A Comparison of Early Juvenile Red Drum Densities Among Various Habitat Types in Galveston

ABSTRACT: Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarily Halodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along the Spartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reef Crassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay

Gulf-Wide Decreases in the Size of Large Coastal Sharks Documented by Generations of Fishermen

Large sharks are top predators in most coastal and marine ecosystems throughout the world, and evidence of their reduced prominence in marine ecosystems has been a serious concern for fisheries and ecosystem management. Unfortunately, quantitative data to document the extent, timing, and consequences of changes in shark populations are scarce, thwarting examination of long-term (decadal, century) trends, and reconstructions based on incomplete data sets have been the subject of debate. Absence of quantitative descriptors of past ecological conditions is a generic problem facing many fields of science but is particularly troublesome for fisheries scientists who must develop specific targets for restoration. We were able to use quantitative measurements of shark sizes collected annually and independently of any scientific survey by thousands of recreational fishermen over the last century to document decreases in the size of large sharks from the northern Gulf of Mexico. Based on records from fishing rodeos in three U.S. coastal states, the size (weight or length) of large sharks captured by fishermen decreased by 50–70% during the 20 years after the 1980s. The pattern is largely driven by reductions in the occurrence and sizes of Tiger Sharks Galeocerdo cuvier and Bull Sharks Carcharhinus leucas and to a lesser extent Hammerheads Sphyrna spp. This decrease occurred despite increasing fishing effort and advances in technology, but it is coincident with the capitalization of the U.S. commercial shark long-line fishery in the GOM

Population Connectivity of Pelagic Megafauna in the Cuba-Mexico-United States Triangle

The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mexico-United States (U.S.) triangle was investigated using electronic tagging data from eight species that resulted in \u3e22,000 tracking days. Transnational movements of these highly mobile marine predators were pronounced with varying levels of bi- or tri-national population connectivity displayed by each species. Billfishes and tunas moved throughout the Gulf of Mexico and all species investigated (blue marlin, white marlin, Atlantic bluefin tuna, yellowfin tuna) frequently crossed international boundaries and entered the territorial waters of Cuba and/or Mexico. Certain sharks (tiger shark, scalloped hammerhead) displayed prolonged periods of residency in U.S. waters with more limited displacements, while whale sharks and to a lesser degree shortfin mako moved through multiple jurisdictions. The spatial extent of associated movements was generally associated with their differential use of coastal and open ocean pelagic ecosystems. Species with the majority of daily positions in oceanic waters off the continental shelf showed the greatest tendency for transnational movements and typically traveled farther from initial tagging locations. Several species converged on a common seasonal movement pattern between territorial waters of the U.S. (summer) and Mexico (winter)

Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead

Conservation and management efforts of marine apex predators are more reliable when information on movement and habitat use patterns are known. The scalloped hammerhead (Sphyrna lewini) was the first shark species to be protected under the U.S. Endangered Species Act and has life history characteristics that make this species particularly at risk for local depletion. Consequently, the goal of this study was to better understand the movement dynamics of this species in the Gulf of Mexico (GOM) where discards through the longline fishery can be substantial. A total of 33 scalloped hammerheads were tagged with fin mounted satellite tags and tracked for an average of 146 days (ranging from 5 to 479 days) to examine horizontal movements and quantify space use. Scalloped hammerheads showed a wide range of movements throughout the GOM continental shelf with limited long-distance dispersal and females displayed a shelf-edge association relative to more mid-shelf use by males. A generalized additive model was developed to identify habitat suitability for scalloped hammerheads in the GOM, while state-space modeling was used to examine movement behaviors. Model results highlighted the use of continental shelf waters with high occurrence at close proximities to both artificial and hard-bottom habitat combined with low chlorophyll a concentrations (∼0–4 mg m-3) and moderate salinities (33–35.5). Habitat suitability for scalloped hammerheads was predicted to be high on the mid to outer continental shelf inside the 200 m isobath and state-space model results suggest area-restricted behavior was most common relative to transient behavior. Findings from this study provide important information on movement of this species in the GOM and highlight their restricted use of continental shelf habitat and resident behavior that will need to be incorporated in future stock assessments and extinction risk analyses

