Harvested species and adaptive management

Harvest (fishing, hunting) is an important mortality factor in many wild populations, but the demographic impacts of harvest and its consequences are still poorly understood.


Atlantic cod. Photo credit: Oystein Paulsen

The Atlantic cod (Gadus morhua) is a fish species severly affected by harvest through its entire global distribution, with some local stocks already extinct or close to commercial extinction. The implementation of Marine Protected Areas (MPAs) is seen as a useful tool to rebound cod numbers and enhance these depleted populations, but there is a lack of scientific evaluations of MPAs and their success at enhancing cod populations is still debated.

My postdoctoral research on Atlantic cod in Norway was focused on the effects of partial protection (i.e. protected areas still supporting some recreational fishing but closed to commercial extraction) on local populations with emphasis on mortality causes and the consequences of alternative management scenarios on population status.

So far, this research has shown a positive effect of partial protection on the survival of cod, and especially large individuals, due to the local closure of commercial fisheries. However, fishing mortality is still very high elsewhere, causing annual survival rates of cod to be consistently below 30% in many parts of Southern Norway. Our findings indicate that current mortality values make regional population recovery impossible unless no-take reserves are implemented in the most depleted areas.

Related publications:

  • Fernández-Chacón A, Moland E, Espeland SH, Kleiven AR, Olsen EM. 2016. Causes of mortality in depleted populations of Atlantic cod estimated from multi-event modelling of mark-recapture and recovery data. Canadian Journal of Fisheries and Aquatic Sciences, doi: 10.1139/cjfas-2015-0313.
  • Kleiven AR, Fernández-Chacón A , Nordahl J, Moland E, Espeland SH, Knutsen H, Olsen EM. 2016. Harvest pressure on coastal Atlantic cod (Gadus morhua) from recreational fishing relative to commercial fishing assessed from tag-recovery data. PLOS One 11(3): e0149595. doi: 10.1371/journal.pone.0149595.
  • Fernández-Chacón A, Olsen EM, Moland E, Espeland SH. 2015. Demographic effects of full versus partial protection from harvesting: inference from an empirical before–after control-impact study on Atlantic cod. Journal of Applied Ecology 52: 1206-1215.