Field survey of the fish populations of the lower Ngaruroro River

Transcription

1 Field survey of the fish populations of the lower Ngaruroro River Glenn Maclean March 2014 HBRC Publication No Report No. RM16-54 CMB 93, RD 2, Owhango 3990 E glenn@technicallytrout.co.nz W P /

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3 Field survey of the fish populations of the lower Ngaruroro River Glenn Maclean An Internal Report prepared for Hawkes Bay Regional Council Technically Trout Client Report: TT March 2014 Technically Trout CMB 93 RD 2 Owhango 3990 Cover: Lower Ngaruroro River at Maraekakaho All rights reserved. This publication may not be reproduced or copied in any form without the permission of the client. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system. 2

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5 Table of Contents Study Sites 3 Methodology 8 Results 8 Notes 11 Acknowledgements 11 3

6 Study Sites Four sites in the main-stem of the lower Ngaruroro River between Fernhill and Whanawhana (figure 1, table 2) were visited on the 24 th and 25 th February 2014, along with a site in the lower Kikowhero Stream. Figure 1 The 5 survey sites in the lower Ngaruroro River Whanawhana Matapiro Road Fernhill Maraekakaho Kikowhero Stream A general description of each site is provided below along with a characterisation of the habitat types in table 1. Table 1 Characterisation of each survey site by habitat type (percentage) Habitat Fernhill Maraekakaho Kikowhero Matapiro Whanawhana Stream Road Still Backwater 5 5 Pool Run Riffle Rapid Cascade 4

7 Fernhill At this site there was very little filamentous algae growing within the flowing water and the stones and small cobbles which comprised the riffles were uncompact (loose) and clean. A small side channel adjavent was also fished. The side channel including debris pile in which a number of small and medium sized eels were caught. 5

8 Maraekakaho The rapids and riffles comprised larger cobbles than at Fernhill and the bed was much more compact. There was significant algal growth on the larger stones and along the margins. Kikowhero Stream This site was heavily shaded with significant instream debris and also mats of exposed willow roots along the banks. The substrate was mainly gravel and stones with occasional large cobbles and was quite embedded. 6

9 Matapiro Road Broad and shallow this habitat was largely riffle comprising gravel and stones with occasional cobbles. Most of the bed was compacted though there were some areas of looser substrate in the faster water, and extensive green filamentous algae on the larger stones. Whanawhana A major side braid with isolated willows and instream debris, and several areas of cobbles and faster water. Generally shallow with deeper holes under the willows. 7

10 Methodology At each site the stream was fished using an EFM300 electric fishing machine set on a pulse width of 3ms and a frequency of 70pps. The operator set the voltage so as to ideally have a maximum of 4 of the 5 lights on the hand wand illuminated and fished back towards a stop net held by a second person using a single pass methodology. Collectively the team endeavoured to fish the range of the habitat types present, other than where the water was too deep or swift for safe or effective fishing. Attempts were made to capture all the fish seen, these held in a plastic container until the completion of the survey. The fish were then carefully identified including using a hand lens to examine for any pores, measured to the nearest mm and recorded. However where a large number of one species were captured a sample of s was taken instead. Fish observed but not captured were also recorded, along with the fishing time of the electric fishing machine. Ideally 20 minutes of fishing time was undertaken at each site. The survey dates co-incided with settled sunny weather and low and clear river flows (8.5 cumecs at Whanawhana) which made for ideal survey conditions. Results The physical parameters measured at each location at the time of survey using a calibrated YSI Pro2030 meter are shown in table 2. Table 2 Dissolved oxygen (mg/l and % saturation), conductivity (us/cm) and water temperature (C o ) for the survey locations in the lower Ngaruroro River February 2014 Location Time of sample Dissolved oxygen (mg/l) Dissolved oxygen (% saturation) Conductivity (us/cm) Water temperature (C o ) Fernhill Maraekakaho Kikowhero Stm * Matapiro Road Whanawhana * The reason for the low dissolved oxygen reading in the lower Kikowhero Stream is not known. Details of the electric fishing effort for each site are listed in table 3. Table 3 Location of each site (NZTM series), voltage used and extent of fishing effort (time in minutes that the wand was activated) Site Location Voltage Fishing duration (m) Fernhill E , N Maraekakaho E , N Kikowhero Stream E , N Matapiro Road E , N Whanawhana E , N

11 Fernhill Table 4 Details of the number and size of each fish species caught at the Fernhill site Species Number Minimum Maximum Average (no. measured) Comments Black flounder (2) Torrentfish (14) Redfin bully (2) Bluegill bully (7) Larger ones gravid Cran s bully (5) Dwarf galaxias (8) Shortfin elver 23 Shortfin (small & medium Longfin (small & medium) 5 4 Maraekakaho Table 5 Details of the number and size of each fish species caught at the Maraekakaho site Species Number Minimum Maximum Average (no. measured) Black flounder Torrentfish (15) Redfin bully 3 Bluegill bully Cran s bully 7 Dwarf galaxias 4 Eel unid. (small & medium) Shortfin (small & medium Longfin (small & medium) Comments 9

12 Kikowhero Stream Table 6 Details of the number and size of each fish species caught at the Kikowhero Stream site Species Number Minimum Maximum Average (no. measured) Black flounder 1 Torrentfish Redfin bully (6) Bluegill bully Cran s bully (20) Dwarf galaxias (2) Shortfin 1 (>500mm) Shortfin (tiny, 27 small & medium Longfin 1 (>500mm) Longfin (small & 10 medium) Eel unid. (small & 5 medium) Rainbow trout Brown trout Koura 2 Comments Matapiro Road Table 7 Details of the number and size of each fish species caught at the Matapiro Road site Species Number Minimum Maximum Average (no. measured) Comments Black flounder 3 Torrentfish (4) Redfin bully (8) Bluegill bully (2) 1 fish gravid Cran s bully (15) Unid. bully 6 All small Dwarf galaxias (28) Shortfin elver Shortfin (small & medium Longfin (small & medium) Brown trout (small) (3) 1 10

13 Whanawhana Table 8 Details of the number and size of each fish species caught at the Whanawhana site Species Number Minimum Maximum Average (no. measured) Comments Black flounder Torrentfish (2) Redfin bully (2) Bluegill bully Cran s bully (4) Dwarf galaxias (3) Smelt (large) ~ 20 Observed in a shoal Shortfin (small & 24 medium Longfin (small & 19 medium) Rainbow trout (9) Brown trout (3) Unid. trout ~ 20 Notes Dwarf galaxias were particularly abundant in very shallow riffles comprising clean loose stones and small cobbles. Densities appeared to be much less where the cobbles were larger and the bed more compact, however these areas also had much more extensive filamentous algal growths (which had developed on the cobbles). No longfin elver were recorded. However good numbers of small and medium eels of both species were evident at all the sites. Small eels were particularly associated with growths of filamentous algae along the stream margins and medium sized eels with any instream debris. No common bullies were recorded at any of the sites Black flounder were recorded at 3 of the 5 sites and I have previously recorded them in the Otamauri Stream downstream of Whanawhana. Torrentfish showed a consistent trend of increasing average the further upstream we surveyed, however there were individual large or very large fish recorded at all the mainstem sites. Acknowledgements Technically Trout would like to acknowledge the valued assistance and also thoughtful discussion provided by Andy Hicks of HBRC. 11

14 Black flounder (Matapiro Road) Torrentfish (Maraekakaho) 12

15 Smelt (Whanawhana) 13