Quantitative molecular detection of larval Atlantic herring (Clupea harengus) in stomach contents of Atlantic mackerel (Scomber scombrus) marks regions of predation pressure

Bridie Jean Marie Allan,Maik Tiedemann,Erling Kåre Stenevik,Jessica Louise Ray,Katrine Sandnes Skaar,Richard D M Nash,Martina H Stiasny,Valeriya Komyakova,Olav Sigurd Kjesbu,Frode Vikebø,Arild Folkvord

doi:10.1038/s41598-021-84545-7

Abstract

Mortality rates in the early life-history stages of fishes are generally high yet identifying the causes remain unclear. Faltering recruitment rates of Atlantic herring (Clupea harengus) in the Norwegian Sea indicate a need to identify which mortality factors influence larval herring survival. Previous research suggests that increased predation pressure by Atlantic mackerel (Scomber scombrus) may contribute to the disconnect between spawning stock biomass and recruitment. To quantify the contribution of predation pressure by Atlantic mackerel to herring larval mortality, two research cruises were conducted within a probable “hot spot” (67–72° N) for intensified mackerel predation based on particle drift simulations. Mackerel stomach contents were analysed for herring larvae content using droplet digital polymerase chain reaction (ddPCR) with a quantitative molecular detection assay specific for herring. The ddPCR results demonstrate clear predation by mackerel on herring larvae and also suggest that the alternative use of visual examination may give misleading results. Our results show that mackerel should be considered a potentially important predator on herring larvae. The quantitative molecular assay presented here shows great promise as an efficient and specific tool to correctly identify and quantify predation pressure on early life-history stages of fishes.

Highlights

Mortality rates in the early life-history stages of fishes are generally high yet identifying the causes remain unclear
Whereas an increasing number of studies have investigated the effects of environmental variability on the recruitment potential of early life-history stages (ELHS)
As a first approach and to increase our ability to more accurately measure predation pressure, we developed an assay to quantify the number of C. harengus mitochondrial 16S ribosomal RNA gene (mt16S) gene copies present in the stomach contents of mackerel collected during the 2017 and 2018 larval drift period

Summary

Introduction

Mortality rates in the early life-history stages of fishes are generally high yet identifying the causes remain unclear. The quantitative molecular assay presented here shows great promise as an efficient and specific tool to correctly identify and quantify predation pressure on early life-history stages of fishes. The inability to correctly identify prey items owing to the level of taxonomic resolution one can achieve through visual analysis alone makes the comparison across studies difficult. This problem reduces the ability for hypothesis-driven ecosystem modelling for predicting the impact of shifts in predator fields due to climate fluctuations and change. Through the use of taxon-specific primers, the magnitude of predation on individual species present in mixed communities can be quantitatively a ssessed[16,19]

Methods

Results

Conclusion