Raising Food in the Ocean

How do you farm in the ocean?  It turns out there are lots of ways. That stands to reason; you’d imagine an oyster and a salmon are going to be raised differently. Culture techniques aren’t innumerable but of the many there are, I cherry-picked these that I find particularly interesting.

Let’s start with that oyster. Whether in open water or in a hatchery, oysters release sperm and eggs into their surroundings.  After fertilization occurs the larval oysters are initially free swimming.  Then, when they are about a quarter of a millimeter long and two weeks old, they stop their meandering ways, settle down and build a permanent home.  Often the best place to settle down and attach is on another oyster shell but a variety of hard surfaces will work.

The most creative substrate I’ve heard of is a bamboo stick.  Lady’s Island Oysters in South Carolina puts bamboo into water just as barnacles are in the attachment phase of their own life cycle.  Fish and crabs then eat the bamboo-bound barnacle leaving behind the shell we are familiar with seeing.  If you swish those barnacle-encrusted bamboo poles around an area when young oysters are attaching, you have an oyster stick you can move to another area to raise dozens of oysters to harvest size from each stick.

A more common practice is that once attached to a substrate farmers put the oysters into mesh bags and suspend them in the water column. Oysters are filter feeders so the object is to place them where they have good access to the phytoplankton and zooplankton that make up their diet. As they grow, the oysters are moved to bags with successively larger mesh size until they reach harvest size 15-30 months later. 

Salmon are also animals with two very distinct phases to their life cycle.  Farm-raised salmon start life in fresh water just as wild salmon do.  Eggs are collected and fertilized in an indoor facility.  Incubating eggs are moved through successively larger tanks as they grow until they hatch about 60 days later. After hatching they live off their yolk sac for a few weeks when they begin eating pelleted food.

The hatchery is usually one of two sorts.  Flow through systems are located near a fresh water supply.  Water is diverted to flow from the source, through the hatchery, and then back to the original stream. 

Modern commercial hatcheries often use recirculating water systems where water moves from fish tanks, through filtration systems, and back into the tanks.  Recirculating systems have a few advantages.  By virtue of recirculating/reusing it they use far less water. Furthermore the regular filtration of the water reduces the possibility of introducing diseases from an outside water source.

In the hatchery salmon grow to between 100 and 500 grams when they start to become smolts ready to transition to ocean life.  This is the stage they begin a series of enormous changes that prepare them to live in salt water. The adaptation to life in sea water requires a significant overhaul of a salmon’s fundamental metabolism.  The largest of these are the changes required to accommodate ocean salinity.  Beyond that, they gain new eye pigments better adapted to sight in the ocean, nucleic acids in their scales to make them silver and they even make new forms of hemoglobin in their blood.  In the wild this occurs largely in response to a combination of day length and temperature.  In hatcheries, temperature and daylight are also varied to initiate smolting.   

Smolts are moved into the ocean where they reside for 16-22 months and grow up to the harvest size of about 4.5 kg (10 pounds). 

Quite unlike oysters, salmon are carnivores.  They are fed a diet high in protein and oil an very low in carbohydrates.  Historically these were supplied with, respectively, fish meal and fish oil.  However, pressures on the fish caught to make salmon feed argue for diminishing the use of marine ingredients in salmon diets.  This is one of the central issues in the sustainability of salmon aquaculture and I will discuss it again in a later post on aquaculture sustainability. 

Along with oysters on the shore and salmon somewhat offshore a new and potentially exciting third type of aquaculture done far offshore in very deep water is being developed.  Kampachi Farms  raises a fish known both as Alamo Jack and Kampachi.  Founded by Neil Sims, Kampachi Farms is a pioneer in far-offshore farming.  In their first test a spherical enclosed pod was seeded with 2000 Kampachi fingerlings.  The pod, built by Lockheed Martin, was allowed to drift (tethered to a boat)  for four months when the Kampachi reached as size of four pounds. The results of their test were encouraging.  Fish grew faster and had extremely low mortality compared to Kampachi grown near shore.  Open water farming is still years off but it offers great promise for both productivity and sustainability.

In a later post I will address the challenges aquaculture must address to grow and simultaneously improve its sustainability.  But first, in my next article, I will discuss the importance of aquaculture in our food system-both now and in the future.

Copyright ©Scott Nichols 2016