Abundance and trends of harbor seals (Phoca vitulina richardii) in Alaska, 1996-2023

Abstract

Pacific harbor seals (Phoca vitulina richardii) were surveyed throughout their range along Alaska coasts over a 28-year period. Twelve management stocks, delineated on the basis of evidence for demographic independence, were monitored for abundance and trends. We employed a two-stage Bayesian hierarchical analysis that integrated aerial survey counts with satellite-linked bio-logger haul-out timelines to account for the proportion of seals in the water and not visible to survey observers and cameras. Overall, harbor seals were abundant (201,122 seals in 2023) but, during the span of our study the population (stock) trends varied. The first half of our study was characterised primarily by growth, with a peak abundance of approximately 225,000 seals in 2015. Since then trends have been variable, with some stocks (e.g., Bristol Bay) showing continued growth while others (e.g. Prince William Sound, South Kodiak) declined. The recent regional declines coincided with observed climate anomalies (e.g., marine heatwaves) and the rapid retreat of tidewater glaciers. Our results provide a basis for managing this species in Alaska, which is protected under the Marine Mammal Protection Act; a vital nutritional and cultural resource for Alaska Native communities; and an important sentinel of change in the Northeast Pacific marine ecosystem.

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BibTeX RIS

BibTeX

@misc{boveng2026abundance,
  title = {{Abundance and trends of harbor seals (Phoca vitulina richardii) in Alaska, 1996-2023}},
  author = {P. L. Boveng and G. M. Brady and M. F. Cameron and C. L. Christman and S. P. Dahle and L. M. Hiruki-Raring and J. K. Jansen and S. M. Koslovsky and J. M. London and B. T. McClintock and R. A. Montgomery and E. E. Moreland and E. L. Richmond and M. A. Simpkins and J. M. Ver Hoef and S. M. Walcott and D. E. Withrow and J. N. Womble and K. M. Yano and H. L. Ziel},
  howpublished = {bioRxiv},
  year = {2026},
  month = sep,
  doi = {10.64898/2026.09.02.748977},
  url = {https://www.biorxiv.org/content/10.64898/2026.09.02.748977v1},
  note = {CC0},
}

RIS

TY  - UNPB
TI  - Abundance and trends of harbor seals (Phoca vitulina richardii) in Alaska, 1996-2023
AU  - P. L. Boveng
AU  - G. M. Brady
AU  - M. F. Cameron
AU  - C. L. Christman
AU  - S. P. Dahle
AU  - L. M. Hiruki-Raring
AU  - J. K. Jansen
AU  - S. M. Koslovsky
AU  - J. M. London
AU  - B. T. McClintock
AU  - R. A. Montgomery
AU  - E. E. Moreland
AU  - E. L. Richmond
AU  - M. A. Simpkins
AU  - J. M. Ver Hoef
AU  - S. M. Walcott
AU  - D. E. Withrow
AU  - J. N. Womble
AU  - K. M. Yano
AU  - H. L. Ziel
PY  - 2026
DA  - 2026/09/02
PB  - bioRxiv
DO  - 10.64898/2026.09.02.748977
UR  - https://www.biorxiv.org/content/10.64898/2026.09.02.748977v1
AB  - Pacific harbor seals (Phoca vitulina richardii) were surveyed throughout their range along Alaska coasts over a 28-year period. Twelve management stocks, delineated on the basis of evidence for demographic independence, were monitored for abundance and trends. We employed a two-stage Bayesian hierarchical analysis that integrated aerial survey counts with satellite-linked bio-logger haul-out timelines to account for the proportion of seals in the water and not visible to survey observers and cameras. Overall, harbor seals were abundant (201,122 seals in 2023) but, during the span of our study the population (stock) trends varied. The first half of our study was characterised primarily by growth, with a peak abundance of approximately 225,000 seals in 2015. Since then trends have been variable, with some stocks (e.g., Bristol Bay) showing continued growth while others (e.g. Prince William Sound, South Kodiak) declined. The recent regional declines coincided with observed climate anomalies (e.g., marine heatwaves) and the rapid retreat of tidewater glaciers. Our results provide a basis for managing this species in Alaska, which is protected under the Marine Mammal Protection Act; a vital nutritional and cultural resource for Alaska Native communities; and an important sentinel of change in the Northeast Pacific marine ecosystem.
ER  -

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