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Life history aspects of seahorses, Hippocampus, in Texas.

ABSTRACT. -- Dwarf seahorses (Hippocampus zosterae) and lined seahorses (H. erectus) occur in Texas, but little quantitative information concerning the life history and status of these species exists. Seahorse stocks in Texas during the 1980s appeared small, relatively stable, and restricted to the bays and adjacent Gulf of Mexico on the central and southern coast. Lined seahorses were more abundant than dwarf seahorses. Most (99 of 143) lined seahorses were caught in the gulf, but most (25 of 31) dwarf seahorses were caught in the bays. Within each bay, lined seahorses were almost completely restricted to water deeper than one meter. Dwarf seahorses occurred both near shore and in water deeper than one meter. Most lined seahorses (70 percent) were caught in summer and autumn (May-October), whereas most dwarf seahorses (70 percent) were caught in autumn or winter (October-January). Lined seahorses were about twice as large as dwarf seahorses (87 millimeters mean total length as compared to 40 millimeters). Lined seahorse growth was described by the relationship Y = 21.4 + 0.107A where Y = TL and A = age in days ([r.sup.2] = 0.65; P < 0.01). Key words: seahorses; Hippocampus; growth; distribution; abundance; Texas.

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Four species of seahorses occur in the United States, dwarf seahorse (Hippocampus zosterae), lined seahorse (H. erectus), longsnout seahorse (H. reidi), and Pacific seahorse (H. ingens) (Robins et al., 1980). Dwarf and lined seahorses occur in the Gulf of Mexico and both are found in Texas (Hoese and Moore, 1977). Dwarf seahorses (synonymous with H. regulus) are small fish (total length less than 30 millimeters) limited to high-salinity grass flats. Lined seahorses reach about 130 millimeters in length and occur in bays and the shallow Gulf of Mexico. The life history of dwarf seahorses was described for fish caught at Cedar Key Florida by Strawn (1958). However, there is little quantitative or comprehensive information concerning the life history and status of these species in Texas. Data collected during routine sampling in Texas bays and the adjacent Gulf of Mexico since 1975 by the Texas Parks and Wildlife Department (TPWD) afford the opportunity to address this situation. This study describes the spatial and temporal distribution, relative abundance, and growth of dwarf and lined seahorses in Texas.

MATERIALS AND METHODS

TPWD initiated two comprehensive sampling programs on the Texas coast in 1975. One used gill nets and bag seines to monitor the relative abundance and size of all species caught in each gear in each bay system (Mambretti et al., 1990). The other used onsite interviews of bay fishermen to monitor the harvest of each species (Maddux et al., 1989). These programs continue and have been expanded to include all bay systems and the Gulf of Mexico. Oyster dredges (bays only) and trawls have been incorporated into the relative abundance sampling program. Data collected by these activities through December 1990 were examined and records containing seahorses (178) were retrieved from the TPWD computer files. No seahorses were encountered during onsite angler interviews. All but four of the seahorses collected in the relative abundance sampling program were caught in bag seines and trawls; thus only data from these gear were used in this study.

Bag seines (18.3 meters long by 1.8 meters deep, with 1.3-centimeters stretched nylon multifilament in a 1.8-meter square bag and 1.9-centimeter stretched mesh in remaining webbing) were pulled at six randomly selected sites each month in each of the Galveston, Matagorda, San Antonio, Aransas, and Corpus Christi bay systems, the upper Laguna Madre, and the lower Laguna Madre starting in October 1977. The number of monthly samples collected in each bay system was increased to 10 in October 1981, 12 in April 1988, and 16 in January 1990. East Matagorda Bay system was added to the program in February 1983 and Sabine Lake was added in January 1986. An equal number of samples were collected in each half of each month. All animals caught were identified to species.

