Molly Lutcavage

Lipid corrections in carbon and nitrogen stable isotope analyses: comparison of chemical extraction and modelling methods

1. Lipids have more negative delta(13)C values relative to other major biochemical compounds in plant and animal tissues. Although variable lipid content in biological tissues alters results and conclusions of delta(13)C analyses in aquatic food web and migration studies, no standard correction protocol exists. 2. We compared chemical extraction and mathematical correction methods for freshwater and marine fishes and aquatic invertebrates to better understand impacts of correction approaches on carbon (delta(13)C) and nitrogen (delta(15)N) stable isotope data. 3. Fish and aquatic invertebrate tissue delta(13)C values increased significantly following extraction for almost all species and tissue types relative to nonextracted samples. In contrast, delta(15)N was affected for muscle and whole body samples from only a few freshwater and marine species and had a limited effect for the entire data set. 4. Lipid normalization models, using C : N as a proxy for lipid content, predicted lipid-corrected delta(13)C for paired data sets more closely with parameters specific to the tissue type and species to which they were applied. 5. We present species- and tissue-specific models based on bulk C : N as a reliable alternative to chemical extraction corrections. By analysing a subset of samples before and after lipid extraction, models can be applied to the species and tissues of interest that will improve estimates of dietary sources using stable isotopes.

Stable isotope dynamics in elasmobranch fishes

Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment, we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values. We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar physiologies would provide accurate estimates for elasmobranchs.

Tagging and tracking of marine animals with electronic devices

Behavioural Insights Based on the Use of Electronic Tags.- Using Telemetry to Monitor Movements and Habitat Use of Cultured and Wild Juvenile Winter Flounder in a Shallow Estuary.- Comparative Behavior of Wild and Hatchery Reared White Sea Bream (Diplodus sargus) Released on Artificial Reefs Off the Algarve (Southern Portugal).- Survival, Migration Speed and Swimming Depth of Atlantic Salmon Kelts During Sea Entry and Fjord Migration.- Small Scale Vertical Behaviour of Juvenile Albacore in Relation to Their Biotic Environment in the Bay of Biscay.- A Review of Acoustic Telemetry Technology and a Perspective on its Diversification Relative to Coastal Tracking Arrays.- The Ocean Tracking Network - Adding Marine Animal Movements to the Global Ocean Observing System.- Observations of the Behaviour of European Sea Bass (Dicentrarchus labrax) in the North Sea.- Vertical Movements and Habitat Utilization of Skipjack (Katsuwonus pelamis), Yellowfin (Thunnus albacares), and Bigeye (Thunnus obesus) Tunas in the Equatorial Eastern Pacific Ocean, Ascertained Through Archival Tag Data.- Investigations of Horizontal Movements of Atlantic Swordfish Using Pop-up Satellite Archival Tags.- Vertical Behavior and the Observation of FAD Effects on Tropical Tuna in the Warm-Pool of the Western Pacific Ocean.- Effects of T-bar and DST Tagging on Survival and Growth of European Hake.- Body Temperature of the Atlantic Bluefin Tuna (Thunnus thynnus L.) in the Western Mediterranean.- Multi-Channel Data-Logging: Towards Determination of Behaviour and Metabolic Rate in Free-Swimming Sharks.- Harnessing the Sun: Testing a Novel Attachment Method to Record Fine Scale Movements in Ocean Sunfish (Mola mola).- An Archival Tag for Monitoring Key Behaviours (Feeding and Spawning) in Fish.- Geolocation Methods.- Lessons from a Prototype Geolocation Problem.- Geolocating Fish Using Hidden Markov Models and Data Storage Tags.- State Space Model for Light Based Tracking of Marine Animals: Validation on Swimming and Diving Creatures.- Removing Bias in Latitude Estimated from Solar Irradiance Time Series.- Positioning Pelagic Fish from Sunrise and Sunset Times: Complex Observation Errors Call for Constrained, Robust Modeling.- Summary Report of aWorkshop on Geolocation Methods for Marine Animals.- Applications of Electronic Tags to Fisheries Management.- Developing Integrated Database Systems for the Management of Electronic Tagging Data.- Electronic Tagging Data Supporting Flexible Spatial Management in an Australian Longline Fishery.- Correction Factors Derived from Acoustic Tag Data for a Juvenile Southern Bluefin Tuna Abundance Index in SouthernWestern Australia.- A Multi-Scale Study of Red Porgy Movements and Habitat Use, and Its Application to the Design of Marine Reserve Networks.- Erratum.

