Estimating Fish Abundance - Mark Recapture Method

Transcription

1 Estimating Fish Abundance - Mak Recaptue Method Autho: Doug Lason Gade level: 7 th 9 th (see basic questions) o 10 th 12 th (see advanced questions) Class size: Goup size: 3-5 Setting: compute lab (o students bing laptops) Time needed: 50 minutes Equipment needed: Computes with Micosoft Office, calculato, Swedish Fish o Goldfish Cackes (100 fo goup 1 and 3; 150 fo Goup 2), (Altenatively, lesson can be conducted with dy kidney beans, o scap pape), scissos and/o a make. Objectives Composite Leaning Objective: Students will lean the basic pocedue by which fisheies manages calculate an estimated population size (N) in a closed system. Knowledge Outcomes: Students will lean the basic assumptions of mak-ecaptue population estimation, specifically the assumptions of a population estimate calculated using the Lincoln-Peteson method. Students will lean how sampling effot can affect estimated population sizes. Skills Outcomes: Students can calculate population size using the Lincoln-Peteson Method. Additionally, students can calculate a 95% confidence inteval. Students can apply the Lincoln-Peteson Method to actual data fom the Black Rive Steamside Reaing Facility and detemine an estimate of the adult male Lake Stugeon population in Black Lake in Disposition Outcomes: Students will have a bette gasp of how fisheies manages calculate the estimated population size of a theatened fish species. Students will view how manages calculate the havest quota using actual data, gaining an appeciation fo how data collection can infom consevation and management effots.

2 Backgound Lake Stugeon ae a highly mobile species that seasonally migate fom the Geat Lakes to ive habitats to spawn. As a esult, Lake Stugeon population numbes can be difficult to effectively estimate in most systems. As a esult of ovefishing, habitat loss, and pollution, many Lake Stugeon populations wee educed o, in some cases, eliminated fom thei histoical ange by the ealy 1900 s. Lake Stugeon ae classified as Endangeed, Theatened, o of Special Concen in 19 of the 20 states of its cuent ange, and potected in the Canadian wates of the Geat Lakes. In some systems, havest seasons exist, though estictions on the numbe of fishes havested by size, sex o pecentage of the population ae set. Lake Stugeon each epoductive matuity much late than othe fishes common to the Geat Lakes egion. A male Lake Stugeon eaches matuity aound age 15, while a female Lake Stugeon may not each matuity until age 25. As they age on a time scale simila to humans, Lake Stugeon pesent a unique challenge to manages looking to estoe histoical populations and manage existing fisheies. To manage annual havest and stocking goals, fisheies manages equie estimates of population size. Manages can use Mak-Recaptue techniques to estimate population size without handling evey individual in a population. Calculating a population estimate equies two sampling visits. Duing the fist visit (the making peiod ), the sample cew will collect as many individuals as possible in a standadized time peiod. Each individual captued will be given an identifying mak. Lake stugeon ae geneally maked with a PIT (passive integated tansponde) tag, which can identify each individual captued. Afte making, all fish ae eleased back into the system and given time to edistibute. Duing the second visit (the census peiod ), the sample cew will, again, captue as many individuals as possible in a standadized time peiod. Unlike the fist sample peiod, the cew will be looking fo ecaptues, o those fish which wee maked duing the fist collection peiod. Using the data collected duing the two sample peiods, we can calculate an estimate of the total population. The atio of the numbe of individuals maked to the estimate of the population size is elative to the atio of ecaptued individuals to the total numbe captued duing the census peiod. By coss-multiplying, we can solve this equation fo N, o ou estimate of the population size. This is epesented visually as: N Making Peiod M C Census Peiod M N C N C M N M C N MC N = Estimated population size M = Numbe of individuals captued and maked duing the Making Peiod C = Total numbe captued, including ecaptues, duing the census peiod. = Numbe of ecaptues