Trawls also were towed in each bay system at 20 randomly selected sites (10 sites in each of upper and lower Laguna Madre) each month starting in January 1982. Trawls (1.2 meters long) were 6.1 meters wide at the mouth with 3.8-centimeter stretched mesh webbing. The doors were 0.6 meters tall. Trawl sampling in Sabine Lake began in January 1986, and in East Matagorda Bay in April 1987. The trawl sampling program began in the Texas Territorial Sea (within 16.7 kilometers of shore) in 1984 off Port Aransas (24.1 Kilometers either side of each jetty) and was expanded to similar areas off the Sabine Pass, Galveston, Port O'Connor, and Port Isabel jetties in January 1986 (off Port Isabel sampling was restricted to 48.2 'kilometers north of the Rio Grande River). The catch in trawls was processed as the catch in bag seines, and all but 13 of the seahorses caught in both gear were measured (total length to the nearest millimeter).

Growth of lined seahorses was estimated by fitting a linear regression to the total length (millimeters) and date of capture data using LOTUS 123. Before analysis, each fish was assigned an age. A spawning date of 1 October was assumed based on data in Allshouse (1983). Each fish then was identified as a member of age zero-, one-, two-, or three-year classes based on their length and month of capture (Fig. 1). The number of days between capture and 1 October (age) was calculated. For fish age one and older, one, two, or three years were added to each age, depending on the year class to which each fish was assigned.

RESULTS

Seahorse stocks in Texas during the 1980s appeared small, relatively stable, and were restricted to the bays and adjacent Gulf of Mexico on the central and southern coast. Less than five seahorses were caught each year before 1983, but about 20 lined seahorses and four dwarf seahorses have been caught annually since 1983 (Table 1). However, trawl collections did not begin coastwide until 1982 in bays and 1986 in the Gulf, and bag seine collections were made at six sites per month per bay until October 1981. The increased sampling effort after 1982 resulted in more seahorses being caught than before, but as sampling effort stabilized in 1986 so did seahorse catches. Both species were caught in each bay system and the adjacent Gulf from Matagorda Bay through the lower Laguna Madre except that no lined seahorses were caught in the upper Laguna Madre (Table 2).

The lined seahorse appears to be more abundant in Texas than the dwarf seahorse. Almost five times more lined seahorses were caught than dwarf seahorses (Table 2). Most (99 of 143) lined seahorses were caught in the Gulf, but most (25 of 31) dwarf seahorses were caught in bays. The relative abundance of each species in Matagorda, San Antonio, and Aransas bays and the lower Laguna Madre was similar (fewer than 10 fish of each species caught in each bay system). Lined seahorses (19 fish caught in seven different months) were more common in Corpus Christi Bay than dwarf seahorses (four fish caught in three months), and the reverse was true in the upper Laguna Madre. Within each bay, the lined seahorse was almost completely restricted to water deeper than one meter. Only one of the lined seahorses was caught along the shore in a bag seine. A 20-millimeter fish was caught in October 1988 in the lower Laguana Madre. Dwarf seahorses occurred along shore and in deeper waters in bays. Fourteen of 25 fish caught in bays were caught in trawls and 11 in bag seines. All but two seahorses caught in bays occurred in areas near the Gulf or where salinities were generally highest.

[FIGURE 1 OMITTED]

Both species of seahorses occur in Texas throughout the year, but their relative abundance is not the same each month. At least one fish of each species was collected in each month except no dwarf seahorse was caught in May (Table 2). Most lined seahorses (70 percent) were caught in summer and autumn (May through October), whereas most dwarf seahorses (70 percent) were caught in autumn and winter (October through January).

