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Title: The efficacy of back calculation methods for determining length at age data and the use of such data to determine growth standards, national growth patterns and recruitment dynamics of roach (Rutilus rutilus (L.)), dace (Leuciscus leuciscus (L.)) and chub (Leuciscus cephalus (L.)) in UK rivers
Author: Rollins, Darren James
ISNI:       0000 0004 2697 3687
Awarding Body: University of Hull
Current Institution: University of Hull
Date of Award: 2009
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The use of fish scales to age and back-calculate previous lengths at age and gain age and growth information has long been used as a management tool in fisheries. Calcified structures from fish, including otoliths, fin rays, and vertebrae have been used to gain length at age data. Scales however, are the most common structure used for aging freshwater fish (Borkholder and Edwards 2001). In order to gain accurate back-calculated length at age data gained from fisheries surveys, an appropriate method of back-calculation was sought. A number of back-calculation methods were found from the literature and applied to data from fish surveys. Back-calculated lengths at age from specific cohorts were compared to observed mean lengths at age from historic surveys, revealing the method proposed by Hile (1941) as being the most consistent method for providing accurate length at age data from fisheries surveys. Comparative assessments of population mean growth rates remain important aspects of stock assessment in river fisheries (Britton 2007). Standard growth curves were originally produced for roach, dace, chub and bream (Hickley and Dexter 1979) and later expanded to include pike (Hickley and Sutton 1984). Habitat rehabilitation (Quinn 1994) and water quality improvements (Environment Agency 2001; 2006) are among a number of factors that have changed in rivers since the inception of the standard growth curves. Comparison of standard growth curves produced in this study and those produced by Britton (2007) against the original growth standards affirm the suggestion that the observed growth of these species has changed. Standard growth curves were produced and proposed for use as an updated comparative data set and an update to these standard growth rates is made on a regular basis. Riverine fish communities are highly structured and follow non-random patterns along a longitudinal profile (Jackson et al. 2001). Plasticity in the growth of fish along the longitudinal gradient of rivers has been demonstrated (Cowx 1988; Zelt et al. 1999). This study affirms the longitudinal plasticity in the growth of roach, dace and chub along the longitudinal gradient and reveals areas where conditions are conducive to better growth in these species, namely the downstream areas for roach and the upstream areas for dace and chub. Many studies have demonstrated growth rates as being dependent on geographical variation (Pyron 1999), with evidence that some fish species attain larger sizes at lower latitudes (Modde and Scalet 1985) while other studies demonstrate increased growth at higher latitudes (Isley et al. 1987, Conover and Present 1990). Latitudinal variation of fish growth characteristics from rivers throughout England and Wales revealed the growth rate of dace as being strongly related to latitudinal position, with the growth of dace showing a preference toward the cooler temperatures in the higher latitudes. Roach were found to prefer the lower latitudes where temperatures were higher, while chub were found to prefer the high latitudes and easterly longitudes. The year class strength of fish is an important index in the management of freshwater fisheries (Cowx and Frear 2004) with early developmental stages representing a crucial period in cyprinid fishes where variations in mortality during this period are critical in determining year class strength (Cowx 2001). A number of specific periods, where elevated flows occurred, were found to be related to the year class strengths of roach, dace and chub and identified as being important in playing a role in determining year class strength. The Gulf Stream was demonstrated as having a relationship with the flow regimes of a number of rivers which in-turn related to variances observed in the year class strengths and mean lengths at the end of the first year of life, of the fish species analysed. Northerly shifts in the Gulf Stream were found to have a positive influence in the growth characteristics and consequently the year class strengths in a number of the populations tested. A lag phase in the influence of the Gulf Stream on year class strengths was also identified in roach, dace and chub from a number of rivers. In this instance it was postulated that northerly shifts in the Gulf Stream produced conditions conducive to the growth of the adult fish stock which may in turn relate to an increased fecundity and/or the production of higher quality gametes from an increased condition of the adult stock.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biological sciences