Aquaculture and Fisheries

The provision of management information on the fisheries of Lakes Malawi and Malombe has been characterised by top–down controlled single species steady-state assessment techniques originating from single gear industrial fisheries but applied to an open access highly diverse and adaptive small-scale multispecies and multi-gear fishery. The result has largely been an unhappy marriage with uncertainties blamed more on the data than the process, although the data collection generally is detailed and comprehensive on catch and effort parameters. An extensive literature review of primary and grey literature on ecosystem drivers, exploitation pressures, and fish population and community states shows that Malawi has the necessary knowledge base for expanding their assessment into multi-causal and exploratory indicator-based methods that can assist in better understanding and more disciplined use of existing data and monitoring systems. Selection and ranking of a suite of indicators focusing on the major fisheries in the Southeast arm of Lake Malawi and Lake Malombe were done by a group of Malawian fisheries researchers and management advisers, thereby testing a framework of scoring criteria assessing an indicator's acceptability, observability, and relatedness to management. Indicators that are close to raw observational data and that require limited permutations and few assumptions appear to be preferable in the Malawian context. CPUE-based assessments can improve the utility of data and information in communicating developments and processes and evaluate fisheries management policies.► We developed an indicator framework for Lake Malawi fisheries management. ► Multi-causal, exploratory indicator based assessments is possible. ► Better understanding and more disciplined use of extant monitoring systems. ► Prefer indicators based in raw observations with few permutations and assumptions. ► CPUE based assessments improve utility of data and information already collected.

Lakes and reservoirs are traditionally characterised from static morphological or chemical parameters such as depth and dissolved solids, while the dynamic impact of shifting water supplies has received little attention. There is increasing evidence, however, that the hydrodynamic regime in tropical water bodies plays a significant role in the injection and re-suspension of nutrients, and consequently has a strong influence on the biological communities and productivity. Lake level fluctuations can therefore be used as a proxy for bottom up driven processes. The application of a relative fluctuation index (RLLF) and its relationship with fish yields in a range of tropical lakes and reservoirs in Asia and Africa is reviewed. The RLLF is a simple empirical indicator defined as the mean amplitude of the annual or seasonal lake level fluctuations divided by the mean depth of the lake or reservoir, times 100. It builds on the classic morpho-edaphic index (MEI) for lakes and the more recent dynamic flood pulse concept (FPC), originally developed for rivers and floodplains. The RLLF index can be used as a predictive indicator for classifying lakes and reservoirs from stable to pulsed systems, and thereby their potential resilience to external disturbances. The index also has a strong log-linear relationship with the fish productivity.

Shallow lakes and man-made reservoirs in general have the highest lake level changes, but also the highest fish yield per unit area, and even extreme fluctuations (amplitude higher than mean depth) seem only to accelerate the biological processes. The influence of water level changes on aquatic productivity should be taken into account when assessing environmental impacts within and outside man-made reservoirs.

Modern fisheries management discourse is supported by two fundamental narratives that have global impacts. One is the fear of open access regimes, and the other is the condemnation of catching under-sized and immature fish. These narratives have existed for more than half a century and originate from the Common Property Theory (Gordon 1954) and the Maximum Yield per Recruit theory (Beverton and Holt 1957).
Our aim is to critically discuss and evaluate these narratives which have been developed within the context of scientific management of single-species industrial fisheries. We will show that the underlying assumptions can be seriously wrong and particularly absurd in fluctuating multi-species, multi-gear artisanal fisheries. Fishing effort in small scale fisheries is often largely regulated by natural production, like other top predators, and many targeted fish stocks and fish communities display a high degree of resilience. Furthermore, in spite of common belief, small scale unregulated, non-selective, adaptive fishing patterns could be healthier and far more ecosystem conserving than the current imposed single species management strategies. Many of these fisheries are serving as a 'social security system' - a common good and thereby function as a 'last resort' for economic mishap. Limiting open access will undermine the role of small-scale fisheries to provide insurance, particularly for the poorest and least advantaged. The immense pressure to adapt to modern fisheries management thinking and economic theory is based on flawed assumptions and will not only have negative social effects, but also negative biological effects.

