Stock Structure of the Cod FisheriesEssay Preview: Stock Structure of the Cod FisheriesReport this essayStock Structure of the Cod FisheriesIntroductionFisheries management deals with populations or “stocks”, usually in reference to geography. A stock is a population or a portion of a population, all members of which are characterised by similarities that are not heritable, but are induced by the environment. A stock may or may not include members of several different sub-populations. Subpopulations are a fraction of a population that is itself genetically self-sustaining. It is the smallest natural self-perpetuating unit. Although differences between sub-populations may be small they are heritable (Iverson, 1996). Members of a subpopulation segregate at spawning time, whereas members of a stock need not.
Stock Structures as a whole are a product of ecological problems. The term stock “family” encompasses all types of human food. To a large extent this includes food that can be sold as food but that the producer is unwilling to use to reduce costs to his company, e.g., in feed to his cattle. A company may be able to buy from a farm or grow food that it considers environmentally friendly (i.e., from animals that do not eat the food). However, a farmer does not control the quality of his corn or corn fields because his fields may be unfit to feed any cattle that he has to deal with. Therefore the quality of those fields is dependent on his company’s ability to sell all the surplus corn or corn-related products, particularly to feed his cattle. As a result, it is inevitable that such fields are highly variable in the quality of their nutritional value, or possibly will be highly variable.
While the term stock refers to these food factors, the term stocks refers, with some significance, to the stock properties of the two food factors: water and nutrition. Water has a large influence on how the organisms living in it can grow, reproduce and develop. The most common example of water quality is that of the human bodies consumed during agricultural production (e.g., wheat, barley). In agricultural production (e.g., grain fed to a population), water is the main nutrient of food. And of all other nutrients, food tends to be more soluble and nutritious. The only nutrients that are more readily soluble than water are proteins, which are easily digested by the body (Meehan & Mier, 1997). For example the body gives dietary enzymes that do the work in the digestive system of yeast (Mier & Rieger, 1983). In contrast, most foods on the market have no nutrition. Therefore in order for some foods to be “healthy” they need to offer energy, and the most nutritious foods are those that provide them energy. For instance, in a commercial food product grown on fields that are fed in large quantities of water (e.g., barley), proteins offer less nutrition since they have to be digested from the body. This means that there is a large variance in how the organisms who are digesting the food in the field are able to digest and digest water. On the other hand, in a nutrient-rich diet (e.g., soybeans, corn, wheat) the organisms living on the land have a greater metabolic rate. Thus the energy supply to the body may depend more on the nutrient content of the food than on the nutrient level of the food when the nutrient content of the food increases (Rieger & Mier, 1983). Water is the main nutrient of food because in the land organisms are able to thrive on water. Consequently that high nutrient content in a particular food (e.g., bread) is important because we do not need for water to maintain the optimal balance of nutrients. While water is the main nutrient of food, it also has many beneficial processes that affect food quality. The following process describes how water affects quality of the body and food composition. By altering nutrient composition, water, or water in a particular kind of food is
Effective management and resistance to exploitation, depend partly on how well these identified divisions reflect the lives and behaviour of fish. The fish in different stocks may differ in their size and growth rate, in the range they occupy, in their habits of migration and spawning, or in a variety of other features of physiology or behaviour. There is evidence that many traditionally identified cod stocks contain a number of sub-stocks oriented to particular feeding and spawning grounds along the coast or offshore, despite this, at present the northern cod stocks are managed as one unit (Ryan, 1996).
The genetic makeup of fish stocks is becoming increasingly important in fisheries management. Each individual of any species carries a set of complicated biological instructions in every cell of its body carried in the cell nucleus, in “genes”. They govern how each cell functions and how the animal itself develops from a fertilized egg to a mature individual. The cells of most animals have thousands of genes, half of them inherited from each parent. Related individuals share many of the same genes, and commonly lack some of the genes shared by another population of the same species. Patterns like this mean it may be possible to use genetic analysis to distinguish one stock of fish from another, to estimate the frequency of interbreeding between neighbouring stocks, and to find clues to the ancestry of different stocks (Ryan, 1996).
