There have been several news stories recently about challenges with Lithium Ion batteries. Most notable is the situation with the Samsung Galaxy 7 but issues with airplanes, hover boards and other personal electronics have been in the headlines.
Since their introduction in the early 1990s, Lithium Ion batteries have become the standard for consumer electronics devices, including smartphones, smartwatches, laptops and cameras. Aquabotix utilizes Lithium Ion batteries to power our ROVs because of their performance and has found them to be very reliable, stable and safe. We have experienced no reports of any problems with these batteries from our customers.
Most Aquabotix ROVs have only internal batteries. That is, the only way to charge the batteries is while they are inside the vehicle and charged through the topside box or vehicle charging port. When charging the batteries inside your vehicle, the danger of fire caused by the overhearing or other failure is minimal. Still it is prudent to charge the batteries only until they are fully charged (charger LED light changes from red to green) and then to unplug the charger from the electric power source.
Some commercial ROV users have purchased additional batteries and external battery chargers from Aquabotix. If you have extra batteries and external chargers, please follow these precautionary steps.
- Always make certain that the batteries, connectors, charger and all other parts are clean and dry.
- Make certain that the batteries and charger are paired as they were supplied to you. Do not mix batteries from one vehicle with another. Do not use any charger other than the one supplied with your vehicle.
- When externally charging batteries, it is advised that the batteries be contained in a fire retardant or fireproof safety bag designed specifically for this purpose. These can be purchased inexpensively or, if you purchased extra batteries and an external charger from Aquabotix, we will be happy to send you a safety bag at no charge. Please contact Aquabotix Customer Service with your vehicle serial number.
If you will be traveling by air with your ROV batteries, please contact Aquabotix Customer Service for further instructions.
Aquabotix is committed to the satisfaction and safety of our customers and users. We appreciate your support and are happy to answer any questions you may have.
Phone: +1 508 676 1000
Many ROV applications require that the operator know the position of the ROV with varying degrees of precision. However, precise navigation for small ROVs is actually a very difficult task to achieve.
There are three basic positioning techniques that are practical for use on ROVs: dead reckoning, Global Positioning System (GPS), and Ultra-Short Baseline (USBL). We will look at each of them in turn.
Dead reckoning is the navigational method used by mariners all over the globe before the invention of compasses, chronometers and sextants. In dead reckoning, the navigator starts with a known (or estimated) position, and from there attempts to gauge the vehicle’s position by applying the vehicle’s heading and speed. Depending on the tools available, dead reckoning can be a surprisingly effective form of navigation. In the modern era, where the starting position of an ROV may be known with great precision and the heading and speed of the vehicle are also known quantities, dead reckoning can be sufficient for many applications. However, dead reckoning has one fatal defect: it cannot account for currents in the water. If the current is significant, the position of the ROV at the end of a run can be vastly different than the reckoned position.
The widespread availability and accuracy of global positioning systems (GPS) has made terrestrial navigation a breeze for motorists and surface vessels. Anyone with a line of sight to four or more GPS satellites – which effectively means anyone on the surface of the Earth – can use an inexpensive computerized navigation device to locate themselves, with an accuracy of as close as ten feet. GPS is cheap, effective, and nearly foolproof – so it’s the perfect solution for ROV navigation, right? Unfortunately, no – GPS is almost useless for most ROV applications. The problem is that the satellite communication signal is severely blocked by fresh water, and totally blocked by sea water. Underwater vehicles cannot use GPS without coming to the surface. There are some specialized use cases for GPS on an ROV, but they are few.
Ultra-Short Baseline (USBL) is a technique for determining a vehicle’s position underwater. It is a fairly complex system which involves a base station/transceiver, usually mounted on a ship, a transponder/transceiver mounted on the ROV, and a sophisticated computer system (usually located with the base station). The base station sends out a powerful acoustic pulse, similar to a sonar “ping”. This pulse is picked up by the transponder on the ROV, and a response pulse is sent from the ROV back to the base station. When the base station receives the response pulse, it calculates the duration between the initial signal and the response, and determines the range between the two transceivers based on that time. A set of transducers in the transceivers permits the calculation of a bearing between the two transceivers; the combination of the range and the bearing gives a precise position for the ROV relative to the base station.
