Coastal Cutthroat Trout Maturity Studies in Southeast Alaska,

Transcription

1 Fshery Data Seres No Coastal Cutthroat Trout aturty Studes n Southeast Alaska, by Roger D. Hardng Alaska Department of Fsh and Game July 2013 Dvson of Sport Fsh and Commercal Fsheres

2 Symbols and Abbrevatons The followng symbols and abbrevatons, and others approved for the Système Internatonal d'untés (SI), are used wthout defnton n the followng reports by the Dvsons of Sport Fsh and of Commercal Fsheres: Fshery anuscrpts, Fshery Data Seres Reports, Fshery anagement Reports, and Specal Publcatons. All others, ncludng devatons from defntons lsted below, are noted n the text at frst menton, as well as n the ttles or footnotes of tables, and n fgure or fgure captons. Weghts and measures (metrc) centmeter declter gram hectare klogram klometer lter meter mlllter mllmeter cm dl g ha kg km L m ml mm Weghts and measures (Englsh) cubc feet per second ft 3 /s foot ft gallon gal nch n mle m nautcal mle nm ounce oz pound lb quart qt yard yd Tme and temperature day d degrees Celsus C degrees Fahrenhet F degrees kelvn K hour h mnute mn second s Physcs and chemstry all atomc symbols alternatng current ampere calore drect current hertz horsepower hydrogen on actvty (negatve log of) parts per mllon parts per thousand volts watts AC A cal DC Hz hp ph ppm ppt, V W General Alaska Admnstratve Code all commonly accepted abbrevatons AAC e.g., r., rs., A, P, etc. all commonly accepted professonal ttles e.g., Dr., Ph.D., R.N., etc. compass drectons: east E north N south S west W copyrght corporate suffxes: Company Co. Corporaton Corp. Incorporated Inc. Lmted Ltd. Dstrct of Columba D.C. et al (and others) et al. et cetera (and so forth) etc. exempl grata (for example) e.g. Federal Informaton Code FIC d est (that s).e. lattude or longtude lat. or long. monetary symbols (U.S.) $, months (tables and fgures): frst three letters Jan,...,Dec regstered trademark trademark Unted States (adjectve) U.S. Unted States of Amerca (noun) USA U.S.C. Unted States Code U.S. state use two-letter abbrevatons (e.g., AK, WA) athematcs, statstcs all standard mathematcal sgns, symbols and abbrevatons alternate hypothess H A base of natural logarthm e catch per unt effort CPUE coeffcent of varaton CV common test statstcs (F, t, χ 2, etc.) confdence nterval CI correlaton coeffcent (multple) R correlaton coeffcent (smple) r covarance cov degree (angular ) degrees of freedom df expected value E greater than > greater than or equal to harvest per unt effort HPUE less than < less than or equal to logarthm (natural) ln logarthm (base 10) log logarthm (specfy base) log 2, etc. mnute (angular) ' not sgnfcant NS null hypothess H O percent % probablty P probablty of a type I error (rejecton of the null hypothess when true) α probablty of a type II error (acceptance of the null hypothess when false) β second (angular) " standard devaton SD standard error SE varance populaton Var sample var

3 FISHERY DATA SERIES NO COASTAL CUTTHROAT TROUT ATURITY STUDIES IN SOUTHEAST ALASKA, by Roger D. Hardng Dvson of Sport Fsh, Douglas Alaska Department of Fsh and Game Dvson of Sport Fsh, Research and Techncal Servces 333 Raspberry Road, Anchorage, Alaska, July 2013 Development and publcaton of ths manuscrpt were partally fnanced by the Federal Ad n Sport fsh Restoraton Act (16 U.S.C K) under Projects F and F-10-14, Job No. R-1-1.

4 ADF&G Fshery Data Seres was establshed n 1987 for the publcaton of Dvson of Sport Fsh techncally orented results for a sngle project or group of closely related projects, and n 2004 became a jont dvsonal seres wth the Dvson of Commercal Fsheres. Fshery Data Seres reports are ntended for fshery and other techncal professonals and are avalable through the Alaska State Lbrary and on the Internet: Ths publcaton has undergone edtoral and peer revew. Roger D. Hardng a Alaska Department of Fsh and Game, Dvson of Sport Fsh P. O. Box , Juneau, AK , USA a Author to whom all correspondence should be addressed: roger.hardng@alaska.gov Ths document should be cted as: Hardng, R. D Coastal cutthroat trout maturty studes n Southeast Alaska, Alaska Department of Fsh and Game, Fshery Data Seres No , Anchorage. The Alaska Department of Fsh and Game (ADF&G) admnsters all programs and actvtes free from The Alaska Department of Fsh and Game (ADF&G) admnsters all programs and actvtes free from dscrmnaton dscrmnaton based on race, color, natonal orgn, age, sex, relgon, martal status, pregnancy, parenthood, or based on race, color, natonal orgn, age, sex, relgon, martal status, pregnancy, parenthood, or dsablty. The dsablty. The department admnsters all programs and actvtes n complance wth Ttle VI of the Cvl Rghts department admnsters all programs and actvtes n complance wth Ttle VI of the Cvl Rghts Act of 1964, Secton Act of 1964, Secton 504 of the Rehabltaton Act of 1973, Ttle II of the Amercans wth Dsabltes Act (ADA) of 504 of the Rehabltaton Act of 1973, Ttle II of the Amercans wth Dsabltes Act (ADA) of 1990, the Age 1990, the Age Dscrmnaton Act of 1975, and Ttle IX of the Educaton Amendments of Dscrmnaton Act of 1975, and Ttle IX of the Educaton Amendments of If you beleve you have been dscrmnated aganst n any program, actvty, or faclty please wrte: ADF&G If you ADA beleve Coordnator, you have P.O. been Box dscrmnated , Juneau, aganst AK n any program, actvty, or faclty please wrte: U.S. Fsh and Wldlfe ADF&G Servce, ADA 4401 N. Coordnator, Farfax Drve, P.O. S Box 2042, , Arlngton, Juneau, VA AK Offce of Equal U.S. Opportunty, Fsh and Wldlfe U.S. Department Servce, 4401 of the N. Interor, Farfax 1849 Drve, C S Street 2042, NW Arlngton, S 5230, VA Washngton DC The Offce department s of Equal Opportunty, ADA Coordnator U.S. Department can be reached of the va Interor, phone at 1849 the followng C Street NW numbers: S 5230, Washngton DC (VOICE) , The department s (Statewde ADA Coordnator Telecommuncaton can be Devce reached for va the phone Deaf) at , the followng numbers: (Juneau TDD) , (VOICE) or (FAX) , (Statewde Telecommuncaton Devce for the Deaf) , For nformaton on alternatve formats (Juneau and TDD) questons , on ths publcaton, or (FAX) please contact: ADF&G, Dvson For nformaton of Sport on Fsh, alternatve Research formats and Techncal and questons Servces, on 333 ths Raspberry publcaton, Road, please Anchorage contact: AK ADF&G, (907) Dvson of Sport Fsh, Research and Techncal Servces, 333 Raspberry Rd, Anchorage AK (907)

