Developing a conceptual model of marine farming in New Zealand

Survey and Geographic Information System (GIS) data analysis describes the relative influence of biophysical and human variables on site choices made by marine farmers in New Zealand. Community conflicts have grown in importance in determining farm location and different government planning strategies leave distinct signature patterns. Recent legislation empowers local governments to choose among three strategies for future regional aquaculture development. This paper suggests each strategy could result in different spatial outcomes. Simulation modelling of the type described here can provide a better understanding of farmer responses to management approaches and the range of futures that could result from planning choices made today.     

Dissolved oxygen criteria for freshwater fish in New Zealand: a revised approach

Maintenance of suitable conditions in lowland rivers for both fish passage and resident species is crucial to ensuring the long-term sustainability of fish populations. The dissolved oxygen concentration of water is a key factor controlling habitat quality for fish and a critical measure of stream health. Continued land use intensification and greater exploitation of water resources has contributed towards increasing the frequency and duration of low dissolved oxygen events in lowland rivers and the associated risk of adverse effects on fish communities. Revised guidelines are therefore proposed to support setting of biologically relevant dissolved oxygen limits for the protection of New Zealand freshwater fish communities. These guidelines account for both event magnitude and duration, identify different protection levels based on the risk of negative impacts and are based on current scientific knowledge on the tolerances of New Zealand fish species.     

Water quality in New Zealand rivers: current state and trends

River water quality, particularly in lowland catchments, is a matter of concern to the New Zealand public. We assessed river water quality and biological state and trends using data from more than 900 monitoring sites. Parallel state and trend analyses were carried out using all sites and a subset of lowland river sites. Median water-quality state in urban and pastoral land-cover classes was poorer than in exotic forest and natural land-cover classes, and lowland sites in the urban and pastoral classes had the poorest water quality. Nutrient and Escherichia coli concentrations increased and visual clarity and Macroinvertebrate Community Index scores decreased as proportions of catchments in high-intensity agricultural and urban land cover increased. Ten-year trends (2004–2013) indicated recent improvements in ammoniacal nitrogen, dissolved reactive phosphorus and total phosphorus in the pastoral and urban classes, possibly reflecting improved land management. In contrast, trends in nitrate-nitrogen in the exotic forest and cool-dry/pastoral classes indicated worsening conditions.     

Water quality in a polluted lowland stream with chronically depressed dissolved oxygen: Causes and effects

Abstract

The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO^? ₃‐N), biochemical oxygen demand (BOD₅), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K₂ ²⁰, using methyl chloride (CH₃Cl) as a gas tracer, yielded values of 1.1–3.0 d^?1 for the upper part of the study reach and 15.5–16.2 d^?1 for the lower reach (overall average 12.5 ± 2.5 d^?1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality.     

Effects of small ponds on stream water quality and macroinvertebrate communities

Six small constructed ponds (surface area 500–7500 m², catchment area 28–158 ha) in rural and native forest catchments in the Auckland region had poorer water quality than the streams they replaced. Temperature (24°C) and dissolved oxygen (DO) (4 mg/litre) criteria were exceeded for up to 46% and 84% of days, respectively, during a critical 40‐day summer period. The poor conditions found in ponds, even within undeveloped native forest catchments, indicated that the physical characteristics of ponds (e.g., lack of shade, organic sediments) affected water quality independently of other factors (e.g., land use, riparian protection). The frequency and severity of the exceedences were related to pond size, retention time, and catchment land use; the most degraded conditions were found in rural ponds with largest surface areas and longest retention times. Ponds affected water quality and macroinvertebrate communities downstream. Exceedences of temperature and DO criteria occurred more frequently and were more severe downstream than upstream of ponds. Ponds in rural catchments increased mean daily stream temperatures 3.1–6.6°C during the critical summer period, and temperature differences were three times higher than those in bush catchments (0.8–2.0°C). Elevated temperatures were observed for hundreds of metres downstream owing to the slow rate of cooling (1°C/ 100 m), expanding the extent of adverse effects well beyond the “footprint” of the pond. Macroinvertebrate community composition (sample area 1–3 m²) and values of four commonly used metrics appeared to be significantly affected by ponds in rural and native forest catchments. These finding have important management implications that should lead to modifications (e.g., breaching dams) of the estimated 4500 existing ponds in the Auckland region, where possible, and restrictions on proposals for new “on‐line” ponds.     

