Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8165
Title: Maternal age effects on Atlantic cod recruitment and implications for future population trajectories
Author: Andrew O. Shelton, J. A. Hutchings, Robin S. Waples, David M. Keith, H. Resit Ak├žakaya
Publication Year: 2015
Journal: ICES Journal of Marine Science
Keywords: cod, Gadus morhua, stock-recruitment relationship, age structure, age truncation, Ricker,
Abstract:

Exploited fish populations frequently exhibit truncated age-structure. To address a fundamental question in fisheries science and conservation biology – how does age truncation affect population dynamics and productivity? - we explored the effect of age structure on recruitment dynamics of 10 stocks of Atlantic cod (Gadus morhua). Based on six alternative stock-recruitment relationships, we compared models that included and excluded maternal age structure effects on recruitment. In all 10 stocks a recruitment model that included a maternal age-dependent effect was preferred over the standard Ricker model and in seven of the ten stocks the preferred statistical model included a positive effect of either maternal age or mass on recruitment. Simulations comparing standard and maternal age dependent recruitment two decades into the future suggest that the inclusion of maternal age in recruitment models has little effect on projected biomasses.  However, this similarity in biomass trajectory masked an increased sensitivity of populations with maternal age dependent recruitment to stock age-structure. In particular, simulations with maternal age-dependent recruitment responded strongly to changes in fishing mortality on the oldest age classes while simulations using standard recruitment models did not. Populations with maternal age-dependent recruitment can exhibit increased biomass catch even if fishing mortality on older individuals was reduced. Overall, simulations suggested that the influence of maternal age on population dynamics are more nuanced than suggested by previous research and indicate that careful consideration of the effects of age-structure on populations may lead to substantially different fisheries management reference points – particularly with respect to age-specific fishing mortality - than classical models. While these results suggest a link between maternal age and population productivity, future research requires the incorporation of biologically reasonable and empirically defensible mechanisms to clarify the effect of age on population dynamics.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Official Citation:

Shelton, A. O., J. A. Hutchings, R. S. Waples, D. M. Keith, and H. R. Akçakaya.  2015.  Maternal age effects on Atlantic cod recruitment and implications for future population trajectories. ICES Journal of Marine Science. (published online 4 April 2015; doi: 10.1093/icesjms/fsv058.