Annual death rates among one to five year-old oyster stocks at tray stations in Galveston Bay ranged from 24 to 45%, representing an increase in mortality among the older stocks over that recorded in the previous year and an above average mortality for one-year old oysters. Labyrinthomyxa marina infections were primarily responsible

Hofstetter, Robert P.

English

Aquatic Commons

(-V^dH^ 
OYSTER STUDIES 1970 
Project CO-2-1 
R. P. Hofstetter 
ABSTRACT 
Annual death rates among one to five year-old oyster stocks at tray 
stations ranged from 24 to 45 per cent, representing an increase in 
mortality among the older stocks over that recorded in the previous year 
and an above average mortality for one-year old oysters. Labyrinthomyxa 
marina infections were primarily responsible. 
Oyster spat setting was again erratic with abundant sets only in 
mid-Galveston and upper East Bays. Survival of the spat was poor. Conse-
quently no substantial increase in market oyster stocks was expected in 
the near future. 
The oyster harvest was over 200,000 barrels, approximately 16 per 
cent larger than that of the previous season. 
INTRODUCTION 
Galveston Bay has been the center of Texas coast oyster production 
for a number of years. The large oyster harvests from the estuary have 
been possible because of an abundant supply of oysters subject to an 
intensive fishery. For these reasons, surveillance of oyster stocks on 
major public beds has been adviseable to detect changes which might affect, 
or be affected by the fishery. 
Major phases of the study include (1) a continual monitoring of the 
growth and mortality of known stocks of oysters, with particular emphasis 
on pathogens; (2) a survey of the distribution and infection incidence of 
the primary pathogen, Labyrinthomyxa; and (3) a sampling program to record 
changes in spat, seed and market oyster stocks on representative reefs in 
the Galveston Bay system as an aid in determining present and future harvest 
potential. 
This report summarizes data collected during 1970. 
-155-
METHODS 
The disease monitor stations at Hanna and Switchover Reefs (Figure 1) 
consisted of wooden platforms containing a lift system to handle a number 
of oyster trays. The Hanna station was stocked with survivors of three 
age groups (1965, 1966 and 1967 year classes) carried over from the previous 
year. Two age groups carried at the Switchover station were stolen early 
in the year. In April, 1000 oysters representing the 1969 year class were 
stocked at this station. No room was available for the group at Hanna Reef. 
All oysters were held in vinyl-coated metal trays with hardware cloth 
tops. Stations were visited monthly; dead oysters were removed and 
measured; gaper tissues were cultured in fluid thioglycollate medium 
containing the antibiotics Mycostatin and Chloromycetin to determine 
Labyrinthomyxa incidence. Live oysters were measured (height) at quarterly 
intervals. 
Reef samples consisted of one standard bushel (2,150 cubic inches) of 
unculled oysters dredged from ten public reefs (Figure 1) at monthly inter-
vals. Live oysters were culled and measured (height) in groupings of 25 
millimeters designated as spat (1-25 mm), seed (26-50 mm), sub-market 51-
75 mm), small market (76-100 mm), medium market (101-125 mm), and large 
market (126-150 mm). Samples were grouped into winter, spring, summer and 
fall quarters. 
Ten market oysters from each sample were cultured in fluid 
thioglycollate medium to determine Labyrinthomyxa infection. The incidence 
was reported on a scale ranging from negative (0), very light (0.5), light 
(1.0) moderate (3.0), to heavy (5.0). 
RESULTS 
Oyster Mortality Study 
Monthly death rates among the 1966 and 1967 oyster groups began to 
increase in May (Table 1). Peak death rates among the older groups occurred 
in August or September but deaths were relatively high throughout the summer, 
coinciding with increased salinity and temperature (Table 2). As salinity 
and temperature values decreased in October, the monthly death rate among 
all four groups declined. 
Annual death rates of 33.9-45.6 among the older oyster groups (at Hanna 
