Does juvenile herring (Clupea harengus) affect the capelin (Mallotus villosus) recruitment in the Barents Sea? - A model study for the years 2001 - 2003 focusing on capelin larvae mortality, spawning sites and drift patterns

Barents Sea capelin (Mallotus villosus) year class strength is thought to be determined during the first months after egg hatching. The now widely accepted Hamre’s hypothesis states that young herring (Clupea harengus) present in the southern Barents Sea potentially may cause poor capelin recruitment. This hypothesis was presently tested through model scenarios, by simulating a realistic spatio-temporal overlap between young herring and capelin larvae in the Barents Sea during the 2001 - 2003 summer seasons. Herring totally consumed 10.6 % (2001), 0.06 % (2002) and 25.2 % (2003) of the capelin larvae populations, and up to 2.36 % of the capelin larvae populations were consumed day-1. Hamre’s hypothesis is therefore supported. Considering the high capelin larvae abundance in June 2002 and the low herring abundance in the Barents Sea that summer, the capelin 2002 year class became unexpectedly weak. Capelin recruitment is thus probably threatened by other factors than predatory herring as well. Nevertheless, it is presently suggested that predation from herring on capelin larvae strongly contributed to the poor capelin recruitment and abundances in the years 2003 – 2006. The choice of capelin spawning ground location is highly variable and is presently suggested to be important regarding the capelin recruitment successfulness. Western spawning grounds may lead to prolonged capelin larvae drift periods along the northern coasts of Norway and Russia, where the predatory herring often are abundant. Yet the capelin larvae originating from western spawning areas often become widely dispersed, while the capelin larvae spawned at eastern spawning grounds experience a rapid drift into the eastern Barents Sea. The present study shows that capelin larvae spawned at western locations might be advected northwards, ultimately ending up in the central or north-western Barents Sea. Survey programs and model studies are characterized by uncertainties and weaknesses. The present study will shed light on such problems and suggest possible enhancements.