USBL is extremely effective and accurate, but it is also expensive - a USBL installation for an ROV can cost upwards of $20,000. It also has a technical weakness in that under “busy” sonar conditions – a crowded harbor, for example – can cause problems for the system. However, for now, USBL represents the state of the art in ROV navigation systems.
Depending on which maritime body you ask, there are somewhere between 50,000 and 100,000 large ships sailing the world’s oceans, with cargo vessels, passenger ships, and warships making up the bulk of this number. Commercial vessels are required to have their hulls inspected on an annual basis, and military vessels generally follow a similar inspection regimen. There are various global and national bodies which provide certification standards, such as ABS (American Bureau of Shipping) and Lloyds of London. The goal of inspecting large vessels is to protect the owners of the ships, the crews, the passengers, the companies using the ships, and the insurance industry.
There are a variety of different certification standards, but the standard ABS inspection regimen is fairly typical for the industry. The ABS regimen is known as HIMP, which stands for Hull Inspection and Maintenance Program. HIMP has a three-tiered system of inspections, with annual inspections, three-year inspections, and five-year inspections. The three- and five-year inspection tiers encompass all the inspection areas of the lower tiers, while adding further areas of the ship to the inspection list. HIMP inspections cover the entire vessel, but the underwater portion of the survey is the trickiest for ship owners. Underwater surveys can be conducted by human divers, but increasingly this job is being handled by remote-operated vehicles (ROVs).
On a commercial vessel, the diver or ROV must provide visual data on the stern and rudder bearings, the sea suctions and sea valves, the propellers, and – most time-consuming - the hull plating. The inspection must look at any markings on the hull, all inlets and discharges, the rudder, the propeller, and all other objects that protrude from the hull. Corroded or damaged areas must be examined closely, and although thickness testing is not automatically part of the HIMP, any area found to be damaged or corroded is likely to be examined internally and have the thickness tested at the affected spot(s).
Military vessels follow a similar inspection regimen, and many military vessels will also have stencil-marked areas of the hull which need to be looked at. Inspections will check the hull and other secondary areas of the vessel for biofouling, to assess the need for having the ship’s bottom scraped. Inspections generally involve several waterline-to-waterline underwater traversals of the vessel, following the seams of welded sections. Propellers need to be inspected on both their front and rear facings.
In the early years of ROVs, their use in underwater hull inspections was relatively rare because the low video quality of early vehicles made their results of marginal utility to inspectors. Today however, with true HD displays and cameras on even consumer-level ROVs, these useful vehicles are an integral tool for large hull inspections. Since inspection divers need to be ABS-certified, many surveying companies are finding that it is highly useful to conduct a pre-inspection using an ROV only. This pre-inspection can find any problems that already exist so that they can be mitigated before the actual inspection, preventing a time-consuming, and expensive, temporary suspension of the vehicle’s certification when the inspector finds significant problems.
It’s Olympic season again and the 2016 Summer Games in Rio are in full swing. More than 11 thousand athletes from over 200 countries around the world are pouring into the Brazilian metropolis for the thirty-first modern Olympiad, which runs from August 5 through 21, 2016. The International Olympic Committee expects half a million foreign tourists to visit Rio during the Games, along with a huge number of local Brazilians. Unfortunately, the lead-up to the Rio Games has been marked by controversies surrounding Brazil’s ability to successfully host this major international event. One of the most pressing issues has been the issue of the water quality in and around Rio.
Rio de Janeiro is an enormous metropolis, with more than 12 million inhabitants, and Guanabara Bay has served as the city’s cesspool and sewage dump for many years. Before the games, a large majority of the sewage generated in Rio was delivered untreated into the bay, along with considerable quantities of ordinary junk and garbage, and the bacterial and viral contamination level in the water were astronomically high. Local officials promised that they would take steps to increase the level of treatment so that 80% of the sewage entering the bay would go through a treatment plant, but it is thought that, at best, only 65% of the sewage is treated at the current writing.
