No description available.

The New Zealand aquaculture industry during the late 1990s and early 2000s experienced a significant and sustained period of growth. Greenshell mussels (Perna canaliculus) are proving to be a popular and valuable cultured species, with large domestic and international markets. Traditionally, these bivalves have been farmed within enclosed embayments and on relatively small scales (~3 Ha). The recent expansion of the industry coupled with the near saturation of existing 'traditional' sites and new culture technologies has led the industry toward alternate environments, notably exposed offshore sites. Initial proposals within the Bay of Plenty have included multiple farms of ~4500 Ha each. This novel approach to shellfish culture created uncertainty with respect to potential environmental impacts, cumulative effects, and sustainable carrying capacities within these exposed open-coast locations. In zoning for Aquaculture Management Areas (AMAs), environmental managers must be informed of each of these aspects to ensure the rational and sustainable use of the coastal-marine space. The overall goal of this study is to determine the potential for environmentally sustainable large-scale offshore mussel culture within the Bay of Plenty marine environment. The long term sustainability of aquaculture development on an open coast is a function of many influences which can vary in both time and space. The benthic environments of the Bay of Plenty exhibit great variability in their ability to assimilate waste inputs from suspended mussel culture; a direct function of the variability in sedimentary environments and benthic habitats within the region. Specifically, silty sediments with low natural organic contents, generally found between 40 and 100 m depths are the most suitable locations for sustainable mussel aquaculture from an environmental impact perspective. Both observations and model predictions indicate productivity potential within the region to be greatest within neritic zones of the western Bay of Plenty. Local wind forcing is the predominant mechanism forcing local shelf currents. Current meter data and numerical modelling tests from this study indicate that local winds explain the majority of water current variability on the shelf, generate the delivery of new nutrients to the shelf through upwelling, and hence create the variability in productivity potential. Complicating the AMA zoning process for environmental managers, however, are existing uses of, and societal values toward, the coastal-marine environment. GIS planning tools have been shown to be effective at minimising conflicts and maximising sustainability potential through informed site selection. Within the Bay of Plenty, these preferential sites are located on the mid-shelf (60-80 m depths) offshore from Pukehina, Matata, and Whakatane. This study shows that the simulated cumulative lower trophic-level depletion impacts of two large (~5000 Ha) proposed offshore mussel farms vary seasonally as a result of subtle changes in ecosystem dynamics and mussel feeding patterns. At proposed stocking densities, largest relative impacts are expected during autumn and winter, when relative phytoplankton biomass is low and growth rates slow. During spring, while absolute impacts are greater than those during autumn/winter, greater phytoplankton-zooplankton biomass and faster growth rates result in quicker recovery times and reduced 'depletion halo' extents. Year-long predicted impacts are below those applied as 'acceptable limits of change', both within New Zealand and internationally, indicative of the ecological carrying capacity.

Lake Rotokakahi is a mesotrophic lake located within the Rotorua Lakes District, North Island, New Zealand. Under the legal guardianship of the Tuhourangi and Ngati Tumatawera tribes of Te Arawa it has remained closed to the public since 1948. Lake Rotokakahi was last monitored regularly in 1996 under the Environment Bay of Plenty (EBOP) water quality monitoring programme with only the lake outlet (Te Wairoa Stream) being monitored since that time. Water quality data collected up to 1996 suggests that there may be degradation of water quality in the lake, as indicated by declining levels of dissolved oxygen in the bottom waters. Lake Rotokakahi steeped in historical significance, as well as having major cultural and recreational values was well known for its abundant resources and as the name suggests, particularly for its massive supply of the freshwater mussel or kakahi (Hyridella menziesi). Freshwater mussel species worldwide are in decline however little is known on factors controlling kakahi abundance and distribution. The overarching objective of this thesis is update water quality data last monitored in Lake Rotokakahi in 1996 while also identifying key environmental variables thought to influence kakahi populations. This objective is underpinned by a number of aims that include: Establishment of a 12-13 month water quality programme within Lake Rotokakahi so that data is obtained for comparisons with previous water quality data (pre-1997) to allow assessment of whether there have been water quality changes in the lake. Conduct a population survey of the resident kakahi population examining possible environmental factors influencing their populations. Present an oral history of Lake Rotokakahi focusing on its historical significance, water quality, and collection of kairoto (food collected form lakes). from the 18 September 2006 to 14 September 2007 monthly water sampling was carried out at a mid lake station, the lake outflow and inflow for measures of nutrients, phytoplankton, zooplankton and chlorophyll a. Vertical profiles of temperature dissolved oxygen and chlorophyll fluorescence were also taken on various part of Lake Rotokakahi. A lengthened period of anoxia in the bottom waters during thermal stratification was recorded with increased levels of chlorophyll a in winter and reduced secchi disk depth indicating an increase in phytoplankton biomass. Nutrient concentrations remain moderate relative to historical data. On going water quality monitoring on Lake Rotokakahi is recommended to further evaluate the extent of which water quality change is occurring. This will provide a better understanding of how Lake Rotokakahi can be best managed to further preserve the lake. On 1 March and 20 April kakahi were sampled at five sites. Large kakahi densities were distributed predominantly in depths above the hypolimnion. Chlorophyll a fluorescence and dissolved oxygen were found to be the best correlates for kakahi density and biomass respectively. Low dissolved oxygen concentrations in the hypolimnion are thought to restrict kakahi distributions to above the thermocline in periods of hypolimnetic anoxia.

