Jacques Boubée

Thermal tolerance and preference of some native New Zealand freshwater fish

Upper lethal and preferred temperatures were determined experimentally for eight common species of New Zealand freshwater fish. Upper lethal temperatures ranged between 28.3 and 39.7°C and preferre...

Avoidance of suspended sediment by the juvenile migratory stage of six New Zealand native fish species

Abstract The avoidance response of the migratory juvenile stage of six species of diadromous fish to different levels of suspended solid (SS) was determined in the laboratory using a two‐choice avoidance tank. Trials were mostly conducted with resuspended sediment from the outlet of Lake Waahi, New Zealand, but a series of tests was also conducted with kaolin for comparison. Banded kokopu (Galaxias fasciatus) was the most sensitive species, displaying a 50% avoidance response to kaolin and Waahi silt at 17 and 25 NTU, respectively. Koaro (Galaxias brevipinnis) and inanga (Galaxias maculatus) were found to be less sensitive than banded kokopu, with a 50% avoidance response to Waahi silt at 70 and 420 NTU, respectively. Shortfinned and longfinned elvers (Anguilla australis and/1, dieffenbachii), and redfinned bullies (Gobiomorphus huttoni) showed no avoidance behaviour, even at the highest turbidities (1100 NTU) tested. Based on these laboratory results, and until field testing is undertaken, a limit of abo...

Factors regulating the downstream migration of mature eels (Anguilla spp.) at Aniwhenua Dam, Bay of Plenty, New Zealand

Abstract The downstream migrations of mature longfinned eels (Anguilla dieffenbachii Gray, 1842) and shortfinned eels (Anguilla australis Richardson, 1848) were investigated at Aniwhenua Dam on the Rangitaiki River between 1992 and 1998. Migrants were mostly females over 1000 mm total length (TL) with otoliths indicating rapid growth rates. Migrations, which occurred on a few nights each autumn, generally began once water temperatures began to decline and ended when temperatures dropped below c. 11 °C. Rainfall and flow increases were found to be key factors triggering migration events. Rainfall exceeding a cumulative total of 40 mm over 3 days accounted for 60% of migrant eels arriving at Aniwhenua. It is proposed that such rainfall triggers could be used as predictors to instigate mitigation activities that would allow mature eels to proceed uninjured past barriers such as hydro‐electric dams.

Effects of riparian manipulation on stream communities in small streams: Two case studies

Abstract The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.

Mouth gape, food size, and diet of the common smelt Retropinna retropinna (Richardson) in the Waikato River system, North Island, New Zealand

Abstract The feeding ecology of the common smelt, Retropinna retropinna, was determined at several locations on the Waikato River system. The mean size of the dominant prey was found to increase as smelt mouth gape increased. Smelt smaller than 40 mm total length fed mostly on zooplankton. Chironomid larvae, pupae, and adults were the dominant foods of larger fish from most sites, although mysids and amphipods were the major prey in Lake Waahi and the Waikato River estuary. Algae were the dominant food in many smelt but ingestion was probably incidental. Seasonal and annual differences in dominant foods were minor. Common smelt are generalists, capable of feeding on the majority of smaller organisms present in their different environments; however, they may grow faster and achieve a larger adult size when food of optimal size and nutritive value is present.

Responses to pH of nine fishes and one shrimp native to New Zealand freshwaters

Abstract The pH values preferred and avoided by adult stages of inanga (Galaxias maculatus), common bully (Gobiomorphus cotidianus), common smelt (Retropinna retropinna), and redfinned bully (G. huttoni), were determined in a gradient tank (pH ranges of 3.2–11.2). Juvenile stages of inanga, common bully, shortjawed kokopu (Galaxias postvectus), koaro (G. brevipinnis), banded kokopu (G. fasciatus), shortfinned (Anguilla australis) and longfinned (A. dieffenbachii) elvers and glass eels, as well as freshwater shrimp (Paratya curvirostris) were also tested. Most species were found to have pH preferences and all except inanga avoided pH values of above c. 9.5. Adult fish showed stronger preferences than juveniles. An avoidance of pH values below 6.5 was apparent in most species except shortfinned elvers, koaro, and banded kokopu. Results indicate that the range of pH encountered in lowland streams are unlikely to have a major impact on the distribution of most New Zealand native freshwater fish.

Eel protection measures within the Manapouri hydro-electric power scheme, South Island, New Zealand

Freshwater eels are in decline worldwide. In New Zealand, although longfin eels (Anguilla dieffenbachii) and shortfin eels (A. australis) are still amongst the most common freshwater fish species, there are concerns about the scarcity of large specimens. There are also indications that recruitment, especially of the endemic longfins, is declining. To protect stocks of this species, a series of mitigation measures have been implemented at the Manapouri Power Scheme (South Island, New Zealand). These include the release of compensation flows, the reconstruction of a fish pass and a catch and transfer programme for upstream migrating juveniles and adult downstream migrants (silver eels). Acoustic telemetry studies aimed at evaluating and improving interception and/or passage for silver eels show that eels were most active when lake levels were rising. Extended searching behaviour was exhibited, especially near the natural lake outlet, and silver eels appeared reluctant to travel to the opposite side of the lake where the hydropower station is located. Overall, just over half of the 31 silver eels tagged were able to find the natural outlet, and means of improving safe passage, including targeted flow releases and more effective methods of capturing the eels in the lake for transfer downstream, are being considered.

Spoiler Baffles in Circular Culverts

In many situations the design of culverts prevents the upstream migration of fish because water velocity in the barrel is greater than that of the natural channel. One way to reduce the water velocity within the culvert is to install spoiler baffles on the base. The current investigation uses a three-dimensional numerical tool to examine the influence of the baffle geometry on flow within culverts of varying diameters. The results indicate that spoiler baffles can reduce velocities in the culvert dramatically. The final choice of design hinges on the need of the fish and the discharge capacity of the culvert.

Characteristics of common smelt, Retropinna retropinna (Richardson), of the Waikato River system

Abstract Populations of lacustrine and diadromous common smelt (Retropinna retropinna), in the Waikato River system, North Island, New Zealand, have different average numbers of first arch gill rakers and vertebrae: c. 28 versus c. 21, and c. 52 versus c. 60, respectively. A third group, inhabiting the 7 hydro‐electric reservoirs of the Waikato system, average both low gill raker (c. 21) and low vertebrae numbers (c.52). Reservoir smelt have approximately 2 fewer first arch gill rakers than Lake Taupo fish. Most diadromous smelt mature in late summer and autumn, whereas reservoir fish mature in spring and early summer. Reservoir and Lake Taupo smelt have smaller eggs and larvae than diadromous smelt. The larger diadromous larvae have larger yolk sacs than Lake Taupo larvae; this is probably an adaptation associated with a direct larval migration to sea. Reservoir and lacustrine post‐larvae were found in the lower Waikato River but diadromous post‐larvae were confined to the estuary and sea. Reservoir popu...

Thermal avoidance in inanga, Galaxias maculatus (Jenyns), from the Waikato River, New Zealand

Abstract Temperature avoidance behaviour of inanga, Galaxias maculatus, was studied in the laboratory using a two‐choice tank. The final preferred temperature of inanga is about 20°C but fish acclimatised to cooler temperatures (15 and 17°Q prefer warmer waters (up to 23 and 26°C, respectively). Fish acclimatised to temperatures of 15,17, and 20°C showed total avoidance at 29.5,31, and 31.5°C, respectively. Water temperature therefore is an important factor influencing upstream migration and distribution of inanga and thermal discharges can be disruptive.