Brazil made a number of promises about cleaning up the city when it won its bid to host the Games, but numerous reports indicate that the cleanup efforts fell well short of promises. Although reports from Olympic athletes indicate that the amount of visible debris and waste have been significantly reduced, it is thought that these have been mainly cosmetic measures. Data from water quality assessments backs up this pessimistic account; an Associated Press investigation done before the Games began showed viral levels 1.7 million times higher than what would be considered problematic in the United States.
The water in Guanabara Bay is contaminated, but how about the water along Rio’s famous beaches, some of which front the Atlantic Ocean? Unfortunately, the beaches may be even worse off than the deep water of the Bay. The beaches of Rio de Janeiro are connected to a criss-cross maze of canals and stormwater drains, which are in turn deeply contaminated with human waste. Most of the residents of the city’s favelas (slums) have no indoor plumbing and the minor waterways of the city are essentially communal sewers. As a result, the beaches always have high levels of coliform bacteria, a problem which worsens exponentially whenever one of Brazil’s torrential rains floods the drains and canals.
Although the water in Rio is dirty, experts do caution against apocalyptic rhetoric concerning the actual level of danger. The World Health Organization notes that the most likely outcome from ingestion of contaminated water is short-term gastroenteritis; not something anyone wants, but not a major life-threatening condition for people in good health otherwise. Olympic athletes are taking precautionary measures for their time in Rio, stocking up on antibacterial wipes and keeping water bottles inside of plastic bags to avoid splash contamination, for example. Some athletes expecting to swim in the most contaminated areas have received Hepatitis A vaccines as a prophylactic step. The athletes and tourists, however, will be going home in a few weeks. Those at most risk from Rio’s dark waters are the people who have been there all along, and it is they who are most in need of a sustained and meaningful effort to address the water pollution in Rio de Janeiro.
Remote Operated Vehicles (ROVs) are of great utility in conducting underwater surveillance, data collection, sonar mapping, and searches for underwater objects. However, information gathering is only one of the things these versatile underwater craft can accomplish. With the addition of manipulator and grabber arms, ROVs can perform a wide array of useful tasks. ROVs have used manipulator arms since the first ROVs were deployed by the US Navy in the 1960s to recover objects on the sea bottom (including, famously, a hydrogen bomb that sank to the bottom of the western Mediterranean following a B-52 crash in 1966). Today’s manipulator arms are considerably more advanced than those early grippers.
Generally, modern ROVs use a master-slave manipulation model, where a human operator based on a surface vessel controls the ROV’s arm(s) either with a control panel or with an actual miniature manipulator matching the manipulator on the ROV. Remote control techniques originally developed in the space program allow any operator to work the arm easily, without the need for specialized ‘crane operator’-type skills. This allows the operator to be a mission specialist or a scientist skilled in what the manipulator needs to be doing, rather than a specialist who can control the arm well but needs to be told what to do with it.
Manipulator arms can be deployed to use a wide variety of tools. These tools are often simple or complex grippers, but can also be power tools like drills, saws, cutters, wrenches, or others. The earliest ROVs were limited to very simple grippers, and it was a major step forward when ROVs became capable of doing simple jobs like opening or closing a valve handle on an underwater platform.
There are three broad general categories of manipulator use for ROVs: industrial, military/law enforcement, and scientific. Industrial ROVs can use manipulators to cut and lay pipe, make and break hydraulic connections, lay and retrieving cable, lubricate underwater machinery, carry heavy tools for human divers, conduct trenching operations, and operate machinery like valves and levers. Military/law enforcement ROVs can use manipulator arms to retrieve or tag items, to place charges (for example, to neutralize underwater mines), and to cut cables. Scientific ROVs can use manipulator arms to select samples, to gather materials for analysis, to drill into the sea bottom, to sieve lighter materials, to take core samples, and to deploy and retrieve sensors.
ROVs equipped with manipulating arms have successfully assisted in exploring sunken vessels, raising ships and objects from the ocean floor, finding victims of crimes and criminal evidence, operating oil and gas platforms, and conducting pure scientific research. The use of manipulators makes these useful tools even more effective.
