Age and Growth Estimating age and growth Using hard structures ~ Otolith Lab How do we read these structures and why? Reading lab Back calculation Lab What can we do with back calculated data? Von Bertalanffy modeling Age and Growth of Fish 1. Age refers to years Age class is the year the fish is born Not that all that interesting in itself (except for maturity), used to describe growth 2. Growth is the change in length, wet weight, or dry weight over time Why so many metrics? Different metrics of fish growth Length -Pros: easy, intuitive, history in angling, length rarely shrinks -Cons: lots of change in biomass not related in length Wet Weight -Pros: used in large calculations (ie population biomass) -Cons: can take more time in field (rocking boat or wind and balance don't mix) Dry Weight fat weighs less then water but is way more valuable to individual hours at 60 degrees C (140 F) -Pros: accurate description of individual's current state -Cons: time intensive and must kill fish 3 ways to estimate growth in natural populations Length Frequency Analysis Recaptures of individually marked fish Back calculation from calcified structures # Caught Length Frequency Analysis Pros: non-destructive, archived lengths Cons: have to catch lots of fish, unknowns are high!, easy to bias sample with gear, time, or location 548 BLG from CPR 6/21 to 6/29; 4mm bins Recaptures of marked individuals Pros: non-destructive, good individual data Cons: have to catch TONS of fish to see a recapture Population is fish You catch and tag 100 fish, good effort, but You Come back a year later at best maybe 60 survived so there are 54 tags in 10,000 fish...maybe only 10% lost their tags Estimating growth from tagging Pros: understand the variability in individual growth Cons: tag loss, tagging may influence growth, behavior, or mortality, cant read tag T-bar, dart, floy tags Coded Wire Tags PIT Tags passive integrated transponder Tags for small fish Visible Implant Elastomer Structures used for aging Cleithra - Esocidae (sacrifice) arvidsfishingreport.com/Opercula (sacrifice) Other structures used for aging Vertebrae-Sharks (no spines, teeny otoliths)Fin Rays anything where scales don't work and you don't want to kill the fish Otoliths What is an otolith? Where exactly is an otolith? Break for lab Reading scales and otoliths Why do we do it? Aging fish Getting length or age Via back calculations Age Age = this 358 mm largemouth bass is 10 years old 10 Age Age = this 227 mm largemouth bass is 3 years old Fisheries Uses of Age and Growth What does the age structure look like Maturity Walleye population in Lake Nevafishd Walleye population in Takemal Flowage Back Calculate Growth Linear regression of scale radius and fish length 447 LMB from 15 lakes in Northern Wisconsin R-squared =.88 !!!!! P - value = E-203 !!!!!!!! Frasier-Lee Chalk Talk L t = c + (L T c)(S t /S T ) Frasier-Lee Chalk Talk L t = c + (L T c)(S t /S T ) Break for lab How do we look at growth? Processed 76 largemouth bass Crampton Lake (border upper penn. and WI) Fisheries Uses of Age and Growth What if the length limit on bluegill was 150mm Problems with back calculation Lee's Phenomenon AgeYr.Class LENGTH AT AGE How do we quantify differences in these populations? Size at age Insert real data here? Von Bertalanffy L t = L - (L - L 0 ) exp (-kt) L t = length at time 't L = length at infinity L 0 = length at time zero (birth) K = constant ( shape of growth line) L t = L - (L - L 0 ) exp (-kt) Linf =523.4 Lzero =57.54 k =0.081 Linf =500.6 Lzero =28.34 k =0.080 AL WS Von Bert Use there data to show how to use the template Break for lab Insert fraser-lee What is back calculation? How do you do it? Should probably walk them through a few examples from cross lakes or LRT (try back calc on WSvs anything else) How do you use the data?/What does it tell us? Maybe spend some time talking about how I am using back calculated data for crosslakes and LRL A section on problems with back calculation (should this be at the end?) Lees Phenomenon Explain to them via chalk talk the formula Walk them through using the conversion on the handout and tell them to back calculate one by hand - probably good to have them all get computers Which fish have been taken out already Which fish are not represented?