Use of in-stream cover types by adult banded kokopu (Galaxias fasciatus) in first-order North Island, New Zealand, streams

The relative importance of wood material in providing in-stream cover for adult banded kokopu (Galaxias fasciatus) was determined in first-order, North Island, New Zealand, streams. Three groups of streams, each differing in the relative amount of three types of in-stream cover (i.e., wood, boulders, undercut banks) were selected and banded kokopu were sampled in their pools using electric fishing. Banded kokopu occurred beneath boulders, undercut banks, and wood material in all pools except those lacking any in-stream cover, or those where large (total length >400 mm) eels were present. Their presence in pools was therefore highly dependent on in-stream cover, provided large eels were absent. In streams where the cover provided by boulders was lacking, banded kokopu selected mainly undercut banks and wood. However, in streams containing large amounts of bank and boulder cover, wood was under-utilised, indicating that it was least preferred. In pools providing a choice of cover types, bank cover was more frequently used than other types, indicating that it is preferred. The mean size of banded kokopu in pools was positively related to their relative abundance, and their abundance was in turn related to habitat quality as defined by in-stream cover. Streams with the least amount of bank cover had the lowest number of pools occupied by banded kokopu, fewer banded kokopu per pool, fewer pools containing two or more banded kokopu, and the smallest banded kokopu. Collectively, these data indicate that bank cover in pools provides optimal habitat for banded kokopu, and that wood material was important only where other types of more permanent cover were lacking. Logs and wood slash from logging operations could therefore be important for increasing banded kokopu habitat in logged streams where bank and boulder cover are scarce.