Harbor seals are an abundant predator in the Salish Sea, with increasing in abundance over the last several decades only recently showing signs of leveling. They primarily feed on fish such as groundfish (e.g. rockfish), forage fish (e.g. herring) and salmonids and the seals themselves are an important prey item in the diet of the mammal-eating Bigg’s killer whales. In parallel to our health studies of endangered Southern Resident killer whales, SR3 started a pilot project in May 2019 to measure growth and body condition of harbor seals in the San Juan Islands using aerial photogrammetry with a small, non-invasive drone. Over the long term, these measures will allow us to identify changes in the Salish Sea ecosystem by monitoring the health of another upper-level predator.
In early May 2020, we recently started the second year of monitoring, with one photogrammetry flight already successful in imaging over 150 individuals conducted to date. The initial aims of this study include validation that: 1) individual harbor seals can be identified from high altitude (>100ft) aerial images using spotting patterns on their pelage, 2) individuals can be re-identified across weeks and possibly across years, and 3) estimates of body length and condition can be obtained from these individuals and monitored over time. There were a large number of pregnant females identified in the images collected, as would be expected as we approach the peak of pupping season.
Aerial image of an aggregation of harbor seals on a tidal haulout in the San Juan Islands, WA collected in May 2020. Analyses are underway to identify individual seals, with the objective of monitoring body condition and growth at an individual level through the collection of quantitative measurement. Image obtained form an unmanned hexacopter that was flown >150ft above the seals under NMFS permit #19091.