JOB BEPGBT. Robert P«Hofstetter J&rine Biologist. Survey of Oyster Beef Populations

Transcription

1 OB BEPGBT obert P«Hofstetter &rine Biologist Projet No. D~»B Date ugust, Projet Name; Oyster Investigations^ igalyeston Bay. Period overed; anuary une ob Ho. B Survey of Oyster Beef Populations Objetive s l) To determine the hanges in the oyster populations on major reefs in Galveston Bay. ) To study the assoiated reef organisms with speial emphasis on pests and predators» Proedures t Bfnthly oyster samples were olleted by dredging and oasionally by tanging. The unit volume per sample was one standard bushel. The uneulied sample was plaed in a box with a apaity of ubi inhes whih^ for all pratial purposes, represented a standard bushel of. ubi inhes. Large oyster lusters were broken up before they were plaed in the box but otherwise^ no sorting was done. This proedure was used to gain some idea of the relative density of the oyster population and the harater of the reef surfae. Sine the apaity of the sample dredge losely approximated one bushel, a full dredge load was frequently used as the unit of measure. The slight differenes 'betwees the two methods did not affet the data. ll live oysters were ulled out and measured. Ifeasurements were taken by dividers from the tip of the beak to the tip of the bill and were reported to the nearest entimeter. lthough spat less than. entimeters were ounted, it was probable that many of them were overlooked. For this reason suh oysters were not inluded in this data. ssoiated reef organisms were olleted and identifiations made whenever possible. Speial attention was gives those organisms whih were known to be oyster predators or whih interfered with the oyster's ativity in one way or another. Findings % Sample stations are indiated ia Figure I. Of the three, Todd s Dump"(Station f) was the only reef produing market oysters. Dollar Beef (Station ) produed few market oysters in past years. She majority of the oyster population.on this reef onsisted of Ostrea eguestris with very few rassostrea vlgsfaieas. The Trinity Hirer flood killed off the Gulf oyster and the reef was repopulated with. virginia spat in the late summer and early fall in. Yingtune Beef '(Station ), whih had produed a good supply of market oysters in past years, suffered total mortality during the flood. Like Dollar Beef it was repopulated with spat in fall. onthly lengthfrequeny measurements for the three stations are presented in Tables,, and. Ugur II presents the same data graphially. lthough differenes exist at eah station the oyster populations have similar teenis 'In spatfall, growth and mortality. During the winter and early spring, spat from the set predominated. These oysters appeared to suffer onsiderable mortality in the late spring and early summer. The population of Yingtune Beef was drastially

2 FIGUE I ob B Sample Station Loations Station Station Station Todd's Dump Dollar eef Vingtune eef Sales miles I

3 TBLE Station (Todd's Dump) Length (m. n T. T ) Lengthfrequeny F F sasurements of Number Per Bushel () () Oysters S ) N D.

4 TBLE Station (Dollar eef) Lengthfrequeny feasurements of Oysters length (m.) T T i. F l F Number Per Bushel ) j " h l i { ^ Ik S " N D TBLE length (Go. ) T St &tion (Vin, gtune eef) Lengthfrequeny easurt sments of Oysters Number Per Bushel Hi F H S ii?ot " is S N D k

5 TBLE ont'd Station (Vingtune eef) Lengthfrequeny sasurements of Oysters Number Per Bushel l k o T H *» redued in numbers and that on Dollar eef experiene a similar, but less severe, loss. Flooding on the Trinity iver nay have been partially responsible. lthough not as severe as the spring flood,, flood waters in redued salinities throughout the bay* uh of the mortality an be attributed to predation. Blue rabs were known to be abundant at all stations and mud rabs were plentiful,, t Dollar eef the onh 'Thais haemastoma and small stone rabs were ommon. By summer the surviving seed oysters from the set still omprised the dominant age group. The modal length at Stations and was four entimeters. t Vingtune eef the modal length remained fairly stationary at two entimeters. Poor growth at this station was no doubt due to the fresh water from the Trinity iver, slight spatfall was notieable at To&d's Bump and Dollar eef in une. lo spat set ourred at Vingtune Beef during this period. In the fall spat beame the dominant group at Dollar Beef. eent spat were evident at Vingtune eef but were still sare at Todd' Dump. These findings ompare well with the observed spat set for eah station (See ob B). In late fall aad early winter bimodal peaks were evident at Stations and «The modal length of the seed oysters ranged 'between three and five entimeters and that of the spat was one entimeter. Growth rates of the seed on Tod&'s Dump were similar to those on Dollar eef but the spat appeared to suffer mortality. During the winter months the seed reahed a modal length of four to six entimeters. The spat also inreased in length with a modal size of two entimeters. Oysters on Dollar eef grew better than those on Todd's Dump or Vingtune eef. Spring brought forth an inrease in mortality. s in the preeeding springy suh mortalities ould be blamed on flooding and predation. t Vingtune eef the seed experiened the most damage while the rop fared very wello Both groups appeared to be equally affeted at Dollar eef. Little hange was observed at Todd s Dump.