Industrial and artisanal ®sheries exploit the pelagic ®sh community of northern Lake Tanganyika with total annual landings uctuating between 16,000 and 30,000 t since 1974. The pelagic catch consists of the commercial categories`small' (<20 cm) (Stolothrissa tanganicae, Limnothrissa miodon and juvenile Lates stappersii),`medium' (20±40 cm) (L. stappersii) and`large' (>40 cm) (three Lates spp.) sized ®sh. Thirty-seven years (1956±1992) of monthly catch rates by the industrial purse-seine ®shery were evaluated for the capacity of ®sheries management authorities to detect possible long-term trends given large variability around such a trend due to inter-annual variability, seasonality and persistence. Variability in 10 log-transformed total catch rates (kg/vessel/month) was high s 0:22, but considerably lower than the variability for the commercial categories`small' s 0:32,`medium' s 0:59 and`large' s 0:69. Long-term downward trends in catch rates were signi®cant for catch rates as total catch (1.6% per year, r 2 0:21) and for the categories`small' (1.4% per year, r 2 0:08) and`large' (2.7% per year, r 2 0:21). Seasonality, confounding the perception of long-term trends in monthly catch rates, although with temporal predictability, explained between 3 and 10% of the total variance in monthly catch rates. Signi®cant short-term persistence in the residuals of series, adjusted for between year and seasonal differences, and as described by ARMA models, must be due to¯eet±stock interactions. Further obscuring trends, this persistence explained 5, 11, 13 and 3% of the variance in total catch rates and of the commercial categories`small' and`medium' and`large'. Basic uncertainty, as variance not explained by trend or seasonality, comprises the largest part of the variance in catch rates (`total' (75%),`small' (83%) and`medium' (89%)). Trend-to-noise ratios (b/s) were calculated with the slope (b) in 10 log-transformed monthly catch rates and the standard deviation in the residuals around the regression line (s). These ratios were high, necessitating long series of data to detect signi®cant long-term trends. Faced with such large uncertainties and compounding effects of the various types of variance around long-term trends, the Burundi management authorities of the Lake Tanganyika ®sheries have few possibilities to evaluate the effectiveness of, for instance, controlling ®shing effort as a direct and basic management measure. #

The organisation of a fisheries statistical system dictates the potential usage of its information output. Information is used for planning of food production (fish as a commodity), for fisheries management (fish as a renewable natural resource), and for nature conservation (fish as an indicator for ecosystem quality). In this sequence, the required temporal, spatial and categorical resolution of data increases, while aggregation into meaningful ecological spaces requires a subtle way of organising the data flow. The effective usage of the present fisheries information of Vietnam is constrained by (1) its low categorical resolution and (2) the non-transparent aggregation of data into mere administrative spaces. Information requirements can be better articulated with the instalment of mandatory evaluation procedures at all levels in the fisheries administration. Our examples range from the national administration of the 4 million ton marine fisheries in Hanoi, to the local administration of a fishing commune in the Red River Delta. r (P.A.M. van Zwieten). 0308-597X/02/$ -see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 3 0 8 -5 9 7 X ( 0 1 ) 0 0 0 3 6 -7

Sustainability in fisheries has over the past decades evolved from a single species maximization concept to covering ecosystem and biodiversity considerations. This expansion of the notion, together with increased evidence that the targeted removal of selected components of the fish community may have adverse ecological consequences, poses a serious dilemma to the conventional fisheries management approach of protecting juveniles and targeting adults. Recently, the idea of balanced harvest, i.e. harvesting all components in the ecosystem in proportion to their productivity, has been promoted as a unifying solution in accordance with the ecosystem approach to fisheries, but this will require a fundamental change to management. In this paper, we review the objectives, theoretical background, and practicalities of securing high yielding fisheries in inland waters, with empirical examples from tropical freshwater fisheries which satisfy the extended objectives of minimal impact on community and ecosystem structure. We propose a framework of ecological indicators to assess these objectives.

Conventional fisheries management encourages highly selective fishing patterns for various purposes, such as increase relative yield, reduce unwanted bycatch, protect various species or sizes and rebuild ecosystems. Recent empirical and theoretical studies, however, show increasing evidence that selective removals of targeted components have unintended adverse effects on stocks, fish communities and the ecosystem. Based on case studies from artisanal African freshwater fisheries, and results from dynamic size-based models, this chapter supports the renewed suggestion that an application of a more balanced fishing pattern will mitigate adverse effects and enhance food security better than increased selectivity. Contrary to common belief, small-scale unregulated artisanal fisheries, with a high diversity of seasonally adapted fishing methods, are probably the closest empirical examples we have of an optimal exploitation pattern with the least disruptive effects on the structure of the ecosystem. As such they are among the best examples of an ecosystem approach to fisheries that we have.

East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’ vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.

