|
Vol. 54, 2015
Adaptive flexibility
in the feeding behaviour of brown trout: optimal prey size
Javier
Sánchez-Hernández1,2* and Fernando Cobo1,3
1Department
of Zoology and Physical Anthropology, Faculty of Biology, University of
Santiago de Compostela, Campus Sur s/n, 15782 Santiago de Compostela,
Spain
2Department of Arctic and Marine Biology, Faculty for
Biosciences, Fisheries and Economics, UiT The Arctic University of
Norway, N-9037 Tromsø, Norway
3Station of Hydrobiology ‘Encoro do Con’, Castroagudín
s/n, 36617 Vilagarcía de Arousa, Pontevedra, Spain
Abstract
Background: Brown trout, Salmo trutta Linnaeus, 1758, is a species
of significant conservation and socio-economic importance. A
consequence of this importance is the enormous amount of literature
that has been published on the species in the last few decades. In
general terms, brown trout has been considered as a size-selective
predator, even though it is able to feed on a wide range of prey sizes.
Nevertheless, there are still some gaps in our knowledge, for example
the theoretical relationship between prey numbers and prey sizes eaten
by the fish need to be addressed. This research aimed to study optimal
prey size in the environment (benthos and drift) as well as the
potential relationship between prey size and two other feeding
variables (prey numbers and stomach fullness). Additionally,
ontogenetic shifts in these variables were addressed.
Results: Brown trout showed a clear preference for
4- to 6-mm-length prey, although the use of prey larger than 10-mm
length may be feasible. The similarity of the prey size frequency
distribution between the environment (benthos and drift) and the diet
in some cases was considerable (from 57.7% to 95.9%). Moreover, the
results revealed that the feeding strategy can be related to prey size
and the numbers of prey eaten by the brown trout; as food size
decreased, prey numbers increased. On the contrary, the correlation
between the average prey size and fish length was positive but
statistically nonsignificant. A significant ontogenetic shift, in terms
of prey size sorted by age classes, was found in only two of eight
studied populations. No clear relationship between prey size and
stomach fullness was found.
Conclusions: The feeding strategy
of this species is flexible and clearly influenced by the size
frequency distribution of potential prey: trout fed on either small
numbers of large prey or large numbers of small, and theoretically low
energy, prey. Our approach covers a general subject in trophic ecology
and animal behaviour that may be applicable to other fish species to
improve our understanding of predator feeding behaviour.
Key words: Trophic ecology; Foraging
behaviour; Flexible behaviour; Salmo trutta; Prey size; Available prey;
Benthos; Drift.
*Correspondence: E-mail: javier.sanchez@usc.es
|
