Scavenging seabirds and selective consumption of discards in a coastal shrimp trawl fishery in Patagonia, Argentina

MARINAO CRISTIAN; YORIO PABLO

Hobart

Congreso; III World Seabird Conference; 2021

World Seabird union

Fishing activities provide marine scavengers with large quantities of fisheries discards, and this anthropogenic food subsidy has become a key component in the trophic ecology of seabirds worldwide. Seabirds determine through their selective consumption which components of the discard fraction are made available to scavenger organisms in the water column and on the seabed. We evaluated the selective consumption of discards by seabirds associated with a coastal fishery targeting Argentine Red Shrimp (Pleoticus muelleri) in Patagonia, Argentina. The fishery consisting of 42 vessels discarded a mean of 682 kg per haul (n = 113). A total of 65 species were discarded, and Argentine Hake (Merluccius hubbsi) (96% FO; 260 kg/haul) and Argentine Red Shrimp (100% FO; 195 kg/haul) dominated the discard fraction of the catch. The Kelp Gull (Larus dominicanus) and Black-browed Albatross (Thalassarche melanophris) were present in all hauls and were the most abundant of the seven seabird species scavenging behind vessels (171 ± 110 and 57 ± 52 individuals per haul, respectively) representing together more than 93.5% of birds in associated assemblages. A total of 29 prey items were experimentally discarded (n = 1392), eleven of which were totally ignored. Ignored invertebrates included tunicates, which constitute a large fraction of discards (>100 kg/haul). Mean sizes of fish and invertebrates consumed were 22.5 ± 8.6 and 10.4 ± 7.8 cm, respectively. Kelp Gulls selected significantly smaller prey than Black-browed Albatrosses (16.3 ± 7.9 and 29.1 ± 8.1 cm, respectively; P