BATHYMETRIC PATTERNS IN SIZE, AGE, SEXUAL MATURITY, WATER CONTENT, AND CALORIC DENSITY OF DOVER SOLE, MICROSTOMUS PACIFICUS

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1 HUNTER ETAL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Yol. 1,199 BATHYMETRC PATTERNS N SZE, AGE, SEXUAL MATURTY, ATER CONTENT, AND CALORC DENSTY OF DOVER SOLE, MCROSTOMUS PACFCUS JOHN R. HUNTER, JOHN L. BUTLER, CAROL KMBRELL, AND ERC A. LYNN Ntionl Mrine Fisheries Service Southwest Fisheries Center f!. Box 71 L Joll, Cliforni 98 ABSTRACT Ninetyeight percent of the spwning biomss of Dover sole, Microstomus pcijicits, in centrl Cliforni wters live in region of the continentl slope between 64 nd 16 m (555 fth.) chrcterized by low oxygen concentrtions (.7.6 ml/l) nd cold tempertures (5.9OC. C). Juvenile Dover sole settle on the continentl shelf nd grdully move down the slope over their lifetime, reching the oxygen minimum zone s they become sexully mture. Fifty percent of Dover sole in centrl Cliforni rech sexul mturity when bout 1 cm long nd bout seven yers of ge. The ontogenetic movement down the slope continues fter sexul mturity nd is ccompnied by mrked increse in wter content of the body nd consequent decrese in cloric density per grm wet weight. For exmple, cloric density decreses from bout 86 kcl per grm wet weight (8% wter) for 75 mm fish living t 4 m, to 6. kcl per grin wet weight (go/, wter) for fish 44 mm long living t bout 9 m. Femle Dover sole my live s long s 5 yers, nd mles 58 yers. ter content ppers to be function of ge s well s length nd depth. RESUMEN El 98% de l bioms del desove del lengudo de ls gus de Cliforni centrl, Microstornus pclficus, vive en un Are del tlud continentl entre 1s 64 y 1s 16 m crcterizd por bjs concentrciones de oxigeno (.7.6 ml/l) y bjs temperturs (5.9OC. C). Los juveniles se estblecen en l pltform continentl y grdulmente, durnte su desrrollo, se vn moviendo hci el tlud y lo lrgo de 61, llegndo l zon de minimo oxigeno cundo lcnzn l mdurez sexul. El 5% del lengudo lcnz l mdurez sexul cundo mide proximdmente 1 cm de longitud, 1s 7 iios de edd. El inoviniiento descendiente lo lrgo del tlud durnte l ontogenesis continu psd l mdurez sexul, y es compfido por un incre ~~~ ~~~~~ ~~~ [Mnuscript received April,199.1 mento mrcdo en el contenido de gu del cuerpo y consequentemente, por un decrecimiento en l densidd cloric por grmo de peso h~medo. Por ejemplo, l deiisidd cloric de un pez que mide 75 mm y vive 4 m de profundidd decrece de 86 kcl por grmo de peso htimedo (8% de gu) 6. kcl (9% de gu) pr un pez que mide 44 mm de longitud y vive 9 m de profundidd. Ls hembrs pueden vivir hst proximdmente 1s 5 fios de edd y 1s mchos hst 1s 58. El contenido de gu prece estr relciondo con l edd y el lrgo del individuo y con l profundidd l cul vive. NTRODUCTON Dover sole, Micvostomus pctjicus, re found from the Aleutin slnds in the Bering Se to Bj Cliforni (Eschmeyer et l. 198). The U. S. fishery for Dover sole occurs from Point Conception, Cliforni, to the Cndin border. Dover sole inhbit depths rnging from bout 55 to 1 m. Older nd lrger fish usully occur in the deeper portion of the depth rnge, nd younger nd smller fish in the shllower depths. A sesonl inshore migrtion hs been described: fish move into deep wter in the fll before the spwning seson nd into shllow wter in the summer (Hgermn 195; Alverson 196; Percy et l. 1977). Most individuls pprently remin in the sme generl loclity throughout their lives. Although longshore movements of up to 6 mi (579 km) in seven yers hve been recorded, 97% of tgged individuls were recptured within 5 km of where they were tgged (estrheim nd Morgn 196). Lrge Dover sole from deep wter re often tiellied (hve flesh with n unusully high wter content). This tjellied consistency limits the mrket vlue of fillets from lrge Dover sole becuse their desirbility is reduced (Hendricksen et l. 1986). Owing to the ontogenetic migrtion into greter depths, nd the extensive depth rnge, the demogrphic nd physiologicl chrcteristics of Dover sole chnge strikingly with depth, ge, nd length. Thus neither the dynmics nor the ecology of Dover 1

2 ~~ ~~~ ~~ ~ ~ ~~~ ~~ ~~ 6 ~~~~~ ~~ ~~~ ~~~ ~~~ ~~~ HUNTER ETAL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 sole popultions cn be properly nlyzed or understood without creful evlution of the reltion between depth nd key physiologicl nd popultion vribles. The objective of this pper is to describe the reltionships between depth, length, ge, sexul mturity, wter content, cloric density, nd biomss of Dover sole. e lso provide dt on the temperture nd oxygen content of the hbitt in which fish of different length nd ge re found. Our nlysis does not include dt for the summer months, when fish my hve shllower distribution (Alverson 196). METHODS Se Collections Reserch trwl collections were tken t depths between 69 nd 194 m (876 fth.) off the centrl Cliforni cost between Point Conception nd Hlf Moon By, Cliforni, during by NOAA Southwest Fisheries Center (SFC) personnel (tble 1). Trwl collections were opportunistic before n 