Abstract.-Upwelling and its as­ sociated offshore advection of surface Distribution of pelagic waters can affect the recruitment of nearshore organisms. Late-stage pelagic metamorphic-stage sanddabs Pacific and speckled sanddabs, Citha­ richthys sordidus and C. stigmaeus, were sordidus and collected with a midwater trawl off cen­ tral California during the spring and C. stigmaeus within areas of summer upwelling season. In both spe­ cies, otolith size increased linearly with upwelling off central California metamorphic development; standard length, however, increased asymptoti­ cally. Earlier stages ofboth species oc­ Keith M. Sakuma curred shallower in the water column, Tiburon Laboratory, Southwest Fisheries Science Center whereas later stages occurred deeper. National Marine Fisheries Service, NOM The deeper distribution oflater stages 3150 Paradise Drive. Tiburon. California 94920 may have been due to decreased buoy­ ancy as a resultofincreasedotolithsize and ossification of bony structures co­ Ralph J. Larson incident with metamorphosis. Earlier stages ofboth species were more abun­ Department of Biology, San Francisco State University dant offshore and less abundant in ar­ J600 Holloway Avenue, San Francisco, California 94132 eas of upwelling, whereas later stages were more abundant nearshore regard­ less ofupwelling. The difference in the horizontal distributions of early and late stages may have been passively driven by different currentpatterns as a Pacific and speckled sanddabs, Ci­ bathymetric distribution as settled result ofthe difference in vertical distri­ tharichthys sordidus and C. stig­ individuals (usuallyfound at depths butions between early and late stages. maeus, are abundant along the Pa­ of 40 m and less)(Rackowski and cific coast ofNorthAmerica (Miller Pikitch, 1989; Kramer, 1990). Both and Lea, 1976). In both species, species are widely distributed as spawningpeaks duringthe summer pelagic larvae (as far as 724 km off­ months butalso occurs at lower lev­ shore for Pacific sanddabs and 320 els during the remainder of the km offshore for speckled sanddabs) year; individuals may spawn more (Rackowski and Pikitch, 1989), but than once during a given season settled individuals occur within a (Arora, 1951; Ford, 1965; Goldberg somewhat more restricted coastal and Pham, 1987; Matarese et aI., region. 1989; Rackowski andPikitch, 1989). The existence oflate-stage Pacific Sanddabs have a long pelagic stage, and speckled sanddabs in midwater which may exceed 324 days in trawls conducted offcentral Califor­ speckled sanddabs and 271 days in nia by the National Marine Fisher­ Pacific sanddabs (Kendall, 1992; ies Service (NMFS) Tiburon Labo­ Brothers!), and settle ata relatively ratory (Wyllie-Echeverria et aI., large size (20 to greater than 39 mm 1990) provided an opportunity to standard length (SL) for Pacific examine ontogenetic changes in dis­ sanddabs and 24 to greater than 36 tribution associated with metamor­ mm for speckled sanddabs) (Ahl­ phosis and settlement ofthese two strom et aI., 1984; Matarese et aI., sanddabs. In this paper we investi­ 1989). Kramer (1990) noted that gated the vertical and horizontal with nearshore nurseries distribution of pelagic-stage sand­ had briefpelagic stages and settled dabs, with the general purpose of at small sizes, whereas those with elucidating the changes that take less restricted coastal nurseries had place at metamorphosis and settle­ longer pelagic stages and settled at ment. Because the NMFS collec­ larger sizes. Kramer (1990) placed tions were made during the spring sanddabs in the latter category;

Manuscript accepted 27 February 1995. however, speckled sanddabs, in par­ 1 Brothers, E. B. EFS Consultants, Ithaca, Fishery Bulletin 93:516-529 (1995). ticular, have a somewhat restricted NY 14850. Personal commun., 1993.

