Gerard P. Closs

Behavior of a Stream-Dwelling Fish before, during, and after High-Discharge Events

Abstract The movements of giant kokopu Galaxias argenteus were recorded before, during, and after high-discharge events in two small streams using radiotelemetry. Giant kokopu remained within defined stream reaches during base flow conditions. During high-discharge events, individuals either stayed within their home reach, moved and settled elsewhere, or moved and returned to their home reach as flows subsided. The variable behavior exhibited by individual giant kokopu suggested that reasons for moving during floods are complex. Reasons that may have influenced movement during floods included reproduction and mate searching, lack of adequate refugia, or some combination of these. In many instances, individual giant kokopu appeared to exhibit adaptive behaviors in response to high discharges. Behaviors supporting this view included fish not moving during the highest floods, fish moving upstream during the peak discharge period, and fish making purposeful “micromovements” (movements <5 m) into low-velocity ...

Relationships between land use and stream invertebrate community structure in a South Island, New Zealand, coastal stream catchment

Abstract Macroinvertebrate community composition was compared across streams draining catchments dominated by either native bush, agricultural or urban land uses within the Water of Leith stream catchment near Dunedin, New Zealand. Land use was associated with differences in taxon richness and faunal composition of communities present in each stream. The mean abundance levels of Ephemeroptera, Plecoptera, and Trichoptera were highest in native bush catchments, and lowest in urban catchments. In contrast, the mean abundance of Oligochaeta exhibited the opposite pattern. Increasing dominance of the urban and agricultural streams by pollution tolerant taxa was reflected in the Macroinvertebrate Community Index and Quantitative Macroinvertebrate Community Index scores.

Non‐diadromous recruitment in coastal populations of common bully (Gobiomorphus cotidianus)

Abstract Otolith microchemistry of common bullies (Gobiomorphus cotidianus) collected from the lower reaches of the Mataura, Clutha, and Taieri/Waipori River systems of New Zealand was examined using particle induced X‐ray emission (PIXE). High strontium:calcium (Sr:Ca) ratios in otolith cores relative to otolith edges suggested either diadromous or estuarine‐reared common bullies are present in all three systems, including fish collected from Clydevale (50 km inland) on the Clutha River. However, constant or slightly variable Sr:Ca ratios from otolith core to edge, suggesting a non‐diadromous life history, were also observed in fish from the lower Mataura and Taieri/Waipori systems, even where access to the sea was continuously available. The results suggest that diadromy in common bully may be facultative, and that a proportion of the common bully population may be non‐diadromous in river systems where suitable larval/juvenile rearing habitat is present.

Migration as an escape from parasitism in New Zealand galaxiid fishes

Parasite avoidance is increasingly considered to be a potential driving factor in animal migrations. In many marine and freshwater benthic fish, migration into a pelagic environment by developing larvae is a common life history trait that could reduce exposure to parasites during a critical window of developmental susceptibility. We tested this hypothesis on congeneric fish (family Galaxiidae, genus Galaxias) belonging to a closely related species complex sampled from coastal streams in southeastern New Zealand. Migratory Galaxias have larvae that migrate to pelagic marine environments, whereas the larvae of non-migratory species rear close to adult habitats with no pelagic larval phase. Both migratory and non-migratory fish are hosts to two species of skin-penetrating trematodes that cause spinal malformations and high mortality in young fish. Using generalized linear models within an Akaike information criterion and model averaging framework, we compared infection levels between migratory and non-migratory fish while taking into account body size and several other local factors likely to influence infection levels. For one trematode species, we found a significant effect of migration: for any given body length, migratory fish harboured fewer parasites than non-migratory fish. Also, no parasites of any kind were found in juvenile migratory fish sampled in spring shortly after their return to stream habitats. Our results demonstrate that migration spares juvenile fish from the debilitating parasites to which they would be exposed in adult stream habitats. Therefore, either the historical adoption of a migratory strategy in some Galaxias was an adaptation against parasitism, or it evolved for other reasons and now provides protection from infection as a coincidental side-effect.

Methyl mercury bioaccumulation in long-finned eels, Anguilla dieffenbachii, from three rivers in Otago, New Zealand

This research focuses on mercury (Hg) bioaccumulation in New Zealand long-tinned eels (Anguilla dieffenbachii) from the aquatic environment. Total Hg (HgT) and methyl mercury (MeHg) concentrations were determined in muscle tissue from eels living in three South Island rivers dominated respectively by urban, native bush and agricultural land-uses. Most of the Hg in eels was MeHg (> 84%) and the MeHg concentrations increased linearly with both length and eel age for a given river habitat. The annual growth rates for eels from the urban and agricultural streams were greater than for eels from the native bush stream. The average MeHg accumulation rate was significantly higher for the eels in the agricultural stream compared with either the urban or native bush catchments. These results are probably due to a combination of factors and further investigations in the lower food web are necessary to elucidate the exact mechanisms of MeHg bioaccumulation in these creatures.