1987, smples were tken t 18m (1fth.) intervls long trnsect lines; in 1988 rndom smpling design strtified by depth ws used (figure 1). n ll yers fish were sexed nd mesured for totl length. Before Jnury 1987, fish were rndomly smpled from ech collection until 5 femles hd been identified nd their ovries preserved for lter ssessment of mturity; the femles nd some mles were frozen for subsequent extrction of otoliths nd determintion of wter content s described below. During JnuryFebrury 1987, either ll of the Dover sole in the trwl collection or 1 fish were rndomly smpled, nd 5 femles were ssessed for gond mturtion. Four to six fish of ech sex were weighed nd frozen for lter removl of otoliths nd tissue. for nlysis of wter content. The bottom temperture (reversing thermometer on Nnsen bottle) nd oxygen content (inkler titrtion) were mesured for 17 Nnsen cst sttions rnging from 18 to 1,8 m (17 fth.; figure 1, left, tringles). The totl trwl ctch of Dover sole ws weighed during 1987 nd n 1988, up to 1 Dover sole were rndomly smpled nd weighed by sex; the mturtion stte of ll ovries ws determined. Age Determintion Ages were determined from otoliths removed from 41 femles nd 64 mles cptured during nd from 154 femles nd 97 mles cptured in Left otoliths were embedded in epoxy resin nd cut with dimond wfering blde in thin cross section through the nucleus from dorsl to ventrl (Chilton nd Bemish 198). Thin sections were mounted on microscope slides with Eukitt mounting medium, polished, nd red with compound microscope. A typicl otolith section is shown in figure. Counting procedures followed those of Chilton nd Bemish (198). Ech otolith ws red independently by three observers without knowledge of the length of the fish. Otoliths whose redings differed by more thn 1% mong the reders were rered using the sme protocol until the redings greed to within 1%. Estimted ge ws the verge of the individul redings. Prmeters of the von Bertlnffy eqution relting length nd ge were estimted by the simplex method (O Neill 1971). TABLE 1 Sources nd Numbers of Dover Sole Used for Anlyses Number of positive trwl collections Number of Dover sole used in vrious nlyses Smpling Depth ~ Percent Size t Sexul Dtes VPe N Min Mx wter Clories Age depth mturity 111/1/85 OP /14/4/86 PS OP /4/86 OP /87 LT /9/88 SR ~ Totl specimens OP = opportunistic trwl smples, PS = port smples, LT = linetrnsect trwl smples, SR = strtified rndom trwl smples Number of Nnsen cst sttions. Oxygen nd 17 1

3 HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1; N FN 16ON 5ON U 1O 1 w 11ow 1 ' Figure 1. Left, trwl sttions occupied on the JnuryFebrury 1987 groundfish cruise of the R/V Dvid Strr Jordn. Right, trwl sttions occupied on the FebruryMrch 1988 groundfish cruise of the R/V Dvid StrrJordn. Figure. Thin section of the left otolith of 4yerold Dover sole. Numbers indicte yers. 14

4 HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 Biomss e used the men biomss in the re swept by trwls, nd totl re within three depth strt to estimte Dover sole biomss. The survey re extended from 4"'N, 1"' to 6"'N, 1"' (Butler et l. 1989). Sexul Mturity The size t first mturity of femles tken in December 1985 ws estimted by logistic regression nlysis (Drper nd Smith 1981; Engelmn 1988). Dt from the other surveys (tble 1) were not pproprite for estimting sexul mturity becuse the spwning seson begn before the first survey. The possibility of mistking immture ovries for postspwning ovries ws minimized becuse December ppers to be erly in the spwning seson (Hunter, unpublished dt). Ovries with yolked oocytes were considered to be mture, nd those without yolked oocytes to be immture. ter Content e mesured wter content by determining the wet weight of tissue smple (bout.5 g) nd then drying it to constnt weight t 6 C. The white muscle smples were tken from the right side of the fish between the lterl line nd the dorsl fin t the insertion of dorsl rys to 6, nd the red muscle smples were tken from the right side bove the lterl line nd behind the eye. To determine whether single tissue smple represented wter content of the whole fish, we mesured the entire wter content of femles, 6 mles, nd one fish of indeterminte sex by grinding nd drying the entire fish fter removing red nd white muscle tissue smples from the loctions described bove. e then regressed wter content (in percent ofwet weight) ofthe entire fish (H) on tissue smple wter content (figure ): H = h,, (1) where h, is wter content of white muscle (r =.96, n = 7; p <.1). The slope of this eqution did not significntly differ from 1., nor did the intercept differ from. On the bsis of these results we ssumed tht the percentge of wter in the white muscle tissue smples ws the sme s tht of the whole fish. hole fish wter content ws estimted (eqution 1) from white muscle tissue smples collected t se for 16 fish collected in 1985, 5 fish collected in 1986 (go/, femles), nd 65 fish (mles nd femles) collected in X u, 9 Y K k 66 s % ATER HTE MUSCLE (h,) Figure. Reltion of wter content of whole Dover sole to wter content of white