Salmon Age And Size At Maturity: Patterns And Processes

Salmon age and size at maturity:Patterns and processes1.2.Age DesignationVariation among populations1.2.3.3.Variation within populations1.2.3.4.5.6.LatitudeWithin regionsWithin watershedsSmolt sizeGrowth rateNon-anadromySize – Sex RatioCatch vs. Spawning PopulationDeclines in Size and/or Age

Age DesignationThe total age of the fish does not capture importantlife history events. Rather, we need to indicate theperiods of time spent in freshwater and at sea todistinguish fish of the same age with different lifehistories.In addition, we need a way to account for the periodof time spent as a developing embryo and alevin.There are two distinctly different but equivalent waysin which salmon ages are commonly designated (plusa third used in Russia).

Age Designations: for example,a sockeye salmonYears spentDesignationFresh- SaltU.S.CanadianTotalwater water (European) (Gilbert-Rich) Age121.2424131.3525222.253510.121This includes2 theN.B.0These “years”are reallywinters02 as0.231“missing” year3 ina free-swimming fish.embryonic stages.

Age DesignationsYears spentFresh- Saltwater an) (Gilbert-Rich) Age1.24241.35252.25350.12120.2313

Age DesignationsYears spentFresh- Saltwater an) (Gilbert-Rich) Age1.24241.35252.25350.12120.2313

Age DesignationsYears spentFresh- Saltwater an) (Gilbert-Rich) Age1.24241.35252.25350.12120.2313

Age DesignationsYears spentFresh- Saltwater an) (Gilbert-Rich) Age1.24241.35252.25350.12120.2313

Features used for AgeDetermination:1. Otoliths (ear bones): Record informationduring embryonic stages, permanent, butnecessitate lethal or post-mortem sampling2. Scales: not deposited until some period ofgrowth has taken place, can fall off and getreplaced, but can be removed from live fishAside: Otoliths are mineral and generallyyield no DNA but scales can yield DNA fromdecades past, before DNA was discovered.

Age 1.2 sockeyesalmon, BristolBaySecondmarinecheck atthe edgefocusFreshwater checkFirst marine check

SW 3SW 2SW 1FW 1Age 1.3 BristolBay sockeyesalmon

Age 4 steelhead from Forks Creek: Michael Dauer2nd winter in SW1st winter in SW2nd winter in FW1st winter in FWScale focus

Spawnedin 2001Winter of2000 at seaReturnedin 2002Smoltedin 1998Winter of 1999at seaEmergedin 1997Repeat spawning hatchery steelheadfrom Forks Creek: Michael Dauer

Wild steelhead: three time spawnerReturnedin 1998Winter 1994 infresh waterReturnedin 1997Returnedin 1996Winter 1995at seaEmergedin 1992Winter 1993 infresh water

For steelhead and otheriteroparous species, theage designation mustindicate spawning eventsas well as the years spentin freshwater and at sea.Michael ParkerA 4-year old fish on its firstreturn might be a 1.3 if itwent to sea at age 1 but afish of the same age thatspawned in the previousyear would be designated1.1S1. Repeat spawnersare smaller than “maidens”of the same age.

Distribution of sockeye salmon by totalage in the Chignik Lake system, AK56.7860% of run5037.124030205.63100.430.0503Dahlberg (1968)45Total Age67

Mean % of runDistribution of Chignik Lake systemsockeye salmon by age 12.13.10.26 0.53 0.170.320.05 0.05 0.0031.22.23.21.3Age Group2.33.31.42.4

Hypothesized costs in mortality andbenefits in fecundity of marine residence1.0Survival to spawningFecundity50000.840000.63000Ocean age 20.42000Ocean age 30.21000Ocean age 40.03200370420470520Fork length (mm)570620670FecundityProportion surviving to spawnOcean age 1

Number of populationsOverall length varies greatly among populations:Mean lengths of North American Chinook salmonpopulations4035302520151050malesfemales400 450 500 550 600 650 700 750 800 850 900Roni 1992Post-orbit to hypural length (mm)

Kitsumkalum River chinook salmon

Levels of variation in age and sizeat maturity among populations Latitude Regional features Local features

Are all the big salmon are in Alaska?Not necessarily.Examination of Chinook salmon did not yield any clear trendof size with latitude once age had been accounted for. Cohosalmon seem to be larger in Alaska but this does not seemto have been documented, and pink and chum are oftensmaller in Alaska than farther south, at a given age.Puget Sound, ca. 50 cm)Roni 1992

32.521.510.50pink weightchum length800750700650600550Chum salmon length (mm)Ala Bri rcs k st tiol caPrPe Binni aycensWuil l Ko laiam diaNSo kBrit SE undS isAhBrit C la sis olu kahC mbFr olu iaas me bW r R iaa s ivhi e rngO tonregonAPink salmon weight (kg)Pink salmon weight and chum salmonlength (e.g., age-4) decreases with latitude