Reef) were higher in 1970 than in 1969 when they ranged below 20 per cent. 
Although deaths among the 1969 group were relatively low, the rate was much 
higher than anticipated. 
Gapers collected from the older age groups were moderately to heavily 
-156- i 
infected with Labyrinthomyxa throughout most of the year with little 
difference between low death and high death periods. Gapers from the 1969 
group did not show infections until July, immediately preceding the high 
death period. This group had been uninfected when stocked in April and 
similar oysters remaining on Bart's Pass (the collection site) did not show 
infections throughout the year. They evidently became susceptible to 
Labyrinthomyxa infection after exposure to an area with a history of con-
tinual infection. At the time of peak deaths the oysters were slightly over 
one year old. 
Reef Population Trends 
Oyster spat setting throughout the bay was generally delayed until 
September (Table 3) but the West Bay (Confederate Reef) peak setting appeared 
to have taken place in June. No sets were observed in the upper bay (Scott's 
and Beezley's). The most abundant set was observed at mid Red Fish Bar-
decreasing noticeably at the eastern (Bart's Pass) and western (Todd's Dump) 
sectors. East Bay sets were most abundant in the upper bay (Frenchy's) and 
lower bay (Hanna) stations. 
Quarterly changes in oyster size groups at the ten sample stations are 
shown in Table 4. All size groups except spat and seed declined in abundance 
in Confederate Reef (CR) samples from spring through winter. This was believed 
due to Thais predation and Labyrinthomyxa infection. Although market oysters 
were not abundant in samples collected prior to the beginning of the season, 
a sizeable hand-dredge fishery was observed. The boats initially concentrated 
in the area of the sample station but soon moved to the opposite (western) 
side of the reef crest. Oysters were confined to a relatively narrow strip 
close to the reef crest in shallow water. 
Oysters of any size groups were scarce at upper bay stations. Scott's 
Reef (SR) oysters consisted of the older market stock while Beezley Reef (BR) 
oysters were young (one-year old). Scott's Reef samples were typically 
covered by "mud mats" formed by polychaete and amphipod tubes. This covering 
may have prevented spat setting. However, Beezley Reef samples did not 
contain "mud mats" and setting did not occur there either. 
At East Bay stations, seed and sub-market stocks increased only in 
Frenchy Reef samples(FR) while market oyster stocks remained at low levels 
at both Frenchy's and Moody's (MR) Reefs. In spite of the limited supply of 
market oysters indicated by the samples, a light hand dredge fishery was 
observed at Frenchy's Reef. Oysters other than spat were scarce in all 
samples taken at Hanna Reef (HR) and, in spite of the relatively abundant 
spat set in late summer, no increase in seed stock occurred. Possibly Thais 
and/or Menippe predation may have been a factor. However, a localized dredge 
fishery developed along the "Bull Hill" section of the reef approximately 
2000 yards west of the sample station. One sample collected in this area in 
December consisted of approximately 50% market stock with no spat and few 
seed oysters. 
-157-
Seed oyster stocks increased in samples from North Red Fish (NRF) and 
South Red Fish (SRF) during the fall, decreased at Bart's Pass (BP) and 
showed little change at Todd's Dump (TD). Sub-market stocks decreased at 
all stations but market oysters generally increased in fall samples. The 
increase was most noticeable at Bart's Pass .as oysters from a relatively 
heavy 1969 set reached minimum legal size. Consequently the reef was 
fished moderately by commercial dredge boats during the season. 
Labyrinthomyxa Infection 
The incidence of Labyrinthomyxa infection among Red Fish Bar oysters 
was highest at South Red Fish (Table 5), remaining above epidemic level 
(2.0) from July through November. Infected oysters were not found at Bart's 
Pass throughout the year although oysters from this reef transplanted to 