muscle. Solid line is regression line fit to dt; dshed line is onetoone reltionship. ter content of the red muscle tissue smple ws lso linerly relted to wter content of the entire fish, lthough the reltionship ws poorer thn tht for white muscle: H = h, () where h, is wter content of red muscle (v =.87, n = 7; p <.1). Cloric Density nd Ft Content To determine cloric density (kcl/gm) of entire fish for 6 Dover sole, we used Prr bomb clorimeter nd stndrd techniques (Prr nstrument Co. 196; Pine 1971). The vlues reported here re the mens of three determintions. Fish were selected by size to obtin cloric mesurements over wide rnge of wter content (the fish smpled rnged from 8% to 94% wter). To determine ft content we used Soxhlet extrction with :l chloroformmethnol. This technique did not provide n ccurte estimte of totl ft content becuse the extrction period (487 hrs) ws too short for fish with high ft content, such s Dover sole. Notwithstnding this bis nd other problems ssocited with chloroformmethnol ex 15

5 HUNTER ETAL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 trctions (Dobush et l. 1985), we believe tht the dt provided useful informtion bout ft concentrtion. RESULTS Length nd Depth The men length of Dover sole increses rpidly with depth over the first fth. (549 m) nd therefter more slowly. The reltionship between depth nd size of Dover sole vried little mong yers (figure 4, top nd middle). The combined dt for ll surveys clerly indicte tht mles tken t given depth re smller thn femles (figure 4, bottom). Age nd Growth Mle nd femle Dover sole differ in size t ge (figure 5). Estimtes from counts of nnuli in thin sections of otoliths indicte tht the fish live long lives. The mximum estimted ge ws 56 yers for 46mm mle nd 51 yers for 49mm femle. E F 4 9 Y z c L 1 5 k 4 E! z E 4 F 9 1 $ 1 / _ A DOVER SOLE MALES LENGTH BY DEPTH c 1988 e 1 J i DEPTH (fthoms) DEPTH (meters) Figure 4 Men length of Dover sole collected t different depths Top, femles, middle, mles, bottom, ll yers combined with? SE E 4 E Y E (7 Z J loo E 4 E v (7 FEMALE DOVER SOLE o! 4 6 AGE (yers) Figure 5. Top, length nd ge (clculted from otolith section) of mle Dover sole. Solid line is von Bertlnffy curve with L = 47 mm, growth prmeter K =,89, nd to = ~ 4.7 yr. Bottom, length nd ge (clculted from otolith section) of femle Dover sole. Solid line is von Bertlnffy curve with L% = 474 mm, growth prmeter K =.85, nd to = 5.5 yr. See text for eqution. Prmeters of the von Bertlnffy growth model, were L, = 47 mm, K =.89, nd to = 4.7 yers (n = 161, p <.1) for mle Dover sole. Estimtes ofprmeters for femles were L, = 474 mm, K =.85, nd t,, = 5.5 yers (n = 495, p <.1). Mle nd femle Dover sole longer thn 4. cm my be ny ge from 8 yers to 4 or 5 yers. Neither our methodology nor ny other hs been vlidted for Dover sole. Nevertheless, we believe our ge estimtes pproximte the true ge, becuse the otolith section method hs been vlidted for nother species in the sme hbitt (Anoploponijirnbvi; Chilton nd Beniish 198). Our ge estimtes re much greter thn those obtined from scles (Demory 197; Merns nd Hrris 1975). However, tgndrecpture studies 16

6 HUNTER ETAL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 (Pikitch nd Demory 1988) hve shown tht scles underestimte the ge of Dover sole. The mximum ge observed in this study (56 yers) is in greement with the longevity tht Pikitch nd Demory (1988) predicted from tgndrecpture studies nd errors in scle redings. A significnt frction (4%) of femles in our smples were older thn yers. Our results suggest tht estimtes of the productivity of Dover sole stocks bsed on ges estimted from scles my be seriously flwed. ter Colztent Dt for femles tken from December 1985 through My 1986 indicte tht the men wter content of white muscle remins constnt t bout 8% in 15cm femles but increses with length in lrger Dover sole to bout 9% in 5cm femles (figure 6). The concentrtion of wter in the red muscle followed similr trend, but the increse in wter content with length ws much less. Averge wter content of red muscle in 5cm femles ws only 85%. These dt indicte tht red muscle is conserved. The red muscle in the nterior upper trunk region of the eyed side of the body is the lrgest concentrtion of red muscle in the body nd is probbly used to control hed movements during feeding. The color of the red muscle chnged with fish length. Lrger fish hd drker red muscle, indicting tht the myoglobin content of the muscle my be higher in lrger fish. The men wter content of mles tken in JnuryFebrury 1987 did not differ from tht of femles from tht smple within the sme 5cm length clss (ANOVA for five 5cm length clsses, 54 4 to mm, per sex where p =.9; ni 9 DOVER SOLE 89 E 88. Z 87. w c z 86 o 85. w 84. $ 8' t MEAN TOTAL LENGTH (mm) Figure 6. ter content in white nd red muscle versus totl length of femle Dover sole. nsert shows loctions of tissue smples for white muscle nd R for red muscle. figure 7). The wter content of Dover sole (both mle nd femle) s function of length showed little vrition between yers; the dt for December 1985My 