Environmental Biology of Fishes (2005) 72: 45-54 @ Springer 200~

Relationship between hatch date and first-summer growth of five species oj

prairie-stream cyprinids

Bart W. Durham & Gene R. WildeWildlife & Fisheries Management Institute, Mail Stop 2125, Texas Tech University Lubbock, TX 79409,U.S.A. (e-mail: bart.durham@ttu.edu)Received 3 July 2003 Accepted 3 March 2004

Key words: growth increments, bet-hedging, overwinter mortality, young-of-the-year

Synopsis

Stream fishes often exhibit a bet-hedging multiple spawning reproductive strategy. In many species, thereproductive season lasts several months. This exposes young fishes to varying environmental conditionsthat may differentially affect growth. We studied the effect of hatch date on first-summer growth amongmembers of a prairie-stream fish assemblage. The reproductive season in both years of the study wasprotracted, lasting from April through August. Due to intermittent stream-discharge, there were twodistinct periods during which most species successfully reproduced. In general, growth rate was greateramong individuals with an early hatch date than among those with a later hatch date. Multiple regressionmodels indicated that hatch date was related to growth in all study species with one exception (red shiner,Cyprinella lutrensis). The results of this study provide evidence that young-of-the-year of multiple spawningstream-fish species that are spawned late in the season may grow at a slower rate than young spawnedearlier in the season.

Introduction

Reproduction by most fishes is seasonal in occur-rence and timed to maximize the probability thatoffspring will have necessary resources for growthand survival (Cushing 1990, Conover 1992,Humphries et al. 2002). Timing of reproduction insome fishes is strongly linked to seasonal cycles infood availability (Cushing 1990, Leggett & DeB-lois 1994), whereas for others reproductive outputappears to be associated with specific environ-mental conditions, such as temperature, photope-riod length, and water level or seasonal rainfall(Lowe-McConnell 1979, Munro 1990). Synchro-nization of reproduction with optimum conditionsfor growth and survival of offspring is more diffi-cult for species that inhabit variable environments.Streams and rivers often are characterized by ex-

tremely variable physical and chemical conditionsand frequent disturbances such as flood anddrought. Prairie and lowland streams, in particu-lar, have been recognized as highly variable envi-ronments that are characterized by rapid andunpredictable changes in discharge, temperature,pH, and dissolved oxygen concentration (Mat-thews 1987, 1988).

Fishes that inhabit prairie and lowland streamscommonly exhibit a classic bet-hedging strategy ofspreading reproductive output over an extendedperiod, thereby increasing the chances that a por-tion of the reproductive output will result in suc-cessful production of offspring (Lambert & Ware1984, Rinchard & Kestemont 1996, Trippel et al.1997). Because these fish spawn multiple clutchesof eggs, several sizes of offspring may be present atany given time during the reproductive season.

46

charges into the Arkansas River (Dolliver 1984).The study portion of the Canadian River isapproximately 218 km in length and is impoundedupstream by Ute Reservoir in New Mexico anddownstream by Lake Meredith in Texas (Figure1). River discharge is variable and is affected byseasonal rainfall, periodic releases from Ute Res-ervoir, irrigation return flows, and discharge froma major tributary, Revuelto Creek (Bonner &Wilde 2000). Arkansas River shiner, pepperedchub, plains minnow, flathead chub, and red shi-ner (the five species studied herein) collectivelycomprise 90% of the fish assemblage in this por-tion of the Canadian River (Bonner &Wilde 2000).

Environmental conditions may differentially affectgrowth of young produced at different times.Individuals resulting from spawning episodes earlyin the season have the advantage of a longergrowing season, compared to individuals spawnedlater (Keast & Eadie 1984, Conover 1992, Trippelet al. 1997). Because individuals spawned later inthe season have a shorter first growing season theymay be subject to size-selective overwinter mor-tality, which has been documented for a number ofspecies (e.g., Henderson et al. 1988, Shuter & Post1990). Thus, hatch date and subsequent growingconditions may be critical determinants of repro-ductive success of prairie-stream fishes.

