Age-growth Structure of Spawning Sea Trout Population from Pomeranian Rivers

The biology of trout in Pomeranian Rivers have been described by many authors. They described the growth and age structure of fry in rivers, smolts flowing into the sea and mature fish migrating from the sea to the river for their spawn. But the last investigation was made in the 80s last century. For this purpose we carried out analysis based on collected in one year materials from the trout to spawn. Materials were taken from most of Pomeranian Rivers. Analysis of length, weight, condition factor, river and sea age and sex were performed on 584 fish caught in late autumn 1999. Fish were caught in six of Pomeranian Rivers, such as: Rega, Parseta, Wieprza, Slupia, Leba and Lupawa. In the study examined fish were from 36 to 88 cm long. The widest range of lengths had fish from Wieprza and the smallest from Lupawa. The biggest trouts of both sexes came from Wieprza. Weight of examined fish ranged from 0.4 to 6.7 kg, and the widest range had sea trout from Wieprza, while the smallest sea trout was from Leba. Condition factor K-F ranged from 0.77 to 1.09 and was higher in males than females. Condition factor variations were small, while variations in size were greater and associated with the fact that we were comparing fish of all sea ages. Size variations among fish of the same age should be smaller. While analyzing fish rivers' age we found that in all rivers dominated 2-years old smolts. They constituted 94.2% to 100% of the total population (average 96.9%). 1-year old fish were accounted for only 0.34% and the 3-years old for 2.74% of the population. This kind of structure in the system of gender was similar in all rivers. The age-growth structure of the sea trout was more diverse. In each river dominated two groups of age, such as: A.1+ and A.2+. From them, in almost all rivers were fish at the sea age A.1+. They ranked from 61.6% in Rega up to 75.2% of the population in Slupia. Only in Wieprza predominated A.2+ fish (65.4%). That school of fish was very numerous, with a predominance of older fish. Ages A.3 + accounted as a small fraction (2.4%). There was also a small proportion of the fish at the age A.0+ (2.7%). However, describing the fish separately by gender, the structure was a little different. Fish at the age A.1+ dominated in all rivers, except Wieprza River, where the largest group were fish A.2 +. Males A.1 + group accounted for more than 3/4 of the trout population from Pomeranians' Rivers. Sizes obtained by spawning trout in 1999 in Pomeranians' Rivers, were within the typical range for these rivers, based on data from literature. Also their nutritional status was similar. In groups of freshwater, dominated as it used to be, 2-years old smolts, but in seawater period fish A.1+ and A.2+.