Long-term effects of climate change on juvenile bull shark migratory patterns.

Seasonal variability in environmental conditions is a strong determinant of animal migrations, but warming temperatures associated with climate change are anticipated to alter this phenomenon with unknown consequences. We used a 40-year fishery-independent survey to assess how a changing climate has altered the migration timing, duration and first-year survival of juvenile bull sharks (Carcharhinus leucas). From 1982 to 2021, estuaries in the western Gulf of Mexico (Texas) experienced a mean increase of 1.55°C in autumn water temperatures, and delays in autumn cold fronts by ca. 0.5 days per year. Bull shark migrations in more northern estuaries concomitantly changed, with departures 25-36 days later in 2021 than in 1982. Later, migrations resulted in reduced overwintering durations by up to 81 days, and the relative abundance of post-overwintering age 0-1 sharks increased by >50% during the 40-year study period. Yet, reductions in prey availability were the most influential factor delaying migrations. Juvenile sharks remained in natal estuaries longer when prey were less abundant. Long-term declines in prey reportedly occurred due to reduced spawning success associated with climate change based on published reports. Consequently, warming waters likely enabled and indirectly caused the observed changes in shark migratory behaviour. As water temperatures continue to rise, bull sharks in the north-western Gulf of Mexico could forgo their winter migrations in the next 50-100 years based on current trends and physiological limits, thereby altering their ecological roles in estuarine ecosystems and recruitment into the adult population. It is unclear if estuarine food webs will be able to support changing residency patterns as climate change affects the spawning success of forage species. We expect these trends are not unique to the western Gulf of Mexico or bull sharks, and migratory patterns of predators in subtropical latitudes are similarly changing at a global scale.

Social media shines light on the "hidden" impact of nighttime guided-gigging charters on Texas' Southern Flounder fishery: A stab in the dark.

Southern Flounder (Paralichthys lethostigma) populations are declining in the Gulf of Mexico basin. This is particularly true in Texas, where this unique and culturally important fishery has been in decline since the 1980s despite increasingly stringent regulatory measures. Current angler-intercept creel surveys used to estimate recreational flounder harvest levels are conducted during daylight hours and do not account for the high levels of nighttime flounder gigging (spearing) activity, a popular and efficient harvest method for this fishery. There are legitimate scientific and logistical concerns that have prevented the use of wide-spread nighttime creel surveys to monitor the flounder gigging fishery in the past, however this has made accurate catch and effort estimates difficult to obtain. Given the concern about this economically important fishery's status, we adopted a unique approach utilizing social media to provide unprecedented information into this fishery's impact during periods that are not traditionally monitored. Specifically, we reconstructed seasonal flounder harvest and effort metrics stemming from the nighttime recreational guided flounder gigging sector over 2.6 years using guided flounder gigging charter photo archives publicly available through Facebook. These metrics show large average client party sizes, large trip harvests, and near-perfect bag limit efficiencies. Temporal trends indicated peak recreational guided flounder gigging effort and harvest occurs during the summer months, a time not traditionally associated with flounder gigging. The addition of nighttime guided-gigging recreational harvest estimates from this study to traditional daytime harvest estimates and commercial harvest estimates resulted in total annual harvest estimates nearly two times greater than current estimates. Overall, this study demonstrates the high pressure guided-gigging charters are placing on Texas' flounder fishery and illustrates the critical need for additional information on the nighttime recreational flounder fishery for both guided and private gigging anglers. Moreover, our results also demonstrate the usefulness of mining social media platforms to capture catch and effort data that are otherwise unavailable.

Wetland water-management may influence mercury bioaccumulation in songbirds and ducks at a mercury hotspot.

