Chapter 21 Key Concepts

Fish populations are renewable resources.
Fishery species are divided into stocks. Various tags and markers can be used to monitor them.
Biochemical and molecular markers of various types can also be used to diagnose differences among fish stocks that have become genetically isolated.
Stocks may be isolated from each other on the basis of use of the same drainage but at different times.
Stock identification can have important societal implications.
Finfishes are mainly caught by (1) hooking fishes individually, (2) entangling fishes in stationary nets, or (3) catching fishes in hauled nets or traps.
Bottom-associated animals are trapped in baited mesh traps. Unintended catches are known as bycatch.
Much of the world’s catch consists of bycatch, used for fishmeal, and targeted pelagic fish taken specifically for fishmeal. Bottom trawling may strongly alter the seabed.
The life history of a fishery species and the size of the stock must be understood before sensible planning can be done regarding fishery management.
The size of a stock is mainly assessed through quantity of landings by fishers, which is principally a function of the population size, the spatial variability of the fish, and the amount of fishing effort.
The health of a stock can be assayed by its production, which is explained in terms of growth of previous year classes and recruitment into the new year class.
At very low population densities, reproductive output per female might decline with declining population density.
Fishing can exert evolutionary changes in life history on fished populations.
More effective fishing approaches use models that show the impact of mortality on different life-history stages.
Fishery management strategies seek to maximize the sustainable yield.
Current thinking suggests that the concept of maximum sustainable yield may be difficult to apply quantitatively in fisheries management, but the principle can be used to create guidelines for catch limits.
Overview: Many fisheries are overfished, but proper management may allow recovery in many cases.
Open-seas fishing has focused on large carnivores at the apex of food chains.
Overfishing has caused major alterations in the trophic structure of the water column.
Apex predators may be in danger worldwide, with many species facing a major collapse.
Fishing pressure at lower levels of the food chain may also produce major ecological impacts.
Stock reduction can result from random variation as well as from environmental change; fishing would be superimposed on the effects of these factors and appears to cause greater fluctuations than when fishing is absent.
Fish stocks characterized by long generation times, small clutches of eggs, and fewer spawnings over time are the most vulnerable to overfishing.
Fishing technology, boat range, and even fishing policy have initiated or accelerated the decline of many stocks.
Ice retreat caused by anthropogenic climate change is opening up new areas for overexploitation, especially in subarctic areas such as the Barents Sea.
Jellyfish blooms around the world may be the combined result of overfishing, climate change, and pollution.
Climate change is a major anticipated cause of stock disruption and reduction.
Temporary closures and fishing limits allow some fisheries to be sustainable.
Catch shares, or individual transferable quotas, might produce a sustainable fishery.
Ecosystem-based management may allow the environment of a fishery to sustain resource populations.
The marine protected area concept can be adapted to fisheries management.
Many fisheries throughout the world, especially in poor, food-insecure nations, are practiced at a small scale and are not understood well enough in a world of big- fisheries policy thinking.
Most fishers in the world today participate in small- scale fisheries, which are crucial to food security for poor people around the world.
Mariculture might release fishing pressure of SSFs, but such benefits have yet to be realized. MPAs might reduce mariculture pressure but enhance artisanal fisheries at borders.
Whaling began as a shore-based fishery and then developed into an open-ocean fishery.
Open-ocean fishing technology resulted in the decline of blue whale populations.
Fish stocks can be affected by human degradation of water quality or fish habitats, or by killing of fish by means other than direct fishing.
Structural habitats are often endangered by human use. A multitiered strategy is essential for protection.
In mariculture, the habitats of some natural populations can be simulated, changed for convenience of harvest, or enhanced to increase yields.
Mariculture may be uneconomical, especially because of some ecologically damaging side effects.
Mollusk mariculture systems enhance the availability of substratum and are located in areas of high phytoplankton supply.
Mariculture of seaweeds may be useful in the production of products such as agglutinants, food, and organic matter suitable for methane production.
Fish farming is a major means of rearing finfishes such as salmon.
Genetic manipulation proves useful in improving performance of organisms in mariculture systems.
Compounds that evolved for a variety of ecological functions—including chemical defense, poisoning prey, and antimicrobial functions—can be adapted for human use as drugs.
Marine natural products are extracted from a wide variety of marine species and may be targeted at a number of specific functional human processes and diseases.
The great diversity of sources of marine bioactive compounds suggests that conservation of biodiversity and diverse marine habitats in turn creates a diversity of sources of compounds for drug discovery.