516 Sakuma and Larson: Distribution of Citharichthys sordidus and C. stigmaeus 517 and summer upwelling season, when the associated not identified to species before 1987. Therefore, data offshore advection of surface waters can adversely were analyzed only from the 1987 through 1991 sur­ affect marine organisms with pelagic life stages veys. In addition to the May-June surveys in each (Parrish et aI., 1981; Bailey and Francis, 1985; year, samplingwas carried out inApril of1987, 1988, Roughgarden et aI., 19881, the effect ofupwelling on and 1990. Sanddabs were identified and enumer­ pelagic-stage sanddabs was also investigated. ated on board the research vessel at sea. In 1990 and 1991, samples were frozen after identification and enumeration and brought back to the labora­ Methods tory where standard length (SL) and stage ofmeta­ morphosis were additionally recorded for each speci­ Data collection men collected. Five metamorphic stages, based on the stagingsystem used by Pearcyet al. (1977), were Pelagic Pacific and speckled sanddabs were collected defined as follows: in conjunction with the annualjuvenile rockfish sur­ veys conducted by NMFS Tiburon Laboratory scien­ Stage 1 = left and right eyes positIoned sym­ tists aboard the National Oceanic and Atmospheric metrically on both sides ofhead; Administration (NOAA) research vessel David Starr Stage 2 = righteye hasbegun to move dorsally; Jordan. Standard stations extending from Point Stage 3 = upper edge ofright eye within close Reyes to Cypress Point (Fig. 1) were sampled with a proximity to the top ofthe right side 26 x 26 m modified Stauffer midwater trawl with a ofthe head; codend liner of 9.5-mm stretched mesh (Wyllie Stage 4 = right eye has begun to cross over to Echeverria et aI., 1990). Standardtrawling depth was the left side ofthe head; 30 m except at shallow-water stations where trawls Stage 5 = right eye completely crossed ov:er to were conducted at 10 m. At certain standard stations left side ofthe head. a series ofthree depth-stratified trawls (depths=lO m, 30 m, and 110 m) were conducted to determine bathymetric distributional patterns (Fig. 1). As time permitted, additional trawls, both stan- dard depth and depth-stratified, were conducted at nonstandard stations. All 38 trawls were 15 minutes in duration and were completed between the hours of 2100 and 0600. Stations were sampled z during a 10-day "sweep" of the survey °...... , area. Three replicate sweeps were com­ pleted from mid-May to mid-June of each year~ in some years one additional sweep was completed in earlyApril. CTD (conductivity, temperature, and depth) castswere made ateach trawl sta­ 37 tion to obtain temperature and salinity information at depth. Additional CTD casts were made during the day along SIaDdanI Depth tracklines interspersedbetweenthetrawl Deplh-Stralified station lines (Schwing et al., 1990). Sur- face temperature and salinity were also recorded continuously by a thermo- 124 123 122 salinometer aboard the vessel. CTD and thermosalinometer data were used to Longitude (oW) detennine therelationbetweenupwelling and the spatial distributions of the dif- Figure 1 ferent pelagic stages ofboth sanddabs. Location ofstandard trawling stations for Pacific and speckled sanddabs. Although the annualjuvenile rockfish Citharichthys sordidus and C. stigmaeus, collected during 1987-91. surveys began in 1983, sanddabs were 518 Fishery Bulletin 93(3). 1995

