More brook lamprey spawning activity

Our brook lampreys surveys continued this week and we recorded a significant amount of brook  lamprey Lampetra planeri spawning activity on the River Maine (and its tributary the Brown Flesk) this week. A selection of the photos are provided below.  We have also provided a link to another one of our websites where we have posted a full set of photographs and also videos of brook lampreys spawning.

To see the full set of photographs and videos from this brook lamprey spawning survey survey please see this post Brook lampreys spawning on the River Maine‘.

We also provide some comments on the link above regarding how a crump weir used for counting salmon and sea trout acts as a major migration barrier to lampreys (and European eels) in the River Maine catchment. We also highlight bridge underpinning works on the Brown Fesk which act as a barrier to brook lampreys.

The Brook lamprey is the smallest of the three Irish lamprey species, with adult lengths ranging from 12–15 cm. The teeth are blunt and less developed than in the other two Irish species (L. fluviatilis and Petromyzon marinus) whoch are parasitic as adults. The brook lamprey is also a non-migratory species, unlike the other two lamprey species which are anadromous. However, the book lamprey does undertake localised river migrations from the nursery areas to spawning areas, which is some cases can be a significant  distance up river.

Larvae (or ammocoetes) are initially semi-translucent and become dull grey-brown in colour as they get older. Larvae occur in suitable beds of silt and silty sand, mainly in rivers but sometimes in lakes. Brook lampreys are usually cryptic and nocturnal and are rarely seen except at spawning time (March to May) when they move into shallow water during daylight to start their communal nest-building and spawning activities.

Lampetra planeri spawning (10)
Scarred, bruised and exhausted, a brook lamprey after spawning waiting to die.

During the spawning season, adults move from nursery areas and migrate upstream at night until they reach suitable spawning habitat. These are areas of small stones and gravel in flowing water where the current is present but not too strong. When the water reaches 10–11ºC they tend to spawn at the lower ends of pools, just where the water is starting to break into a riffle. The spawning areas they select are often very similar to those used by brown trout. The nest (or redd) may be constructed by 10 or more adults moving stones with their suckers and is normally an oval depression 20–40 cm across and 2–10 cm deep. Females produce about 1,500 ova each and hatched larvae (3–5 mm long and blind) drift downstream to burrow in suitable areas of silty sand. The adults die soon after spawning.

Larvae live for around 6.5 years in Ireland, filtering fine organic particles from the silt. Metamorphosis occurs during July to September, after which they are more silvery, though the back remains dark. They also develop teeth and full vision, though adults do not feed. Upstream migration can only occur in the absence of barriers, either natural (i.e. waterfalls or cascades) or anthropogenic (i.e. weirs, dams or polluted stretches of river). Obstacles such as crump weirs used to count adult salmonids are total barrier for brook lampreys (and river lampreys).

Inland Fisheries Ireland crump weir fish counter on the River Maine blocks access for river lampreys, brook lampreys and eels.
This crump weir fish counter on the River Maine blocks access for river lampreys, brook lampreys and eels.

Brook lampreys do have some tolerance to pollution, but it is considered that their spawning areas and ova/larvae are very vulnerable to pollution. Channelisation, drainage maintenance works and even fisheries development works  have been damaging to lamprey habitats in Ireland. Dredging of silt beds can entirely eliminate lampreys from a river.

Brook lampreys are the most abundant and widespread of the Irish lampreys; however it is clear that they are under numerous pressures in Irish rivers.  They have declined in several parts of Europe, and it is clear that they could quoite quickly go the same way here if we do not meet their relatively basic acquirements in rivers. The brook lamprey has some legal protection in Ireland and is listed under Annex II of the EU Habitats Directive.

We are Ireland’s leading aquatic ecology experts. If you have any queries regarding  lampreys or require a lamprey survey or other aquatic ecology survey or assessment please do not hesitate to contact Dr. William O’Connor at +353 61 419477.

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