Common Resource Problem-Fishing

Transcription

1 Common Resource Problem-Fishing Many examples exist of how overfishing has brought about the collapse of fisheries such as Canada s northern cod fishery, innumerable salmon fisheries, many shell- fish fisheries, and important sardine and herring fisheries. Where fish stocks have not declined precipitously, fishing has reduced the resource stock or biomass (measured as the total weight of all fish species in the sea) of some fisheries to such a level that they are vulnerable to environmental shocks. According to Hilborn and Walters,(1992), a substantial part of the world s fisheries are biologically overexploited in the sense that if stocks were allowed to recover they would generate a higher yield or catch Biomass is a measure of the amount and the weight of fish that is in the sea at any moment in time Despite this observation, the world s catch has continued to increase.

2 Fishing Inputs Increased fishing pressure in capture fisheries can also be measured in terms of fishing inputs. TOTAL FISHING EFFORTS is measured by the vessels and engines, the gear used to find and harvest fish, the labor, fuel, and bait used up when catching fish and the processing facilities to render the fish into a consumable product. A common used single measure of fishing effort is the gross registered tonnage(grt) of fishing vessels. GRT indicates both a boat size and its ability to catch fish. Often larger vessels can stay longer at sea, fish in more difficult weather conditions, have more sophisticated search gear for finding fish etc Past twenty years, the GRT of all fishing vessels has increased in every region except Europe. Regional growth in GRT has ranged from 94 percent for the former Soviet Union (FSU) to 230 percent for Oceania over the period By contrast, over the same period, the world fish catch has increased by a little over 50 percent while the world s GRT has almost doubled.

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5 Fishing efforts and Related Catches

6 Fishing efforts and Related Catches We study the increasing fishing effort and declines in the catch and stocks of certain fisheries through both biological and economic models

7 The biology of Fisheries Many fish ensure their survival by producing enormous quantities of eggs (for some species a single female may produce hundreds of millions of eggs) but only a tiny proportion mature to larval fish, to juvenile fish, and eventually adults of spawning age. To help reduce predation, some species will spawn in shallower water or relatively protected areas (such as mangroves or reefs) where the likelihood of being eaten by larger fish is reduced. Fish are classified into 3 broad categories based on the location in the water column, feeding, migration habits and how they are caught

8 Fish Classifica4ons Pelagic species: they include tuna, sardines, herring, and anchoveta. They can travel large distances as adults and are nearly caught near the surface in schools. A favored method for larger pelagic is with baited hooks and lines. Demersal species: Examples include cod, plaice, pollock, snapper, haddock. They are often caught in mid-water or towards the sea bottom. Bottom trawls and mid-water trawls are the favored methods for catching demersal species. Shellfish species: examples include mollucs(mussels, clams,scallops, oysters, abalone) and crustaceans(lobsters, crabs, and shrimps). They are often caught close to the shore. Crustaceans are often caught with pots or traps where bait is used to lure the animals into a pot from which they cannot escape.

9 Biological Models To understand the dynamics of fish population, we will introduce 2 main classes of biological models. These models are used to estimate the current and desired levels of fish stocks and to determine the preferred harvest levels. : Stock-recruitment models Surplus production models.

10 Stock-recruitment models This model examines the relationship between the future recruitment into fishery to the current stock of fish.

11 Stock-recruitment models Stock-recruitment models postulates a density-dependent relationship between the number of recruits and the current stock. Thus, higher levels of stock do not necessarily imply higher levels of recruitment. This is because there is also a density-dependent mortality rate where higher levels of the stock increase the predation on the larval and juvenile fish due to cannibalism. The area under the curve can be classified into tow regions. The depensation region and non-depensation region. The Depensation region is the region to the left of the maximum recruits level. In this region, the recruit-stock ratio is increasing in the stock. In the depensation region, small changes in the stock can lead to large changes in recruitment. Equilibrium stock level is where the curve intersects the 45 degree line. At the equilibrium, recruitment exactly equals the current stock level.

12 Surplus Yield Models These models simply analyze the interac4on effects of the biomass and growth in the biomass on the fishery. They all assume density-dependent growth. Under this assumption, it is observed that the biomass has a tendency even in the absence of fishing to approach its maximum level(carrying capacity) but at a rate that depends on the size of the biomass.