5 TABLE OF CONTENTS Page LIST OF TABLES... LIST OF FIGURES... LIST OF APPENDICES... ABSTRACT... 1 INTRODUCTION... 1 OBJECTIVES... 2 ETHODS... 2 RESULTS... 6 aturty... 6 Fecundty... 7 Ovary Weght Egg Sze Age DISCUSSION aturty Fecundty Ovary Weght Egg Sze Age anagement Implcatons Hgh-Use Lakes Regonwde nmum Sze Lmt Small Cutthroat Trout Lakes Trophy Lakes Specal Regulaton Lakes Anadromous versus Resdent Trout ale versus Female aturty Summary of anagement Implcatons CONCLUSIONS AND RECOENDATIONS ACKNOWLEDGEENTS REFERENCES CITED APPENDIX A APPENDIX B... 31

6 Table LIST OF TABLES Page 1. Estmated surface area, maxmum depth, abundance of cutthroat trout, speces present, relatve average sze of cutthroat trout, and lake type germane to Southeast Alaska lakes selected for cutthroat trout length-at-maturty studes, Fgure LIST OF FIGURES Page 1. Lakes sampled n Southeast Alaska durng the cutthroat trout sexual maturty study by lake sze n ha, Lakes sampled for cutthroat trout sexual maturty n Southeast Alaska, Average percentage of sexually mature female cutthroat trout sampled n Southeast Alaska lakes, Average percentage of sexually mature female cutthroat trout sampled by lake type n Southeast Alaska lakes, Resduals from the allometrc model versus length and predcted fecundty for cutthroat trout sampled n Southeast Alaska lakes, Fecundty-at-length relatonshp wth addtve and multplcatve error structures for cutthroat trout sampled n Southeast Alaska lakes, Ovary weght and fork length of cutthroat trout classfed durng feld collecton as mmature or mature at lakes sampled n Southeast Alaska, Fork length and mean egg dameter for all eggs collected from 21 lakes that were sampled n Southeast Alaska, The dstrbuton of egg dameter by lake for cutthroat trout ovares sampled n Southeast Alaska, The cumulatve fracton of cutthroat trout egg dameter from anadromous and resdent lakes sampled n Southeast Alaska, The number and age of sexually mature and mmature female cutthroat trout sampled n Southeast Alaska, The proporton of sexually mature female cutthroat trout by age class sampled n Southeast Alaska, The cumulatve percentage of sexually mature female cutthroat trout by age class sampled n Southeast Alaska, Length dstrbutons of mature female cutthroat trout n 5 lakes managed for hgh angler use n Southeast Alaska wth lnes showng regonwde mnmum length restrctons and hgh angler use mnmum length restrctons Length dstrbutons of mature female cutthroat trout n 12 lakes managed under the regonwde mnmum sze regulatons as hgh angler use n Southeast Alaska wth lnes showng the 11-nch and 9-nch mnmum sze lmts Length dstrbutons of mature female cutthroat trout n 3 lakes managed under the small cutthroat trout lake strategy wth a 9 nch mnmum sze regulatons wth a lne showng the 9- nch mnmum sze lmt Lakes n Southeast Alaska that are managed as ether hgh angler use or small cutthroat trout lakes Length dstrbutons of sexually mature female cutthroat trout grouped by the management strategy used to manage lakes n Southeast Alaska The percent maturty by total length of cutthroat trout for anadromous and resdent lake populatons sampled n Southeast Alaska,

7 Appendx LIST OF APPENDICES Page A1. Regresson formula for convertng cutthroat trout fork length nto total length B1. Computer data fles contanng data for use n preparng ths report. Ths table wll be completed after the peer revew