the Switchover mortality station near Todd's Dump became infected by summer. 
In upper Galveston Bay, the incidence among Scott's Reef oysters was 
light with maximum infection detected in May or June. No market oysters 
were available at Beezley Reef in Trinity Bay. 
Infection incidence was generally light at the East Bay stations (no 
market oysters were sampled at Hanna Reef). The highest incidence was 
found among West Bay oysters at Confederate Reef in June, dropping sharply 
in July and remaining low until November. 
Infection incidence did not follow the pattern often observed in other 
years with spring peaks followed by early summer lows and late summer highs. 
The typical early summer drops occurred at different times and maximum inci-
dence did not necessarily coincide with high salinity and temperature (Table 
6). Above normal temperature in November and December favored an increase 
in incidence at most stations. 
The Oyster Fishery 
Much of the Galveston Bay harvest was dredged from South Red Fish Reef 
where the majority of the commercial fleet worked throughout the season. 
North Red Fish Reef and the adjoining Humble "A" Lease area also contributed 
heavily to the harvest. Bart's Pass was not fished as extensively as 
anticipated, possibly because the majority of the oysters were very close to 
the minimum size limit (3 inches). 
Other areas fished included Todd's Dump and Switchover Reef, Parallel 
Reef below Todd's Dump, the Houston Ship Channel spoil banks between Beacons 
59 and 67, the artificial reefs (Gaspipe, Triangle and Missing), Frenchy's 
Reef, the Bull Hill area of Hanna Reef, Bull Shoals or North Hanna, the mid-
East Bay Moody's Reef area. Later in the season the artificial reefs in 
-158-
Trinity Bay (Dry Hole and Tern) were fished along with Lost Reef and the 
"Little Sun" oil field. 
Approximately 200,000 barrels of oysters were reported from the bay 
during the season (Table 7), an increase of 28,000 barrels over that of the 
previous season or a 16 per cent increase in production. As in past years 
a number of out-of-state boats, mostly from Louisiana, participated in the 
fishery. Louisiana dealers reported over 110,000 barrels of oysters 
harvested and shipped from Galveston Bay, representing approximately 547o 
of the total recorded harvest. 
DISCUSSION 
Spring rainfall on the Trinity River watershed was less than in the 
previous year and salinity values decreased little. Mortality rates among 
the older tray station oysters increased well above those observed in 1969, 
probably associated with an increase in Labyrinthomyxa incidence in a more 
saline environment. Spatfall was not consistent and spat survival appeared 
to be poor. Thus seed stock which would ultimately supply the bulk of the 
harvest in the 1971-72 season showed no consistent increase. 
The supply of oysters for the 1970-71 season was good with large reef 
areas in the mid-bay contributing most of the harvest. As in past years, 
inconsistent setting, and/or poor survival of the set appear to be prime 
factors in determining the distribution and quantity of market oyster 
stocks. Disease among the older oysters, although important, has had less 
effect upon the harvest than has lack of sets which resulted in depletion 
of Upper Trinity Bay stocks and low production in East Bay. 
-159-
Figure It Outline of Galveston Bay/ 
showing approximate 
locations of oyster 
sample stations* 
# Reef sample stations 
D Oyster mortality 
platforms 
-160-
Table 1: Monthly mortality rates (7C) among four year-class oyster 
groups at Switchover and Hanna Reef tray stations in 
Galveston Bay during 1970 
MORTALITY RATE 
MONTH 
1965 Class 
* 
0.3 
1.0 
.0 
1.0 
1.2 
3.1 
9.2 
9.3 
14.5 
1.7 
1.7 
1.8 
1966 Class 
* 
0.4 
0.4 
0.7 
1.5 
3.0 
7.2 
9.9 
13.7 
10.3 
2.7 
0.9 
0.9 
1967 Class 
* 
0.3 
0.9 
1.3 
2.0 
4.4 
7.6 
10.7 
13.6 
12.5 
2.8 
1.6 
1.0 
1969 Class 
*** 
0.1 
0.2 
0.9 
1.8 
7.7 
9.9 
3.4 
2.6 
0.5 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
Annual Mortality (%) 33.9 41.8 45.6 24.3 
* 1965, 1966 and 1967 year-classes at Hanna Reef only 