13 Surplus Yield Models The fastest growth occurs when the biomass is at an intermediate level and its slowest growth is when the biomass is either close to zero or close to its carrying capacity. Growth in the biomass is zero when there are no fish, or when the biomass is at its carrying capacity. Maximum Sustainble Yield(MSY) is the equilibrium. It determines the biomass level that maximizes the growth of the biomass. MSY can also be explained as the biomass level that yields the highest harvest of fish without reducing the biomass.

14 Economic Models(Sta4c) Economic models differ from the biology models in that economic models focus on the maximization of the resource rent. In the economic fishing models, the concept of cost, revenue and profit is added to the biological concepts.

15 The total cost of harvesting decreases in biomass. That is, it takes more effort to catch a fish if the stock of fish is lower. The total revenue curve is inverted u-shaped. Maximum Economic Yield is the biomass level that maximizes the resource rent. In this case, the fish stock level that maximizes profit. In the absence of regulation, positive profit would further increase fishing that reduces the stock below MEY. It is also worthy to note that X MEY > X msy Additional fishing would occur until the resource rent is completely dissipated at point X iinf -Bionomic equilibrium. The tendency for a common resource to move towards X inf is called the tragedy of the commons. The bionomic equilibrium occurs below MSY

16 North Atlan4c Fishery

17 Development of North Atlantic Fisheries Earliest account show that there was abundant fish population including marine mammals, seabirds and turtles. On the eastern side of the North Atlantic, archeological evidence going back several thousand years shows that prehistoric hunters in other areas caught a wider variety of larger fish than now. In parts of northern Asia (now the Russian Federation), the salmon and sturgeon harvested were bigger, and there were 40% more species than found there now By all accounts, the western side of the North Atlantic was teeming with marine life. Early navigators, fishers and biographers report that one didn t need a hook, just a basket, to catch big cod and ships would bump into whales lazing on the surface.

18 There is good evidence that overfishing, (taking too many fish in a given area in a given 4me) has been going on in the North Atlan4c for several centuries. The sturgeons, salmon and tuna have all but ex4nguished, sailfish are rare. The evidence of overfishing is seen in indices such as: 1. Declining Catch:

19 Biomass Decline

20 Declining Trophic Level Trophic levels is a number ranging from 1in plants to 4 or 5 in larger predators. It expresses the relative position of organisms in the food chain hierarchically. Each type of fish has a certain position in a food web. Plants are at the lowest level (trophic level 1) in a food web, eaten by herbivores (level 2), which are eaten generally by successively larger animals, i.e., at higher trophic levels (e.g., levels 3 to 4). in the case of oceans, marine mammals and humans are at the highest levels (usually up to 5). Most marine species have mixed diets: a shark feeding only on cod that have a trophic level of 4.0 would itself be at level 5.0, but if the shark feeds equally on a small carnivore of level 3.0, then its trophic level would be 4.5. Most fish have trophic levels between 3.0 and 4.0. Various studies have shown that such changes in catch composition indicate changes in relative abundance in the underlying ecosystems., and thus reflect the collapse of large populations.

21 Declining Trophic levels

22 What is responsible for the problem 1. Conceptual failure: There was an erroneous mindset that the oceans cons4tuted a plen4ful supply of protein and the only management problem was was how best to exploit it. Even when it became apparent that was not the situa4on, scien4st in the 1950s developed the concept of Maximum Sustainable Yields(MSY) which predicated on the idea that up to a point catch fish actually increased the amount that could be caught. The theory jus4fied an annual catch allowances at about half the popula4on size of the fish. Problem is it is difficult to know th popula4on size of fish accoun4ng for the environmental variability, ecosystem and the food web. Distorted Economics: the price of fish which reflect the rela4ve scarcity rent has not deterred consumers. The price of fish has been rising faster than other food items but there is s4ll high demand. Also, governments all over the world subsidize fishing. The total annual cost of fisheries subsidies ranges between $15 billion and $20 billion. In north Atlan4c alone, annual subsidies are es4mated to be 2.5 billion per year for the late 1990s.

23 Interna4onal Arrangements: Fish are not restricted in their movement and thus, the prisoners dilemma problem is rife in fishery management. There is li[le incen4ve to curtail fishing in one country knowing that the other country benefits from your conserva4on.