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Age and Growth 


Grayling Scale

 

The easiest way to age relatively young grayling is by taking a scale sample for examination under a low powered microscope or microfiche. 

Scales develop when grayling reach a length of 33-40mm (1,2). Scales first begin to form along the lateral line close to the caudal fin (2,3,4,5). They provide protection to the grayling and the ridges on their surface have a show pattern of wide summer rings and narrower winter rings.

 

Grayling become more difficult to age from scales as they get older because their rate of growth decreases and the distinction between summer and winter growth becomes more difficult.

 

Grayling in some waters have a relatively short life span of 3-5 years, but other populations are longer lived. Particularly old individuals can be found at higher latitudes and altitudes with associated lower water temperature (6). Males often mature at a lower mean age than females.

 

Scales grow as the grayling grows, although not exactly in proportion to the fish size. Appropriate correction for this allometric growth allows fisheries scientists to calculate the size of the fish at the end of each year's growth. This is called back-calculation. Growth in length is fastest in the first year and decreases as fish age. Grayling in the UK become sexually mature between 2 and 4 years old. Male grayling grow faster than females, this often becomes evident with the onset of sexual maturity, and the terminal length (Linfinity) is usually greater in males.

 

Many factors abiotic and biotic affect the growth rate of grayling including; temperature, flow, food availability, population density and predation.

 

Grayling growth curve (Britton 200&)

 Graphical presentation of reference grayling growth rate bands and expected growth curve as described by Britton (2007), based on UK populations. 

 

 

References 

1 Wootton, R.J. (1990). Ecology of teleost fishes. Chapman and Hall. Fish and Fisheries Series 1.

2 Taylor, R.J. (2012). Applications of fish scale analysis to understand growth dynamics of fish populations.

PhD Thesis. University of Hull.

3 Brown, C.J.D. (1943). Age and growth of Montana grayling. Journal of Wildlife Management 7,        

353 - 364.

4 Gustafson, K.J. (1948). Movements and growth of grayling. Report of the Institute of Freshwater

Research, Drottningholm 29, 35 - 44.

5 Peterson, H.H. (1968). The Grayling, Thymallus thymallus (L.), of the Sundsvall Bay area. Institute of

Freshwater Research, Drottningholm 48, 36 - 56.

6 Cihar, J. (1998). Freshwater Fish. Blitz Editions.

7 Britton, J.R. (2007). Reference data for evaluating the growth of common riverine fishes in the UK.

Journal of Applied Ichthology 23, 555 - 560.


 

 

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.