Aquaculture International (2006) 14:171–177 DOI 10.1007/s10499-005-9023-0
Springer 2005
Changes in commercially exploited populations of tench, Tinca tinca (L.), in littoral zones of lakes of northeastern Poland ANDRZEJ MAMCARZ* and ANDRZEJ SKRZYPCZAK Department of Lake and River Fisheries, University of Warmia and Mazury in Olsztyn, 10-957 Olsztyn-Kortowo, Poland; *Author for correspondence (e-mail:
[email protected]) Received 19 November 2004; accepted in revised form 30 June 2005
Key words: Exploitation, Lakes, Littoral zones, Long-term changes, Stockings, Tinca tinca Abstract. Commercially exploited tench, Tinca tinca, (L.) populations in 480 lakes in the northeastern Poland were analyzed on the basis of the fishery data from 1949 to 1994. The long-term changes in tench catch were studied in four categories of lakes with respective proportions of littoral zones (90% littoral zone were the largest group in our study (Figure 2). Mean size of these lakes was 102 ha, mean maximum depth of lakes was 4.2 m (ranging: 1–10 m) (Table 1).
Figure 2. Littoral size frequency distribution of studied lakes in northwestern Poland.
174 Mean relative catch of tench for the 1949–1994 period varied from 0.36 kg ha)1 month)1 for lakes with the smallest littoral zone (90%) (Table 2). The value of this parameter increased as the contribution of littoral zone increased. Long-term trends in mean relative catch of tench reached maximum at the beginning of 1960s and 1970s (Figure 3). Later, in lakes with proportionally smaller littoral zones (60%). Lakes with different littoral zone proportions were stocked at similar rates throughout the studied period (Table 3). Mean stocking rates ranged from 421 to 584 one-year-old fish per ha of littoral in studied lakes. There were no significant differences among lakes categories during the 1949–1994 period. For all lake categories, mean relative catch increased as stocking rate of tench increased (Figure 4). Lakes with proportionally less littoral zone also had reduced stocking efficiency. In lakes with >90% littoral zone, an average of about 398 one-year-old tench were needed as the equivalent for 1 kg ha)1 month)1 of tench catch. In lakes with the smallest littoral (
