The Gulf of Maine Council's objective is to support restoration and enhancement of riverine habitats and to improve access for fish and wildlife. Emphasis is placed on restoration of migratory fish, whose historic spawning habitat has been greatly diminished.

The conservation and restoration of riverine habitat is of special concern to the Gulf of Maine Council because rivers have great economic, recreational, and environmental importance. Rivers sustain the Gulf of Maine�fs anadromous and catadromous fish species, which are valuable members of the region�fs biological diversity. Anadromous fish are those that spend their lives in salt water and migrate into fresh water to spawn. Catadromous fish spend their lives in freshwater and migrate to the ocean to spawn. Collectively, anadromous and catadromous fish are called diadromous. Only 87 of 24,700 fish species in the world are anadromous (Atlantic Salmon Federation, 2002). The Gulf of Maine supports 12 diadromous species, including the Atlantic salmon, rainbow smelt, alewife, and striped bass. The catadromous American eel was historically found in almost all water bodies in the Gulf of Maine watershed. Rivers support various species and life stages of freshwater and diadromous fish. The rich diversity of habitats—particularly different substrate types, flow conditions, wetlands, and floodplain forests—are vitally important for aquatic biological diversity. For example, sea-run brook trout prefer cold, fast-flowing streams; blueback herring and alewife prefer larger streams, backwater areas, and lakes; and American shad prefer large rivers. Riparian vegetation is an important food source for aquatic invertebrates and influences the growth and survival of many fish. Healthy riparian habitats are essential to maintain water quality conditions, such as cool water temperatures preferred by Atlantic salmon and brook trout.

Degraded stream morphology and riparian buffers
The Gulf of Maine's rivers have been affected by a long history of environmental degradation. Portions of rivers have been straightened in a misguided effort to divert water to flush impoundments or reduce the incidence of floods. Log drives had drastic effects on natural stream morphology. Restoration of natural channel morphology is an effective technique for improving fish habitat and reducing flooding by reconnecting the natural absorption capacity of the floodplain to the river.

Natural riparian buffers moderate water temperatures, provide in-stream habitat and a food source for aquatic organisms, and reduce erosion by stabilizing riverbanks. Humans have removed or altered natural riparian vegetation, thereby reducing their buffering capacity. Stabilizing riverbanks with native shrubs and trees is a valuable restoration technique for riverine habitats.

Dams and other barriers to fish passage
According to current databases, the U.S. side of the Gulf of Maine has 4,867 dams: 2,506 in New Hampshire, 782 in Maine, and 1,579 in Massachusetts. States categorize and inventory dams in different ways, and this is reflected in state totals. In New Hampshire, all dams are counted regardless of height, size of impoundment, and use. In Maine, dam owners voluntarily registered dams between 1983 and 1993—registration required a minimum dam height and a minimum water capacity behind the dam. There are undoubtedly many more dams in Maine because some owners may not have registered their dams, and many abandoned log driving dams or milldams were not included in the inventory.

Dams can greatly restrict or prohibit upstream and downstream fish passage for resident and migratory fish. Migratory fish are vulnerable because barriers affect spawning behavior and success. From an ecological perspective, dams that block fish passage should be reengineered or removed to allow fish passage. Dam removal reconnects artificially fragmented river systems, restores habitat for migratory and resident fish, restores natural flow regimes, and improves water quality.

Dam removal may create economic and social benefits. Dam removal is a favorable option when the long-term costs of dam maintenance are high compared to financial returns. For instance, a state-regulated obsolete milldam may require significant investment to meet safety requirements, or a federally regulated power-producing dam that requires fish passage may only be marginally economical. Another consideration is the liability associated with dams that have deteriorated and are in danger of failure, causing downstream flooding, property damage, or even loss of life. Restoring river habitat can create new social, economic, and recreational opportunities such as boating, fishing, and wildlife viewing. Angling for migratory sea-run fish, such as American shad and striped bass�\as well as festivals surrounding annual springtime alewife runs�\provide tourist attractions and nature-based tourism opportunities in many areas of the Gulf.

Dam removal should be considered when evaluating project alternatives. A comprehensive analysis of dam removal options enables well-informed decisions on the future of dams throughout the Gulf of Maine watershed. Dam removal may not always be feasible because of social and economic factors, such as water supply needs, hydropower production, recreational activity, and cultural desires. In these cases, installation of upstream and downstream fish passage may reduce the dam�fs effects on fisheries.

Installing a fishway on a dam can greatly improve fish migration. However, fishways do not provide the full benefit of dam removal because a fishway does not restore riverine function or habitat—only fish access. Fishways are often designed to improve access for particular species. Several types of fishways are highly effective, particularly for migratory species like American shad and river herring (e.g., Denil-type, Alaskan steep pass). There is increasing interest in innovative fishways that are designed to mimic nature, either in the form of a riffle (i.e., rock ramp fishway) or a tributary to the main river (i.e., bypass channel). These "nature-like fishways" have been shown to pass a broader diversity of fish species, and even reptiles and amphibians.

Regardless of the type of fishway, the design and placement must take into consideration many critical factors, such as adequate hydraulics within the fishway and proper attraction flow so that the fish are able to find and navigate the structure. Identifying an entity to take long-term maintenance and operational responsibility for the fishway is also critical to the success of the project.

Improperly designed or maintained culverts can be just as effective as dams at blocking fish migration. The following are a few guidelines for replacing culverts that are restricting or preventing fish passage:

• Match the culvert (pipe) dimensions to hydraulic geometry of the natural banks and full stream channel.
• Use corrugated elliptical pipe arches with the largest feasible corrugations
• Embed the pipe invert to 12-48 inches depending on the size of the pipe
• Place the pipe at zero slope
• The pipe should pass 50-year flood with capacity lost to embedding included
• If a culvert is being rehabilitated rather than replaced, hydraulic analysis is needed to calculate water velocities and depths under design flows, and to design mitigation measures needed to achieve velocities and depths that will pass fish.