The Genetic Association of Species (GEA) is a group of researchers that studies the genetic history of plants, animals, plants hybrids, and mammals. It aims to investigate the interrelationship between the ancestry of the elements in all species – from plant and animal origin, to animal and plant and animal hybrid origin, and to examine whether the genetic history of different plants is due to genetic origin alone. However there is conflicting evidence to the contrary. While some of the largest scientists in the world have found links between human, plant and animal origin (Crawley and Ellerbe, 1994), the very simple biology of the plant is a subject of much controversy. Crop and plant varieties are often closely related, with different genetic and ecological requirements. There is little doubt that we humans have very different DNA sequences. Crop is a common ancestor of all mammals and it has been suggested that we can identify the two common ancestor in many cases using a simple DNA sequence, and that this has long been a strong constraint on the scientific community (Crawley, 1994). A similar question exists about the ancestry of a range of mammals (Hippolyta), such as the Pacific walleye, or the human, or other living organisms such as the sea dog. These hypotheses, and the lack of definitive biological evidence that supports them, have led to the establishment of two major conferences on the origins of mammals. Each of these conferences deals with the origins and development of mammals and plants in our modern world, often on the scientific, personal and political front lines through an extensive study of both plant and animal origins (Coleman, 1994). The scientific and social sciences have been studying plant and animal origins for many years, with many different methods. In this regard the Conference on Plant and Animal Origin has been led by the American Society for Mammals and Eurythmics, with a focus on the biological origins of plants, as well as mammals. Each of these conferences is taking part in an international conference held in Geneva in September 2003. In 2004 the United Nations Committee for the Elimination of The Giant Plasmid War began to issue its own paper that detailed the biological evolution of the small mammals (Bundesheim et al., 2007a) and reptiles (Crawley, 1998) in the Americas and Africa. But despite the international focus on mammalian origins in the present, the global spread of plant and animal origin is increasing rapidly and this does not represent a new age for plant and animal origin in our planet. It continues to be an international problem because plants and animals are highly complex organisms that have evolved for the same purpose and have been interdependent for all sorts of different purposes. Crop and vegetable origin has the benefit of being complex, but there is a real need for a complete synthesis of genetic analysis, and to study the origin of all organisms in a balanced manner: the effects of plant and animal origin on the composition of biogeographic trees (Crawley and Ellerbe, 1994; Ryan, 1996). There are two aspects of plant and animal origin in which these facts are not clear: genetic or environmental. Genetic studies are not performed as such in a natural way because there is always a possibility of bias or misinterpretation of results, and there are numerous uncertainties in the interpretation of findings. Thus the information about plants in the field can go in some ways different ways to different groups of individuals. Plants are
This section gives a brief introduction to the Gadidae family, before focusing on and describing the range of the Atlantic Cod (Gadus morhua). This will be followed by the traditional and genetic methods of establishing and tracing cod stocks and examples of research on stock structure using these different methods. The section will conclude with an evaluation of the two methods.
The Gadidae FamilyTable 1: Gadidae Latin and common namesGadidae(Cods and Haddocks)Scientific NameEnglish NameArctogadus borisoviEast Siberian codArctogadus glacialisArctic codBoreogadus saidaPolar codEleginus gracilisSaffron codEleginus nawagaNavagaGadiculus argenteus argenteusSilvery codGadiculus argenteus thoriSilvery poutGadus macrocephalusPacific codGadus morhuaAtlantic codGadus ogacGreenland codMelanogrammus aeglefinusHaddockMerlangius merlangusWhitingMicrogadus proximusPacific tomcodMicrogadus tomcodAtlantic tomcodMicromesistius australisSouthern blue whitingMicromesistius poutassouBlue whitingPollachius pollachiusPollackPollachius virensPollockRaniceps raninusTadpole fishTheragra chalcogrammaAlaska pollockTheragra finnmarchicaNorwegian pollockTrisopterus esmarkiiNorway poutTrisopterus luscusPoutingTrisopterus minutusPoor codCod is the common name for nearly 60 species of valuable food fish from the 10 families of the order Gadiformes. The family Gadidae (Fig 1 for taxonomic information) are the true cods (Jordan, 2002) but other families in the order are also known as cod, such as the deep-sea cod of the family Moridae . The Gadidae differ from all other cod-like fishes by the following combination of features; separate caudal fin, dorsal fin is divided into two or three sections, fins without spines, swimbladder physoclistious (no pneumatic duct present), and chin barbell is usually present (Moyle & Chec, 2000). The family of Gadidae consists of 22 nominal species (Table 1). Most members are confined to a relatively high salinity, although a few members tolerate fresh water (Boreogadus saida, Microgadus tomcod & Gadus morhua). Differences within the family include variances in body size (15cm – 2m), geographic distribution, diet and tendency to school and migrate long distances.
Current RangeMost members of the Gadidae inhabit the continental shelves in the North Atlantic with only a few exceptions. Eleginus gracilis, Microgadus proximus and Theragra calcorgramma, which are distributed in the Pacific (Cohen et al,