In a recent entry we talked about the importance of monitoring aquatic environments. Today we are going to talk about the various ways in which that monitoring can be performed. Each way has advantages and disadvantages.
Perhaps the simplest method of monitoring is manual observation, either with measuring instruments or with the naked eye. An example of this type of monitoring is a marine biologist who manually counts the number of whales surfacing off the coast in a particular spot in a particular time. The advantages of this type of monitoring are that it requires little investment in equipment, and has the highest degree of flexibility – if the biologist sees something else of interest at the survey site, he or she can make direct, first-hand observations without the need to redesign or redeploy instrumentation. Human observers may also be able to fix errors in the monitoring protocol “on the fly” in a way that a more instrument-focused approach cannot. For example, if a site survey has a particular set of GPS coordinates and the human observer arrives at those coordinates and realizes that the site location is off, the observer can fix the mistake and carry out the survey. The primary disadvantages of manual observation are that recurring observations quickly become very expensive, and there may also be reliability issues. For example, a graduate student can forget to come in to conduct a set of observations. Manual observations may also be subject to greater biases and subjectivity effects.
Another fairly simple, though powerful, technique for monitoring is the deployment of fixed sensors, whether singly or as part of a sensor network. An example of this type of monitoring is the global network of fixed data collection buoys and shore stations maintained by the National Oceanic and Atmospheric Administration’s National Data Buoy Center. This network of more than 1300 stations collects ocean temperature, current, conductivity, wave height, and wave frequency data, along with meteorological data, for use in weather forecasting, tsunami detection and alerts, and scientific and commercial research. The advantages of a fixed sensor network are in the acquisition of historical data sets which can be continuously compared to new data, the relative ease of maintenance of a network of fixed sites, and the ability to develop a comprehensive network. Indeed, the NDBC’s network has achieved global reach, making it one of the most valuable and useful fixed sensor networks in existence. The disadvantage of fixed sensors is that, being fixed, they cannot easily be redeployed to cover a new area of the aquatic region being monitored.
A more flexible approach to sensor deployment is the use of drop sensors, or temporary sensors for a particular location, which are then collected for re-use or allowed to degrade in place. An example of this type of sensor deployment would be the temporary placement of water-quality sondes along a flooding river system; the data collected from the sondes would be used for a limited time and then the sondes would be picked up and put back into storage or used on a different project. The advantage of this type of deployment is that it is extremely flexible; the sensors can be placed at the specific points where data collection is most important, and easily relocated as needs shift or if the initial deployment was less than optimal. The disadvantages of a drop sensor approach are that the sensors are generally not in a hardened or protected structure and are subject to theft, vandalism, or damage or destruction from environmental causes, and there is also potential for data loss owing to the ad hoc nature of the network infrastructure. For example, a set of inexpensive temporary buoys might be deployed to record ocean currents over a period of time, with the data to be collected at the end of the study period, only to have a major storm hit the network on the last day before collection, sinking half of the buoys and compromising the entire project.
The most sophisticated approach to monitoring the aquatic environment is to place the survey instruments on a ship, boat, or other craft and take the desired measurements from that vessel. For example, an aquaculture facility might have small craft with water quality sensors mounted in the hull to patrol the edge of the fish pens, testing the level of contaminants in the water. This approach has the advantages of most of the other approaches described here; it is flexible, it is protected from the environment, it has human observers on-site to address problems or concerns, etc. The main disadvantage of this approach is that ships and boats tend to be very expensive. The NBDC would need a much larger budget if it wanted to keep 1300 crewed ships on station to watch for tsunamis!
One way of greatly reducing the costs of this approach is to utilize ROVs as the data collection platforms. As ROVs are small, often portable by just one person, they can be deployed very flexibly in any aquatic environment, from water tanks to the deep ocean. Since they are controlled by a human operator, they maintain great flexibility and ability to adapt on the spot to problems that may arise, and are also protected against theft or vandalism by the proximity of the operator. When adverse weather or environmental conditions arise, the ROVs can be pulled out of the water, reducing the risk of data loss or loss of the vehicle itself owing to those kinds of conditions. Most importantly, ROVs can be equipped with a very wide array of top-quality scientific sensors, enabling them to monitor aquatic conditions just as well as sensor buoys or shore stations.
