Trophic ecology of incubating Kelp Gulls (Larus dominicanus) and its relationship with coastal trawl fisheries in northern Patagonia, Argentina

KASINSKY, T.; MARINAO, C.; SUÁREZ, N.; YORIO, P.

Conferencia; 3rd World Seabird Conference; 2021

Fishing discards are of great relevance to seabirdtrophic ecology worldwide. The Kelp Gull (Larus dominicanus) is a generalistand opportunistic species that feeds on a wide variety of prey obtained in naturaland human-related environments. We analyzed the spatial association withoperating coastal bottom trawl vessels and the contribution of discards to thediet of incubating individuals at Punta Tombo (44°02'S, 65°11'W), Argentina.Based on carbon and nitrogen isotopic values of whole blood samples from 22 and20 adults in 2016 and 2017, respectively, Bayesian mixing model outputs showed thatdiscards (demersal prey normally unavailable to surface feeding predators) werethe main prey, with similar contribution in both years (2016 = 47 ± 4%; 2017 =52 ± 5%), followed by mussels (Perumytilus purpuratus) (2016 = 29 ± 4%;2017 = 24 ± 5%), and Argentine anchovy (Engraulis anchoita) (2016 = 14 ±6%; 2017 = 14 ± 7%). We also tracked 14 and 13 of these incubating adults usingGPS loggers during 2016 and 2017, recording 134 and 122 foraging tips,respectively. Linear mixed models showed no significant differences betweenyears in the maximum distances from the colony, total distance traveled andduration of foraging trips. Open sea environments were the most visited in bothseasons and included areas where fishing vessels were operating according tovessel monitoring system data. Fisheries discards were the main prey for mosttracked individuals even for those who did not travel to fishing areas duringthe few days of the tracking period, indicating plasticity in individualfeeding behavior likely in response to the differential availability ofalternative prey. Our results show that discards generated by coastal trawlfisheries are an important diet component for incubating Kelp Gulls at PuntaTombo.