A great white shark circles gray seals off Chatham, MA. Photo via Mass. Office of Energy and Environment
A great white shark circles gray seals off Chatham, MA. Photo via Mass. Office of Energy and Environment

The Ocean’s Top Predators

In “Ocean Soul,” world-renowned National Geographic photographer Brian Skerry says, “It’s been said that sharks have remained unchanged for hundreds of millions of years because they are perfect and that no further evolutionary change is necessary.”

Sharks have certainly reached the top of the food chain as the ocean’s apex predators. Apex is a word of Latin origin meaning peak or tip. In ecological terms, apex is used to describe an animal that has no natural predator within its ecosystem—terrestrial examples include wolves and cougars.

Although humans might find them terrifying, apex predators are crucial for maintaining healthy ecosystems. Sharks, for example, play a vital role in balancing ocean food webs. They aid in population control of smaller predators, so that prey species are able to exist at healthy levels. They also regulate the behavior and abundance of prey species, protecting habitat like seagrass beds and coral reefs from overgrazing, and promote biodiversity by preventing any single prey species from monopolizing resources.

Sharks also tend to prey on weak or sick members of a species, so as to minimize their caloric hunting expense. This natural tendency towards efficiency promotes healthier populations by advancing the transmission of strong genes, as weaker genes are taken out of the gene pool.

Despite the enormous amount of good we know sharks do for ocean ecosystems, humans hunt sharks for their meat, especially their fins. Sharks can also become collateral damage to commercial fishing for other species—accidental net entanglements or hooking often prove lethal. According to a 2013 report published in “Marine Policy,” humans killed approximately 100 million sharks in 2000, and 97 million in 2010. Annually, humans kill between 63 and 273 million sharks.

What happens when the oceans begin to feel the loss of sharks? Populations of smaller predator species boom, stressing habitats and depleting populations of prey species. These changes can be very detrimental to the fishing industry. For example, depleted great white shark populations have been linked to the boom in gray seal numbers in New England, and the voracious appetite of the seals may be harming the recovery of overfished cod. In North Carolina, a decline in large sharks because of overfishing led to an increase in cownose rays, one of the sharks’ prey species. Cownose rays eat shellfish, and so an increase in their population caused the bay scallop fishery to collapse.

Clearly, apex predators like sharks are absolutely critical to maintaining healthy marine ecosystems. The role of apex predators is better understood today than ever before, and now that we know how vital their role is, it is time to protect and respect the ocean’s top predators.

A salt marsh in Bourne, MA. Image via Roey Ahram, Flickr
A salt marsh in Bourne, MA. Image via Roey Ahram, Flickr

Ocean Plants Part 1: Salt Marshes

Categories: Guest Posters

Here on New England Ocean Odyssey, we talk a lot about the marine animals that make New England’s ocean so special—from fish to turtles to whales and everything in between. But we thought it might be time to recognize some of the plants—and the habitats they create—that support the incredible productivity of our ocean. This series of posts will focus on just a few of these important types of plant life.

We’ll start with salt marshes, one of the most important plant-based habitat types in New England. Salt marshes are coastal wetland areas that are flooded and drained by salt water tides. They exist on shorelines around the world, where freshwater habitats meet saltwater habitats and terrestrial environments meet marine environments.

Marsh soil comprises peat moss and mud. In New England, the diverse plant life that supports this habitat ranges from reeds and grasses to flowering roses, succulent worts, and shrubs like bayberry and elder.

Conditions in marshes can be tough. In New England, salt marshes are exposed to two high and two low tides each day, creating strong currents, very salty soil, and widely varying moisture levels. The ecosystem must also endure temperatures ranging from below freezing to 90° F in the summer. The frequent submersion of salt marshes under water, along with the constant decomposition of plant matter, also leads to low levels of oxygen in soil. This condition is referred to as hypoxia, and it’s also related to the bacteria that give off the sulfurous, rotten-egg smell of many marshes.

Salt marsh plants are well adapted to deal with these tough conditions. For example, near surface roots of S. alterniflora help to oxygenate roots further down in the soil. Another plant mechanism to achieve oxygenation is to have aerenchyma tissue, air passages that allow a plant to transport oxygen from the atmosphere to its roots beneath the soil.

