Survey methods

Introduction

Most protocols developed for juvenile lamprey surveys are based on ammocoete surveys. Early developments in this field emerged largely in North America during
the effort to control invasive sea lamprey in the Great Lakes region of North America, but recent sampling developments have been in a context of lamprey conservation (Moser et al, 2007).

The methodology we use follows 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). We identify lamprey habitats using the descriptions given in the ‘Ecology of River, Brook and Sea Lamprey‘ by Maitland (2003), and we identify lampreys using the manual ‘Identifying Lamprey. A Field Key for Sea, River and Brook Lamprey‘ by Gardiner R (2003). We also undertake River Habitat Survey (RHS) following the ‘River Habitat Survey in Britain and Ireland Field Survey Guidance Manual’ published by the Environment Agency (2003).

It is noted that we formerly placed a fine mesh on our anodes to capture lampreys; with an assistant also with a dip net. This is apparent from the photos below. Although we have never had issues with this and exercised due care to avoid full electronarcosis of captured lampreys, we no longer use mesh on electrodes as a precautionary approach and to align ourselves with current international best practice. 

Habitat survey

Any lamprey surveys needs to be preceded by a lamprey habitat survey, to allow surveys sites to be picked in advanced. This is probably the most important part of the sure, as it will determine which sites you will end up sampling. Optimal habitat for juvenile lampreys would be areas where several square meters of stable fine sediment overlain with a layer of fine organic detritus occur. These areas are also likely to be be shaded and occur in slow flowing stretches of a river.

Optimal juvenile lamprey habitats? We moved over 1,250 brook lampreys from a 100m of this stream that had been described a 'just a drain'. The stream had to be diverted to facilitate construction works. We said that there might be lampreys here, and there sure were!

Optimal juvenile lamprey habitats? We moved over 1,250 brook lampreys from a 100m of this stream that had been described a ‘just a drain’. The stream had to be diverted to facilitate construction works. We said that there might be lampreys here, and there sure were!

Juvenile lamprey surveys

When surveying juvenile lampreys we use a stop net and back-pack electrofishing unit. The standard methodology is to enclose three patches of habitat of 1 sq-m at each sub-site, and fish for 2 mins per sq-m (or until lampreys stop emerging). At sites where densities of lampreys are low however we use larger sub-sites (5m each).  You don’t have to use stop nest, but we do as it makes it easier to stay within the chosen area and measure it accurately. Using a stop net often helps stop lampreys fleeing the area; particularly if you are working on a large patch of sub-optimal habitat. It is often difficult to find exactly 1m sub-sections of optimal lamprey habitat and their are practical difficulties with type of survey, on drained rivers in particular. Enclosing a 5 m area is much easier to achieve, but if you are surveying a river which has very high densities of juvenile lampreys you will have too many lampreys to process if you use larger sub-sites.  Surveys should only be undertaken during normal or low water levels. Our own opinion is that you quantitative sites should only be completed at a selection of sites within the overall survey, as it is so time consuming and you get so little additional information from it. You are better to do more sites, than spend time doing depletion fishing at every site.  We also fee this way about salmonid surveys.

This photos in the gallery above shows a selection of  sub-sites we have surveyed, and we would look at three areas (sub-sites) like this over a 100m of river to make one site.

Some of the equipment required for lamprey measurement and identification

Some of the equipment required for lamprey measurement and identification

At selected sites we undertake depletion fishing to provide fully quantitative data if necessary. However, this is very time consuming and provides little additional information in our opinion but should be done a few representative sites during each catchment survey. Detailed habitat information is recorded at each sub-site, including River Habitat Survey (RHS) and Rapid Assessment Technique (RAT) methodology.

Adult lamprey surveys

Adult lamprey surveys can be undertaken using visual observations in the the spring and early summer at sites where habitats are considered suitable.  The lamprey spawning season extends from March to July and depends on species and water temperature.  Generally when water temperatures approach 12ºC it is likely that lampreys will commence spawning. River and brook lampreys spawning earlier in the season than seas lampreys. Lamprey redds (especially sea lamprey redds) are conspicuous constructions and it is not difficult to detect new activity by the disturbance to the substrate.

We are Ireland’s leading ecological consultancy, and no other company in Ireland has the range of expertise in aquatic ecology and fisheries as we have

Walkover surveys require wading with chest waders, or snorkelling with a wet suit. Sea lamprey spawn in strong flows, so a wading stick, to aid balance, is recommended. Care should also be taken to not disturb the lampreys; however they are usually oblivious to your presence as long as you keep at least 5m away from them.

The disturbances apparent on the gravels on this part of the River Mulkear, Co Limerick, are evidence of recent sea lamprey spawning

The disturbances apparent on the gravels on this part of the River Mulkear, Co Limerick, are evidence of recent sea lamprey spawning

Adult sea lampreys on the River Fergus, Co Clare

Adult sea lampreys on the River Fergus, Co Clare

Sea lamprey passage can also be monitored through some fish passes which they are able to use.  They can use denil passes to at least some extent, and have been picked up on video cameras using such passes. We have also seen them on video passing through video monitoring facilities at Ardnacrusha dam on the lower River Shannon where up to 20 use the fish lift (or fish lock) at this location each year; probably accidentally.

Juvenile lamprey identification

Lampreys can be identified to species level in the field (for the majority of specimens) using the key ’Identifying Lamprey. A field key for Sea, River and Brook Lamprey‘ by Gardiner (2003). In terms of identifying lampreys we do not think that destructive sampling is necessary. It is generally possible to identify most ammococoete individuals as being either sea lampreys or river/brook lampreys in the field with reference to their tail shape and tail and oral hood pigmentation. We are able to count the  number of trunk muscle blocks (myomeres) running down the ammocoete body from the anterior gill opening to the anus; sea lamprey myomere counts range from 69–75, but Lampetra sp. counts range from 57–66. This provides a definitive identification between sea lamprey ammocetes and Lampetra sp. juveniles and can be completed under anaesthetic in the field with the individual then revived and released. If you are surveying lampreys in a part of a catchment not accessible to anadromous river lampreys (i.e. upstream of a dam like the ESB dams on the Shannon, Lee, Liffey, Erne and Lee you can be sure that it will be impossible for river lampreys to here. There is always the possibility of  landlocked populations however,, particularly sea lampreys.

Lamprey identification

Four age groups of brook of juvenile Brook Lampreys from the River Brosna catchment in the Irish Midlands. The smallest individual is a young of the year larvae, while the largest specimen is fully transformed. We can be sure that these are brook lampreys as this site is above the Shannon hydroelectric scheme and other obstacles.

References

If you require any additional information on lampreys please do not hesitate to contact us. We are Ireland’s leading ecological consultancy, and no other company in Ireland has the range of expertise in aquatic ecology and fisheries as we have.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s