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9 ABSTRACT Proportons of female coastal cutthroat trout Oncorhynchus clark clark that were sexually mature were estmated for 21 lakes n Southeast Alaska that spanned a range of lake szes, lake types (resdent or anadromous), and fsh szes present n the regon. Samplng occurred between late September and the mddle of November n 1997 and Each captured fsh was measured, and each sacrfced fsh was weghed to the nearest gram, classfed by sex, sampled for scales and otolths, and later evaluated for sexual maturty. Overall, 60% (SE = 1.1%) of the females sampled were sexually mature n the 11-nch total length category, and 62% (SE = 1.1%) of the females were sexually mature n the 12-nch length category. At lengths below 11 nches, anadromous cutthroat trout maturty rates quckly dropped. At 10 nches, only 28% (SE = 2.2%) of the anadromous females were mature. Fecundty-at-length, ovary weght, and egg sze n relaton to maturty were also evaluated. Current trout (cutthroat and ranbow trout) regulatons are evaluated and varous management optons are dscussed, ncludng mplcatons from ths study. Keywords: length at maturty, fecundty, egg sze, egg dameter, cutthroat trout, ranbow trout, ovary weght, age at maturty, trout regulatons, steelhead, management INTRODUCTION In 1994, new trout regulatons were adopted n Southeast Alaska (SEAK) that combned creel lmts, sze lmts, and bat restrctons. A 12-nch mnmum sze lmt for trout, was mplemented throughout the regon to: 1) protect coastal cutthroat trout Oncorhynchus clark clark (henceforth called cutthroat trout) and resdent/nonanadromous ranbow trout O. mykss untl the majorty could spawn at least once; and 2) provde protecton for juvenle steelhead O. mykss and cutthroat trout before they emgrate to the ocean. Although both cutthroat and ranbow trout n SEAK can exhbt resdent and anadromous lfe hstores, the regulatons do not dfferentate between them. A larger sze lmt (14-nch mnmum sze) was adopted for areas wth developed access and/or ntensve sport fsheres. A maxmum sze lmt of 22 nches was also mplemented to protect returnng adult steelhead trout, even though t could unnecessarly restrct the harvest of larger cutthroat and ranbow trout. In addton, a 10-month (November 16 through September 14) ban on fshng wth bat was mplemented n freshwater systems to reduce hookng mortalty on trout and steelhead. The regulatons were germane to cutthroat and ranbow trout because of dffcultes anglers had n dstngushng between the two speces (Hardng and Jones 2005). Alaska Department of Fsh and Game, Dvson of Sport Fsh (ADF&G-SF) staff based the ntal 12- and 14-nch sze lmts on avalable length-at-maturty data collected from anadromous fsh n Petersburg Creek (ADF&G fles) n SEAK, landlocked populatons n osquto Lake n the Queen Charlotte Islands, Brtsh Columba (de Leeuw 1987), and lterature on trout populatons n Washngton and Oregon (Wrght 1992). The need for more extensve length-at-maturty data from a varety of trout populatons and lake types n SEAK was apparent. For example, advsory commttee reports and publc testmony gven at the 1997 Board of Fsheres (BOF) meetng ndcated the 1994 regulatons were too restrctve n lakes that contan few trout of legal harvestable sze (.e., >12 nches). In general, ADF&G-SF staff recognzed that length- and/or age-at-maturty n fsh populatons was an expresson of the growth of ndvdual populatons (Trppel and Harvey 1990; Clark 1992), and the type, sze, and locaton of the lake (Schmdt 1994; Hardng 1995). However, very lttle data were avalable for trout populatons n lakes n SEAK. In 1997, the BOF requested ADF&G to evaluate cutthroat trout length-at-maturty n more lakes and report the results durng the next meetng n 2000; ths report summarzes the results of that project. Length- and age-at-maturty, fecundty, and egg dameter of cutthroat trout were nvestgated n a range of locatons and lake types throughout SEAK. The focus was on cutthroat trout because ths speces s more vulnerable to fshng pressure and habtat degradaton than ranbow trout 1

10 (Behnke 1992), so the bologcal prncples used to protect cutthroat trout would also serve to adequately protect ranbow trout populatons (Hardng and Jones 2005). The data collected were used to help reevaluate the mnmum sze lmts for trout n a range of lakes n SEAK. The products of the analyss were used to further develop the scentfc bass for regonal trout fshng regulatons that should ensure ample fshng opportuntes and sustanable fsheres. uch of the nformaton reported here may be relevant to other cutthroat trout subspeces and t s noted when comparsons are made between other coastal cutthroat trout populatons as well as to other subspeces (e.g., westslope cutthroat trout O. clark lews). The objectve of ths project was to: OBJECTIVES 1) Estmate the proporton of sexually mature female cutthroat trout n 1-nch length ncrements n a range of lake types throughout SEAK. In addton to the objectve outlned above, the project was responsble for the followng tasks: 2) Evaluate fecundty-at-length of female cutthroat trout n a range of lake types throughout SEAK. 3) Collect scales and otolths to allow estmaton of the proporton of sexually mature cutthroat trout by age, and fecundty-at-age. ETHODS Area management bologsts selected 21 lakes that spanned a range of lake szes, lake types (resdent or anadromous), and fsh szes present n the regon (Table 1; Fgures 1 and 2). It was beleved that these lakes were not, n general, heavly exploted so that a range of fsh szes were present, and that destructve samplng (e.g., subsample of fsh klled to vsually examne gonads) would not jeopardze the health of the populatons. It was also beleved that these lakes were representatve of most lakes n SEAK and would not lead to any bas ether geographcally (northern versus southern) or by lfe hstory type (resdent versus anadromous). Samplng occurred between late September and the mddle of November durng 1997 and Although cutthroat trout n SEAK typcally spawn n early sprng, gonads must be n an advanced stage of development by fall f the fsh are gong to spawn the next sprng (Behnke 1992). Test samplng at Florence Lake durng July, August, and September 1997, and at Lttle Lake on Prnce of Wales Island durng September 1997, ndcated that sexual maturty could be determned wth confdence by the mddle of October. Samples were thus collected late enough n each year so that the maturty stage could be easly determned and before nclement weather, freezng condtons, and sprng spawnng occurred. Cutthroat trout n each lake were captured usng 3 gear types: floatng and snkng varable mesh gllnets, hoop traps, and hook-and-lne gear. Gllnets were set parallel to the bottom of the lake at depth ntervals <30 m usng random or systematc placements across the lake. Hoop traps bated wth Betadne, 1 treated salmon roe were smlarly set. Hook-and-lne samplng was conducted n vared habtats by castng towards shore from a boat travelng along the permeter of the lake. 1 Ths and subsequent product names are ncluded for a complete descrpton of the process and do not consttute product endorsement. 2