1986 were essentilly the sme s those for JnuryFebrury 1987 (figure 7). Combining dt for ll yers nd sexes indictes tht the verge wter content for fish less thn 75 mm ws constnt t 8.9% (n = 9, SD = 1.), nd for fish greter thn 75 mm it incresed with length (L) ccording to the eqution H = L (4) (v =.58, n = 56; p <.1). ter Content, Age, Length, nd Depth n the previous sections we showed tht wter content increses with fish length nd tht length increses with depth nd ge. n this section we describe the reltionships between wter content, length, depth, nd ge of Dover sole femles. A n z 8 ' * Mle,? Femle w TOTAL LENGTH (mm) Figure 7. Top, wter content of white muscle versus totl length of femle (N = 16) nd mle (N = 98) collected in Bottom, wter content in white muscle of both sexes for (dshed line), 1987 (thin line), nd (thick line). z 17

7 ~~~~ ~~ ~~ HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ColCOFl Rep., Vol. 1,199 stepwise multiple regression nlysis indicted tht ll three independent vribles (ge, length, nd depth) ccounted for significnt vrition in the dependent vrible, wter content: the coefficient for ge ws the first selected (tble ). The finl eqution ws H = T +.1 L +.6 D (5) where H is wter content (percent of wet weight), T is ge (yers), L is length (mm), nd D is depth (fth.) (R =.69, n = 519; p <.1). Biologicl interprettion of the significnce of the individul regression coefficients in this eqution could be misleding (Sokl nd Rohlf 1981) becuse, s is indicted in the correltion mtrix (tble ), ll the vribles re correlted with ech other; length is correlted with ge nd depth s well s wter content. Cloric Density Cloric density (kcl per g shfree dry weight) ws correlted with ft concentrtion (F, in percent of dry weight). This reltionship ws less precise (Y =.57, n = 6; p <.1) thn one would expect TABLE Anlysis of the Reltion Between ter Content (H) of Dover Sole nd Their Age (T), Length (L), nd Depth (D) Stepwise regression Step 1 Constnt Age (T) trtio Length (L) trtio Depth (D) trtio S RZ Anlysis of vrince Source DF ss MS F P Regression Error Totl Source Age (T) Length (L) Depth (D), < , ,44.5 DF SeqSS 1, Mtrix of correltion coefficients ter (H) Age (r) Length (L) Age.779 Length Demh Forp =.5, the trtio is 1.96 on physiologicl grounds becuse of our filure to extrct ll the lipids in some of the fish. Nevertheless, figure 8 clerly indictes tht cloric density nd ft concentrtion re linked, s would be expected. No significnt reltionship existed between cloric density nd wter content. There ws no pprent reltionship between ft concentrtion nd wter content (v =.) when length ws not included s vrible. hen length (L) ws included s n dditionl third dependent vrible in stepwise multiple regression nlysis (tble ), definite reltionship existed between cloric density (C,) nd + P 7 $ > 6.5 U $ 6 u 5.5 s 7 5 Figure 8. : FAT CONCENTRATON ( A) m Cloric density versus ft concentrtion in Dover sole. TABLE Anlysis of Vrince Stepwise Regression of the Cloric Density of Dover Sole (C,, kcl/g shfree dry weight) on Their Totl Length (., in mm) nd ter Content (H, in Percent) Step Constnt ter (H) trtio Length (L) trtio S R Summry Anlysis of vrince Source Regression <O 5 Error Totl DF ss MS F P Source DF SeqSS L 1.58 H _ Forp =.5, the trtiois.7. 18

8 HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 wter content of white muscle (H, in percent wet weight) yielding the eqution C, = L.144 H (6) with R =.6, n = 6; p <.1 (figure 9). To further evlute these dt we nlyzed covrince by rrnging the dt into three length clsses ( mm, 96 mm, nd 4856 mm) nd regressed wter content on clories within length clss. This nlysis indicted tht the reltionship between clories nd wter content differed significntly mong the three length clsses (, 5, nd 45 mm men totl length; p <.1). For the overll men wter content (85.6'/), the djusted men kcl per g shfree dry weight re 5.64 t mm, 6.78 t 5 mm, nd 6.44 t 45 mm. The reltionship between cloric density nd length ws not significnt (Y' =.7, y1 = 7; p =.169). Thus, the reltionship between cloric density nd wter content chnges with length. The reltionship between length, wter content, nd cloric density in terms of wet weight (C,) ws lso evluted. The multiple regression eqution ws e lso wished to exmine how clorie content vried with depth. e used the multiple regression eqution 6 to compute the cloric density (C, in kcl per g shfree dry weight) of femle Dover sole s function of length nd wter content. e grouped the estimted cloric densities into seven 1fth. (18m) depth clsses nd clculted men nd stndrd devition (SD) for ech clss; the SD includes the vrince ssocited with eqution 6 (Drper nd Smith 1981; figure 1, top). A significnt difference existed between the men cloric density of femles in the 1fth. depth clss nd those in ll other depth clsses combined (t = 7.4, d.f = 7.7, p <.1; d.f ws computed from the formul given by Zr [1984]). The men cloric density for femles tken in the 1fth. depth clss ws kcl per g shfree dry weight (n = 4, SD = 9) nd tht of femles tken t C,, = L 7.6 H (7) where C, = kcl per 1 g wet weight, L = length, nd H = wter content of white muscle (R =.98, n = 6; y <.1). R is high becuse the wter content of the fish lrgely determines the cloric density when it is expressed on the bsis of wet weight.." P w 6.4 t : n 6. w : ( 5.6 Y 5.4 C = 1,54 14H + 4.L 1 L = mm L = 96mm L = 48 56mm 5.,,,,,,,,,,,,,,,, PERCENT ATER (H) Figure 9. Cloric density nd wter content of Dover sole in three size clsses. (See eqution 6 in text for multiple regression reltion of cloric density with length nd wter content.) ".T.1.9 P g.8 L.7? DEPTH (fthoms) DEPTH (meters) DEPTH (fthoms) 18 CT 16 $ z 14 U w 1 4 z 1 Figure O. Top, kcl perg shfree dry weight, SD nd Nwithin 1fth. depth clsses. Arrow is men cloric density for depths >15 fth. Bottom. kcl per 1 g wet weight (left xis) nd the complement of wter content (right xis) within 1fth. depth clsses

9 ~ HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol:1,199 depths greter thn 15 fth. ws kcl (n = 46, SD = 7). Thus, the Dover sole living in shllow wter (515 fth.; 9174 m) hve lower cloric density per unit dry weight thn Dover sole living t greter depths. A different pttern in the chnge in cloric density with depth occurs if cloric density is expressed in terms of wet weight rther thn dry. Using the sme dt nd eqution 7, we reclculted the verge cloric density of femles on wetweight bsis per depth clss. On wetweight bsis, the cloric density (kcl per g wet weight) declines with depth becuse of the increse in wter content (figure 1, bottom). As would be expected, the decrese with depth in cloric density of Dover sole wet weight mimics the decline in the complement of the wter content (1 percent wter; figure 1). These mesurements were mde during the period in which Dover sole mture sexully nd begin to spwn (DecemberFebrury). Other ptterns my exist t other times of the yer. Sexul Mturity The sexul mturity of Dover sole femles ws estimted by clculting the frction mture (n/r) for ech of seven 5mm length clsses (5556 mm). These dt were fit by mximum likelihood estimtes of the prmeters to logistic model v) E U if. 7( / ' / /.lo HAGERMAN 195 i.4!. LL / t MEAN TOTAL LENGTH (mm) Figure 11. Circles, observed frction of Dover sole tht re mture in December within 5mrn length clsses with N indicted, solid line, clculted frction mture from logistic regression eqution (eqution 8); Hgermn line clculted similrly; dshedline, length t 5% mturity. where = 9.947, stndrd error (SE) of =.688, nd t = (d.f = 1, p <.1); b =., SE of b =.159, nd t = 4.68 (d.f. = 1, p <.1); nd n = 14. This eqution predicts tht 5% of Dover sole femles of 11mm length re mture (figure 11). The smllest Dover sole with dvnced yolked oocytes in our collections ws 9 mm long. Judging from our gelength reltion for femle Dover sole (eqution ), length of 1 1 mm corresponds to n ge of bout 7 yers, nd length of 9 mm corresponds to bout 6 yers. The men lengths per depth clss were used to clculte how sexul mturity vried with depth. Men femle lengths were computed for ech of eight 1fth. (18m) depth clsses (ll trwl dt, ; n = 4,41; tble 1; figure 4), nd the mturity ws clculted using eqution 8. This nlysis indicted tht sexul mturity incresed with depth from bout 6% t fth. to 9% or more t depths of fth. (549 m) or greter. Oxygen Minimum Zone Perhps the most striking fetures of the environment occupied by Dover sole re the oxygen minimum nd dyserobic zones. n the 1987 survey the oxygen minimum zone (, <.5 ml/l) occurred between 64 m (5 fth.) nd 11 m (55 fth.), which is similr to the depth rnge (855 fth.) during reported by Mullins et l. (1985) off Point Sur, Cliforni. The dyserobic zone (, < 1 ml/l) begn t 457 m (5 fth.). Most sexully mture femles were observed in the dyserobic zone. e estimted tht 86% of the spwning biomss existed in the oxygen minimum zone (tble 4; figure 1) on the bsis of the middle depth strtum (5 549 fth.) used in the 1987 nd 1988 surveys (Butler et l. 1989). e lso estimted tht nerly ll (9%) of Dover sole living bove the dyserobic zone were juvenile. The oxygen minimum zone is lso chrcterized by low tempertures (figure 1). The wter in the dyserobic zone rnged from 5.9"C t 5 m (9 fth.) to."c t 16 m (69 fth.), nd tht in the 14

10 HUNTER ETAL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 9 DEPTH (Fthoms) g 5 TEMPERATUR OXYGEN u m ml u r. m. P r r.4 b. m.% m u 5 p 'f w L u Y v o DEPTH (Fthoms) d r. r. d. " , DEPTH (Meters) Figure 1. Bottom temperture, dissolved oxygen, biomss (MT) in study re, length (mm), nd energy content (kcv1 g wet weight) of Dover sole s function of depth for ic P oxygen minimum zone from 4.9"C (7 m; 8 fth.) to 4."C (9 m; 49 fth.). Reduced metbolism due to temperture my help Dover sole cope with the low oxygen concentrtions in the region. P P d f ic ic m m ic P d K d DSCUSSON Mu tu vity Our estimte ofthe length t first mturity differs from tht estimted by Hgermn (195). e fit eqution 8 to Hgermn's dt (56 mm, tz = 846) nd estimted the length t 5% mturity of femle Dover sole lnded in Eurek, Cliforni, during to be 6 mm (u = 17.85, SE of u = 1.975, t = 9.4, d.f = 84, p <.1; b =.49, SE of b =.5, t = 9.89, d.6 = 84, p <.1; nd n = 844). e compred the coefficients of the logistic regressions for our dt to those collected by Hgermn using the Ztest (Zr 1984; n r. P P d c ic ic 141

