Case Study: Developing a conservation strategy for spined loach
The inclusion of Spined Loach on Annex II of the EC Habitats and Species Directive meant that this poorly-studied small, bottom-dwelling fish suddenly became a focus of conservation attention. We were initially commissioned by English Nature (becoming Natural England) to undertake a literature review of its biology, ecology and behaviour throughout its European range and to compile the records of the species in the UK.
It quickly became clear what an unusual little fish Spined Loach is:
In the UK, Spined Loach occurs naturally in just five east-flowing river catchments: Trent, Welland, Witham, Nene and Great Ouse. Spined Loach thus was one of a group of fishes including Silver Bream, Barbel and Burbot (now extinct) indigenous to the UK as a result of the connection to the continental Rhine system prior to separation of Britain from continental Europe at the end of the last ice age. The tiny size of Spined Loach meant that it had not been translocated into other catchments for angling purposes, although its occurrence in the Essex Stour catchment appeared to result from a water transfer scheme and it appeared to have colonised some sites such as Little Paxton and Great Linford gravel pits naturally from nearby rivers as a result of flood events.
The Habitats and Species Directive required the designation and appropriate management of Special Areas of Conservation (SACs) for the species. To begin the process we needed to assess Spined Loach population size and structure in the catchments it occurred. In order to do that we had to develop one or more sampling methods geared to this cryptic and very small species with only the largest adults reaching 10 cm and most of the individuals in the population being 6 cm or less. Using our experiences with Dr Bob James in sampling shrimps and small fishes in shallow inter-tidal waters, we developed the hand trawl for Spined Loach. This small trawl on sled-like runners was set from a small boat at a measured distance and then pulled to shore, with the tickler chain in from of the net ensuring that any loach buried in the sediment were disturbed and captured. Where dense vegetation cover precluded the use of the hand trawl, point-sample electric fishing proved to be an effective alternative quantitative sampling technique.
After sampling a range of ditches, drains, streams, rivers and lakes (36 water bodies in all) we determined that a good population of Spined Loach contains 3-4 age classes with a preponderance (more than 50%) of fish less than one-year of age, at a density of at least 0.1 individuals per m2. Spined Loach was also often a good indicator of higher ecological condition, although its adaptations to low dissolved oxygen with a high gill surface area and the ability to gulp air from the water surface, meant that it could survive conditions that other fish could not. The lack of larger fish competitors and predators meant that Spined Loach could then thrive and even reach high population density (more than 1 individuals per m2) in waterbodies with relatively poor water quality.
As a result of our research we recommended the designation of at least one SAC within each of the catchments in which Spined Loach occurred would be prudent considering the possibility that Spined Loach could occur as different races or even species within the UK. Ultimately, we are very pleased to note that five Special Areas of Conservation (SACs) have been selected: River Mease in the Trent, Baston Fen in the Welland catchment, Nene Washes (including Moreton's Leam) in the Nene and Ouse Washes and Fenland (including Wicken Fen) in the Ouse. Research at UEA by Mark Culling and Isabelle Côté has since shown that although genetic diversity of the species was generally low in the UK, samples from the Trent and Witham catchments harboured haplotypes that were not known to occur anywhere else in Europe, indicating these catchments are important for Spined Loach conservation. We hope that a SAC within the Witham catchment can ultimately be designated.