<p>Abstract</p><p>This study takes up a local issue in the village of Lekhyttan, where Johan Molin is concerned about the freshwater pearl mussels (Margaritifera margaritifera) situation. He is a landowner and wonders what the situation is for the mussels and what he himself possibly can do, to hopefully improve their situation.</p><p>This paper looks at the different aspects on why the mussels are distributed as they are in the stream and trying to understand why new recruitment is poor in the Lekhyttan Stream.</p><p>Dividing the area into two zones, east (that has a population of mussels) and west (which has none), makes it easier to analyse which type of habitat they prefer. Why the mussels can be found in one zone and not in the other can be due to several different factors.</p><p>The factors investigated were: 1) bottom structure, 2) trout (Salmo trutta) - spawning area and mature trout habitat as the trout play an important role in the mussels lifecycle,</p><p>3) surrounding vegetation, 4) predation from signal crayfish (Pacifastacus leniusculus) and 5) water quality checked with a pH and iron test – from the inflows of ditches and pipes.</p><p>There was a significant difference between the two zones in the bottom sediment structure: the west zone had a high percentage of stone, whilst the east zone consisted of finer materials and had far more suitable habitat areas for the trout (both in spawning as well as for larger trout). Tests from the inflowing water in the west zone had water with low and high pH levels, as well as high iron contents. These inflows need to be fixed with a pond and reed filtration bed, as well as a recommendation on cutting back the number of crayfish that can be a potential threat to juvenile mussels. Following these recommendations will hopefully improve the situation locally for the Lekhyttan freshwater pearl mussel and maybe even lead to new recruitment.</p>

Thesis (Ph.D.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 129-148.

Abstract This study takes up a local issue in the village of Lekhyttan, where Johan Molin is concerned about the freshwater pearl mussels (Margaritifera margaritifera) situation. He is a landowner and wonders what the situation is for the mussels and what he himself possibly can do, to hopefully improve their situation. This paper looks at the different aspects on why the mussels are distributed as they are in the stream and trying to understand why new recruitment is poor in the Lekhyttan Stream. Dividing the area into two zones, east (that has a population of mussels) and west (which has none), makes it easier to analyse which type of habitat they prefer. Why the mussels can be found in one zone and not in the other can be due to several different factors. The factors investigated were: 1) bottom structure, 2) trout (Salmo trutta) - spawning area and mature trout habitat as the trout play an important role in the mussels lifecycle, 3) surrounding vegetation, 4) predation from signal crayfish (Pacifastacus leniusculus) and 5) water quality checked with a pH and iron test – from the inflows of ditches and pipes. There was a significant difference between the two zones in the bottom sediment structure: the west zone had a high percentage of stone, whilst the east zone consisted of finer materials and had far more suitable habitat areas for the trout (both in spawning as well as for larger trout). Tests from the inflowing water in the west zone had water with low and high pH levels, as well as high iron contents. These inflows need to be fixed with a pond and reed filtration bed, as well as a recommendation on cutting back the number of crayfish that can be a potential threat to juvenile mussels. Following these recommendations will hopefully improve the situation locally for the Lekhyttan freshwater pearl mussel and maybe even lead to new recruitment.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 78-89.

