With catches being compressed into shorter fishing periods and many fishermen increasing the number of baskets they can hold onboard to take advantage of windows of high beach price, onboard live holding tanks are being subjected to peak loads more often. Given these changes, it is important to make sure your holding tanks and pumps are keeping up. Most importantly, is the dissolved oxygen in your tanks sufficient?
Lobsters must have high levels of oxygen at all times. Without adequate oxygen, your lobsters may appear healthy, but they will experience problems down the track, perhaps dying in GFC’s tanks or during export. Any such losses come out of your pocket, so it is in your interests to invest in better lobster storage tanks.
The next few months are the ideal time to ensure your onboard holding tanks are running properly for the coming whites.
There are two main ways to ensure holding tank oxygen levels are high enough: 1) supply adequate volumes of well oxygenated seawater water and 2) aeration of water in the tanks.
Water supply: Water pumps that deliver a constant flow of water are best. Pumps that have variable output that depends on engine revs (e.g. Jabscos, etc. that supply your deck hose) are not ideal.
Aeration: Using an air pump to deliver a constant stream of fine bubbles to your holding tanks is the best step you can take to ensure lobster quality. Many types of air pumps are available, but the GFC Marine Store stocks a solid proven model called a Hiblow HP200. These pumps are high output, very low maintenance and draw little power.
Setting up aeration is best done by a professional marine outfitter or shipwright, but you can install a simple set up yourself. There are some important things to remember when designing your system:
- Air distribution – this is best achieved with a balanced layout of air diffuser hose (see diagram below). The type of diffuser hose used is critical to maintaining the health of your lobsters. The GFC Marine Store stocks a brand of hose that we recommend as proven and reliable – ask for ‘Brolos Blue Stripe’ air diffuser hose. This hose has low resistance and produces lots of fine bubbles (the smaller the bubble the better the oxygenation). It is cheap to buy and if maintained properly, can last several seasons.
Example of a well-designed, balanced pump and hose layout (bottom)
- For DIY set ups, always ensure that the pump is installed at least 50 cm higher than the water level of the holding tanks. It also a good idea to install a gooseneck between the pump and the holding tank to prevent siphoning of water from the tank and back through the pump (see diagram below). The delivery line from the pump to the holding tank can be as simple as black poly pipe or braided garden hose.
Once you have your aeration system installed, keep air flow high by occasionally emptying your holding tanks, covering the air diffuser hose with freshwater and allowing aeration to flow for a couple of hours. This will dissolve any salt crystals that may have started to clog the air diffuser hose pores.
When landing your catches, remember to always keep aeration running until the tanks have drained completely. This will prevent the lobsters in lower baskets from being in stagnant, deoxygenated water during draining.
Lastly, don’t let your baskets crush the aeration hose as this will cut off the air supply. One easy way to overcome this is to use short lengths aluminium right angle to ‘house’ the aeration tube. This keeps the aeration tube on the bottom of your holding tank (in the pattern you originally designed) and protects your hose by providing a support for the baskets.
Cross section of aluminium right angle housing to support baskets and protect air diffuser hose
Every lobster boat in GFC’s fleet should have tank aeration as a minimum, and we are keen to support fishermen to achieve this. Every home aquarium has a bubbler for a few ten dollar fish: shouldn’t you look after your valuable catch in the same way?
If you would like any assistance with a new system design, or even tips for your existing setup, contact GFC Continuous Improvement Manager, Brad Armstrong (0437 513 837) or GFC Research and Development Officer, Joel Durell (0407 135 712).