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Migration


Grayling make small migrations for foraging within a home range (the area which an animal normally travels), shifts in habitat with age or season, and occasionally long distance migrations such as spawning migrations from river to tributary. These spawning migrations to find suitable habitat for spawning can result in grayling migrating 100 m or several km. In each case a degree of homing behaviour is displayed. Grayling regularly perform small short term foraging movements, returning to a specific spot in their own territory, or sometimes called its lie. A grayling's home range can be as small as 1km radius but can be as large as 10 km.


Grayling display 2 distinct behavioural strategies

  • A large static group occupy a home range and hold a specific station in their territory, occasionally foraging trips within a specified area around it
  • A smaller group which forage widely and do not appear to hold any particular territory

This second behaviour may be related to poor habitat or high population density.

 

Grayling make seasonal movements, changing shifts in relation to depth and position.
Grayling move to deeper slower flowing water in winter, and fast, shallower more well oxygenated water in the summer, especially associated with spawning.

 

Spawning

 

Grayling make spawning migrations to suitable spawning habitat. Homing in this case is the ability of fish to return to its natal river and is one method of ensuring reproductive isolation. Grayling display high site fidelity, returning to the precise pool-riffle sequence in which they were before they left to spawn. The mechanism controlling such homing behaviour is unknown but the use of chemical cues as guidance has been suggested.

 

Barriers to Migration

 

The inhibition of grayling migration is of concern where habitats required for different life-stages are separated by man-made obstacles, or where local extinction has occurred in areas above impassable barriers that prevent recolonisation from populations which still exist downstream. Where the former applies, distribution may become patchy and the populations may demonstrate high local fluctuations in population size.

 

 

There is very limited evidence of populations having become extinct in the UK as a direct consequence of the interference of migration between essential habitats, but this does mean they have not occurred. It is easier to identify patchiness in the local population sizes of grayling which may result from barriers in many river systems. In many cases what seem to be quite minor barriers appear to inhibit grayling mobility and the ability to populate particular areas. Similarly, grayling have been found below barriers, after being washed downstream during flooding and were unable to regain their upstream position due to the presence of an impassable barrier.

 

Fish Pass Design

 

There is very little information on fish pass design which has been specifically tailored for grayling requirements. Barriers negotiable by other Salmonids, such as trout and salmon, may restrict grayling migration. The problem of negotiating apparently minor barriers may be a behavioural reluctance to migrate past them. As a result, the characteristics of river structures that act as barriers to grayling require further research.


 

 

GS Symposium Speakers

GRT Funded MSc, PhD Studies

Two degree project interim reports were among presentations at the most recent Grayling Society symposium. Both studies are currently funded by the GRT and both operate on a premise that alongside the intrinsic value of grayling as a game fish, their survival challenges provide early indication of problems that are or will likely become problems for other salmonids.

 

Stephen Gregory (Game and Wildlife Conservation Trust) described an MSc study plan for statistical mining of the existing Wylye Study data, questioning the effect of extreme climate events on grayling population dynamics. He emphasized that the GWCT now leads all processing aspects of the 30-year Wylye Grayling Study (WGS) dataset - the longest and most complete in Europe...possibly in the world.

 

Vanessa Huml's (Manchester Metropolitan University) PhD study is titled Assessing adaptive genetic variation for effective management and conservation of European grayling. Read her description of planned work, noting reference to new sequencing technology and reference to the four U.K. genetically distinct groups identified in the earlier genetic census funded by the GRT.

 

The two studies both look at grayling population health/stability under extant environmental conditions but the doctoral work extends inquiry to genetic proclivity for survival ('evolvability').

 

Both investigators will submit detailed results for publication here after review in their respective peer literature.