6 m I n a m H i H an. Feb. ar. pril ay fn N $ H. ^ s$* N* Na [ h Station # N E i Station # m n N s r fln B "' I «jsa, _. I nn=i L i= r une B» T^. uly ugust Sept. I» = N= ft \ ^ = I " N^ ar ^ tfi r t «N^ *» ^ T^ Station # FTBT % Hu * j. t n r H s\ \ V N s I y K^ N Length Gentiffieters =^ Trb" FIGUE II " length Frequeny easureaents of Oysters, Galveston Bay, *

7 Ot. Nov. De. N. ^ " H. n L. Station #. \ an. Feb. \ N PH L H s fin t arh pril ay a N = rr h une Station # K «V N I r N N V N = N» n N s f " N =. n N. a r Station # / k. Length entimeters FIGUE II Length Frequeny sasurements of Oysters, Galveston Bay,.

8 Spat from a set had not appeared at the end of the sampling periodo Sine onditions were similar to those in t ie» redued salinities due to Trinity iver floods), a late set ould be expeted» By summer both fingtune Beef and Dollar Beef ontained oysters of market size ( entimeters). t fingtune eef the market rop was too small to justify harvesting. Dollar eef, however, produed a harvestable amount of oysters and ompared favorably with Todd's Dump. In fat, fodd's Dump seemed to be in a period of deelininij produtivity whereas Dollar eef had a vigorous population suitable for exploitation. She population figures do not indiate the quality of *k«oysters. Eah reef produed oysters quite disimilar in many respets. For example, oysters on fingtune eef were thikly lustered., This was espeially notieable after the spat set. Onder these rowded onditions the older oysters grew long aai then, and their shells were usually thinner than those on the other reefs. Dollar eef produed broad, single oysters with thik, wellupped shells sny of the Dollar eef oysters developed salloped bills during the winter Suh oysters would be exellent for the halfshell trade but, unfortunately, the reef has been onsidered polluted for a number of years and harvesting is not permissible. fodd's Dump oysters tended to grow in lusters but ommerial harvesting prevented the development of large lusters. Ifst of the oysters were well shaped with thik shells and were very suitable for the xmrket. ssoiated reef organisms are listed in fable k Sine olletion methods were limited to dredge and tongs, all organisms ommonly assoiated with a reef habitat were not inluded. notable example was the blue rabo lthough none were taken in the samples, an abundane of rabs was known to exist in eah area. The most abundant organisms were barnales, bryoaoans and mussels. The barnale Balaaus iaprovisus was present in large numbers at all stations, but the larger B&lanus eburneus was found only oasionally. issels, Brahidontes reurvus, were oupon at all stations; but those on Dollar eef were generally smaller and fewer in number. The largest lusters were found at Vlngtune eef. Enrusting bryozoans were ommon at all stations, Shere were at least two speies present but identifiations were not made. The onh Thais haemastoass was foaad on y at Dollar eef where it was present at ah times exept torlng the wiafer months. The oaeh populatii>n appeared to have inreased in ^ over that observed in, and. the individuals were larger. The stone rab jfegipjje mergemria ourred only at Dollar Beef. Small rabs were abundant in late wiater and "early spring but had disappeared by summer. This was true both In and in «Bgtrolisthes armatus was also ommon in fall and early winter but absent in spring and rare in stammer. The ativity of both organisms may have been influened by salinity. Both are high salinity forms and would be epxeted to move out of an area when the salinity was redued. Eurypaaopeus deoressus was the most abundant mud rab at all stations. ganopeas_ herbstil was less ommon., espeially at fingtune eef. t this station ghithropanopeus harrisl was more ommonly found. It is possible that. harrisi also ourred at efehsr stations aad, due to its small size, was overlooked.

9 TBIE h ssoiated eef Organisms Organism Ov& X Station Sta. Sta. Porifera liona sp_. oelenterata Bydroids (Unidentified) Platyhelmia Polylad worm (Unidentified) nnulata Polyehaeta Hereids (Unidentified) Polydora Serpulids rthropoda irripedia Balanus improvisus Balanus eburneus felaostraa Isopods (Unidentified) mphipods (Unidentifed) Dee&pods l&rura Palaemonetes sp nomura Petrolisthes anaatus lioinarius sp» Braehyura snippe merenaria Eurypanopeus depressus Panopeus depressus f a w * i i *"T firimrnifttr Bhithropanopeus harrisi Ifollusa Peleypoda, alinia lateralis Bangia sp Oonaeria leuophaeta Brahidontes reurvus Bferf.es ia s_ «Gastropoda repidula plana Odostomia sp«thais haemastoma Nudi"branhis Dorid (Unidentified) Bryozoa lostomata (Unidentified) «_ Q. G G m s» i *ft are., few individuals in samples; G ommon,,, many individuals in samples; () Hot found in samples

10 Boring organisms were present only at Todd's Dump and Dollar eef. The boring sponge liona was ommon Dollar eef living in the oldj, dead shells. It was rare at Todd's Dump and was never found on exposed surfaes. Usually, it was not observed until oyster lusters had been broken apart sine the most ommon habitat was between the shells of adhering oysters. The boring lam artsia was ommon at Dollar eef, but living individuals were rare at Todd's Dump. Prepared by: obert P. Hofstetter pproved by: Howard T. Lee arine Biologist Date pproved: nnelids were plentiful on all reefs living in the raks and revises. The mudworm Folydora was observed at all stations but was not abundant. Other organisms, although prominent in the reef habitat, had little effet on the ativity of the oyster.