Age and growth of Anguilla anguilla in the Camargue lagoons

Abstract

Age and total length (L T ) data from a 11 year monitoring of the Anguilla anguilla eel population of the Camargue lagoons (Rhoˆne delta, southern France) were collected for glass, yellow and silver eels. Three distinct models were calibrated to describe the growth process of undifferentiated eels, females and males, respectively. Uncertainty of parameter estimates was evaluated by bootstrapping. Females were characterized by larger asymptotic body size (L T ) than males (580 AE 50 v. 388 AE 13 mm) and faster growth, whilst the Brody growth coefficient was larger for males than for females (means AE S.D. 3Á00 10 À3 AE 1Á68 10 À3 v. 1Á73 10 À3 AE 0Á50 10 À3). Sexual differentiation was estimated to begin at 204 AE 38 mm mean AE S.D., i.e. at the end of the second year in the lagoons, well before the L T at which macroscopic differentiation became possible (c. 300 mm). Males probably leave the lagoon or die (due to either natural or fishing mortality) within the first 3 years, whilst females can remain up to 5 years. Sexual differentiation and maturation have a major role in shaping the L T structure of the population. The L T and mass (M) data were fitted by allometric curves M ¼ aL T b À Á . The calibration of distinct curves for data from different years indicated that the allometric coefficient a was subject to wider interannual fluctuations than the allometric exponent b. A negative correlation linked the average L T and the allometric exponent (r ¼ À0Á58, P < 0Á01).

Genetic patchiness in European eel adults evidenced by molecular genetics and population dynamics modelling

“…where l 0 is body length at recruitment (6 cm, Melià et al, 2006) and g represents the annual growth rate (cm year…”

Assessing the freshwater distribution of yellow eel

“…Differences in individual size may be attributable to age differences as much as to the differences in growth rates that depend mainly on local and/or regional conditions, e.g. temperature and salinity of the growth habitat (Yalcin-Ozdilek et al, 2006;Edeline, 2007) and sex (Vøllestad, 1992;Naismith and Knights, 1993;Aprahamian, 2000;Graynoth and Taylor, 2000;Melià et al, 2006). The more time individuals spend in continental waters, the more variable these size-age relationships become (Panfili and Ximénès, 1994;Reynolds, 1996, 1998;Graynoth and Taylor, 2004).…”

“…As a consequence, the size of small eels is a better predictor of age than that of large eels, notably silver ones. For instance, we can assume with reasonable confidence that European eels ≤ 300 mm in length range from 0+ to 4 years (Panfili and Ximénès, 1994;Reynolds, 1996, 1998;Melià et al, 2006), whereas it is very difficult to age larger eels on the basis of length alone (Mounaix, comm. pers.).…”

Habitat residence during continental life of the European eel Anguilla anguilla investigated using linear discriminant analysis applied to otolith Sr:Ca ratios

“…They were photographed under a binocular microscope to al low detection of annual growth increments (opaque zones) from digitized images, following validated methods for age estimation in the European eel (Pan- . Only this entrance/exit allows eels to migrate between the lagoon and the freshwater canal J a n 0 0 J a n 0 2 J a n 0 4 J a n 0 6 J a n fili & Ximenes 1994, Melia et al 2006a). For each fish, the 2 sagittae images were used for age estimation and verification.…”

“…Investigating Anguilla anguilla movements during continental life and its variation at both local and global scales is of paramount importance for the conservation of this endangered species (Bonhommeau et al 2008, Belpaire et al 2009), especially within the context of littoral habitat alteration due to anthropogenic activities and climate change. Because the abiotic and biotic conditions experienced by the eels within their continental habitats can induce strong differences in growth rate, age at maturity, sex ratio and lifetime reproductive success (Panfili & Ximenes 1994, Jessop et al 2004, Walsh et al 2004, Bevacqua et al 2006, Daverat & Tomas 2006, Melia et al 2006a, habitat loss during continental life can also threaten the maintenance of eel stocks in the future through a loss in reproductive success (Bonhommeau et al 2008, Belpaire et al 2009). In this regard, most of the investigations have focused on the continental habitats identified along the west European coasts (Daverat et al 2005, Laffaille et al 2005, Daverat & Tomas 2006, and nothing is known about the migratory behaviour of A. anguilla within its Mediterranean coastland habitats.…”