Retrospective study of seagull poisonings in central Portugal: can marine phycotoxins be involved?

The Lisbon's Wildlife Rehabilitation Center (LxCRAS) primarily receives birds, with seagulls making up a large share. Most of these were Larus fuscus (62%), accounting for 73% of total seagulls showing signs of intoxication (paresias). Admissions of animals originating in the Lisbon and Setúbal districts peaked annually in spring and autumn, coinciding with this species’ departure and return from migration, respectively. Larus michahellis, a resident species, comprised 21% of admissions and accounted for 16% of seagulls presenting paresias. Fish and shellfish consumed by seabirds can contain marine biotoxins which originated from certain microalgae in their diet. The seasonal occurrence of amnesic shellfish poisoning (ASTs) and paralytic shellfish poisoning (PSTs) toxins was compared with the number of seagulls admitted weekly at LxCRAS with paresias during the last decade (2016-2025). The weekly occurrence of AST neurotoxins was very short-lived and rarely attained concentrations above the human safety level. These episodes did not coincide with admissions above each year’s weekly average. The occurrence of PSTs neurotoxins above the human safety level was sporadic, restricted to winter 2016/17 and autumn 2018. There was no evidence that the strong contamination in the Lisbon area during 2018 could have affected seagulls, due to the recurrent autumnal peak in admissions. Paresias incidence increased mainly with the number of L. fuscus but not L. michahellis admissions, and also with ambient air temperature. Mortality from paresias was higher in autumn than in spring, coinciding also with higher temperatures. As demonstrated earlier in seagulls from the south of Portugal, botulism might be implicated in these intoxications. Seagulls’ habits are opportunistic, eating terrestrial prey and human leftovers besides seafood. The high energy expenditure required for migration seems to be driving these animals to seek easily accessible leftovers, which might be spoiled.