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Our Dying Planet An Ecologist's View of the Crisis We Face

  • by Peter Sale (Author)
  • September 2011
  • First Edition
  • Paperback
    $29.95,  £24.00
    eBook
    $29.95,  £24.00
  • Title Details

    Rights: Available worldwide
    Pages: 360
    ISBN: 9780520274600
    Trim Size: 6 x 9
    Illustrations: 12 b/w photographs, 8 line illustrations

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Overfishing

We have always been fishermen. Fishing extends far back into our human past, and as our last remaining hunter-gatherer activity it ties us to that past in a tangible way. We capture wild aquatic organisms for personal use and to trade with other people. Most, but not all, of these fishery products are used for food. A trout fisherman on a Scottish stream who ties his own flies and approaches his sport with a quasi-religious fervor may have very little in common with the Malaysian peasant who fossiks at low tide for edible shellfish and crabs to feed her family, but both are part of fishing. So too are the giant multinational corporations, with their fleets of factory trawlers, their thousands of miles of longlines and nets, and their flash-frozen tuna air-lifted from deck to jet to Japan. Fishing is a vast global enterprise with a sophisticated array of technology and millions of people all engaged in extracting aquatic organisms from rivers, lakes, and oceans, trading them around the world, and consuming them in many different ways.

While we have always fished, we seem also to have usually overfished, leading to the reduction and sometimes the loss of formerly valuable fishery resources. Until recently, the consequences of such overfishing were generally local and temporary. Now, for the first time in human history, we face the possibility of widespread, essentially permanent collapse of the most important fisheries around the globe. Our continuing tendency to overfish is surprising given the investment in fisheries management around the world; on the surface, it does not seem to be that difficult to manage catch so that it does not exceed the capacity of the fished populations to supply.

Coastlines throughout the world provide scattered evidence of ancient fishing successes in the form of aboriginal middens-large piles of shells, bones, or other debris resulting from the capture, butchering, and presumably eating of the catch over many days and years by members of past cultures. In many middens, the size of the shells and bones varies with depth, with the largest buried deep in the oldest layers and the smallest occurring in the younger layers near the surface. This is evidence of ancient overfishing. The sizes of organisms being caught declined over time because, in all probability, the fishing was sufficiently intense to lower the life expectancy of the fished species. They lived less long, on average, before being caught and no longer reached the sizes they had in past years. And while we cannot tell this from examining a midden, it is very likely that as they became smaller over time, the animals being caught also became less common and harder to catch. Ancient fishermen often overfished and at some point had to search for new fishing grounds.

Most fish are remarkably fecund animals, producing thousands, sometimes millions, of eggs in a lifetime. Most also reproduce through external fertilization so that the female matures a clutch of eggs within her body before mating with a male. Most fish also grow in size throughout life, and because eggs take up space in the body cavity before they are laid, older, larger females are markedly more fecund than youngsters. Many fish also live for decades if not caught first. These life-history characteristics mean that fish populations can be remarkably productive, able to replenish their numbers rapidly following a decline in population size. The relative lack of parental care and the small size of newly hatched fish ensure that fish breeding success is strongly dependent on environmental conditions and a certain amount of luck-a fish population of a given size can produce an enormous cohort of young fish one year and far fewer the next.

Fishing is currently big business and vital to our food supply. The United Nations Food and Agriculture Organization (FAO) reports that, according to 2008 data, fishing provides 15.3 percent of the animal protein needs of the human population worldwide, or about 16.7 kg of fish per person per year. Commercial fishing directly employs about 44 million people and brings about 92 million metric tons of product to market every year, while aquaculture provides an additional 51.7 million metric tons. These fishery products are worth about US$91.2 billion and $78.8 billion per year, respectively, and the international trade in fishery products exceeds $92 billion per year. Adding in so-called illegal, unreported, and unregulated catches and the fish caught by recreational fishermen and by artisanal fishermen to feed their families around the world further increases the total tonnage of fishery species captured to 130 million metric tons per year.

The FAO also reports that the total world catch has been declining at the rate of about 0.7 million metric tons per year since about 1988, despite increases in fishing efforts. Globally, fishing is still very big business, but fisheries are failing to provide as they used to.

