Life history traits of Mediterranean brown trout (Salmo trutta complex) in Pyrenean headwater streams

Abstract

The Mediterranean brown trout (Salmo trutta complex) is native to basins draining to the Western Mediterranean Sea, and natural populations are currently declining in abundance and distribution due to habitat degradation and introgression with stocked trout of the Atlantic lineage. Data on its life history traits are limited, although is an essential first step in developing effective conservation and management strategies. We studied age, growth and reproduction of Mediterranean brown trout from three headwater streams in northeast Iberian Peninsula. The maximum observed fork length was 382 mm in males and 322 mm in females, and six age groups (from 1+ to 6+) were identified. There was large variation in the back-calculated lengths for individual fish within ages. The von Bertalanffy growth curves were similar among streams and comparable to other European populations from small streams, but growth rate was lower when compared to larger and more productive rivers. Overall, sexual maturation began at age 1+, and the estimated L50 was 136 mm for males and 150 mm for females. Monthly variations in the gonadosomatic index showed that spawning occurred between late autumn and early winter, mainly in November and December. Mean fecundity and egg diameter were positively correlated with fish length, and values were within the typical range reported in other brown trout populations. Most of the differences among streams can be explained by differences in water temperature. These results constitute a contribution to better understanding of key aspects of Mediterranean brown trout biology, and to develop conservation and management strategies for preserving their populations.