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A fishery population is affected by three dynamic rate functions: Birth rate or recruitment. Recruitment means reaching a certain size or reproductive stage. With fisheries, recruitment usually refers to the age a fish can be caught and counted in nets. Growth rate. This measures the growth of individuals in size and length.
At first, the population growth rate is fast, but it begins to slow as the population grows until it levels off to the maximum growth rate, after which it begins to decrease (figure 2). The equation for figure 2 is the differential of equation 1.1 ( Verhulst's 1838 growth model ): [ 13 ]
In fisheries and conservation biology, the catch per unit effort (CPUE) is an indirect measure of the abundance of a target species. Changes in the catch per unit effort are inferred to signify changes to the target species' true abundance. A decreasing CPUE indicates overexploitation, while an unchanging CPUE indicates sustainable harvesting. [1]
Fishing mortality (F) can be estimated by dividing the catch by the mean stock size. The catch includes annual commercial and recreational landings, along with dead discards. Bycatch discards would be estimated by estimating the percent of fish that are captured in a certain gear and the mortality associated with being captured in this gear.
Discards are the portion of a catch of fish which is not retained on board during commercial fishing operations and is returned, often dead or dying, to the sea. The practice of discarding is driven by economic and political factors; fish which are discarded are often unmarketable species, individuals which are below minimum landing sizes and catches of species which fishers are not allowed to ...
Catch shares provide long-term secure privileges to participants and, in theory, an incentive for efficient, sustainable use of fish stocks. [2] Actual outcomes in terms of efficiency and ecological sustainability are varied, based on design and implementation of the program. Catch share programs generally fall into two categories.
A metastudy in 2005 found that the average catch and release mortality rate was 18%, but varied greatly by species. [17] During an Oklahoma Department of Wildlife Conservation study, up to 43 percent of fish released after being caught died within six days as a result of inadequate holding and weigh in procedures during tournaments. [ 18 ]
Mark and recapture is a method commonly used in ecology to estimate an animal population's size where it is impractical to count every individual. [1] A portion of the population is captured, marked, and released.