Northward range expansion of Bay of Biscay anchovy into the English Channel

European anchovy Engraulis encrasicolus is a widely distributed, warm-water species which has been postulated to be a climate change ‘winner’. For decades, the northern-most stock resided in the Bay of Biscay, where it typically spawned during late spring, mostly in the south. An apparent regime shift in the mid-1990s saw the sudden appearance and subsequent increase of anchovy further north. This northward range expansion was found to be driven by remnant spawning populations in the North Sea. During the autumn of 2019 and 2020, for the first time, post-larval anchovy were found in the English Channel, far from their nearest known spawning grounds. Identifying the origin of these anchovy is important for management purposes and to understand the mechanisms driving populations at the limits of their distribution. Microsatellite- and mtDNA-based analyses confirmed that the observed post-larval anchovy originated from the Bay of Biscay and were genetically distinct from English Channel and southern North Sea specimens. By combining acoustic and egg data from local surveys with larval drift modelling, we examined the processes underpinning this northward expansion. Our analysis suggests that due to population increase, spawning activity in the Bay of Biscay has expanded in space and time, increasing larval transport and survival into the Channel area. This newly recorded process underpinning an observed poleward shift is different from the one driving the anchovy expansion that started in the mid-1990s. However, both caused range expansion at the species’ northern distribution limit, demonstrating the potentially complex impacts of climate change.