Aquaculture environmental impact assessment

Aquaculture environmental impact assessment

L. Molina Dom?nguez1 & J. M. Vergara Mart?n2

1Instituto Canario de Ciencias Marinas, P.O. BOX 56, 35200 Telde, Canary Islands, Spain 2Departamento de Biolog?a, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira 35017 Las Palmas de Gran Canaria, Canary Islands, Spain

Abstract

All human activities produce some impact on the surrounding environment, and aquaculture is not an exception, as it utilises natural resources and releases waste into the environment. As the aquaculture sector developed, environmental aspects became of an increasing concern, in parallel with maximum public environmental concern developed from the second half of the 20th century. Up to now, most aquaculture practices have produced little negative effects on the ecosystems, even being beneficial in some cases. However, frequently a deficient management or accidents in aquaculture facilities have been reported to cause negative effects. Potential effects of aquaculture activities include water and sediment quality, and negative impacts on natural populations, landscape, and other pre-existing economical activities. To a great extent, these effects depend upon factors such as type of facilities, geographical location, and produced species. The ultimate origin of this variety of effect consists of a small number of sources, including feeds offered, chemicals, animals excretions, dead animals, and the interactions between cultured and wild animals. Despite the availability of scientifically based monitoring techniques, there is a wide range of different methods presently used for sampling, analysing, and estimating these effects. In addition, there are different assessment approaches, including chemical, ecological, and nutritional. All of these aim to produce models in order to predict this interaction between aquaculture and the environment. Different models have been proposed, from the classic Vollenweider diagrams, to ecometric, and mass balance analyses. Keywords: aquaculture, environmental impact, assessment metodology, modelling.

Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) ? 2004 WIT Press, , ISBN 1-85312-738-8

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1 Introduction

World aquaculture production was 45'7 million tonnes in 2000 (FAO [1]), representing 57% of total fisheries landing for that year. After some years of significant development, the fisheries sector showed a dramatic decrease in its growth due mainly to overexploitation. World fisheries landings are now stabilised in around 80-90 million tonnes per year, and it is broadly accepted that an increased pressure over these fisheries would produce irreversible damages in these aquatic ecosystems.

Both FAO and World Health Organisation recommend a 30% increase of per capita aquatic products consumption, reaching 25 Kg per person and year (now it is around 19 kg). But even assuming the above could not be achieved, the increase of world population alone will generate a demand of some 168 million tonnes by year 2025 (Cardenete [2]). It seems evident that this growing demand for aquatic products could not be satisfied by a corresponding increase in fisheries landings, resulting in a foreseeable expansion of aquaculture. Aquaculture growth in the last decade was 253 % (Ackefors [3]). However, a sustainable growth of this sector needs to overcome some basic problems (Read et al. [4]).), among which are a significant research effort on the biology of cultured and potential species, the development of appropriate culture technologies, and last but not least the improvement of interactions between aquaculture and the environment. This last aspect, in contrast with other similar activities such as agriculture and stock land farming, far more ancient and as a minimum as contaminating as aquaculture, deserves a considerable attention as the sector develops. A good quality of the surrounding environment is a basic premise for aquaculture production, as the negative impacts will firstly affect to the cultured organisms (Ackefors and Enell [5]). However, very frequently, environmental issues are used as arguments to hold up the progress of aquaculture as a new activity when exists competition for the use of sites with other traditional activities (Vergara et al. [6]).

2 Aquaculture effects

Up to the present, most aquaculture practices have produced little negative effects on the ecosystems due to deficient management or accidents (Barg [7]), even resulting beneficial in some cases (Pullin [8]). Potential effects of aquaculture activities can be included within a range of different aspects (Garret et al. [9]); Midlen and Redding [10]), among which can be emphasize:

2.1 Landscape

Similarly to other human activities, the presence of aquaculture facilities can modify the landscape. It has a greater impact in tourist areas (Iwama [11]).

2.2 Water quality

Parameters which can be altered include: turbidity, pH (particularly in fresh water), hypernutrification and eutrofication (increase of nutrients concentration

Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) ? 2004 WIT Press, , ISBN 1-85312-738-8

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and primary production) (Gowen et al. [12]), decrease of dissolved oxygen (DO) concentration, alteration in bacterial growth (particularly in closed systems) (Moriarty [13]; Sich [14]), and toxicity (Bergheim et al. [15]; Rosenthal et al. [16]; Alderman and Michel [17]); Alderman et al. [18]).

2.3 Sediments

Physical, chemical, and biological changes can be produced in the sediments, including: variation in particle size (Guiral [19]; Carroll et al. [20]), increase in organic matter and nutrients (Hall and Holby [21]; Kupka- Hansen et al. [22]), increase in biological oxygen demand (BOD, between 3 and 15 fold) (Enell and L?f [23]; Holby and Hall [24]), decrease in REDOX potentials (Gowen et al. [25]; Earll et al. [26], Mazzola et al. [27]), release of gas bubbles (Samuelsen et al. [28]), alteration in bacterial growth (Enger [29]; Vezzulli, et al. [30]), presence of chemicals (Rosenthal et al. [16], Alderman and Michel [17])

2.4 Wild populations

Algal growth, particularly in fresh water, could be affected when certain conditions are given (Gowen and Bradbury [31]; Persson [32]). Modification of nutrients equilibrium can alter species composition and the structure of animal communities (Takanashi and Furazawa [33]). In general terms, aquaculture can modify natural biodiversity (Beveridge et al. [34]), decreasing macro fauna diversity (Brown et al. [35]; Weston [36]) and increasing opportunistic species such as the polychaete Capitella capitata. The decrease or even disappearance of echinoderms (Gowen et al. [37]) and molluscs (Tsutsumi [38]), have been also reported. Published data on total biomass are controversial, having been reported both an increase (Gowen et al. [39]; Carss [40]) and a decrease (Tenore et al. [41]), and even little effects (Kaspar et al. [42]). In all cases, however, this effect on benthic communities tends to be very localised, at distances not longer than 15 to 50 m from small and medium size farms (Aure et al. [43]; Weston and Gowen [44]). The escape of cultured organisms (or their gametes) can influence wild populations by cross or hybridisation (Youngson et al. [45]), depredation, competition, habitat destruction, or disease spread. Consequences are difficult to assess, but their importance will be higher when foreign species are cultured.