Anthropogenic increases of catchment nitrogen and phosphorus loads in New Zealand

Spatial regression models were used to predict yields (kg?ha^?1?yr^?1) of nitrogen (N) and phosphorus (P) discharged from catchments throughout New Zealand under natural and current conditions. The models were derived using loads (kg?yr^?1) of TN, NO₃-N, TP and DRP calculated for 592 river water quality monitoring sites. Anthropogenic increases in yields above natural levels were associated with the proportions of catchments occupied by the intensive agricultural land cover and were unevenly distributed across regions. Anthropogenic increases in national loads of TN, NO₃-N, TP and DRP exported to the ocean were 74%, 159%, 48% and 18%, respectively. Increases in loads exported to the ocean varied considerably at smaller scales, with catchments having significant load increases between 4- and 26-fold for N and 6- to 9-fold for P. Predictions of yields and loads reported here have utility in the development of strategies to manage nutrients.     

Effects of paraquat on invertebrates in a Canterbury stream,New Zealand

During 1966 and 1967, paraquat was applied on three occasions at 2 ppm for 30 min to control aquatic weeds in the South Branch experimental stream, a tributary of the lower Waimakariri River, Canterbury, South Island, New Zealand. Effects on the invertebrate fauna of the stream were studied before, during, and after the applications, by Surber and drift‐net samples.

After a heavy initial kill, the paraquat treatment reduced the number of amphipods caught in the drift fauna to 5% of the pre‐treatment level, and there was a slight reduction in the numbers of hemipterans. The total numbers in Surber samples increased markedly a year after treatments ended, mainly due to increased numbers of trichopterans.     

Sediment-related water quality of small hill-country streams near Whatawhata,New Zealand. Response to integrated catchment management (ICM)

ABSTRACT

Degradation of aquatic ecosystems by fine sediment is a global environmental problem, and damages reflect particle properties as well as mass concentration. We studied sediment-related water quality (SRWQ) of small streams in hill-country near Whatawhata, NZ, that have been monitored since 1995. In 2001, an integrated catchment management (ICM) plan was implemented in the Mangaotama (originally sheep-beef) catchment – including conversion of steep headwaters to pine plantation, cattle exclusion, and native riparian plantings. The long-term SRWQ within the Mangaotama catchment was examined with reference to a nearby native-forested control catchment. Correlations between visual clarity, suspended particulate matter concentration and related variables were moderate to fairly strong. The ICM has not improved SRWQ as expected – plausibly because removal of cattle disturbance has been offset by decline in pasture ground cover under increasing shade of tree plantings. Worsening SRWQ is expected over the next several decades as channels widen towards a ‘forest’ morphology.     

Responses of two trophic levels to patch enrichment along a New Zealand stream continuum

We carried out a benthic survey and two experiments in runs at eight sites down the Kakanui River (South Island, New Zealand) during summer low flows, to investigate the interaction between nutrients, periphyton, and macro‐grazers. Benthic periphytic biomass was generally low (< 20 mg m^‐2 chlorophyll a) at most sites, but high densities of macro‐grazers (mainly snails) were observed at six of the eight sites. Chlorophyll a and cellular P concentrations were generally higher on artificial substrates in the first‐ to third‐order tributaries, compared with downstream. Macro‐grazer densities (mainly snails) were also highest in the second‐ and third‐order tributaries. Enrichment of patches with N and P did not translate into significant increases in chlorophyll a concentrations. Instead there was a general increase in macro‐grazers, and an increase in the relative abundance of Cocconeis placentula. In a second experiment, the chlorophyll a level was five‐fold higher on the substrates where macro‐grazers were excluded and there was no significant response of chlorophyll a to nutrient addition on these substrates. On the grazed substrates, densities of snails and caddis‐larvae were two‐fold higher with N+P enrichment. These experiments provided evidence for a tight coupling between first and second trophic levels, and strong grazer control of periphyton, in this river.     

Studies of a mangrove basin,Tuff Crater,New Zealand: III. The flux of organic and inorganic particulate matter

Water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove-covered basin of Tuff Crater, Auckland, New Zealand. The samples were filtered and total suspended sediment (TSS), inorganic suspended sediment (ISS) and organic suspended sediment (OSS) were determined. Variation in TSS was high, the concentration varied over a tidal cycle and during over-bank flows concentrations were lowest at or near slack high water. Covariance between TSS concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux. The hypsometrically-based volumetric method was found to be inappropriate, predicting a positive budget (import) more often than observed. Instead particulate matter budgets were calculated by means of the velocity-area method and indicate a net export of TSS, ISS and OSS. Floating macrodetritus was observed on both the flood and ebb tides, but a net export was found on the two tides monitored. It is considered that on an annual basis floating macrodetritus export accounts for less than 2% of the detrital production in the basin, and organic suspended sediment export from the basin is less than 3 kg C ha^?1 day^?1 and is below the rate of detrital production. It is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ.     