[FIGURE 2 OMITTED]

Lined seahorses caught in Texas were about twice as large as dwarf seahorses. The mean total length ([+ or -] 1 SD) of 139 measured lined seahorses was 87 millimeters ([+ or -] 22 millimeters); 26 measured dwarf seahorses averaged 40 millimeters ([+ or -] 23 millimeters) (Table 3). All measured seahorses ranged from 17 to 160 millimeters with most fish ranging from 60 to 120 millimeters. Small (less than 35 millimeters) dwarf seahorses were restricted to bays, but larger fish were caught in both the bays and Gulf (Table 2). Only one small (less than 43 millimeters) lined seahorse was caught (a 20-millimeter fish in the lower Laguna Madre), and fish caught in the bays each month were generally larger than those caught in the Gulf (Table 2). One age class of fish comprised the majority of the lined seahorse catches; however, fish of at least three age classes occurred in the collections (Fig. 2). Fish larger than 20 millimeters grew about 0.11 millimeter per day ([+ or -] 0.007 millimeter per day). The relationship between size and time (total length = 21.4 + 0.107, age in days; SE of y-intercept = 13.0) explained a significant (P < 0.01) amount of the variation in the data ([r.sup.2] = 0.65). The length data were too few to estimate growth of dwarf seahorses (Table 3).

DISCUSSION

Seahorses are not common in Texas. However, their status has apparently changed little over the past 50 years. Collections with seines and trawls made inconsistently in Texas bays and adjacent areas of the Gulf of Mexico since 1942 resulted in few (less than five) individuals caught in a bay in collections each year (Table 4). Lined seahorses were more commonly caught in the Gulf of Mexico off Port Aransas than in any other sampled location. Catches before 1975 are generally consistent with the data collected during this study. However, the geographic range of seahorses in Texas may have changed slightly since the 1960s. One dwarf seahorse was caught in the Galveston Bay system in 1963 and one in 1973, and an unknown species was caught in Sabine Lake in 1959 (Table 4). No seahorses were caught in either bay system during the 1980s. Seahorses were caught in San Antonio and Corpus Christi Bay systems in the 1980s, but they were not caught in either bay system in the 1970s. It is possible, but unlikely, that fish were caught in the Galveston Bay system during the 1970s and 1980s, but were not found during collection processing because they are easily overlooked if the collection contains substantial amounts of vegetation (Hildebrand and King, 1975). Lined seahorses were caught in Cedar Lakes in 1973 (Johnson, 1977), but this area was not sampled in the 1980s.

Lined seahorses probably spawn in the Gulf of Mexico and juveniles use the Gulf as a nursery area, whereas adults tend to use the bays. Eight fish over 125 millimeters were caught only in bays, and fish in bays averaged 10 millimeters larger than those in the Gulf. However, fish spawned in the Gulf may be carried into bays as larvae. Allshouse (1983) caught four lined seahorses in channels near Port Aransas, Texas, on incoming tides--one on 30 September, one on 18 October, and two on 22 November.

Dwarf seahorses apparently can spawn throughout the year, spending most of their lives in bays. However, larger individuals also occur in the nearshore Gulf of Mexico. During this study, 25 of 31 dwarf seahorses were caught in bays. Fish less than 24 millimeters long were caught in bays every month except February through June, indicating that spawning had occurred from May through December (Strawn, 1958). Spawning in Florida occurs from mid-February through October (Strawn, 1958). Dwarf seahorses were caught in Halodule grass beds in the upper Laguna Madre in the 1970s (Table 4), and a larval fish was caught in Alazan Bay in July 1979 (Dokken et al., 1984). However, no dwarf seahorses were caught during the period March 1978 through February 1979 in Aransas Pass and its associated channels near Port Aransas, Texas (Allshouse, 1983).

