Rapid visual assessment of spawning activity and associated habitat utilisation of sea lamprey (Petromyzon marinus Linnaeus, 1758) in a chalk stream: implications for conservation monitoring

Abstract

The anadromous sea lamprey (Petromyzon marinus L.) has a native geographic range extending across the Northern Atlantic, colonising the rivers of countries abutting coastal shores between Labrador, Canada to Florida in the West (Renaud, 1997) and from Norway into the western Mediterranean to the East (Kottelat and Freyhof, 2007). Beyond its native range, the species has capitalised on the anthropogenically-engineered connectivity between the West Atlantic and the Great Lakes (Hartman, 1972). In this extended range, it is invasive and considered a pest (Smith and Tibbles, 1980). In its native range, however, their populations are in general decline through factors including river fragmentation, habitat loss and declining water quality (Renaud, 1997; Almeida et al., 2002; Maitland et al., 2015). Correspondingly, it has conservation designations under Annex II of the EU Habitats Directive (Directive 92/43/EEC). These designations require their populations to be monitored regularly and conservation status evaluated.

The monitoring of P. marinus populations currently focuses on the cryptic, relatively sedentary and extended (~5–6 years) life stage of the ammocoetes (larvae) and thus attempts to quantify recruitment success and nursery mortality in these early life stages (Harvey and Cowx, 2003; Quintella et al., 2003). Data validity, however, remains sensitive to the confidence associated with preferred microhabitat utilisation; most studies have focused on water depths below 1 m (e.g. Malmqvist, 1980; Potter, 1980; Beamish and Jebbink, 1994; Beamish and Lowartz, 1996; Almeida and Quintella, 2002; Sugiyama and Goto, 2002; Torgersen and Close, 2004; Lasne et al., 2010) yet the recent development of habitat utilisation curves suggests marked preferences for deeper nursery habitats (>2 m; Taverny et al., 2012). Moreover, there is little attention given to their adult life-stages, despite the number of returning adults being potentially important for the subsequent numbers of ammocoetes (Quintella et al., 2003). Whilst this may be understandable when the adults are at sea, their presence in freshwater potentially provides valuable monitoring opportunities that would provide complementary population level data, such as adult numbers, nest counts and upstream migration distances.

Consequently, the aim of this study was to utilise the P. marinus spawning migrants of an English chalk stream to provide initial assessments of (i) the value of nest counts as a population and conservation monitoring tool; (ii) distances moved upstream to spawn and in relation to potential blockages to migration; and (iii) identify the habitat utilisation of spawning adults. The value of these data are then discussed within a conservation context.