Every data collection mission has its own objectives and special needs, and finding the right type of monitoring solution for the mission requires judgment. ROV-based data collection is one option among many, but it is an option that is very flexible and has the potential to keep costs low without compromising the data collection process.
A vast array of organizations, governments, and individuals conduct monitoring in aquatic environments for an equally vast array of purposes. Monitoring is done for ecological reasons, for example, to record changes in the volume of a lake or stream so that managers will know whether to fill or drain a particular reservoir. Monitoring is done for legal reasons, for example, a factory that discharges waste into a river will be required to measure the levels of pollutants in order to comply with water quality laws. Monitoring is done for scientific and research reasons, for example, to assess changes in the temperature or salinity of the water in an area. Monitoring is also done for commercial reasons, for example, to check the bacterial counts in an aquaculture tank to ensure that the fish population is staying healthy and free of disease.
Some types of monitoring focus on the water itself, and its physical, chemical, and biological characteristics. This type of monitoring may look at the temperature of water over time, changes in its rate of flow or total volume in an area such as a lake or pond, or the pH (acidity/alkalinity) of the water. The monitoring may be done in order to assess the safety of the water for use by humans for drinking; is water from this stream low enough in harmful microorganisms to be directly usable without treatment, or does it require biological filtration? Monitoring may be done to ensure that water used in irrigation stays below a certain level of salinity and does not contain any of a number of pollutants. Monitoring could also be done in order to make sure that a pollution-control system upstream is working as intended.
Other types of monitoring are focused more on the species living in the aquatic environment. Marine biologists often engage in population surveys in a particular region, measuring the prevalence and population of a specific species or group of species. One famous example of this type of research is the tracking of salmonid numbers in the 20th century, which led to the discovery that increasing acidification of streams and oceans was impacting salmon and trout populations. This type of monitoring is done in several different ways; for large species such as oceangoing mammals, scientists may actually attach tracking devices to specific members of the species and gather data from the individuals’ movements, while for smaller creatures like fish, techniques such as gill-netting an area and then counting the fish in the net may be employed. Less invasively, water sampling might be done to measure bacterial levels when that is the focus of the research goal.
The specific environment being studied is of course highly relevant to how that environment can be monitored. Environmental monitoring of an aquatic environment can be done at a very “micro” level – a single sensor taking readings from a small aquatic habitat like a fish tank is technically monitoring that aquatic environment. At the opposite extreme, satellites in space can monitor vast expanses of ocean, at least coarsely. Most commonly, the scope of the aquatic environment to be monitored will dictate the range of appropriate monitoring solutions, whether that be simple cameras or sophisticated orbital satellites.
In next week’s blog we will take a look at the various ways in which monitoring of the aquatic environment is actually carried out.
Global warming has the potential to have major impacts on aquaculture. Over the past century, global warming (both human-caused and deriving from natural cycles) has increased the average global air temperature by around 1 degree Fahrenheit, 0.6 degrees Celsius. The world’s oceans, which have a vastly greater thermal mass than the atmosphere, have changed by only 0.18 degrees Fahrenheit (0.1 degree Celsius), with nearly all of that warming occurring in the surface layers. Even this relatively small change is enough to have major impacts on human food production in the ocean.
One significant impact from global warming is likely to be the reduction in the growth rate of krill. Krill are a family of tiny crustacean species that live in all of the world’s oceans and are the foundation of the aquatic food chain. Krill feed on phytoplankton and zooplankton, and are in turn consumed by fish and other aquatic animals in enormous quantities. Krill are fished commercially and used as a feedstock for aquaculture operations. As ocean temperatures rise, the reproductive rate of krill has been shown to decline significantly. This will make food stocks for aquaculture more expensive.