Salt marshes are a critical ecosystem component in New England. They support healthy fisheries, protect coastlines and coastal communities from flooding, nurture 75 percent of fisheries species such as shrimp, blue crab and finfish, and aid in carbon sequestration. Salt Marshes also filter pollutants like excess nitrogen prior to their reaching the ocean.

Unfortunately, salt marshes are threatened by coastal development, nutrient pollution from fertilizers, marsh draining to attempt to control mosquitoes, and other environmental stresses. For example, 50 percent of Narragansett Bay’s salt marshes have been lost in the last three centuries, and much of what remains is damaged.

For the four million remaining acres of salt marshes along the United States’ coastline, sea level rise is an imminent threat. Given enough adaptation time, salt marshes are able to increase their elevation by accumulating layers of soil matter while simultaneously receding inland, but they may not be able to keep up. Currently, Rhode Island documented a sea-level rise of 3.6 millimeters a year, but salt marshes are only growing at 2.9 millimeters per year.

Hopefully, efforts to mitigate sea level rise and restoration efforts will give our critically important salt marshes and the marine life that depend on them a little more time to adapt.

A great white swims in a Cape Cod salt pond in 2004. Image via Mass EEA
A great white swims in a Cape Cod salt pond in 2004. Image via Mass EEA

Gearing Up for Shark Week

The Discovery Channel’s Shark Week starts in just ten days! As ocean fans around the world gear up for the annual celebration of all things shark, New Englanders are turning their eyes to the North Atlantic Great white population. It seems these days Cape Cod beachgoers can’t help but scan the ocean horizon for a dorsal fin before taking a chilly but refreshing dip.

This year’s Cape Cod shark-spotting season kicked off on June 23rd when Captain Tyler Macallister captured video footage of a great white, Carchardon carcharias, six miles southwest of Provincetown, in Cape Cod Bay. Upon seeing the shark, Macallister began recording his calm and somewhat mystical encounter with the estimated 16-to-18 foot great white. A Massachusetts Division of Marine Fisheries biologist confirmed that the fish captured on Macallister’s video camera was a great white, but that the lack of scale in the footage meant its size could not be accurately determined.

Five days after Captain Macallister’s encounter with a great white shark in Cape Cod Bay, researchers from the Atlantic White Shark Conservancy saw a great white one-quarter of a mile off of Nauset Beach, near Orleans, Cape Cod. The researchers were able to identify the fish as a 12-to-14 feet long female great white and named her “Ping.” Ping was first spotted by a spotter plane and then tracked by boat. The Atlantic White Shark Conservancy sends out both a spotter plane and boat twice a week to study Ping and other great whites.

The increase in great white shark sightings has been going on for the last decade or so, and in the Cape Cod area it’s been partially attributed to the growing gray seal, Halichoerus grypus, population around the Cape. Gray seals were previously hunted by fishermen as a precaution towards preserving fish populations that the Gray seals consume, but the seals are presently protected by the Marine Mammal Protection Act of 1972. Great white sharks prey on seals and as seal populations expand in the Cape Cod area, there appears to be a growing number of white sharks.

If you are curious where these sharks spend their days, when they are not busy stalking Cape Cod’s massive seal populations, you can track tagged sharks through Ocearch.com or through the Ocearch app. And get ready for more information on New England’s sharks as we celebrate Shark Week here at New England Ocean Odyssey!

A striped bass fisherman on Chappaquiddick. Image via John Piekos, Flickr
A striped bass fisherman on Chappaquiddick. Image via John Piekos, Flickr

Striped Bass and Forage Fish

As the summer heats up along Atlantic coast, coastal residents and visitors alike head out in boats, stake out spots on docks and bridges, or don rubber waders and forge into the waves along a beach’s breakwater. Each is armed with a long pole and a zeal for the chase. Their quarry is the striped bass, a silvery fish with trademark dark stripes running the length of its body from head to tail. The striped bass, or striper, is an anadromous fish native to the Atlantic coast of North America, and usually grows to around three and half feet. The historic abundance of the striped bass, as well as its ideal size for recreational fishing, makes it a highly valued sport fishing species. In 2004, recreational fishermen landed more than 2.5 million stripers.

