Applications of fish scale analysis to understand growth dynamics of fish populations

Taylor, Ryan James

Biological sciences
April 2012

Thesis or dissertation

© 2012 Ryan James Taylor. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The use of hard structures to derive ecological information about fish populations is a fundamental tool in fisheries assessment, specifically the back-calculation of fish lengths. This study highlights the potential errors associated with correction factors (c) because of poor sampling and provides a validation of (c) values. In addition, classical fisheries assumptions about the relationship between scale radius and fish body length were tested. As a result, variability or error of correction factors can be reduced by having a minimum of 30 samples with at least 4 age classes represented. Alternatively the (c) provided can be used as a standard (c) factor for each species, eliminating the variance caused by poor sampling. Finally, the development of standard intercept values (based on observation of juvenile fish) should be promoted to replace or validate mathematically derived (c).

The ability to accurately determine the age and growth of fish is an important tool in fishery biology and therefore it is fundamental to this work that all steps should be taken to increase the accuracy of back-calculated length-at-age data and account for size when fish lay down scales. To account for potential error associated with a correction factor, larval fish were routinely sampled to identify patterns of squamation, providing preliminary reference data for correction factors used in back-calculation of fish length-at-age. Determination of the length at squamation for more specimens will allow for the derivation of standard correction factors for each species that can be used across the species’ distribution.

Geometric morphometric (GM) analysis of fish scales has been shown to be a good discriminator of genera using a fixed landmark approach. However, freshwater fish scales are often irregular in shape; therefore it is not possible to identify identical locations on all individuals. This study provides evidence that scale morphology can be used to discriminate riverine fish species. The analysis of fish scale morphology is inexpensive, quick, non-destructive, and informative and could easily be added to existing monitoring programmes. This study highlights the potentially important and opportunistic information that can be gained from the GM analysis of fish scales. It is therefore anticipated that this study will be fundamental in shaping future fish population assessments.

It is recognised amongst scientists that fish growth rates vary across a catchment, with species typically achieving greater growth rates in their ‘preferred’ habitats. Similarly, previous authors have identified that growth variation exists for different species and populations. This study has found that the geographic location of a river/region influences the growth rates of freshwater fishes commonly found in England. The method of constructing regional growth curves and subsequent statistical analysis discussed in this study should be adopted by fisheries scientists, because current national growth rates may be unachievable in specific regions. Furthermore, current national curves are inappropriate for growth and population analysis because they may be biased by an individual river and/or region. This study is one of the few studies to examine the differences between regional recruitment success, and found similarities and differences at both the regional and national level. With recruitment success a key requirement of monitoring fish populations under the WFD, it is hoped the information provided here will aid fisheries scientists to understand the factors affecting regional and national recruitment success.

Studies on the impact of climate change on fish populations have typically focused on suggesting, rather than predicting, the effects on lentic species rather than lotic species. Furthermore, these studies often deal with American rather than European ecosystems. To address this, predicted changes in the climate of the UK were used to model likely influences on fish populations, expressed as the length of young of year (YOY) fish achieved by the end of the first growth period (May-September), juvenile and adult growth (annual growth increment, AGI) and recruitment success (year class strength, YCS), for three cyprinid fish. This study found that climate change is likely to increase the propensity for cyprinid fish to thrive, although the exact mechanism will depend on inter-annual variability in temperature rises and the timing of flow events. Notwithstanding the limitations of this study, it provides ecologists with a greater understanding of climate change and its potential impact on European, lotic fish populations.

Department of Biological Sciences, The University of Hull
Cowx, I. G. (Ian G.); Harvey, Jon P.
Qualification level
Qualification name
Filesize: 2 MB
QR Code