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Age class structure refers to the distribution of individuals in a population through different age groups. This is one tool used in fisheries and wildlife management as part of population assessment and modeling.
Age class structures can be used to model population structures of many species including vertebrates, invertebrates, and vegetation. These models allow for the prediction of growth or decline in a population based on current conditions or future management practices. Age class structures can be used to help focus management on a certain age class to obtain the desires population size outcomes.
For example, when managing a population of white tail deer targeting a specific age and sex can alter the population pyramid type to either increase, decrease, or stabilize population growth. If you start off with a rapid growth age class structure, then targeting the juveniles who are not reproductive yet will help stabilize the population to a slower growth or no growth. This will make the number of juvenile females to closer the number of females who are aging out of the reproductive age. Targeting a specific sex will also alter the age class data. If looking to reduce the population then targeting hunting efforts on females will have a more impactful change. [1] Removal of older individuals and males will increase the population by opening up resources for reproductive females and juveniles.
Age can be determined by counting growth rings in fish scales, otoliths, cross-sections of fin spines for species with thick spines such as triggerfish, [2] or teeth for a few species. [3] [4] Each method has its merits and drawbacks. Fish scales are easiest to obtain, but may be unreliable if scales have fallen off the fish and new ones grown in their places. [5] Fin spines may be unreliable for the same reason, and most fish do not have spines of sufficient thickness for clear rings to be visible. Otoliths will have stayed with the fish throughout its life history, [2] but obtaining them requires killing the fish. [6] Also, otoliths often require more preparation before ageing can occur. [5]
An example of using age class structure to learn about a population is a regular bell curve for the population of 1-5 year-old fish with a very low population for the 3-year-olds. An age class structure with gaps in population size like the one described earlier implies a bad spawning year 3 years ago in that species. [7] Often fish in younger age class structures have very low numbers because they were small enough to slip through the sampling nets, and may in fact have a very healthy population. [8] This could skew class structure data and result in imaccurate management techniques.
Aging trees is perforned throough several methods, the first being to count the trees annual growth rings and the second is to calculate using the growth factor and circumference. After a wildfire, depedning on the severity, some of the forest will experience a loss in the population of several species. This interference can drastically alter an age class structure. If the fire was low intensity and burned low to the ground killing only young trees, then the age strucutre would be heavily skewed towards having many older mature trees and very few young trees. Wild fires can alter age class structures [9] by removing individuals in certain age classes and altering the type of population pyramid the species is experiencing. This shift in age class structures can also help predict how quickly the forest will rebound from the disturbance.
In population ecology and economics, maximum sustainable yield (MSY) is theoretically, the largest yield that can be taken from a species' stock over an indefinite period. Fundamental to the notion of sustainable harvest, the concept of MSY aims to maintain the population size at the point of maximum growth rate by harvesting the individuals that would normally be added to the population, allowing the population to continue to be productive indefinitely. Under the assumption of logistic growth, resource limitation does not constrain individuals' reproductive rates when populations are small, but because there are few individuals, the overall yield is small. At intermediate population densities, also represented by half the carrying capacity, individuals are able to breed to their maximum rate. At this point, called the maximum sustainable yield, there is a surplus of individuals that can be harvested because growth of the population is at its maximum point due to the large number of reproducing individuals. Above this point, density dependent factors increasingly limit breeding until the population reaches carrying capacity. At this point, there are no surplus individuals to be harvested and yield drops to zero. The maximum sustainable yield is usually higher than the optimum sustainable yield and maximum economic yield.
The orange roughy, also known as the red roughy, slimehead and deep sea perch, is a relatively large deep-sea fish belonging to the slimehead family (Trachichthyidae). The UK Marine Conservation Society has categorized orange roughy as "vulnerable to exploitation". It is bathypelagic, found in cold, deep waters of the Western Pacific Ocean, eastern Atlantic Ocean, Indo-Pacific, and in the eastern Pacific off Chile. The orange roughy is notable for its extraordinary lifespan, attaining over 200 years. It is important to commercial deep-trawl fisheries. The fish is a bright, brick-red color, fading to a yellowish-orange after death.
A marine reserve is a type of marine protected area (MPA). An MPA is a section of the ocean where a government has placed limits on human activity. A marine reserve is a marine protected area in which removing or destroying natural or cultural resources is prohibited, marine reserves may also be "no-take MPAs,” which strictly forbid all extractive activities, such as fishing and kelp harvesting. As of 2007 less than 1% of the world's oceans had been set aside in marine reserves. Benefits include increases in the diversity, density, biomass, body size and reproductive potential of fishery and other species within their boundaries.
An otolith, also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule and utricle, in turn, together make the otolith organs. These organs are what allows an organism, including humans, to perceive linear acceleration, both horizontally and vertically (gravity). They have been identified in both extinct and extant vertebrates.
Broodstock, or broodfish, are a group of mature individuals used in aquaculture for breeding purposes. Broodstock can be a population of animals maintained in captivity as a source of replacement for, or enhancement of, seed and fry numbers. These are generally kept in ponds or tanks in which environmental conditions such as photoperiod, temperature and pH are controlled. Such populations often undergo conditioning to ensure maximum fry output. Broodstock can also be sourced from wild populations where they are harvested and held in maturation tanks before their seed is collected for grow-out to market size or the juveniles returned to the sea to supplement natural populations. This method, however, is subject to environmental conditions and can be unreliable seasonally, or annually. Broodstock management can improve seed quality and number through enhanced gonadal development and fecundity.
