Gear Description

The CalCOFI Vertical Egg Tow net was developed to collect samples of clupeoid eggs for estimates of spawning biomass. The 20-cm diameter net is attached to a hydrographic cable by both the mouth and codend. With the ship at rest, it is lowered vertically to 70 m, and then raised to collect the sample. This procedure routinely takes only about 5 minutes, and allows a large area to be sampled quickly, thus increasing the synopticity of the sampling and decreasing the variance by increasing the number of samples collected. This procedure relies on the fact that the eggs of interest reside in the upper 70 m of the water column, and that they cannot escape the small-mouthed net as it is slowly raised through the water column. Since the net is towed vertically, calculation of volume of water sampled is simplified, and does not require use of a flowmeter.