Reproductive performance of a tropical apex predator in an unpredictable habitat

Kalberer, Stephanie; Meise, Kristine; Trillmich, Fritz; Krüger, Oliver

doi:10.1007/s00265-018-2521-7

Cited by 14 publications

(9 citation statements)

References 98 publications

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“…Our estimates of peak reproductive output in Steller sea lions in Southeast Alaska were moderately high compared to those for other otariids. Our estimates were similar to published estimates for subantarctic fur seals, Arctocephalus tropicalis, on Amsterdam Island (0.721 at age 12;Dabin et al, 2004) and New Zealand fur seals, Arctocephalus forsteri, at Kangaroo Island (0.60-0.70 at age 8+;McKenzieet al, 2007), and much higher than the endangered Galapagos sea lion, Zalophus wollebaeki (0.40-0.48 at ages 6+;Kalberer et al, 2018). In contrast, our estimates at peak ages were lower than published estimates for the California sea lion, Zalophus californianus (0.77-0.80;Hernández-Camacho et al, 2008;Melin et al, 2012), the endangered New Zealand Sea Lion, Phocarctos hookeri (~0.75 to 0.88 at age 7+;Childerhouse et al, 2010) and the Antarctic fur seal, Arctocephalus gazella (0.80 at ages 7-9 at Bird Island;Lunn et al, 1994; 0.90 at ages 8-16 at Livingston Island;Schwarz et al, 2013).Although the combined survival probabilities and reproductive output was sufficient for population stability or growth in SoutheastF I G U R E 5 Annual variation in the proportion of female Steller sea lions (a) With-Pup or (b) With-Juvenile in Southeast Alaska, 2005-2019.…”

supporting

confidence: 89%

Age‐specific reproduction in female Steller sea lions in Southeast Alaska

Hastings,

Jemison,

Pendleton

et al. 2023

Ecology and Evolution

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Age‐, region‐, and year‐specific estimates of reproduction are needed for monitoring wildlife populations during periods of ecosystem change. Population dynamics of Steller sea lions (Eumetopias jubatus) in Southeast Alaska varied regionally (with high population growth and survival in the north vs. the south) and annually (with reduced adult female survival observed following a severe marine heatwave event), but reproductive performance is currently unknown. We used mark‐resighting data from 1006 Steller sea lion females marked as pups at ~3 weeks of age from 1994 to 1995 and from 2001 to 2005 and resighted from 2002 to 2019 (to a maximum age of 25) to examine age‐, region‐, and year‐specific reproduction. In the north versus the south, age of first reproduction was earlier (beginning at age 4 vs. age 5, respectively) but annual birth probabilities of parous females were reduced by 0.05. In an average year pre‐heatwave, the proportion of females with pup at the end of the pupping season peaked at ages 12–13 with ~0.60/0.65 (north/south) with pup, ~0.30/0.25 with juvenile, and ~0.10 (both regions) without a dependent. In both regions, reproductive senescence was gradual after age 12: ~0.40, 0.40, and 0.20 of females were in these reproductive states, respectively, by age 20. Correcting for neonatal mortality, true birth probabilities at peak ages were 0.66/0.72 (north/south). No cost of reproduction on female survival was detected, but pup production remained lower (−0.06) after the heatwave event, which if sustained could result in population decline in the south. Reduced pup production and greater retention of juveniles during periods of poor prey conditions may be an important strategy for Steller sea lions in Southeast Alaska, where fine‐tuning reproduction based on nutritional status may improve the lifetime probability of producing pups under good conditions in a variable and less productive environment.

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supporting

confidence: 89%

Age‐specific reproduction in female Steller sea lions in Southeast Alaska

Hastings,

Jemison,

Pendleton

et al. 2023

Ecology and Evolution

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“…Since 2012, counts have followed a standardized method based on the management plan for Galapagos sea lion’s conservation 29 . As animal counts for 2018 remain close to that recorded in 2001 and that the average age of reproducing individuals is ~ 10 years with a typical lifespan ≥ of 18 years 47 , the population may have been relatively stable over the past 20 years. If so, this suggests that a population reduction of 50% is maintained in the last four generations (1978–2018), which would ratify its classification as an endangered species 27 .…”

Section: Discussionmentioning

confidence: 60%

“…The northern region is characterized by having a slight influence of the South Equatorial Current and Panama Bight Cyclonic Gyre that causes a low marine production 32 , while the central region is considered a mixing area 33 . Both conditions limit the resilience of GSL females since after anomalous oceanographic events (such as El Niño) they usually need between one and two years to regain their reproductive synchrony 47 , 72 . While the upwellings of the western region 33 , and the greater abundance of females in the southeast region 10 could compensate or facilitate the generation of new cohorts.…”

Section: Discussionmentioning

confidence: 99%

Declines and recovery in endangered Galapagos pinnipeds during the El Niño event

Páez‐Rosas

Torres

Espinoza

et al. 2021

Sci Rep

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Currently, the Galapagos sea lion (GSL, Zalophus wollebaeki) and Galapagos fur seal (GFS, Arctocephalus galapagoensis) are among the most important endemic species for conservation in the Galapagos Archipelago. Both are classified as “Endangered” since their populations have undergone drastic declines over the last several decades. In this study we estimated the abundance of both otariids, and their population trends based using counts conducted between 2014 and 2018 in all their rookeries, and we analyzed the influence of environmental variability on pup production. The GSL population size in 2018 in the archipelago was estimated to be between 17,000 to 24,000 individuals and has increased at an average annual rate of 1% over the last five years after applying correction factors. The highest number of GSL counted in the archipelago was in 2014 followed by a population decline of 23.8% in 2015 that was associated with the El Niño event that occurred during that year. Following this event, the population increased mainly in the northern, central and southeastern rookeries. The GSL pup abundance showed a decreasing trend with the increase in intensity of the El Niño. The GFS population in 2018 was counted in 3,093 individuals and has increased at an annual rate of 3% from 2014 to 2018. A high number of GFS counted in 2014 was followed by a population decrease of 38% in 2015, mainly in the western rookeries. There was interannual population fluctuations and different growth trends among regions of the archipelago. GSL and GFS pup abundance has a strong decreasing tendency with the increase in the subthermocline temperature (ST) and the El Niño 1 + 2 index. Our results provide evidence that both species are highly vulnerable to periodic oceanographic-atmospheric events in the Galapagos Archipelago which impact prey abundance and the flow of energy in the unique Galapagos ecosystem.

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“…This pattern was seen regardless of individual differences in background energy expenditures (Figure 4). Previous work has demonstrated that female seals may adjust their reproductive output between years, when faced with changing environmental conditions prior to the lactation period, in order to maximize lifetime reproductive output (Bowen et al, 2015; Desprez et al., 2018; Kalberer, Meise, Trillmich, & Krüger, 2018; McMahon et al., 2016; Pomeroy et al., 1999; Smout et al., 2020), but research has yet to reveal the mechanism for terminating lactation in grey seals (e.g. by investigating metabolite trends leading up to weaning; Mellish & Iverson, 2001; Watson, Pomeroy, Al‐Tannak, & Kennedy, 2020).…”

Section: Discussionmentioning

confidence: 99%