2.5 Site competition

Aquaculture can compete for the use of site or resources with other human activities, such as agriculture, tourism, navigation or fisheries. In all cases, it is broadly accepted that these negative effects can be avoided or minimised (Read and Fernandes [46]).

3 Sources of impact

To a great extent, the effects of aquaculture activities on the environment depend upon factors such as type of facilities, geographical location, produced species,

Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) ? 2004 WIT Press, , ISBN 1-85312-738-8

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and surrounding waters characteristics. As an example, fresh waters and seawater, respectively, are particularly sensitive to changes in phosphorus or nitrogen concentration levels as main limiting factors for algal growth (Schindler [47], Gowen et al. [48]).

Different cultured species have different biological characteristics and feeding habits, and will then produce different effects. Thus, bivalve molluscs culture rely on natural phytoplankton can decrease primary production in coastal areas (Hickmann [49]). Prawn culture is mainly carried out in coastal ponds (Tookwinas [50]), and related with mangrove destruction, and water and sediments quality alterations. The latest effects can also be produced by intensive fish farming through organic matter and nutrients enrichment.

Site and species selection is usually related to culture system to be employed, (Barg [7]). Extensive systems are considered as producing the less impact on the environment (Papoutsoglou [51]) than, intensive systems In addition, and for either intensive and extensive systems, land based or water based aquaculture facilities will also determine different effects with the environment.

In all cases, the variety of effects of aquaculture have their ultimate origin in a small number of sources, including feeds offered, chemicals, animals excretions, dead animals, and the interactions between cultured and wild animals. Intensive systems, particularly those where carnivorous or omnivorous aquatic animals are cultured, are highly dependant on dry, formula feeds (Beveridge et al. [52]). A variable proportion of this feed offered is not consumed, either due to overfeeding, or to different inappropriate feeding management practices. In addition, ingested food will condition soluble and particulate excretions of cultured animals (Munday et al. [53]; Persson [54]).

The use of chemicals (mainly drugs and antifouling products) in aquaculture varies significantly with system and cultured species, and despite they are commonly used in a much diluted form, they can accumulate in sediments, affecting their quality and nature.

4 Environmental impact assessment methodology

Because the wide range of possible environmental effects of aquaculture, there are also a wide range of different scientifically based methods presently used for sampling, analysing, and estimating these impacts. In addition, there are different assessment approaches, including chemical, ecological, and nutritional.

4.1 Chemical approach

Based in the assessment of different physical-chemical parameters of both the water column and sediments, it requires a proper design of a sampling programme (points and frequency), according to specific objectives, culture system, and species produced. Most used parameters include (ICES [55]):

- Water quality: Temperature, salinity, turbidity, chlorophyll-a content ([Chla]), DO concentration, BOD, organic and inorganic nutrients content, presence of

Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) ? 2004 WIT Press, , ISBN 1-85312-738-8

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sulphide (dissolved and in gas form), presence of faecal bacteria, and water renewal rate. - Sediments: Organic sediments extension, settling rate, water and organic/inorganic nutrients content, presence of sulphide, REDOX potential, and particle size.

In order to provide useful information, the sampling programme must include data before the aquaculture operation starts. However, very frequently it is difficult to compare data from different studies, and it is broadly recognised the need for the use of standard sampling and analyses techniques (ICES [55]). Despite the enormous amount of environmental regulations that are applied in different countries (Ari?o [56]), most protocols are based on outlets and effluents sampling (Cho et al. [57]), as well as with most reported research works carried out in commercial farms (Bergheim et al. [58]; Krom and Neori [59]). However, these estimations based on the concentration of certain elements per water volume unit can very frequently lead to wrong conclusions, when different water volumes were used. In addition, these concentrations may vary depending on sampling time, which can only be overcome with an expensive increased sampling frequency (Vergara and Molina [60]).

The effects of solid organic wastes on the sediments depend both on bottom morphology and on water renewal. Hakanson et al. ([61]) classify bottom types in: zones of erosion, transport and settling, which show different effects. In the other hand, estimations of settling rates assess solids flow, not the total amount of solid wastes produced by the aquaculture facility (Gowen [37]).

4.2 Ecological approach

It concentrates on alterations in composition and structure of populations. The accumulation of aquaculture wastes of different nature significantly influences the species of an unaltered ecosystem, producing next changes (Weston [36]):

- diminution of species diversity - increase in the total number of individuals, reflected in a high density of opportunistic species - general biomass decrease, although sometimes the opposite can be also appreciated, due to the circumstance above described - diminution in average body size of present organisms - trend of infauna to concentrate in upper layer of sediment

The above studies require a detailed knowledge of ecosystems structure previous to the operation of the farms, as well as enough duration as to show possible changes. Several authors (Weston and Gowen [44]; Gowen [37]) suggest that these studies provide a better information on aquaculture environmental effects, as in some cases the chemical approach alone does not show significant alterations in cases where the fauna presents important changes.

Benthic species are good indicators of aquaculture effects on sediments, particularly those who show specific reactions to organic pollution, which are

Waste Management and the Environment II, V. Popov, H. Itoh, C.A. Brebbia & S. Kungolos (Editors) ? 2004 WIT Press, , ISBN 1-85312-738-8

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