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Monitoring Filters Around Aquaculture Cages

Monitoring Excess Nutrients in Fjords

The installation of monitoring filters around sea cage aquaculture pens, owned by Arctic Fish, is now complete and monitoring has begun. The collaboration between Arctic Fish and Eldey Aqua was spurred by an interest in where the excess nutrients from aquaculture operations end up in Dýrafjörður and how these excess nutrients can be minimized to reduce the impact on wildlife in the area. 

Impacts on Wildlife and Habitats

Sea cages are an enclosure built with nets, buoys, and weights and designed to keep farmed fish separate from wild fish while allowing water to freely flow through the cage. As the water flows through the cage excess feed and nutrients are carried by the current away from the cages. The shared water is a vector for pathogens and parasites to be transferred from wild fish to farmed fish or vice versa (Frazer, 2009). 

Escapees from sea cages are also a real concern when it comes to sea cage aquaculture. If the farmed fish is not native to the area in which it is being raised, it can, upon escape, alter the local ecology. This is done by increasing competition with similar species in the ecosystem, for example, and if the farmed fished are not selected for single-sex then a new population of fish could establish itself in the ecosystem if the environmental conditions are satisfactory (Jensen et al., 2010).  

Sea cage aquaculture is also known to increase sedimentation underneath the cages with volatile solids increasing up to seven-fold natural rates in some cases. These studies have also shown that there is an increase in ammonium, organic nitrogen, and total phosphorus underneath the cages. The excess nutrients can lead to eutrophic zones or dead zones on the sea floor (Kaspar et al., 1988). The majority of this damage is seen within 20-50 meters from the cage. However, at times damage to the seafloor can be seen up to 100 meters from the cage (Mente et al., 2006). 

Our Filters

On May 08, 2019, Eldey Aqua installed three monitoring filters after the aquaculture pens were cleaned. The filters are made up of different wire mesh size that was organized from largest to smallest starting from the ends of the filters to the middle. This layout was used to catch the smallest particles possible while not limiting the collection of larger ones. These filters are suspended four meters below the surface of the water, and they are held in place with an anchor and labeled buoys. The filters were placed in on opposite sides of each other along the sides of the pens in order to better understand the flow of nutrients. The filters were placed at the following coordinates in the sea farming zoned area:

  • Filter 1:     65⁰53.489’/ 23⁰29.440’
  • Filter 2:     65⁰53.523’/ 23⁰29.289’
  • Filter 3:    65⁰53.228’/ 23⁰28.994’

On May 12, 2019, the final filter was put in the water. However, this installation was not as easy as before. A dingy was launched from shore and even though the seas were relatively calm waves crashed over the sides till we passed the break. This filter has been deemed the control filter. Due to scheduling conflicts and inclement weather the deployment of the filter had to be postponed slightly. The purpose of the filter is to collect naturally occurring sediment, nutrients, flora, and fauna in Dýrafjörður so the team, Eldey Aqua, can compare the results of the control to the results from the filters around the aquaculture pens. The coordinates of the control filter were not recorded.

As this is just our first attempt a few things are already plainly clear. First, we need to install more filters and at different depths. This would help fill in the gaps between filters and enlarge the area monitored as a means of increasing our precision in locating hotspots of nutrient overload spatially and at various depths. All filters should be installed on the same day and weigh the same.

Future Analysis

To analyze the nutrient content, flora and fauna captured in the filters they will be retrieved after one month after their installation. The identification of species present and the dry weight of all organic material will be recorded by filter number and mesh size. The material used for identification of species will be set aside and frozen for later analysis and will be done visually with the aid of a microscope.  Afterward, the remaining organic material will be dried and weighed. Since a variety of mesh sizes were used this analysis will provide useful data for determining the appropriate mesh sizes required for future standardization of the mesh sizes in the filters. 

The data received from the analysis of filters will then be added into a georeferencing software for spatial analysis. This method is intended to reveal areas in which excess nutrients are located, known as hotspots. These hotspots will be potential sites for multi-trophic aquaculture farms, as a means of reducing nutrient loading on the seafloor and increasing water quality, in the future. 

Once these hotspots are identified, it will be necessary to ensure that access to these sites is secured while not restricting access to the sea cages. This is a collaborative effort in protecting our shared resources after all and it is of utmost concern that access is unencumbered to all parties involved. In order to identify proper accessibility and that the multitrophic farms are placed accordingly, the participatory mapping tool, SeaSketch, will be used. This program allows all users to manipulate potential routes or access point, sea cages, and multi-trophic farms to best suit their needs. As a result commonalities and disagreements can be brought up for discussion to find the best use of space.

References

Frazer, L. N. (2009). Sea-Cage Aquaculture, Sea Lice, and Declines of Wild Fish. Conservation Biology,23(3), 599-607. doi:10.1111/j.1523-1739.2008.01128.x

Jensen, Ø, Dempster, T., Thorstad, E., Uglem, I., & Fredheim, A. (2010). Escapes of fishes from Norwegian sea-cage aquaculture: Causes, consequences and prevention. Aquaculture Environment Interactions,1(1), 71-83. doi:10.3354/aei00008

Kaspar, H. F., Hall, G. H., & Holland, A. (1988). Effects of sea cage salmon farming on sediment nitrification and dissimilatory nitrate reductions. Aquaculture,70(4), 333-344. doi:10.1016/0044-8486(88)90117-2

Mente, E., Pierce, G. J., Santos, M. B., & Neofitou, C. (2006). Effect of feed and feeding in the culture of salmonids on the marine aquatic environment: A synthesis for European aquaculture. Aquaculture International,14(5), 499-522. doi:10.1007/s10499-006-9051-4