Feeding Ecology of Coastal Sharks in the Northwest Gulf of Mexico

The feeding ecology of three coastal shark species consisting of Atlantic Sharpnose (Rhizoprionodon terraenovae), Bonnethead (Sphyrna tiburo), and Atlantic Blacktip (Carcharhinus limbatus) was examined in the northwest Gulf of Mexico (GOM). A total of 601 (305 R. terraenovae, 239 S. tiburo, and 57 C. limbatus) sharks were collected through the recreational fishery offshore Galveston, Texas over 2013 and 2014. Stomach contents were examined for all individuals and quantified for short-term diet information (days) and stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) in muscle tissue were analyzed for a subset of samples to examine longer term (weeks to months) feeding patterns. Both C. limbatus and R. terraenovae stomach contents primarily consisted of teleost fish with % index of relative importance (IRIs) of 91.16 and 98.95%, respectively. Primary prey categories for R. terraenovae included unidentified Teleostei (87.40 %IRI), Panaeidae (3.56 %IRI), and Tuthoidea (2.92 % IRI). Dominant prey in C. limbatus consisted of Unidentified Teleostei (88.52 %IRI) and Micropogonias undulatus (7.46 %IRI), additional non-teleost fish prey categories including Crustacea and Cephalopoda accounted for 1.15 %IRI. S. tiburo had a diet primarily of crustaceans (87.20 % IRI), the top three contributors were unidentified Brachyura (48.91 %IRI), Callinectes sapidus (18.06 %IRI), and C. similis (3.32 % IRI). Stable isotope results revealed similar trends as the stomach contents. Mean δ13C was significantly enriched for S. tiburo (-16.84 ‰) relative to the other two species, which had similar mean δ13C (R. terraenovae -17.07 ‰ and C. limbatus -17.06 ‰). Mean δ15N was significantly enriched for C. limbatus (16.64 ‰) and similar between R. terraenovae (15.94 ‰) and S. tiburo (15.90 ‰). δ34S was a useful tracer for benthic invertebrate consumption consisting of significantly depleted values for S. tiburo (15.45 ‰), relative to R. terraenovae (16.01 ‰) and C. limbatus (16.30 ‰). Collectively, both stomach contents and stable isotopes support unique feeding strategies of three common shark species that occupy similar habitats in the northwestern GOM

The Role of the Estuarine Habitat Mosaic in the Trophic Ecology and Secondary Production of Coastal Marine Consumers

Estuarine food webs are influenced by multiple distinct abiotic and biotic processes resulting in complex interactions that shift across space and time. Investigating the relationship between estuarine fauna and their food helps build our understanding of processes that support healthy fisheries, maintain biodiversity, and provide diverse ecosystem services to coastal communities. My dissertation examines the relationship between estuarine fauna and their food resources across multiple scales and conceptual frameworks. The prevailing question I attempt to answer throughout this dissertation is; how do the abiotic and biotic dynamics of an estuary influence the trophic ecology of estuarine consumers? The first question I asked focused exclusively on this concept; specifically, how does the abiotic configuration of habitat alter the biotic transfer of food resources across the interface between terrestrial (saltmarsh) to aquatic (seagrass) habitats (Ch. 1)? Also, central to the observations we make about fauna in the estuary is the question; how does the trophic ecology of consumers affect the ways in which we observe them for study? To answer this question, I investigated how biotic food web interactions may influence and bias how the abundance of estuarine predators is estimated, specifically when predators are concurrently collected presence of prey (Ch. 2). Fundamental understanding of how species interact with each other in estuaries is essential to interpreting how estuarine food webs function. As such, the next two chapters focus in the inter and intra-specific trophic relationships for migratory predators within the estuary. Migratory coastal sharks are found in high abundances across the temperate estuarine-ocean ecotone during the summer months. I found that this increase in taxonomic predator diversity also coincided with changes in inter- (Ch.3) and intraspecific (Ch.4) trophic ecology resulting in food web relationships ranging from trophic redundancy to diverse feeding strategies within and among-species. Overall, it is apparent that the trophic interactions occurring in estuaries are species and habitat specific. This work in whole provides additional evidence to the need of increased conservation measures among both fauna and habitat to preserve diverse food web relationships, specifically in highly productive estuaries.Doctor of Philosoph

Fish assemblages associated with artificial reefs assessed using multiple gear types in the northwest Gulf of Mexico

