Maturity, age and growth of Oreochromis karongae (Teleostei: cichlidae) in Lake Malawi and Lake Malombe

Size-at-50% maturity, age and growth, of Oreochromis (Nyasalapia) karongae (‘chambo’) in Lakes Malawi and Malombe were studied. Similar size-at-50% maturity and growth patterns were found for populations in Lake Malawi, but differences were observed for Lake Malombe populations, suggesting that current chambo fisheries management regulations, based on findings from the southern part of Lake Malawi, may be applicable to the central and southern parts of that lake, but not to Lake Malombe.

Effects of water quality in Bassenthwaite Lake on anglers' catches of salmon and sea-trout in the River Derwent

This is the report on the Effects of Water Quality in the Bassenthwaite Lake on Anglers Catches of Salmon and Sea-trout in the River Derwent April 1993 by the Institute of Freshwater Ecology. An analysis of the catch statistics for salmon and sea-trout in the Rivers Derwent and Cocker was undertaken in relation to available information on the algal water quality in Bassenthwaite Lake to test the hypothesis that poor catch returns were associated with a deterioration of water quality within the lake. Analysis of the catch statistics failed to reveal any correlation between water quality and catch returns for either species of fish and it is concluded that any water deterioration in Bassenthwaite Lake has not caused any major damage to the salmon and sea trout fisheries of the Derwent/Cocker system. This conclusion is supported by the analysis of the Windermere/Leven and Crake system, where no correlation could be found between lake water quality and downstream catches of migratory salmonid fish. However, the possibility still exists and such an effect might be detected by further field work on the macroinvertebrates and on the composition of potential salmonid spawning in the area.

Climatic controls on diatom succession at Elk Lake, Minnesota [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Sediment traps placed in the profundal region of Elk Lake, north central Minnesota during the 1979 spring and 1983-84 fall and spring seasons monitored seasonal diatom production for two climatically distinctive periods.

Estuarine use assessment: trial project in Casco Bay, Maine

The National Centers for Coastal Ocean Science (NCCOS) of the National Oceanic and Atmospheric Administration (NOAA) is interested in developing a project to determine the health of estuaries based on the stated or desired uses of society. An estuarine use assessment could complement the National Coastal Assessment, which tracks coastal and estuarine health through a series of environmental indicators. These indicators are used to assign a “score” to each coastal region, with some indicators reflecting the ability of the region to support desired uses such as fishing and swimming. An estuarine use assessment could also provide valuable information to resource managers and other decision-makers as they face decisions about the optimal and most sustainable mix of activities in an estuary. An initial step of an estuarine use assessment would be to define and quantify the desired societal uses of the estuary. Society includes residents living near the estuary or industries relying on the estuary, seasonal residents and tourists that use the estuary on a more limited basis, and the public at-large that may use or value the estuary indirectly. The desired uses may include discrete, visible uses such as swimming, recreational or commercial fishing, and navigation. They also may extend to broader, more intangible uses such as maintaining ecological functions or aesthetic appeal. National legislation such as the Estuary Restoration Act, which promotes and funds the restoration of estuaries in the U.S., reflects the public’s desire for estuaries to retain their ecological structures and functions. This report summarizes a project carried out in 2003 that attempted to quantify the desired human uses of a specific estuary in Maine and to determine current measures of success used by coastal managers in Maine to track the ability of the estuary to support desired uses. Casco Bay was chosen as the spatial embayment for which to delineate uses, and nutrient enrichment was selected as the parameter for confirming assumptions about current measures of outcomes related to uses. The report highlights some of the challenges to completing an estuarine use assessment and offers general recommendations for addressing these challenges.

Improving methods and indicators for evaluating coastal water eutrophication: a pilot study in the Gulf of Maine

Study Goals and Objectives: 1) Improve existing nutrient-related eutrophication assessment methods, updating (from early 1990s to early 2000s) the eutrophication assessment for systems included in the study with the improved method. 2) Develop a human-use/socioeconomic indicator to complement the assessment indicator. The human-use indicator was developed to evaluate costs of nutrient-related degradation in coastal waters and to put the issue into a broader context relevant to the interested public and legislators as well as to scientists. 3) Project objectives included collecting existing water quality data, developing an accessible database appropriate for application to a national study, and applying the assessment methods to 14 coastal systems – nine systems north of Cape Cod and five systems south. The geographical distribution of systems was used to examine potential regional differences in condition. 4) The intent is to use the lessons learned in this pilot study on a national scale to guide completion of an update of the 1999 National Estuarine Eutrophication Assessment.

Sensitivity of Lake Sturgeon population dynamics and genetics to demographic parameters [Powerpoint Slide]

Lake sturgeon Acipenser fulvescens restoration is a priority throughout the Great Lakes basin, where sturgeon have been reduced to less than 1% of historic levels due to habitat degradation, overharvest, and fragmentation of spawning populations. The population parameters most important to long-term lake sturgeon persistence are unknown.

