Grayling & Trout

Grayling/Trout interactions   Why conserve grayling stocks?   Conservation recommendations                   

Further information

Oaul Colley truot and grayling

Photo courtesy of  Paul Colley

This page has been produced with the kind assistance of Dr. Richard Cove, Grayling Society and Grayling Research Trust.

The Grayling Thymallus thymallus belongs in a cold-water fish family of 6 species distributed across parts of the Northern hemisphere (notably absent from Ireland). The presence of an adipose fin; a small fleshy protrusion between the dorsal fin and tail, places them firmly in the salmonid family - subfamily Thymallinae. They are typically smaller than trout with the largest specimens falling around the 2 kg mark. The largest species is the Mongolian grayling – thought to grow up to 4 kgs.

Grayling are familiar to many brown trout anglers; they are a well-known and easily recognizable species (see below; photo courtesy of David Miller) and because they often feature in anglers catches, there is a perception that grayling have the same habitat requirements as trout.

 

grayling david miller

 

On the face of it, grayling habitat; rivers and streams with strong flows and flow diversity and requirements; cool, clean well oxygenated water, resemble those of trout. There are subtle differences however for example: microhabitat use (time spent by grayling in different instream habitat during the course of the day), a lower pollution tolerance and slightly gentler river gradient. Even diets show a degree of segregation, partly due to differences in mouth shapes. For more, detailed information on grayling and their natural history see the links in Further Information).

Grayling/Trout interactions

Historically grayling have been widely trans-located within the UK from what are believed to be their original native rivers, the Thames, Yorkshire Ouse, Trent, Hampshire Avon, Severn, Wye, Ribble and Welsh Dee. Where they co-exist with trout, either as trans-located or native populations, there has often been a perception that competition for food and space between the two species has negative impacts on fisheries management for trout. In some Southern rivers, large-scale programmes of grayling culls were carried out to remove grayling from fisheries; anglers also viewed grayling as vermin, killing any they caught.  

A review of the literature strongly suggests that the division of resources and habitat between grayling and trout allows the two species to co-exist (Table 1 – adapted from Ibbotson et al, 2001).

Table 1 – Key differences in life history traits between Brown Trout & Grayling


Stylized picture showing typical trout (head of pool, faster current, near marginal cover) and grayling shoals (open water, tail of pool, slower current, deeper water) locations in a river pool. A study on the Hampshire Itchen found the highest densities of grayling in wooded sections with less macrophyte cover (see references).

Why conserve grayling stocks?       

Increasingly, across Europe as well as Britain, the perceived value of grayling as a sporting fish has grown. Grayling culling as a valid fisheries management practice is no longer supported (Policy 11 EA NTGS). Wholesale removal of one species, an almost impossible task, might (as yet uncorroborated by the literature) benefit the other species by freeing up habitat previously restricted to them. The benefits of a mixed fish population however outweigh removal as:

  • A mixed fish population allows more efficient use of available resources because of the different preferences displayed by both (Table 1). Therefore, a mixed fishery is ultimately more productive.
  • The habitat partitioning displayed by both species is likely to minimise competition.
  • Grayling are more active than trout during the colder winter months and their different spawning season extends the fishing season after the close of the brown trout season.

 

Conservation recommendations

  • Grayling are a valuable asset in any wild game fishery; many of the habitat enhancement/restoration techniques outlined by the WTT (click here to be redirected to the library) will help conserve and enhance grayling stocks.
  • New EA regulations are in place across England and Wales. Under these regulations, you may only remove two grayling between 30-38cm. Click here for more information.
  • The presence of grayling is an indicator of excellent water quality.
  • Grayling in the Thames, Yorkshire Ouse, Trent, Hampshire Avon, Severn, Wye, Ribble and Welsh Dee are thought to be original, native populations and should be protected from practices like stocking from other sources. The EA is reviewing grayling stocking practice based on a genetics project which found that UK grayling can be grouped into distinctive populations (see further information).

 

Grayling Conservation Trust – Grants available

The Grayling Society makes a direct contribution to the conservation and sustainability of the grayling, its habitat and fisheries. For some years the Society has, each year, allocated a sum of money to be made available to suitable projects which will directly benefit the conservation of grayling anywhere in the world.

Such projects could range from part-financing habitat improvement works, through initiatives such as the promotion of catch-and-release of grayling, to increasing access to grayling anglers on the riverbank.

If you would like to apply for a grant, check out relevant page on the the Grayling Society website: http://www.graylingsociety.net/conservation/

Further information

Academic references:

Dawnay, N., Dawnay, L., Hughes, R., Cove, R., & Taylor, M. (2011). Substantial genetic structure among stocked and native populations of the European grayling (Thymallus thymallus, Salmonidae) in the United Kingdom. Conservation Genetics, 12(3), 731–744. doi:10.1007/s10592-010-0179-4. Click here to read. With kind permission of Richard Cove.

Haugen, T. O., & Rygg, T. A. (1996). Food- and habitat-segregation in sympatric grayling and brown trout. Journal of Fish Biology, 49(2), 301–318. doi:10.1111/j.1095-8649.1996.tb00025.x

Ingram, A., Ibbotson, A., & Gallagher, M. (n.d.). The Ecology and Management of the European Grayling Thymallus thymallus (Linnaeus) Interim Report.

Riley, W. D., & Pawson, M. G. (2010). Habitat use by Thymallus thymallus in a chalk stream and implications for habitat management. Fisheries Management and Ecology, 17(6), 544–553. doi:10.1111/j.1365-2400.2010.00756.x