Seasonal variation in survival of pelagic fish larvae and juveniles on the Faroe shelf

Demersal fish species such as cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are key fish species for
the Faroese economy and community. The stocks do however show large fluctuations in year class strength, with
severe economical and sociological consequences. Other species such as Norway pout (Trisopterus esmarkii) and
sandeel (Ammodytes marinus) are important intermediate level species carrying energy from plankton to the larger
fish species and to seabirds. All four fish species (i.e. cod, haddock, Norway pout and sandeel) have one thing in
common: they spawn during spring and their offspring are pelagic and plankton consumers during the first months of
life. Together, these four species are around 90% of the total pelagic fish juvenile community during spring and
summer on the Faroe shelf.
Although there are many bottlenecks affecting the final year class strengths of fish, the early life phase of the
individuals (i.e. larva land pelagic juvenile stages) is generally considered to be essential for successful further
development. During the pelagic phase, the fish undergo a period of rapid development with considerable changes in
size, structure, physiology and behavior. Survival of eggs and larvae are mainly dependent on drift and distribution,
feeding and growth conditions, and extent of predation.
Monitoring of pelagic 0-group fish on the Faroe Plateau in late June from 1983 until present has revealed large
variations in fish juvenile abundances and sizes. The mean abundance has fluctuated by factors of around 500 between
good and poor years and the mean yearly sizes (in weight) at the time of sampling have fluctuated inter-annually by a
factor of 8 between largest and smallest individuals. Interestingly, the abundance and individual sizes of the four fish
species to a large extent seem to co-vary between years, indicating simultaneous environmental influences on
mortality and individual sizes of all four species.
The aim of this project is to investigate the life history of co-occurring fish larvae and pelagic juveniles on the Faroe
shelf using weekly measurements during a season (i.e. April-July 2019), and to relate this to oceanographical
parameters and feeding conditions. This information has the potential of revealing how growth and survival of fish
juveniles during their pelagic phase is affected by the dynamic environmental conditions on the Faroe Shelf, and reveal
when possible bottlenecks occur and why.