No stage-1 individuals were collected, probably be­ 1991, the April surveys alone, and the May-June cause their small size allowed them to pass through surveys alone. To determine changes in vertical dis.­ the net. tribution ~ith development, the paired comparisons To determine if metamorphic stage was a more were also carried out on each of the metamorphic useful character than SL in resolving spatial pat­ stages, by using data from the April and May-June terns, twenty individuals from each metamorphic surveys of1990 andfrom theMay-June surveyof1991. stage of each species were randomly selected from To determine the similarity ofhorizontal distribu­ the May to June survey of 1991, and their otoliths tions among metamorphic stages, Spearman rank were removed. The diameter of the largest otolith, correlation coefficients were calculatedfor the abun­ the sagitta, was measured with a compound micro­ dances of different stages over standard stations scope connected to a video camera, monitor, digitizer, during the 1990 and 1991 surveys. and computer. CTD salinity at the surface (average salinity at 3-5 m depth) and at the standard mid-depth of30 m Data analysis (average salinity at 28-32 m) from each sweep ofthe May-June surveys of 1990 and 1991 was contoured Statistical analyses were performed by using the byusing the Kriging option in the program SURFER program SAS (SAS Institute, Inc., 1988). Abundances (Golden Software, Inc., 1990). Owing to problems were transformed by In(x+1) to normalize the data. with the CTD during the second sweep ofthe May­ Mean abundances from theApril surveys andfor each June survey of 1991, thermosalinometer data were sweep ofthe May-June surveys were then calculated incorporated into the available CTD data to gener­ for all standard stations successfully sampled to de­ ate the surface contours. The log-transformed abun­ scribe temporal differences in abundance. dances ofmetamorphic stages 2 and 5 were overlaid Means and ranges of SL's of the metamorphic onto the salinity contours to observe the relation (if stages of both sanddab species were calculated by any) between the abundances ofthese two metamor­ using specimens measured from theApril and May­ phic stages and salinityfeatures indicative ofcoastal June surveys of 1990 and from the May-June sur­ upwelling. These two stages had the greatest poten­ vey of 1991. Mean SL's were calculated separately tial for differences in spatial relations with salinity for the specimens randomly selected for otolith re­ features, given thatstage-2 individuals were notcom­ moval in order to compare the observed changes in petent for settlement, whereas stage-5 individuals otolith size relative to metamorphic stage with SL. were relatively close to settlement. Tukey's studentized range tests were performed to Thermosalinometer data were used to determine determine ifthere were significant differences in SL trawls conducted in areas of recent upwelling. andotolith diameterwithmetamorphic development. Schwing et al. (1991) designated recently upwelled Owing to changes in the width of the net mouth water as having surface temperatures less than with depth (width=8 m at 10 m depth, 11 m at 30 m 10.5°C and surface salinities greater than 33.6 ppt. depth, and 13.5 m at 110 m depth), abundances for We used surface salinities greater than 33.6 ppt but the depth-stratified trawls were adjusted prior to surface temperatures less than 11.0°C to allow for analysis (Lenarz et al., 1991). Abundances for 10-m marginal surface layer warming during the daylight depth trawls were multiplied by 11/8, abundances hours prior to the nighttime trawls. Log-transformed for 30-m depth trawls were not adjusted, and abun­ abundances obtained at standard stations from the dances for 1l0-m depth trawls were multiplied by May-June surveys of1990 and 1991 were converted 11/13.5. Because of the large spatial variability in to standard scores (log-transformed abundances abundances and the fact that not all depth-strati­ rescaled for each year so that mean=O and standard fied trawls sampled every depth (i.e. because oftime deviation=1) to adjust for year effects, allowing the constraints only the 10 m and 30 m depths were data from both years to be combined. T-tests were sampled at some stations, and only the 30 m and used to compare the mean standard scores ofmeta­ 110 m depths were sampled at others), differences morphic stages in upwelling and non-upwelling ar­ in abundance with depth, were evaluated by paired eas. Separate analyses were performed for shallow­ comparison t-tests. Pairing was by station; each depth (10-m) trawls and standard mid-depth (30-m) depth pair available was considered (10 m versus 30 trawls because ofthe possibility ofa depth effect due m, 30 m versus 110 m, and 10 m versus 110 m). When to metamorphic stage and the fact that upwelling bothobservations ofa pair were equal to 0, that pair typically affects only the upper 20 m of the water was deleted from the analysis. To determine ifthere column (Parrish etal., 1981). To increase sample size, was a seasonal change in depth distribution, analy­ trawls at nonstandard stations were included in the ses were performed on all the surveys from 1987 to analysis. Sakuma and Larson: Distribution of Citharichthys sordidus and C. stigmaeus 519