Mercury is a persistent, biomagnifying contaminant that can cause negative behavioral, immunological, and reproductive effects in wildlife and human populations. We examined the role of wetland water-management on mercury bioaccumulation in songbirds and ducks at Kellys Slough National Wildlife Refuge Complex, near Grand Forks, North Dakota USA. We assessed mercury concentrations in blood of wetland-foraging songbirds (80 common yellowthroats [Geothlypis trichas] and 14 Nelson's sparrows [Ammospiza nelsoni]) and eggs of upland-nesting ducks (28 gadwall [Mareca strepera], 19 blue-winged teal [Spatula discors], and 13 northern shoveler [S. clypeta]) across four wetland water-management classifications. Nelson's sparrow blood mercury concentrations were elevated (mean: 1.00 µg/g ww; 95% CL: 0.76-1.31) and similar to those reported 6 years previously. Mercury in songbird blood and duck eggs varied among wetland water-management classifications. Songbirds and ducks had 67% and 49% lower mercury concentrations, respectively, when occupying wetlands that were drawn down with water flow compared to individuals occupying isolated-depressional wetlands with no outflow. Additionally, songbirds within impounded and partially drawn-down wetland units with water flow had mercury concentrations that were 26-28% lower, respectively, than individuals within isolated-depressional wetlands with no outflow. Our results confirm that mercury concentrations in songbirds at Kellys Slough continue to be elevated and suggest that water-management could be an important tool for wetland managers to reduce bioaccumulation of mercury in birds.

Spatial assessment of water quality in the vicinity of Lake Alice National Wildlife Refuge, Upper Devils Lake Basin, North Dakota.

Runoff from concentrated animal feeding operations and croplands in the Upper Devils Lake Basin (Towner and Ramsey Counties), North Dakota, has the potential to impact the water quality and wildlife of the Lake Alice National Wildlife Refuge. Water samples were collected at eight locations upstream and downstream of the refuge, beginning in June 2007 through March 2011, to identify the spatial distribution of water quality parameters and assess the potential impacts from the upstream land use practices. Geographic Information Systems, statistical analysis, and regulatory standards were used to differentiate between sample locations, and identify potential impacts to water quality for the refuge based on 20 chemical constituents. Kruskal-Wallis analysis of variance (ANOVA) showed significant differences between sample locations based on boron, calcium, Escherichia coli, phosphorus, aluminum, manganese, and nickel. Hierarchical agglomerative cluster analysis of these constituents identified four distinct water quality groupings in the study area. Furthermore, this study found a significant positive correlation between the nutrient measures of nitrate-nitrite and total Kjeldahl nitrogen, and the percentage of concentrated animal feeding operation nutrient management areas using the non-parametric Spearman rho method. Significant correlations were also noted between total organic carbon and nearness to concentrated animal feeding operations. Finally, dissolved oxygen, pH, sulfate, E. coli, total phosphorus, nitrate-nitrite, and aluminum exceeded state of North Dakota and/or US Environmental Protection Agency water quality standards and/or guidelines. Elevated concentrations of phosphorus, nitrate-nitrite, and E. coli from upstream sources likely have the greatest potential impact on the Lake Alice Refuge.

CHEMOAUTOTROPHIC SYMBIONTS IN THE BIVALVE LUCINA FLORIDANA FROM SEAGRASS BEDS.

Enzymatic and histological evidence suggest that the eulamellibranch bivalve Lucina fioridana possesses bacterial endosymbionts capable of a chemoautotrophic metabolism. Dense populations of L. floridana (83 ± 11 per m2; 95% CI, n = 33) are found closely associated with the O2-releasing root systems of seagrasses in sulfiderich sediments; the sandy sediments of both Thalassia and Ruppia beds contain 1.67 ± 0.3 1 mM (95% CI, n = 13) and 2.49 ± 0.55 mM (95% CI, n = 13) sulfide, respectively. Both transmission electron microscopy of gill tissue and scanning electron microscopy of freeze-fractured gills reveal numerous rod-shaped procaryotic inclusions in vacuoles of large, eucaryotic cells ("bacteriocytes") located deeply within demibranch cross sections; no such inclusions are seen in the ciliated gill epitheium which is rich in mitochondria. Activities of ribulose 1,5-bisphosphate carboxylase (RuBPCase), phosphoribulokinase, APS reductase, ATP sulfurylase, and nitrite reductase have been measured and partially characterized in homogenates of fresh gill tissue. Light microscopy reveals numerous aggregations of pigmented granules localized to the interior of the gill in association with the bacteriocytes. Histochemical staining demonstrates the presence of iron in these granules, consistent with the idea that their composition, in part, may be respiratory pigment and/or iron-containing cytochromes. Energy dispersive X-ray analysis reveals sulfur as a dominant inorganic element in the gill tissue. Based on abundance data of L. fioridana and in vitro levels of RuBPCase (half-maximal velocity) this bivalve could potentially contribute 336 ± 96 g C/m2/year (95% CI) to the gross carbon fixation of seagrass beds.