Identification of benthic egg masses and spawning grounds in commercial squid in the English Channel and Celtic Sea: Loligo vulgaris vs L. forbesii

European squid, Loligo vulgaris and veined squid, Loligo forbesii have nearly coinciding distributions in the northeast Atlantic, a similar reproductive seasonality, and largely overlapping depth ranges of spawning grounds. There are no unambiguous criteria to distinguish between egg masses of both species. This pioneering study was focused on the Celtic Sea and western part of the English Channel and combined both research survey data and observations by recreational divers (“citizen science”). Loligo vulgaris was found to reproduce there in late winter – spring; distribution of egg masses coincided with a bottom temperature range of 8.5-10° C and bottom salinities of 35–35.5 psu. No L.forbesii egg masses were found across the study area though they are known from literature to occur in deeper areas further west. Based on original material and data from the literature, we provide a guideline to distinguish between egg masses of both squids based on egg size and embryonic stage as a tool to map species-specific spawning grounds, towards improved understanding of population structure, migrations and development of fisheries management measures.