For uncommon species like seahorses, it is unlikely that a short term (one to three years) sampling program would yield data necessary to estimate life history parameters. But, a comprehensive, long-term monitoring program like that conducted by TPWD can provide these types of data. The TPWD program has continued uninterrupted for more than 15 years, has expanded in geographic distribution and effort, and does not limit data collection to a select group of animals. As a result, the same types of data are available on infrequently encountered species like seahorses, nonfisheries species like searobins (Triglidae), and even undesirable species like Tilapia sp. as are available on economically important species like red drum (Sciaenops ocellatus), penaeid shrimp, or blue crab (Callinectes sapidus). Fortunately, data are now collected on all species caught in each gear thus allowing for the types of analyses conducted in this study. Growth rates currently are available for lined seahorses, and now can be produced for other uncommon species.
TABLE 1. Number of seahorses caught in each Texas bay system and the
Gulf of Mexico--24.1 kilometers either side of each jetty at Port
O'Connor (19) and at Port Aransas (20), and 48.2 kilometers north of the
Rio Grande River (21)--in TPWD bag seines and trawls in each year from
October 1977 through December 1990. Blanks indicate no fish caught.

 Upper
 San Corpus Laguna
Species Year Matagorda Antonio Aransas Christi Madre

Lined Seahorse (a) 1982 1
 1983 1 3 9
 1984 1 1 1
 1985 1 2 1
 1986 2 2
 1987
 1988 1 1
 1989 4 4
 1990 1
 Total 8 1 8 19
Dwarf Seahorse (b) 1977 2
 1978
 1979 1
 1980
 1981 1
 1982 1 3
 1983 3
 1984 1 1
 1985 2
 1986
 1987 1 1
 1988 1
 1989 1 5
 Total 2 2 6 4 10

 Lower
 Laguna Gulf
Species Year Madre 19 20 21 Total

Lined Seahorse (a) 1982 1
 1983 1 14
 1984 2 1 6
 1985 3 3 10
 1986 2 14 12 32
 1987 4 6 10
 1988 1 1 1 12 17
 1989 4 9 14 35
 1990 2 1 14 18
 Total 8 9 29 61 143
Dwarf Seahorse (b) 1977 2
 1978
 1979 1
 1980
 1981 1
 1982 4
 1983 3
 1984 2
 1985 2 4
 1986 1 3 4
 1987 2
 1988 1 2
 1989 6
 Total 1 3 2 1 31

(a) No lined seahorses caught from 1977 through 1981.
(b) No dwarf seahorses caught in 1990.

TABLE 2. Number of seahorses caught each month in each Texas bay system
and the Gulf of Mexico--24.1 kilometers either side of each jetty at
Port O'Connor (19) and at Port Aransas (20), and 48.2 kilometers north
of the Rio Grande River (21)--in TPWD bag seines and trawls during the
period October 1977 through December 1990. Blanks indicate no fish
caught.

 Location Month
Species (Bay or Gulf) 1 2 3 4 5 6 7 8 9 10

Lined Seahorse Matagorda 1 1 1 2 1
 San Antonio
 Aransas 2 2 2
 Corpus Christi 2 3 2 2 3 4 1 1
 Lower Laguna Madre 1 2
 Gulf 19 1 1 2 3
 Gulf 20 1 1 1 4 4 3 9 4 2
 Gulf 21 2 1 3 13 8 9 8 6 8
 Total 2 6 5 8 18 16 17 25 14 16
Dwarf Seahorse Matagorda 1
 San Antonio 1 1
 Aransas 2
 Corpus Christi 2
 Upper Laguna Madre 3 1 1 2 2
 Lower Laguna Madre 1
 Gulf 19 1 2
 Gulf 20 1
 Gulf 21 1
 Total 5 1 1 1 3 2 1 2 7

 Location Month
Species (Bay or Gulf) 11 12 Total

Lined Seahorse Matagorda 1 1 8
 San Antonio 1 1
 Aransas 1 1 8
 Corpus Christi 1 19
 Lower Laguna Madre 5 8
 Gulf 19 2 9
 Gulf 20 29
 Gulf 21 2 1 61
 Total 5 11 143
Dwarf Seahorse Matagorda 1 2
 San Antonio 2
 Aransas 4 6
 Corpus Christi 1 1 4
 Upper Laguna Madre 1 10
 Lower Laguna Madre 1
 Gulf 19 1
 Gulf 20 1
 Gulf 21 1
 Total 3 31

TABLE 3. Monthly mean ([bar.X]) and total length (mm) of seahorses
caught and measured (N) in Texas bays and adjacent Gulf of Mexico during
the period October 1977 through December 1990.

