Use of hydrodynamic and benthic models for managing environmental impacts of marine aquaculture

Abstract

Regulation to minimize impacts from aquaculture is of key concern in coastal zone management for the sustainability of the industry and the receiving environment. Market and consumer forces are presently driving much of this regulation and its implementation. Mathematical modelling can provide the tools for planning and monitoring as well as regulation, and a number of countries have well‐developed policies and procedures in place which utilize modelling tools. The main impacts currently modelled are nutrient enhancement, organic waste deposition and the dispersion and deposition of medicines and chemicals. The release of these wastes is influenced by species‐ and site‐specific characteristics, as well as culture and husbandry techniques. The modelling process requires consideration of definitions and limitations; standards for model development including clear objectives and justification; good technical description; use of good and appropriate data; calibration; validation; sensitivity analysis; quality assurance; auditability and consideration of the operational needs of the user, the grower and/or the regulator. Models should have simplicity and clarity; be fit for purpose; be open to scrutiny; be accessible, user‐friendly and be used with caution. Current models are considered to be limited in scope but do cover the main hydrodynamic and particulate processes. The regulation and monitoring of finfish aquaculture involving the direct use of models is apparently restricted to relatively few countries where they are involved in setting holding capacity, the licensing of medicines and for assessing site applications. Different approaches have been developed in different countries as required. In contrast, many countries do make considerable indirect use of modelling techniques within the regulation process. With respect to shellfish, models are in current use to predict and optimize exploitation capacity but there is scope for studying nutrient flux, habitat degradation and deposition below suspended systems. Future developments for finfish need to better address the main question of holding capacity or exploitation capacity in relation to nutrients and medicines release, including whole water body/regional impacts. The relationship and predictability of toxic algal blooms remains some way off. Modelling the complexities of degradation, resuspension and the effect of the scavenging process on the transport of in‐feed medicines is required. Keys to future developments across Europe include accessibility, setting of Environmental Quality Standards or targets, training and support for users, resources and structured research.

Temporal changes in the polychaete infaunal community surrounding a Hawaiian mariculture operation

“…Tsutsumi 1987, Pohle et al 2001, Yokoyama 2002, which usually contain low energy environments with reduced dilution effects from currents. Open-ocean mariculture operations are relatively new and provide a location in which enrichment effects can be buffered by increased current activity and dilution as well as a deeper operation site (Fernandes et al 2001, Henderson et al 2001.…”

A fully integrated GIS-based model of particulate waste distribution from marine fish-cage sites

“…Across Europe the extent to which such models are used for this purpose 64 varies widely (Henderson et al, 2001). In Scotland, DEPOMOD (Cromey et al, 2002) is 65 now widely used for Environmental Impact Assessments and to estimate the likely 66 seabed deposition of in-feed sea-lice treatments (SEPA, 2001).…”

“…Such influences may particularly affect the 493 dispersion directly under cages, the area where the GIS dispersion model predictions 494 are least accurate. Henderson et al, (2001) noted that all of these processes would 495 need to be investigated to provide a comprehensive model, with data tested for 496 sensitivity within the model. Importantly, increasing the validation accuracy under 497 certain conditions and at certain sites may limit the general applicability of the model 498 18 to represent species specific cage culture as a whole, which must remain the ultimate 499 goal of such a model.…”

Review of recent carrying capacity models for bivalve culture and recommendations for research and management

“…The first of these uses the output from a spatially explicit hydrodynamic-dependent particle tracking models to predict (organic) flux from culture sites to the bottom. A quantitative relationship between flux and a benthic community descriptor is developed and then used to predict the influence different levels of bivalve culture on benthic community structure (Henderson et al, 2001). Although initially developed for finfish aquaculture, the DEPOMOD program (Cromey et al, 2002) has also been used to this end for mussel aquaculture in Ireland (Chamberlain, 2002), and is also being evaluated in Canada and the Mediterranean (Daniele Brigolin, pers comm.).…”