Twaite shad | European Tracking Network

Twaite shad

Alosa fallax

 

Image: Pieterjan Verhelst ©

 

Species description and statusThe twaite shad (Alosa fallax Lacépède) is an iteroparous (although semelparous populations exist1), anadromous Clupeid with a pelagic lifestyle, distributed from the Mediterranean basin, along the European Atlantic coast to the North Sea basin2 (Fig. 1). Its body is laterally compressed and the upper jaw contains a median notch. Spawning migrations commence between February and May, with northern populations migrating later than southern populations. Twaite shads show a substantial variability related to spawning locations, with some subpopulations spawning in the relative deep tidal freshwater parts of estuaries and others in shallow, non-tidal parts of rivers (up to 400 km from the sea)2. Twaite shads spawn pelagically, at night3 and when the water temperature reaches 18 – 22°C4. After three to five days, larvae hatch from the eggs and grow in areas with slow water flows, such as backwaters and tributaries. In general, the juveniles migrate seaward during autumn and winter2.

A decline in twaite shad populations was apparent halfway through the 20th century and is attributed to migration barriers, canalization, pollution and the increase in sedimentation5,6. Although the twaite shad has the status of least concern under the IUCN Red List7, it is included in Appendix III of the Bern Convention and Annexes II and V of the EC Habitats Directive2. Both legislative acts aim to conserve vulnerable or endangered species that are of interest for Europe, following the criteria described by the respective convention or directive.

Knowledge gapsTwaite shad is highly sensitive to handling and stress, making it a difficult species to tag. However, recently success stories have been conducted to tag the species with acoustic transmitters8,9. Hence, basic knowledge on their spawning migration is still lacking, such as migration speed and homing behaviour. Major knowledge gaps exist in the marine environment. Thus far, it is unknown to what extent shads move away from their natal rivers and if there is exchange between populations at sea. Also, it is unknown if they use artificial hard substrate such as shipping wrecks, wind mills or oil platforms.

Fig 1. Twaite shad distribution. ©IUCN distribution data

 

Regions of interest:  The regions of interest are Central to Western Europe, including the Mediterranean region.

Telemetry tools: Due to their sensitivity to tagging, twaite shad telemetry is at its infancy and currently only involves acoustic tagging8,9. However, to gain insight in their marine migration behaviour data storage tags are promising tools to test on twaite shads.

Benefits: The ETN can especially help in requiring a better insight in the marine movement and habitat use of twaite shads through detection of tagged twaite shads on various European telemetry networks. This could also lead to more insight if twaite shad use more than one river for spawning during a single spawning season.

Contacts:  Pieterjan Verhelst (Pieterjan.Verhelst@ugent.be), Mirjana Lenhardt (lenhardt@ibiss.bg.ac.rs)

References:

1Sabatié, M. R. 1993. Recherches sur l’écologie et la biologie des aloses du Maroc (Alosa alosa Linné, 1758 et Alosa fallax Lacépède, 1803). Exploitation et taxinomie des populations atlantiques; bioécologie des aloses de l’oued Sebou. Doctoral dissertation. Université de Bretagne Occidentale, Brest, France.

2Aprahamian, M.W., Baglinière, J.L., Sabatié, M.R., Alexandrino, P., Thiel, R. & Aprahamian, C.D. 2003. Biology, status, and conservation of the anadromous Atlantic twaite shad Alosa fallax fallax. In American Fisheries Society Symposium 35, 103-124.

3Maitland, P. S., & A. A. Lyle. 1991. Conservation of freshwater fish in the British Isles: the current status and biology of threatened species. Aquatic Conservation: Marine and Freshwater Ecosystems 1, 25–54.

4Breder, C. M., & D. E. Rosen. 1966. Modes of reproduction in fishes. Natural History Press, New York.

5de Groot, S. J. 1989. The former allis and twaite shad fisheries of the lower Rhine, The Netherlands. International Council for the Exploration of the Sea, Anadromous and Catadromous Fish Committee, C.M. 1989, M:19, Copenhagen.

6Aprahamian, M. W., & C. D. Aprahamian. 1990. Status of the genus Alosa in the British Isles; past and present. Journal Fish Biology 37, 257–258.

7Freyhof, J. & M. Kottelat, Alosa fallax. The IUCN Red List of Threatened Species 2008: e.T904A13092303. 2008.

8Breine, J., Pauwels, I. S., Verhelst, P., Vandamme, L., Baeyens, R., Reubens, J., & Coeck, J. 2017. Successful external acoustic tagging of twaite shad Alosa fallax (Lacépède 1803). Fisheries research 191, 36-40.

9Bolland, J. D., Nunn, A. D., Angelopoulos, N. V., Dodd, J. R., Davies, P., Roberts, C. G., Britton, J.R. & Cowx, I. G. 2019. Refinement of acoustic-tagging protocol for twaite shad Alosa fallax (Lacépède), a species sensitive to handling and sedation. Fisheries Research 212, 183-187.