The decline in total commercial catch is one of several signs that our tendency to overfish is pushing us up against firm limits and that future catches may become far less bountiful than they have been. In this chapter we will look at fishing, sustainable fishing, and overfishing. We'll get into the science behind fisheries management and the reasons why management so often fails. I hope you'll become more aware of what takes place to make those fish available in grocery stores, and that you will appreciate the need to fish much more sustainably than we currently do. Along the way I will also touch on the more general problem of overuse of natural resources.

The Cod Fishery of the Northwest Atlantic

When John Cabot returned to England in 1497, he brought with him tales of plentiful Atlantic cod (Gadus morhua) of such size and abundance that catching these fish was simple. There were even claims that the fish were so abundant as to impede the progress of ships. Southern Europeans came to refer to the lands Cabot had found as Baccalaos, from the Spanish bacalao, the cod. The Portuguese had commenced fishing for cod off Newfoundland by 1501, followed shortly by the French and Basques. This commercial cod fishery was to last for almost five hundred years.

Initially, fishing off Newfoundland was an entirely ship-based operation. Ships sailed from Europe in the spring, fished intensively, salting down the catch in barrels, and returned home to the markets. But early on, the British, French, and Basques established shore camps where they could land the catch, salt it, and air-dry it. It was then packed dry for transport to the European markets; as a lighter product it was more economical to ship and, as a less heavily salted product, it was preferred by the public. To this day, many Europeans along the Mediterranean coast prefer dried, salted cod to the fresh product.

The colonization of Newfoundland was a direct consequence of the growing commercial fishery. Initially it involved the construction of seasonal dwellings for the people who worked the fishery processing the catch for shipment home. Gradually, seasonal dwellings became year-round homes as investments in real property began to require guarding it through the winter, but it was always the cod industry sustaining the development. Wars in Europe altered the overall fishing effort and the countries involved in the trade, and periodically the cod stocks failed, but on average the overall harvest grew year by year. As early as 1683, the problem of "overcapacity" was recognized by the Colonial Office in London-an excess demand for fish had fueled development of excess capacity (too many ships and nets) to catch them, and fishery stocks were failing.

Farther south, the Gulf of Maine cod fishery was "discovered," and Cape Cod named, by the crew of the Concord, a British ship sent to the New World to hunt for supplies of sassafras in 1602. Fishing vessels followed soon after, using the shores and the offshore islands of the gulf as suitable fish-drying sites. Fishing, and a Europe-based industry using seasonal dwellings on suitable shorelines, was well established by the time the first colonial settlements were being established in New England in 1620. However, the industry quickly became an American-based one, as local populations took up fishing, first in their immediate vicinity, and later in larger vessels venturing as far afield as the Grand Banks and northern Newfoundland. This was in contrast to the situation farther north, where the local Newfoundland and Nova Scotia populations operated inshore fisheries from smaller vessels and left the offshore fishery on the Grand Banks and the Labrador coast to be operated by larger vessels whose home ports were mostly in Europe. By the start of the eighteenth century, the Grand Banks fishery included vessels from England, France, Spain, and Portugal along with vessels from New England.

The cod trade grew so important that it became a vital source of foreign exchange for the developing American and Canadian colonies. It was incorporated into a profitable transatlantic trade in which the vessels that shipped dried cod to Europe returned with African slaves for the West Indies and southern American colonies, stocking up with sugar and salt in the West Indies before moving again to the fishing grounds of New England and the Grand Banks. Simultaneously, some vessels shipped the lower-quality fish south to feed the slaves in the West Indies and transported sugar back to Europe.

In these early days, fishing was done by hand-line from the decks of the vessel. Beginning in the nineteenth century, however, new methods were developed. Cod seines, gill nets, and cod traps were used to a limited extent in coastal waters, and small dories began to be carried by the offshore vessels so that hand-liners could spread out over a wider area to fish. By the 1850s, longlines with hundreds of hooks began to replace hand-lining in the offshore fishery, but it was at the start of the twentieth century, with the arrival of trawling, that fishing methods made a major advance in effectiveness.

The otter trawl was introduced to the U.S. Atlantic seacoast in 1908 but was not used in Newfoundland waters until 1935. An otter trawl consists of a large baglike net that can be dragged across the seafloor, with two large otter boards, or doors, mounted on the towing lines at the ends of the trawl's wings-the outer corners of its mouth. The doors can be as big as garage or barn doors and may each weigh 1,000 kg in commercial trawls that have mouths 100 meters wide. The doors are rigged so that hydrodynamic forces tend to move them outward, spreading the wings and pulling the mouth of the net open. Floats or kites lift the headline of the net to keep the mouth open vertically, and the footline is weighted and protected in various ways to keep the net in close contact with the substratum. The otter trawl proved to be very efficient at catching cod and other groundfish, and trawling became the principal method of capture in this fishery.

