Report: TR 2007/03

Author: Johlene Kelly, Kevin Collier

Abstract

A significant number of indigenous freshwater fish of New Zealand are diadromous and move between freshwater and marine environments at various stages of their lifecycle (Boubee et al.1999). In-river artificial structures such as culverts, fords, diversion structures, weirs and dams can pose a barrier to fish migration when poorly designed or installed.

In-river structures in six territorial authority areas of the Waikato Region were evaluated between 2000 and 2005 for their restriction to fish passage. These areas were Thames-Coromandel, Matamata-Piako, Waikato, Waipa, Otorohanga and Franklin (the portion which falls within the Waikato region). An evaluation method adapted from Boubee et al. (1998) was used in the survey.

A total of 1,614 structures or 36% of total potential public road crossings were assessed in these six areas. Structures were assessed as to whether they were likely to restrict fish passage at high, low or most flows, or pose none or minimal restriction to fish passage.

Of the 1614 structures surveyed, 725 or 45% were not considered to pose any restriction to fish passage. 481 (30%) were considered to pose a restriction at most flows while 151 (9%) were assessed as posing a restriction at high flows and 213 (13%) were considered to pose a restriction at low flows. Of those structures assessed a combined total of 845 structures or 52% were considered to pose some form of restriction to fish passage. 44 or 3% of structures visited were not assessed for fish passage restriction.

From the survey data a ranking process was developed to prioritise surveyed structures for remediation. The variables utilised in this ranking system were: severity of fish passage restriction, distance to the sea, upstream watercourse length and percentage of upstream length in indigenous forest in conjunction with the upstream catchment area. A weighting system was then applied to these variables and a district and regional rank given to each structure.

It is hoped that by providing this priority information to the relevant roading authorities and working in conjunction with these agencies, fish passage and subsequent access of fish to upstream habitats can be improved.

It is recommended that continued work be undertaken to reduce the impact of in-river structures on the restriction of fish passage within the Waikato Region. Work should focus on the provision of ongoing advocacy, advice and assistance to staff within both regional and local authorities, consultants, roading engineers and contractors with the design, installation and remediation of appropriate waterway crossings within the Waikato Region.

Assessment of Fish Passage Within Selected Districts of the Waikato Region [PDF, 641 KB]