This thesis aims to investigate causes of variation in the condition of Atlantic cod using long-term, high-resolution liver-weight databases. The Liver Condition Index (LCI), the weight of the liver as a percentage of total body weight, is used as a measure of condition. The first study presented in this thesis is an analysis of the causes of inter- and intraannual variation in the condition of Northeast Arctic cod. Temperature is identified as an important factor influencing condition. Increasing temperature is shown to positively impact condition at both inter- and intraannual timescales. Greater availability of the cod’s preferred prey, a monthly timescale. A time lag of one month between the change in capelin consumption and the subsequent change in condition, or ‘latency’, is demonstrated. Herring (<i>Clupea harengus</i>) are shown to have an indirect impact upon cod condition through competition for energy-rich capelin. The second study presented in this thesis is an investigation of sex-dependent variation in the condition of Northern cod. Differences in condition are mainly seen in mature fish, with mature female cod in consistently higher condition throughout the year than male. However, the only season for which a significant difference was identified was spring, suggesting that pre-spawning females are able to acquire more energy than pre-spawning males. In addition, a greater decline in post-spawning condition was found in females. Later maturation and slightly faster growth in mature females provide further verification of variation in energy allocation dependent on sex. The analyses presented in this chapter suggest that individual-level analyses of condition in cod should, in future, takes account of the effect of sex on energy usage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:542657 |
| Date | January 2010 |
| Creators | Sandeman, Lillian Ruth |
| 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=167788 |
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