Results rate analyses of the April and May-June surveys showed similar results (Table 1). Overall abundances and seasonal abundance pat­ In contrastto Pacific sanddabs, speckled sanddabs terns Qf the two sanddab species were variable (Fig. were significantly more abundant in shallow and 2). In 1991, the abundance ofboth species increased mid-depth trawls thanin deep trawls (Table 2). Ana­ monotonically duringthe May-June samplingperiod, lyzed separately, the May-June surveys showed a whereas in 1987 and 1988, catches were relatively similar pattern to the overall analysis, but theApril high in April but showed a marked decrease by the surveys showed less distinct differences indepth dis­ end of May-June, suggesting that pelagic sanddab tribution (Table 2). TheApril surveys showed a trend abundance frequently declines duringtheApril-June of decreased abundance in deep trawls relative to period (Fig. 2). However, catches ofPacific sanddabs shallow and mid-depth trawls, but the differences in April of1990 were low relative to May-June, and were not significant (Table 2). the May-June catches in 1988 and 1989 did not Depth distributions differed among the metamor­ change monotonically, suggesting interannual varia­ phic stage~ ofbothsanddab species~ Stage-2 individu­ tion in seasonal patterns (Fig. 2). Although April­ als ofPacific sanddabs were significantlymore abun­ June abundances were variable (Fig. 2), the inter­ dant in mid-depth trawls thanin deep trawls, with a annual variation in year-class strength of pelagic trend for increased abundance in shallow trawls ver­ sanddabs could not be determined without complete sus deep trawls (Table 3; Fig. 6). Although both stage­ seasonal data. 3 and stage-4 sanddabs showed a relatively even dis­ In both species, SL increased asymptotically with tribution throughout the water column (with no sig­ metamorphic stage (Fig. 3). In addition, the range of nificant differences among depths), stage-3 individu­ lengths within each stage was quite large (Fig. 3). als tended to be less abundant with increased depth, Pacific sanddabs were generally larger than speck­ whereas stage-4 individuals tended to be more abun­ led sanddabs at each metamorphic stage (Fig. 3). dant with increased depth (Table 3; Fig. 6). Stage-5 Although stage-2 individuals were significantly individuals were generally less abundant in shallow smaller than individuals of subsequent stages, the trawls and showed a tendency toward increased mean SL's did not differ significantly among the three abundance with increased depth (Table 3; Fig. 6). later stages (0.=0.05, df=76 for Pacific sanddabs and In speckled sanddabs, stage-2 individuals were df=75 for speckled sanddabs). Whereas SL increased significantly more abundant in mid-depth trawls asymptoticallywith metamor- phic development in both sanddabs, otolith diameter showed a linear increase (Fig. Pacific SaDddabs Speclded SancIdabs 4). In addition, otolith diam­ 3.S eter increased dramatically ...I I with SL (Fig. 5), and mean T 1 I , otolith diame~rincreased sig­ ~ ..I ...I ... I I I nificantly with each successive I I J. stage (0.=0.05, df=76 for Pacific •...I sanddlJbs and df=75 for speck-. ~ ~ ~t led sanddabs). It appears that metamorphosis in sanddabs is possible at a range ofsizes (30 ~ ~ mm to >50 mm SL in Pacific A,\ sanddabs and 25 to 40 mm SL , ~ in speckledsanddabs) andthat once initiated, there is little o .growth in length butcontinued 1987 1988 1989 1911O 1991 1987 1988 1989 1911O 1991 Year otolith growth (Figs. 3--5). In general, Pacific sanddabs Figure 2 were relatively evenly distrib­ Means and standard errors ofthe log-transformed abundances of Pacific and speck­ utedthroughout the water col­ led sanddabs, Citharichthys sordidus and C. stigmaeus, collected at "tandard sta­ umn; there was a slight de­ tions during April and May-June 1987-91 (means of the three sweeps for the May­ crease in abundance with in­ June surveys are connected by a line). creasingdepth(Table 1). Sepa- 520 Fishery Bulletin 9313). J995

Pacific Sanddabs Speckled Sanddabs 60

T T I so I I I I

T T I T I T I I T I I

I I I t !tI .L I ttI I I aI I I I ItI I I I I I I I I I I I I ...... I I ItI I I I I ... I I .II I 20 I I I I ...I ...I

10 Stage 2 Stage 3 Stage 4 Stage S Stage 2 Stage 3 Stage 4 Stage S

Figure 3 Means and ranges of standard lengths of Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, in 1990 and 1991 as a function ofmeta­ morphic stage. All specimens measured are represented by dotted lines; those subsampled for otolith removal are represented by solid lines. Standard devia­ tions for the specimens selected for otolith removal are shown with thick lines; ranges are shown with thin lines.

Pacific Sanddabs Speckled Sanddabs 1,800

1,600

1,400 i ...... 1,200

.11,000 Q ;fI 800 i 8 t 600 I t 400 t t 200 t Stage 2 Stage 3 Stage 4 Stage S Stage 2 Stage 3 Stage 4 Stage S Figure 4 Means, standard deviations, and ranges ofotolith diameters ofmetamorphic stages ofPacific andspeckled sanddabs, Citharichthys 80rdidus and C. 8tigmaeus, collected in 1990 and 1991. Standard deviations are shown with thick lines; ranges are shown with thin lines. sakuma and Larson: Distribution of Citharichthys sordidus and C. stigmaeus 521

Table 1 Table 2 Paired comparison t-tests of log-transformed abundance Paired comparison t-tests of log-transformed abundance Cln(x+1» of Pacific sanddabs, Citharichthys sordidus, (In(x+1)) of speckled sanddabs, , from 1987 to 1991 at depth-stratified stations. Ifboth num- from 1987 to 1991 atdepth-stratified stations. Ifboth num· bers within a pair were = 0, that pairwas deleted from the bers within a pair were = 0, that pair was deleted from the analysis. analysis.

