Mackerel predation on herring larvae during summer feeding in the Norwegian Sea

Abstract

In the course of the past two decades, Atlantic mackerel, Scomber scombrus, have expanded their summer feeding distribution in the Norwegian Sea substantially, and now potentially overlap with pelagic larvae of Norwegian spring-spawning herring, Clupea harengus, as these drift northwards. Mackerel are known to be opportunistic predators, and the aim of this study was to evaluate mackerel predation in an area of overlap between mackerel and herring larvae, with particular focus on predation on herring larvae. In early June 2013, we followed a predefined transect in the expected core larvae distribution area on the Norwegian coastal shelf between about 66°N and 69°N. The transect was repeated twice, and samples of mackerel for stomach analyses and subsequent herring larvae samples were obtained at pre-defined stations. Mackerel were caught in all but one of the trawl hauls, but were hardly ever observed acoustically, suggesting that they were dispersed close to the surface throughout the study area. Herring larvae were caught in all samples. Calanoid copepods were the dominant prey of the mackerel, but 45% of the mackerel guts contained herring larvae, with a maximum of 225 larvae counted in a single gut. Both the frequency of guts containing herring larvae and the average amount of herring larvae increased in line with increasing abundance of larvae. On the other hand, no spatial correlation between mackerel abundance and herring larvae abundance was found at the station level. The results suggest that mackerel fed opportunistically on herring larvae, and that predation pressure therefore largely depends on the degree of overlap in time and space. Rough areal projections suggest that the mackerel would be capable of consuming the herring larvae present in the investigation area in 6–7 d, and that such predation therefore could have regulatory effects on stocks of Norwegian spring-spawning herring.

Density regulation in Northeast Atlantic fish populations: Density dependence is stronger in recruitment than in somatic growth

“…Besides density‐dependent processes analysed in this study, major drivers of population dynamics are environmental conditions (Borja, Fontan, Sáenz, & Valencia, ; Skagseth, Slotte, Stenevik, & Nash, ; Stachura et al., ), ecological interactions (Huse, Salthaug, & Skogen, ; Skaret, Bachiller, Langøy, & Stenevik, ), additional intraspecific feedbacks (Ricard, Zimmermann, & Heino, ) and fishing (Anderson et al., ). Growth is sensitive to various factors that cause inter‐ and intra‐annual variations, confounding estimation of density dependence.…”

A spatial approach to understanding herring population dynamics

“…In the recent period, there has been a lot of mackerel distributed in the drift route of the herring larvae. Mackerel is highly efficient in eating larval herring and a recent field study shows a high prevalence of herring larvae in the mackerel stomachs outside Lofoten Islands (Skaret et al 2015). This predation mechanism is therefore of a magnitude that it potentially could constrain herring recruitment in some years given the combination of very high mackerel densities and high prevalence of herring larvae in the stomach (Skaret et al 2015).…”

“…Another potential process affecting herring during the larval drift is predation from pelagic fish such as mackerel, blue whiting, and juvenile conspecifics (Holst 1992;Saetre et al 2002a;Skaret et al 2015). In the recent period, there has been a lot of mackerel distributed in the drift route of the herring larvae.…”

“…Furthermore, the spiky recruitment pattern that Hjort revealed for the NSS herring has proven to be a prominent feature of the stock, which is defined by relatively infrequent strong year classes that tend to dominate the stock (Dragesund et al 1980;Toresen and Østvedt 2000;. Whereas the causes for these occasional strong year classes are far from being understood and predicted, there are some promising avenues for research related to climatic conditions (Toresen and Østvedt 2000;Saetre et al 2002a), growth and hatching time (Husebø et al 2009;Vikebø et al 2012), and predation (Skaret et al 2015). Initial studies of races or population structure in herring were tightly coupled to the understanding of fluctuations in the fisheries (Sinclair 2009).…”

Food-Web Structure in Four Locations Along the European Shelf Indicates Spatial Differences in Ecosystem Functioning

“…With the ongoing climate change, feeding migrations of mackerel to the North are expected earlier in the season (Utne et al, 2012). This will lead to a large temporal overlap of mackerel and larvae of Norwegian spring spawning herring, and the resulting predation could have regulatory effects on the herring stock (Skaret et al, 2015), and consequently on the available food for cod. In contrast, North Sea cod relied approximately equally on pelagic and benthic affinity prey, which is in accordance with previous studies of stable isotopes from Newfoundland and Labrador (Sherwood and Rose, 2005), and stomach contents from the North Sea (Hislop et al, 1997).…”