This thesis focuses on the temporal variations in growth affecting commercial species of fish in the North Sea. The aims were firstly to review the modelling tools available to study fish growth in the North Sea, and secondly to investigate the implications of the observed increase in North Sea temperature on the growth of commercial fish species. The von Bertalanffy growth function (VBGF) is a reliable and flexible model to study fish growth and was employed throughout this thesis. The age-length keys (ALKs) used to model fish growth were length-stratified samples and were showed to result in biased VBGF parameter estimates. Thus, ALKs should be corrected by the length frequency observed in the population when possible. A warming trend has been observed in the North Sea over the last decades, with an overall increase of 1 °C in the northern North Sea. These warming temperatures were significantly linked with a decrease in asymptotic length (L∞) and an increase in the rate at which L∞ is reached (K) observed for North Sea haddock (Melanogrammus aeglefinus). Incorporating the temperature covariate into an extended VBGF to model haddock growth allowed quantifying a decrease in weight-at-age up to 40% at age 10 occurring at warmer temperatures, resulting in a 20% loss of individual yield. A meta-analysis was then conducted across North Sea commercial species and confirmed that most species experienced a synchronous decline in L∞, with the exception of cod (Gadus morhua) and sprat (Sprattus sprattus). This strongly suggests that the increase in temperature is the cause of the changes observed in VBGF parameters. Overall, the findings suggest that, in many commercial fish species of the North Sea, the increase in temperature induced a faster growth towards a smaller asymptotic length. This is likely to jeopardize fisheries yields and thus to affect the economic efficiency of North Sea fisheries. The results of this thesis advocate that the effect of temperature on growth is large enough to be incorporated into North Sea fish stock assessment models.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569592 |
| Date | January 2011 |
| Creators | Baudron, Alan Ronan |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=192287 |
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