A major fraction of aquaculture is conducted in areas immediately offshore and in riparian (river) environments. Rising ocean temperatures may disrupt these operations by altering the sea level, changing coastlines and impacting river systems. Rising ocean temperatures alter the sea level in two ways – first, by causing increased melt rates at the polar ice caps, and also because of the fact that warmer water expands and takes up a larger volume. Even very small increases in temperature can have measurable impact on sea level. In riparian aquaculture, increased incursions of salt water can reduce yield or make operations untenable. Changes in water salinity also has enormous impacts on the presence and prevalence of species, which can throw aquaculture operations into chaos.
Further offshore, higher ocean temperatures are likely to cause stronger and more frequent storms. This is problematic for deep-water aquaculture operations, requiring a more robust infrastructure and increasing costs from storm damage. Warmer temperatures can also cause instability in marine ecosystems, as invasive species enter areas that were formerly too cold for them. This can cause issues for aquaculture operations that were predicated on a particular local ecosystem. Inshore operations are not immune to this change; many aquaculture operations rely on the monsoon season and it is expected that changing water temperatures will tend to disrupt this major weather pattern.
A significant portion of global aquaculture comes from the cultivation of mollusks. Mollusks as a group tend to be very temperature sensitive, and as waters warm, mollusk-growing operations will need to move to colder waters in order to maintain yield. When that is not possible, that portion of the aquaculture system could cease to function.
One major, albeit indirect, disruption could come from changing availability of freshwater inshore. Ecologists anticipate that global warming will cause reductions in the availability of freshwater, particularly in Africa and Asia, and as a result of this water stress, water for aquaculture development may simply not be available.
Unfortunately, it seems likely that future water temperature increases will have an increasing impact on the development of new aquaculture projects. Currently, the majority of world aquaculture is in the tropics, and although those areas are still growing strongly, new development is likely to center around the temperate zones of our planet. Increases in ocean temperature is expected to be significantly higher in the colder northern and southern waters than in the equatorial zone. That means that new aquaculture projects, for example off the eastern seaboard of the United States, are likely to be severely impacted by water temperature changes.
There are basically two kinds of power systems for tethered underwater remote operated vehicles (ROVs). One type of ROV has a power cable running down the tether, and the ROV gets the electricity to run its motors, operate its lights and sensors, etc., from a shore station, either a large battery pack or an electrical connection. The other type of ROV carries its power supply internally, generally in the form of high-capacity rechargeable lithium battery pack.
For some specialized missions, an ROV powered from the shore has its uses. However, for most types of ROV operations, a battery-powered ROV like the Aquabotix Endura or Hydroview Sport has the clear advantage. There are three main factors that make running an ROV from battery power the better choice.
First, battery power is portable. A battery-powered ROV can be deployed anywhere the ROV can be carried to, and the lightweight ROVs made by Aquabotix can be carried by one person to almost any location on Earth. Battery-powered ROVs can be deployed from the beach, from a small boat, from an oceangoing ship, from an offshore platform – if a person or vehicle can get there, then a battery-powered ROV can go with them and engage in missions from that spot.
Second, battery power is compact. The person or team deploying a battery-powered ROV does not need to carry a bulky generator with them to remote areas in order to send the ROV on missions. They can carry the charged ROV to the entry point and work from there without needing any expensive and heavy infrastructure. This makes a one-off mission even in the remotest areas simply a matter of putting the charged ROV in a vehicle (or even a backpack) and heading out.
Third, because radio waves do not carry well underwater, all non-autonomous ROVs use a tether to provide control and communication with the operator. In an ROV that relies on shore-based power, this tether also carries the electrical power the ROV uses for its operations. That means the tether must be much thicker for a shore-powered ROV. For example, a typical power-carrying cable might be [X – Beats me <g>] millimeters in diameter, while the tether for an Aquabotix ROV has a diameter of only [X] millimeters. Of course, a thicker tether is also a heavier tether – 250 meters of standard power-carrying tether weighs [X] kilograms, while the same Aquabotix tether weighs only [X]. This makes moving and deploying the battery-powered ROV much simpler and easier.
Battery-powered ROVs are simply easier to deploy, easier to carry, and able to operate in places that powered ROVs cannot.
