The most recent SCM for lampreys within the Tweed SSSI/SAC conducted in 2011 (Watt et al., 2012) reports on the spatial distribution and relative abundance of lamprey larvae across a network of 42 sampling sites within the Tweed catchment. The Statement of Requirement (SoR) for the 2018 Site Condition Monitoring (SCM) for Tweed lampreys states that the objective is to provide “a detailed description of the population size, composition, and distribution of brook, river and sea lamprey larvae in the River Tweed SSSI/SAC”.
We are mindful that the current CSM approach of larval sampling (JNCC, 2015) has recently attracted criticism as constraining the collection of biologically meaningful data (Pinder et al., 2017), since the association between larval abundance and conservation status of lamprey populations (stable, increasing or declining) is uncertain and remains largely untested. There is a strong argument that SCM monitoring strategies should be adapted for individual SACs, building wherever possible on existing data sets to illuminate issues of concern, while still allowing for reliable condition assessment within the constraints of the required monitoring techniques and SCM targets.
We are also conscious that the current SCM targets (JNCC, 2015) for Lampetra species and sea lamprey are based on measuring different variables. Lampetra targets are based largely on density, whereas the sea lamprey target is based on spatial extent. This presumably recognises the low confidence attached to any density estimations based on the small number of sea lamprey larvae typically encountered during larval surveys. With limited resources, this means a balance will need to be struck between a) maximising the reliability of density estimates for Lampetra and b) optimising the likelihood of encountering sea lamprey throughout their current range.
Identifying the status of river lamprey is also of biological concern, but to some extent may be a lesser priority due to the constraints imposed by larval monitoring i.e. the inability to distinguish river and brook lamprey larvae. Furthermore, Lampetra density targets for SCM encompass both species.
With the need for achieving a reliable condition assessment that is based on the density and distribution of larvae as our priority, we believe that simply repeating the 42 sites sampled in 2011 may not be the most efficient or effective use of resources at this time. This is particularly true in relation to the provision of reliable and useable condition assessment data for the sea lamprey population within the Tweed SSSI/SAC. We are mindful that the current prescribed SCM methodology may be relatively effective for determining Lampetra abundance, and enable comparison against density thresholds, but that it is likely to be inefficient for optimising information on sea lamprey distribution.