The influence of spatial and temporal scale in detecting offshore recruitment signals of Atlantic cod (Gadus morhua) based on coastal juvenile surveys

Cooke, Emma L. L. (2019) The influence of spatial and temporal scale in detecting offshore recruitment signals of Atlantic cod (Gadus morhua) based on coastal juvenile surveys. Masters thesis, Memorial University of Newfoundland.

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Abstract

The moratorium on the Newfoundland Atlantic cod (Gadus morhua) fishery in 1992 motivated studies on the factors influencing population stability and tools to forecast future cod abundance. Unfortunately, short-duration time series compromised most efforts to link life stages. I used coastal seine surveys of juveniles (age-0 and -1) to predict offshore pre-adult (age-3) cod abundance at multiple spatial scales (individual bays to offshore regions), temporal scales (short and long-term time series from 7 to 18 years in length) and environmental and biological factors influencing recruitment signal strength. These analyses detected strong recruitment signals among all early age classes from the Newman Sound Survey (1995 – 2013) and demonstrated interactions between juvenile abundance and environmental variables. In contrast, a strong recruitment signal was only detectable from a single bay using the shorter Fleming Survey (1992 – 1997, 2001). For both surveys, recruitment signal strength varied with distance from the index sites, among management zones, and between areas of known ecological and biological significance. Studies evaluating year-class strength often overlook the value of coastal juvenile surveys. These results demonstrate the utility of using information from long-duration coastal seine surveys when forecasting adult population strength. The implications of my results could help stakeholders prepare for socio-economic implications of poor recruitment years, and can be used in management decision-making.

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