Comparisons of whole body energy content of captive fasting age zero Alaskan Pacific herring ( Clupea pallasi Valenciennes) and cohorts over-wintering in nature

Abstract

Changes in whole body energy content (WBEC) of captive age-0 Pacific herring ( Clupea pullasi Valenciennes) forced to fast during winter was measured and compared to cohorts collected in the field. Somatic energy content (kJ·g −1 wet wt) of fasting captives declined at a rate of 23 J·g −1 wet wt per day from 1 December 1995 to 25 January 1996 (56 days) at a mean temperature of 6.6°C. In another observation, fish captured on 1 December 1995 and held without feeding until 1 April 1996 (122 days) had an average WBEC that changed from 5.2 to 3.2 kJ·g −1 wet wt during captivity at about 5.2°C. Fish that died during fasts had WBEC values ranging from 2.8 to 3.6 kJ·g −1 wet wt. During March 1996 the WBEC of field collected age-0 herring averaged 3.8 kJ·g −1, with ≈40% having WBEC ≤3.6 kJ·g −1 wet wt. Thus, by March the average recruit had used most of its stored energy. These observations confirm that in the northern Gulf of Alaska region age-0 herring rely heavily on stored energy to survive their first winter.