Physical alteration

Environmental Impact of Fishing
Human activities may damage marine ecosystems in various ways, some by direct physical damage and others more indirectly by removing key fauna or introducing invasive species. Many activities impact the marine environment in multiple ways; for example coastal runoff not only introduces pollutants such as pesticides, it also adds nutrients that can create harmful algal blooms. Although there are myriad human activities that cause problems for marine ecosystems, many are restricted in geography and impact; the exception to this is fishing, which has impacted virtually every marine ecosystem on earth, from estuaries to the deep sea, from the poles to the tropics.

Destructive Fishing
Destructive fishing practices are those that not only capture fish, but also damage the habitat in some way. Many fish rely on seafloor structure for food, shelter and spawning, and when that structure is damaged or destroyed by destructive fishing practices, the ecosystem services provided by the structure is compromised. Fishing methods differ in how they impact the habitat; hand-lines, small scale trolling and spearfishing, while they can deplete fish populations, do not change the habitat structure. Other methods such as bottom longlines, long strings of traps and especially bottom trawling cause some level of direct physical damage to the seafloor. Some habitats are more resilient to bottom impact. Sandy habitats have low faunal diversity both in the sand and on the surface and recovers quickly from disturbance. Soft muddy environments can support a large abundance of ‘infauna’ that live in the sediment. These animals (mainly worms and mollusks) provide food for various fish species, and recovery from physical damage in these types of habitats is not well understood. Structure on the seafloor may be provided by rocks and other non-biological substrate, or by animals such as corals, sponges or colonial mollusks. These animals generally form very complex structure that provides shelter and food for a diverse community of associated fauna. In the deep sea, where species grow slower and live longer in the cold water, the corals that create habitat structure can be hundreds to thousands of years old. When these types of habitats are damaged, they recover extremely slowly, if at all.

Bottom Trawling
Bottom trawling is widely considered to be the most damaging fishing method in common use today. Bottom trawl gear consists of a cone-shaped net with a wider mouth tapering to a sealed back or cod end. The mouth is held open either by large heavy doors and a heavy chain or a solid metal beam. Tickler chains are often attached to drive fish from the seafloor into the net. Small trawls used over soft substrate cause limited disturbance of the seafloor but the massive industrial trawls used by offshore and high seas fleets can rapidly destroy fragile coral habitat. A single trawl pass can harvest tons of fish and is completely indiscriminate, collecting everything in the path of the net. In some fisheries, the non- target or ‘bycatch’ species far outweighs the target species. Some bycatch has value, but much is simply discarded back into the ocean. By the time the catch has been sorted, the bycatch is dead and can include marine mammals, turtles or other threatened species. Modern trawls can fish as deep as 1600m, which allows access to some of the most fragile and ancient ecosystems on earth. Deep sea corals are very slow growing and long lived; they form highly complex reefs that support incredibly abundant and diverse and associated communities. These reefs attract many different species of deep sea fish, which are also slow growing and long lived, and are targets of deep sea trawl fishing. One of the most heavily exploited of these fish is orange roughy, which can live over a 100 years and aggregate over deep coral reefs. Massive trawls with heavy ‘rockhopper’ gear smash the coral infrastructure to access the fish, which are rapidly depleted. Once the fish are gone, the vessels move on to the next reef. New Zealand has an extensive orange roughy fishery that is highly regulated; however their trawls still destroy ancient coral habitat and capture large amounts of non-target fauna.