In addition to the introduction of trawling technology, the twentieth century saw increased use of steam and diesel power, of refrigeration and flash-freezing, and of long-distance rapid transport to market by truck, train, and plane. The result was that the Northwest Atlantic fishery was presented with an ever-expanding market and the temptation to continue to expand the fishing effort to supply the demand.

So what do we see when we look at the catch of cod? Detailed examination of the early fishery, region by region, reveals many examples of stock declines and resulting poor catches, but the solution was simply to expand to new fishing grounds. For example, a failure of the southern and southeastern inshore Newfoundland fishery in 1715 provided the impetus for expansion to the northeastern Newfoundland shore and for a progressive expansion of fishing on the Grand Banks. And with each shift to more distant fishing grounds there was a shift toward larger vessels and more fishing effort to cover the additional costs. The growth in the catch proceeded as the area being fished expanded, as technology advanced, and as markets opened up. By 1765, the total catch for Newfoundland, the Grand Banks, Georges Bank, and coastal waters was about 180,000 metric tons, supporting a brisk trade with Europe and the West Indies. Catches declined during the American War of Independence but then recovered. By the mid-1800s, the total catch of cod from the Northwest Atlantic was about 200,000 metric tons, but it increased further, reaching 260,000 by the early 1870s. By 1895, the Northwest Atlantic cod fishery was landing 420,000 metric tons, and it continued at about this level, fluctuating between 400,000 and 700,000 metric tons, through to the Second World War. By 1955, the catch had reached about 1,000,000 metric tons, and it peaked at about 1,900,000 metric tons in 1968. Thereafter, catches declined progressively, to about 500,000 metric tons in 1975 and 80,000 metric tons in 1990. The Canadian government closed the northern cod fishery in 1992 and all groundfishing in Canadian Atlantic waters in 1993. Since then, cod stocks have shown minimal recovery. A commercial fishery that had provided enormous economic and nutritive benefits over five hundred years was finished.

From the commencement of commercial fishing, there were local declines or outright failures in the cod fishery. With hindsight, it's possible to see that in a situation in which anyone with the funds to secure a vessel could join the fishery, there was always a tendency to overfish local cod stocks. In the 1600s and 1700s, fishing was restricted to those locations that were near to land or home ports. When fishing yield declined in those locations, it was possible to travel to new locations. The result was that diminished stocks often had a chance to recover, while the fishery was sustained commercially by turning to previously unfished stocks. However, once the fishery grew so large that all fishable locations in the region were being fished, the tendency to overfish still reduced stocks, but there was nowhere else for the fishing effort to go.

If fishermen were not inventive and had continued using hand-lines from relatively small boats, it is possible that the catch of cod would never have grown to the size it did, and the collapse of the 1990s would not have occurred. But that is not the nature of fishing. Fishermen are wily predators, always looking to innovate to capture their prey faster and more economically.

The collapse of the cod fishery provides three clear lessons. First, there is a profound difference between the local failures that occurred from time to time during the early years of the fishery and the final overall collapse. Second, the combination of growing demand and improving technology led to ever-expanding effort and ever-growing yield up until the eventual collapse. Third-but not evident from the information I've provided so far-the fishing effort acted in concert with other factors to bring about the decline in cod populations. To fully understand what happened, it is necessary to move beyond a focus on effort and catches to examine the myriad factors that determine how abundant a population of fish will be and how fishing changes that. To do this we have to dip into theory. It's not particularly complicated theory, so bear with me.

Effects of Fishing on Fish Populations

Logic dictates that populations of fish (or other species) grow when more fish are born than are dying, and they decline when more fish die than are being born. Ideally, a population will remain at constant size if each female produces, on average, the number of offspring needed to ensure that exactly two of them will reach adulthood and breed in their turn. (Two are required because in most species of fish, as in other animals, 50 percent of offspring are males.) That a female cod spawns millions of eggs each year and can live up to twenty more years after reaching maturity at five or six years tells us that very few hatched cod eggs grow up to become adult spawning cod. There are lots of things that happen to kill cod, nearly always well before they reach sexual maturity. Only one of these is fishing, which principally kills older fish.

