The complexities and challenges of conserving common whelk (Buccinum undatum L.) fishery resources: Spatio-temporal study of variable population demographics within an environmental context

Abstract

The commercial fishery for common whelk (Buccinum undatum L.) has expanded significantly in the Irish Sea since 1990 and continues to grow, particularly in Welsh waters and the Isle of Man territorial sea, with landings throughout the region increasing by 227% between 2011 and 2016. Whilst whelk populations are known to be vulnerable to localised overexploitation due to inherent life-history parameters, fisheries remain relatively unrestricted by conservation measures in comparison to other fisheries operating in the area. With the exception of the northernmost fishing ground between the Isle of Man and Scotland (Point of Ayre), the size-at-maturity (L50) estimate for populations sampled during peak-aGSI (the months in which adjusted gonadosomatic index is highest) indicates that whelk are being fished before the time at first spawning throughout the study area. A correlation was detected between the size (total shell length) and depth, with smaller whelks found in deeper waters where there generally is greater fishing effort, although effort data is not available at a resolution to investigate this relationship quantitatively. No clear link between benthic infauna biomass and the average size (total shell length) or reproductive capacity (aGSI) of whelk sampled throughout ICES Area VIIa was found, indicating that the ecological energetics of whelk populations are more likely to be a function of scavenging opportunities than predation on benthic communities. A mixed cohort analysis utilized length-based data to infer a size-at-age relationship in the absence of direct age observations (e.g. statolith rings), with whelk recruiting into the Isle of Man fishery five years after hatching. The evidence presented in this study suggests that, prior to recommending a MLS that will adequately protect the spawning stock biomass, L50 values should be adjusted for pre-spawning growth between the ideal time of assessment (when aGSI values are at a peak) and the spawning season (when aGSI values decrease).