Unfortunately, recent evidence indicates that this time-honored recreational fishery may be in danger of collapse. Recreational fishermen in Massachusetts reported a staggering 85% drop in striper numbers between 2006 and 2011, and Massachusetts is not alone: states up and down the coast are seeing fewer stripers, and the schools of bass that migrate up the coast from the Chesapeake Bay to Maine are thinning out. More and more fishermen are heading home empty-handed at the end of the day, and more importantly, the disappearance of the striped bass leaves a lack of an important member of the marine ecosystem and food web.

Image credit: Timothy Knepp/Wikimedia Commons

Image credit: Timothy Knepp/Wikimedia Commons

Many factors are responsible for the decline of the striper, but one is often overlooked: food. Small forage fish, including Atlantic herring and river herring, compose around 90% of the striped bass diet, and these forage fish face the pressure of a significant fishery of their own. While ignored by recreational fishermen, Atlantic herring are heavily fished by commercial fishermen, largely for use as bait in the lobster industry. In 2011, for instance, U.S. commercial fishermen harvested over 174.3 million pounds of Atlantic herring.

Recent assessments indicate that Atlantic herring are not overfished, but surveys of population levels and safe catch limits rarely take proper account of the amount of a forage fish required to feed its predator species. As a result, after the herring fishery has hauled in its 170 million pounds of fish, there may not be enough herring left to both maintain a steady herring population and provide the striped bass with sufficient prey.

River herring, meanwhile, have been depleted by years of overfishing and habitat loss due to dams. Total landings of commercially fished river herring have decreased steeply over the years: in the 1950s, over 60 million pounds of river herring were harvested by commercial fisheries throughout the US, but this number had decreased to around 2 million pounds by 2012. In response to this decline, many states have implemented moratoriums on intentional catch of river herring and have made strong efforts to remove dams and restore upstream habitat; river herring runs in many New England rivers seem to be on the rebound. But river herring are still at risk at sea, where they are caught as bycatch by the Atlantic herring and mackerel fisheries.

This scarcity of prey spells danger for the striped bass. Without sufficient forage fish, there will be fewer striped bass in the sea, and more fishermen with empty hooks.

Blue crabs. Photo via Benjamin Wilson, Flickr
Blue crabs. Photo via Benjamin Wilson, Flickr

Crab Chowder?

In 2012, northeast sea surface temperatures reached an all-time high. Many speculate that rising water temperatures have contributed to a record high catch of 126 million pounds of American lobster, Homerus americanus, in the Gulf of Maine. However, the steady rise in New England’s sea surface temperatures may have also made southern areas of New England inhospitable for lobster. In a recent interview with AccuWeater, Maine Lobstermen Association’s Patrice McCarron said, “In southern New England, Buzzard Bay, Mass., and the waters off of Rhode Island, temperatures in the Long Island Sound area have become too warm for lobsters.” Lobster catch in these areas has plummeted since the 1990s.

The warming trend in New England waters has caused alarm for local fishermen, and we’re only beginning to understand the ways climate change might affect our fisheries. While some treasured New England species may relocate father north, it’s possible that other species will move into this region and create new economic opportunities.

We’ve written before about some of these species moving north as water temperatures rise, and now we can add another to the roster—blue crabs. Although blue crabs are traditionally caught off Maryland and Virginia, fishermen in Long Island Sound have been seeing more of them lately. Some think that, in time, Long Island Sound could replicate the blue crab fishery of southern areas like Chesapeake Bay.

The blue crab, Callinectes sapidus, whose Latin name can be translated to mean “beautiful savory swimmer,” is the Maryland state crustacean and the most valuable shellfish in the mid-Atlantic region. The crabs can grow to be around 4 in long and 9 in wide, weighing around 1 pound, and reaching maturity in 12 to 18 months. The bottom-dwelling blue crab can live in a range of salinities, feeding off of crabs, claims, snails, eelgrass, sea lettuce and decayed vegetation. Blue crabs can be found all along the Atlantic Coast, with a prominent population in Chesapeake Bay presently suffering from habitat degradation and overfishing.

Could Maryland’s pride species create a new industry in New England Waters? The blue crab, caught for sale in both hard and soft shell forms, is currently sold at a market price in Maryland of $39.25 per dozen. With the growing blue crab population and a high demand market, does New England clam chowder have a new competitor on the way?

Scientists are careful to note that the long-term effects of climate change on species like blue crabs are still far too uncertain to predict the future of a fishery, but one thing is for sure—New England’s ocean is changing, and marine life is on the move.