Reproductive structure of Rainb

Glen Canyon and advancing met

capability capability

James Crossman, Molly Webb, Josh Ko

Glen Canyon Dam Adaptive Mana

Annual Reporting Meetin
Acknowledgements Acknowledgements 

 USGS GCMRC 

o Mariah Giardina (and crews) o David Ward o Kim DibblKim Dibble 

 In-kind contributions 

o BC Hydro o USFWS o USGS GCMRC 
Why are rey are reproductiproductive indices i

e indices i
Examples of reprodu

Examples of reprodu

 Sex ratio (Population)  Age and size e and size at maturity at maturity (Individual + Pop)  Fecundity (Ind + Pop)  Spawning periodicity (Ind + Pop)  Reproductiproductive structure (Pop) 

 e.g. proportion of the popul the population that is that is 

reproductiproductively active 

Rainbow Trout data from Crossman, Webb, Korman and Yard, 2022 
How do you determine sex and 

Invasive Less-invasive Least-invasi

Dissection Sex steroids Ultrasound (euthanize) (blood plasma) (requires physic

or anesthetic restraint) 

Endoscopy Genetic markers Secondary sexu

(surgical incision) (tissue sample) characteristics 

(e.g. tubercles, kype) 

Biopsy Manual 

(surgical incision) expression 

(i.e. squeezing) 

Histology (sample collection dissection/bisopsy) 

How do you determine sex and 
Trout reproduct

Reproduced from Korman

Trout reproduct

Reproduced from Korman 

Follicular atresia: the resorption of ovarian follicles (eggs) 

Normal 

Atresia 

Regressing 

(October – March) 

Mass 

follicula

atresia 

Post-ovulatory 

Post-spermiation 
Objective

Objective

 Describe Describe population re population reproductiproductive structure 

cture 

in Glen Cany in Glen Canyon 

 Better understand causes understand causes for population 

for population 

Population reproductive structure: the proportion of the p

 Evaluate the aluate the accuracy ofaccuracy of less invasive meth

th

reproductiproductive conditione condition 
Methods Methods 

 Integrated clasated classification fication of gametogenesis 

from the from the literature within the literature within the framework of 

standardized ter standardized terminology for reproductiproductive development in teleosts lopment in teleosts 

 Result: Specific sult: Specific reproductiproductive stages and 

phases 
Methods Methods 

 Samples Samples collected collected across Nov, Jan, Apr tripsn, Apr trips  1-2 fish per sampling 1-2 fish per sampling site (random/spatiall site (random/spatially balanc

balanc

 Data Collected: Data Collected: 

 Length and wngth and weight  Manual expression ofession of gametes gametes  Ultrasonography  Gonad weight  Gonad tisGonad tissue for histology 
Methods Methods 

 Integrated clasated classification fication of gametogenesis 

from the from the literature within the literature within the framework of 

standardized ter standardized terminology for reproductiproductive development in teleosts lopment in teleosts 

 Result: Specific sult: Specific reproductiproductive stages and 

phases 
Method

Method

Histological analyses to quantify seasonal-, size-, and sex-sp

Females 
Less invasive methods to assign sex 

Less invasive methods to assign sex 

Expression of gametes Ultrasonograp

http://sustainablefishfarming.blogspot.com/2010/11/browntrout-spawning.html 
Ultrasonography to assign sex an

Ultrasonography to assign sex an
Results from 2018-2019 Rainbow 

Results from 2018-2019 Rainbow 
Reproductive condition across 

Reproductive condition across 
Ultrasonography works well for 

Ultrasonography works well for 
Rainbow Trout result

Rainbow Trout result

 Spawning occurrng occurred over a highly protracted period from O

from O

 Proportion of spawning capabl wning capable female Rainbow Trout ap

ap

atresia (compared atresia (compared to other populother populations) 

 A relatively high propor high proportion of male Rainboe Rainbow Trout were 

spawning period 

 Large immature mal e immature males suggests delests delayed maturation maturation 

 These patterns suggest that est that females drive the reproductiproductive 

output of the popul the population 
Comparative reproductive st

Comparative reproductive st

 Immature Immature and developing Brooping Brown 

Trout are smaller smaller than Rainbow 

Trout 

 Large immarge immature males in both 

species species (have never spawned) 

% Female Spawning Capabng Capable 

 Nov 2021 Brown: 50% spawning 

capable 

 Jan 2019 Rainbow: 50% 

spawning capabng capable 
Next Step

Next Step

 Describe population reproductive structure over 

multiple years 

 Combine with growth rates and condition factor to 

determine linkage to population abundance 

 Comparison of Rainbow and Brown Trout provides 

a unique opportunity to compare the reproductive structure of two species and improve our understanding of population dynamics of trout within the Colorado River 

 Ultrasonography was effective for spawning capable 

females and males which is being further evaluated 

in 2021-2022 in both trout species 

 Including incorporation into standard fish processing 

protocols 
Ultrasonography for spaw

aw
Question

Question