#FishInThePost – Twaite Shad

This week’s #FishInThePost was created and written by Sayali Pawar. 

On Thursday we tweeted our most recent #FishInThePost question: ‘I’m a fish hearing specialist, and can respond to sounds my comrades make up to 180 kHz, what Welsh native fish species am I?’. There were a lot of great guesses, and while several people came very close, Eric Lawton guessed the correct species, and linked to a local article too! Below we share a bit more about the fish species we had in mind for this week’s post, and reveal the answer to our question! 

This week’s #FishInThePost species is Alosa fallax aka Twaite Shad.  Belonging to the herring family of Clupeidae, the anadromous fish twaite shad- is widely distributed across Western Europe with the majority of its population residing in the rivers which flow into the Atlantic. Particularly in Britain, the spawning population of these fish can be found in the rivers Severn, Wye, Usk and Tywi or (Towy) (Natural England, 2018). The Twaite population have been widely depleted because of over fishing, pollution and impoundment of large rivers. The species is protected under the Annex II and V of the European Habitats and Species Directive, Appendix III of the Bern Convention and is listed as a Priority species in the UK Biodiversity Action Plan (Teague and Clough, 2013, Natural England, 2018).

The shad is a colourful fish and has a row of distinctive six to ten spots along its silvery flank. The adult shads start entering the estuaries and migrate upstream to headwaters between May and July when environmental conditions become suitable for spawning (FishBase, 2018). However, shad are more regularly found in lower reaches of unpolluted rivers and most commonly in sea waters. 

Alosa fallax aka Twaite Shad (artwork by Sayali Pawar)
Alosa fallax aka Twaite Shad (artwork by Sayali Pawar)

So, how can this fish be such a great listener? Behavioural studies on the American shad (Alosa sapidissima) have suggested that the members of the genus Alosa display particular responses, for example; a “wild” movement to higher levels of ultrasounds up to at least 180 kHz which is which is greater than the hearing capacity for whales and porpoises. This behaviour in shads develops during the adult stage when the “utricle” (region of the inner ear) becomes highly specialized. It is speculated that this hearing capacity helps them escape and avoid predators like the dolphins (Popper et al., 2004).

If any of our readers are aware of similar behavioural responses for the Twaite population specifically, please tweet us @FireLabTweets!

Twaite Shad was a royal favourite in the 13th Century, massively favoured by King Henry III for its taste and quality, as they were once abundant in the upper river Severn. Sadly, today these fish are rare in the UK, so much so that it is now illegal to fish for the Twaite shad. This iconic fish hasn’t been seen in the River Severn north of Worcester for over a century, but if you ever find yourself near the river south of Worcester at night time during the summer, listen out for loud noises on the surface waters and you might be able to spot these rare fish spawning!

Thanks for joining in for the third edition of #FishInThePost and stay tuned for our next fishy post on November 29.

References

FishBase. (2018). Alosa fallax summary page. [online] Available at: https://www.fishbase.de/summary/5355 [Accessed 15 Nov. 2018].

Natural England (2018). Ecology of the Allis and Twaite Shad: Alosa alosa and Alosa fallax. Available online at: <http://publications.naturalengland.org.uk/file/111013&gt; [Accessed 15 Nov. 2018].

POPPER, A., PLACHTA, D., MANN, D. and HIGGS, D. (2004). Response of clupeid fish to ultrasound: a review. ICES Journal of Marine Science, 61(7), pp.1057-1061.

Teague, N. and Clough, S. (2013). Investigations into the response of 0+ twaite shad (Alosa fallax) to ultrasound and its potential as an entrainment deterrent. WIT Transactions on State of the Art in Science and Engineering, 71, pp.153-163.

 

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