Dredge sampling

Dredge sampling with a hand net

Juvenile lampreys can be sampled qualitatively using a string framed kick sampling net which is used to “dredge” a small area of sediment. This method can be used to determine the presence or absence of juvenile lampreys at site. As the method caused disturbance to habitats this approach should only be used in localised areas, and as an approach to establish presence / absence only. We have found this approach useful to quickly establish if lampreys are present at a site. It should be limited to small areas of habitat only and sampling should be stopped once it is confirmed that juvenile lampreys are present.

Substrate selection by subyearling European river lampreys (Lampetra fluviatilis) and older larvae (Lampetra spp)

Brook lamprey sampled by dredge sampling with a kick sampling net

Surber type sampling

Lasne et al (2010) describe a new sampling technique for larval lamprey population based on a Surber sampler. In this study larval lampreys were sampled in a small river using a new method modified from the Surber bottom sampler for invertebrates. This method uses a rectangular dredge to sample a constant and small surface of sediments in soft substrate areas. We have also used a standard surber sampler to survey lampreys, with some success.

Examining lamprey catch using standard surber sampler

Examining lamprey catch using standard surber sampler

Monitoring of Dredging

Lampreys can be examined within any sediments removed from a river; for example during river dredging with machine bucket or suction dredging undertaken as part of river or navigation maintenance schemes.  This approach results in juvenile lamprey habitat loss, but on many Irish rivers this type of work is done and collecting lampreys from dredged material can provide both information on lamprey populations, and also allow lampreys to be returned to the river.

It is noted that monitoring of spoil for lampreys (and crayfish) dredged from river during drainage maintenance works in Ireland is not regularly undertaken, although it is feasible to do this.  It is claimed by Irish state authorities that machine operatives look out for lampreys, crayfish (and indeed even Freshwater Pearl Mussels) and keep records and return specimens to the water. However, it is clear that none of this is ever done.

Reference

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