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The present study determined the average mercury bioaccumulation in the muscle tissue of four shark species (Carcharhinus falciformis, Prionace glauca, Sphyrna zygaena and Isurus oxyrinchus) captured in the Baja California Peninsula. We also evaluated biomagnification of some prey consumed by sharks. All sharks' species had mercury levels over the limit specified by the Mexican government for human consumption. Blue shark (P. glauca) presented highest mercury values (1.96 ± 1.48 μg/g Hg d.w.) and it was the unique specie that showed a negative correlation with mercury content (Rs = -0.035, p = 0.91). Scomber japonicus was the prey with high content of mercury (0.57 ± 0.02 μg/g).

Early naturalists suggested that predation intensity increases toward the tropics, affecting fundamental ecological and evolutionary processes by latitude, but empirical support is still limited. Several studies have measured consumption rates across latitude at large scales, with variable results. Moreover, how predation affects prey community composition at such geographic scales remains unknown. Using standardized experiments that spanned 115° of latitude, at 36 nearshore sites along both coasts of the Americas, we found that marine predators have both higher consumption rates and consistently stronger impacts on biomass and species composition of marine invertebrate communities in warmer tropical waters, likely owing to fish predators. Our results provide robust support for a temperature-dependent gradient in interaction strength and have potential implications for how marine ecosystems will respond to ocean warming.

Se analizó el espectro trófico de 122 tiburones zorro Alopias superciliosus capturados artesanalmente en playa Tarqui, Manta (Ecuador), entre julio y diciembre de 2003. Los individuos fueron categorizados por sexo y estados de madurez (maduro e inmaduro) y sus contenidos estomacales se fijaron y separaron por componentes. Se aplicaron índices tróficos cuantitativos (numérico, gravimétrico y frecuencia de ocurrencia) que se analizaron en la escala temporal. Se encontraron 27 componentes alimentarios, siendo las principales presas Larimus argenteus (IIR= 1497), Merluccius gayi (IIR= 333), Dosidicus gigas (IIR= 281) y Benthosema panamense (IIR= 239). El índice de Levin permitió definir a A. superciliosus como un depredador especialista, presentando tendencia a alimentarse en zonas oceánicas.