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

Henderson, Angus F.; McMahon, Clive R.; Guinet, Christophe; Picard, Baptiste; Wotherspoon, Simon; Hindell, Mark A.

doi:10.3389/fmars.2020.517901

Cited by 10 publications

(14 citation statements)

References 77 publications

(97 reference statements)

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“…There is also evidence that seals on the Kerguelen Plateau experience higher levels of predation than those on the Antarctic Continental Shelf. Satellite tag failures, a proxy for at sea mortality, were higher for males on the Kerguelen Plateau (Henderson et al., 2020) than on the Antarctic Shelf. Further, changes in isotopic signatures with age suggests mortality rates of young males are higher on the Kerguelen Plateau than on the Antarctic Continental Shelf (Chaigne et al., 2013).…”

Section: Discussionmentioning

confidence: 99%

Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal

Hindell

McMahon

Jonsen

et al. 2021

Ecology and Evolution

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Partitioning resources is a key mechanism for avoiding intraspecific competition and maximizing individual energy gain. However, in sexually dimorphic species it is difficult to discern if partitioning is due to competition or the different resource needs of morphologically distinct individuals. In the highly dimorphic southern elephant seal, there are intersexual differences in habitat use; at Iles Kerguelen, males predominantly use shelf waters, while females use deeper oceanic waters. There are equally marked intrasexual differences, with some males using the nearby Kerguelen Plateau, and others using the much more distant Antarctic continental shelf (~2,000 km away). We used this combination of inter and intrasexual behavior to test two hypotheses regarding habitat partitioning in highly dimorphic species. (a) that intersexual differences in habitat use will not appear until the seals diverge in body size and (b) that some habitats have higher rates of energy return than others. In particular, that the Antarctic shelf would provide higher energy returns than the Kerguelen Shelf, to offset the greater cost of travel. We quantified the habitat use of 187 southern elephant seals (102 adult females and 85 subadult males). The seals in the two groups were the same size (~2.4 m) removing the confounding effect of body size. We found that the intersexual differences in habitat use existed before the divergence in body size. Also, we found that the amount of energy gained was the same in all of the major habitats. This suggests that the use of shelf habitats by males is innate, and a trade‐off between the need to access the large benthic prey available on shelf waters, against the higher risk of predation there. Intrasexual differences in habitat use are another trade‐off; although there are fewer predators on the Antarctic shelf, it is subject to considerable interannual fluctuations in sea‐ice extent. In contrast, the Kerguelen Plateau presents more consistent foraging opportunities, but contains higher levels of predation. Habitat partitioning in this highly dimorphic species is therefore the result of complex interplay of life history strategies, environmental conditions and predation pressure.

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Section: Discussionmentioning

confidence: 99%

Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal

Hindell

McMahon

Jonsen

et al. 2021

Ecology and Evolution

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“…Similarly, diagnostic data revealed that although there was some biofouling of tags, this was not the reason why data relay stopped. Biofouling of tags has been implicated as an Achilles heel of many satellite tracking studies, particularly in warmer waters where epibiont settlement and growth may be quicker (Hays & Hawkes, 2018), with this issue being much less acute in colder areas (Henderson et al, 2020). Painting tags with antifouling paint will certainly help to alleviate the issue of biofouling and is now widely advocated (Hays & Hawkes, 2018).…”

Section: Discussionmentioning

confidence: 99%

“…Over 10 years ago, it was shown how data relayed via the tags themselves might be used to assess the reasons for tag failure (Hays et al, 2007). Of the reasons why tags may stop relaying tracking data, animal mortality is perhaps the only one that has received much attention, with a number of studies across taxa including turtles, birds, fish, and mammals inferring mortality rates from satellite tagging data (Byrne et al, 2017;Hays et al, 2004;Henderson et al, 2020;Klaassen et al, 2014). However, there are a number of other reasons why data relay from satellite tags may stop, including the tag detaching, damage to the tag (the Argos antenna is often particularly vulnerable), biofouling, and battery exhaustion (Hays et al, 2007).…”

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confidence: 99%

Why do Argos satellite tags stop relaying data?

Hays

Laloë

Rattray

et al. 2021

Ecology and Evolution

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Satellite tracking of animals is very widespread across a range of marine, freshwater, and terrestrial taxa. Despite the high cost of tags and the advantages of long deployments, the reasons why tracking data from tags stop being received are rarely considered, but possibilities include shedding of the tag, damage to the tag (e.g., the aerial), biofouling, battery exhaustion, or animal mortality. We show how information relayed via satellite tags can be used to assess why tracking data stop being received. As a case study to illustrate general approaches that are broadly applicable across taxa, we examined data from Fastloc‐GPS Argos tags deployed between 2012 and 2019 on 78 sea turtles of two species, the green turtle ( Chelonia mydas ) and the hawksbill turtle ( Eretmochelys imbricata ). Tags transmitted for a mean of 267 days ( SD = 113 days, range: 26–687 days, median = 251 days). In 68 of 78 (87%) cases, battery failure was implicated as the reason why tracking data stopped being received. Some biofouling of the saltwater switches, which synchronize transmissions with surfacing, was evident in a few tags but never appeared to be the reason that data reception ceased. Objectively assessing why tags fail will direct improvements to tag design, setup, and deployment regardless of the study taxa. Assessing why satellite tags stop transmitting will also inform on the fate of tagged animals, for example, whether they are alive or dead at the end of the study, which may allow improved estimates of survival rates.

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“…The tag attachments to the seals did not affect their reproduction or survival patterns (McMahon et al 2008). Tracking data received from the tags, such as location and diving behaviour, were transmitted via the ARGOS satellite network (Myers et al 2006; Henderson et al 2020).…”

Section: Methodsmentioning

confidence: 99%

Dispersal of southern elephant seals (Mirounga leonina) from Davis Base, Antarctica: Combining population genetics and tracking data

Chua

McMahon

et al. 2021

Preprint

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Marine animals such as the southern elephant seal (Mirounga leonina) rely on a productive marine environment and are vulnerable to oceanic changes that can affect their reproduction and survival rates. Davis Base, Antarctica, acts as a moulting site for southern elephant seals that forage in Prydz Bay, but the genetic diversity and natal source populations of these seals has not been characterized. Determining the genetic diversity of moulting populations like this one provides essential information on seal dispersal, inter-population mixing, and foraging behaviours. In this study, we combined genetic and animal tracking data on these moulting seals to identify levels of genetic diversity, natal source population, and movement behaviours during foraging and haul-out periods. Using mitochondrial sequence data, we identified two major breeding lineages of seals at Davis Base. We found that the majority of the seals originated from breeding stocks within the South Atlantic Ocean and South Indian Ocean. One seal was grouped with the Macquarie Island breeding stock (South Pacific Ocean). The Macquarie Island population, unlike the other two stocks, is decreasing in size. Tracking data revealed long-distance foraging activity of the Macquarie Island seal around Crozet Islands. We speculate that changes to the Antarctic marine environment have resulted in a shift in foraging and dispersal strategies, which subsequently affects seal population growth rates. These findings have implications for conservation management plans aimed at improving the population status of the southern elephant seal.

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

Cited by 10 publications

References 77 publications

Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal

Inter‐ and intrasex habitat partitioning in the highly dimorphic southern elephant seal

Why do Argos satellite tags stop relaying data?

Dispersal of southern elephant seals (Mirounga leonina) from Davis Base, Antarctica: Combining population genetics and tracking data

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