Mean Mean Depth pair n cliff. BE P Depth pair n diff. BE P

All surveys All surveys 10m-30m 57 0.07 0.1723 0.4047 0.6872 10m-30m 54 -0.01 0.1379 -0.1024 0.9188 30m-110m 63 0.03 0.1358 0.2075 0.8363 30m-110m 51 0.62 0.1395 4.4494 0.0001 10m-110m 39 0.43 0.2122 2.0419 0.0482 10m-110m 37 0.69 0.1555 4.4301 0.0001

April surveys April surveys 10m-30m 15 0.11 0.4375 0.2515 0.8051 10m-30m 14 0.02 0.3319 0.0499 0.9610 30m-110m 11 -0.35 0.3193 -1.0889 0.3018 30m-110m 13 0.59 0.3488 1.7036 0.1142 10m-110m 8 0.53 0.5727 0.9192 0.3886 10m-110m 8 0.75 0.3479 2.1487 0.0687

May-June surveys May-June surveys 10m-30m 42 0.06 0.1779 0.3109 0.7574 10m-30m 40 -0.02 0.1484 -0.1675 0.8678 30m-110m 52 0.11 0.1491 0.7223 0.4734 30m-110m 38 0.63 0.1476 4.2666 0.0001 10m-110m 31 0.41 0.2278 1.7962 0.0825 10m-110m 29 0.67 0.1768 3.8038 0.0001

than in deep trawls with a trend for increased abun­ dance in shallow trawls versus deep trawls

Contours for sweep 1 of the May-June survey of1990 showed I 8..2 Stqe3 Stqe4 StqeS I Pacific SlIIIddabs 0 l),. 0 * Speckled SaDddabs a pattern of recent or ongoing I.BOO upwelling occurring off Point * 1,600 * Reyes and the Davenport area * ** * (see Fig. 1 for place names) as 1.400 * * ** * evidenced by the filaments of • higher salinity water projecting ~ 1,200 * ** 0 * seawardand shorewardimpinge­ * ** ~ l),. 1 000 ** 0 8 ment oflower salinity, more oce­ .1 • o ~w.l),. l),. ~ anic water(Simpson, 1987) atthe Q BOO l),. l),.l),. ;fj ~~~ surface north ofPoint Rey~s(Fig. l),..} 008 8). The contours for sweep 2 in­ S 600 o~ 0 dicated a reduction in offshore cP 400 8000 transport due to upwelling, with 0 CIJ 00# lower salinities closer to shore 200 (Fig. 8). The contours for sweep 3 showed upwelling activity oc­ 2S 30 3S 40 4S so 20 2S 30 3S 40 4S so St8DdaJd Lqth (mm) curring off Point Reyes but not off Davenport (Fig. 8). Figure 5 The contours for the May-June Otolith diameterversus standard lengthofmetamorphic stages ofPacific and speck­ surveyof1991 showed pronounced led sanddabs, Citharichthys sordidus and C. stigmaeus, collected in 1990 and 1991. seaward filaments off Point Reyes and Davenport during sweep 1, which indicated recent or ongoing upwelling (Fig. 9). During sweep 2, upwelling was still evident off Davenport, but owing to problems with the CTD, patterns off Point Reyes were not easily discernible (Fig. 9). During sweep 3, there was a relaxation ofupwelling as evidenced by the lack of seaward-projecting filaments of higher salin­ Sballow ity water (Fig. 9). (10m) The overlaid abundances of stages 2 and 5 showed that large abundances of stage-5 indi­ viduals of both species generally occurred nearshore and could be found within centers of Mid-depth upwelling (Figs. 8 and 9 off Davenport and (3Om) Monterey Bay; Fig. 9 off Point Reyes). In con­ trast, large numbers of stage-2 individuals of both species were relatively more abundant in the offshore transitional zone between coastal Deep water (nearshore, high salinity due to up­ (110m) welling) and oceanic water (offshore, low salin­ ity) (Figs. 8 and 9), In addition, large numbers ofstage-2 individuals were observed nearshore Stage 2 Stage 3 Stage 4 Stage 5 in the area north ofPoint Reyes during sweep 1 of 1990 associated with the shoreward im­ Figure 6 pingement ofoceanic water (Fig. 8). Depth distributions ofmetamorphic stages ofPacific and speck­ Although the effects of upwelling would be led sanddabs, Citharichthys sordidus and C. stigmaeus, collected expected to be most intense near the surface, in 1990 and 1991, based on paired comparisons ofabundance at no significant differences in the abundances of different depths (Tables 3 and 4). Small dotted linesindicate non­ significant (P>0.05) trends of decreased abundance at the given the metamorphic stages ofeither sanddab spe­ depth. cies were observed between upwelling and non­ upwelling areas at the shallow trawl depth of Sakuma and Larson: Distribution of Citharichthys sordidus and C. stigrnaeus 523

