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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.


 

Latest News

                                                                                                                                                                    Take Part in our Spawning Survey

The Grayling Research Trust launched a project in 2013 to record sightings and the timing of grayling spawning and we are continuing this project annually. If you are out on the river bank and notice grayling spawning, please let the GRT know: the River, Date, Location (NGR, or marked up map, if possible but certainly at least nearest town/village) and any additional observations. To make reporting sightings easy, complete the short submission form or simply tweet us (@GRT_Updates or #graylingspawning). Further details or latest sightings.

More News ...

GRT_Updates RT @IFMFish: We have 5 #fishy events coming up in the next 2 months incl Lamprey, smolts and enforcement. Check the website http://t.co/v2p
GRT_Updates @WildTroutTrust brilliant thank you
GRT_Updates RT @RiverFishUk: @GRT_Updates bit further up will fill in the grayling spawning survey, fantastic to see the male wraping his fin over the …
GRT_Updates @RiverFishUk was this at bakewell on the Wye?

 

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