| Abstract [eng] |
A survey for the presence and abundance of brook lamprey (Lampetra planeri), river lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus) ammocoetes were conducted in West and East Lithuania rivers, which are mainly chosen for lampreys to spawn. The research was carried out in Minija, Danė–Akmena, Merkys, Žeimena and Šventoji River basins during 2007 09 013 – 2010 04 11 period. Lampreys were surveyed at 67 pre-selected sites. Ammocoetes habitat was present at each site and full quantitative sampling was undertaken using a 1m2 quadrant and the density estimated by scooping out substrate. All lampreys encountered were retained and examined under anaesthesia (3-4% diethyl ether water solution) prior to being returned to the water unharmed. Ammocoetes were examined and identified as either Lampetra spp. or P. marinus (Gardiner, 2003). A total of 848 Lampetra spp. ammocoetes, 1 transformer of L. fluviatilis and 6 L. planeri adults were sampled from the 50 sites. As well 1 P. marinus ammocoete occurred in samples. The mean densities of sites ranged from 0 m–2 to 54,3 m–2. The highest density occurred at River Mišupė, in the River Minija basin, although this was a single case with such a high density. Overall comparing ammocoetes densities with the available data from former studies a huge decline in ammocoetes density is observed during 4 decades (from 15 to 30 times). This is mainly the impact of increasing environmental pressure on rivers such as dam construction, development of drainage system and increasing eutrophication of water bodies’. According to ammocoetes abundance and densities there was determined river sections and tributaries in already mentioned rivers, which are chosen by lampreys for spawning. Additionally there were created two log-log regression models in small and medium scale rivers for ammocoetes distribution down the spawning grounds. The effect of granulometric composition of substrate (particles size from 0,001mm to 100 mm) in sites on ammocoetes abundance in samples, as well as the effect of specific electric conductivity on ammocoetes density were evaluated. |