Table 4 Table 5 Paired comparison t-tests of log-transformed abundance Spearman rank correlations oflog-transformed abundance Iln(x+11) of each metamorphic stage of speckled sanddabs, (lnlx+1) ofeach metamorphic stage ofPacific and speckled Citharichthys stigmaeus, from 1990 and 1991 at depth- sanddabs, Citharichthys sordidus and C. stigmaeus, col- stratified stations. Ifboth numbers within a pair were =0, lected at standard stations during 1990 and 1991 Isignifi- that pair was deleted from the analysis. cance probabilities of each correlation are listed in bold type under the coefficients). Mean Depth pair n diff. SE P Pacific. sanddabs (n =257 I

Stage 2 Stage 2 Stage 3 Stage 4 Stage 5 10m-30m 21 -0.08 0.2339 -0.3240 0.7493 30m-110m 18 0.49 0.2408 2.0436 0.0568 Stage 2 0.58 0.31 0.06 lOm-110 m 14 0.52 0.3199 1.6392 0.1251 0.0001 0.0001 0.3559

Stage 3 Stage 3 0.62 0.47 0.13 10m-30m 23 -0.46 0.2438 -1.8982 0.0709 30m-110 m 17 0.51 0.2350 2.1629 0.0460 0.0001 0.0001 0.0316 10m-110 m 16 0.44 0.2647 1.6492 0.1199 Stage 4 0.15 0.37 0.38 Stage 4 0.0181 0.0001 0.0001 10m-30m 17 -0.79 0.2212 -3.5700 0.0026 30m-110m 14 0.67 0.2532 2.6485 0.0201 Stage 5 0.04 0.13 0.53 10m-110m 10 0.05 0.2604 0.1739 0.8658 0.4827 0.0346 0.0001 Stage 15 10m-30m 10 -0.72 0.4615 -1.5548 0.1544 Stage 2 Stage 3 Stage 4 Stage 5 30m-110 m 4 -0.27 0.3705 -0.7186 0.5243 10m-110 m 5 0.11 0.4416 0.2584 0.8088 Speckled sanddabs (n =257)

Surface 30m

38

37

123 122 123 122

Figure 7 Salinity contours at the surface compared with salinity contours at 30 m depth during 1990 sweep 1. 524 Fishery Bulletin 93(3). 1995

10 m (Table 6; Fig. 10). However, at the mid-depth of abundance in upwelling areas (Table 6; Fig. 10). In 30 m, stages 2 and 3 of Pacific sanddabs were sig­ contrast, stage 5 in each species tended to be more nificantly less abundant in upwelling areas than in abundant in upwelling areas than in non-upwelling non-upwelling areas, and stages 2 and 3 ofspeckled areas (Table 6; Fig. 10). sanddabs showed a strong tendency for decreased Discussion

1990 During the springtime series Pacific Sanddabs Sweep lr-r-T"lTl:Snpec,....,lded Sanddabs covered by this study, metamor­ phosis in both sanddab species 38 occurred at a wide range of sizes, indicatinglittle growth in body size during metamorpho­ sis (Figs. 3 and 5). Later meta­ morphic stages tended to occur in deeper water than did earlier 37 stages; Pacific sanddabs shifted to deeperwater at earlierstages than speckled sanddabs (Tables 3 and 4; Fig. 6), Later metamor­ phic stages ofboth sanddabs oc­ curred nearer to shore than ear­ lier stages, despite the upwel­ 38 ling-associated offshore advec­ Z .....,o tion ofsurface waters (Table 6; Figs. 8-10). ~ Given the reported variabil­ ity of size at metamorphosis in 3 both sanddab species

Table 6 Comparisonofstandard scores oflog-transformed abundance (In(x+1»ofeach metamorphic stage ofPacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus, in upwelling and non-upwelling areas during 1990 and 1991 (upwelling areas were defined as having surface salinities >33.6 ppt and surface temperatures

Pacific sanddabs Speckled sanddabs

Stage df P Stage df P

Shallow trawls (upwelling 11=38, non-upwelling 11=44) 2 0.6797 78.0 0.4987 2 -0.4730 76.2 0.6375 3 0.6911 76.4 0.4916 3 0.6346 78.0 0.5275 4 0.1171 78.0 0.9071 4 0.4846 78.0 0.6293 5 -0.4135 77.0 0.6804 5 -0.3190 78.0 0.7506