The crevalle jack, also known as the common jack, black-tailed trevally, couvalli jack, black cavalli, jack crevale, or yellow cavalli is a common species of large marine fish classified within the jack family, Carangidae. The crevalle jack is distributed across the tropical and temperate waters of the Atlantic Ocean, ranging from Nova Scotia, Canada to Uruguay in the western Atlantic and Portugal to Angola in the eastern Atlantic, including the Mediterranean Sea. It is distinguishable from similar species by its deep body, fin colouration and a host of more detailed anatomical features, including fin ray and lateral line scale counts. It is one of the largest fish in the genus Caranx, growing to a maximum known length of 124 cm and a weight of 32 kg, although is rare at lengths greater than 60 cm. The crevalle jack inhabits both inshore and offshore waters to depths of around 350 m, predominantly over reefs, bays, lagoons and occasionally estuaries. Young fish dispersed north by currents in the eastern Atlantic are known to migrate back to more tropical waters before the onset of winter; however, if the fish fail to migrate, mass mortalities occur as the temperature falls below the species' tolerance.
The gulper shark is a long and slender dogfish usually about three feet in length generally found in deep, murky waters all around the world. It is a light grayish brown, paler ventrally, with a long snout and large greenish eyes. This deep water shark has two dorsal fins with long, grooved spines and the second dorsal fin smaller than the first. Its upper teeth are blade-like and lower have finely serrated edges. This tertiary consumer feeds on mainly fish such as bony fish, but also cephalopods such as squid and other invertebrates like crustaceans. The gulper shark is currently an endangered species mainly because of exploitation by humans and their abnormally long gestation period and low fecundity, preventing their population from recovering. Because of the depth of their habitat, they are considered little to no threat to humans.
The pink cusk-eel, Genypterus blacodes, is a demersal species of cusk-eel in the family Ophidiidae found in the oceans around southern Australia, Chile, Brazil, and around New Zealand except the east coast of Northland, in depths of 22 to 1,000 metres. It is found in the Chilean Patagonia fjords, one of the least researched ocean regions in the world.
The California sheephead is a species of wrasse native to the eastern Pacific Ocean. Its range is from Monterey Bay, California, to the Gulf of California, Mexico. It can live for up to 20 years in favorable conditions and can reach a size of up to 91 cm (3 ft) and a weight of 16 kg (35 lb). It is carnivorous, living in rocky reef and kelp bed habitats, feeding primarily on sea urchins, molluscs, and crustaceans.
The lingcod or ling cod is a fish of the greenling family Hexagrammidae. Despite it's name, the lingcod is neither a cod nor a ling. It is also known as known as the buffalo cod, cultus cod, or Buckethead. It is the only extant member of the genus Ophiodon. A slightly larger, extinct species, Ophiodon ozymandias, is known from fossils from the Late Miocene of Southern California.
Scombrops boops is a species of marine ray-finned fish, a gnomefish from the family Scombropidae in the suborder Percoidei. This species is the most widespread of the Scombropidae, which consists of only four extant species globally. Most of the information about the Scombropidae family is unknown, as they are rarely researched.
The Pacific ocean perch, also known as the Pacific rockfish, rose fish, red bream or red perch, is a fish whose range spans across the North Pacific : from southern California around the Pacific rim to northern Honshū, Japan, including the Bering Sea. The species appears to be most abundant in northern British Columbia, the Gulf of Alaska, and the Aleutian Islands.
The narrownose smooth-hound is a species of houndshark in the family Triakidae.
The leopard coral grouper, also known as the common coral trout, leopard coral trout, blue-dotted coral grouper or spotted coral grouper, is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serranidae, which also includes the anthias and sea basses. It is found in the Western Pacific Ocean.
A fishery is an area with an associated fish or aquatic population which is harvested for its commercial or recreational value. Fisheries can be wild or farmed. Population dynamics describes the ways in which a given population grows and shrinks over time, as controlled by birth, death, and migration. It is the basis for understanding changing fishery patterns and issues such as habitat destruction, predation and optimal harvesting rates. The population dynamics of fisheries is used by fisheries scientists to determine sustainable yields.
This is a glossary of terms used in fisheries, fisheries management and fisheries science.
Stock assessments provide fisheries managers with the information that is used in the regulation of a fish stock. Biological and fisheries data are collected in a stock assessment.
Knowledge of fish age characteristics is necessary for stock assessments, and to develop management or conservation plans. Size is generally associated with age; however, there are variations in size at any particular age for most fish species making it difficult to estimate one from the other with precision. Therefore, researchers interested in determining a fish age look for structures which increase incrementally with age. The most commonly used techniques involve counting natural growth rings on the scales, otoliths, vertebrae, fin spines, eye lenses, teeth, or bones of the jaw, pectoral girdle, and opercular series. Even reliable aging techniques may vary among species; often, several different bony structures are compared among a population in order to determine the most accurate method.
Fisheries-induced evolution (FIE) is the microevolution of an exploited aquatic organism's population, brought on through the artificial selection for biological traits by fishing practices. Fishing, of any severity or effort, will impose an additional layer of mortality to the natural population equilibrium and will be selective to certain genetic traits within that organism's gene pool. This removal of selected traits fundamentally changes the population gene frequency, resulting in the artificially induced microevolution by the proxy of the survival of untargeted fish and their propagation of heritable biological characteristics. This artificial selection often counters natural life-history pattern for many species, such as causing early sexual maturation, diminished sizes for matured fish, and reduced fecundity in the form of smaller egg size, lower sperm counts and viability during reproductive events. These effects can have prolonged effects on the adaptability or fitness of the species to their environmental factors.
The Deacon Rockfish is a marine ray-finned fish belonging to the subfamily Sebastinae, which is part of the family Scorpaenidae. Its body is compressed with large pectoral fins, prominent head ridges, well-developed spines, and large eyes, making it well-adapted for life along rocky substrates-from which its common name is derived. Native to the Eastern Pacific Ocean, Deacon Rockfish ranges from British Columbia to central California where it is found on nearshore and offshore rocky reefs.
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