No description available.

I examined the suspension feeding of four freshwater unionid mussels, Elliptio complanata, Elliptio dilatata, Fusconaia flava and Strophitus undulatus to help explain how more than 30 species can coexist in a single river, as well as to contribute new insights into their basic biology. I examined whether the flux of algae affected the suspension feeding (clearance rate, CR) of unionids in a flow chamber. CR varied with seston flux (J = UC, where U is the velocity and C is the algal concentration) for the 4 species examined. The lotic species (E. dilatata) cleared up to four times more water than lentic species (E. complanata). Differences in CRs were found among E. dilatata, F. flava, and S. undulatus from the same hydrodynamic habitat at the highest flux tested; the CR of E. dilatata varied with the hydrodynamics of its native river. These results provide new insight into how seston flux influences unionid suspension feeding, which may help to explain niche breadth in this group.

Growth, mortality, production, spat collection, seasonal cycles of condition index, biochemical composition, carrying capacity of commercial raft culture systems and population genetic characteristics of blue mussel (Mytilus edulis) were studied at different sites in Loch Etive and Loch Kishorn on the west coast of Scotland between May 1993 and May 1995. The main objective of the study was to evaluate current suspended mussel culture production in raft systems and to obtain basic information on the biology and the genetic structure of the two mussel populations in the lochs. There were some water quality differences between the sites in relation to seston, salinity and transparency but not to temperature, particulate organic matter and chlorophylla. When food is available (as particulate organic matter and chlorophyll-a), there was a clear seasonal cycle in mussel somatic growth and shell growth. Mussel growth was relatively high from mid-spring until late autumn, but very slow during the rest of the year. The spring-summer period of rapid shell length and somatic growth coincided with relatively optimum environmental conditions and positive relationships were indicated between growth rates, temperature and salinity, indicating the limiting effect of these two primary factors on growth from late-autumn to mid-spring when there is also a lack of available food. Mussel growth was higher at 2m depth on the raft-rope systems, but in lantern nets experimental growth did not show differences between depths. Growth was found to be similar in the lantern nets and on culture ropes in the two lochs in the first year of experiments (from May 1993 to May 1994). Overall, mean length increments were 31.01mm in Loch Etive and 28.75mm in Loch Kishorn over a 15 month period. The mussels reached marketable size (&gt;50mm) in two years from the known time of spat settlement. A cross-transplantation experiment showed that site rather than stock is the main factor explaining differences in mussel growth in Loch Etive and Loch Kishorn. The position of the mussels within a raft has a significant effect on their growth; mussels at the inflow of a raft have a better growth than those near the outflow (p&lt;0.05) due to greater availability of food. Mean mussel biomass was higher in Loch Kishorn while production was higher in Loch Etive, but there were seasonal and monthly fluctuations in both biomass and production at both sites. Biochemical composition and energy content were similar in both sites, while mussel meat yield and condition indices were significantly higher in Loch Kishom than Loch Etive. Meat content, condition index and carbohydrate values were high during the summer and low from autumn to spring, reaching minimum values in March and April at the time of spawning. Spat settlement occurred in June-July in Loch Etive and June-December in Loch Kishorn. Sea squirt, starfish and eider duck are problems effecting spat collection at the Loch Kishorn site, whereas spat collection in Loch Etive is unaffected by these pests/predators. The carrying capacities for cultured mussels were found to be about 24 metric tons per raft for Loch Etive and 38 metric tons per raft for Loch Kishorn using a particulate organic matter based model; these are reasonable estimates in comparison to the known mussel production levels reported by producers. However, a seston-based model gave an overestimate of carrying capacity for both sites. Cross-transplantation of mussels, electrophoresis and shell morphological measurements showed significant differences between the Loch Etive and Loch Kishorn mussel populations. Mortality rates were higher in transplanted mussels than in the native mussels (p&lt;0.001).