The importance of fish, and in particular small fish, for sustainable and healthy livelihoods in Africa, as well as their strong relationship with climate driven water dynamics are generally undervalued and little understood as most are consumed locally and go unrecorded in catch statistics. Fish are vital providers of animal protein and indispensable micronutrients in many African societies, but modern food production and policies is almost unilaterally associated with terrestrial agriculture and livestock production. The majority of fish species are carnivores and by primarily targeting large adult fish, such as e.g. Nile perch in Lake Victoria, humans feed about two trophic levels higher in water than on land, which in terms of energy is a very inefficient utilization of available food. Small fish are lower in the food web and much more abundant and productive but their capture is inhibited by old fashioned selectivity regulations. Small fish are ubiquitous in all aquatic environments from large lakes to seasonal ponds and productivity is highly correlated with rainfall patterns and water level fluctuations. Catching small fish, which are sun-dried and consumed whole, is the most high-yielding, eco-friendly and nourishing way of utilizing the natural food that aquatic ecosystem provide. Maintaining healthy aquatic ecosystems are more important than traditional fishery management.

We studied the effects of environmental
driving factors (maximum depth, visibility, oxygen,
temperature, and prey densities) on the distribution
and diet composition of Nile perch (Lates niloticus) in
south-east Lake Victoria from 2009 to 2011. We tested
the hypotheses that (i) Nile perch distribution is
regulated by the same environmental factors on a local
scale (Mwanza Gulf) and on a regional scale (Mwanza
Gulf, Speke Gulf and the open lake in Sengerema
district), and (ii) driving factors act differently on
different Nile perch size classes. Fish were sampled
with gillnets. Nile perch densities were highest in the
shallow part of the Mwanza Gulf and during the wet
seasons, mainly caused by high densities of juveniles.
The environmental driving factors explained Nile
perch distributions on both regional and local scales in
a similar way, often showing non-linear relationships.
Maximum depth and temperature were the best
predictors of Nile perch densities. Prey densities of
shrimp and haplochromines did not strongly affect
Nile perch distributions, but did explain Nile perch
diet on a local and regional scale. We conclude that
abiotic variables drive Nile perch distributions more
strongly than prey densities and that feeding takes
place opportunistically.

The development of shrimp farming in Vietnam has eroded the social-ecological resilience of the coastal
ecosystem. Recent literature supports the idea that integrated mangrove-shrimp production systems can
contribute to rebuilding this resilience in the Mekong Delta. Two experts panels, international and
Vietnamese, were consulted to validate and weight drivers identified from literature that enable or
constraint farmers to shift from extensive production system to integrated mangrove-shrimp system or
to continue such integrated system. Though a combination of drivers is needed to enhance changes, two
sets of drivers were given the highest weight. Experts considered the ecosystem function of the
mangrove an enabling driver pushing farmers to plant mangrove in order to improve the pond's water
quality and limit disease outbreaks. They perceived the drivers related to the current regulatory
framework as constraining because these limit the financial return associated with integrated mangroveshrimp
systems. The analysis indicates that the adoption of these integrated systems requires more
equitable distribution of benefits from shrimp and timber production between farmers and other
stakeholder in these value chains. We recommend to develop a regulatory framework that can optimize
the financial benefits of the integrated mangrove-shrimp production systems for farmers.

Conversion to aquaculture affects the provision of important ecosystem services provided by mangrove
ecosystems, and this effect depends strongly on the location of the conversion. We introduce in a bioeconomic
mathematical programming model relevant spatial elements that affect the provision of the
nursery habitat service of mangroves: (1) direct or indirect connection of mangroves to watercourses; (2)
the spatial allocation of aquaculture ponds; and (3) the presence of non-linear relations between
mangrove extent and juvenile recruitment to wild shrimp populations. By tracing out the production
possibilities frontier of wild and cultivated shrimp, the model assesses the role of spatial information in
the trade-off between aquaculture and the nursery habitat function using spatial elements relevant to
our model of a mangrove area in Ca Mau Province, Viet Nam. Results show that where mangrove forests
have to coexist with shrimp aquaculture ponds, the inclusion of specific spatial information on
ecosystem functions in considerations of land allocation can achieve aquaculture benefits while largely
preserving the economic benefits generated by the nursery habitat function. However, if spatial criteria
are ignored, ill-advised land allocation decisions can easily lead to a collapse of the mangrove’s nursery
function.

East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In
particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole
region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately
connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out
piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to
disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a
whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system
through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its
contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that
can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that
high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’
vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple
pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management
toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt
or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a
paving stone for future quantitative analyses of system dynamics at local scales.