Use an alternative method to commercially harvest plankton
Overall effectiveness category Awaiting assessment
Number of studies: 1
Background information and definitions
Zooplankton (tiny drifting organisms) is a valuable source of protein and is harvested in the wild for use as aquaculture feed and pet fish food (Wiborg 1976). Fishing for zooplankton is done using fine-meshed trawls that results in lots of unwanted organisms being caught, including fish eggs and larvae. To help reduce mortality of unwanted fish eggs and larvae, an alternative method of plankton harvesting using air bubbles may enable selective transport in the water column of the targeted zooplankton such as copepods, up towards the surface (bubble flotation method). These can then be harvested by a plankton trawl leaving the fish eggs and larvae untouched at lower depths.
Wiborg K. F. (1976) Fishery and commercial exploitation of Calanus finmarchius in Norway. ICES Journal of Marine Science, 36, 251–258.
Supporting evidence from individual studies
A replicated, controlled study in 2008 of pelagic waters in the Norwegian Sea, Norway (Grimaldo et al. 2011) found that using a bubble-plume harvester in combination with fine-meshed trawls to harvest Calanus spp. zooplankton reduced the amount of unwanted fish larvae and eggs caught compared to using only fine-meshed trawls. Data were not tested for statistical significance. Fewer fish larvae and eggs were caught after the bubble raft was deployed compared to without deployment of the bubble raft, at all depths tested: 25 m (larvae: 70%, eggs: 98% reduction); 15 m (larvae: 96%, eggs: 94% reduction); and 10 m (larvae: 12%, eggs: 92% reduction). Catches of target Calanus spp. were between 30–130% higher in nets after bubble harvesting. In June 2008, a bubble raft was towed at three depths (25, 15, 10 m) by a research vessel. Standard plankton nets (20 cm diameter, 0.5 mm mesh) were towed for 30 min before and after the bubble raft was deployed (number of hauls not reported) and target Calanus spp. and non-target catches compared. The bubble raft produced 0.5–1 mm bubbles from eight perforated hoses towed in parallel. Full details of the bubble raft design are provided in the original paper.Study and other actions tested