrast, the e...
Sources of error in estimating food requirements of seals
Polar Record, 1988
Grey seals Halichoerus grypus are common along some parts of the coasts of the North Atlantic Ocean, and many believe they compete with man for common food resources. This also applies to other species of pinnipeds. Sergeant (1973) suggested an estimate of annual weight of food items eaten by the northwest Atlantic population of harp seals Phoca groenlandica, and later food uptake and growth have been studied both in captive ringed seals Phoca hispida (Parsons 1977), harp seals (Keiver and others 1984), grey seals (Ronald and others 1984), and harbor seals Phoca vitulina (Boulva and McLaren 1979). In these studies, however, the animals were either not fed as much as they desired, photoperiod was either not controlled or did not parallel natural changes, and/or the studies lasted only for a short period of time. In the present study we have recorded daily energy intake and growth in a captive grey seal over a period of 3 years under semi-natural light conditions, and exposed important potential sources of error in experimentally estimating energy requirements of northern pinnipeds.
Many animals rely on stored energy through periods of high energy demand or low energy availability or both. A variety of mechanisms may be employed to attain and conserve energy for such periods. Wild grey seals demonstrate seasonal patterns of energy storage and foraging behaviour that appear to maximize the allocation of energy to reproduction-a period characterized by both high energy demand and low food availability. We examined seasonal patterns in resting rates of oxygen consumption as a proxy for metabolic rate (RMR) and body composition in female grey seals (four adults and six juveniles), testing the hypothesis that adults would show seasonal changes in RMR related to the reproductive cycle but that juveniles would not. There was significant seasonal variation in rates of resting oxygen consumption of adult females, with rates being highest in the spring and declining through the summer months into autumn. This variation was not related to changes in water temperature. Adults increased in total body mass and in fat content during the same spring to autumn period that RMR declined. RMR of juveniles showed no clear seasonal patterns, but did increase with increasing mass. These data support the hypothesis that seasonal variation in RMR in female grey seals is related to the high costs of breeding.
Energy requirements for maintenance and growth of captive harbour seals, Phoca vitulina
Canadian Journal of Zoology, 1990
Four captive harbour seals were fed with herring both at restricted and at ad libitum levels during 1985 to 1988. The maintenance requirement, calculated from the x-intercept of the regression, was 194 ± 71 kcal∙kg body weight−0.75∙day−1. Assuming that metabolizable energy is 82.8% of gross energy, the maintenance requirement is 161 kcal∙kg body weight−0.75∙day−1. There was no significant difference in maintenance requirement between individuals or between age classes, and neither was there any significant difference between seasons. The gross energy requirement of growth was 909 kcal/100 g.