11 HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 TABLE 5 Comprison of the Coefficients for Logistic Length nd Mturity Equtions for Femle Dover Sole Present study Heermn (195) Vrince Z b Vrince Z tble 5). Becuse both smple sizes were lrge, we used the norml devite Z with criticl vlue of > 1. The regression coefficients re significntly different t the.5 level, ssuming tht these distributions re norml. Thus it ppers tht Dover sole femles from centrl Cliforni mtured in 1985 t smller size thn did those from Eurek, Cliforni, in the 194s. For exmple, 5% of femle Dover sole from centrl Cliforni mture when they rech 11 mm, wheres 5% mturity occurred t 6 mm in femles from Eurek (194849). This 5mm difference my be equivlent to n verge difference in 'the ge of first mturity of four to five yers (ssuming fish from centrl Cliforni in the 198s grew t bout the sme rte s fish from Eurek in the lte 194s). Similrly, Yoklvich nd Pikitch (1989) compred their 1985 mturity estimte for Dover sole from Oregon to one mde for the sme re 5 yers erlier. They found ll femles greter thn mm were mture in 1985, wheres 5 yers erlier (Hrry 1959) only 5% of Oregon femles of 8 mm were mture nd only 15% of the Dover sole less thn 8 mm were mture. Yoklvich nd Pikitch concluded tht Dover sole from Oregon presently mture t smller size nd probbly younger ge thn they did 5 yers go. Becuse of possible smpling bises, we hesitte to ttribute the differences between recent nd older estimtes to rel biologicl differences. Bis could result from filure to obtin representtive smple over the full bthymetric rnge of Dover sole. n ddition, the two older estimtes (Hgermn 195 nd Hrry 1959) my be bised becuse smples were tken from the fishery during spwning seson. This process could led to n overestimte of the verge size of fish t first mturity, becuse femles in postspwning condition could hve been wrongly clssified s immture. On the other hnd, the methods employed by ourselves nd Yoklvich nd Pikitch (1989) were similr; in both studies the smples were tken in December 1985, which is erly enough in the spwning seson tht bises from misclssifiction of postspwning fish seem unlikely. f our smples nd those of Yoklvich nd Pikitch (1989) ccurtely represent their respective regionl popultions, then femles in Oregon m tured t smller size thn those in centrl Cliforni. For exmple, ll Oregon femles longer thn mm were mture, wheres in centrl Cliforni, only 57% (SD = 8%) of mm femles were mture. Yoklvich nd Pikitch (1989) suggest tht the longterm effects of the sizeselective trwl fishery off Oregon ws compenstory decrese in the size of first mturity of Dover sole. This hypothesis my lso explin the difference between our estimtes for centrl Cliforni nd theirs for Oregon, since the centrl Cliforni fishery (Morro By) for Dover sole is new fishery with only minor lndings until the lst four or five yers, wheres the Dover sole fishery in Oregon hs been ctive for over forty yers. High ter Content High wter content (jellied flesh) hs been reported for four mrine fltfishes: Dover sole (Fisher et l. 1987; Puckett 1989); winter flounder, Pseudopleuronectes mevicnus (Percy 1961); yellowfin sole, Limundu uspevu (Kizevetter et l. 1965); nd Americn plice, Hippoglossoides pltessoides (Templemn nd Andrews 1956). Roff (198, 198) ttributed high wter content in fltfishes to degrdtion of muscle tissue during periods of gond development nd mintennce during winter fsting (Roff 198, 198). On the other hnd, Puckett (1989) concluded fter exmining the wter content of Dover sole tht depth, nnul reproductive cycles, size, ge, nd the onset of sexul mturity were ll involved, but depth ws the most importnt fctor. Most significntly, Puckett's nlysis indicted tht reproductive condition of mture femles living t 651 m ws not correlted with their wter content. He found tht the verge wter content of mles nd femles from deep wter remined high throughout the yer; for exmple, qurterly mens for femles rnged from 89.6% in the winter to 91.6% in the spring. He concluded tht the effect of the reproductive seson on wter content ws miniml, nd tht movement into deepwter hbitt ws the key vrible. Dover sole differ from other fltfishes with high wter content in two wys: the dult popultion lives t considerble depths (815 m) nd in the 14

