STANDARDIZED ENVIRONMENTAL MONITORING OF OPEN-OCEAN CAGE SITES:  BASIC CONSIDERATIONS

January 2004

Dallas E. Alston *, Alexis Cabarcas, Christopher Bridger, Charles E. Helsley, Daniel Benetti, Paul Zajicek

Puerto Rican Commercial Aquaculture Research and Development Center
Department of Marine Sciences, PO Box 9013
University of Puerto Rico, Mayagüez Campus
Mayagüez, PR 00681-9013 USA

Email: aacabarcasn@hotmail.com

Interest is increasing in marine fish culture in open-ocean environments. As governments receive petitions for these operations, agencies granting permits will need information concerning potential environmental impacts. Because every site is different, standardization of the sampling methodology will be difficult, but some common and basic measurements must be considered. The purpose of this paper is to initiate discussions leading to effective monitoring plans to provide information for agencies to make informative decisions. Further, standardized methodology must be identified that is the most cost-effective and practical methods to collect pertinent data and will be appropriate for a future open-ocean aquaculture industry to continue beyond the research and development phase.

Currents vary by location and time of day. For safety, sampling methodologies need to minimize risks to divers, e.g. sampling at slack tide, or adaptation for boat-side sampling. From a practical aquaculture perspective, however, nutrient discharge would likely be more concentrated a few hours following a feeding period and therefore some environmental sampling procedures need to be coordinated with farm operations.

Accumulation of organic matter in the sediment is usually not widespread and at several hundred meters distance from the cages the impact will probably be minimal. However, accumulation of organic matter and changes in the flora and fauna are important indicators of environmental status. Dredge samples may be suitable in soft sediment, but may be problematic in areas with sand and/or rubble. We suggest that benthic samples be monitored under and around the farm site and at a “control” station some distance from the site but not immediately up or down current.

Because of high dilution rates, information gathered concerning the impact on water quality may be difficult to interpret while operating at experimental scales. In the case of multiple nearby farms, care must be taken to compare to pre-farm ambient levels, for water quality can be progressively changed by small increases in nutrients such as phosphorus and nitrogen. Many of the water quality variables of interest may be monitored automatically using devices taking continuous information for 1 to 3 months duration. Unfortunately, some in situ measurements are neither reliable nor sensitive to minute changes in variables. Thus, laboratory analyses will continue to be important. The significance of the monitoring results will be enhanced if basic oceanographic information, e.g. currents, tide-phase, wind, sea state, and time and rate of feeding are measured concurrently with water quality parameters.


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