In this study we examine first-summer growth offive members of a prairie stream-fish assemblage.Species studied are all members of the familyCyprinidae and include: Arkansas River shinerNotropis girardi, peppered chub Macrhybopsistetranema, plains minnow Hybognathus placitus,flathead chub Platygobio gracilis, and red shinerC}'prinella lutrensis. Except for red shiner, thesefish are members of a reproductive guild thatbroadcast spawns non-adhesive, semi-buoyanteggs that are carried downstream by the currentduring incubation and larval development (Plata-nia & Altenbach 1998). Red shiner spawns adhe-sive demersal eggs that attach to substrate or otherinstream structures during development. Ourstudy objective was to determine if growth ofyoung-of-the-year fish is related to hatch date. Thenull hypothesis underlying this investigation wasthat growth rates are similar for all young-of-the-year of a given species regardless of hatch date.

Sampling

We collected young-of-the-year fish from two siteson the Canadian River (Figure 1). Site 1 is locatedat the junction of U.S. Highway 287 (PotterCounty, Texas; 35028' 13" N, 101052' 45" W). Site2 is located near the junction of U.S. Highway 385(Oldham County, Texas; 350 31' 25" N, 1020 15'42" W). We collected fish from May throughSeptember in 2000 and 2001 with a small meshseine (1.8 x 3.4m, 1-mm mesh). We made collec-tions bimonthly in May and September andweekly during June through August unless riverconditions prevented sampling. We preserved allsamples in 95% ethanol in the field.

Laboratory procedures

We identified fish to species and measured totallength (TL) to the nearest millimeter. We removedthe largest pair of otoliths, the sagittae, from eachfish. Procedures for otolith preparation andcounting of daily growth increments generallyfollow the methods outlined by Secor et al. (1992)and Miller & Storck (1982). We attached oneotolith to a clear glass microscope slide withthermoplastic cement and stored the other otolithfor use in the event that the first one was broken orlost. We ground otoliths of larger specimens withfine grit sandpaper and polished them (Taubert &Coble 1977, Secor et al. 1992) to make growthincrements more visible. Two experienced readersindependently counted daily growth incrementsfor all otoliths using a compound light microscopeat 40x magnification. We accepted age estimates

Material and methods

Study area

The Canadian River is located in south centralUnited States and is characterized by sand sub-strate and shallow braided channels typical ofGreat Plains prairie streams (Matthews & Hill1980). The Canadian River is the southernmosttributary of the Arkansas River and rises on theeastern slope of the Sangre de Cristo Mountains ofnortheast New Mexico and southern Colorado.The river flows generally eastward through easternNew Mexico. Texas. and Oklahoma where it dis-

47

Figure J. Study area and location of two collection sites on the Canadian River, Texas. Collection sites are indicated by arrows.

showed a strong positive correlation with assigneddaily ages (r = 0.81-0.95, p < 0.001).

Data analysis

Hatch date was determined for each fish as thedifference, in days, between date of collection andage of the fish (determined by the number of dailyrings). Mean daily increase in length, a commonlyused measure of growth, was calculated for eachfish by dividing TL by age. Because growth inyoung fishes is generally non-linear, for examplefish at five days old add more body length per daythan fish at 50 days old, and because our samplesincluded fish of varying ages, we adjusted lengthfor age using linear regression after log-transfor-mation of length and age. We used multiple linearregression to assess the effects of length and hatchdate on growth.

from the two readers that were within 10% of eachother and assigned final daily ages as the mean ofthese two estimates. When initial readings variedby more than 10%, a third reader counted growthincrements. If the third reading fell within 10% ofone or both of the other two readings, we assigneda mean of the two closest readings as the final ageestimate (Miller & Storck 1982). However, if thethird reading was within 10% of the two initialreadings and fell exactly between the two initialreadings, all three readers re-read the otolith andwe either assigned a final age according to theguidelines above or excluded the otolith fromanalyses. We excluded all otoliths for whichreadings could not be reconciled to within 10% byany two readers.

