Life Science Mass Spectrometry Facility

Validating the use of historical scale libraries for long-term studies of salmonid ecology: the effect of nutritional status and growth rate on diet-tissue N isotope spacing.

Stocks of many commercial fish have declined significantly over the past 30 years. Both over-fishing and climate change have been implicated in this decline, but it is difficult and expensive to monitor wild fish populations directly. The effect of ocean climate change on salmon populations consequently remains uncertain. An alternative to direct observation lies in reconstructing ecological and life history information retrospectively from the stable isotope chemistry of incrementally grown tissues such as scales. The stable isotope composition of scale collagen records diet composition and indirectly reflects the extent of phytoplankton blooms. To use stable isotope composition as proxies for diet and ocean conditions, however, the precise relationship between the isotropic composition of diet and scale collagen must be determined, particularly with respect to variations in metabolic factors such as growth rate in individual fish.

This proposal by Clive Trueman at the University of Portsmouth, involves measuring the isotopic spacing between diet and tissue (e.g. scale collagen, muscle) in Atlantic salmon reared on an isotopically constant diet under varying conditions of temperature and photoperiod, designed to modify growth rates. At the conclusion of the project, the effect of growth rate on diet-tissue isotope spacing in C and N will be determined, allowing the use of archived salmon scales to reconstruct dietary and ecological patterns. The long-term goal is to produce decadal records of salmon diet and ocean conditions. These may be compared to population data and records of sea surface temperature to investigate linkages between climate change and salmon populations and to identify causal mechanisms responsible for the declining wild populations of Atlantic salmon.

C N Trueman, R McGill and P H Guyard. (2005). The effect of growth rate on tissue-diet isotopic spacing in rapidly growing animals. An experimental study with Atlantic salmon (Salmo salar). Rapid Comm. Mass Spec. 19, 3239-3247.