11 Table 1. Estmated surface area (ha), maxmum depth, abundance of cutthroat trout, speces present, relatve average sze of cutthroat trout, and lake type germane to Southeast Alaska lakes selected for cutthroat trout length-at-maturty studes, Estmated abundance of cutthroat trout for each lake was obtaned from abundance studes when avalable (e.g., Hardng et al. 1999b); f no abundance estmates were avalable then abundance was guesstmated by multplyng the respectve surface area (ha) by the densty from studed lakes wth smlar sze and characterstcs (e.g., depth, bathymetry, anadromous access, speces n lake, and geographc locaton). Area Surface area axmum Estmated cutthroat Speces Relatve average sze Lake name Ketchkan North Saddle (ha) 25.3 depth (m) 20 trout abundance a 550 d present b CT, DV of cutthroat trout c edum Lake type Resdent Upper Wolf ,233 e CT,DV edum Resdent rror ,633 f CT,DV edum Resdent Wnstanley NA g CT,KO edum Resdent POW Island Lttle d CT Small Resdent Neck ,714 h CT,DV,KO edum Resdent St. Ncholas 96 >30 NA g CT,DV edum Resdent Klawock 1207 >30 NA g CT,RB,DV edum Anadromous Wrangell/Petersburg Long CT,DV Small Resdent Colp CT Very small Resdent Thoms NA g CT edum Anadromous Slppery j CT edum Anadromous Stka Buck e CT Small Resdent Gouldng ,300 k CT,DV edum Resdent Eva ,150 l CT edum Anadromous Stkoh ,000 m CT edum Anadromous Juneau Shelter CT,DV Small Resdent Thayer ,500 k CT,DV,KO edum Resdent Florence ,000 n, e CT,DV,KO edum Resdent cknney ,400 o CT,DV,KO edum Resdent Kook NA g CT,RB,DV edum Anadromous a Resdent fsh >180 mm FL, unless otherwse noted. b CT = cutthroat trout; DV = Dolly Varden; KO = kokanee; RB = ranbow/steelhead trout c <170 mm FL = very small, mm FL = small, mm FL = medum. d Based on densty of Buck Lake (Schmdt 1994); small landlocked lake wthout kokanee). e Densty estmate based on data from mark-recapture estmate (Schmdt 1994). f Jones, D.E. Unpublshed report. ADF&G, Douglas Offce Trout Bblography Reports Record #32: Darwn E Jones. Recreatonal surveys of selected lakes n southern Southeast Alaska- rror Lake Accessed 1/11/2013 g NA = not enough nformaton or data avalable to estmate fsh densty pror to maturty samplng. h Average densty of 18 fsh/ha (calculated from hgh densty (Florence Lake; 21 fsh/ha; Rosenkranz et al. 1999) and low densty (Alexander Lake; 14 fsh/ha; R. Hardng, 1996, unpublshed memo). Hgh densty calculated usng hghest trap catch n shallower areas of Florence Lake; 22 fsh/ha (Rosenkranz et al. 1999). j Densty estmated usng unpublshed data from several lakes for trout>120 mm FL (Hubartt and Bngham 1989). k Densty estmate based on data from Hasselborg Lake (Laker 1994). l Densty estmate based on data from mark-recapture estmate (Yanusz and Schmdt 1996). m Densty estmate based on data from mark-recapture estmate (Brookover et al. 1999). n Densty estmate based on data from mark-recapture estmate (Rosenkranz et al. 1999) o Densty estmate based on data from mark-recapture estmate (Hardng et al. 1999a). 3

12 Wnstanley Upper Wolf Thoms Thayer St. Ncholas Slppery Stkoh Shelter Neck N. Saddle Lake rror cknney Long Lttle Kook Klawock Gouldng Florence EVA Colp Buck ,000 1,200 1,400 Sze of lake (ha) Fgure 1. Lakes sampled n Southeast Alaska durng the cutthroat trout sexual maturty study by lake sze n ha, Anadromous lakes have clear bars and resdent lakes have sold bars. Fgure 2. Lakes sampled for cutthroat trout sexual maturty n Southeast Alaska,

13 In an effort to mnmze destructve samplng, an a pror model was used to predct the medan or most common sze of trout that mght be expected to be found n each lake. A maturty-atlength relatonshp (a logstc curve) for brown trout (Avery 1985) was adopted that ncorporated data from a prelmnary maturty sample collected at Florence Lake (Foster 2003). The lakes that were selected for samplng were roughly categorzed by sze-at-maturty ( small versus large fsh) based on the brown trout-florence Lake model. Sample szes by length nterval were subsequently selected so that most samplng would occur n the nterval contanng the mddle of the logstc curve. Ths model guded samplng such that: 1) specfc 20 mm FL sze ntervals were targeted (each 20 mm FL nterval approxmately equals a 1-nch TL ncrement); 2) sample szes were mnmzed; and 3) estmates met statstcal objectves (±20 percentage ponts for a 95% confdence nterval). Each fsh captured was measured to the nearest mm (FL and TL), and the lengths were converted to nches (because the fshng regulatons specfy total length n nches). Each sacrfced fsh was weghed to the nearest gram, classfed by sex, sampled for scales and otolths, and later evaluated for sexual maturty. Ovares taken from sacrfced fsh (ncludng all resdual eggs from pror spawnng) were extracted and preserved on the day of capture. Before ovary extracton, the poston of the most dorsally extended edge of the egg sack n relaton to the front edge of the dorsal fn was recorded (.e., anteror, posteror, or algned wth tp of dorsal fn). Ovares were placed n a val contanng 10% buffered formaln. Upon collecton, ovares were classfed as ether mature or mmature based on vsual characterstcs. Small ovares that were granular n appearance and located dorsally were classfed as mmature, and ovares that were much larger, salmon egg n color, and a more pronounced feature of the abdomnal cavty were classfed as mature (Downs 1995; Downs et al. 1997). Sacrfced males were also classfed as mature, mmature, or uncertan based on vsual characterstcs. Testes were classfed as mmature f they conssted of 2 clear or cloudy-whte thread-lke vessels that ran dorsally along the kdney. Testes were classfed as mature f the testes were more pronounced (pencl-szed dameter), whte and chalky n appearance, and an obvous feature of the abdomnal cavty (Downs 1995; Downs et. al. 1997). Testes classfed as mature or mmature were dscarded; testes classfed as uncertan (not mature or mmature) were preserved on the day of capture by placng them n vals contanng 10% buffered formaln. All samples were clearly labeled and ncluded: lake, date, length of fsh, and sample number. Scales and otolths were taken to estmate the proporton of sexually mature fsh at age, and fecundty-at-age. Scales were collected from the left sde of the caudal peduncle mmedately above the lateral lne (Brown and Baley 1949, 1952; Laakso and Cope 1956). Pror to takng a scale sample, the sample area was wped wth the blunt sde of a knfe to remove excess slme. A sample of scales was removed from each fsh and spread unformly across a pece of transparent flm. The flm was stored nsde a con envelope labeled wth the sample number. Both left and rght otolths were extracted, wped to remove excess flud, and stored dry n a small plastc val. The sexual maturty of females was further evaluated n the laboratory after assessng the sze and weght of ovares, egg dameter and color, and number of eggs. A random sample of eggs (30 eggs n 1997, and 10 eggs n 1998) was selected from each ovary sample categorzed as mature, and egg dameter was measured usng a small camera and the software computer program Image-Pro. Fecundty of every mature fsh was determned by countng the eggs. If needed, the number of eggs n each mature ovary was counted under a dssectng scope. Scales 5

