Salish Sea Marine Survival Project

62 Figure 2. Estimates of the impacts of seal predation on Coho and Chinook based on scat analyses for 2012-2014 from a number of estuary sites in the Strait of Georgia. These values are under review. Figure provided by Ben Nelson. Figure 3. Age-specific salmon proportions in the diets of harbour seals from estuary and non-estuary sites in the Strait of Georgia in 2016: Left graph, proportions for juvenile salmon in spring (April-July); Right graph, proportions for adult salmon in fall (August- November). Figure provided by Sheena Majewski, DFO. HOW? Three key studies have been carried out: 1. Scat analysis 2012-2018: Researchers have been assessing the impact of seals on salmonids in the Strait of Georgia by counting the number of predators, quantifying predation events from visual observations and determining diets from morphological and genetic analysis of fecal samples. Initial studies were done at a few sites, including Cowichan Bay and a small number of estuaries. Data collected 2012- 2014 were subse- quently used in a model developed by PhD student Ben Nelson to test the impact of pinnipeds on Pacific Salmon in the Strait of Georgia (Figure 2). Since 2015, scat collections have been expanded to a number of non-estuary haul-outs in the Strait, to provide a more realistic estimate of overall impacts of predation. One of the criticisms of the seal diet work was that the DNA method used had not been validated or compared with other techniques. Thus, 2016 estimates of diet derived from DNA meta-barcoding and hard-part frequen- cy-of-occurrence were compared with a third method, biomass reconstruction. 2. PIT tag study 2015: Researchers directly measured predation near Big Qualicum River by capturing 20 adult harbour seals and equipping them with a satel- lite-linked PIT tag scanner that is designed to quantify the number of PIT tagged fish ingested by harbour seals. PIT tags were implanted in 36,900 Coho smolts at the Big Qualicum hatchery more than one month prior to the release of 381,800 total Coho smolts in early May 2015. The Pit-Tag Readers were affixed to the heads of harbour seals, and the internal PIT tag scanner was activated when seals attempted to capture fish (head- strikes), thereby detecting the presence of PIT tagged fish in the mouths of the seals. PIT tag detections were logged by the instrument and then transmitted via the ARGOS satellite network, providing the number consumed and the unique PIT tag code. Estuary Non-Estuary 0 1 2 3 4 SEAL DIET % 0.4 0.8 Fall 2.4% 1.4% SPRING (Apr – May) Juveniles Estuary Non-Estuary 0 10 20 30 40 SEAL DIET % 35% 9% FALL (Aug – Nov) Adults COHO 47% smolts lost (95% CI: 44-52%) Peak mortality in April and May 5-fold increase since 1970s 26-45K adults lost annually 40% smolts lost (95% CI: 32-45%) Peak mortality in July 61-83K adults lost annually CHINOOK Estuary Non-Estuary 0 1 2 3 4 SEAL DIET % 0.4 0.8 Fall 2.4% 1.4% SPRING (Apr – May) Juveniles Estuary Non-Estuary 0 10 20 30 40 SEAL DIET % 35% 9% FALL (Aug – Nov) Adults

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