Cyprinid fishes produce daily and annular oto-lith increments (Victor &Brothers 1982, Escot &Granado-Lorencio 2001). There is a strong rela-tionship between number of daily increments andotolith diameter, which allows validation of dailyages by regressing age on otolith diameter(Folkvord et al. 2000). Among the species westudied otolith diameter, measured to the nearest0.0 I mm along the longest axis (Secor et al. 1992),

Results

The five study species produced offspringthroughout a protracted spawning season, from

48

2000 2001

-'!oE.s:5OJc:.E!..5Q)cnmQ)'-u.5

:?::o"ffi"Cc:mQ)

~

1.1

0.9 .0.7 .

0.5 .

0.3.0.1 .1.1 .0.9 .0.7 .0.5 .

0.3 .

0.1'

1.1.

0.9 .

0.7 .

0.5 .0.3 .

0.1

1.1

0.9 .

0.7 .

0.5.0.3 .

0.1 .

1.1 .

0.9 .

0.7 ;

0.5

0.3

0.1

Apr May Jun Jul Aug Sap Apr May Jun Jul Aug Sap

Hatch date

Figure 2. Mean daily increase in length for young-of-the-year prairie-stream cyprinids from the Canadian River, Texas in 2000 and2001.

April through August during both years of thestudy. In each year, there were two distinct periodsof successful reproduction separated by a period inwhich no reproductive success was evident (Figure2). This pattern appeared to be associated withperiods of drought, which occurred during the

reproductive season of both years (Figure 3).Mean daily increase in length (growth) was highlyvariable in all species in both years of the studyand ranged from 0.22 to 0.83 mm day-I forArkansas River shiner, 0.26-0.75mmday-1 forpeppered chub, 0.22-1.0 mm day-I for plains

1.1 .

0.9 .

0.7.

0.5.

0.3.

0.1

1.10.9 .

0.7 .

0.5 .

0.3 .

0.1

1.1 .

0.9 .

0.7 .

0.5 .

0.3 .

0.1 .

1.1 .

0.9.

0.7 .

0.5 .

0.3.

0.1.

1.1 .

0.9.0.7 .

0.5 .

0.3 .

0.1

49

Figure 3. Canadian River discharge during 2000 and 2001 reproductive seasons.

flathead chub in 2001 (Table 2), showing thatgrowth rates of these species were related to hatchdates. Including hatch date in these models ex-plained an additional I % (Arkansas River shiner,2000) to II % (flathead chub 2001) of the variationin length. Hatch date was negatively related togrowth rate in Arkansas River shiner, plainsminnow, and flathead chub, indicating that indi-viduals spawned later in the reproductive seasongrew at a slower rate than individuals spawnedearlier in the season. There was a positive rela-tionship between hatch date and length in pep-pered chub, indicating that individuals spawnedlater in the season grew at a greater rate than thosespawned earlier.

minnow, 0.25--0.76 mm day-I for flathead chub,and O. 18---Q.88 mm day-I for red shiner (Figure 2).Mean daily increase in length for plains minnow in2000 and Arkansas River shiner, plains minnow,flathead chub, and red shiner in 2001 appeared tobe less for individuals spawned and hatched duringthe second period of successful reproduction(Figure 2).

There was a significant positive (p < 0.001)relationship between log-length and log-age for allspecies in both years of the study, with log-ageexplaining 46--86% of the variation in log-length(Table 1). The slopes of all regressions were sig-nificantly different (p < 0.001) from].O indicatingthat growth is not isometric.

To fully assess the effect of hatch date on growthwe used multiple regression to adjust for the affectsof age on length. Multiple regression models weresignificant (p < 0.00]) for Arkansas River shinerand plains minnow in 2000 and for ArkansasRiver shiner, peppered chub, plains minnow, and

Discussion

Hatch date significantly affected growth rate inmost species studied. Except among peppered

50

Table J. Linear regression models for total length and age (independent variable) of young-of-the-year prairie-stream fish collectedfrom the Canadian River, Texas during the 2000 and 2001 reproductive seasons.