 Bay Gulf
 Total length (mm) Total length (mm)
Species Month N Range [bar.X] SD N Range [bar.X] SD

Lined seahorse 1 1 75 75 1 84 84
 2 4 53-115 80 26 2 64-74 69 7
 3 3 90-110 97 11 2 58-74 66 11
 4 4 73-160 102 39 4 55-105 81 21
 5 0 18 57-94 79 9
 6 3 94-101 95 6 13 60-101 78 11
 7 3 93-115 101 12 14 47-111 84 17
 8 7 59-145 114 28 16 47-125 90 17
 9 1 115 115 10 57-116 95 18
 10 6 20-91 60 23 9 66-124 98 18
 11 3 52-130 89 39 2 48-100 74 26
 12 6 55-135 103 30 3 43-114 75 29
 All 41 20-160 94 29 94 43-125 85 18
Dwarf seahorse 1 4 17-67 32 24 0
 2 1 75 75 0
 3 1 70 70 0
 4 0 1 35 35
 5 0 0
 6 0 3 45-82 65 19
 7 1 20 20 1 70 70
 8 1 20 20 0
 9 0 0
 10 5 20-32 26 5 1 85 85
 11 3 23-69 39 26 0
 12 4 19-34 27 7 0
 All 20 17-75 33 20 6 35-85 64-20 20

 Combined
 Total length (mm)
Species Month N Range [bar.X] SD

Lined seahorse 1 2 75-84 80 6
 2 6 53-115 76 19
 3 5 58-110 85 18
 4 8 55-160 92 29
 5 18 57-94 79 9
 6 16 60-101 81 11
 7 17 47-115 87 17
 8 23 47-145 97 23
 9 11 57-116 96 18
 10 15 20-124 83 27
 11 5 48-130 83 31
 12 9 43-135 94 31
 All 135 20-160 87 22
Dwarf seahorse 1 4 17-67 32 24
 2 1 75 75
 3 1 70 70
 4 1 35 35
 5 0
 6 3 45-82 65 19
 7 2 20-70 45 35
 8 1 20 20
 9 0
 10 6 20-85 36 25
 11 3 23-69 39 26
 12 4 19-34 27 7
 All 26 17-85 40 23

TABLE 4. Number of seahorses caught during previous studies conducted in
Texas bays and the adjacent Gulf of Mexico (off Port Aransas). Numbers
in parentheses represent total length in millimeters.

 Upper Lower
Sampling Cedar Laguna Laguna Gulf of
period Galveston Lakes Aransas Madre Madre Mexico

Dwarf seahorse
 1/63-12/64 (a) 1
10/71-9/73 (b) 1 (23)
 1/72-12/74 (c) 1
 8/71-7/73 (k) 1
 1/79-12/79 (d) 1

Lined seahorse
 3/41-11/42 (e) 1(74)
 7/58-9/61 (l) 1
 1/61-12/61 (f) 4(90-120)
 1/62-12/62 (g) 24(90-100)
 1/63-12/63 (h) 7(80-130)
 2/73-1/74 (i) 1(45)
 1/82-12/82 (n) 4

Unknown species
 8/71-12/72 (j)
 2/59-1/60 (m) 6

(a) Sheridan (1983); (b) McEachron et al. (1977); (c) Hildebrand and
King (1975); (d) Dokken et al. (1984); (e) Gunter (1945); (f) Compton
(1962); (g) Compton and Bradley (1963); (h) Compton and Bradley (1964);
(i) Johnson (1977); (j) Breuer (1973); (k) Harrington (1974); (l) Lyon
(1962); (m) Stevens (1960); (n) Allshouse (1983).