Fish farming in the ocean and off the coasts has become an enormous business. Declining wild fisheries and an insatiable (and growing) global appetite for fish have created tremendous opportunities for the development of oceanic aquaculture. Local cultures have conducted aquaculture (generally in lakes and river systems, rather than the ocean) for thousands of years, but modern aquaculture has become a globally important food source. The UN’s Food and Agriculture Organization estimates that about half of the world’s food fish come from aquaculture, and the sector continues to grow at an astonishing rate – five to six percent annual increases in production are the norm. Total aquaculture production is over 80 million tons per year of fish, crustaceans, mollusks, and aquatic plants.
There are two basic types of oceanic fish farming. Coastal farming involves shallow-water farms located on the coast, along rivers, or in lakes. Open ocean farming involves deep-water farms that are not tied to a specific coastal location. There are important differences in these two approaches to oceanic aquaculture.
Coastal fish farming is the predominant form of oceanic aquaculture today. In a coastal aquaculture facility, pens or fish cages are deployed along the coastline, often in a protected bay or inlet. Most crustacean and mollusk farming is done inshore, using racks on which the food animals are grown. Depending on the species being farmed, the nutrients for the farmed food animals might come from the water itself, from the provision of forage fish, or from the addition of nutrients into the water in soluble form.
There are advantages to farming fish along the coast. Because the facility is located near the shore, storms are attenuated by the proximity of the landmass, and both workers and shipping infrastructure are close at hand. Operators can bring in supplies and export product from the convenience of local railheads and ports. Because the water is generally shallow at the coastline, it is also possible for operators to use ranch-style techniques, building habitats on the sea bottom for desirable fish such as abalone, and then simply catching the fish in the normal fashion without needing to closely manage the population.
Coastal farms have a number of significant disadvantages as well. Coastal areas are subject to intense competition from other uses such as recreational activities, fisheries, ports, and renewable energy development. Fixed-site aquaculture also has fairly severe environmental impacts on the delicate coastal ecosystem. Fish farms produce large quantities of waste and excess nutrients, which settle onto a fixed location on the sea bottom. This can utterly disrupt or even extinguish the local benthic ecosystem, causing repercussions to fisheries and tourism. Disease among the fish stocks is also a major problem, and because coastal fish farms can be close to one another, a disease which decimates one population can spread to other operations, even crossing species barriers.
Offshore fish farming, or deep-ocean aquaculture, cuts the ties to the shore, although not to the sea bottom. Generally, an offshore facility is tethered to the bottom and anchored to buoys, so that cages can move up and down in the water column but are still at a fixed location in the ocean. An offshore aquaculture can be sited almost anywhere, and does not have to compete with pleasure boating or fishing fleets. In addition, the much greater area (and stronger currents) available for dispersal of waste products and excess nutrients means that the environmental impact is significantly reduced or eliminated. Disease transmission is less problematic, and experimental offshore aquaculture operations have found that parasitic infestations are much more easily managed in the relative isolation of an offshore facility. Offshore locations are also more able to coexist with other uses of the same area of the ocean; since the cages can be moved deeper into the water than is possible in a coastal area, other uses such as boating can be accommodated.
Offshore aquaculture has its own set of problems, however. The expense of building cages that can withstand the storms and currents of the open ocean is considerable. Because the environmental conditions are more rigorous in the open sea, fish escapes are more likely to occur, which has ramifications both in terms of cost and in the potential for the introduction of invasive species to ecologically vulnerable areas of ocean. In addition, the laws and regulatory environments that apply close to shore (within the three-mile limit, for example) become more complex further out to sea; for this reason, off-shore aquaculture in the United States has primarily developed only in areas of the ocean that are unambiguously under Federal jurisdiction so that operators can have a predictable legal environment in which to do business.
Despite the potential issues and problems that arise in both coastal and offshore aquaculture, it is a certainty that these areas of economic activity will continue to grow and expand. Fish are a vital part of the global food infrastructure and aquaculture is rapidly becoming the dominant way in which this sector produces its output.