The area where salmon enter theocean has little effect on their finalbody size. Small-bodied populationsmay be located near large-bodiedones, so the differences in size mustbe related to other things.

giakNaknekkahag KvichakNusEgegikBristol BayUgashikNaknekRiver

Sockeye salmon ocean age varies amongdistricts within Bristol Bay, and among riversystems within districtsOcean age 5544234117653074854658

% ocean-age 3 salmonOlder and larger fish tend to predominate inlarger rivers (e.g., Wood River sockeye) but theyhave access to the same growing conditions10080Stream width (m) in theWood River system15.15.1604077.33.81.8200A and CcreeksHansenCreekBear CreekIce CreekAgulowakRiver

Some individuals andpopulations tend to growfaster than others. In addition,individuals and populationsdiffer in the “norm of reaction”between growth andmaturation. That is, growingat the same rate, some willmature in the next yearwhereas others with stay atsea, grow larger, and matureat an older age. Really bigfish are not faster growing.

Male chinooksalmonAge 4Age 1

What controls age at maturitywithin populations? Growth in freshwater or smolt size Growth at sea GeneticsCoho smoltChinook

Back-calculated lengths of Chinook salmon (in mm)at different ages, as a function of their final age atmaturity (data from Parker and Larkin 1959).Age at 8466425368456676622549813730917

Lengths of Asian chum salmon sampled at sea thatwere maturing or immature at successive ages.Maturing fish were consistently larger than theimmature fish of their age.750Fork length (mm)LaLanne 1-May

% of each marine age groupNot only growth rate at sea but smolt sizeaffects age at maturity. Fish that mature at anearly age generally were older/larger as smolts(e.g., Wood River sockeye salmon).100Age-1 smolts80Age-2 smolts6040200123Number of years spent at sea before returning

Mature male UW Chinook salmonAge 1Age 2Age 3Age 4

Average smolt weight affected the percent of male UW Chinookthat matured as jacks and especially age-1 “mini-jacks”100age 1 jacksall jacks9080% of males706050403020100051015Average smolt weight (g)2025

The tendency of female UW Chinook to mature at age 3rather than age 4 was also related to average smolt weight% age 3 females10080604020005101520Average smolt weight (g)25

Size, sex and survival In most populations, the sex ratio is nearly50:50, and males are slightly larger for their agethan females (Why?) In many coho salmon populations, males outnumber females but are smaller So, do females incur a higher mortalityassociated with their larger size? And why arefemales larger than males in coho, but smaller insockeye salmon, for example?N.B. Fishing rate on jacks is low, so surveys instreams inflate their apparent abundance.

Is there also a genetic controlover age at maturity?Insert photo of adult cohoand jackDo jacksbeget jacks?

Females mated with jack Chinook salmonproduced more jacks and fewer old males thanfemales mated with older malesSired by jacks% of adult offspring802 xSired4 byolder4 x 4 males60402002Hankin et al. 1993.345Age at maturity of males6

Genetic controlover age at returnin steelheadOcean age of offspring (%)Ocean age ofparents23257.043.0320.679.4Tipping 1991

Fisheries can be selective with respect tosize, and thus age (e.g., Nushagak Riverfemale sockeye in 1984)Proportion caught or 535545555Length565575585595605

Further complexities There may be non-anadromousindividuals (typically males) inanadromous populations Variation in size within non-anadromouspopulations related to food resources,selection from physical habitatlimitation, predation risk, etc.

Cedar River 1 Chinook salmon smoltCedar River precocious male Chinook salmon

Large-bodied rainbow troutfrom British Columbia

Residentcutthroat trout

Genetic and Environmental FactorsInfluencing Age and Size at MaturityAge at Maturity: Primarily represents a trade-offbetween the reproductive benefits of increasedsize against the risk of mortality in the nextyear. Age at maturity is negatively related togrowth rate or size at age.Size at Age: Results from 1) natural selectionfrom factors associated with reproductivesuccess, predation, and physical features of themigratory route and spawning grounds, and2) environmental influences on growth rate.

Declines in size or age at maturity havebeen recorded in many populationsAverage Length (mm)700r 2 0.566506005505004504001950UW femalecoho salmon19601970198019902000

Possible reasons for declines in sizeand age at maturity (Ricker 1980)1.Biased data1.2.2.Genetic changes1.2.3.3.Selective loss of large-bodied populationsFishing selects for fish that mature early in lifeSize selective fishing selects for small/young fishEnvironmental changes1.2.4.Fish caught earlier in the seasonFish caught in the year prior to maturityChanges in temperature affect growth and maturationChanges in density affect growth and maturationEffects of hatcheries1.2.Large smolts mature at an earlier age than small onesSelection for large fish actually selects for slow growth

The total age of the fish does not capture important life history events. Rather, we need to indicate the . Lake Kvichak River Naknek River Wood River Bristol Bay. District System 2 3 Naknek-Kvichak Alagnak 58 41 Kvichak 83 17 Naknek 34 65 total 70 30 Nushagak Igushik 26 74