From the perspective of the fish, fishing is just one more form of predation-one more challenge in its struggle to survive and reproduce. When fishing commences on a previously unfished population, it increases the chance of mortality, with the result that fish live, on average, less long before they die. In addition, fishing is a size-selective form of predation that tends to have the greatest impacts on the larger and older members of the population. While Atlantic cod can live for twenty-five years or more, by the early 1990s fishing was so intense that most cod were being caught before they were seven years old.

Because of these basic facts, there are several consequences of starting to fish a population. First, because animals tend to die younger, the population tends to become smaller than it was before, because each individual is present for a shorter period of time. Second, because the animals tend to die younger, they have fewer seasons after reaching sexual maturity in which to spawn-two or three seasons versus as many as twenty seasons in the case of cod. The result is that each successful fish (one that reproduces at least once) produces fewer offspring over its (shortened) lifespan. Furthermore, because fish are more fecund when they are older, the actual reduction in the production of offspring is substantially greater than the reduction in the number of spawning seasons might suggest.

Given these simple facts, how do we manage a fishery so that it can be maximally profitable without leading to the decline and extinction of the fished population? Managers have relied traditionally on three factors that may make it possible for fishing to increase predation on a population without wiping it out. These are density dependence, the storage effect, and the relationships among cost, catch, and effort in a fishery. The first two are aspects of how populations grow; the third is an economic relationship in the fishing activity.

Density dependence is central to ideas concerning the regulation of numbers in a population and for that reason has featured importantly in the history of ecology. It is also central to the simplest ecological model of population growth-the logistic model. As already noted, the pattern of growth of any population is determined by the pattern of births and deaths within it. Both birth and death rates depend upon the average age and condition of the individuals that make up the population, and by convention we speak of a per capita rate of increase, meaning "the rate per individual at which the population grows." Each member of the population requires food, shelter, and other resources in order to survive, grow, and potentially reproduce. When a population is small relative to its available resources, its individuals are likely in good condition-well fed, growing at maximal rates, healthy. They should possess a relatively high life expectancy and should produce offspring at a higher rate than individuals of a larger and denser population. The high per capita rate of increase causes that population to grow, but, following the logistic model, as the population grows the individuals will begin to experience shortages of resources such as food or shelter space. These shortages will cause the individuals to grow more slowly, be less fit overall, produce fewer offspring, and die at a younger age on average. As a result, per capita rate of increase falls, leading to a decline in the rate of growth of the population. Thus we can see that per capita rate of increase is dependent on the density of the population relative to its resources; because the dependence is negative, there is a tendency for any episode of population growth to cease and for the size of the population to stabilize. The population size at which this occurs is termed the carrying capacity of its environment-that size at which the availability of resources relative to the numbers of individuals competing for them sets birth and death rates to be exactly equal (see Figure 1). Animals are still busily growing, reproducing, and dying, but the rates at which these happen balance one another and keep the size of the population constant. The logistic model can be redrawn to show the rate of growth of the population at any given population size. The growth rate is at a maximum when the population is half the size it will ultimately reach at carrying capacity.

Looked at from the perspective of the fishing industry, this logistic curve indicates that if fishing reduces the size of the population from where it was before fishing started (its virgin state when it was presumably at carrying capacity), the capacity of the population to grow will become progressively greater until the point that the population has been reduced to half its virgin size. By fishing at a rate that removes individuals quickly enough to keep the population at this size, the fishery will gain the maximum sustainable catch that the fish population is capable of providing. (This statement is correct, but doing this in a real fishery is more difficult than it might seem.)

Very similar approaches are used to maximize yields in other harvested populations. We mow pastures for hay at a frequency designed to capture the burst of rapid plant growth before the plants become large and crowded. We harvest forests on a longer cycle but follow the same principle. And we take cattle and pigs to market at an age that optimizes growth prior to sale. In all these examples, we maximize yield because of density dependence, relying on the idea that younger and less-crowded organisms grow more rapidly.

Theoretically, by doing sufficient fishing to keep a fish population at this one-half of maximum size, a well-managed fishery will be able to fish indefinitely, taking the maximum sustainable yield (MSY) of fish per year, and the population will continue to produce into the distant future. Clearly this rosy future did not befall the cod or any of a number of other species.