A Review of the Ecological Performance and Habitat Value of Standing versus Reefed Oil and Gas Platform Habitats in the Gulf of Mexico

In the northern Gulf of Mexico (GOM), approximately 1,800 oil and gas production platforms (hereafter “standing platforms”) function as de facto artificial reefs. As a large number of platforms are reaching the end of their production lifespans, some of these structures will be converted to permanent artificial reefs via state Rigs-to-Reefs (RTR) programs (many others have already been “reefed”), which involve partial removal or toppling of the platforms (hereafter “reefed platforms”) either in place or moved to alternate approved locations. The conversion of standing platforms into artificial reefs results in a structure with a lower vertical relief, and no physical connection to the upper water column. As decommissioned standing platforms are increasingly converted into artificial reefs, it is important to evaluate the ecological effects of this physical transformation on platform-associated communities. Furthermore, the number of standing platforms in the northern GOM continues to rapidly decline as removals through the decommissioning process exceed new installations. Thus, there is a central need for science-based decision making on the proper use of these structures and to establish the best management practices to maximize RTR programmatic goals. Here, we review the current state of scientific knowledge comparing the ecological function and habitat value of standing and reefed platforms in the northern GOM and identify critical information gaps in need of future research with special emphasis on the ecological functionality of standing platforms and performance related to upper-water column benefits. Allowing platforms to remain standing would ameliorate the loss of biodiversity and fish biomass due to the loss of shallow water substrate. While the ~85-ft (26-m) clearance guidelines observed in current RTR practices reduce some aspects of biodiversity (e.g., upper water column species) associated with standing platforms; nevertheless, there is evidence to suggest that partially removed platforms do continue to provide an effective means of preserving the community structure and ecological functions associated with standing platforms, particularly for economically important species. Furthermore, reefed platforms retain the majority of the fish community in the lower depth strata, including species that are targeted by recreational and commercial fisheries. As a result, studies evaluating how standing and reefed platforms function to support fish populations in the GOM have primarily focused on the biological characteristics of the economically important red snapper (Lutjanus campechanus) given this species iconic status and importance as the most valuable reef fish in the GOM. As a demersal species, both standing and reefed platforms appear to provide suitable habitat with sufficient resources to support its biological needs. Though, the lack of similar trends among artificial and natural habitats in the northwestern and north-central GOM highlights the complex nature of habitat- and region-specific contributions to the GOM red snapper stock and warrants further investigation, especially into the loss of structure and function of habitat as well as los of species in the upper water column. Nevertheless, increased emphasis on a wider range of species, including other broadly distributed fisheries species of commercial and/or recreational value (e.g., greater amberjack, Seriola dumerili), and on whole-community and functional approaches will build towards a more mechanistic understanding of the broader ecosystem values provided by both standing and reefed platforms. The extensive variability in marine life and environmental conditions such as water depth, distance from shore, size, and many other characteristics associated with existing standing platforms makes it difficult to establish a generic set of predictions regarding the ecological consequences of 2 different decommissioning alternatives. Hence, decisions should be made on a case-by-case basis using all available scientific information. As standing platforms in the GOM reach the end of their productive lives at an increasing rate, long-term monitoring studies are critically needed to empirically assess changes to community structure and functionality prior to and following reefing or complete removal. These studies will ensure that RTR programs are operating at maximum efficiency and performance as it relates to reefing goals, and facilitate data-driven decisions to determine which standing platforms would be most economically and ecologically viable to remain standing and/or converted to artificial reefs. In summary, this comprehensive literature review identified several key findings comparing the ecological function and habitat value of standing and reefed platforms in the GOM: • Allowing platforms to remain standing would ameliorate the decline in biodiversity and fish biomass due to the loss of shallow water (<26 m) substrate. • Reefed platforms, especially partially removed platforms, continue to provide an effective means of preserving the community structure and ecological functions associated with standing platforms, particularly for economically important species. Thus, even some structure retained is highly valuable. • At this time, the ecological consequences of different decommissioning alternatives and decisions should be made on a case-by-case basis by the platform owner in conjunction with resource managers until a scientifically informed set of predictions can be formulated based on short- and long-term monitoring studies. • Future research, including long-term monitoring studies and increased emphasis on a wider range of species, is critically needed to fully understand the impact of decommissioning standing platforms and different reef configurations on the ecology and productivity of the GOM.Gulf Offshore Research Institut

