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An important part of environmental biology is determining the size of populations. Scientists, farmers, and wardens need to know a population size of species to make important decisions. For example the DNR needs to know the population of a species so they can set a hunting season. Farmers may need to know a size of an insect population to determine how much pesticides are needed or how much damage could be done to a crop.
However, animal populations are often too large and/or scattered to count directly. Therefore, scientists try to capture some of the animals, let them go, then recapture animals of the same species after the marked ones have mixed in with the general population. Obviously, when scientists try to catch animals the second time, they may get many which were NOT marked the first time. This is important because it allows them to make a good guess at how many animals in that species are really out there. Knowledge of a species' population size, then, is important for conservation scientists to make necessary decisions.
Mark and recapture, also known as the Lincoln-Pearson method in honor of two early contributors to its development, involves capturing individuals from a population of interest, marking them, releasing them for a relatively short period of time, and then later recapturing individuals from the same population and counting the number of marked and unmarked individuals. The size of the entire population can be accurately estimated from the proportion of marked and unmarked animals given that certain assumptions are met (as far as practicable).
These assumptions, taken from Southwood (1978) are:
1. The marked animals are not affected (neither in behavior nor life expectancy).
2. The marked animals are completely mixed in the population.
3. The probability of capturing a marked animal is the same as that of capturing any member of the population.
4. Sampling must be at discrete time intervals and the actual time involved in taking the samples must be small in relation to the total time.
When using the simple Lincoln Index it is also assumed that:
5. The population is a closed one, or, if not, immigration and emigration can be measured or calculated.
6. The are no births or deaths in the period between sampling or, if there are, allowance must be made for them.
DNR officers capture, mark ducks and record information about the animals
Source: DNR Iowa
Tagging Great White Sharks
Source: AP news
Even with additional mortality from hunting, trapping and depredation control efforts, Wisconsin's wolf population is about the same as this time last year, according to a preliminary estimate from the Department of Natural Resources.
The state's wolf population was estimated at between 809 and 831 animals in 216 packs over the winter of 2012-'13. The previous winter's estimate was 815 to 880 wolves in 213 packs.
The estimate was announced Friday in Wausau at the annual meeting of state wildlife officials, volunteer wolf trackers and other stakeholders.
The estimate is derived from aerial counts, ground observations of radio-collared wolves and tracking surveys. The work is conducted in winter when wolves are easiest to track and count, but also at a time when the population is near its annual low.
Wolf populations typically double in late spring after pups are born and then decline through late winter because of various sources of mortality.
"The population estimates from the last two years overlap, so we're considering it about even, perhaps a little bit down," said Dave MacFarland, DNR carnivore staff specialist. "The estimate this year tells us we had conservative measures in place last year, which was a goal."
From 1993 to 2012, wolves in Wisconsin had shown annual increases in both number of individuals and packs.
But in January 2012 the federal government removed the wolf from protections of the Endangered Species Act and states in the Great Lakes region resumed management of the species.
The Wisconsin Legislature passed Act 169 in April 2012, authorizing the first regulated wolf hunting and trapping season in state history.
With state management restored, the DNR announced its desire to reduce the wolf population to a "biologically and socially acceptable level."
The DNR established a nontribal harvest quota of 116 wolves in the state. Hunters and trappers killed 117 in a season that lasted slightly more than two months.
In addition to the wolves taken by hunters and trappers, 124 wolves were confirmed killed through other means in 2012, according to DNR records.
The other sources of mortality include 57 killed by federal wildlife agents, 22 hit by vehicles, 18 killed by landowners and nine killed illegally.
The DNR has begun a years-long process to update the state's wolf management plan. The plan will include a wolf population goal.
State wildlife managers will meet with its wolf advisory committee Tuesday in Wausau to begin setting wolf harvest quotas for the 2013 hunting and trapping season.
Weather for the birds: Faced with a mix of cold and snow and generally poor weather, hunters registered 7,092 turkeys in the first period of the 2013 Wisconsin spring turkey season, down 39% from the same period last year.
The figures are from a preliminary harvest report compiled by the DNR on Friday. The 2013 number is likely to change as reports are verified and finalized in the coming weeks and months.
Hunter success was 18% in this year's first period, down from 30% in 2012 and about half the average of 35% from 1998 to 2012.
As it stands, the 2013 first-period turkey registration is likely to be the second-lowest since period-specific data was collected in 1998.
Only in 1998, when 6,671 birds were taken, have fewer turkeys been registered in the first period.
And in each year, the first period was highest in turkey harvest. As weather improves this year, the following periods will have a chance to surpass the first period total. As an example, last year 8,868 turkeys were registered in the second period.
And as many as 8,766 (in 2008) turkeys have been taken in the third period and 7,854 killed in the fourth period (2007).
Weather is a primary factor in turkey reproduction and survival. It's also obviously a significant player in turkey harvest.
Source: Paul Smith Journal Sentinal
Source: Great Pacific Media