Assessment of lamprey abundance and distribution in the River Tweed SAC/SSSI, 2004

Ammocoete larvae of the two Lampetra species (L. fluviatilis and L. planeri) were widespread throughout the survey area, though larvae of the sea lamprey (Petromyzon marinus) were found only in the most downstream section of the main river Tweed. However, several age classes of P. marinus larvae were found, indicating regular breeding in this section of the river in recent years. Variable numbers of age classes of Lampetra larvae were also apparent. Post-larval macropthalmia stages of both Lampetra species were also found. Generally, those of L. fluviatilis were in the larger channels of the main Tweed and major tributaries, while those of L. planeri were in the smaller channels as well. Historic and recent records of adults confirm the wide spread of the Lampetra species, but suggest a more extensive range for P. marinus breeding than shown by this survey. High abundances of Lampetra juveniles were found at relatively few survey locations. This indicates that most bankside habitat in the Tweed catchment is of little importance for lamprey, but that the areas of good habitat where high levels of abundance do occur could be of critical importance for local populations.