Population structure and spatial distribution of porbeagles (Lamna nasus) in Irish waters

• Published in: ICES Journal of Marine Science
• Main Authors: Cameron, Luke W J, Roche, William K, Houghton, Jonathan D R, Mensink, Paul J
• Other Authors: Grabowski, Jonathan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2019
• Subjects: Lamna nasus; North Atlantic; Porbeagle
• Online Access: http://dx.doi.org/10.1093/icesjms/fsz046; http://academic.oup.com/icesjms/article-pdf/76/6/1581/31247382/fsz046.pdf

Abstract Porbeagles throughout the North Atlantic have experienced severe population decline through overfishing, with the northeastern population listed as critically endangered. Management of this population is constrained by the paucity of data on porbeagle population structure, distribution and behaviour in this region. Here we use a long-term (47 year) Irish capture-mark-recapture dataset to investigate the population structure, spatial distribution and seasonal movements of this species. From 1970–2017, a total of 268 sharks (9 recaptures) were ID tagged, with most individuals likely being juvenile based on length at maturity estimates (mean total length = 143.9 cm, SD = 35.4). Almost all captures were recorded at three distinct locations near angling hubs along the south, west and north coasts with catches peaking in August. Long-term trends in capture date indicated a shift towards earlier capture dates in the northern site (n = 153). Our findings suggest Irish waters may act as a persistent summer aggregation site for juveniles, which show evidence for seasonal site fidelity, returning to nearby locations between years. These findings demonstrate the utility of such programmes, which can be implemented, with minimal expense by engaging with the angling sector, to elucidate the population structure and distribution of wide-ranging fish species.