Mid-depth trawls (upwelling 11=83, non-upwelling 11=99) 2 -2.3877 159.9 0.0181 2 -1.7268 160.0 0.0861 3 -3.0253 160.0 0.0029 3 -1.7147 160.0 0.0883 4 -0.5325 160.0 0.5951 4 0.7201 160.0 0.4275 5 0.9655 160.0 0.3259 5 1.5650 100.4 0.1207

ing to stage 3 to those corre- UpweDed sponding to stage 5 takes ap­ INon-upwelled ==1 proximately five weeks. Pacific Sanddabs Shallow S"""kled SIIIIddabs Morphological changes associ­ 0.3 i i I i 0.2 I T I I ated with metamorphosis prob­ I I T I I I I I I I T I i 0.1 I I I I ably decrease the buoyancy of •I T I I I I I •I • I • I + I pelagic sanddabs. Laroche et a1. o I I I • I •I • •I I • t (1982) found an increase in -0. 1 I I • I • I • I otolith growth relative to growth e -0.2 • • in length at metamorphosis for JI-o.3 Parophrys vetulus, which was Mid-depth similar to that observed for the I 0.3 .------, i two sanddabspecies in this study T I CI.l 0.2 I I 1 I T and for Rhombosolea tapirina I I 0.1 I I •I I 1 ~ •T • (Jenkins, 1987). Reared Paro­ o1----=------t-I---4---TlI I I T +I 1 I phrys vetulus that were close to I · -0.1 I 1 i T ·1 + settlement frequently rested on • I -0.2 I their sides on the bottom and I -0.3 +I • swamwiththeirbodies atanangle L..--'--__--""'--__---'- ...... J Stage 3 Stage 4 Stage S (Laroche et aI., 1982), This behav­ Stage 2 Stage 3 Stage 4 Stage S Stage 2 ior may be related to decreased Figure 10 buoyancy as a result ofthe ossifi­ Mean standard scores and standard errors of metamorphic stages of Pacific and cationofbonystructures andtothe speckled sanddabs, Citharichthys sordidus and C. stigmaeus, collected in shallow and mid-depth trawls during 1990 and 1991 in upwelling and non-upwelling areas large increase in otolith size lupwelling=surface salinity >33.6 ppt and surface temperature <11°C). (Laroche et aI., 1982). In addition, thegasbladderislostduringmeta- morphosis in some species offlat- fish, including the related Atlan- tic species (Richardson and Joseph, 1973; Ahlstrom et aI., 1984). Laidig2 observed 2 Laidig, T. E. Tiburon Laboratory, Southwest Fish. Sci. Cent., that the gas bladder was reduced in stage-4 Pacific Nat!. Mar. Fish. Serv., NOAA, 3150 Paradise Drive, Tiburon, sanddabs and absent in 90% ofstage-5 specimens. CA 94920. Personal commun., 1994. Sakuma and larson: Distribution of Citharichthys sordidus and C. stigmaeus 527

