Effect of climate variability on weaning mass in a declining population of southern elephant seals Mirounga leonina

Abstract

Details of the environmental variables used to explain the weaning mass of southern elephant seal pups. The variables are divided into global and regional variables Global Climate Modes: The high latitudes of the Southern Hemisphere experience large-scale, sub-decadal climatic variation as a result of a number of global modes of atmospheric variability present in the region, including: Southern Annular Mode: The Southern Annular Mode (SAM, or Antarctic Oscillation) is the dominant mode of extra-tropical atmospheric variability in the Southern Hemisphere, that acts over intra-seasonal to inter-annual timescales (Thompson & Wallace 2000, Lovenduski & Gruber 2005). The SAM is characterized by synchronous atmospheric pressure anomalies of opposite sign between the mid-and high-latitudes that drives the northsouth movement of a circumpolar band of strong sub-polar westerly winds (Stammerjohn et al. 2008b). During positive SAM (+SAM) phases, positive pressure anomalies over the mid-latitudes and negative pressure anomalies over the high-latitudes drive the northward expansion and weakening of the sub-polar westerlies, while the opposite is true for negative phases of the SAM, with the subpolar westerlies contracting poleward and subsequently strengthening (-SAM; Stammerjohn et al. 2008a).

Density-dependent effects on reproductive output in a capital breeding carnivore, the northern elephant seal (Mirounga angustirostris)

“…Southern elephant seals exhibit a stronger relationship between reproductive investment and ocean conditions [24,26,[56][57][58], although maternal traits and colony conditions still show similar relationships to weaning mass as were found here [26,46]. Further comparisons between the species and between colonies within each species would provide insight into the interaction between population dynamics and the environment.…”

Decadal changes in blood δ 13 C values, at-sea distribution, and weaning mass of southern elephant seals from Kerguelen Islands

“…Antarctic versus sub-Antarctic habitat) are of critical importance for their pups' survival rate, and ultimately for the future of the population [44,75,76]. The influence of some abiotic factors such as sea ice extent and chlorophyll-a concentration on pup weaning mass has been suggested for SES breeding on Kerguelen, Macquarie, and Marion Islands [23,32,77–79]. A similar strong positive relationship was found between annual primary production in an Antarctic polynya and pup production in Weddell seals ( Leptonychotes weddellii ) [80].…”

Inferring Variation in Southern Elephant Seal At-Sea Mortality by Modelling Tag Failure

“…The Southern Annular Mode (SAM) is a large-scale climatic index (Lovenduski and Gruber, 2005) which influences variability in annual foraging success of a suite of Southern Ocean marine predators (Trathan et al, 2007;Bost et al, 2015), including southern elephant seals (Oosthuizen et al, 2011). For southern elephant seals, female fecundity (van den Hoff et al, 2014), pup survival (Clausius et al, 2017), and pup weaning mass (McMahon et al, 2015(McMahon et al, , 2017Oosthuizen et al, 2015) are all positively correlated with the SAM. Accordingly, if the failure rate differs between years of contrasting SAM, and we assume mechanical tag failure rate is independent of SAM, these differences could be attributed to a difference in relative at-sea mortality among years ( Table 1).…”

“…The hazards plot (B) suggests an increased hazard associated with seals deployed in negative SAM years (red points). resource allocation (McMahon et al, 2017) and reproductive output (van den Hoff et al, 2014;McMahon et al, 2015;Oosthuizen et al, 2015;Clausius et al, 2017) are compromised by poor foraging conditions. The cost of reproduction to females is high, and they lose an average of 35% of their mass over the 24-day lactation period (Fedak et al, 1996).…”

“…At-sea mortality is thought to be largely due to starvation (Pistorius et al, 2011) dictated by an individual's ability to forage successfully, or to predation (Guinet et al, 1999). Climate-driven inter-annual variation on the availability of prey has a measurable effect on annual survival rates and reproductive output (van den Hoff et al, 2014;Oosthuizen et al, 2015;Clausius et al, 2017;McMahon et al, 2017McMahon et al, , 2015 and we may see this reflected in tag failure rates. Long-term changes to Southern Ocean foraging conditions are linked to population trends (Hindell et al, 2017), so identifying when and where southern elephant seals die during their annual life cycle would provide valuable insight into the factors that influence mortality.…”