Forsøksdyr: Effects of temperature and prey availability on the foraging ability and escape performance of larval Norwegian Spring Spawning herring.

Godkjenningsdato 09.04.2018

Norwegian spring spawning herring (NSSH) is one of the largest fish stocks in the world and a key component in the North Atlantic ecosystem.

NSSH adults spawn at the major spawning grounds (Møre and Haltenbaken) and the subsequent larvae hatch and begin their drift northwards towards the Barents Sea where they recruit to the juvenile population. However, it is during the larval drift phase that high numbers of larvae appear to undergo a severe population bottleneck with the proximate causes of this bottleneck uncertain. Annual cohort strength is underpinned by rapid growth and successful predator evasion during the larval period. However, these behaviours can be affected by environmental conditions, such as increasing water temperature and prey availability. Therefore, it is a key challenge to understand how these environmental drivers may contribute to the high variability in late larval mortality.

The aim of the proposed research is to focus on both top-down and bottom-up processes regulating recruitment of NSSH larvae. To understand the potential behaviourial effects of increasing temperatures and decreasing prey availability on larval recruitment, we will focus on two behaviours important for successful recruitment: foraging behaviour and escape responses. Understanding the potential sub-lethal impacts of increasing temperatures and decreasing prey availability on commercial fisheries is important for both fisheries scientists and the fishing industry.

For behavioral studies, NSSH larvae will be transferred to an observation tank together with their prey (Zooplankton). Foraging behavior and escape responses will be observed with videography. Escape responses will be elicited using water movement from a pipette (details below).

In total, this experiment requires 962 individuals, 160 for each treatment (6 treatments with 4 replicates per treatment). By allowing for 30% mortality during the treatment period, total numbers of larvae are approx. 1286 individuals.

To quantify the effects of temperature increases and prey availability on behaviour (foraging ability and predator evasion), live animals must be used. This dynamic is important for successful recruitment.
As a way to minimize the number of larvae required for statistical robustness, we will use the same fish for both behaviour assays. Further, we will take a subsample of these larvae from each treatment for lipid analysis. Also, previous studies have helped to estimate “latent” mortality. This information reduces number of larvae and has been incorporated into the design.
Technicians doing daily husbandry will have extensive experience working with various marine fish larvae. Larvae in this experiment will be handled according to a “best choice practice” based on the extensive experience with marine fish larvae at the location.