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

MARINAO, C.; YORIO, P.

Conferencia; 3rd World Seabird Conference; 2021

Fishing activities provide marine scavengers withlarge quantities of fisheries discards, and this anthropogenic food subsidy hasbecome a key component in the trophic ecology of seabirds worldwide. Seabirdsdetermine through their selective consumption which components of the discardfraction are made available to scavenger organisms in the water column and onthe seabed. We evaluated the selective consumption of discards by seabirdsassociated with a coastal fishery targeting Argentine Red Shrimp (Pleoticusmuelleri) in Patagonia, Argentina. The fishery consisting of 42 vesselsdiscarded a mean of 682 kg per haul (n = 113). A total of 65 species werediscarded, and Argentine Hake (Merluccius hubbsi) (96% FO; 260 kg/haul)and Argentine Red Shrimp (100% FO; 195 kg/haul) dominated the discard fractionof the catch. The Kelp Gull (Larus dominicanus) and Black-browedAlbatross (Thalassarche melanophris) were present in all hauls and werethe most abundant of the seven seabird species scavenging behind vessels (171 ±110 and 57 ± 52 individuals per haul, respectively) representing together morethan 93.5% of birds in associated assemblages. A total of 29 prey items were experimentallydiscarded (n = 1392), nine of which were totally ignored. Ignored invertebratesincluded tunicates, which constitute a large fraction of discards (>100kg/haul). Mean sizes of fish and invertebrates consumed were 22.5 ± 8.6 and10.4 ± 7.8 cm, respectively. Kelp Gulls selected significantly smaller preythan Black-browed Albatrosses (16.3 ± 7.9 and 29.1 ± 8.1 cm, respectively;P<0.001), showing partitioning of prey resources. Results indicate that alldiscarded fish species, but not all sizes, were consumed by seabirds, and someof the most abundant discarded invertebrates were ignored. Thus, only afraction of fish and mostly invertebrates would remain available for scavengingorganisms in the water column and benthic habitats.