Blue whiting Micromesistius poutassou diel feeding behaviour in the Irminger Sea

S Post,T Jansen,Ah Ólafsdóttir,Sh Jónasdóttir,H Andreasen

doi:10.3354/meps13918

Abstract

With warming ocean temperatures, the abundance of blue whiting Micromesistius poutassou is increasing in the waters around Greenland. However, in this region, knowledge about the species’ trophic role in the ecosystem is scarce. Consequently, we investigated the diet composition and diel feeding behaviour of blue whiting in the north-eastern part of the Irminger Sea in Greenland waters by analysing their stomach contents and the vertical position/movements of their prey from zooplankton samples and hydroacoustic measurements. We collected the data during a designated experimental survey in July 2016 with repeated sampling at the same location. Results from the stomachs of 624 blue whiting individuals ranging from 22-39 cm long (total length) showed that the highest food intake took place from noon until late evening, with minimum feeding occurring in the morning. The most essential prey groups consisted of euphausiids, copepods, amphipods and fish, in that respective order. Regarding copepod prey, blue whiting had a strong affinity for Calanus hyperboreus and Paraeuchaeta spp. and showed potential for local depletion of these large copepods. On the other hand, the more abundant but smaller C. finmarchicus was almost absent in the fish stomachs, in contrast to findings in other regions. This new understanding provides an early indication of some of the emerging trophodynamics in the Irminger Sea and similar subarctic zooplankton communities with increasing numbers of blue whiting. Our results confirm the importance of accounting for diel and size-specific differences in blue whiting feeding when studying various aspects of its food intake.

Highlights

Climate change scenarios predict an increase in the abundance of boreal fish species in Arctic and Subarctic areas, such as Greenland waters (Fossheim et al 2015, Andrews et al 2019, Hastings et al 2020)
The final generalized additive models (GAMs) differed between the different prey groups (Table 3; Akaike’s Information criteria (AIC) score and summaries of the model output in R can be found in Tables S2 & S3, respectively)
In the central part of the Irminger Sea, further away from the East Greenland Current, C. hyperboreus abundance was much lower in samples from June 1997 and 2013 (Gislason 2003, Strand et al 2020) compared to what we found in the present study (>1000 ind. m−2; Table S5)

Summary

Introduction

Climate change scenarios predict an increase in the abundance of boreal fish species in Arctic and Subarctic areas, such as Greenland waters (Fossheim et al 2015, Andrews et al 2019, Hastings et al 2020). Since the mid-1990s, the summer surface temperature has generally increased, and several long-term climate projections forecast a continuation of this trend (Jansen et al 2016). The off-shelf areas in the central part of the Irminger Sea have recently, concurrently with warmer temperatures, experienced colonisation of certain boreal species, e.g. the highly mobile Atlantic mackerel Scomber scombrus and bluefin tuna Thunnus thynnus, which otherwise traditionally prefer warmer waters than usually prevailing in the Irminger Sea (Jansen et al 2016, 2021)

Methods

Results

Discussion

Conclusion