Spatial, temporal, and environmental influences on Atlantic cod Gadus morhua offshore recruitment signals in Newfoundland

El Lunzmann-Cooke,C Fuentes-Yaco,D Cote,Rs Gregory,Pvr Snelgrove

doi:10.3354/meps13806

Abstract

Numerous studies demonstrate the utility of information from coastal seine surveys for monitoring juveniles of Atlantic cod Gadus morhua, but few studies have linked such surveys to older ages within cohorts. We related juvenile (age-0 and -1) cod population components at a long-term monitoring site in Newfoundland to offshore pre-adult (age-3) cod recruitment at multiple spatial scales and explored some environmental and biological factors that affect juvenile-recruit relationships. Our models revealed significant relationships between juvenile and pre-adult abundance. The strength of these relationships varied with distance from nursery habitats and among fisheries management zones. Additionally, chlorophyll a concentration and body length during early life stages appeared to influence the strength of the relationship between juvenile and age-3 abundance. The potential to use juveniles as general indicators of future pre-adult abundance can aid in planning for low recruitment years and improve inferences about the response of cod population abundance to environmental changes. This study contributes to the growing body of knowledge demonstrating the utility of juvenile surveys in anticipating future year-class strength.

Highlights

Many of the world’s most valuable marine fish species (e.g. Atlantic cod Gadus morhua, Baltic Sea sprat Sprattus sprattus, herring Clupea harengus L.) exhibit strong recruitment variability, driven by a mixture of environmental and anthropogenic drivers that often leave fish populations vulnerable to depletion (e.g. Sætre et al 2002, Stige et al 2013, Rose & Rowe 2015)
We investigated the potential for nearshore seine surveys to detect recruitment signals in pre-adult cod abundance in coastal Newfoundland at multiple spatial scales
Our study focused on determining whether an empirical link exists between juvenile and pre-adult abundance of cod to allow anticipation of good versus poor year classes

Summary

Introduction

Many of the world’s most valuable marine fish species (e.g. Atlantic cod Gadus morhua, Baltic Sea sprat Sprattus sprattus, herring Clupea harengus L.) exhibit strong recruitment variability, driven by a mixture of environmental and anthropogenic drivers that often leave fish populations vulnerable to depletion (e.g. Sætre et al 2002, Stige et al 2013, Rose & Rowe 2015). Estimates of cohort strength in long-lived marine fishes often use adult abundance (e.g. spawning stock biomass, SSB; Stige et al 2013) because many confounding factors (e.g. predation, advection, temperature) limit the utility of early life stages (e.g. eggs and larvae) for such estimates. Whereas several northeast Atlantic stock assessments, including cod (ICES 2017), integrate offshore pre-recruit indices, lack of understanding of empirical linkages between coastal pre-recruit and offshore adult life stages remains an obstacle to improved fisheries management more broadly (Sissenwine 1984, Skern-Mauritzen et al 2016). Utilization of older age classes yields better predictions of future population estimates as a result of decreased vulnerability and sampling complications, forecasting population abundance further in advance using juvenile data would provide a considerable advantage to management, given the ecological and socioeconomic consequences of unexpected stock collapses

Methods

Results

Conclusion