?Species Year Slope Range of ages(days)

Intercept p

Arkansas River shiner 20002001

20002001

20002001

20002001

20002001

0.5200.085

-0.\420.0\6

0.669-0.077

-0.\9\

0.354

0.3470.994

0.6280.764

0.8760.821

0.6360.876

0.9050.664

0.6720.467

14-11513-65

15-10016-60

16-13114-72

21-9915-70

12-12812-100

0.740.63

0.860.67

0.710.75

0.860.61

0.810.46

<0.001<0.001

<0.001<0.001

<0.001<0.001

<0.001<0.001

<0.001<0.001

210143

15441

Peppered chub

Plains minnow 190112

2244

162100

Flathead chub

Red shiner

Both total length and age variables were log-transformed.

chub spawned in 2001, individuals with a laterhatch date grew slower than those with an earlierhatch date. Given average differences in watertemperature early and late in the reproductiveseason, these results are consistent with thecountergradient hypothesis advanced by Conover(1990) and Conover & Present (1990), althoughour study did not have a latitudinal component.We offer two alternative explanations for the ob-served differences in growth between early and latespawned fish. First, variation in water temperatureduring the summer may differentially affectgrowth. Second, differences in the size of spawningadults may affect size of young at hatching andtheir subsequent growth. At this time, we can notdismiss the possibility that other factors, not ad-dressed here, may have contributed to the ob-served growth patterns.

Growth and survival of young-of-the-year fishesare related to water temperature (Houde & Zas-trow 1993, Stags & Otis 1996), which may explainas much as 50% of the variation among popula-tions in growth and survival (Houde 1997). Al-though growth and survival generally arepositively correlated with water temperature, thisis true only up to a thermal optimum (Kamler1992). When temperature exceeds the optimum,increased energetic demands compromise growthand survival. Populations of Arkansas River shi-ner, peppered chub, plains minnow, and flatheadchub in the Canadian River are at or near thesouthern limit of their respective ranges (Lee et al.1980). High summer temperatures in this regionlikely exceed the thermal optimum for growth inthese species. Further, drought conditions in thelatter portion of summer often result in the river

Table 2. Multiple regression models for growth of young- of- the-year prairie-stream fish collected from the Canadian River during the2000 and 2001 reproductive seasons.

-0.002

-0.002

0.004

-0.006

-0.003

-0.002

20002001

2001

20002001

2001

0.8000.275

0.167

1.6690.501

0.524

0.6320.797

0.586

0.6170.856

0.720

0.750.67

0.72

0.760.83

0.72

<0.001<0.001

<0.001

<0.001<0.001

<0.001

210143

41

190112

44

Peppered chub

Plams minnow

Flathead chub

Total length (dependent variable) and age were log-transformed. Hatch date was not transformed. Only species and years for whichhatch date was significant are shown.

51

26 2000

24

22

20

G'.';' 18..~~; 16CoEGI

I- 26>.:c§ 24~~IVGI 22~

2001

20

18

16

April May June July August

Figure 4. Mean monthly water temperature for Canadian River during 2000 and 2001 reproductive seasons. Data is taken from USGSgauging station #07227500 near Amarillo, Texas.

being confined to a series of isolated pools. Indeed,periods of intermittent stream-discharge duringboth years, especially the 2001 reproductive sea-son, likely resulted in the two distinct periods ofreproductive success observed in this study (Dur-ham 2002). Our collections were made in temper-atures as high as 38°C, which exceeds the reportedcritical thermal maxima for Arkansas River shiner(3S.9°C) and red shiner (36.6°C) (Matthews 1987)and is near that reported for plains minnow 39.7°C(Ostrand & Wilde 2001). High temperatures inJuly and August (Figure 4) may result in decreasedgrowth in Canadian River fishes as a result ofcessation in feeding (e.g., Lochmiller et al. 1989) orincreased metabolic demands that can not becompensated for by increased food consumption(e.g., Hayward & Arnold 1996).

