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Eyed eggs

The fecundity and egg size of grayling increases with size, females have between 3500-10000 eggs per kg. As a result the weight of an individual increases prior to spawning, female grayling are often heavier than males of the same length. Grayling eggs are smaller than those of salmon and trout and are approximately 3-5 mm in diameter, yellow in colour and normally located on the surface of gravel, although the activity can result in the burial of some eggs up to a depth of about 5 cm.



How to sex graylingSpawning occurs in spring, usually late April to mid-May, but can occur between the end of March to the first weeks of June. Spawning commences when river temperature are between 3-11 oC, up to 14 oC. Males arrive on the spawning grounds several days before the females and defend their territories, courting females as they approach. Males usually out number females and the oldest and largest grayling spawn first.

Spawning is initiated by the males vibrating display, which attracts females, visual and olfactory stimuli are important. The spawning substrate is of importance even though the grayling do not create a large redd. This behaviour can be seen in the video below at approximately 1 minutes.


Eggs hatch after 177 degree days (25 days at a temperature of 7.08 oC), the optimum temperature for hatching is between 7 oC and 11oC. An approximate time for emergence post hatching is 10 days. An increase in temperature increases the hatching rate, up to 15 oC where a further increase in temperature has little effect.  Eggs can suffer mortality from abiotic (predation, disease, genetic fitness) and biotic (flooding, drought, temperature) factors. After hatching, grayling feed on their yolk sac for 4-5 days before emerging from the gravel. Fry begin feeding near the water surface before the yolk sac has been fully absorbed, complete re-absorption occurs after 12 days (156 degree days).  Grayling fry first emerge at length between 10-19 mm. Emergence from the gravel, unlike other Salmonids, is diurnal rather than nocturnal (occurs during the day). Emergence peaks at dawn, but displacement downstream does not occur until nightfall.



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.