There are two important things to notice about this simple model of density-dependent logistic growth. First, while the capacity of individuals to grow and reproduce is highest when the population is smallest (because there are ample resources available for each individual), the overall capacity of the population to grow more abundant will decline once the population is pushed below one-half of its virgin size (because a few individuals cannot produce large numbers of offspring quickly). The desirable one-half of virgin size for the population is not a stable equilibrium-the population will tend to move away from this point unless fishing is very closely regulated, and the further it is pushed below this point, the less capacity it will have for growth and recovery. If one is interested in the long-term yield of the fishery, seeking to fish at a rate that will achieve MSY is a very risky goal that demands exquisite control of the rate of fishing.

Second, this model assumes that the production of resources and the status of all other things in the environment that impinge on the condition of the fish are unvarying. If the availability of resources varies independently of the size of the fish population, if environmental temperature changes (so that metabolic rates, and therefore rates of growth for given caloric intake, change), or if any other environmental feature changes in a way that modifies the growth, fecundity, or survivorship of the fish, then carrying capacity, rate of population growth at a given population size, and the size of the population at which maximum yield is obtained all change. Under these circumstances, maintaining the population at the magic equilibrium size can become a very difficult task indeed. Needless to say, environments are rarely unvarying.

Variability of environmental characteristics is so pervasive that we should never forget it, even if the simple logistic model of population growth assumes variability is unimportant. In fact, fish populations have been telling us for a long time just how variable their environments are. They do this by demonstrating tremendous variability in recruitment.

Recruitment is the addition of a cohort to a population. It happens to armies when raw recruits go to boot camp, and it happens to biological populations when new groups of juveniles are added to the population each breeding season or when new groups of juveniles reach adulthood. Recruitment is a measure of progress through the ranks of the population, and it can be measured at any life stage. Fishery biologists frequently measure recruitment at the time that young individuals become large enough to be caught by the particular fishing gear being used. Ecologists tend to measure recruitment to specific life stages, such as to the juvenile stage following a larval period or to the adult stage at the time of maturation.

In a fish population, recruitment-whether you measure it at the end of larval life, at sexual maturation, or at the time the fish get big enough to be caught by a gill net of a particular mesh size-is profoundly variable from year to year. Science has known about this since 1914, when the Norwegian fishery biologist Johan Hjort documented the very great variation from year to year in recruitment to populations of a number of commercial fishery species in the North Sea. In the years since, it has become abundantly clear that the production of a new cohort of fish is a very risky business that is sometimes crowned with massive success and is at other times an absolute failure. Looked at another way, while only two of a female cod's millions of offspring are likely, on average, to reach maturity, the actual breeding success of individuals varies very widely around this average, and thus the breeding success of populations varies very widely from year to year.

In species that have relatively lengthy lives, such as most fishes, the population at any particular time is composed of a number of cohorts of individuals, each the product of recruitment in a particular year. Recruitment variability means that these successive cohorts start out at very different sizes and will probably preserve these differences throughout life. Indeed, the main conclusion of Hjort's classic study was that variation in recruitment results in the formation of occasional particularly abundant cohorts, so-called strong year-classes, that tend to dominate the catch and sustain the fishery over several years.

The main reason in fishes for variation in production from year to year is that there are years when greater proportions of newly hatched eggs survive and years when smaller proportions do. Why this happens is less easy to explain but has to do with environmental variability that modifies the likelihood of survival in these early stages. Given that a cod lays several million eggs in a season, it's clear that the probability of survival is normally very low indeed (or we'd be up to our necks in cod), so very modest changes in the chance of survival will lead to very large changes in the number of fish recruiting. Among the environmental changes that may be important are weather patterns that delay the plankton blooms the newly hatched fish depend on for food, ocean current patterns that carry the larvae to places that are quite unsuitable (or, alternatively, very suitable) for their survival and development, and temperature patterns that cause them to grow more quickly or more slowly than usual and thus alter the risk of predation on or the demands for food by these tiny larvae. (A slowly growing larva is small for a longer time and runs a greater risk of getting eaten because of this.)

In a population made up of relatively long-lived individuals, the effects of good recruitment can be "stored," meaning that the reproductive capacity of strong year-classes remains for many years, buffering recruitment variability. While a population with many year-classes of animals present will receive only a modest boost in overall numbers in years when recruitment is highly successful (because each year-class is only a small component of the total population), it can survive many years with very po