Greater growth of individuals with an earlierhatch date in the Canadian River also may berelated to body size of spawning fish. Bonner(2000) found that two-year-old Arkansas River

shiner and peppered chub were present incollections from the Canadian River only throughthe end of May. Presumably, these fish spawnedearly in the reproductive season (late April andMay) and then died. Similarly, Taylor & Miller(1990) reported that two-year-old plains minnowin the Cimarron River, Oklahoma, made up themajority of spawning population during the firsthalf of the reproductive season. Thus, there issome evidence that larger fish spawn early in theseason. Such fish often produce larger eggs thansmaller individuals of the same species that arespawning for the first time (Kamler 1992, Cham-bers 1997). Egg size is positively correlated withsize of emerging larvae (Hislop 1988, Miller et al.1988, Chambers 1997) and an initial size advan-tage may be retained for some time (Chambers &Miller 1995).

Production of multiple clutches of eggs is acommon tactic among cyprinids that inhabitenvironmentally variable streams and rivers in

52

aspects of reproductive ecology and early life-hi.story.

Acknowledgements

We thank Jesse Shuck, Scott Sebring, Kevin Offill,and Felix Martinez Jr. for aiding with field col-lections. Mike Irlbeck provided additionallogisti-cal support. We also thank Monte Brown andChris Chizinski for counting otolith growthincrements. Funding for this project was providedby the United States Bureau of Reclamation. Ke-vin Pope, Richard Strauss, and Mike Irlbeckprovided helpful suggestions on earlier drafts ofthis manuscript. This is contribution number T -9-1000 of the College of Agricultural Sciences andNatural Resources, Texas Tech University.

References

which discharge, temperature, habitat, and foodavailability range widely. For example, in theregulated River Meuse, Belgium where dischargeand temperature often fluctuate, white breamBlicca bjoerkna and bleak Alburnus alburnus pro-duce multiple clutches of eggs from May to Juneand May through July, respectively (Rinchard& Kestemont 1996). Zacco pachycephalus, a smallendemic cyprinid inhabiting intermittent streamsof Taiwan is a multiple spawning species that hastwo periods of reproductive activity from Febru-ary through April and from July through Sep-tember (Wang et al. 1995). The ability to spawnrepeatedly during a protracted reproductive sea-son increases the probability that at least someyoung will be produced successfully in eachreproductive season (Weddle & Burr 1991, Rin-chard & Kestemont 1996, Trippel et al. 1997).Prairie stream cyprinids can reproduce well intoAugust and September (Olund & Cross 1961,Farringer et al. 1979, Taylor & Miller 1990, Bon-ner 2000), which may leave individuals spawnedlate in the season relatively little time for growthbefore the onset of winter.

Most studies of overwinter mortality of young-of-the-year fishes have been conducted forimportant forage fish species (Keast & Eadie 1984)and recreationally or commercially valuable spe-cies (Keast & Eadie 1984, Miyakoshi et al. 2003).Further, these studies have been conducted almostexclusively on populations from northern temper-ate latitudes where there is a short growing season(Conover 1992). The relationship between bodysize and overwinter mortality is not well under-stood in populations at lower latitudes and theextent of size-dependent mortality through the firstwinter for young-of-the-year prairie-stream fishesis unknown. The fate of the slow-growing late-spawned fish observed in our study is uncertain.Our results, however, document reduced growthfor a substantial portion of offspring producedduring the reproductive season. If indeed offspringof prairie-stream fishes with hatch dates late in thereproductive season do experience size-selectiveoverwinter mortality, reproductive output early inthe season may be most important for maintainingpopulations. Given recent widespread declines inthe distribution and abundance of stream fishpopulations, this information could prove partic-ularly important for conservation efforts as critical

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