Sea lamprey are the largest of the three species of lamprey found in Ireland and may reach a length of almost 1 meter. Lamprey resemble eels in external appearance and, although not related, are sometimes called “lamper eels” by fishermen. The life cycle of sea lampreys is anadromous, like that of salmon.
The young are born in inland rivers, live in the ocean as adults, and return to the rivers to breed. Young emerge from the egg as larvae, blind and toothless, and live that way for 3 to 8 years, buried in mud and filter-feeding. These young lamprey are called ammocoetes. Once they have grown to a certain length, they metamorphoses into their parasitic form, after which they migrate to the sea. During metamorphosis they develop a sucking oral disk that allows them to attach onto host fish. Parasitic lamprey feed on the tissue and blood of fish. After several years they become sexually mature and stop feeding. Sexually mature lampreys return to their natal freshwater rivers and streams to spawn, after which they die. Due to their larger size, they are capable of moving quite large rocks to construct their spawning nest or redd. Spawning takes place in May – June. Sea lamprey are commonly observed in the Mulkear River at this time above the Annacotty Bridge. The main anthropogenic threats to lamprey are habitat destruction, migration barriers and pollution.
Upstream passage has been a major problem for sea lamprey on the Mulkear River and in most years, adults do not have access to most of the river channel. The weir at Annacotty has been modified to ease lamprey passage but its effective must be tested.
The weir at Annacotty is a migration barrier that prevents lamprey from accessing the rest of the river. Modifications to the weir have allowed some lamprey to ascend and access the upper watershed. The project aims to find a permanent solution to lamprey passage at the weir and monitor lamprey movements throughout the catchment by radio-tracking, snorkeling and electrofishing surveys. In addition, the other weirs in the catchment will be assessed to determine the need for possible work.