12 HUNTER ET AL.: BATHYMETRC PATTERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 oxygen minimum zone. n deepse fishes, the cloric density per g wet weight typiclly decreses with depth (Somero et l. 198). The chnge in cloric density of Dover sole with depth follows similr pttern (figure 1). The wter content of deepliving Dover sole is t the high end of the rnge for the deepse fishes exmined by Childress nd Nygrd (197), where 9.5% ws the highest vlue recorded. This indictes tht the ontogenetic chnge in wter content in Dover sole my be simply n dpttion to deepwter existence, nd the explntions proposed for low cloric density of deepse fishes my pply eqully well to Dover sole. These include the scrcity of food nd development of feeding strtegies tht permit gret reduction in propulsive systems demnding high metbolic rte (Somero et l. 198). Another plusible explntion for high wter content is one linked to life in the oxygen minimum zone. The oxygen nd energy required to mintin white muscle in the oxygen minimum zone could be significnt. Reduction of white muscle content would reduce bsl oxygen demnd nd increse the scope for ctivity in n oxygenlimited environment. n contrst to white muscle, red muscle tissue is conserved in Dover sole. This red muscle is locted behind the hed nd t the bse of the pectorl fin. This loction my indicte role in feeding. Feeding behvior hs been described for the congeneric lemon sole, Microstomiis kitt, by Steven (19). This species feeds on polychetes nd lso inhbits muddy bottoms. hen feeding, lemon sole rises its hed nd til nd sits perched on its side, scnning the substrte. hen polychete is found, the fish pounces with forwrd lep, bringing its hed down on the prey nd strongly rching the nterior body (Steven 19). Dover sole lso feed on polychetes (Percy nd Hncock 1978; Gbriel nd Percy 1981; nd kefield 1984), nd we hve observed similr feeding behvior in cptive Dover sole in our lbortory. Dover sole perched on the substrte hve lso been observed by Allen (198) nd kefield (pers. comm., October 1988). Conserving red muscle while scrificing white muscle s the fish becomes more wtery my be mechnism to preserve levels of feeding performnce while reducing bsl oxygen demnd. Ontogenetic nd Sesonl Movements Tgging studies (estrheim nd Morgn 196; Quirollo nd Klvss 1987) nd fishery dt (Alverson 196) indicte tht Dover sole move inshore in the summer. This rises some interesting questions concerning the ontogenetic movements we hve described. Do the fish precisely resort themselves by depth ech fll s they leve their shllow summer hbitt? How do they grdully (over decdes) increse the depth of their winter hbitt? Does high wter content ffect the extent of sesonl movements? No dt exist to fully nswer these interesting questions, but some inferences cn be mde on the bsis of tgging study conducted by Quirollo nd Klvss (1987). Their dt indicte tht ll Dover sole my not prticipte in the summer inshore movement. Mture fish tgged nd relesed in shllow wter were usully recovered from deep wter in the winter nd fll nd from shllow wter in the spring nd summer, indicting nnul inshore movement. n contrst, most of the mture fish tgged nd relesed in deep wter were recovered in deep wter regrdless of seson. Thus the tgging dt indicte tht two substocks my exist, one tht migrtes nd one tht does not. e suggest tht the fish composing the migrtory substock my be younger nd hve lower wter content thn those composing the nonmigrtory substock. CONCLUSONS The deep, cold, nd poorly oxygented region of the continentl slope known s the oxygen minimum zone is the hbitt for the mture Dover sole in centrl Cliforni. Ninetyeight percent of the spwning biomss of Dover sole occurs in this region. Dover sole spwn t these depths, nd their eggs rise to the surfce lyers. Juveniles settle on the continentl shelf nd, with sexul mturity, grdully move down the continentl slope. The onset of sexul mturity nd the ontogenetic movement into the cold oxygen minimum zone (555 fth.; 6411 m) is usully ssocited with n increse in wter content, myoglobin content of red muscle, nd ft stores. The movement down the slope corresponds with consistent pttern of incresing size, ge, nd wter content. The ontogenetic movement down the shelf is grdul nd occurs over decdes. The verge femle Dover sole in centrl Cliforni reches mturity when bout 7 yers old nd 11 mm long. At this time she lives t depth of bout 9 m (18 fth.), nd her wter content is bout 8.8%. e speculte tht over the next nine yers the nnul inshore nd offshore movement grdully ceses. Over the sme period the wter content of the verge femle grdully increses s she descends to 14

13 HUNTER ETAL.: BATHYMETRC PATERNS OF DOVER SOLE ClCOFl Rep., Vol. 1,199 greter depths nd enters the oxygen minimum zone (64 m; 5 fth.). By then she is 16 yers old, is lmost 4 mm long, nd hs wter content of 87%. By this time she, like 9% of her cohort, is sexully mture, nd growth hs slowed from 14 mm per yer when she ws 7 yers old to 6 mm per yer. Eleven yers lter the verge femle hs descended to 16 m (55 fth.), is 7 yers old, hs grown 44 mm (bout 4 mm per yer), nd hs wter content of 88.7%. ter content continues to increse slowly over the next decdes, nd the fish continue to spwn nd move deeper. The oldest femle we ged ws 51 yers. The highest wter content ws 94.1%. The gretest depth t which we collected Dover sole ws 169 m. LTERATURE CTED Allen, M. J Functionl structure of softbottom communities of the Southern Cliforni Shelf. Ph.D. thesis, Univ. Cl. Sn Diego, 577 pp. Alverson, D. L A study of nnul nd sesonl bthymetric ctch ptterns