Understanding fish passage in New Zealand

NIWA scientists have been investigating the different capabilities of our native freshwater fish species in order to help design effective solutions for overcoming barriers to migration

The issue

Many of our iconic native fish species, such as whitebait and eels, need to move between freshwater and the sea to complete their life-cycle. Instream man-made structures, such as culverts, weirs, tide gates and dams, can delay or block these migrations meaning that fish are unable to reach critical habitats they require to breed, feed and live. The result is many kilometres of streams and rivers across New Zealand where the natural abundance and diversity of fish is reduced due to a lack of connectivity.

Some of the key features of a structure that can impede the upstream movement of fish are highlighted in Figure 1. The most common problems are high water velocity (i.e. fast flowing water) and drops (i.e. excessive fall heights) at structures. In addition to the physical barrier effects, instream structures can also alter the natural cues (e.g. flow patterns) that motivate fish to move upstream.

To reduce the impact of migration barriers on fish numbers and distribution, there is a need to find better ways to design instream structures and fix existing structures to allow for fish passage.

The solution

NIWA scientists have been investigating the different capabilities of our native freshwater fish species in order to help design effective solutions for overcoming barriers to migration. We have also been involved in implementing and testing these solutions at a range of different barriers around the country.

Working with the Department of Conservation (DOC) we are also promoting improved management of fish passage in New Zealand. This includes developing resources to support fish passage management informed by the outcomes of our research and establishing the New Zealand Fish Passage Advisory Group. For more information on this work please visit DOC's website: Department of Conservation - fish passage

The New Zealand Fish Passage Guidelines sets out recommended practice for the design of instream infrastructure to provide for fish passage. The intent of these guidelines, developed by NIWA and DOC in partnership with the New Zealand Fish Passage Advisory Group, is to set the foundation for improved fish passage management in New Zealand.

The results

The objectives of our research on fish passage are to understand how instream man-made structures impede the movement of fish and how we can design new structures, or fix old ones, in a way that minimises the risk of them blocking our fish.

Some of our fish are more affected by migration barriers than others because they have different characteristics and capabilities. Understanding these differences is a focus of some of our research. For example, inanga (Galaxias maculatus), the main whitebait species, are weak swimmers and cannot climb. They are, therefore, highly susceptible to being blocked by instream structures. However, koaro (G. brevipinnis) and juvenile eels (Anguilla australis and A. dieffenbachii) are really good climbers and can even make their way past big waterfalls!

References for further information

Baker, C.F. (2003) Effect of fall height and notch shape on the passage of inanga (Galaxias maculatus) and common bullies (Gobiomorphus cotidianus) over an experimental weir. New Zealand Journal of Marine & Freshwater Research, 37: 283-290.

Baker, C.F., Boubée, J. (2006) Upstream passage of inanga Galaxias maculatus and redfin bullies Gobiomorphus huttoni over artificial ramps. Journal of Fish Biology, 69: 668-681.

Baker, C.F. (2014) Effect of ramp length and slope on the efficacy of a baffled fish pass. Journal of Fish Biology, 84(2): 491-502. 10.1111/jfb.12298

Stevenson, C., Kopeinig, T., Feurich, R., Boubée, J. (2008) Culvert barrel design to facilitate the upstream passage of small fish. Auckland Regional Council Technical Publication No., 366.

Feurich, R., Boubée, J., Olsen, N.R.B. (2011) Spoiler baffles in circular culverts. Journal of Environmental Engineering, 137(9): 854-857. 10.1061/(ASCE)EE.1943-7870.0000384

Feurich, R., Boubée, J., Olsen, N.R.B. (2012) Improvement of fish passage in culverts using CFD. Ecological Engineering, 47: 1-8. http://dx.doi.org/10.1016/j.ecoleng.2012.06.013

Franklin, P.A., Bartels, B. (2012) Restoring connectivity for migratory native fish in a New Zealand stream: effectiveness of retrofitting a pipe culvert. Aquatic Conservation: Marine and Freshwater Ecosystems, 22(4): 489-497. 10.1002/aqc.2232