Deep water sampling

Deep water sampling for juvenile lamprey

It has been suggested for some time that sea lamprey ammocoetes may utilise deeper water habitats which are not covered by the standard methodology given in Natural England’s publication ‘Monitoring the River, Brook and Sea Lamprey, Lampetra fluviatilis, L. planeri and Petromyzon marinus‘ by Harvey & Cowx I (2003).

Lamprey survey
Sea lamprey (top) and Lampetra sp. ammocoetes.

Surveys conducted lamprey in Scotland showed that sea lamprey ammocoetes used sediments in deeper pools to  greater extent river/brook lamprey ammocoetes (Teague, 2003). Taverny et al (2001) undertook an important study in the Gironde-Dordogne catchments in France.  In this study the habitat requirements of lamprey ammocoetes, of both sea lampreys (Petromyzon marinus) and Lampetra sp.), were investigated from shallow to deep waters using a water suction dredge. This important study found that sea lamprey larvae occurred in deeper areas than their Lampetra genus counterparts. Taverny et al (2001) found that ‘pools’ of 2 m’ depth and more were optimal habitats for juvenile sea lampreys. It is noted that this is beyond the reach of standard backpack electrical fishing surveys which are limited to water depths of less than 1m.  This finding may explain why sea lamprey ammocoetes often not observed or are only found in disproportionately smaller numbers than river/brook ammocoetes, even in rivers where extensive and obvious spawning of sea lampreys occurs. The finding of the Taverny et al (2001) and previous studies have significant implications for the monitoring of sea lamprey populations in Natura 2000 rivers. The preliminary results of the Taverny et al (2001) study suggested that the use of water suction dredges may be an effective way to monitor sea lamprey populations.

Bergstedta & Genoveseb (1994) also describe an effective device for sampling sea lampreys ammocoetes in waters too deep to wade and sample using standard backpack electrofishing equipment. The sampler they proposed uses electricity to stimulate emergence of larvae from the substrate and a pump to move them to the surface for collection. Capture efficiency was negatively related to larval length, but these authors considered that it would be possible to correct population density estimates to account for this factor if length data are collected from the catch. Suction or dredging methods sometimes combined with electrofishing may be required in deepest waters; however dredging methods can severely damage riverbeds and lamprey nursery habitats. However, sampling small surface areas limits the impact of such a protocol.  It is clear that a combination of different methods is probably the best way to sample all the kinds of river habitat for ammocoetes.

snorkelling survey
Snorkelling surveys can help locate lamprey habitats in deeper water. Lampreys could then be sampled by dredging within a serber type quadrate as described in the Lasne et al (2010) study.

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 are experimenting with using this approach to sample deep water habitats using two people snorkelling.

ECOFACT are at the forefront of this research and have been investigating a number of methods to sample juvenile lampreys from deeper habitats. Contact us for for further information.

References

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