Environmental variability controls recruitment but with different drivers among spawning components in Gulf of St. Lawrence herring stocks

Abstract

The factors affecting herring recruitment are still poorly understood, complicating the prediction of stock dynamics and the choice of operational management strategies. We investigated effects of intrinsic (SSB) and extrinsic factors (physical and biological environments, including competition and predation) on recruitment of the spring and fall spawning components of each of the two herring stocks occurring in the Gulf of the St. Lawrence between 1971 and 2014. Effects of potential explanatory factors on recruit (age 2) abundance were tested using Generalized Additive Models. Model fit was significantly improved by incorporating both physical and biological environmental variability, but effects of herring SSB and predation were not significant. Indices of zooplankton abundance and phenology explained more variance in recruitment than physical indices. Our results emphasize the dominance of bottom‐up processes over SSB in the regulation of herring recruitment. Environmental variability did not seem to act uniformly on the recruitment of either stock or their respective spawning components. A long‐term trend of decreasing recruitment in spring spawners was associated with a long‐term decline in abundance of cold water copepods. In fall spawners, optimal recruitment was dependent on warmer environmental conditions combined with an adequate supply (species composition and phenology) of zooplankton. These results provide the first empirical evidence that spring and fall spawning herring are adapted to contrasting environmental conditions and shed light on the potential mechanisms linking herring recruitment to key zooplankton community characteristics and phenology. Management strategies can be improved by incorporating this new knowledge on environmental drivers of herring recruitment.

Modelling Atlantic mackerel spawning habitat suitability and its future distribution in the north‐west Atlantic

“…This also corroborates previous studies underlining the importance of zooplankton abundance and phenology on pelagic fish recruitment in the GSL (e.g. mackerel, Plourde et al, ; herring, Brosset et al, ). Moreover, C. finmarchicus and Temora sp.…”

Fish population growth in the Gulf of St Lawrence: effects of climate, fishing and predator abundance

“…Temperature data were obtained from regular monitoring in the GSL (see Galbraith et al 2018), specifically monthly sea surface temperature in August, and the average between May and November were utilised. Surface temperature may affects the growth and survival of early life stages and juveniles (depending on their spawning season), as already shown for the recruitment process for mackerel (Plourde et al 2015) and herring (Brosset et al 2019). Cold intermediate layer (CIL), and deep layer temperature data at 150, 200, 250 and 300m, were used as indicators of habitat and spawning ground suitability for demersal species adult and juvenile stages.…”

Influence of larval transport and temperature on recruitment dynamics of North Sea cod (Gadus morhua) across spatial scales of observation

“…Critically, the spatial scale of observation can affect the stock–recruitment relationship, providing contrasting results across scales (Chang, Chen, Halteman, & Wilson, 2016). The importance of environmental drivers for recruitment can also differ across subunits within a stock (Brosset et al., 2018). We therefore expect the importance of larval transport variability for recruitment to differ across spatial scales (i.e.…”