Thirteen years (2006–2018) of capelin diet were examined from the Barents Sea where capelin is a key species in the food web, both as prey and predator. The PINRO/IMR mesozooplankton distribution usually shows low plankton biomass in the central Barents Sea, most likely due to predation pressure from capelin and other pelagic fish. This pattern was also observed in 2017-2019. In the Barents Sea, a pronounced shift in the diet from smaller (<14 cm) to larger capelin (≥14 cm) is observed.
Interactions, drivers and pressures 2019
Causes of capelin stock fluctuations
The Barents Sea capelin has undergone dramatic changes in stock size over the last four decades. Three stock collapses (when abundance was low and fishing moratoriums imposed) occurred during 1985–1989, 1993–1997, and 2003–2006. During the recent period 2014-2019 the stock estimates have fluctuated considerably. A rapid decline in stock size was recorded from 2014 onwards, and in 2016 the lowest biomass of capelin since 2005 was estimated from the joint Russian-Norwegian autumn Barents Sea Ecosystem Survey (BESS).
Causes of polar cod stock fluctuations
The Barents Sea polar cod stock was at a low level in 2017 and 2018. Norway conducted commercial fisheries on polar cod during the 1970s; Russia has fished this stock on more-or-less a regular basis since 1970. However, the fishery has for many years been so small that it is believed to have very little impact on stock dynamics. Stock size has been measured acoustically since 1986 and has fluctuated between 0.1–1.9 million tonnes.
Cod-capelin-polar cod interaction
The summer overlap between cod and capelin has increased, especially in the northern area, mainly due to the increased size of suitable habitat for cod, and the size of the cod stock. There is, however, a low correspondence between changes in horizontal overlap and changes in capelin consumption. The cod-capelin feeding interaction mainly takes place on the banks of the northern Barents Sea, where a vertical overlap with capelin is much more important for explaining variation in capelin consumption than capelin density. The northward expansion of cod has probably also affected the polar cod negatively, since polar cod has become more available to cod.