for commercilly importnt groundfishes of the Pcific Northwest cost of North Americ. Pc. Mr. Fish. Comm. Bull. 4, 66 PP. Butler, J. L., C. Kimbrell,. C. Flerx, nd R. D. Methot The demersl fish surveys off centrl Cliforni (4 N to 6 N). Southwest Fish Cent., Ntl. Mr. Fish. Serv., NOAA, Tech. Memo. TMNMFSSFC1,44 pp. Childress, J. J., nd M. H. Nygrd The chemicl composition of midwter fishes s function of depth of occurrence off southern Cliforni. Deepse Res. : Chilton, D. E., nd R. J. Bemish Age determintion methods for fishes studied by the groundfish progrm t the Pcific Biologicl Sttion. Cn. Spec. Publ. Fish. Aqut. Sci. 6, 1 pp. Demory, R. L Scles s mens ofging Dover sole (Micvosfomur prifeus). J. Fish. Res. Bord. Cn. 9: Dobush, G. R., C. D. Ankney, nd D. G. Krementz The effect of pprtus, extrction time, nd solvent type on lipid extrctions of snow geese. Cn. J. Zool. 6: Drper, N., nd H. Smith Applied regression nlysis. New York: John iley & Sons, 79 pp. Engelmn, L LR stepwise logistic regression, n BMDP sttisticl softwre mnul, vol.,. J. Dixon, ed. Pp Eschmeyer,. N., E. S. Herld, nd H. Hmmnti A field guide to Pcific Cost fishes of North Americ. Boston: HoughtonMifflin Co., 6 pp. Fisher, R. A,, R. A. Fritzche, nd G. L. Hendrickson Histology nd ultrstructure of the jellied condition in Dover sole, Microstomus pcifictts. Proc. V Congr. Europ. chthyol., Stockholm 1985, pp Gbriel,. L., nd. G. Percy Feeding selectivity of Dover sole, Micvosfomrrs pcificus, off Oregon. Fish. Bull., U.S. 79(4): Hgermn, F. B The biology of the Dover sole (Micvostomus prifeus) (Lockington). Clif. Dep. Fish Gme Fish Bull. 85, 48 pp. Hrry, G. Y Time of spwning, length t mturity, nd fecundity of the English, petrle nd Dover soles (Pvophvys t~etulirs, Eopsett.jordni nd Micvostomtrs ptifcur, respectively). Fish. Comm. Oregon. Res. Briefs 7(1):51. Hendrickson, G. L., R. A. Fritzsche, nd H. M. Puckett Ecology nd possible cuses of the >ellied condition in Dover sole, Microstomus pcificus. Cliforni Se Grnt biennil report, , University of Cliforni Se Grnt College Progrm, Rep. No. RCSGCP:191. Kizevetter,. E., E. F. Kleie, A. A. Kirillov,. M. Mel Nikov, V. M. Mysoedov, nd L. Y. Ertel Technologicl chrcteristics of Bering Se fishes, in Soviet fisheries investigtions in the northest Pcific. Prt V,? A. Moiseev, ed. (Trnsl. from Russin by srel Progrm for Sci. Trns., Jeruslem, 1968.) Pp Merns, A. J., nd L. Hrris Age, length, nd weight reltionships in southern Cliforni popultions of Dover sole. S. Cl. Cost. ter Res. Proj. TM 19, 17 pp. Mullins, H. T., K. McDougll, nd T. L. Vercoutere Oxygenminimum zone edge effects: evidence from the centrl Cliforni costl upwelling system. Geology 1: O Neill, R Function minimiztion using simplex procedure. Algorithm AS47. Applied Sttistics, 8. Pine, R. T The mesurement nd ppliction of the clorie to ecologicl problems. Annu. Rev. Ecol. Syst Prr nstrument Co Oxygen bomb clorimetry nd combustion methods. Technicl Mnul No. 1, 156. Moline, ll. Percy,. G Sesonl chnges in osmotic pressure of flounder ser. Science 14: Percy,. G., nd D. Hncock Feeding hbits of Dover sole, Microstomits pcificus; rex sole, Glyptocephlus zchirus, slender sole, Lyopsett exilis; nd Pcific snddb, Citlirichthys sordidus, in region of diverse sediments nd bthymetry off Oregon. Fish. Bull., U.S Percy,. G., M. J. Hosie, nd S. L. Richrdson Distribution nd durtion of pelgic life of lrve of Dover sole, Microstornus pcificus; rex sole, Glyptocephlrrs zchivttr; nd petrle sole, Eopsetr jordrii, in wters offoregon. Fish. Bull., U.S. 75:1718. Pikitch, E., nd R. Demory Assessment of scles s mens of ging Dover sole. Trns. Am. Fish. Soc. 117:4549. Puckett, H. M Ecology nd possible cuses of the jellied condition in Dover sole (Micvostomuspcificus). M. S. thesis, Humboldt Stte Univ., Arct, Clif., 8 pp. Quirollo, L. E, nd P. Klvss Results of Dover sole tgging in wters off northern Cliforni, Clif. Dep. Fish Gme Mr. Res. Admin. Rep. No. 874, 7 pp. Rofc D. A Reproductive strtegies in fltfish: first synthesis. Cn. J. Fish. Aqut. Sci. 9: An lloction model of growth nd reproduction in fish. Cn. J. Fish. Aqut. Sci. 4: Sokl, R. R., nd F. J. Rohlf Biometry. nd ed.. H. Freemn rid Co., 859 pp. Somero, G. N., J. F. Siebenller, nd P.. Hochchk Physiologicl dpttions of deepse nimls. The se, vol. 8: deepse biology, G. T. Rowe, ed. N.Y.: iley nterscience. Steven, G. A. 19. Bottom fun nd the food of fishes. J. Mr. Biol. U.K Templemn,., nd G. L. Andrews Jellied condition in the Americn plice Hippogossoides pltcssoides (Fbricius). J. Fish. Res. Bd. Cn. 1: kefield, Feeding reltionships within ssemblges of nershore nd midcontinentl shelf benthic fishes off Oregon. M. S. thesis, Oregon Stte Univ., Corvllis, Oregon, 1 pp. estrheim, S. J., nd A. R. Morgn Results from tgging spwning stock of Dover sole, Microsrornits pcificits. Pc. Mr. Fish. Comm. Bull. 6:141. Yoklvich, M. M., nd E. K. Pikitch Fecundity nd sttus of mturity of Dover sole, hfitrosrotnrts pcifetrs, off northern Oregon, Fish Bull., U.S. 87(4). Zr, J. H Biosttisticl nlysis. New Jersey: PreiiticeHll, 718 pp. 144