Natal and adult dispersal among four elephant seal colonies

Dispersal plays a key role fostering recovery of endangered species because reoccupying a former range can only happen via dispersal. The northern elephant seal (Mirounga angustirostris) is a large, marine predator that was nearly exterminated in the 19th century by over-hunting. Once they were afforded protection from harvest, the species spread from a single remnant colony to reoccupy its former range. As colonies in central California were reestablished during the 1960s-1990s, tagged seals documented northward dispersal from southern California. The central California colonies are now large and well-established, and tagging programs at the four northernmost colonies allowed us to quantify the extent and direction of dispersal. Natal dispersal by females was highest from the southernmost colony at Piedras Blancas, where 61% of surviving females emigrated to breed. Dispersal from the other three colonies was much lower, 5.6% from SE Farallon Island, 10.3% from Ano Nuevo, and 16.6% from Point Reyes. Adult dispersal of females, after breeding, was rare, with an annual rate < 2%. Juvenile dispersal is thus frequent in elephant seals, highest northward but also occurring southward, suggesting that continued expansion to new colonies throughout the west coast is probable.

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Mercury offloaded in Northern elephant seal hair affects coastal seawater surrounding rookery

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1506520112 ◽

2015 ◽

Vol 112 (39) ◽

pp. 12058-12062 ◽

Cited By ~ 12

Author(s):

Jennifer M. Cossaboon ◽

Priya M. Ganguli ◽

A. Russell Flegal

Keyword(s):

Marine Mammal ◽

Total Mercury ◽

Elephant Seal ◽

Food Chains ◽

Mirounga Angustirostris ◽

Northern Elephant Seal ◽

Central California ◽

Marine Predator ◽

Marine Food Chain ◽

Marine Food

Methylmercury (MeHg) is a potent neurotoxin that is biomagnified approximately 1–10 million-fold in aquatic carnivores such as the Northern elephant seal (Mirounga angustirostris), whose excreta and molted pelage, in turn, constitute a source of environmental MeHg contamination at the base of marine food chains. The potential for this top-down contamination is greatest in coastal areas with productive marine ecosystems that provide ideal habitats for large marine mammal colonies that can number in the thousands. This recycling of MeHg was evidenced by comparing total mercury (HgT) and MeHg concentrations in seawater, and HgT in molted pelage of M. angustirostris, at the Año Nuevo State Reserve pinniped rookery with concentrations at neighboring coastal sites in Central California. Seawater MeHg concentrations around the rookery (average = 2.5 pM) were markedly higher than those at the comparison coastal sites (average = 0.30 pM), and were as high as 9.5 pM during the M. angustirostris molting season. As a consequence, excreta and molts from this marine mammal colony, and presumably other marine predator populations, constitute a major source of MeHg at the base of the local marine food chain.

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In-air hearing in Hawaiian monk seals: implications for understanding the auditory biology of Monachinae seals

Journal of Comparative Physiology A ◽

10.1007/s00359-021-01498-y ◽

2021 ◽

Author(s):

Brandi Ruscher ◽

Jillian M. Sills ◽

Beau P. Richter ◽

Colleen Reichmuth

Keyword(s):

Marine Mammals ◽

Elephant Seal ◽

Critical Ratio ◽

Mirounga Angustirostris ◽

Northern Elephant Seal ◽

Hearing Ability ◽

Highly Sensitive ◽

Monk Seals ◽

Management And Conservation ◽

Hearing Abilities

AbstractThe auditory biology of Monachinae seals is poorly understood. Limited audiometric data and certain anatomical features suggest that these seals may have reduced sensitivity to airborne sounds compared to related species. Here, we describe the in-air hearing abilities of a Hawaiian monk seal (Neomonachus schauinslandi) trained to participate in a psychophysical paradigm. We report absolute (unmasked) thresholds for narrowband signals measured in quiet conditions across the range of hearing and masked thresholds measured in the presence of octave-band noise at two frequencies. The behavioral audiogram indicates a functional hearing range from 0.1 to 33 kHz and poor sensitivity, with detection thresholds above 40 dB re 20 µPa. Critical ratio measurements are elevated compared to those of other seals. The apparently reduced terrestrial hearing ability of this individual—considered with available auditory data for a northern elephant seal (Mirounga angustirostris)—suggests that hearing in Monachinae seals differs from that of the highly sensitive Phocinae seals. Exploration of phylogenetic relationships and anatomical traits support this claim. This work advances understanding of the evolution of hearing in amphibious marine mammals and provides updated information that can be used for management and conservation of endangered Hawaiian monk seals.

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