3 Definitions Endangeed A species of animal o plant that is seiously at isk of extinction. Theatened - Any species which ae vulneable to endangement in the nea futue. Special Concen - Though not endangeed o theatened, the species o has unique o highly specific habitat equiements o deseves caeful monitoing of its status. Repoductive matuity - The capability of an oganism to epoduce. Havest To take o kill fo food, spot, o population contol. Population size is the actual numbe of individuals in a population. Estimated Population size (N) - is the estimated numbe of individuals in a population. Mak-Recaptue A technique by which an estimated population size (N) is calculated by multiplying the numbe of maked individuals duing the making peiod by the numbe of individuals captued duing the census peiod, then dividing the poduct by the numbe of individuals ecaptued duing the census peiod. Making peiod (M) The fist sampling peiod of a Mak-Recaptue suvey. Duing this peiod, all individuals captued ae maked, and eleased. PIT (passive integated tansponde) tag - a small adio tansponde that contains a specific code, which allows individual fish to be assigned a unique 10 o 15-digit alphanumeic identification numbe. Census peiod (C) The second sampling peiod of a Mak-Recaptue suvey. Duing this peiod, all individuals ae checked fo maks fom the fist peiod. The numbe of ecaptues is documented as well as the numbe of fist time captues. Recaptues () Individuals captued duing the Census Peiod which wee captued and maked duing the Making Peiod. Immigation New individuals migate into the system. Emigation Individuals migate out of the system. Potamodomous A fish that migates to epoduce within fesh wate only Iteopaous An oganism that can undego many epoductive events thoughout its lifetime. Students will use a simple Lincoln-Peteson design, which opeates with the following assumptions: 1. All individuals in the population have an equal chance of being caught. 2. Making does not alte an individual s behavio making them moe likely to leave the aea, moe susceptible to pedation, o influence thei likelihood of being ecaptued. 3. Thee is no movement of new individuals into the population duing the sampling peiod as this changes the atio of maked vs. unmaked individuals in the population. This esults in an inceased likelihood of captuing unmaked individuals, inceasing you population estimate. (Immigation). 4. Fish leaving the population does not occu duing the sampling peiod as this changes the atio of maked vs. unmaked individuals in the population. This esults in a deceased likelihood of

4 captuing both maked and unmaked individuals, which can alte you population estimate (Emigation). 5. No new fish (biths) can ente the population, no can fish die. Pat 1. Mak Recaptue Activity (7 th 12 th gade) In pat 1, we will be estimating the population size of Swedish Fish o Goldfish Cackes so that you can examine the effect of violating assumptions on the final population estimate. Goup one will mak a numbe of fishes to simulate a making effot. Goup two will add unmaked individuals (immigation/bith) afte the making peiod. Goup 3 will emove individuals at andom (emigation/death) afte the making peiod. If the teache would pefe wok in smalle goups, goups one though thee can be eplicated, as needed. Pat A Testing Assumptions 1. Povide each goup with 100 Swedish Fish o Goldfish Cackes. 2. At andom select 10 individual fish and mak them. If using Swedish Fish o Goldfish Cackes, pefom a fin-clip by emoving a small potion of a fin. 3. Reintegate population allowing fo andom edistibution of maked and unmaked individuals. 4. Students in Goup 1 can move on to step 6. Students in Goup 2 should add an additional 50, unmaked fish to thei population. Goup 3 should emove 50 fish fom thei population at andom. Take cae to emove this fish without noting whethe the fish is maked. 5. Afte fish have been edistibuted, andomly sample 10 fish, ecoding the numbe of ecaptued fish fom the making peiod (ie: fin clipped fish). These fish ae the maked cohot. 6. Pefom the following calculation: N = MC whee: N = Estimated population Size M = The numbe maked duing the making peiod (10) C = Those captued duing the census peiod (C = 10) = Those captued duing the census peiod which wee maked duing the making peiod 7. Compae goup esults, identifying how violating the assumptions of the Lincoln-Peteson method changes the estimated population size (N). Pat B Modifying Effot

5 1. Split students into two goups low effot and high effot. 2. Povide each goup with 100 Swedish Fish o Goldfish Cackes. 3. Low effot goup At andom, select 10 individual fish and mak them. High effot goup At andom, select 25 individual fish and mak them. 4. Reintegate population allowing fo andom edistibution of maked and unmaked individuals. 5. Make sue you don t eat any fish! As seen in Pat 1, this can affect you population estimate. 6. Low effot goup At andom, select 10 individual fish ecoding the numbe which wee ecaptued fom the making peiod. High effot goup At andom, select 25 individual fish ecoding the numbe which wee ecaptued fom the making peiod. 7. Pefom the following calculation: N = MC ; whee: N = Estimated population Size M = The numbe maked duing the making peiod (10) C = Those captued duing the census peiod (C = 10) = Those captued duing the census peiod which wee maked duing the making peiod 8. Compae goup esults, identifying how violating the assumptions of the Lincoln-Peteson method changes the estimated population size (N). Pat 2. Mak Recaptue Black Rive Steamside Reaing Facility Data (10 th 12 th gade). In pat 2, we will take the concepts leaned in pat 1, and apply them to actual data collected by the field cew at the Black Rive Steamside Reaing Facility in 2017 and Fo this activity, you will use the BlackRiveMales xlsx speadsheet. Left: 23 mm Radio Fequency Identification Tag (RFID). Right: Technician Zack Witzel implanting an RFID tag into an adult Lake Stugeon.

