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Case Study

Matching your Farm Site to your Crop’s Ecological and Environmental Needs

The last thing you want to discover, after investing your time and money, is that you chose a site that doesn’t suit your species so here are some key factors to consider.

Author(s)

Chris Davis, Ph.D., Executive Director

Source

Maine Aquaculture Innovation Center & partner in Pemaquid Oyster Company

Date
2020
casestudy_ChrisDavis.jpg

Deciding on a location of your farm site is probably the most important decision you will make in starting up your farm. Why you ask? Well given the one to three years you’ll spend navigating the permitting process followed by another one to three years rearing your first crop, the last thing you want to discover after investing that much time and money that you chose a site that doesn’t suit the species you are growing. Unfortunately, having to move your farm to a better site is not as simple as filing a “change of farm address” form with the Maine DMR. It requires a completely new permitting application, so you want to get it right the first time.

Factors to Consider

There is a long list of factors you ought to consider in choosing your site (accessibility, exposure, navigation, competing stakeholder issues, etc.) but linking the site’s environmental conditions to the ecological requirements of the species you plan to grow is essential.

Let’s say you are interested in growing Belon oysters (Ostrea edulis) to supply product to the emerging European market for these tasty bivalves. The optimal water temperature range for rearing this species falls in the mid to high 60’s F and water temperatures below 35 °F can be lethal. Furthermore, this species is intolerant of very low salinities. Thus, selecting a farm site in one of Maine’s upper estuaries where water temperatures and salinities may exceed the ecological tolerance limits may well be unsuitable for producing Belon oysters. You don’t want to find this out after your crop has perished. Therefore, gather some environmental data for the site you’re interested in. Gathering water temperatures a few times during the summer certainly won’t give you the whole picture. You need to understand the environmental conditions through out the year. Fortunately, miniaturized environmental data loggers are inexpensive and you can let them gather the data for you (while you are at home writing that business plan).

Biology of your Species

Understanding the biology of the species you’re growing can greatly help you establish husbandry practices on the farm. For example, Maine’s native Eastern oyster (Crassostrea virginica) is cold-blooded and thus its metabolism is largely dependent on the temperature of the water it inhabits. In Maine, as water temperatures cool in the fall, growth of oysters slows down and the animals gradually reduce their feeding and respiration rate until, at around 45 °F, they essentially enter a state of hibernation. It is at this point in the late fall that farmers can condense their crop of juvenile oysters and store them at very high densities to reduce the amount of space they need to “over-winter” the crop. This is often done using cages suspended off the bottom or perhaps in rafts located in ice-free areas. More often than not, first time farmers fail to monitor the water temperatures the following spring and, come April when water temperatures return to 45 °F and above the oysters “wake up”. Without the required attention of cleaning and thinning the oysters, the growing densities will be too high and massive mortalities can occur.

Determine your Culture System

Matching your farm site to the culture system you plan to use is also important. For example, if you choose to grow your oysters unprotected on bottom to reduce capital and operating expenses, you’ll want to know what predators are commonly found in the area and decide if you can tolerate the expected mortalities that will occur. Oyster survival from predators will largely depend on the size of the oyster you plant on bottom (termed the “refuge size”) since the larger the oyster (greater than 1.5 - 2” in shell height) the lower the expected mortality. In addition, the sediment type will greatly impact oyster growth. High energy bottom environments tend to have courser sediments, whereas low current environments (e.g. the head of a cove) will generally have very soft sediments. Oysters planted on very soft sediments tend to settle into the bottom at a rate exceeding the oyster’s growth rate and they can often be smothered in silt or grow into an elongated “banana” shape which is less marketable. Alternatively, oysters reared on a higher energy hard bottom may grow more rapidly but may also be covered by barnacles that then need to be removed when harvested. Thus, determining the “sweet spot” in terms of bottom conditions (a sandy/silty bottom) can make a big difference in the quality of your product and economic sustainability of your farm.


Case studies are authored by industry members at the request of The Maine Aquaculturist. Authors are selected based on experience and expertise in a key business aspect of aquaculture. See our About page for more information.

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