Despite being landed in commercial cephalopod fisheries, species of
Alloteuthis
are not yet well defined, with
A. subulata
and
A. media
often confused. DNA barcoding combined with morphometric ...analyses has begun to clarify the distinction between these two morphologically similar species but has been limited in its geographic coverage to date. Herein, we provide DNA barcodes for 228 specimens collected from Guinea Bissau in the south, up the Atlantic coast, to the Irish shelf and North Sea. Employing species delimitation analyses, and with comparison to the literature, we identified 24 individuals of
A. africana,
66 individuals of
A. subulata
and 138 individuals of
A. media
. We confirm that
A. media
has the northernmost distribution and is the only species identified by DNA sequencing from the Irish shelf and North Sea. We analysed morphometric measures and indices from 388 individuals from the North Sea, a subset of which (
n
= 58) were barcoded. The most useful traits for identification were tail length as a percentage of dorsal mantle length, and largest club sucker width as a percentage of head width. By comparison to other published data, we determined that
A. media
phenotypes vary substantially across the geographic range of this species. This partly explains the difficulties in morphological identification and suggests regional identification guides may be required in support of fisheries management. Interregional analyses suggest character displacement may occur where species co-exist.
Abstract
Knowledge of stock structure is a priority for effective assessment of commercially-fished cephalopods. Loligo forbesii squid are thought to migrate inshore for breeding and offshore for ...feeding and long-range movements are implied from past studies showing genetic homogeneity in the entire neritic population. Only offshore populations (Faroe and Rockall Bank) were considered distinct. The present study applied mitchondrial and microsatellite markers (nine loci) to samples from Rockall Bank, north Scotland, North Sea, various shelf locations in Ireland, English Channel, northern Bay of Biscay, north Spain, and Bay of Cadiz. No statistically significant genetic sub-structure was found, although some non-significant trends involving Rockall were seen using microsatellite markers. Differences in L. forbesii statolith shape were apparent at a subset of locations, with most locations showing pairwise differences and statoliths from north Ireland being highly distinct. This suggests that (i) statolith shape is highly sensitive to local conditions and (ii) L. forbesii forms distinguishable groups (based on shape statistics), maintaining these groups over sufficiently long periods for local conditions to affect the shape of the statolith. Overall evidence suggests that L. forbesii forms separable (ecological) groups over short timescales with a semi-isolated breeding group at Rockall whose distinctiveness varies over time.
•The paper provides a pioneer tool to differentiate visually between egg masses of two sympatric commercial squids, L. vulgaris and L. forbesii.•Celtic Sea and western English Channel are spawning ...grounds of L. vulgaris in late winter – spring. No reproduction of L. forbesii was found there during this season.•L. forbesii forages in Celtic Sea and English Channel but reproduces in deeper water further west, mostly west of Ireland.
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.
Abstract
The inshore commercial squids, Loligo vulgaris and L. forbesii, co-occur in the ecoregions of Celtic Seas and Greater North Sea but the spatio-temporal structure of their spawning ranges is ...poorly understood. To help solve the problem, data sets collected during the last 30 years by British, German, French, and Irish scientists, as well as observations from multinational Citizen Science, were combined. Spawning grounds of L. forbesii were found to form an external semi-circle around the spawning grounds of L. vulgaris, with the latter being centred on the English Channel and southernmost North Sea. The nursery grounds of both species appear to coincide with the respective spawning grounds, though L. forbesii makes much wider use of the North Sea. Seasonally, the position of the spawning grounds of both species is driven by the local temperature regime, although this is possibly subject to interannual variability. Spawning of both species begins around November and gradually progresses eastward following favourable currents and increasing water temperatures. Spawning in both species is mostly over by July, though some egg masses persist until August–November. Nursery grounds follow the same seasonal shift from west to east, at least in L. forbesii.