LITERATURE CITED

Allshouse, W. C. 1983. The distribution of immigrating larval and post-larval fishes into the Aransas-Corpus Christi Bay complex. Unpublished M.S. thesis, Corpus Christi State Univ., Corpus Christi, Texas, 118 pp.

Breuer, J. P. 1973. Ecological survey of the Brownsville Ship Channel. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., 52 pp.

Compton, H. 1962. Survey of the commercial shrimp and associated organisms of Gulf area 20. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., M-R-6, 19 pp.

Compton, H., and E. Bradley. 1963. Survey of the fish found in Gulf area 20 from 0-15 fathoms. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., MF-R-4, 14 pp.

______. 1964. Survey of the fishes found in Gulf area 20 from 2-17 fathoms and of post-larval fishes in Aransas Channel. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., MF-R-5, 25 pp.

Dokken, Q. R., G. C. Matlock, and S. Cornelius. 1984. Distribution and composition of larval fish populations within Alazan Bay, Texas. Contrib. Mar. Sci., 27:205-222.

Gunter, G. 1945. Studies on marine fishes of Texas. Publ. Inst. Mar. Sci., 1:1-190.

Harrington, R. A. 1974. Faunistic changes in Corpus Christi Bay, Texas, after completion of an artificial pass and use of the pass by organisms important to the seafood industry, 1971-1973. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., 43 pp.

Hildebrand, H., and D. King. 1975. A biological study of the Cayo del Oso and the Pita Island area of the Laguna Madre. Ann. Rept., 1973-74, Central Power and Light Co., Corpus Christi, Texas, 290 pp.

Hoese, H. D., and R. H. Moore. 1977. Fishes of the Gulf of Mexico, Texas, Louisiana, and adjacent waters. Texas A & M Univ. Press, College Station, 327 pp.

Johnson, R. B., Jr. 1977. Fishery survey of Cedar Lakes and the Brazos and San Bernard River estuaries. Texas Parks and Wildlife Dept., Tech. Ser., 23:1-65.

Lyon, J. M. 1962. Composition of fish species in area M-4 according to specific sampling. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Rept., M-4-R-3, 8 pp.

McEachron, L. W., C. R. Shaw, and A. W. Moffett. 1977. A fishery survey of Christmas, Drum, and Bastrop Bays, Brazoria County, Texas. Texas Parks and Wildlife Dept., Tech. Ser., 20:1-83.

Maddux, H. R., H. R. Osburn, D. L. Trimm, and K. W. Spiller. 1989. Trends in finfish landings by sport-boat fishermen in Texas marine waters, May 1974-May 1988. Texas Parks and Wildlife Dept., Fisheries Div., Manag. Data Ser., 8:1-496.

Mambretti, J. M., J. A. Dailey, and L. W. McEachron. 1990. Trends in relative abundance and size of selected finfishes and shellfishes along the Texas coast: November 1975-December 1988. Texas Parks and Wildlife Dept., Fisheries Div., Manag. Data Ser., 20:1-261.

Robins, C. R., R. M. Bailey, C. E. Bond, J. R. Brooker, E. A. Lachner, R. N. Lea, and W. B. Scott. 1980. A list of common and scientific names of fishes from the United States and Canada. Spec. Publ. Amer. Fish. Soc., 12:1-174.

Sheridan, P. F. 1983. Abundance and distribution of fishes in the Galveston Bay system, 1963-1964. Contrib. Mar. Sci., 26:143-164.

Stevens, J. R. 1960. Checklist of the fishes of area M-1. Texas Parks and Wildlife Dept., Coastal Fisheries Branch Project Repts., M-1-R-1, 3 pp.

Strawn, K. 1958. Life history of the pygmy seahorse, Hippocampus zosterae Jordan and Gilbert, at Cedar Key, Florida. Copeia, 1958:16-22.

GARY C. MATLOCK

Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, Texas 78744
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Author:Matlock, Gary C.
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:May 1, 1992
Words:3880
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