Using Satellite Tracking and Isotopic Information to Characterize the Impact of South American Sea Lions on Salmonid Aquaculture in Southern Chile

Abstract

Apex marine predators alter their foraging behavior in response to spatial and/or seasonal changes in natural prey distribution and abundance. However, few studies have identified the impacts of aquaculture that represents a spatially and temporally predictable and abundant resource on their foraging behavior. Using satellite telemetry and stable isotope analysis we examined the degree of spatial overlap between the South American sea lion (SASL) and salmon farms, and quantify the amount of native prey versus farmed salmonids in SASL diets. We instrumented eight SASL individuals with SRDL-GPS tags. Vibrissae, hair and skin samples were collected for δ13C and δ15N analyses from five of the tagged individuals and from four males captured in a haul-out located adjacent to salmon farms. Tracking results showed that almost all the foraging areas of SASL are within close proximity to salmon farms. The most important prey for the individuals analyzed was farmed salmonids, with an estimated median (±SD) contribution of 19.7 ± 13.5‰ and 15.3 ± 9.6‰ for hair and skin, respectively. Using vibrissae as a temporal record of diet for each individual, we observed a remarkable switch in diet composition in two SASL, from farmed salmonids to pelagic fishes, which coincided with the decrease of salmon production due to the infectious salmon anemia virus that affected salmon farms in Chile at the end of 2008. Our study demonstrates the usefulness of integrating stable isotope derived dietary data with movement patterns to characterize the impacts of a non-native prey on the foraging ecology of an apex marine predator, providing important applied implications in situations where interactions between aquaculture and wildlife are common.

Stable isotope records of sei whale baleens from Chilean Patagonia as archives for feeding and migration behavior

“…Potential food sources may include crustaceans and planktivorous fish from Patagonian fjords representing the last whereabouts of the investigated sei whales. Elsewhere in Chilean Patagonia, similar values were recorded for this species(Sepúlveda et al, 2015) and other planktivorous fish(Mayr et al, 2011) (Figure 4). Patagonian sprat (Sprattus fuegensis), an important forage fish in the Patagonian marine ecosystems, provided δ 15 N values of 14.5 ± 0.4‰ and δ 13 C values of −16.6 ± 0.8‰ in the Aysén region close to where the stranded sei whales were found (44 − 47°S;Montecinos, Castro, & Neira, 2016).…”

“…Clearly, more baseline data obtained in future studies could improve evaluating migration patterns using southern sei whale baleen isotope records. Additionally, values of potential prey items are given: Sprattus fuegensis (Montecinos et al, 2016;Sepúlveda et al, 2015), small planktivorous fish (Mayr et al, 2011), Munida gregaria (Pérez-Barros et al, 2010), euphausiids (Mayr et al, unpublished;Montecinos et al, 2016), and copepods (Montecinos et al, 2016). In the latter study, the baleen plates of F I G U R E 4 δ 15 N versus δ 13 C values of baleen plates (small filled circles) corrected for trophic fractionation (Δ 13 C and Δ 15 N, respectively, from Borrell et al, 2012).…”

Spatial, temporal, age, and sex related variation in the diet of South American sea lions in southern Chile

“…Sepúlveda et al . () showed that SASL, which previously consumed a high proportion of salmon (Muñoz et al . ), changed their diet during this period, likely in response to the decrease in salmon availability.…”

“…Along the Pacific coast, recent studies using time‐depth recorders and satellite tags also indicated that SASL from southern Chile displayed a mesopelagic‐benthic diving strategy (Sepúlveda et al . , Hückstädt et al . ).…”

Environmental issues in Chilean salmon farming: a review

“…Sepúlveda et al . () examined the degree of spatial overlap between the South American sea lions and salmon farms using satellite telemetry and stable isotope analysis, and quantified the amount of native prey versus farmed salmonids in their diets. The most important prey were farmed salmonids, with an estimated median of 19.7% and 15.3% for hair and skin, respectively.…”