Measurement of organic loading under an open-ocean aquaculture cage, using sediment traps on the bottom

Abstract

SummaryOrganic loading under a submerged fish cage in commercial operation has been quantified for the first time in the open ocean. Sediment traps out to 100 m sampled the loading continuously over the 15 months of a complete grow-out cycle for cobia (Rachycentron canadum). Typically 4% or 5% of the feed arrived directly to the sediment, although this benthic percentage became much higher in the last two months of this study. Almost all the loading (90%) lands within 30 m of the cage mooring block. The loading consists of fragments of feed pellets that wash out from the mouths and gills of the fish. The fragments sink rapidly and almost vertically; they are not carried horizontally into large dilution volumes. Dispersal on the sediment surface is much more extensive than dispersal in the water. This study developed expeditious and cost-effective techniques for sampling and analyzing organic loading, using a minimum of technological resources.

Advances in hatchery and grow-out technology of cobia Rachycentron canadum (Linnaeus)

“…Environmental monitoring has not shown any cumulative impacts in the water column and at the sea floor bottom around the sites of the cobia offshore aquaculture operations in either Puerto Rico or the Bahamas (Alston, Cabarcas‐Nuñez, Helsley, Bridger & Benetti 2006; Benetti et al 2006, 2007; Rapp, Ramirez, Rivera, Carlo & Luciano 2007). This was qexpected as the submerged cages are deployed in exposed areas, where currents ranging from 0.5 to 1.5 knots, dissipate nutrients and other waste products and these farms are still operating at the demonstration stage with permits not allowing to exceed production of 50 tonnes year −1 .…”

Controlling feed losses by chewing in gilthead sea bream (Sparus aurata) ongrowing may improve the fish farming environmental sustainability

“…Usually, the feed supplied (but not necessarily ingested) is estimated intuitively by farmers since it largely depends on the care taken in handling (e.g. 5-15%: Beveridge et al (1997), Cho and Bureau (1997), Findlay and Watling (1994)), and only in a few cases has it been experimentally measured in the field (Rapp et al, 2007), and never for GHSB. Most environmental impact assessments for GHSB projects include both gross waste production and estimated uneaten feed (Mateus and Neves, 2013), but the LbC has never been included.…”

Nutrient load estimation in the waste of Nile tilapiaOreochromis niloticus(L.) reared in cages in tropical climate conditions

“…That is, in locations with lower current speeds, there tends to be an organic enrichment of the sediments in areas immediately below the aquaculture structures or in an area of up to 10 m surrounding the structure. In this case, the greatest impact of fish farming occurs in the centre of the exploration area (Findlay & Watling ; Rapp, Ramirez, Rivera, Carlo & Luciano ).…”