You are what you eat: is suboptimal larval diet linked to the slow recovery of the Newfoundland capelin stock?

Abstract

Capelin on the Newfoundland and Labrador shelves (Northwest Atlantic Fisheries Organization Divisions 2J3KL) collapsed in 1991 and have experienced only a modest recovery in 30 + years. Year-class strength of Newfoundland capelin is set early in its life history. Using 6 years of larval data (2002, 2006, 2014, 2020–2022), the main objective of this study was to use trophodynamics to identify potential bottom-up drivers of capelin larval survival. The proportion of empty guts generally decreased with ontogeny; however, prey presence was low with only 18.9% of larvae containing at least one prey item in their guts. Larval diet was mainly composed of calanoid copepodites, Pseudocalanus spp., Temora spp., Oithona spp., and phytoplankton. There was a shift in diet with ontogeny, with copepodite stages increasing in importance with ontogeny. Although larval trophodynamics since 2002 differed from those described in the 1980s, with a higher proportion of empty guts and a broader prey spectrum, this comparison is confounded by spatial and temporal limitations of the available dataset. Using general additive models, mean recent 3-day larval otolith growth rate was related to in situ zooplankton prey availability, temperature, salinity, presence/absence of prey, and prey carbon contents. Larval growth was positively associated with copepod nauplii densities in 2 of the 3 years, indicating that a match between larval occurrence and copepod nauplii may be an important driver of larval growth. A match-mismatch between larval occurrence and their preferred prey may be a potential bottom-up mechanism to explain the prolonged Newfoundland capelin stock recovery.

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