The long road to recovery: consequences of harassment of Guadalupe fur seals pups

The wide-eyed, whiskered Guadalupe fur seal species is on the road to recovery after being hunted to near extinction over a century ago. Guadalupe Island, Mexico, is the only former colony the species has managed to re-establish, and was the exclusive breeding site for the species until seals were recently observed breeding at a second historic breeding site, San Benito Archipelago. Immature male seals, who are often unable to compete with adults for breeding territories, make up the majority of seals that left the growing Guadalupe Island colony to establish themselves at San Benito. Breeding activity at the San Benito site inspired hope for the species’ recovery, but researchers were shocked by the disturbing behaviour they observed from immature males that may jeopardize this progress.

In a recent publication, University of British Columbia researchers documented abduction and sexual coercion of seal pups by immature male seals at San Benito. While this behaviour is expected to help immature males gain experience for future reproductive success, the frequency of harassment was completely unexpected. “The extent of harassment we observed at San Benito Island is far higher than has been reported for any other species,” says Dr. Andrew Trites, professor and Director the Marine Mammal Research Unit (MMRU) at the Institute for the Oceans and Fisheries. New colonies like San Benito have a higher proportion of immature male seals, which could explain the frequency of harassment. “There are not yet enough older males to provide the social structure needed to protect the females and pups,” explains Trites.

Harassment threatens species recovery

Despite the potential reproductive benefits of this behaviour, it could ultimately hinder the recovery of the species. Pups may be physically traumatized by harassment, and starved if separated from their mothers for long periods. “We plan to continue studying the sexual coercion of pups, as we suspect this behaviour is contributing to increased pup mortality, which may be slowing the recovery process of the population,” says Dr. Claudia Hernández-Camacho, UBC Affiliate Professor with Mexico’s Centro Interdisciplinario de Ciencias Marinas-IPN. Beyond harming pups, harassment by immature males often disrupts female nursing. These disruptions may influence females to breed at the well-established colony at Guadalupe Island the following year, slowing the establishment of the colony at San Benito.

Re-establishing former breeding sites like San Benito supports the recovery and secures the future of Guadalupe fur seals. “The presence of multiple breeding colonies contributes to a species’ resilience against stochastic factors, such as environmental variability, low genetic diversity, and catastrophic events,” says Hernández-Camacho. Trites echoes the importance of establishing former colonies: “Having all the breeding seals living on a single island—Guadalupe Island—is like putting all your eggs in one basket. One accident, one oil spill, or one extreme heat wave could wipe them all out.” While seals were first observed at San Benito over 30 years ago, the breeding colony still remains to be fully established. Dr. Hernández-Camacho and Dr. Trites suspect abduction and sexual coercion of seal pups and disruption of mothers nursing at San Benito is slowing the recovery and re-establishment of the species.

The future of the Guadalupe fur seal

Despite the challenges the species has faced, there has been an increasing number of seals born each year at San Benito, indicating that the former breeding site is on its way to becoming an established colony. “We now appreciate that the road to recovery is a much longer process than we ever realized,” says Trites, whose work with Dr. Hernández-Camacho is continuing to improve understanding of the role of abduction and sexual coercion in this process. As researchers continue to monitor the slow but steady progress at San Benito, the future of the Guadalupe fur seal remains uncertain, but there are reasons for optimism. “The establishment of two more resting colonies within the Gulf of California gives us great hope for the recovery of this species, which once faced extinction,” says Hernández-Camacho.

Abduction and sexual coercion of Guadalupe fur seal pups, was published in Marine Mammal Science.

Tags: Andrew Trites, birth, Claudia Hernández-Camacho, Guadalupe fur seals, harassment, Mexico, MMRU, seals