The decrease in buoyancy due to increased otolith 1990 associated with an extension ofoceanic waters size, the ossification of other bony structures, and toward shore (Fig. 8) and the large abundances of theloss ofthe gasbladder may account for the deeper stage-2 individuals occurringwithin the transitional bathyn;tetric distribution oflater metamorphic stages areas between offshore oceanic waters and nearshore in both sanddab species (Tables 3 and 4; Fig. 6). The coastal waters (Figs. 8 and 9) suggestthat these early greater water density at deeper depths may reduce stages were subject to transport by ocean currents. the energy expenditure required for less buoyantfish Analysis of California Cooperative Oceanic Fisher­ to remain pelagic; however, beyond a given range of ies Investigations (CaICOFI) data by Ahlstrom and SL and otolith size, individuals may sink more rap­ Moser (1975) and Loeb et a1. (1983) indicated that idly. Therefore, the decrease inbuoyancy may account the larvae ofboth sanddab species were collected both directly for the deeper bathymetric distribution of nearshore and well offshore. Therefore, sanddabs of later-stage pelagic sanddabs, although fish may be­ both species are probably passive drifters during haviorally seek deeper water as well. theirearlylife history stages as evidenced by the pre­ Lenarz et a1. (1991) reported thatyounger, smaller dominantly offshore distribution of~h~irearly meta­ juveniles ofthe shortbelly rockfish, Sebastesjordani, morphic stages (Figs. 8 and 9) and the somewhat dis­ were found deeper in the water column than larger persed distribution of their larvae (Ahlstrom and individuals during May-June. It was suggested that Moser, 1975; Loeb et aI., 1983). the smaller individuals were adapted to seeking In contrast to the distributional patterns ofearly deeper water as a method of avoiding offshore ad­ stage metamorphic sanddabs; the tendency for later vection due to upwelling (Lenarz etaI., 1991). In con­ stages of both species to be more abundant in up­ trast, the earlystages ofbothsanddab species showed welling areas was probably due to the fact thatlater a shallower distribution than the later stages (Tables stage individuals occurred predominantly nearshore 3 and 4; Fig. 6). The shallow distribution of early (Figs. 8 and 9). Although large numbers of stage-5 stages may explain the comparisons of abundance individuals ofboth species occurred within upwelling in upwelling and non-upwelling areas for the 30-m plumes (Figs. 8 and 9), large abundances of stage-5 depth trawls, which suggest that early stages are individuals could also be found nearshore in areas subject to offshore advection due to coastal upwelling outside ofthe upwelling plume13 (Figs. 8 and 9). Be­ (Table 6; Figs. 6, 8, 9, and 10). The offshore advec­ cause later-stage individuals were more abundant tion ofearly stages may also explain their predomi­ at deeper depths, they were ·probably less suscep­ nantly offshore distribution (Figs. 8 and 9). tible to offshore advection by upwelling. The deeper The lack of significant differences in abundance and more shoreward distribution of later-stage between upwelling and non-upwelling areas for the sanddabs parallels the observations ofBarnettet a1. shallow depth trawls observed in both sanddab spe­ (1984) onlater stages ofnorthern anchovy, Engraulis cies might be explained by the fact that the majority mordax, white croaker, Genyonemus lineatus, and ofthese trawls were conducted nearshore where queenfish, Seriphus politus, offsouthern California. early stages were generally less abundant and that Larson et a1. (1994) also found that late-stage pe­ laterstages were generally less abundantat the shal­ lagicjuvenile rockfish (Sebastes spp.) offcentralCali­ low trawl depth (Tables 3, 4, and 6; Figs. 6, 8, 9, and fornia had a more shoreward distribution, although 10). In contrast, the 30-m mid-depth trawls, in which there was no evidence that later-stage fish were dis­ mostmetamorphic stages occurred, were more widely tributed at greater depths (Lenarz et aI., 1991). distributed and probably indicated better the rela­ In summary, it appears that physical changes in tion between upwelling and the distribution ofmeta­ metamorphosing sanddabs are correlated with morphic stages (Tables 3, 4, and 6; Fig. 6). Figure 10 changes intheir depth distributions; more developed, shows a change in distribution ofmetamorphic stages less buoyant individuals occur deeper in the water in the 30-m mid-depth trawls; earlier stages tended column (Fig. 6). This may influence the horizontal to be more abundant in water that had not been up­ distributions of pelagic sanddabs in the upwelling welled recently, whereas later stages were more regions offcentral California. Early-stage sanddabs abundant in recently upwelled water. present within the upper mixed layer would be sub­ The reduction in abundance of early stages in ject to offshore advection associated with coastal trawls within upwelling areas may have been due to upwelling or to onshore advection associated with the fact that these stages were present predomi­ downwelling (Table 6; Figs. 8-10). In contrast, the nantly offshore while upwelling events occurred deeperdistribution oflater-stage sanddabs decreases nearshore (Figs. 8 and 9), However, the large abun­ their susceptibility to upwelling-associated offshore dances ofstage-2 individuals ofbothspecies observed advection and could potentially lead to onshore ad­ nearshore north of Point Reyes during sweep 1 of vection facilitated by the shoreward movement of 528 Fishery Bulletin 93(3). 1995 deeper water (Tables 3 and 4; Fig. 6). In addition, other flatfishes in shallow waters of southern California. the vertical and horizontal distributions ofboth early Ph.D. diss. Univ. Calif., San Diego, 266 p. Laroche, J. L., S. L. Richardson, and A. A. Rosenberg. and late-stage sanddabs may have a substantial be­ 1982. Age and growth ofa pleuronectid, Parophrys vetulus, havioral component; however, themeansto resolve such during the pelagic larval period in Oregon coastal behavioral patterns is beyond the scope ofthis study. waters. Fish. Bull. 80:93-104. Larson, R. J., W. H. Lenarz, and S. Ralston. 1994. The distribution of pelagic juvenile rockfish of the Acknowledgments genus Sebastes in the upwelling region off central California. Calif. Coop. Oceanic Fish. Invest. Rep. 35: 175-221. We thank the crew of the RV David Starr Jordan Lenarz, W. 8., R. J. Larson, and S. Ralston. and the staffofthe Tiburon Laboratory. James Bence 1991. Depth distributions of late larvae and pelagic juve­ assisted us in early data analysis. 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