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Predation and ingestion of a barred grass snake Natrix helvetica by a rainbow trout Oncorhynchus mykiss in Lot, France

Authors:
Oliver Thomas
Oliver Thomas
Steven J R Allain at Anglia Ruskin University
Steven J R Allain
Harry Owen at MRAG
Harry Owen
  • MRAG
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Abstract

Natural history record of trout predation on Natrix helvetica
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40 Herpetological Bullen 156 (2021)
Barred grass snakes (Natrix helveca) are found throughout
north-west Europe (Kindler & Fritz, 2017) and potenally
grow to 1.5 m but rarely aain this size (Speybroeck et al.,
2016). They are thought to feed primarily on amphibians and
are adept swimmers although rarely seen hunng in open
water (Gregory & Isaac, 2004).
The rainbow trout (Oncorhynchus mykiss) has been
introduced to many European countries and is valued as a
game sh and for its economic importance as food (Crawford
& Muir, 2008). Despite the introducon, the species has
rarely formed self-sustaining populaons in the wild in
France (Stanković et al., 2015). However, rainbow trout
predaon has been shown to reduce amphibian populaons,
e.g. Rana muscosa in the USA (Vredenburg, 2004) and Rana
temporaria in Sweden (Nyström et al., 2001).
At around 16:00 h on the 18th July 2020, a rainbow trout,
recently released for the purpose of recreaonal shing,
was caught by HO while angling along the Saint-Matré (a
small stream) in Grézels, Lot, France (GPS: 44° 28’ 03.7” N,
1° 09’ 01.8” E). The sh was a mature specimen, roughly
30 cm long. The trout was gued minutes aer capture
and surprisingly, a live hatchling barred grass snake was
found inside the gastrointesnal tract (Fig 1). The hatchling
snake measured approximately 20 cm long and appeared
sluggish, but otherwise relavely unharmed. Aer a quick
visual inspecon, the snake was released onto a patch of
grass where it remained sll for approximately 20 minutes.
Subsequently, it moved directly to a nearby pond and swam
aw ay.
It’s reasonable to assume that the hatchling snake must
have been consumed a short me prior to the trout’s capture
for it to have remained alive unl discovery. It is also likely
that the snake was swallowed whole whilst it was traversing
the small river. The occurrence of sh within a grass snake
diet is well documented (Gregory & Isaac, 2004); however,
there are no scienc reports of sh predang N. helveca
or other Natrix spp. There are, however, online references to
grass snakes forming part of the diet of Pike (Esox lucius).
Barred grass snakes are well known for their an-
predatory responses such as feigning death and musking
(Hagman et al., 2015), however, these behaviours would be
less eecve in the aquac environment. What evidence
there is suggests that the consumpon of N. helveca
by sh is rare and restricted to small specimens. The
current observaon suggests that it would be worthwhile
invesgang whether grass snakes close to commercial
sheries are at a signicantly increased risk of predaon.
ACKNOWLEDGEMENTS
Thanks to Sam Preston for the presence of mind to circulate
this observaon to the rst author. Thanks also to the
Robertson family, for everything.
REFERENCES
Crawford, S.S. & Muir, A.M. (2008). Global introducons of
salmon and trout in the genus Oncorhynchus: 1870–2007.
Reviews in Fish Biology and Fisheries 18: 313-344.
Gregory, P.T. & Isaac, L.A. (2004). Food habits of the grass
snake in southeastern England: Is Natrix natrix a generalist
predator? Journal of Herpetology 38: 88–95.
Hagman, M., Löwenborg, K. & Shine, R. (2015). Determinants
of an-predator taccs in hatchling grass snakes (Natrix
natrix). Behavioural Processes 113: 60-65.
Kindler, C., Chèvre, M., Ursenbacher, S., Böhme, W., Hille, A.,
Jablonski, D., Vamberger, M. & Fritz, U. (2017).
Hybridizaon paerns in two contact zones of grass
The Herpetological Bulletin 156, 2021: 40-41
Predaon and ingeson of a barred grass snake Natrix helveca
by a rainbow trout Oncorhynchus mykiss in Lot, France
OLIVER THOMAS1*, STEVEN J. R. ALLAIN2 & HARRY OWEN3
1Department of Biosciences, Swansea University, Swansea, SA2 8PP, UK
2Cambridgeshire & Peterborough Amphibian and Reple Group, UK
3MRAG, 18 Queen Street, Mayfair, London, W1J 5PN, UK
*Corresponding author e-mail: olliethomas444@gmail.com
hps://doi.org/10.33256/hb156.4041
NATURAL HISTORY NOTE
Figure 1. Hatchling barred grass snake head and neck clearly seen
coming out from the gastro-intesnal tract of the captured trout
Herpetological Bullen 156 (2021) 41
snakes reveal a new Central European snake species.
Scienc Reports 7: 7378.
Nyström, P., Svensson, O., Lardner, B., Brönmark, C. & Granéli,
W. (2001). The inuence of mulple introduced predators
on a lioral pond community. Ecology 82: 1023-1039.
Speybroeck, J., Beukema, W., Bok, B. & Van Der Voort, J.
(2016). Field Guide to the Amphibians and Reples of
Britain and Europe. London, Bloomsbury Publishing. 432
pp.
Stanković, D., Crivelli, A.J. & Snoj, A. (2015). Rainbow trout in
Europe: introducon, naturalizaon, and impacts.
Reviews in Fisheries Science & Aquaculture 23: 39-71.
Vredenburg, V.T. (2004). Reversing introduced species eects:
experimental removal of introduced sh leads to rapid
recovery of a declining frog. Proceedings of the Naonal
Academy of Sciences 101: 7646–7650.
Accepted: 24 December 2020
Predaon and ingeson of a barred grass snake by a rainbow trout in France
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