Environmental influences on the occurrence of coastal sharks in estuarine waters

Long-term fisheries independent gill net surveys conducted in Texas estuaries from 1975 to 2006 were used to develop spatially explicit estuarine habitat use models for 3 coastal shark species: bull shark Carcharhinus leucas, blacktip shark C. limbatus, and bonnethead shark Sphyrna tiburo. Relationships between environmental predictors and shark distribution were investigated using boosted regression trees (BRT). Bull shark was the most abundant species (n = 5800), followed by blacktip (n = 2094), and bonnethead sharks (n = 1793). Environmental conditions influenced distribution patterns of all species and relationships were nonlinear, multivariate, and interactive. Results showed very good model performance and suggested shark distribution is most closely linked to salinity, temperature, and proximity to tidal inlets. By interpolating the BRT models, maps of the probability of capture were produced using ordinary kriging. Results showed that the central region along the Texas coast contains the most important estuarine shark habitat. This area was characterized by warm temperatures, moderate salinities, and abundant tidal inlets. Bull sharks also extended into low salinity estuaries, while blacktip and bonnethead sharks were restricted to areas near tidal passes with moderate salinities. Juvenile sharks were frequently captured, suggesting the Texas coast may constitute important nursery areas for all 3 species. The development of these spatially explicit models allows for prioritization and conservation of areas in a region that has great potential for human disturbance and climate change impacts. These results provide new insight into the habitat requirements of coastal sharks in the northwestern Gulf of Mexico and practical information for managing this resource.Publishe

Benchmarking community structure of estuarine-dependent nekton near the Aransas Pass inlet

The purpose of this study is to determine the baseline seasonal community structure of estuarine-dependent nekton (fish, shrimp, and crab) in the Aransas Pass inlet region to establish a pre-operational benchmark prior to newly proposed industrial development in this area. Many nekton occurring in coastal waters share a common estuarine-dependent life history strategy characterized by near-shore spawning in the Gulf of Mexico with larvae migrating through tidal inlets into shallow estuarine nursery habitats. Access to high-quality habitat and spawning grounds via tidal inlets is essential for the reproduction, growth, survival, and maintenance of these populations. Because 75% of commercially or recreationally important species in the Gulf are estuarine-dependent, evaluating how anthropogenic activities may impair this connection between Gulf and bay waters is critical to understanding the population dynamics in this system and how these factors may affect juvenile fish development and fishery productivity. The Aransas Pass inlet is the major tidal inlet for the region, and anthropogenic activities that may alter water chemistry, flow, and quality have the potential for significant negative impacts on the marine life using this migration corridor. The proposed industrial development of the Aransas Pass inlet region (e.g., Harbor Island) presents a critical opportunity to establish baseline community structure in the adjacent estuarine habitats. We found strong evidence that the Aransas Pass, where impacts from industrial development are likely to occur, and Packery Channel (located ~35 km south), where these impacts will likely be absent, inlets have wide-ranging differences in nekton recruitment and development at individual species and community levels. Based on the findings of this study, we recommend continued long-term monitoring in the Aransas Pass and Packery Channel inlet regions to establish baseline variability and appropriately capture planned and unplanned future natural and anthropogenic disturbances and scenarios of environmental change. Baseline studies such as this facilitate effective management plans to preserve the function of these inlet regions as nurseries and fulfill the CBBEP mission to protect and restore the health and productivity of Coastal Bend bays and estuaries while supporting continued economic growth and public use of the bays

Folding patterns of immunoglobulin molecules identified by urea gradient electrophoresis.