Occurrence and recruitment of fish larvae in a northern New Zealand estuary

The occurrence of fish larvae and the effect of diel and tidal variation on catches was studied at about biweekly intervals for a year in Whangateau Harbour, a small well mixed northern New Zealand estuary. Larvae from 31 taxa were identified. The annual pattern of larval occurrence was typical for fish in temperate waters, with a major peak of abundance in early summer. For six taxa, larval densities were significantly greater in night-time than in daytime catches, and analysis of length-frequency distributions suggested that for two species this was due to daytime net avoidance.No significant differences were found between the densities of larvae caught on flood and ebb tides, but changes in length-frequency distributions were significant for two species. Recently hatched larvae of an unidentified goby were found leaving the harbour, where they were probably spawned, while older larvae of this species appeared to be recruiting back in. Larvae of the flounder Rhobosolea plebeia were also apparently recruiting into the harbour. In the absence of a two-layered circulation pattern larvae relied upon tidal transport for recruitment, and probaby ensured their retention by rapidly settling to the bottom.     

Maintenance of Near-Surface Stratification in Doubtful Sound, a New Zealand Fjord

The surface waters of Doubtful Sound, a glacially carved fjord in south-western New Zealand, feature a quasi-permanent low-salinity-layer (LSL). The LSL is maintained year round by the extreme precipitation in the catchment (7 m yr⁻¹) and discharge from a hydroelectric power station (450 m³ s⁻¹). The robust, stable LSL has been shown to play a major role in controlling intertidal and subtidal community structure. By contrast, little is known about the dynamics of the LSL itself. The work presented here elucidates the response of the LSL to perturbations in the wind stress and rainfall.Frequency-domain analysis of salinity data collected from an array of moored instruments revealed that the LSL responded to perturbations in both the winds and rainfall. However, the specific roles of the wind stress and rain could not be adequately resolved in these analyses. By contrast, simulations of the response of the LSL using a three-dimensional primitive equation model revealed that strong up-fjord directed wind events set up a storm surge at the head of the fjord. This surge significantly deepens the LSL at the head of the fjord and retards or reverses estuarine circulation. The subsequent relaxation of the surge after the abatement of the wind stress resulted in a redistribution of buoyancy throughout the fjord over a two-day period. It is shown that the development and relaxation of the storm surge is a major process controlling the maintenance of the near-surface stratification.     

The influence of habitat availability on juvenile fish abundance in a northeastern New Zealand estuary

Management of fish populations is often focused on the exploitation of adult fish. Maintaining the habitat requirements of all life stages may also be an important consideration. We investigated the value of structured habitat to juvenile fishes within a northeastern New Zealand harbour using artificial seagrass units (ASUs). Specifically, we deployed ASUs across treatments with high vs. low habitat manipulations. We hypothesised that if the abundance of recruiting juvenile fishes was greater on the high habitat availability treatments this would suggest that the availability of habitat was limiting juvenile fish abundance. Our analyses were focused on the four most abundant fishes that settled on our ASUs: snapper (Pagrus auratus); spotty (Notolabrus celidotus); trevally (Pseudocaranx dentex); and an assemblage of pipefish species. For snapper, spotty and pipefish, abundance was greater on the high habitat availability treatments. This result would be unlikely to occur if the availability of juvenile fishes was limiting, suggesting that juvenile fish abundance is more likely to be limited by habitat. In terms of spatial gradients, spotty abundance and size increased with distance into the harbour. The spatial gradient present for spotty indicates the importance of placing the habitat dependency of juvenile fish into a landscape context. Overall, these results demonstrate that maintaining structured habitats may be an important consideration for some valuable inshore fish populations in northeastern New Zealand.     

Maintaining a balance between resource utilisation and protection of the marine environment in New Zealand

New Zealand's brief history of human habitation has led to widespread and often irreversible change in the biophysical environment. Most of the wetlands were drained and de-forestation led to major gully and channel erosions and high amounts of sediment yield in the estuarine and marine environments. The scale of land-based effects on marine species is indeterminable. The legislation for managing the land–sea interface is widely acknowledged as having fallen short of its full potential. After the 2008 general election the new government commenced review of this legislation while consideration was given to ‘unlocking New Zealand's energy potential’ as a key component to an export-led economic recovery. The government is promoting oil, gas and mineral exploration on land and at sea. The government is also enacting boundaries that extend continental shelf jurisdiction. These developments may lead to further progress on an integrated system that covers all aspects of marine management that began in 2000. In any case, New Zealanders face important decisions regarding the tradeoffs between further resource utilisation and environmental protection. This article contributes to the discussion on integrated management to maintain a balance between utilisation and protection and does not reflect the view of the Ministry of Fisheries.     