14 and otolths were prepared and read accordng to the procedures and recommendatons n Ercksen (1997). Ages were estmated from both scales and otolths collected from sacrfced fsh. Age readng was standardzed by readng each otolth twce and f the readngs agreed, then that age was assgned; a thrd readng was done f the readngs dd not agree. If after 4 readngs there was stll no agreement, the supervsor was consulted and an age was assgned once agreement was reached concurrently between the reader and supervsor. The proporton calculated as: pˆ a of mature fsh n length (mm and nches TL and FL) or age group was pˆ ma a =, (1) na where m a s the number n length or age group a that are mature, and n a s the number n length or age group a that were successfully classfed wth respect to maturty. The varance for pˆ s: pˆ a [ ] ( 1 pˆ a ) ˆ v p a =. (2) na 1 Nonlnear regresson analyss was used to estmate the relatonshp between fecundty and fsh length, based on a general 2-parameter allometrc model: The allometrc model wth an addtve error structure s modeled as: b F= al. (3) b al F = + ε, (4) where F = fecundty (eggs per female), L = length, and ε s a random error term wth mean 0 and constant varance σ 2. The allometrc model wth a multplcatve error structure s modeled as: L ln F = lna + bln + ε. (5) Regresson dagnostcs (e.g., Draper and Smth 1981) were employed to determne approprate transformatons, error structures, etc., to ensure model adequacy. Cutthroat trout length n SEAK has tradtonally been measured and reported by ADF&G as fork length. anagement regulatons, however, are always specfed n total length. Appendx A1 provdes a regresson formula for convertng cutthroat trout fork length (mm) nto total length (mm) usng length measurements collected durng ths project (n = 3,533). ATURITY RESULTS Cutthroat trout from 21 lakes were sampled n 1997 (n = 1,635) and 1998 (n = 1,550) for maturty and fecundty. Fork lengths averaged 220 mm (SE = 0.9 mm) and ranged from 92 to 425 mm FL. Total lengths averaged 230 mm (SE = 0.9 mm), or 9.1 nches (SE = 0.04 nches), and ranged from 96 to 433 mm TL. Weghts averaged 122 g (SE = 1.6 g) and ranged from 6.4 to 901 g. a 6

15 Samplng ncluded 5 anadromous (mxed lfe hstory, overwnterng stocks) lakes and 16 resdent cutthroat trout lakes (.e., lakes above mgratory barrers). Overall, 60% (SE = 1.1%) of the 1,864 females sampled regonwde were mature n the 11-nch TL category, and 62% (SE = 1.1%) of the females were mature n the 12-nch TL category (Fgure 3). At lengths below 11 nches, anadromous cutthroat trout maturty rates quckly decreased. At 10 nches, only 28% (SE = 2.2%) of the anadromous females were mature (Fgure 4). FECUNDITY Fecundty was determned for 760 ovary samples collected from sexually mature female cutthroat trout. The number of eggs per mature female averaged 259 (SE = 4.7), and ranged from 54 eggs n a 249 mm FL fsh to 802 eggs n a 357 mm FL fsh. Eggs n mmature females were not counted because they were too small to easly dstngush. Fecundty-at-length was modeled by assumng ether an addtve or multplcatve error structure. The estmates of a were assumng addtve error, and assumng multplcatve error; estmates of b were 2.16 assumng addtve error, and 2.08 assumng multplcatve error. Resduals from both error structure models (allometrc model) were plotted aganst length and predcted fecundty (Fgure 5). The resdual plots for each model were smlar and ndcated that each volated the assumpton of homoscedastcty. The addtve error model ft the data slghtly better than the multplcatve model (r 2 = 0.77 versus 0.75; Fgure 6). 100% 90% n =1,864 80% Percent sexually mature 70% 60% 50% 40% 30% 20% 10% 0% Length category (nches TL) Fgure 3. Average percentage of sexually mature female cutthroat trout sampled n Southeast Alaska lakes,

16 Percent mature 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% n = 1, Resdent 8% 28% 44% 52% 54% 60% 61% 71% 91% 100% 100% Percent mature 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% n = Anadromous 0% 3% 14% 28% 28% 59% 62% 91% 100% 100% 100% Length category (nches TL) Fgure 4. Average percentage of sexually mature female cutthroat trout sampled by lake type (resdent and anadromous) n Southeast Alaska lakes,

17 Resduals (eggs/female) Predcted fecundty 400 Resduals (eggs/female) Length (mm FL) Predcted fecundty Length (mm FL) Fgure 5. Resduals from the allometrc model versus length and predcted fecundty for cutthroat trout sampled n Southeast Alaska lakes, ultplcatve error structure resduals are plotted n the left sde panels, and addtve error structure resduals are plotted n the rght sde panels. Fecundty (eggs/female) Observed fecundty Predcted fecundty, addtve error Predcted fecundty, multplcatve error Length (mm FL) Fgure 6. Fecundty-at-length relatonshp wth addtve and multplcatve error structures for cutthroat trout sampled n Southeast Alaska lakes,

18 OVARY WEIGHT A total of 1,295 ovares were weghed from all lakes except Florence Lake (see analyss n Foster 2003). Only complete ovary samples (.e., 2 ntact ovares per female), were used n ths analyss. The mean ovary weght from fsh categorzed as mature at the tme of collecton was 7.8 g (SE = 0.34 g), and ranged from 0.8 to 61.5 g. Ovary weght from fsh dentfed as mmature averaged 0.4 g (SE = 0.01 g), and ranged from 0.01 to 3.0 g. Ovary weght as a functon of fork length for fsh classfed as mmature or mature s presented n Fgure 7. Approxmately 2% of ovares sampled had resdual eggs n some state of reabsorpton, and approxmately 0.5% of the samples classfed as mmature also had resdual eggs. EGG SIZE Egg dameter was measured for 30 randomly selected eggs per ovary collected durng It was determned that a smaller sample (10 eggs) generated the same precson, so the number of eggs measured n 1998 was reduced to 10 eggs per ovary sample. The CV n egg sze from a sngle fsh was mnmal (all CV 0.033%) n both years. For comparatve purposes, the mean egg dameter from each fsh wll be used to sngularly represent egg sze for that fsh. Fgure 7. Ovary weght and fork length of cutthroat trout classfed durng feld collecton as mmature or mature at lakes sampled n Southeast Alaska, Fork length (mm) Ovary weght (g) = ature I = Immature 10

