Seasonal and spatial variability of Atlanto-Iberian pelagic fish diet with estimates of intraguild predation

Abstract

The diets of 3 of the most abundant coastal pelagic fish species in the eastern Atlantic (sardine, anchovy and Atlantic chub mackerel) were investigated, including seasonal, geographical and ontogenetic variability of the diets. We also estimated the impact of cannibalism and intraguild predation on egg mortality, and a different method to evaluate egg mortality is proposed taking the spatial overlap of predators and eggs into account. Diet overlap occurred between the 3 pelagic species, which derive most of their dietary carbon from mesozooplankton prey. However, calanoid copepods were mostly important for anchovy and sardine, whereas the diet of the Atlantic chub mackerel also included crustacean eggs, nauplii, small copepodites and larger prey such as decapods. Sardine was the main predator of fish eggs (90% of all identified eggs), followed by Atlantic chub mackerel (8%) and anchovy (2%). Cannibalism by anchovies and sardines on their eggs was low (<10% of spawned eggs) for all areas and seasons. The impact of sardine predation on anchovy egg mortality was high (71% of the anchovy eggs spawned per day during the spring off northwestern Iberia) and may explain why anchovy abundance has only peaked in recent years, when sardine abundance was at its lowest level, highlighting the importance of taking an ecosystem approach to fisheries management into account. However, species-specific data of gastric evacuation rates and feeding durations are needed to obtain more accurate estimates of the impact of cannibalism and intraguild predation on egg mortality.

Hydrology and small pelagic fish drive the spatio–temporal dynamics of springtime zooplankton assemblages over the Bay of Biscay continental shelf

“…For example, taking into account the eight major SPF species inhabiting the BoB, Bachiller and Irigoien (2015) described an overall high diet overlap and concluded to a topdown control by these planktivorous fishes on zooplankton. Elsewhere, such links between ecosystem components were highlighted in the Mediterranean Sea (Feuilloley et al, 2020), on the Portuguese continental coast (Fonseca et al, 2022), in the North Sea (Capuzzo et al, 2018) and in Barents Sea (Stige et al, 2014). Here, the spatial structures in the hydrological parameters, primary producers and SPF were similar to that in mesozooplankton assemblages and were also consistent in time.…”

“…Mesozooplankton is the preferential prey of small pelagic fish (SPF, e.g. sardine and anchovy; Plounevez and Champalbert, 1999;Van Der Lingen, 2002;Bachiller and Irigoien, 2015;Fonseca et al, 2022). It is therefore a key trophic link that enables the transfer of matter and energy from the primary production to higher trophic levels in oceanic (Banse, 1995), upwelling ecosystems (Rykaczewski and Checkley, 2008) as well as in continental shelf ecosystems (Irigoien et al, 2008;Dessier et al, 2018;Noyon et al, 2022).…”