A comparison of carbon and nitrogen stable isotope ratios of fish tissues following lipid extractions with non-polar and traditional chloroform/methanol solvent systems.

Stable isotope ratios act as chemical tracers of animal diet, and are used to study food web dynamics. Because carbon stable isotope values are influenced by tissue lipid content, a number of extraction methods have been used to remove lipid bias, but, in some species and tissues, extractions also alter nitrogen isotope values. We have analyzed delta(13)C and delta(15)N in Atlantic bluefin tuna liver and white muscle, and whole Atlantic herring, fish tissues covering a wide range of lipid content (bulk C:N 3.1-12.5). In order to compare delta(13)C and delta(15)N values from traditional chloroform/methanol extractions with non-polar solvent alternatives, we analyzed samples following (1) no treatment, (2) lipid removal using chloroform/methanol (2:1), and (3) Soxhlet extractions using chloroform, diethyl ether or hexane. Chloroform/methanol and chloroform extractions produced the lowest C:N values and highest delta(13)C values. In bluefin tuna, chloroform and hexane extractions significantly altered liver delta(15)N, and all methods significantly altered delta(15)N values in white muscle. Whole Atlantic herring delta(15)N was not altered by any extraction method, while the 2:1 chloroform/methanol extraction most completely removed fish tissue lipid components. Our results indicate that delta(15)N effects are not limited to common chloroform/methanol extractions and suggest that chloroform/methanol is the most effective extraction for delta(13)C correction. Given evidence for delta(15)N alteration among all tested methods, mathematical correction approaches should be further explored as an alternative to lipid correction.

Dispersal Routes and Habitat Utilization of Juvenile Atlantic Bluefin Tuna, Thunnus thynnus, Tracked with Mini PSAT and Archival Tags

Between 2005 and 2009, we deployed 58 miniature pop-up satellite archival tags (PSAT) and 132 implanted archival tags on juvenile Atlantic bluefin tuna (age 2–5) in the northwest Atlantic Ocean. Data returned from these efforts (n = 26 PSATs, 1 archival tag) revealed their dispersal routes, horizontal and vertical movements and habitat utilization. All of the tagged bluefin tuna remained in the northwest Atlantic for the duration observed, and in summer months exhibited core-use of coastal seas extending from Maryland to Cape Cod, MA, (USA) out to the shelf break. Their winter distributions were more spatially disaggregated, ranging south to the South Atlantic Bight, northern Bahamas and Gulf Stream. Vertical habitat patterns showed that juvenile bluefin tuna mainly occupied shallow depths (mean  = 5–12 m, sd  = 15–23.7 m) and relatively warm water masses in summer (mean  = 17.9–20.9°C, sd  = 4.2–2.6°C) and had deeper and more variable depth patterns in winter (mean  = 41–58 m, sd  = 48.9–62.2 m). Our tagging results reveal annual dispersal patterns, behavior and oceanographic associations of juvenile Atlantic bluefin tuna that were only surmised in earlier studies. Fishery independent profiling from electronic tagging also provide spatially and temporally explicit information for evaluating dispersals rates, population structure and fisheries catch patterns.

Health Evaluation of Leatherback Turtles (Dermochelys coriacea) in the Northwestern Atlantic During Direct Capture and Fisheries Gear Disentanglement

Abstract Health evaluations were conducted in the northwestern Atlantic for 19 leatherback turtles, which included 12 turtles directly captured as part of a satellite telemetry study and 7 turtles entangled in fishing gear. Assessment included physical examination; determination of heart rate and respiratory rate; and hematologic, plasma biochemical, nutritional, toxicologic, parasitologic, and microbiological investigations. Significant differences were found between directly captured and entangled turtles for curved carapace length, curved carapace width, blood urea nitrogen, chloride, sodium, triglycerides, relative heterophil count, relative monocyte count, relative and absolute eosinophil count, pH, bicarbonate, lead, and beta-hydroxybutyrate. Directly captured turtles showed evidence of mild respiratory acidosis. Significant differences were found between sexes for curved carapace length, curved carapace width, total protein, globulin, sodium, relative monocyte count, gamma-globulin, and anion gap. Relatively high blood concentrations of selenium and cadmium were found in all turtles.

