Ecosystem Status Report for the Northeast Large Marine Ecosystem

Figure 7.1

The U.S. Northeast Shelf Large Marine Ecosystem (NES LME) is an important habitat for a number of marine mammal species. The Gulf of Maine and Georges Bank shelf regions in particular are essential summer feeding grounds for a number of migratory large whales including humpback, fin, sei, minke, and North Atlantic right whales; smaller toothed whales including harbor porpoise, short-beaked common dolphin, Atlantic white-sided dolphin, offshore bottlenose dolphin, short-finned and long-finned pilot whales, and seal species including harbor and gray seals. These animals benefit from the strong spring phytoplankton bloom and feed on the resulting high abundance of zooplankton, krill, and fish species on the shelf. The distributions of these species are generally influenced by oceanographic features including temperature, depth and currents, and how these features relate to each animal’s physiology, behavior, and ecology.

Many of the marine mammal species that can be found in the U.S. NES LME only visit the region during part of the year or only use part of the region. During winter, most of the large whales migrate south from the Gulf of Maine along the Mid-Atlantic shelf to warmer water breeding grounds as far south as the Caribbean Sea. Blue and sperm whales occasionally use the U.S. NES LME shelf regions although they are more commonly found in deeper water off of the shelf. Other toothed whales that occasionally use the shelf waters include killer whale, Northern bottlenose whale, Cuvier’s beaked whale, Blainville’s beaked whale, Gervais beaked whale, Sowerby’s beaked whale, True’s beaked whale, Risso’s dolphin, white-beaked dolphin, spotted dolphin and striped dolphin, although these species are more commonly found in off-shelf waters.

The numbers of harbor and gray seals on the U.S. NES LME have increased in recent years where some seals are present year-round, though they migrate within and outside of the U.S. NES LME (Wood 2009). These seal populations eat a wide variety of fish and invertebrates, and despite controversy over consumption of Atlantic cod (Savenkoff et al. 2008), they tend to primarily consume small pelagic fish, hakes and flatfish (Col et al. 2012). Other seal species such as the harp and hooded seals primarily use the region as a feeding ground during winter months.

All of the above species found in the U.S. NES LME are protected under the Marine Mammal Protection Act, and all of the large whales (excluding minke whales) are listed as endangered under the Endangered Species Act (ESA). The North Atlantic right whale is one of the most critically endangered populations of large whales in the world. Because of the ESA status of North Atlantic right whales, specific monitoring programs are in place including annual counts of right whale calves. The best estimate of the total North Atlantic right whale population size shows an increase in the population from 261 in 1990 to 455 in 2010 (Figure 7.1). More general NEFSC aerial and shipboard marine mammal surveys occur as funding and time permit, and further details on current status and distributions of marine mammal species can be found in the annual assessments (Waring et al. 2013).

Figure 7.2

Sea turtles are commonly observed in the U.S. NES LME in the late spring, summer, and early fall months when ocean temperatures are warmer. Of the four species that typically occur in this region, loggerhead turtles are the most abundant. Other species present in the region include leatherback, green, and Kemp’s ridley turtles. Loggerheads foraging in the U.S. NES LME typically nest on beaches from Florida to North Carolina. Leatherbacks nest on beaches throughout the Caribbean Sea, Florida, and Central and South America. Kemp’s ridley turtles primarily nest at a single nesting location in Mexico, while green turtles mostly likely derive from Florida beaches. While leatherbacks are exclusive foragers of gelatinous zooplankton, loggerheads primarily feed on benthic invertebrates.

All sea turtles are protected under the U.S. Endangered Species Act and those that occur in the U.S. NES LME are listed as threatened (loggerhead and green) and endangered (leatherback and Kemp’s ridley). Population abundances and trends have typically been estimated using nesting female count data from the primary nesting beaches. Aerial surveys of in-water turtles are also useful for population estimates but are subject to a much higher level of uncertainty due to temporal inconsistencies in the survey, variability in turtle surfacing behavior, perception bias, and the previous small spatial coverage of surveys.

Figure 7.2 shows the location of juvenile and adult turtles based on the summer of 2010 aerial survey along U.S. NES LME waters and shelf waters south of Cape Hatteras. Preliminary abundance estimates for juvenile and adult loggerheads in the summer of 2010 ranged from 521,000 to 1,111,000 individuals in the shelf waters between Cape Canaveral, Florida and the Gulf of St. Lawrence, Canada (NEFSC 2011).

Figure 7.3

Figure 7.4

Figure 7.5

Figure 7.6

Figure 7.7

Figure 7.8

Changes in sea surface temperature (SST) can influence marine prey distribution and abundance (Perry et al. 2005). Seabirds are considered “ecological indicators” or “sentinels of the sea” since they are easily visible, and feed on fish and zooplankton. Changes in abundance and prey distributions might negatively or positively impact migrating or breeding seabird populations along the Northeast continental shelf. As waters warm, many species might shift northward, reducing the range for species that are adapted to cold water (Righton et al. 2010). For example, in the Pacific Ocean, between 1987 and 1994, sooty shearwaters declined 94 percent over the California Current (Veit et al. 1997). This decline was negatively correlated with warming SST and consistent with increase of sooty shearwaters in the northern part of the California Current, suggesting a shift in their foraging range (Ainley et al. 1995; Spear and Ainley 1999; Oedekoven et al. 2001). A temperature increase of less than 1°C of the upper 500 meters between 1950 and 1982 was the main reason (Roemmich 1992). Sooty shearwaters feed principally on Euphausia Pacifica and warming temperatures have been accompanied by a 70% decline in zooplankton abundance (Roemmich and McGowan 1995; Veit et al. 1996). Some seabirds adapt effortlessly to new scenarios while others may be affected by a changing ecosystem (“Winners” versus “Losers”). Migratory species can be vulnerable to fast environmental changes, but might show variation in their capacity to respond to these changes (Berteaux et al. 2004). Northern gannets (Sula bassana) are the largest seabirds in the Northwest Atlantic, breeding in Newfoundland. They are generalist, opportunist, and travel where resources are generally predictable due to higher productivity (Montevecchi et al. 2009; Pettex et al. 2010). Their breeding population and distribution have been increasing since 1900 in Canada (Montevecchi and Myers 1997). They have been able to adapt their diet to new conditions over the past 100 years. In 2012, Razorbills (Alca torda) were observed in large number along the southeast continental shelf during the winter. This seabird was considered primarily as a species associated to Arctic, subarctic waters (Huettmann et al. 2005); Exceptional large aggregations of these Alcids were spotted offshore Florida, around Tampa Bay or even Gulf of Mexico during the past winter. Simultaneously, their breeding population has been slowly increasing in Maine since 1970s.