6 Lake stugeon ae potamodomous (live in lakes, migate upsteam to spawn) and iteopaous, meaning they spawn multiple times duing adulthood. We can take advantage of that stategy to estimate the population size of males migating upsteam duing two consecutive yeas. The Black Rive Steamside Reaing Facility uses Radio Fequency Identification (RFID) tags to collect data on adult fish moving in and out of the Uppe Black Rive, MI (Figues 1 and 2) duing the spawning season. Like a PIT tag, a RFID tag is a small adio tansponde that contains a specific code, which allows individual fish to be assigned a unique alphanumeic identification numbe. Howeve, a RFID tag is much lage (12 mm PIT vs 32 mm RFID), with a much lage detection ange. When a tagged fish passes a detection antenna, the unique tag ID is detected and stoed in a database with the date and time the tag was detected. Fom this data, Black Rive Steamside Reaing Facility staff can evaluate behavioal data fo each fish migating the ive in a given yea. Specifically, we can detemine if a specific male is captued duing 2017 (the making peiod ) o in 2018 (the census peiod ). Fo this lesson, we will assume the Black Rive and Black Lake ae a single, closed system. 1. In the 2017 Male Captues tab, you will find data on the male Lake stugeon detected in a. RFID Tag is the unique ID of each male which enteed the ive in b. Captue Date is the fist date the fish was detected in the spawning gounds in Using the 2017 Male Captues Tab, detemine the numbe of males detected in the spawning gounds in These males epesent the fish captued in the Making Peiod (M). 3. Using the 2018 Male Captues tab detemine the numbe of males detected in the spawning gounds in These males epesent the total captued in the Census Peiod (C). 4. Finally, in column H in the 2018 Male Captues tab, we maked whethe a fish was captued both in the making peiod and the census peiod. A fish with the label Yes epesents a captue in both yeas. These fish ae you Recaptues (). 5. Using the skills leaned in Pat 1. Estimate the population size (N) of male Lake stugeon in the Uppe Black Rive, MI in 2018.

7 Lesson Questions Basic Questions (7 th 12 th ) 1. How did the esulting population estimate fom the Goups diffe in Pat A when assumptions wee violated? Why would Goups 2 and 3 answes diffe fom Goup 1? 2. How did the esulting population estimates diffe between the low effot and high effot goups? 3. What can we conclude about the amount of effot we put in to sampling a population? Advanced questions (10 th -12 th ) 4. Fisheies manages use Mak-Recaptue population estimates to calculate the numbe of fish that can be havested on a system. The Black Lake system allows a seasonal annual havest of 1.2% as descibed in the Black Lake Management Plan. Based on you calculation of the male population size in Black Lake, what would a hypothetical havest numbe be? 5. A majo assumption of a mak ecaptue model is that you have an equal likelihood of catching fish duing the making and ecaptue peiods. Lake stugeon females do not etun to the ive to spawn annually, but athe spawn evey 3-4 yeas. How might this affect calculated population size if female data wee included?

8 6. The actual calculated population size of Black Lake Male Lake stugeon in 2018 was 637. How does you calculated population size compae? 7. Bonus question: A 95% confidence inteval is an estimate of whee the calculated sample mean (o in this case, estimated population size, N) would fall if we took epeated samples. The 95% confidence level loosely quantifies the level of confidence with which one can expect to find the tue population size in the calculated inteval. In shot, the 95% confidence inteval quantifies uncetainty in ou calculation of the population, as we cannot be 100% confident in the population size unless we sample evey single individual fish in a system. The wide the inteval, the geate the uncetainty in ou sample collection. We can decease uncetainty by inceasing sample effot. Uppe Limit: Utilizing a nomal appoximation, one can calculate the 95% confidence inteval of Lincoln- Peteson mak-ecaptue estimate as follows. Fo this population, calculate the 95% confidence inteval. Does the tue population size (calculated in question 6) fall in this inteval? Use the equations below. M C 1.96 ( 1 2C + (1 M ) C (1 C ) C 1 ) Lowe Limit: M C ( 1 2C + (1 M ) C (1 C ) C 1 )