Better Science Needed for Restoration in the Gulf of Mexico

In the wake of the BP oil spill, U.S. agencies need research plans to collect data that will aid in managing and assessing marine species and ecosystems. The 2010 BP Deepwater Horizon oil spill in the Gulf of Mexico (GoM) has damaged marine ecosystems and jeopardized endangered and commercial species under U.S. jurisdiction (see the figure). Agencies that manage protected species—including the U.S. National Marine Fisheries Service and the U.S. Fish and Wildlife Service—are tasked with recovering these populations. But many populations have not been adequately assessed, so recovery cannot be measured. Achieving mandated recovery goals depends on understanding both population trends and the demographic processes that drive those trends. After the 1989 Exxon Valdez Alaskan oil spill, evaluations of effects on wildlife were ambiguous, in part because limited data on abundance and demography precluded detection of change (1). Sadly, the situation in the GoM is similar more than 20 years later. As concluded in the National Commission report on the BP spill (2) released 11 January, “Scientists simply do not yet know how to predict the ecological consequences and effects on key species that might result from oil exposure…” We argue that scientists know how to make these assessments, but lack critical data to achieve this goal.

Investigations of Horizontal Movements of Atlantic Swordfish Using Pop-up Satellite Archival Tags

The long-distance horizontal movements of swordfish tagged in Canadian waters are described, using information obtained from pop-up satellite archival tags. Some of the satellite tags remained attached to the fish for up to 411 days, among the longest periods of attachment of pop-up satellite tags reported for any fish species. The results to date challenge the assumption employed in current stock assessments that swordfish move freely from the western North Atlantic to the eastern North Atlantic, as no such movement has been found. The results also demonstrate a consistent pattern of movement with residence in temperate waters from June to October, followed by migration to the south into the Caribbean Sea, with fish remaining there until April. Tagged swordfish returned to temperate waters by June, with evidence of precise homing to feeding areas.

Analysis of foraging movements of Atlantic bluefin tuna (Thunnus thynnus): individuals switch between two modes of search behaviour

We investigate the application of quantitative techniques for distinguishing adaptive search behaviour in Atlantic bluefin tuna (Thunnus thynnus). The analysis demonstrates the application of a novel spectral analysis technique for resolving and measuring periodicity in animal behaviour patterns. Two different search strategies are identified that include regulation of turning (klinokinesis) and speed (orthokinesis). Our results provide evidence that bluefin tuna attempt to optimize their searching efficiency through adjustments in the duration and timing of switching between these two searching strategies. Repetitive, diurnal deep dives were also found to coincide with switching of search behaviour. Additional tracking experiments with larger sample sizes are needed to better identify how individuals switch between the two search strategies and how such decisions may collectively improve the searching and foraging efficiency of their schools (synchrokinesis, social taxis) in response to changes in the size or composition of prey aggregations.

Behaviour and buoyancy regulation in the deepest-diving reptile : the leatherback turtle

SUMMARY In the face of the physical and physiological challenges of performing breath-hold deep dives, marine vertebrates have evolved different strategies. Although behavioural strategies in marine mammals and seabirds have been investigated in detail, little is known about the deepest-diving reptile – the leatherback turtle (Dermochelys coriacea). Here, we deployed tri-axial accelerometers on female leatherbacks nesting on St Croix, US Virgin Islands, to explore their diving strategy. Our results show a consistent behavioural pattern within dives among individuals, with an initial period of active swimming at relatively steep descent angles (∼–40 deg), with a stroke frequency of 0.32 Hz, followed by a gliding phase. The depth at which the gliding phase began increased with the maximum depth of the dives. In addition, descent body angles and vertical velocities were higher during deeper dives. Leatherbacks might thus regulate their inspired air-volume according to the intended dive depth, similar to hard-shelled turtles and penguins. During the ascent, turtles actively swam with a stroke frequency of 0.30 Hz but with a low vertical velocity (∼0.40 ms–1) and a low pitch angle (∼+26 deg). Turtles might avoid succumbing to decompression sickness (‘the bends’) by ascending slowly to the surface. In addition, we suggest that the low body temperature of this marine ectotherm compared with that of endotherms might help reduce the risk of bubble formation by increasing the solubility of nitrogen in the blood. This physiological advantage, coupled with several behavioural and physical adaptations, might explain the particular ecological niche the leatherback turtle occupies among marine reptiles.