Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus)

Foraging theory predicts that animals should proportionately increase their food intake to compensate for reduced food energy content and (or) prey availability. However, the theoretical intake levels will, at some point, exceed the digestive capacity of the predator. We tested the ability of Steller sea lions, Eumetopias jubatus (Schreber, 1776), to compensate for short-term changes in prey energy density and availability, and quantified the maximum amount of food a young sea lion could consume. Five 1–2-year-old captive Steller sea lions were offered either herring (high energy) or capelin (low energy) each day or every second day. When prey were available on a daily basis, the sea lions compensated for differences in the energy content of herring and capelin by consuming sufficient quantities of each (8.3 vs. 14.0 kg·d–1, respectively) to maintain equivalent gross energy intakes. When herring was available only on alternate days, the sea lions increased their consumption by 52% to 11.5 kg·d–1, which was not sufficient to maintain an average gross intake equal to that maintained when herring was available every day. When capelin was available only on alternate days, some animals increased their intake for a few days, but average intake (15.2 kg·d–1) was far below levels observed during daily feeding. Generally, the sea lions appeared to reach their digestive limit at a level equivalent to 14%–16% of their body mass. Our findings suggest that Steller sea lions can alter their food intake in response to short-term changes in prey quality or availability, but that these variables can quickly combine to necessitate food intake levels that exceed the physiological digestive capacities of young animals.

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Metabolic Effects of Low‐Energy Diet on Steller Sea Lions,Eumetopias jubatus

Physiological and Biochemical Zoology ◽

10.1086/316705 ◽

1999 ◽

Vol 72 (6) ◽

pp. 723-731 ◽

Cited By ~ 32

Author(s):

David A. S. Rosen ◽

Andrew W. Trites

Keyword(s):

Low Energy ◽

Metabolic Effects ◽

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Sea Lions ◽

Low Energy Diet

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Pollock and the decline of Steller sea lions: testing the junk-food hypothesis

Canadian Journal of Zoology ◽

10.1139/z00-060 ◽

2000 ◽

Vol 78 (7) ◽

pp. 1243-1250 ◽

Cited By ~ 73

Author(s):

David AS Rosen ◽

Andrew W Trites

Keyword(s):

Body Mass ◽

Energy Content ◽

Gulf Of Alaska ◽

Aleutian Islands ◽

Net Energy ◽

Junk Food ◽

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Sea Lions ◽

Gross Energy

The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and the Aleutian Islands may be the result of them eating too much pollock (a gadid fish) instead of a more balanced and diverse diet containing fattier fishes, such as herring or sandlance. We sought to test this junk-food hypothesis by feeding six captive Steller sea lions (ages 0.9-4.5 years) only pollock or herring. All sea lions gained mass while eating herring. However, eating only pollock for short periods (11-23 d) caused the study animals to lose an average of 6.5% of their initial body mass (0.6 kg/d) over an average feeding trial of 16 d (initial mass averaged 125 kg). The animals were allowed to eat as much pollock as they wanted but did not increase their food intake to compensate for the low energy they were receiving. The sea lions showed progressive metabolic depression while losing body mass on a pollock-only diet. The loss of body mass while eating pollock was due to the lower gross energy content of pollock versus herring, the higher cost of digesting pollock, and the increased energy loss from digesting the larger quantity of fish needed to compensate for the lower energy content of pollock. Thus, our sea lions would have had to eat 35-80% more pollock than herring to maintain similar net energy intakes. Results from our captive-feeding studies are consistent with the junk-food hypothesis and have serious implications for Steller sea lions that have been eating primarily pollock in the Gulf of Alaska and the Aleutian Islands.

