Re-visiting the drivers of capelin recruitment in Newfoundland since 1991

Abstract

Capelin is a small forage fish that plays a key role in the transfer of energy from secondary producers to vertebrate predators in Arcto-boreal food webs. Profound changes in abundance and distribution of capelin occurred in 1991 in Newfoundland, which corresponded with the collapse of the groundfish stocks. There has been minimal recovery of capelin biomass since 1991. We re-assessed the relationships between larval survival, recruitment, and onshore winds post-1991. We also investigated the link between larval capelin vital rates (growth) and recruitment for three current years of data: 2002, a collapsed population state; 2006, a transitioning state; and 2013, a recovering state. Like research pre-1991, we found a positive relationship between the age-2 recruitment index and larval abundance of the same cohort. However, the relationship between onshore winds and recruitment failed post-1991. Capelin are spawning persistently later since 1991 when there are fewer onshore wind events, which is likely a factor hindering the recovery of the capelin stock. Instead, the age-2 recruitment index was related to Pseudocalanus spp. density during the larval stage. Increased availability of preferred prey in autumn, due to a shift in zooplankton phenology seen around 2006, may have improved larval survival in recent years. We found faster growth in the recovering population state (2013) which suggests better larval growth conditions in recent years. Low larval survival from beach spawning may be inhibiting the recovery of the capelin stock, but enhanced productivity of small copepods in autumn can potentially compensate for the negative effect of later spawning.