Annual pattern of brooding and settlement in a population of the flat oyster Ostrea chilensis from central New Zealand

Temporal patterns of larval brooding and settlement were investigated in a flat oyster (Ostrea chilensis) population in Tasman Bay, central New Zealand. The proportion of the population brooding larvae and larval settlement rates were monitored over 26 months. A peak period of brooding activity began in late spring and continued through summer. Maximum rates of 17% and 23% of adult oysters brooding larvae occurred in November and December, and an estimated 55–78% of adult oysters incubated larvae over the entire summer breeding period. These proportions of brooders are higher than those previously reported for Tasman Bay. A very low level of brooding activity (1%) occurred during winter. Temporal trends in larval settlement closely tracked brooding patterns. Settlement was greatest between November and January, and there were very low rates in winter. The seasonal breeding pattern in the population was intermediate between northern and southern populations, confirming a latitudinal gradient of reproductive behaviour for O. chilensis in New Zealand. Results are useful in optimising the timing of substrate deployment in an enhancement programme for the oyster fishery.     

Genetic and morphological evidence for a single species of pink ling (Genypterus blacodes) in New Zealand waters

Two species of ling, Genypterus blacodes (Forster in Bloch & Schneider, 1801) and G. microstomus (Regan, 1903) have been recorded from New Zealand and Australian waters; a third species, G. tigerinus (Klunzinger, 1872) has been recorded from Australia. Specimens of ling collected from northern, central, and southern localities in the New Zealand Exclusive Economic Zone (EEZ), and specimens of G. blacodes from Australia were shown to be similar with respect to partial sequences of mitochondrial (mt)DNA, and morphometric and meristic characters. DNA sequences of part of the cytochrome b and control region showed that G. blacodes from Tasmania and New Zealand differed by 1/291 and 4/284 nucleotides respectively, but there was much greater genetic differentiation between G. blacodes and G. tigerinus (14/291 and 14/284 nucleotides), and between G. blacodes and G. capensis (23/291 and 8/284 nucleotides). MtDNA haplotypes within New Zealand show that G. blacodes is subdivided into northern and southern stocks. It is concluded that ling in New Zealand represent a single species referable to G. blacodes, and that G. microstomus Regan is a junior synonym.     

Long-term effects of a toxic algal bloom on subtidal soft-sediment macroinvertebrate communities in Wellington Harbour, New Zealand

The long-term effects (>1 year) of a naturally occurring toxic plankton bloom (Karenia brevisulcata) on subtidal benthic macroinvertebrate communities were investigated in Wellington Harbour, a semi-enclosed temperate embayment in New Zealand. For 3 years communities were sampled at three different sites in the harbour. Analyses revealed that community recovery following the bloom was site-specific. Multivariate analyses indicated that at one site community composition was approaching recovery 3 years post-bloom. At the second site, a sequential recovery process was indicated, whereas at the third site the community composition oscillated from year to year, but did not show any signs of a sequential recovery process. The nature of the hydrodynamic regime was identified as a major factor influencing the observed recovery processes. Communities exposed to an active hydrodynamic regime were less affected by the bloom and differed little in their composition pre- and post-bloom, as they were naturally in a perpetual state of recovery as indicated by a dominance of r-selected species. The community at the hydrodynamically less active site was more affected by the bloom and exhibited temporal differences in composition consistent with successional models. Complete recovery to a pre-disturbance climax community dominated by K-selected species is likely to take 4–5 years, if not interrupted by other disturbances. Given the increased occurrence of harmful algal blooms worldwide, more monitoring and manipulative studies are needed to further evaluate the effects of such disturbances on macrobenthic communities.     

Role of scavenging in a synaphobranchid eel (Diastobranchus capensis,Barnard, 1923), from northeastern Chatham Rise,New Zealand

Scavengers perform an important role in deep-sea ecosystems, recycling carrion. However, scavenged material can be difficult to discern from predation. The synaphobranchid eel Diastobranchus capensis Barnard, 1923, is common bycatch in deep-water fisheries for orange roughy (Hoplostethus atlanticus Collett, 1889) in New Zealand waters. Despite anecdotal reports of scavenging in D. capensis, their ecology and feeding are little known. Scavenged material was estimated to be approximately 39 per cent (by weight) of the diet of D. capensis from northeastern Chatham Rise, New Zealand, from water depths of 1062–1196 m. Scavenged material was defined as fragmentary food items from animals and plants either not normally available to the eel, or from animals larger than the eel consuming them (e.g., fish heads and tails, spent squid spermatophores, beaks and tentacle crowns, and seaweed). D. capensis were primarily piscivorous, with the diet supplemented by squid, natant decapods and mysids. The weight or number of food items did not increase with the size of the eel, nor was there any major ontogenetic shift in the composition of the diet. D. capensis probably plays an important role in mid-slope communities, recycling carrion.