A coupled stock-recruitment-age-structured model of the North Sea cod under the influence of depensation

Population models that assume logistic growth and a constant flux of recruits predict the recovery of depleted stock once a moratorium on capture is imposed. Despite long-term closure or strict regulation, many fisheries hardly show any recovery after the stocks have been brought to low levels, which suggest that other mechanisms may be responsible for such behavior. Here we show, using a coupled stock-recruitment – age-structured model that the increasing fishing mortality on the North Sea cod (Gadus morhua) has pushed the cod population into the region where depensatory dynamics prevails. The declining trend of the North Sea cod population, which had reached its lowest historical level in the last decade, has recently been showing improvement. We show that the future sustainability of the cod population depends highly on the change in fishing mortality within the next few years. We found a fishing mortality limit of 0.86, consistent with the ICES estimates, beyond which stock extirpation is assured.

[1]  K. Frank,et al.  Fisheries Ecology in the Context of Ecological and Evolutionary Theory , 1994 .

[2]  W. Ricker.  Stock and Recruitment , 1954 .

[3]  Terrance J. Quinn,et al.  Quantitative Fish Dynamics , 1999 .

[4]  H. Akaike,et al.  Information Theory and an Extension of the Maximum Likelihood Principle , 1973 .

[5]  W. C. Allee.  Animal Aggregations: A Study in General Sociology , 1931 .

[6]  N. Stenseth,et al.  Spawning stock and recruitment in North Sea cod shaped by food and climate , 2010, Proceedings of the Royal Society B: Biological Sciences.

[7]  C. O’Brien,et al.  Fisheries: Climate variability and North Sea cod , 2000, Nature.

[8]  E. Wagenmakers,et al.  AIC model selection using Akaike weights , 2004, Psychonomic bulletin & review.

[9]  M. Heath,et al.  The implications of warming climate for the management of North Sea demersal fisheries , 2005 .

[10]  K. Stokes.  Basic fishery science programs , 1990 .

[11]  R. Hilborn,et al.  Rebuilding Global Fisheries , 2009, Science.

[12]  Ray Hilborn,et al.  Depensation in fish stocks : a hierarchic Bayesian meta-analysis , 1997 .

[13]  D. P. Swain,et al.  Predicted extirpation of the dominant demersal fish in a large marine ecosystem: Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence , 2008 .

[14]  Ray Hilborn,et al.  Causes of Decline and Potential for Recovery of Atlantic Cod Populations , 2009 .

[15]  P. C. Reid,et al.  Plankton effect on cod recruitment in the North Sea , 2003, Nature.

[16]  William J. Sutherland,et al.  What Is the Allee Effect , 1999 .

[17]  R. A. Leibler,et al.  On Information and Sufficiency , 1951 .

[18]  Clive Fox,et al.  North Sea cod and climate change – modelling the effects of temperature on population dynamics , 2003 .

[19]  Jae S. Choi,et al.  Trophic Cascades in a Formerly Cod-Dominated Ecosystem , 2005, Science.

[20]  R Core Team,et al.  R: A language and environment for statistical computing. , 2014 .

[21]  Carl J. Walters,et al.  Cultivation/depensation effects on juvenile survival and recruitment: implications for the theory of fishing , 2001 .

[22]  J. Hutchings.  Collapse and recovery of marine fishes , 2000, Nature.

[23]  Hilborn,et al.  Depensation: evidence, models and implications , 2001 .

[24]  A. Rosenberg,et al.  Population Dynamics of Exploited Fish Stocks at Low Population Levels , 1995, Science.

[25]  U. H. Thygesen,et al.  The evolutionary pressure from fishing on size at maturation of Baltic cod , 2007 .

[26]  E. Odum.  Fundamentals of ecology , 1972 .

[27]  H. Araki,et al.  Genetic Effects of Captive Breeding Cause a Rapid, Cumulative Fitness Decline in the Wild , 2007, Science.

[28]  M. Quaas,et al.  Mismanagement of the North Sea cod by the European Council , 2012 .

[29]  Cóilín Minto,et al.  Trends in the abundance of marine fishes , 2010 .

[30]  R. Cook,et al.  Potential collapse of North Sea cod stocks , 1997, Nature.

[31]  K. H. Andersen,et al.  Direct and indirect community effects of rebuilding plans , 2010 .

[32]  May T. Lim,et al.  Effect of variable fishing strategy on fisheries under changing effort and pressure: An agent-based model application , 2010 .

[33]  Edward A. Codling,et al.  Managing mobile species with MPAs: the effects of mobility, larval dispersal, and fishing mortality on closure size , 2009 .

[34]  Y. Lambert,et al.  Environmental and fishing limitations to the rebuilding of the northern Gulf of St. Lawrence cod stock (Gadus morhua) , 2011 .

[35]  B. Planque,et al.  Temperature and the recruitment of Atlantic cod (Gadus morhua) , 1999 .

[36]  J. Dugan,et al.  Applications of marine refugia to coastal fisheries management , 1993 .

[37]  D. Bekkevold,et al.  Depensation, probability of fertilization, and the mating system of Atlantic cod (Gadus morhua L.) , 2004 .

[38]  W. C. Allee.  The social life of animals , 1938 .