Age class structure in fisheries and
wildlife managementWildlife management is a general term for the process of keeping wild species at desirable levels which are determined by the wildlife managers. Wildlife management can include game keeping, wildlife conservation and pest control...
is a part of population assessment. Age can be determined by counting growth rings in
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
scales, otoliths, cross-sections of fin spines for species with thick spines such as
triggerfishTriggerfishes are various, often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit warm coastal waters of the Atlantic, Mediterranean and the Indo-Pacific.-Anatomy and appearance:...
, or teeth for a few species. Each method has its merits and drawbacks. Fish scales are easiest to obtain, but may be unreliable if scales have fallen off of the fish and new ones grown in their places.
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Age class structure in fisheries and
wildlife managementWildlife management is a general term for the process of keeping wild species at desirable levels which are determined by the wildlife managers. Wildlife management can include game keeping, wildlife conservation and pest control...
is a part of population assessment. Age can be determined by counting growth rings in
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
scales, otoliths, cross-sections of fin spines for species with thick spines such as
triggerfishTriggerfishes are various, often brightly colored fish of the family Balistidae. Often marked by lines and spots, they inhabit warm coastal waters of the Atlantic, Mediterranean and the Indo-Pacific.-Anatomy and appearance:...
, or teeth for a few species. Each method has its merits and drawbacks. Fish scales are easiest to obtain, but may be unreliable if scales have fallen off of the fish and new ones grown in their places. 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, but obtaining them requires killing the fish. Also, otoliths often require more preparation before ageing can occur.
Analyzing fisheries age class structure
An age class structure with gaps in it, for instance a regular
bell curveIn probability theory and statistics, the normal distribution or Gaussian distribution is a continuous probability distribution that describes data that cluster around a mean or average. The graph of the associated probability density function is bell-shaped, with a peak at the mean, and is known...
for the population of 1-5 year-old fish, excepting a very low population for the 3-year-olds, implies a bad
spawningSpawning is the production or depositing of large quantities of eggs in water. The process is done by aquatic animals such as amphibians and fish.- Types of egg-layers :*egg scatterers*nest builders*egg hangers*mouth breeders*egg buriers...
year 3 years ago in that species.
Often fish in younger age class structures have very low numbers because they were small enough to slip through the
samplingSampling is that part of statistical practice concerned with the selection of individual observations intended to yield some knowledge about a population of concern, especially for the purposes of statistical inference....
nets, and may in fact have a very healthy population.
See also
- Population pyramid
A population pyramid, also called age-sex pyramid and age structure diagram, is a graphical illustration that shows the distribution of various age groups in a population , which normally forms the shape of a pyramid.It typically consists of two back-to-back bar graphs, with the population plotted...
- Population dynamics of fisheries
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...