The reversible denaturant-induced unfolding of immunoglobulin molecules has been analyzed by transverse urea gradient gel electrophoresis and the effects that urea-induced unfolding exerts on the functional properties associated with their variable region, i.e. antigen binding and idiotypic expression, have been determined by Western blot analysis. Results obtained from these experiments indicate that urea-induced unfolding of the immunoglobulin molecule is a highly cooperative reversible process that occurs through a two-state transition with no accumulation of intermediates. The unfolding transition has its midpoint at about 6.5 M urea and appears to be slow on the time scale of electrophoresis. Folding intermediates in rapid equilibrium with the unfolded state as well as molecular forms with different electrophoretic mobility can be detected during refolding reactions. Results from Western blot analysis confirm the highly cooperative reversible urea-induced unfolding of immunoglobulin molecules and demonstrate that the unfolding transition leads to disappearance of both antigen binding and idiotypic expression, whereas the ability to interact with antibodies directed to continuous epitopes of the variable region is preserved. After progressive removal of the denaturing agent, the variable region refolds into structures that regain the functional properties of the native conformation.Publishe

Characterizing Nekton use of the Largest Unfished Oyster Reef in the United States Compared with Adjacent Estuarine Habitats

Characterizing density patterns of fish and crustaceans across estuarine habitat types can provide useful information regarding their relative value. The oyster reef complex within Sabine Lake Estuary is the largest known in the United States with no record of commercial harvest, and it presents a unique opportunity to understand the habitat value of an unfished reef system in comparison with adjacent estuarine habitats. High abundances of relatively large oysters with complex formations were observed throughout the 2-y study period. Average densities of fish and crustaceans were 6 times greater at the marsh edge than the nonvegetated shallow habitats, and 40 times greater than both the oyster reef and nonvegetated deep habitats. Low faunal densities observed in the oyster reef habitat may be the result of spatial configuration and connectivity to surrounding habitats, collection limitation resulting from its large vertical relief (>1 m) and complex 3-dimensional structure, or habitat selection resulting from water depth. Because the majority of crustaceans and resident and transient fish were observed within the marsh edge and nonvegetated shallow habitats, it is difficult to determine whether oyster reefs within Sabine Lake Estuary provide essential habitats for these species. Although low densities of organisms were observed in the oyster reef habitat, multivariate analysis indicates that the unfished reef supports a unique community of fish and crustaceans. Results provide a valuable baseline for future conservation, restoration, and management actions as we seek to understand more completely and to protect important estuarine habitat types.Publishe

Growth of newly settled red drum Sciaenops ocellatus in different estuarine habitat types

We examined growth of recently settled juvenile red drum in salt marsh, seagrass, oyster reef, and on nonvegetated bottom areas in the Galveston Bay system of Texas (USA). We estimated growth using otolith microstructure from free-ranging fish collected in different habitat types and also measured growth of red drum in experimental enclosures where fish movement was restricted. Otolith growth was closely related to somatic growth in fish of 13 to 33 mm SL, and we used daily otolith increments from the last 10 d before capture as an indicator of growth following settlement into estuarine habitats. Growth rates of red drum captured at marsh, nonvegetated, and seagrass sites were not significantly different; no fish were collected on oyster reef. While reducing potential problems of a lagged response between otolith growth and somatic growth, the use of a 10 d growth period may have increased the likelihood of fish movement among habitats affecting our comparisons. The overall post-settlement growth rate of 0.45 mm d-1 was similar to rates reported in the literature. Movement among habitat types was eliminated in experiments employing 24 solid-walled enclosures (60 cm diameter). Growth rates in enclosures over the 7 d experiment were 0.12 mm d-1 in oyster reef, 0.21 mm d-1 on nonvegetated bottom, 0.40 mm d-1 in salt marsh, and 0.42 mm d-1 in seagrass; rates in vegetated enclosures approximated natural growth rates. Significantly higher growth in marsh and seagrass enclosures suggests that growth potential for red drum may be highest in these vegetated areas. However, growth results in enclosures need to be evaluated carefully, because fish movement among habitat types may be important in these shallow estuarine systems.Publishe