Other destructive fishing methods
There are several other fishing methods that can damage benthic ecosystems. Dredges for scallops and clams disturb the seafloor, but are smaller than bottom trawls. Bottom long-lines are heavy weighted lines that are dragged across the seafloor in search of bottom dwelling fish. Some crab fisheries use lines of traps that are strung together for up to a mile, and may damage fragile habitat as they are hauled in. The practice of blast fishing on shallow coral reefs is illegal in most places, but still persists, especially in Southeast Asia, the Aegean Sea and coastal Africa. Blast or dynamite fishing involves dropping explosives onto coral reefs to stun fish that can then be collected for food or the aquarium trade. This practice indiscriminately kills marine life in the area and blows coral heads apart, causing localized but severe damage to shallow reef ecosystems. There are other fishing methods that do not impact or affect the seafloor, but cause other impacts to the marine environment. These include surface long-lines which can be miles in length and have thousands of baited hooks. These surface lines are usually used to target pelagic species such as tuna and swordfish but frequently attract seabirds, mammals and sharks as bycatch.

How We Fish Matters
Fisheries management plans are based on stock assessments of the target species or species complex. This approach does not take into consideration the incidental damage caused by different fishing methods. For example, the same species can be fished using lines or trawls, but the former causes no physical damage to the seafloor and has considerably lower incidence of bycatch. Some fishing practices are excluded from defined areas, but these are inconsequential when considered on the scale of global fisheries. If fisheries management entities would consider habitat and not target species impact in fisheries management plans, there would be less waste and unnecessary impact on our already overexploited oceans. Bottom trawls are considered to have the greatest ecological impact, followed by, dredges and bottom long-lines, then mid-water trawls, seine nets and surface long-lines, with hand-lines and trolling being least damaging methods. Fishing gear today is made from long lasting monofilament or other synthetic material that is extremely durable. This causes problems when gear is lost or discarded as it becomes ‘ghost’ gear, entangling or attracting fish and other marine life indefinitely. Traps are often required to have breakaway panels that biodegrade so prevent them becoming ghost traps, but lost purse seines and gill nets do not have this kind of solution.

What can be done to help
Governmental regulations are slow to be implemented and regulations are often influenced by the fishing industry so improvements to environmental stewardship are slow. An alternative route to changing fishing behavior is through market driven processes. If consumers demand sustainable fisheries, including habitat and bycatch considerations, then suppliers will respond. Dolphin safe tuna came about as a result of a consumer ‘grass routes’ outrage to the killing of thousands of dolphins in tuna nets. This kind of public support can move changes quickly. Banning some fishing methods in particularly sensitive areas (such as bottom trawling over deep coral habitat) will protect the ancient reefs, and the long lived species that inhabit them.

How coastal development affects our oceans
Coastal development can include the construction of industry, homes, recreational areas, hotels, shipping ports, marinas, oil refineries and more.

Poorly managed coastal development is one of the biggest causes of near-shore pollution globally. Housing developments, recreational areas, aquaculture operations and many other human activities along coastlines increase the environmental load of fertilizers, pesticides and other toxins, and harmful bacteria. Excavating mangroves, wetlands and sand dunes removes the natural filters for pollutants, and leaves shorelines exposed to erosion and sediment runoff. Dredging channels for ports and marinas changes the water flow and can have serious detrimental effects on near-shore ecosystems. Lights from buildings can disrupt endangered sea turtle nesting and roadways kill thousands of migrating crabs as they move from inland swamps to the ocean to spawn. Coastal development also degrades and alters the course of salmon spawning rivers. Coastal development also creates population centers that generate garbage and increase fishing and other ocean use.

What can be done to help
Responsible coastal development includes recycling water that is laden with nutrients, leaving buffers of natural vegetation along shorelines, regulating effluent from ports, marinas, aquaculture and agriculture, and taking the needs of marine life into consideration. For example, in south Florida, there is a ban on lights along the shoreline during turtle nesting season. Restoration of degraded coastal areas is occurring in some areas; improving salmon streams, restoring natural flow to the Everglades and removing large dams that are disrupting waterways and impacting the environment.

How Marine Protected Areas can help
MPAs can be part of an overall strategic plan for responsible coastal management, as they recognize the value of healthy marine ecosystems and the services they provide for coastal communities.

What you can do to help
Participation in local discussions on coastal development can help guide regulatory decisions. Support restoration programs and efforts to establish MPAs in your area.