Distribution of fish in tributaries of the lower Taieri/Waipori rivers, South Island, New Zealand

Abstract The distribution of fish within eight small streams feeding into the lower Taieri and Waipori Rivers on the east coast of New Zealands South Island was examined. A total of eight native and two introduced species were recorded. Eels (Anguilla spp.) and giant kokopu (Galaxias argenteus Gmelin) were the most widely distributed species being located in all streams surveyed. Common bullies (Gobiomorphus cotidianus McDowall) and brown trout (Salmo trutta Linnaeus) were also widely distributed being detected in seven and six of the streams respectively. Three streams of potential conservation significance were identified. These were Picnic Gully Creek which contained a significant population of banded kokopu (Galaxias fasciatus Gray), a Category C threatened species, and Cullens and Alex Creeks which contained significant populations of giant kokopu, a Category B threatened species. The population of giant kokopu in Cullens and Alex Creeks currently represents the largest known population of this species on the east coast of New Zealand (excluding Southland). It has been suggested that brown trout may influence the distribution of native galaxiids. The longitudinal distribution of giant kokopu and brown trout in streams was examined at night using a continuous spotlight sampling approach. Distributions of these two species rarely overlapped at a local scale. Coarse habitat use data indicated that brown trout regularly occupied a variety of habitat types including modified agricultural channels. In contrast, giant kokopu rarely used agricultural channels being predominantly located in pool habitats.

Impact of Didymosphenia geminata on hyporheic conditions in trout redds: reason for concern?

Didymosphenia geminata (Lyngbye) Schmidt (commonly called didymo) is an invasive diatom and of concern to fisheries managers in North America and more recently New Zealand. Didymo grows in thick mats in several river systems on the South Island of New Zealand, often smothering entire river beds. Salmonid eggs, deposited in gravel nests (redds), depend on constant water exchange across the riverbed to provide oxygen-rich water for development. Thick didymo mats might restrict the flow of oxygen-rich water into spawning gravels, resulting in increased egg mortality and reduced trout recruitment. The present study measured hyporheic hydraulic conditions in trout redds with varying didymo cover in the Clutha River catchment, South Island, New Zealand. Didymo cover had no significant effects on several hydraulic variables (flow into the substrate, hydraulic conductivity and hyporheic oxygen concentration). However, there was a significant difference in the potential surface water-groundwater exchange between sites, suggesting some effect of didymo on hydraulic conditions. Considering the limited number of replicates, the impact of didymo on trout redds in the Clutha River cannot be excluded. The present study highlights the need for further research on the possible effects of didymo on important surface water-groundwater exchange processes.

Impact of Berm Breaching on Hyperbenthic Macroinvertebrate Communities in Intermittently Closed Estuaries

Berm breaching of intermittently closed estuaries, either naturally or due to management practices, results in a physicochemical disturbance due to the flushing of water, material and biota into the ocean and the subsequent tidal influx. In 2007 and 2008 comparative and controlled studies were employed in three New Zealand estuaries: Sawmill Creek (46°04′ S 170°12′ E), Otokia Creek (45°57′ S 179°20′ E) and Kaikorai Lagoon (45°56′ S 170°23′ E), to investigate the impact of berm breaching on the hyperbenthic macroinvertebrate community in intermittently closed estuaries. Significant changes in community structure occurred in both the weekly comparative and the controlled studies (ANOSIM P < 0.01). Furthermore, the catch per unit effort of both total and key invertebrate taxa significantly increased after breaching (ANOVA P < 0.01). However, substantial numbers of individuals were expelled into the ocean (5,800 individuals, 20-min sample) while new taxa immigrated into the estuaries. Along with migration-related changes to community structure, berm breaches also resulted in the loss of ∼80% of inundated habitat and the concentration of existing populations. Consequently, the management of intermittent estuary connections to the ocean has implications for the ecology of individual, managed estuaries and also for regional coastal populations of epibenthic invertebrates.

Spatial and temporal variation in the fish community of a South Island, New Zealand coastal lake

Abstract Communities in shallow coastal lakes are exposed to frequent environmental variation owing to their proximity to marine environments, and seasonal and daily variation in climate. Consequently, variability in these communities is likely to be considerable. The fish community of Lake Waihola, a shallow coastal South Island/New Zealand lake, was assessed by monthly day and night sampling by push net. A total of eight fish species were collected between January 1998 and January 1999. Common bully (Gobiomorphus cotidianus) comprised 78.92% of the total catch collected over the study period. Highest catches of common bully occurred inlate summer and autumn, mostly at night. Juvenile perch (Perca fluviatilis) were also caught in high numbers for a short period in mid‐summer, also mostly at night. Common smelt (Retropinna retropinna) and inanga (Galaxias maculatus) were collected in low numbers from late winter through to late autumn. Other species collected included shortfin eel (Anguilla australis), yellow‐eyed mullet (Aldrichetta forsteri), lamprey (Geotria australis), and black flounder (Rhombosolea retiaria). Variation in abundance was attributed to life history and ontogenic shifts in habitat use, and changes in habitat structure related to the development of submerged macrophyte beds during warmer summer periods.

Spatial and temporal variation in the abundance and composition of ichthyoplankton in a large South Island, New Zealand river estuary

Abstract Larval and juvenile fish drifting on ebb tides were collected from early summer to mid autumn at various locations in the Taieri River and Waipori River estuary, South Island, New Zealand. A total of seven species of fish were recorded, however only three species were regularly collected. These were the larval common bully (Gobiomorphus cotidianus McDowall), larval inanga (Galaxias maculatus Jenyns), and postlarval cockabully (Tripterygion nigripenne Valenciennes). Common bully densities were highest in mid January, with the highest densities being recorded drifting out of Lake Waihola. Inanga densities were highest in March and April, with the highest densities being recorded in the channels draining wetland areas where extensive tidal inundation of riparian vegetation occurred. Cockabully were recorded from February to April, mostly at more downstream sites. Inland penetration by marine species was considerable, with two marine species, clingfish (Trachelochismus pinnulatus Forster) and smooth leatherjacket (Parika scaber Forster), being recorded c. 12 km upstream in late summer.