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LOIE FULLER

FACTORS THAT INFLUENCE TIDES

THE ATLANTIC COD FISHERY

Off the northeastern shore of North America, from the island of Newfoundland in Canada south to New England in the United States, there is a series of shallow areas called banks. Several large banks off Newfoundland are together called the Grand Banks, huge shoals on the edge of the North American continental shelf, where the warm waters of the Gulf Stream meet the cold waters of the Labrador Current. As the currents brush each other, they stir up minerals from the ocean floor, providing nutrients for plankton and tiny shrimp-like creatures called krill, which feed on the plankton. Herring and other small fish rise to the surface to eat the krill. Groundfish, such as the Atlantic cod, live in the ocean’s bottom layer, congregating in the shallow waters where they prey on krill and small fish. This rich environment has produced cod by the millions and once had a greater density of cod than anywhere else on Earth.

Beginning in the eleventh century, boats from the ports of northwestern Europe arrived to fish the Grand Banks. For the next eight centuries, the entire Newfoundland economy was based on Europeans arriving, catching fish for a few months in the summer, and then taking fish back to European markets. Cod laid out to dry on wooden “flakes” was a common sight in the fishing villages dotting the coast. Settlers in the region used to think the only sea creature worth talking about was cod, and in the local speech the word “fish” became synonymous with cod. Newfoundland’s national dish was a pudding whose main ingredient was cod.

By the nineteenth century, the Newfoundland fishery was largely controlled by merchants based in the capital at St. John’s. They marketed the catch supplied by the fishers working out of more than 600 villages around the long coastline. In return, the merchants provided fishing equipment, clothing, and all the food that could not be grown in the island’s thin, rocky soil. This system kept the fishers in a continuous state of debt and dependence on the merchants.

Until the twentieth century, fishers believed in the cod’s ability to replenish itself and thought that overfishing was impossible. However, Newfoundland’s cod fishery began to show signs of trouble during the 1930s, when cod failed to support the fishers and thousands were unemployed. The slump lasted for the next few decades. Then, when an international agreement in 1977 established the 200-mile offshore fishing limit, the Canadian government decided to build up the modem Grand Banks fleet and make fishing a viable economic base for Newfoundland again. All of Newfoundland’s seafood companies were merged into one conglomerate. By the 1980s, the conglomerate was prospering, and cod were commanding excellent prices in the market. Consequently, there was a significant increase in the number of fishers and fish-processing plant workers.

However, while the offshore fishery was prospering, the inshore fishermen found their catches dropping off. (1) In 1992 the Canadian government responded by closing the Grand Banks to groundfishing. (2) Newfoundland’s cod fishing and processing industries were shut down in a bid to let the vanishing stocks recover. (3) The moratorium was extended in 1994, when all of the Atlantic cod fisheries in Canada were closed, except for one in Nova Scotia, and strict quotas were placed on other species of groundfish. (4) Canada’s cod fishing industry collapsed, and around 40,000 fishers and other industry workers were put out of work.

Atlantic cod stocks had once been so plentiful that early explorers joked about walking on the backs of the teeming fish. Today, cod stocks are at historically low levels and show no signs of imminent recovery, even after drastic conservation measures and severely limited fishing. Fishermen often blame the diminishing stocks on seals, which prey on cod and other species, but scientists believe that decades of overfishing are to blame. Studies on fish populations have shown that cod disappeared from Newfoundland at the same time that stocks started rebuilding in Norway, raising the possibility that the cod had migrated. Still, no one can predict whether and when the cod will return to the Grand Banks.

FEEDING HABITS OF EAST AFRICAN HERBIVORES

CLOUD FORMATION

Water vapor is an invisible gas, but its condensation and deposition products - water droplets and ice crystals - are visible to us as clouds. A cloud is an aggregate of tiny water droplets or ice crystals suspended in the atmosphere above the earth’s surface, the visible indication of condensation and deposition of water vapor within the atmosphere.

Laboratory studies have demonstrated that in clean air - air free of dust and other particles - condensation or deposition of water vapor requires supersaturated conditions, that is, a relative humidity greater than 100 percent. When humid air is cooled, usually by convection, unequal heating of the ground surface creates rising air currents. As the air ascends, it expands and cools. Eventually it reaches its dew point, the temperature at which the invisible water vapor in the air condenses into a collection of water droplets. From the ground, we see these tiny particles as a cloud. If the droplets continue to acquire moisture and grow large enough, they fall from the cloud as rain.

Clouds occur in a wide variety of forms because they are shaped by many processes operating in the atmosphere. In fact, monitoring changes in clouds and cloud cover often will provide clues about future weather. British naturalist Luke Howard was among the first to devise a system for grouping clouds. Formulated in 1803, the essentials of Howard’s classification scheme are still in use today. Contemporary weather forecasters still divide clouds into two main groups: heaped clouds, resulting from rising unstable air currents; and layered clouds, resulting from stable air.

Clouds are also classified according to their appearance, their altitude, and by whether or not they produce precipitation. Based on appearance, the simplest distinction is among cumulus, stratus, and cirrus clouds. Cumulus clouds occur as heaps or puffs, stratus clouds are layered, and cirrus clouds look like threads. Based on altitude, the most common clouds in the troposphere are grouped into four families: low clouds, middle clouds, high clouds, and clouds exhibiting vertical development. Low, middle, and high clouds are produced by gentle uplift of air over broad areas. Those with vertical development generally cover smaller areas and are associated with much more vigorous uplift.

Cumulus clouds are dense, white, heaped clouds capped with a cauliflower-like dome created by convection. Low-level cumulus clouds are detached from one another and generally have well-defined bases. Their outlines are sharp, and they often develop vertically in the form of rising puffs, mounds, domes, or towers. The sunlit parts are brilliant white; the base is relatively dark and roughly horizontal.

Stratus, or layered, clouds grow from top to bottom in wide sheets, or strata, with minimal vertical and extended horizontal dimensions. These clouds spread laterally to form layers that sometimes cover the entire sky, to the horizon and beyond, like a formless blanket. The air is stable, with little or no convection present.

While cumulus and stratus clouds generally form at low or middle altitudes, a third type of cloud forms at high altitudes. (1) Cirrus clouds are detached clouds that take the form of delicate white filaments, strands, or hooks. These clouds can be seen at close hand from the window of a jet plane flying above 25,000 feet. (2) When viewed from the ground, bands of threadlike cirrus clouds often seem to emerge from a single point on the western horizon and spread across the entire sky. Cirrus clouds are composed almost exclusively of ice crystals. (3) Their fibrous appearance results from the wind “stretching” streamers of falling ice particles into feathery strands called “mares’ tails.” (4) Snow crystals may fall from thicker, darker cirrus clouds, but they usually evaporate in the drier air below the cloud.