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

Abstract

Worldwide, river fragmentation is primarily responsible for the decline of populations of migrating fish. In particular, anadromous fish species, which necessarily migrate to fresh water to reproduce, are endangered since many are no longer able to reach their natural spawning sites. In addition, pollution of rivers effectively prevents upstream or downstream movements and blocks access to spawning grounds. This article investigates how poor water quality interferes with the life history cycle of twaite shad Alosa fallax fallax (Lacépède, 1803), an anadromous clupeid fish, in the watershed of River Scheldt, a heavily impacted environment in West Europe. We used two models based on known ecological and environmental information to explain past and present twaite shad distribution within the watershed and to make inferences about a future population recovery and juvenile habitat value. We demonstrated that historical spawning areas satisfy water quality conditions necessary to support spawning and successful development of early life history stages of the twaite shad. However, poor water quality conditions just upstream the freshwatersaltwater boundary still act as an effective migration barrier for upstream movement. As a consequence, spawning grounds are inaccessible and the population is dominated by seasonal adults occurring in the lower estuarine part of the watershed. This article provides testable and diagnostic information to the watershed management in that it identifies habitat and water quality requirements needed to support the expected recovery of an endangered anadromous fish population.

Stock recovery, spawning period and spawning area expansion of the twaite shad Alosa fallax in the Elbe estuary, southern North Sea

“…Higher mean abundances and higher numbers of spawning individuals suggest that, within this range, the main spawning area might be located within the middle part of the estuary (rkm 660−675) and therefore further downstream than before. For various European river systems such as the rivers Ebro, Scheldt and Severn, twaite shad is known to spawn exclusively in freshwater (Maitland & Lyle 2005, Maes et al 2008, López et al 2011). The same is true for the congeners American shad in the Hudson River in New York and major rivers in Virginia (Massmann 1952, Limburg 2001 and blueback herring in the Connecticut and Thames rivers in Connecticut (Loesch & Lund 1977).…”

Monitoring van het visbestand in het Zeeschelde-estuarium.: Viscampagnes 2017

“…sprot), maar tijdens de migratie naar de paaiplaats eten ze niet (Aprahamian et al, 2003;CTGREF, 1979). Voedsel is dus geen beperkende factor voor hun migratie, zuurstof wel (Maes et al, 2008). Juveniele finten eten in het zoete water voornamelijk Crustacea, Mysidacea en Amphipoda (gammariden).…”

MONEOS – Geïntegreerd datarapport INBO: Toestand Zeeschelde 2016: Monitoringsoverzicht en 1ste lijnsrapportage Geomorfologie, diversiteit Habitats en diversiteit Soorten

“…sprot), maar tijdens de migratie naar de paaiplaats eten ze niet (Aprahamanian et al, 2003;CTGREF, 1979). Voedsel is dus geen beperkende factor voor migratie, zuurstof wel (Maes et al, 2008). Juveniele finten eten in het zoetwater voornamelijk Crustacea, Mysida en Amphipoda (gammariden).…”