Upstream migration and reproductive patterns of a population of allis shad in a small river (L'Aulne, Brittany, France)

Abstract

The characteristics and activity of adult allis shad [Alosa alosa (L.)] were analysed during the last part of their upstream migration in the L'Aulne, a small river in Brittany, and during reproduction on a unique spawning ground downstream of an insurmountable dam. The age of the spawners ranged from three to seven years, females being larger and older than males. Population-level migration and reproduction were studied by counting the number of migrating fish, by estimating the sex ratio, and by counting the number of nocturnal spawning acts for three consecutive years starting in 2000. The influence of the environment, especially water temperature and discharge, was highlighted: temperature during migration may supplant the influence of water flow, although high flow could allow passage over the dam. Such factors partly explain the annual pattern of migration and reproduction during the spawning season. The study showed that the biological features and characteristics of this population of allis shad in a small river were similar to those of western Atlantic stocks in large rivers.

Poor water quality constrains the distribution and movements of twaite shad Alosa fallax fallax (Lacépède, 1803) in the watershed of river Scheldt

“…We expected an opposite relationship with freshwater flow, following observations that the upstream movement behaviour of American shad decreases at stream velocities above 1 m s -1 (Stier & Crance, 1985). Similarly, Acolas et al (2006) observed that migration activity in allis shad increased while temperature increased and water flow decreased, and slowed when temperature decreased. The response to temperature was assumed to follow a bell shaped curve which can be approximated by a second order polynomial, which results in a temperature optimum.…”

Thermal tolerance of allis shad (Alosa alosa) embryos and larvae: Modeling and potential applications

“…A direct application of the thermal thresholds to daily river temperatures from Nivelle and Garonne rivers showed that cold temperatures were more likely to affect young stages survival than warm temperatures, though behavior may limit this effect by preventing shads to lay eggs at too cold temperatures as observed in other rivers (Acolas et al 2006). The fact that allis shad did not postpone reproduction (to take advantage of warmer temperature) could be explained by a possible adaptive trade-off between river survival and estuarine survival.…”

“…For the Garonne River they were recorded at the control station at the Golfech dam fish pass located two kilometers upstream of the main spawning grounds. Spawning acts of allis shad are usually recorded mainly from mid-May to mid-June but can start at the beginning of May and cease by mid-July (Taverny 1991;Cassou-Leins et al 2000;Acolas et al 2006).…”

Refugia of marine fish in the northeast Atlantic during the last glacial maximum: concordant assessment from archaeozoology and palaeotemperature reconstructions

“…These temperatures thresholds for haddock and pollock are broadly consistent with Lenoir et al (2010) using a statistical analysis of a larger database. For the allis shad, which spawns in freshwater in springtime, the observed migration from the ocean takes place when river temperatures are between 13.3-23 • C as measured by Acolas et al (2006), and this defines the proper freshwater environment for spawning and early rearing of young. This observed temperature range is very close to the empirical climatological average summer SSTs that have been used to define the spatial distribution (13-22 • C; shown in Fig.…”