Spawning delays of northern capelin (Mallotus villosus) and recovery dynamics: A mismatch with ice-mediated spring bloom?

Abstract

The capelin stock off the northeast coast of Newfoundland and southern Labrador collapsed in the early 1990s along with most of the finfish community. Among a host of concomitant physical and behavioral changes was the onset of delayed spawning, a phenomenon that has persisted for over two decades. From the mid-1990s onward, the Newfoundland and Labrador shelf has been warming with ice levels reduced in most years, generally leading to earlier spring plankton blooms. The delayed spawns and earlier blooms have resulted in an increased mismatch between plankton production and larval emergence, which we hypothesized could result in reduced early-life survival and prolonged stock recovery. Among indices associated with the mismatch, including time between blooms and spawning, composition and abundance of zooplankton during early ontogeny, and sea surface temperature and ice coverage, potential linkages were found with first year capelin survival. Increased capelin productivity in recent years has been associated with an increase in preferable and total zooplankton abundance and a decreasing trend in the mismatch with the spring bloom. A generalized linear model incorporating a match–mismatch index and stage I–IV calanus copepods explained 82% of the variance associated with annual age 0 capelin abundance estimates since stock collapse. A central mechanism underlying improvements in capelin productivity appears to be a general reduction in ice coverage associated with a recent warm oceanographic regime that reached record high levels in 2011.