New Zealand's rivers and streams, and the diverse fish that live in them, are worth protecting. But the question of which species prefer to live where was unanswered until NIWA completed this major survey.
The problem
Water resources have complex demands place upon them. Irrigation and industry compete with native species and fishing grounds. Making the right decisions about water abstraction and allocation requires and understanding about habitat suitability, to determine the effects of flow changes on fish in streams and rivers and to set minimum flow requirements.
Habitat suitability can include water velocity and depth, substrate (material on the bottom), and perhaps in-stream cover (for example, undercut banks, boulders, large wood). However, the relationship between different species and the habitats they prefer is unknown.
The solution
Who lives where?
Staff at NIWA, regional councils, consultancies, Fish and Game NZ and the Department of Conservation (DOC) have surveyed habitat use by fish in New Zealand streams and rivers over the past 15 years, and have built up a large database of observations. We now have measurements of habitat use for over 21 000 individual fish. The data were obtained mainly from daytime single-pass electric-fishing surveys in wadeable rivers and streams. For some species, such as banded and giant kōkopu, these data have been replaced or supplemented by night-and-day observations from the bank and by netting. In total, we’ve measured fish and habitat in 5104 different locations in 123 streams and rivers.
Charting the curve
To describe the relationship between fish species and habitat, fisheries biologists use ‘habitat suitability curves’. This is a way of graphing the likelihood of a particular species being found in a particular habitat.
We developed habitat suitability curves for 10 new fish species or life stages and revised existing curves for 20 species or life stages. We used a consistent set of procedures that examined habitat use and preference in a number of different ways. These included simply plotting fish density with depth and velocity to see where fish were most abundant. We also developed models that could be used to predict fish occurrence and checked the model predictions against our data on fish presence.
The result
Micro vs meso habitats
Eels were the most widespread species, found in about half of the rivers surveyed. Upland and bluegill bully were the most abundant widespread species, followed by eels, brown trout, and common bully, all with more than 1200 individuals being caught. We left three fish out of the study – giant bully, black flounder, and shortjaw kōkopu – because we caught fewer than five of each of these species.
While many fish undoubtedly make use of habitat on a micro scale, most habitat suitability observations describe mesohabitats – the characteristics of the area in which the organism lives – rather than the microhydraulics of its precise location.
Our data show that, generally, different fish favour different mesohabitats:
- rapid/riffle – torrentfish, bluegill bullies, kōaro, alpine galaxias, and upland longjaw galaxias
- run – juvenile eels, trout, and some galaxiid and bully species
- pool – adult eels, lamprey, various juvenile galaxiid species, and adult kōkopu.
Habitat preferences
We found that the curves for each species were similar from river to river. The only exception was the landlocked kōaro population in tributaries of Lake Chalice, where the kōaro tended to be in small pools rather than the tumbling torrents that are usually described as their habitat.
This information contributes to decision making in relation to aquatic restoration, biodiversity planning and management of the range of activities that alter stream habitat and water allocation.
Key findings
Data on more than 21 000 fish have been collected from over 5000 locations throughout New Zealand.By comparing fish presence with the physical characteristics of the locations, we have graphed 'habitat suitability curves'.Understanding the habitat requirements of each species can inform decisions about water management.
New Zealand's rivers and streams, and the diverse fish that live in them, are worth protecting. But the question of which species prefer to live where was unanswered until NIWA completed this major survey.