19 The average dameter of eggs collected from sexually mature female cutthroat trout n all lakes was 3.3 mm; (SE = 0.02 mm; n = 612), and ranged from 1.9 to 5.2 mm. Egg dameter vared consderably by fork length of fsh (Fgure 8) and lake (Fgure 9). There was a sgnfcant dfference (Kolmogorov-Smrnov: d = 0.44, P 0.001) n dstrbuton of mean egg dameter from anadromous and resdent cutthroat trout populatons (Fgure 10). AGE Female cutthroat trout as young as 1-year old were classfed as mature and approxmately 30% of the female cutthroat trout sampled were classfed as mature at age 3 and 4 (Fgure 11). Not untl age 3 dd the cumulatve percent of mature females exceed 50% (Fgures 12 and 13). 5 ean dameter of egg (mm) Fork length (mm) Fgure 8. Fork length and mean egg dameter for all eggs collected from 21 lakes that were sampled n Southeast Alaska,

20 5 ean egg damter (mm) Buck Colp Eva Florence Gouldng Klawock Kook Lttle Long cknney rror N. Saddle Neck Shelter Stkoh Slppery St. Ncholas Thayer Thoms Upper Wolf Wnstanley Fgure 9. The dstrbuton of egg dameter by lake for cutthroat trout ovares sampled n Southeast Alaska, The notches n the box-plots provde an approxmate 95% test of the null hypothess that the medan egg dameters are equal; wdth of the boxes represent sample sze. Lake 12

21 Cummulatve fracton of samples Anadromous Resdent Egg damater (mm) Fgure 10. The cumulatve fracton of cutthroat trout egg dameter from anadromous and resdent lakes sampled n Southeast Alaska,

22 Number of fsh Immature ature Age Fgure 11. The number and age of sexually mature and mmature female cutthroat trout sampled n Southeast Alaska, % 30% Proporton of mature females 25% 20% 15% 10% 5% 0% Age Fgure 12. The proporton of sexually mature female cutthroat trout by age class sampled n Southeast Alaska,

23 120% Cummulatve percent of mature females 100% 80% 60% 40% 20% 0% Age Fgure 13. The cumulatve percentage of sexually mature female cutthroat trout by age class sampled n Southeast Alaska, ATURITY DISCUSSION The objectve of ths project was to estmate the proporton of sexually mature female cutthroat trout n 1-nch length ncrements (approxmately 20 mm FL) n a range of lake types throughout SEAK. However, the prmary goal of the sample desgn was to mnmze, as much as possble, the number of fsh that needed to be sacrfced. Thus, the samplng desgn was not completely random and fsh were selected from a predetermned set of crtera to ensure an adequate number fsh were selected for each 20 mm length category. Whenever possble, samplers strove to: 1) sample smlar numbers of fsh captured usng each gear type; 2) sample the dverse range of lake habtats and depths (<30 m) present n the lake; and 3) meet overall sample sze requrements for each 20 mm length category. Each of these goals had practcal lmtatons (e.g., floatplane, vehcle, or foot access to lake, and avalablty of cabn or boat) that vared by the lake. The frst objectve assumed that CPUE for each gear type n a lake was such that samplng effort could be effectvely regulated to acheve samplng goals (e.g., traps could be set multple tmes per day).yet regulatng effort n some lakes would not yeld the desred sample sze f CPUE for a partcular gear type n a lake was very low. However, the 2 year samplng desgn was farly robust to ths possblty because samples could be pooled across years n lakes that had smlar characterstcs. Dependng on logstcs (boats and weather), t also proved dffcult to deploy samplng gear effectvely across a dverse range of habtat types and depths n larger lakes. In these cases, gear was dspersed as wdely as possble. Results from ths project showed no meanngful dfference for management purposes n the average percent of sexually mature fsh between the 11 and 12 nch categores n the 21 lakes sampled throughout SEAK. Overall, 60% of the 1,864 females sampled were mature 15

24 n the 11-nch length category, and 62% of the females were mature n the 12-nch length category. The department s management strategy to protect cutthroat and ranbow trout untl the majorty could spawn at least once could thus be met wth an 11-nch mnmum sze lmt whle provdng more harvest opportuntes for sport anglers. Subsequently, the department recommended to the BOF that the regonwde mnmum sze lmt be reduced from 12 nches to 11 nches, and the BOF adopted the lower mnmum sze lmt n The BOF has made several regulaton changes and exceptons to the regonwde mnmum sze lmt snce adoptng the more conservatve trout regulatons n 1994, and detals of these actons can be found n Hardng and Jones (2005) and Hardng and Coyle (2011). FECUNDITY The fecundty of several subspeces of cutthroat trout, ncludng westslope, Bonnevlle O. clark utah, and Yellowstone O. clark bouver has proven to be an mportant parameter or varable when modelng trout populatons. Estmates of fecundty have contrbuted to estmatng female reproductve output (Peterson et al. 2010), for evaluatng stock status (Pauley et al. 1989), and assessng envronmental rsk for potental Endangered Speces Act lstngs. Fecundty vares greatly among western trout and s nfluenced by both envronmental and heredtary factors, but fecundty typcally ranges from 1,200 to 3,200 eggs/kg of body weght, or 1.2 to 3.2 eggs/g (Behnke 1992). The average number of eggs/g estmated by ths study was 1.7 (SE = 0.02; n = 725), and ranged from 0.63 to 6.1 eggs/g. Although the average fecundty (n eggs/g) estmated by ths study falls wthn the wde range reported by Behnke (1992) for all western trout, t s consderably less than the most relevant analyss of fecundty, reported by hatcheres n Oregon and Washngton for coastal cutthroat trout (Wydosk and Tppng 2001). Although ther analyss prmarly conssted of larger cutthroat trout, comparson between fsh n the smallest common length range ( mm FL) ndcated that the fecundty estmated by ths study was substantally less. Based on 2 fsh sampled at Cowltz Hatchery and 5 from Beaver Creek Hatchery, the average predcted fecundty was 871 (SE = 11.5) and 1,029 (SE = 3.0), respectvely; for dentcally-szed fsh sampled n the SEAK study, the mean fecundty was 479 (SE = 15; n = 53), and ranged from 250 to 713 eggs per female. Dong more meanngful fecundty and length comparsons s lmted because other studes generally report the mean number of eggs per female from a range of lengths, e.g., n Washngton no specfc nformaton about locaton or whether fsh were anadromous or resdent was provded when reportng that females rangng n total length from 200 to 430 mm produced between 226 to 4,420 eggs (Johnston and ercer 1976). The only fecundty nformaton for SEAK comes from a few dozen fsh captured at Petersburg Creek n the mddle 1970s. Jones (1974) reports that fecundty from a small number of anadromous cutthroat trout sampled at Petersburg Creek ranged from 500 eggs for a 370 mm TL fsh to 1,100 eggs for a 440 mm TL fsh. In a subsequent report (Jones 1976), 12 fsh from Petersburg Creek were sampled for fecundty, whch ranged from 460 eggs for a 340 mm fsh to 1,342 for a 422 mm fsh, and averaged 862. The average estmated fecundty for fsh sampled n ths study s also less than Jones (1974, 1976) when smlarly szed fsh from anadromous systems are compared. A thorough comparson of fecundty from ths study wth other coastal cutthroat trout s dffcult due to the paucty of comparable studes, dfferences n length-at-maturty throughout ther range, and adequate sample szes. However, the comparsons that could be made suggest that 16

