Trophic polymorphism in the Arctic charr (Salvelinnus alpinus (L.)) of Lochs Rannoch, Ericht and Tay, Scotland

Morphometric analysis of Loch Rannoch charr indicated that in addition to the pelagic morph previously described, the benthic morph previously described consists of two distinct morphs. Thus one form had a relatively small head, short gill rakers and consumed only benthic invertebrates, whilst the other had a relatively large head and consumed benthic invertebrates until a size of 16cm at sizes above which it consumed other fish. These two forms were termed the benthivorous and piscivorous morphs respectively. Morphometric and dietary analysis agreed with the previous description of the third form as a pelagic planktivore which had fine head and jaw features, long gill rakers and a relatively streamlined morphology and differed from the other two morphs in that it was highly coloured as opposed to being cryptically coloured. This form was termed the planktivorous morph. Each morph was reproductively isolated by each spawning in a discrete location. Thus, the benthivorous morph spawned in the mouth of the largest afferent river, the River Gaur which enters the west basin of the loch, the piscivorous morph spawned in sublittoral regions of the east basin of the loch and the planktivorous morph spawned in shallow littoral regions throughout the loch but mainly in the east basin. Outwith the spawning period benthivorous and piscivorous charr were restricted to the west and east basins respectively, indicating that each is adapted to the biotic conditions within each basin and that the basins have effectively isolated these two morphs. Morphometric analysis of the charr of Loch Ericht, a similarly sized lake within the same catchement as Loch Rannoch, demonstrated the existence of two distinct morphs. One morph exhibited cryptic colouration and had a large head and was found to consume benthic invertebrates until a size of 16cm at sizes above which it consumed other fish. The other morph was highly coloured, had a relatively small head and streamlined body and consumed predominately zooplankton.

Level dc:type.qualificationlevel

PhD

Grantor dc:publisher.institution

University of Glasgow

Year dc:date.issued

1998

Author dc:creator

• Fraser, David

• QH301 Biology
• QL Zoology

Language dc:language

en