Age class structure

[[File:Wildfire_in_California.jpg|link=https://en.wikipedia.org/wiki/File:Wildfire_in_California.jpg|thumb|Age class structures can be used to determine when wildfires occurred within a forest population.]] '''Age class structure''' in [[fisheries]] and [[wildlife management]] is a part of population assessment. Age class structures can be used to model many populations include trees and fish. This method can be used to predict the occurrence of forest fires within a forest population.<ref name=":3">{{Cite journal|last=Wagner|first=C. E. Van|date=1978-06-01|title=Age-class distribution and the forest fire cycle|url=http://www.nrcresearchpress.com/doi/abs/10.1139/x78-034|journal=Canadian Journal of Forest Research|volume=8|issue=2|pages=220–227|doi=10.1139/x78-034|issn=0045-5067}}</ref> Age can be determined by counting growth rings in [[fish]] scales, [[otoliths]], cross-sections of fin spines for species with thick spines<ref name=":0">{{Cite book|title=Fisheries Long Term Monitoring Program|last=O’Sullivan|first=Sandra|publisher=Queensland Department of Primary Industries and Fisheries|year=2007|isbn=|location=Brisbane, Australia|pages=}}</ref> such as [[triggerfish]], or teeth for a few species<ref>Field, I.C., Meekan, M.G. & Bradshaw, C.J.A. (2009). ''Development of non-lethal methods for determining age and habitat use of sawfishes from northern Australia''. Australia: Australian Department of the Environment and Energy.</ref>. 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<ref name=":4">{{Cite web|url=http://www.fao.org/docrep/003/f0752e/F0752E04.HTM|title=MANUAL OF FISHERIES SCIENCE Part 2 - Methods of Resource Investigation and their Application|website=www.fao.org|access-date=2018-03-24}}</ref>. 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<ref name=":0" />, but obtaining them requires killing the fish<ref name=":5">Lux, Fred E. "Age Determination in Fishes". Washington, DC, United States: United States Bureau of Commercial Fisheries. Available at http://spo.nmfs.noaa.gov/Fishery%20Leaflets/leaflet488.pdf. Accessed 24/03/2018.</ref>. Also, otoliths often require more preparation before ageing can occur<ref>{{Cite web|url=http://www.fao.org/docrep/003/f0752e/F0752E04.HTM|title=MANUAL OF FISHERIES SCIENCE Part 2 - Methods of Resource Investigation and their Application|website=www.fao.org|access-date=2018-03-24}}</ref>. == Analyzing fisheries age class structure == An example of using age class structure to learn about a population is a regular [[Normal distribution|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 [[Spawn (biology)|spawning]] year 3 years ago in that species{{Citation needed|reason=This example needs a published source, to ensure this is not original research.|date=March 2018}}.

Often fish in younger age class structures have very low numbers because they were small enough to slip through the [[Sampling (statistics)|sampling]] nets, and may in fact have a very healthy population<ref>{{Cite book|title=Intensive Studies of Stream Fish Populations in Maine|last=Haines|first=Terry A.|publisher=U.S. Environment Protection Agency, Office of Acid Deposition, Environmental Monitoring and Quality Assurance|year=1990|isbn=|location=Washington, D.C., USA|pages=17}}</ref>.

See also

• Identification of aging in fish
• Population pyramid
• Population dynamics of fisheries