25 fecundty of cutthroat trout n SEAK sampled n ths study s substantally lower than n ther southern range. OVARY WEIGHT A meanngful comparson between ovary weghts collected durng ths study wth smlar data s also dffcult to acheve due to the same reasons stated prevously regardng fecundty. any of the studes that provde ovary weghts are generally related to artfcal propagaton programs wth other subspeces and tend to be ncomplete or nconsstent wth the samplng protocol mplemented n ths study (e.g., weghng ovares fresh versus preserved). EGG SIZE Eggs from anadromous coastal cutthroat trout n Washngton reportedly ranged n dameter from 4.3 to 5.1 mm at the tme of deposton (Johnston and ercer 1976); no other detals or specfc locaton are provded. Egg dameter for anadromous cutthroat trout n the SEAK maturty study were slghtly smaller (Fgure 10) and ranged from 2.6 to 4.7 mm (n = 49). Although there s a scarcty of comparable data, t appears that egg dameters of cutthroat trout n SEAK are smaller than n the central and southern ranges of coastal cutthroat trout (Wydosk and Tppng 2001). Beacham and urray (1993) also suggest that egg dameter may be smaller n northern populatons of salmonds as a result of ncreased fecundty due to ther older ages at maturty, and a lmted amount of energy that can be expended on egg producton. There are several authors who provde nsght as to the ecologcal and evolutonary adaptatons of coastal cutthroat trout as t relates to egg sze, length, fecundty, and sze at maturty. Trotter (1997) states that larger cutthroat trout are more successful at spawnng because they produce larger eggs and can effectvely compete for the best spawnng stes. Pearcy et al. (1990) theorzes that as coastal cutthroat trout co-evolved wth coho salmon and steelhead trout, ther small sze at maturty may be an adaptaton that allows cutthroat trout to spawn n the numerous small trbutares of coastal streams where no other salmonds (e.g., steelhead trout) are present or are less abundant. Consstent wth results presented by Wydosk and Tppng (2001), egg dameter of cutthroat trout n SEAK generally ncreased as female lengths ncreased (Fgure 8). It s assumed, as wth other speces of fsh, that a larger egg dameter results n hgher fry survval, and thus, survval to other lfe stages. Larger alevns and fry are produced from larger eggs (Beacham and urray 1990) and these larger alevns and fry may provde for a compettve advantage n survval of coastal cutthroat trout (Wydosk and Tppng 2001). Ths s farly unform across other trout speces and most speces of salmonds. However, n Atlantc salmon Salmo salar repeat spawners had sgnfcantly smaller eggs and sgnfcantly lower egg survval rates than frst-tme spawners (Red and Chaput 2012). The reason gven for ths was the short tme spent recondtonng, and consequently a shortage of avalable energy reserves. It should be ponted out that the SEAK maturty study focused prmarly on estmatng the length at whch cutthroat trout frst mature, and the relatonshp of fsh length to egg sze and fecundty mght dffer on larger trout not targeted for samplng n ths study. Varatons n egg dameter of cutthroat trout n SEAK may provde nsght nto the bology of ndvdual populatons and ther reproductve potental, but does not appear to be a sgnfcant canddate varable n any maturty model. 17