Atlantic Puffin (Fratercula Fratercula) and Artic tern (Sterna paradisaea) have seen a decline in their breeding productivity negatively correlated to diet change and SST increase (Figure 7.3 and Figure 7.4). Atlantic puffin was close to extinction in North America until 1980s. A program of chick translocation was organized by the Audubon Society (Puffin Project) and since then the numbers have increased steadily. Since 2002, a serious decline in productivity has been noticed on two islands (Figure 7.5). In 2012, the lowest breeding productivity result was observed. Atlantic puffins now feed their juveniles with more butterfish (Peprilus triacanthus) relative to Atlantic herring (Clupea harengus) (Figure 7.6). Chicks are unable to swallow the rounder fish and can result in choking. Artic tern adults also now feed their chicks with more butterfish, and a decline in their breeding success has also been observed (Figure 7.5 and Figure 7.7) but Artic terns can feed on a wider range of prey items (Figure 7.8). Butterfish are pelagic fishes forming loose schools at the surface (Brodziak 1995). Butterfish grow quickly; their life span is relatively short (1-3 years); and they are adapted physiologically to a wide thermal range (eurythermal) or salinity (euryalin). Juvenile butterfish are found along the northeast continental shelf in waters between 4.5°C and almost 30°C and adults are found in waters between 4.5°C and 26°C . These fish reproduce in waters up to 15°C (Murawski et al. 1978). Oceanographic conditions in the Gulf of Maine have become extremely favorable for the spawning and fast development of this species during the summer months before they migrate south in the winter (Fritz 1965). We interpolated data points from three buoys (including the summer months) around Puffin nesting sites and found an almost 2°C increase between 1984 and 2012.

In the Northwest Atlantic, the diet of northern fulmar (Fulmarus glacialis), great shearwater (Puffinus major) and sooty shearwater (Puffinus griseus) is primarily composed of species considered cold water fish species such as Capelin or mackerel (Brown et al. 1981; Cherel et al. 2001; Ronconi et al. 2010). Capelin is distributed in northern oceans where temperatures range from -1°C to 14°C. Spawning sites, migration, and feeding areas can shift with water temperature (Rose 2005). Atlantic herring or mackerel abundance is also negatively correlated to water temperature. Cory’s shearwater (Calonectris diomedea) density has been increasing abruptly in 2009 along the northeast continental shelf and southeastern Canada. This large seabird breeds in the Azores and Mediterranean islands (Granadeiro et al. 1998). Stomach contents analyses collected in 1994 during the breeding period suggested that they feed on small schooling fish such as saury (Scomberesox saurus), trumpet fish (macrorhamphosus sp.), boarfish (Capros aper) (Granadeiro et al. 1998). A similar field study conducted in 2005 showed that adult breeders fed mostly on Blue Jack mackerel (Trachurus picturatus), trumpet fish and boarfish (Xavier et al. 2011). There appears to be variation in Cory’s shearwater diet as a function of their location, environmental conditions, and fishery activity (Granadeiro et al. 1998; Paiva et al. 2010). The abundance of warm water fish species has been increasing in the Northwest Atlantic (Montevecchi and Myers 1997; Rose 2005b). Saury abundance has been increasing in southeastern Canadian waters and the Gulf of Maine (Pohle et al. 1992). They are mostly found in temperate to warmer waters in the Atlantic Ocean, and range from Newfoundland to North Carolina. Cory’s shearwater may benefit from the proliferation of warm water fish species in the study area. Consequently, seabird species adapted to colder waters, a distributional shift or change in foraging movements might lead to spatio-temporal overlapping with fisheries. Fishing boats can increase food availability, but can also be lethal to many seabird species (bycatch).

Figure 7.9

A number of diadromous species utilize the Northeast Shelf for feeding and reproductive migrations. These species are impacted by stressors in both freshwater and marine habitats, which have resulted in population declines that have put distinct population segments for these species in endangered status or have made them species of concern. Atlantic salmon transit the Gulf of Maine as juveniles and adults on feeding migrations. The cumulative impacts of changes in freshwater habitats and marine survival during the early marine phase have resulted in a loss in salmon populations and lower abundances among the surviving populations (see Figure 7.9). Sturgeon has been similarly impacted by habitat changes in freshwater; however, the greatest stressor in the marine environments appears to be related to fishery impacts. Unlike salmon and sturgeon which spawn in freshwater habitats, American eel spawn in the Sargasso Sea after a long and highly precise oceanic migration. Both the American and European eel migrate to the Sargasso Sea for spawning and both appear to have been impacted by changes in subtropical climate conditions.