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Three-dimensional photogrammetry as a tool for estimating morphometrics and body mass of Steller sea lions (Eumetopias jubatus)

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f07-014 ◽

2007 ◽

Vol 64 (2) ◽

pp. 296-303 ◽

Cited By ~ 24

Author(s):

Jason N Waite ◽

Wendy J Schrader ◽

Jo-Ann E Mellish ◽

Markus Horning

Keyword(s):

Body Mass ◽

Standard Length ◽

Three Dimensional ◽

Body Volume ◽

Multiple Time ◽

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Sea Lions ◽

3D Photogrammetry ◽

Measured Mass

A technique was developed to estimate morphometrics and body mass of Steller sea lions (Eumetopias jubatus) using three-dimensional (3D) photogrammetry. 3D photogrammetry reduces many of the problems associated with camera and body position encountered with two-dimensional photogrammetric techniques, allowing body mass estimation of free-ranging, active sea lions, without sedation, heavy weighing equipment, and disturbance. 3D computer wireframes of 53 Steller sea lions of various age classes were generated from multiple time-synchronous digital photos and used to estimate length, girth, and volume. Average estimates of standard length and axillary girth were within ±2.5% and ±4.0% of physically measured dimensions, respectively. Average estimates of standard length and axillary girth using only wireframes based on ideal body postures were within ±1.7% and ±3.1% of physically measured dimensions, respectively. Regressions of physically measured mass on photogrammetrically estimated body volume yielded a predictive model. Body mass estimates using this model were on average within 9.0% (95% confidence interval = ±1.7%) of the physically measured mass. This technique was also successfully applied to reptiles and fish.

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Evidence of partial deferment of digestion during diving in Steller sea lions (Eumetopias jubatus)

Journal of Experimental Marine Biology and Ecology ◽

10.1016/j.jembe.2015.04.017 ◽

2015 ◽

Vol 469 ◽

pp. 93-97 ◽

Cited By ~ 10

Author(s):

David A.S. Rosen ◽

Carling D. Gerlinsky ◽

Andrew W. Trites

Keyword(s):

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Sea Lions

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Diet composition of Steller sea lions (Eumetopias jubatus) in Frederick Sound, southeast Alaska: a comparison of quantification methods using scats to describe temporal and spatial variabilities

Canadian Journal of Zoology ◽

10.1139/cjz-2014-0292 ◽

2015 ◽

Vol 93 (5) ◽

pp. 361-376 ◽

Cited By ~ 7

Author(s):

D.J. Tollit ◽

M.A. Wong ◽

A.W. Trites

Keyword(s):

Pacific Salmon ◽

Biomass Energy ◽

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Southeast Alaska ◽

Merluccius Productus ◽

Sea Lions ◽

Sampling Protocols ◽

Dietary Indices

We compared eight dietary indices used to describe the diet of Steller sea lions (Eumetopias jubatus (Schreber, 1776)) from 2001 to 2004 in Frederick Sound, southeast Alaska. Remains (n = 9666 items) from 59+ species categories were identified from 1684 fecal samples (scats) from 14 collection periods. The most frequently occurring prey were walleye pollock (Theragra chalcogramma (Pallas, 1814) = Gadus chalcogrammus Pallas, 1814; 95%), Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847; 30%), Pacific hake (Merluccius productus (Ayres, 1855); 29%), and arrowtooth flounder (Atheresthes stomias (Jordan and Gilbert, 1880) = Reinhardtius stomias (Jordan and Gilbert, 1880); 21%). These species, along with Pacific salmon (genus Oncorhynchus Suckley, 1861) and skate (genus Raja L., 1758), accounted for 80%–90% of the reconstructed biomass and energy contribution, with pollock contributing 37%–60%. Overall, 80% of fish were 14–42 cm long and mainly pelagic, though 40% of scats contained benthic-associated prey. Steller sea lions switched from adult pollock to strong cohorts of juvenile pollock, and took advantage of spawning concentrations of salmon in autumn and herring in late spring and summer, as well as a climate-driven increase in hake availability. Observed temporal and site differences in diet confirm the need for robust long-term scat sampling protocols. All major indices similarly tracked key temporal changes, despite differences in occurrence and biomass-energy-based diet estimates linked to prey size and energy-density effects and the application of correction factors.

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Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

Canadian Journal of Zoology ◽

10.1139/z03-008 ◽

2003 ◽

Vol 81 (2) ◽

pp. 340-348 ◽

Cited By ~ 35

Author(s):

Linda L Milette ◽

Andrew W Trites

Keyword(s):

Prey Availability ◽

A Priori ◽

Population Decline ◽

Perinatal Period ◽

Eumetopias Jubatus ◽

Steller Sea Lions ◽

Sea Lions ◽

First Feeding ◽

Attendance Patterns ◽

The Mean

Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

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