26 AGE The predomnant age classes of cutthroat trout sampled durng ths study were age 3 and 4 (Fgure 12). There were 13 fsh classfed as mature at age 1, but t s suspected mproper ages were assgned to some of these fsh. In revewng the age-at-length data for the smaller and younger fsh, several anomales arose. There were 3 fsh 250 mm FL that were estmated to be age 1, one of whch was a recaptured (ventral fn clpped) fsh from a mult-year mark-recapture experment at Neck Lake (Hardng et al. 1999a) that concluded only several months pror to maturty samplng; ths fsh could not have been only 1 year old. It s beleved a smaller fsh s otolth and scale sample was nadvertently placed n the wrong samplng envelope. There are reported dffcultes n agng fsh at 1 year of age (Ercksen 1997) and t s lkely there was some type of age error assocated wth the 13 fsh estmated to be mature at age 1. Three of the 13 mature fsh estmated to be age 1 were <200 mm FL and were the only ones that could have realstcally been that age. The lfe hstory of coastal cutthroat trout may be the most dverse of any Pacfc salmond (Northcote 1997; Johnson et al. 1999) and ther populatons show a perplexng dversty n sze and age-at-maturty, as well as tmng of mgratons and frequency of repeat spawnng. The lterature reports consderable varaton n age- and sze-at-maturty for coastal cutthroat trout. Trotter (1997) reports that resdent or nonmgratory coastal cutthroat trout typcally mature at 2 to 3 years of age, whereas anadromous cutthroat trout rarely spawn before age 4. Behnke s (1992) lfe hstory revew reports that coastal cutthroat trout reach maturty and spawn for the frst tme as 3 or 4 year old fsh. Coastal cutthroat trout scales are notorously dffcult to read and nterpretatons of scale patterns often vary greatly between readers (Ercksen 1997; Knudsen 1980); these dffcultes may hnder meanngful comparsons among studes (Johnson et al. 1999). There s nothng to suggest that cutthroat trout from SEAK mature much dfferently than those found elsewhere n ther range. The natural varaton n age-at-maturty found n SEAK encompasses the varatons observed throughout ther natve range. Dfferences n growth rates, varatons n lfe hstory strateges (anadromous versus resdent), dfferent envronmental factors, ncludng water temperature, contrbute to the varaton n age-at-maturty, fecundty, and egg sze n SEAK. ANAGEENT IPLICATIONS The proporton of sexually mature female cutthroat trout from the SEAK maturty study was averaged by length ncrement across the 21 lakes sampled to help develop mnmum sze lmt regulatons (Hunt 1970). anagng several thousand trout populatons usng average length-atmaturty does provde a practcal and cost-effectve way to manage wthout the need for detaled bologcal data on each system. However, applyng a management strategy developed from a small sample sze (21 lakes) to several thousand populatons could undoubtedly create stuatons where some populatons are overly-protected, whle some populatons may not be fully protected. In an effort to evaluate the effectveness of the current trout regulatons, length-atmaturty data from ndvdual lakes were evaluated aganst the management strategy currently used at these lakes; the results for each management strategy are presented below. 18

27 Hgh-Use Lakes A larger sze lmt (14 nch mnmum sze) was adopted for areas wth developed access and/or ntensve fsheres wth hgh angler use ( hgh-use ). Ths more restrctve lmt was ntended to protect all female cutthroat trout from harvest untl they had the opportunty to spawn at least one tme. The a pror goal of protectng all trout untl they have had an opportunty to spawn at least once appears to be defned ncorrectly or unobtanable. Length-at-maturty results suggested that no populaton sampled had length categores where 100% of the females were mature, ether as a result of not spawnng annually once reachng sexual maturty, or because larger fsh avoded the samplng gear. A more realstc bologcal management goal may be to protect 90% of the populaton untl they have had an opportunty to spawn at least once. Fve of the 21 lakes sampled for maturty are beng managed as hgh-use lakes and the management goal of protectng all (>90%) of the spawners s beng acheved (Fgure 14). In Kook Lake the regonal mnmum sze lmt of 11 nches would also meet the hgh-use management objectve, thus the regulatons n Kook Lake may be overly protectve. Sample szes for the larger fsh sampled for maturty were small and ranged from 5 at Stkoh Lake to 54 at Kook Lake. Regonwde nmum Sze Lmt Twelve of the lakes sampled are managed under the regonwde mnmum sze lmt of 11 nches (Fgure 15). The dstrbuton of lengths for mature female trout sampled from these lakes fall below the 11-nch regonwde sze lmt, clearly meetng the strategy of protectng the majorty (>50%) of female trout untl they can spawn at least once. The length dstrbuton of mature females from rror and Slppery lakes, however, fall above the 11-nch mnmum sze lmt and few f any mature fsh are beng protected under ths management strategy. Although not as clearly defned as the other lakes, 52% of the mature female trout are beng protected n Wnstanley Lake. A mnmum sze lmt of 9 nches would protect nearly all of the mature female trout n 2 of the lakes (Colp and Lttle lakes, see next secton). Small Cutthroat Trout Lakes Three of the lakes sampled were ultmately assgned to the management strategy category called small cutthroat trout lakes (Fgure 16). The lakes managed under ths strategy have a 9-nch mnmum sze lmt and the length of female trout sampled n ths lake show that few, f any, fsh are >9 nches (Fgure 16). There are a total 7 lakes n SEAK, ncludng the three that were sampled (Fgure 17), that are managed under the small cutthroat trout lakes regulatons. Two addtonal lakes sampled durng the maturty project (Colp and Lttle lakes) have length-atmaturty length dstrbutons showng that >90% of the mature female populaton n these lakes would be protected under a 9-nch mnmum sze lmt (Fgure 15). Several other lakes (North Saddle, St. Ncholas, Thayer, cknney, and Upper Wolf lakes) would have between 70% and 90% of ther mature female trout protected under a 9 nch mnmum sze lmt (Fgure 15). Trophy Lakes No trophy lakes were sampled as part of ths study prmarly due to the destructve samplng requred at the tme of the study. Snce the maturty study concluded there has been promsng results of nondestructve samplng usng ultrasound technology (Bangs and Nagler 2007) and technques requrng only a blood sample (Bangs and Nagler In press). 19

28 400 14" mnmum sze lmt 350 Total length (mm) " mnmum sze lmt Eva Klawock Kook Stkoh Thoms Fgure 14. Length dstrbutons of mature female cutthroat trout n 5 lakes managed for hgh angler use n Southeast Alaska wth lnes showng regonwde mnmum length restrctons (11 nches) and hgh angler use mnmum length restrctons (14 nches). 20

29 400 11" mnmum sze lmt Total length (mm) " mnmum sze lmt Colp Gouldng Lttle cknney rror N. Saddle Neck Slppery St. Ncholas Thayer Upper Wolf Wnstanley Fgure 15. Length dstrbutons of mature female cutthroat trout n 12 lakes managed under the regonwde (11 nch) mnmum sze regulatons as hgh angler use n Southeast Alaska wth lnes showng the 11-nch and 9-nch mnmum sze lmts " mnmum sze lmt 220 Total length (mm) Buck Long Fgure 16. Length dstrbutons of mature female cutthroat trout n 3 lakes managed under the small cutthroat trout lake strategy wth a 9 nch mnmum sze regulatons wth a lne showng the 9-nch mnmum sze lmt. 21 Shelter

30 Fgure 17. Lakes n Southeast Alaska that are managed as ether hgh angler use (14 nch mnmum sze lmt) or small cutthroat trout lakes (9 nch mnmum sze lmt). 22