Huntingdon, Cambridgeshire, PE28 4NE, U.K. and §Centre for Conservation Ecology & ... chub were sampled from (1, Tees; 2, Swale; 3, Wensum; 4, Colne;.
Journal of Fish Biology (2007) 71, 1810–1819 doi:10.1111/j.1095-8649.2007.01650.x, available online at http://www.blackwell-synergy.com
Lifetime consequences of variable 0 year group length in riverine populations of chub Leuciscus cephalus (L.) J. D. B OLLAND *†, J. R. B RITTON ‡§
AND
I. G. C OWX *
*University of Hull International Fisheries Institute, Cottingham Road, Hull, HU6 7RX, U.K., ‡National Fisheries Laboratory, Environment Agency, Bromholme Lane, Brampton, Huntingdon, Cambridgeshire, PE28 4NE, U.K. and §Centre for Conservation Ecology & Environmental Change, School of Conservation Sciences, Bournemouth University, Fern Barrow, Poole, Dorset, BH12 5BB, U.K. (Received 24 November 2006, Accepted 10 July 2007) The fork length (LF) of individual chub Leuciscus cephalus in English riverine populations at the end of their first growth season varied considerably, ranging from 70 mm. This had a significant influence on the subsequent growth of individuals over their lifetime. Chub of small LF at age 1 year generally produced smaller annual growth increments throughout life than those of longer LF at age 1 year, although they had the potential to attain greater ultimate LF. This variability in LF at age 1 year resulted, at least in part, from multiple spawning events over a protracted period, that caused variation in the growing seasons for 0 year group chub of the same year class. Since the adult population contained individuals that only attained LF of 55 mm LF were also present in the year classes that could not be assigned to modes by the software again because of too few fish (Fig. 3). Whilst Bhattacharya’s method was unable to determine whether modal grouping remained throughout the life of the year class, construction of the composite growth curves throughout the life of each mode suggested no convergence of the mean LF for age of the modes (ANCOVA, P < 001; Fig. 4). Individuals in modes of smaller body LF modes at age 1 year generally remained comparatively smaller over the age range examined, a result of generally smaller annual
Journal compilation
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# 2007 The Authors 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1810–1819
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GROWTH OF CHUB IN RIVERS
8 6
4
2
2
0
0
6
8
River Wensum n = 1151
4
2
2
0
0
6
River Medway n = 136
6 4
2
2
0
0
8 6
River Blackwater n = 165
8
4
8 6 4 2 0
River Tove n = 92
6
4
8
River Tees n = 133
6
4
8
Frequency ( )
8
River Swale n = 96
8
River Thames n = 215
River Blythe n = 100
6 4 2 0 8 6 4 2 0
River Colne n = 1221
4 2 0 1 10 19 28 37 46 55 64 73 82 91 100
River Arrow n = 399
1 10 19 28 37 46 55 64 73 82 91 100
LF (mm) FIG. 2. Fork length (LF) frequency distributions of chub at backcalculated age 1 year from 10 rivers in England.
growth increments than those produced by individuals from modes with higher realized LF at age 1 (Fig. 4). Despite the modes with smaller LF at age 1 year producing lower annual growth increments, their potential ultimate lengths (LN) were higher than in modes of intermediate and large LF (ANCOVA, P < 0001; Table II) and were also coincident with lower growth coefficient values. This suggests modes of low realized LF at age 1 year contained individuals with slower annual growth rates but with the eventual possibility of larger realized LF, while the converse was found for individuals from modes of large realized LF at age 1 year. Although this suggests that the slower growing individuals also have the potential for longer life spans, this could not be tested in this study. # 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1810–1819
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J. D. BOLLAND ET AL.
FIG. 3. Year-class strengths of chub in the Rivers (a) Wensum and (b) Arrow ( , the year classes used in the frequency distribution). Fork length (LF) frequency distributions for a weak year class from the Rivers (c) Wensum and (d) Arrow for a strong year class from the Rivers (e) Wensum and (f) Arrow (LF backcalculated), including the modes identified by decomposition analysis ( ).
DISCUSSION A feature of each chub population and year class under investigation was the production of LF frequencies at the end of the first growth season exhibiting considerable variation in realized LF (>50 mm between individuals in the same year class). Modes were identified within these frequencies at age 1 year; individuals within modes of small mean LF remained relatively slow growing
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# 2007 The Authors 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1810–1819
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GROWTH OF CHUB IN RIVERS
TABLE I. Output of decomposition assessment using Bhattacharya’s method for each mode identified in the backcalculated fork lengths (LF) at age 1 year for the Rivers Wensum and Arrow. Difference between the modes was significant at P < 0001 (ANCOVA) Mode River Wensum 1984 year class
River Arrow 1995 year class
1 2 3 4 1 2 3
Mean S.D. LF (mm)
Separation index
— 41 38 46 — 28 46
26 36 43 51 25 39 51
2 3 2 2 3 3 3
through life, with the converse for modes of relatively large mean LF. Individual variation in somatic growth prevented tracking of modes beyond an early age, but LF at age 1 year appears to be indicative of subsequent growth rate and ultimate lengths in individual fish. In addition, adult chub that achieved LF of