Quantitative surveys of fishes associated with artificial reefs in the northwest Gulf of Mexico were conducted over a 4-yr period (2014-2017). Artificial reefs surveyed were comprised of three types: concrete structures, rig jackets, and decommissioned ships. All reefs were surveyed using vertical long line ( VLL), fish traps, and Adaptive Resolution Imaging Sonar (ARIS 1800). Mean fish abundance did not significantly differ using VLL [1.7 ind set(-1) (SD 2.2)] among the three reef types. However, relative abundance among all fishes collected was significantly highest on rig reefs using traps [6.2 ind soak(-1) (SD 3.8)], while results from sonar surveys indicated that the mean relative fish density was highest on concrete reefs [15.3 fish frame(-1) (SD 26.8)]. Red snapper (n = 792), followed by gray triggerfish (n = 130), pigfish (n = 70), tomtate (n = 69), and hardhead catfish (n = 57) were the most numerically abundant species using VLL and traps; red snapper comprised 90.7% of total catch using VLL and 43.9% using traps. Mean Brillouin\u27s diversity (HB) was highest on ships using VLL [0.41 (SD 0.14)] and highest on rigs using traps [0.87 (SD 0.58)] compared to the lowest diversity found on concrete [VLL 0.07 (SD 0.11); traps 0.36 (SD 0.32)]. Findings from this study can be used to inform the planning of future artificial reefs and their effect on the assemblages of reef-associated fishes. Additionally, these results highlight the value of using multiple gear types to survey reef fish assemblages associated with artificial reefs

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.Peer reviewe

Increasing duration of heatwaves poses a threat to oyster sustainability in the Gulf of Mexico

The future of the wild oyster fishery in the northern Gulf of Mexico is largely uncertain due to changing environmental conditions and declining abundance of harvestable oysters. Specifically, rising temperatures can directly impact the physiological thresholds of the eastern oyster (Crassostrea virginica) at all life history stages and alter the narrow ecological niche this oyster occupies. The impact of rising temperatures is likely most pronounced during atmospheric heatwaves, defined as three or more days above the 90th percentile of daily maximum air temperatures, which have been shown to be increasing in frequency. Increasing exposure to high temperature extremes may contribute to and exacerbate an already declining oyster fishery. Critical to fishery health is recruitment i.e., the addition of new harvestable biomass, which is a dynamic process strongly driven by temperature. Here, we examine the relationship between heatwave characteristics and the prediction of poor oyster recruitment, measured as the abundance of post-larval oysters (e.g. spat) below the site-specific median density observed in historically productive oyster fisheries over 46-years (1976 – 2020) in Mobile Bay, Alabama and 21-years (1993 – 2014) in Apalachicola Bay, Florida. We acquired daily maximum air temperature measurements measured over 50 years (1970 – 2020) at weather monitoring stations adjacent to the bays to identify site specific annual heatwave events (maximum yearly air temperature, yearly and consecutive heatwave days, and number of annual heatwaves). Then, years with extreme heatwaves that exceeded the 75th percentile for the 50-year measurements were compared to years with non-extreme heatwave events. Years with extreme total heatwave days and extreme consecutive heatwave days were correlated with low post-larval oyster density. Across both bay systems, if consecutive heatwave days exceeded 11 days, then poor recruitment of oysters occurred 83 % of the time. Extreme heatwave duration as an indicator for poor recruitment has the potential to be a powerful tool for fishery managers to forecast recruitment and inform sustainable oyster harvest based on year-to-year variability in heatwave duration and long-term warming trends. Our findings illustrate how extreme temperatures can exacerbate multiple physiological and ecological stressors resulting in the loss of a keystone species for healthy and resilient coastal ecosystems

Exome sequencing of hepatocellular carcinoma in lemurs identifies potential cancer drivers:A pilot study

BACKGROUND AND OBJECTIVES: Hepatocellular carcinoma occurs frequently in prosimians, but the cause of these liver cancers in this group is unknown. Characterizing the genetic changes associated with hepatocellular carcinoma in prosimians may point to possible causes, treatments and methods of prevention, aiding conservation efforts that are particularly crucial to the survival of endangered lemurs. Although genomic studies of cancer in non-human primates have been hampered by a lack of tools, recent studies have demonstrated the efficacy of using human exome capture reagents across primates. METHODOLOGY: In this proof-of-principle study, we applied human exome capture reagents to tumor–normal pairs from five lemurs with hepatocellular carcinoma to characterize the mutational landscape of this disease in lemurs. RESULTS: Several genes implicated in human hepatocellular carcinoma, including ARID1A, TP53 and CTNNB1, were mutated in multiple lemurs, and analysis of cancer driver genes mutated in these samples identified enrichment of genes involved with TP53 degradation and regulation. In addition to these similarities with human hepatocellular carcinoma, we also noted unique features, including six genes that contain mutations in all five lemurs. Interestingly, these genes are infrequently mutated in human hepatocellular carcinoma, suggesting potential differences in the etiology and/or progression of this cancer in lemurs and humans. CONCLUSIONS AND IMPLICATIONS: Collectively, this pilot study suggests that human exome capture reagents are a promising tool for genomic studies of cancer in lemurs and other non-human primates. LAY SUMMARY: Hepatocellular carcinoma occurs frequently in prosimians, but the cause of these liver cancers is unknown. In this proof-of-principle study, we applied human DNA sequencing tools to tumor–normal pairs from five lemurs with hepatocellular carcinoma and compared the lemur mutation profiles to those of human hepatocellular carcinomas