*** 1969 year-class at Switchover Reef only. 
-161-
Table 2: Monthly salinity and water temperature values at Hanna and 
Switchover stations in 1970 
Salinity (o/oo) Temperature (oC) 
Month Hanna Reef Switchover (Average) 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
21 
22 
19 
13 
14 
20 
21 
24 
23 
17 
22 
23 
20 
20 
19 
13 
13 
17 
21 
22 
22 
17 
18 
22 
9 
12 
16 
18 
22 
27 
29 
30 
27 
20 
16 
16 
•162-
I 
I 
I 
I 
I 
I 
I 
I 
I 
_ 
I 
I 
I 
I 
I 
TABLE 3: Peak setting period and relative abundance of oyster 
spat at Galveston Bay stations In 1970 
Station Peak Setting Month Relative Abundance 
Beezley 
Scott Reef 
Todd's Dump 
N. Red Fish 
S. Red Fish 
Bart's Pass 
Frenchy's Reef 
Moody's Reef 
Hanna Reef 
Confederate Reef 
None 
None 
7 
9 
10 
9 
9 
9 
9 
6 (?) 
0 
0 
20 
500 
200 
30 
400 
150 
300 
200 
Relative abundance Is the maximum number of spat per bushel 
sample encountered during, or immediately after, the peak 
setting period. Numbers have been rounded off. 
-163-
TABLE 4: Average number of oysters per bushel sample collected each 
quarter at Galveston Bay stations during 1970 
Station 
TD 
NRF 
SRF 
BP 
FR 
MR 
HR 
BR 
SR 
CR 
Quarter 
W 
SP 
S 
F 
W 
SP 
s 
F 
W 
SP 
s 
F 
W 
SP 
S 
F 
W 
SP 
S 
F 
W 
SP 
S 
F 
w 
SP 
s 
F 
w 
SP 
s 
F 
w 
SP 
S 
F 
w 
SP 
S 
F 
Number o 
SP 
3 
2 
. 17 
9 
13 
13 
307 
49 
15 
5 
96 
82 
22 
12 
20 
9 
6 
2 
135 
161 
0 
1 
56 
69 
9 
0 
118 
97 
0 
0 
1 
0 
0 
0 
0 
0 
44 
175 
54 
S 
20 
11 
20 
22 
54 
39 
31 
67 
46 
30 
40 
97 
140 
89 
25 
23 
24 
16 
8 
45 
15 
7 
9 
26 
40 
6 
1 
3 
7 
4 
1 
1 
0 
0 
0 
0 
90 
55 
101 
f Oysters 
SuM 
28 
23 
24 
22 
60 
50 
45 
49 
47 
44 
66 
46 
103 
112 
103 
75 
8 
14 
18 
21 
13 
12 
12 
17 
3 
1 
0 
0 
2 
5 
4 
5 
0 
0 
0 
0 
34 
7 
6 
in Each 
SM 
22 
17 
19 
29 
32 
28 
31 
38 
24 
30 
42 
37 
12 
22 
38 
54 
9 
4 
7 
13 
12 
6 
6 
15 
0 
2 
3 
0 
0 
0 
0 
1 
2 
2 
2 
2 
30 
15 
3 
Size Group 
MM 
1 
5 
4 
4 
2 
4 
2 
5 
5 
6 
8 
8 
2 
3 
2 
3 
5 
4 
3 
3 
3 
2 
4 
4 
0 
0 
0 
0 
0 
0 
0 
0 
2 
3 
2 
2 
8 
10 
4 
LM 
0 
0 
1 
1 
0 
0 
0 
0 
1 
1 
0 
1 
0 
0 
0 
0 
1 
1 
1 
0 
0 
1 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 
1 
1 
2 
1 
0 
2 
1 
-164-
TABLE 5: Incidence of Labvr inthomyxa infection among market oysters at 
eight reef stations in Galveston Bay during 1970 
Month 
|H
 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
SR 
0.4 
0.0 
-
1.4 
1.3 
0.1 
0.9 
0.1 
-
0.3 
0.4 
TD 
0.4 
1.4 
0.8 
1.3 
0.6 
2.0 
1.2 
1.1 
2.0 
1.7 
1.8 
0.8 
NRF 
1.4 
1.3 
0.8 
1.7 
1.4 
1.6 
0.8 
2.5 
0.9 
1.9 
2.6 
2.0 
Station 
SRF 
1.4 
0.2 
1.8 
1.6 
0.8 
1.4 
2.6 
2.2 
2.6 
2.0 
2.1 
1.5 
BP 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
0.0 
MR 
0.8 
0.0 
0.1 
0.4 
1.2 
0.0 
0.2 
0.0 
1.9 
0.7 
0.2 
0.9 
FR 
0.1 
0.2 
0.3 
0.1 
0.0 
0.1 
0.1 
0.0 
0.0 
0.0 
0.1 
0.7 
CR 
3.1 
1.0 
-
1.8 
1.6 
2.5 
2.6 
-165-
TABLE 6: Monthly salinity and water temperature values at ten reef sample 
stations in Galveston Bay during 1970 
Salinity (°/oo) Temperature (°C) 
Month BR SR TD NRF SRF BP FR MR HR CR (Average) 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
17 
2 
2 
6 
11 
12 
12 
16 
13 
14 
12 
18 
17 
11 
11 
12 
18 
20 
18 
17 
16 
19 
22 
20 
18 
14 
12 
17 
22 
22 
22 
19 
16 
22 
22 
18 
17 
13 
11 
17 
22 
24 
22 
19 
17 
22 
21 
18 
17 
13 
11 
17 
22 
24 
22 
19 
17 
22 
19 
16 
16 
11 
8 
12 
17 
22 
18 
17 
12 
17 
18 
20 
22 
12 
11 
17 
16 
20 
18 
11 
12 
18 
19 
19 
19 
12 
13 
11 
17 
18 
18 
12 
10 
19 
22 
22 
19 
18 
12 
22 
19 
19 
22 
17 
22 
24 
19 
30 
-
33 
24 
22 
23 
9 
12 
16 
23 
24 
27 
28 
30 
28 
21 
15 
19 
-166-
Table 7: Oyster harvest in barrels from Galveston Bay during the 
1970-71 season 
Month 
it 
November 
December 
January 71 
February 
March 
April 
TOTAL 
Harvest in Barrels 
(Figures Rounded") 
37,000 
52,500 
39,800 
27,800 
22,800 
22,200 
201,100 
Season opened on November 15th. 
-167-


Oyster Studies, 1970

http://aquaticcommons.org/14272/1/2139-Oyster%20Studies%2C%201970.pdf_sequence%3D1

Oyster Studies, 1970

Abstract

Similar works

Full text

Available Versions

Aquatic Commons