Characterizing a cyanobacterial bloom in western Lake Erie using satellite imagery and meteorological data

The distribution and intensity of a bloom of the toxic cyanobacterium, Microcystis aeruginosa, in western Lake Erie was characterized using a combination of satellite ocean-color imagery, field data, and meteorological observations. The bloom was first identified by satellite on 14 August 2008 and persisted for more than 2 months. The distribution and intensity of the bloom was estimated using a satellite algorithm that is sensitive to near-surface concentrations of M. aeruginosa. Increases in both area and intensity were most pronounced for wind stress less than 0.05 Pa. Area increased while intensity did not change for wind stresses of 0.05–0.1 Pa, and both decreased for wind stress greater than 0.1 Pa. The recovery in intensity at the surface after strong wind events indicated that high wind stress mixed the bloom through the water column and that it returned to the surface once mixing stopped. This interaction is consistent with the understanding of the buoyancy of these blooms. Cloud cover (reduced light) may have a weak influence on intensity during calm conditions. While water temperature remained greater than 15°C, the bloom intensified if there were calm conditions. For water temperature less than 15°C, the bloom subsided under similar conditions. As a result, wind stress needs to be considered when interpreting satellite imagery of these blooms.

An environmentally based growth model that uses finite difference calculus with maximum likelihood method: its application to the brackish water bivalve Corbicula japonica in Lake Abashiri, Japan

We present a growth analysis model that combines large amounts of environmental data with limited amounts of biological data and apply it to Corbicula japonica. The model uses the maximum-likelihood method with the Akaike information criterion, which provides an objective criterion for model selection. An adequate distribution for describing a single cohort is selected from available probability density functions, which are expressed by location and scale parameters. Daily relative increase rates of the location parameter are expressed by a multivariate logistic function with environmental factors for each day and categorical variables indicating animal ages as independent variables. Daily relative increase rates of the scale parameter are expressed by an equation describing the relationship with the daily relative increase rate of the location parameter. Corbicula japonica grows to a modal shell length of 0.7 mm during the first year in Lake Abashiri. Compared with the attain-able maximum size of about 30 mm, the growth of juveniles is extremely slow because their growth is less susceptible to environmental factors until the second winter. The extremely slow growth in Lake Abashiri could be a geographical genetic variation within C. japonica.

Age and growth estimates of the winter skate (Leucoraja ocellata) in the western Gulf of Maine

Age and growth estimates for the winter skate (Leucoraja ocellata) were estimated from vertebral band counts on 209 fish ranging in size from 145 to 940 mm total length (TL). An index of average percent error (IAPE) of 5.8% suggests that our aging method represents a precise approach to the age assessment of L. ocellata. Marginal increments were significantly different between months (Kruskal-Wallis P<0.001) and a distinct trend of increasing monthly increment growth began in July. Estimates of von Bertalanffy growth parameters suggest that females attain a slightly larger asymptotic TL (L∞=1374 mm) than males (L∞=1218 mm) and grow more slowly (k=0.059 and 0.074, respectively). The oldest ages obtained for the winter skate were 19 years for males and 18 years for females, which corresponded to total lengths of 932 mm and 940 mm, respectively. The results indicate that the winter skate exhibits the characteristics that have made other elasmobranch populations highly susceptible to exploitation by commercial fisheries.

Recovery of the Gulf of Maine--Georges Bank Atlantic herring (Clupea harengus) complex: perspectives based on bottom trawl survey data

NMFS bottom trawl survey data were used to describe changes in distribution, abundance, and rates of population change occurring in the Gulf of Maine–Georges Bank herring (Clupea harengus) complex during 1963–98. Herring in the region have fully recovered following severe overfishing during the 1960s and 1970s. Three distinct, but seasonally intermingling components from the Gulf of Maine, Nantucket Shoals (Great South Channel area), and Georges Bank appear to compose the herring resource in the region. Distribution ranges contracted as herring biomass declined in the late 1970s and then the range expanded in the 1990s as herring increased. Analysis of research survey data suggest that herring are currently at high levels of abundance and biomass. All three components of the stock complex, including the Georges Bank component, have recovered to pre-1960s abundance. Survey data support the theory that herring recolonized the Georges Bank region in stages from adjacent components during the late 1980s, most likely from herring spawning in the Gulf of Maine.

Innovations to strengthen aquatic resource governance on Cambodia’s Tonle Sap Lake

Cambodia’s recent freshwater fishery sector reform, instigated at the top level of government, is one of the country’s most significant contemporary policy developments addressing natural resources management and rural development. Implemented in two main waves, the reforms culminated in the complete removal of inland commercial fishing lots. Yet serious problems still need to be addressed, including reportedly widespread illegal fishing, difficulties in protecting critical habitats, and competition among state agencies over resource management authority. This report summarizes the context of the recent fishery reforms, analyzes challenges and opportunities for policy implementation after the reforms, and details the outcomes of local institutional innovations in Kampong Thom Province, followed by a discussion of the implications for ongoing efforts aimed at reducing resource conflict and building livelihood resilience.

Strengthening collective action to address resource conflict in Lake Kariba, Zambia

Where natural resources are a key component of the rural economy, the ability of the poor to realize their visions for the future depends significantly on institutional structures that govern resource access and management. This case study reports on an initiative on the shores of Lake Kariba in Zambia, where lakeshore residents face competition over fishing, tourism, and commercial aquaculture. Multistakeholder dialogue produced agreements with investors and increased accountability of state agencies and traditional leaders, enabling communities to have greater influence over their futures through improvements in aquatic resource governance. The report documents the rationale for the approach followed and steps in the capacity-building process, discusses obstacles encountered, and identifies lessons for policymakers and practitioners seeking to implement a similar approach.