Brook lampreys spawning in the River Maine

Spawning survey

We took these photos and videos of brook lampreys Lampetra planeri spawning in the River Maine catchment, Co Kerry, during early April 2014. This work was undertaken as part of an ongoing survey of lamprey populations we are undertaking in this catchment. Water levels and clarity were ideal for the survey this week, although water temperatures were still a bit on the cold side at 10 degrees Celsius. However, brook lampreys were very active and we found several groups actively spawning both on the River Maine, and also on its tributary the Brown Flesk.

Videos of brook lampreys spawning

We took the following videos of brook lampreys spawning on the River Maine and Brown Flesk this week. These are just selected clips from over an hour of footage that we recorded.

Barriers to migration survey

There are also River lampreys Lampetra fluvialitis populations in the River Maine; although they are prevented from ascending into most of the catchment due to the presence of a barrier to migration – Inland Fisheries Ireland’s crump weir salmon counter which is located immediately upstream of the N22 road bridge. This prevents river lampreys from accessing most of the River Maine catchment, including the major Brown Flesk sub-catchment. This crump weir is also an impassible barrier for European eels. It is very disappointing that this structure was placed into the river in the name of conservation and now is causing such significant ecological damage. The counter when we visited it this week had electrodes which were heavily corroded and covered with algae, and cameras pointing away from the weir, so it is not clear if this counter produces any counts. It certainly could not produce accurate counts and no counts from this barrier to migration are publicly available.

Inland Fisheries Ireland's salmon counter is a barrier to migration to river lampreys, brook lampreys and eels.
Inland Fisheries Ireland’s salmon counter is a barrier to migration to river lampreys, brook lampreys and eels.

There are also some sea lampreys in the River Maine and they can pass this barrier, and we have found sea lamprey ammocoetes in the Brown Flesk. However, neither sea lampreys or river lampreys had commenced spawning at the time of writing the current post.

Bridge underpinning on the N23 road bridge on the Brown Flesk also acts as barrier to migration for Brook lampreys.

Bridge underpinning works are a barrier to migration for brook lampreys.
Bridge underpinning works are a barrier to migration for brook lampreys (and eels).

Other pressures

Water quality is a significant pressure on lamprey populations, and other aquatic life, in the River Maine catchment. Recent media reports about water quality problems in the Maine catchment suggest that the source of this pollution is some kind of mystery. However, there are a number of obvious point sources in the catchment and diffuse agricultural inputs are a major issue.

There are also a number of major siltation sources in the catchment that are affecting biological water quality. Parts of the river catchment have very unstable banks and are a significant source of siltation in the river. In some areas, such as the lower Brown Flesk, river works have destabilised the channel and are causing ongoing problems of bank erosion. For example a significant stretch of the Brown Flesk was diverted to construct Farranfore Airport and the river corridor here has never fully recovered from this.

A significant amount of OPW drainage maintenance works takes place on the river downstream of the N22 bridge to the sea, and much of this stretch of the river is channelised and has embankments. As drainage maintenance works specifically target and remove silt, this practice directly impacts on lamprey nursery habitats. Due to the presence of Inland Fisheries Ireland’s crump weir salmon counter, which is a barrier to migration for river lampreys, this species is disproportionately affected by the OPW drainage maintenance works on the river.

Non-native invasive species are a major concern in the catchment with Japanese knotweed Fallopia japonica and Himalayan balsam Impatiens glandulifera colonising large areas of river bank. These plants are further destabilising the banks, particularly on the lower reaches of the Brown Flesk.

Other observations

The River Maine catchment also contains Freshwater Pearl Mussels Margaritifera margaritifera and we also recorded this species during our surveys this week. The Freshwater Pearl Mussel population in the Maine catchment is on the verge of extinction due to absence of recruitment, over perhaps several decades, due to unsatisfactory water quality and siltation. This population currently has a poor prognosis based on the current water quality situation in the River Maine catchment.

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We also recorded significant numbers of juvenile trout and salmon during the survey.

If you have any queries about the work we do, or require any information on lampreys, please do not hesitate to contact us.

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