Showing papers by "Molly Lutcavage published in 2008"
TL;DR: This work 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 (d delta(15)N) stable isotope data.
Abstract: Summary 1. Lipids have more negative δ 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 δ 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 ( δ 13 C) and nitrogen ( δ 15 N) stable isotope data. 3. Fish and aquatic invertebrate tissue δ 13 C values increased significantly following extraction for almost all species and tissue types relative to nonextracted samples. In contrast, δ 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 δ 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.
639 citations
TL;DR: It is suggested that chloroform/methanol is the most effective extraction for delta(13)C correction and mathematical correction approaches should be further explored as an alternative to lipid correction.
Abstract: 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.
104 citations
TL;DR: This work investigates here how classic time series technique, such as the Kalman Filter, can be made robust to uncover patterns in the data, and shows how measurement errors interact with the assumed movement model.
50 citations
TL;DR: In this paper, the authors analyzed the vertical movements of 17 bigeye tuna (Thunnus obesus) near the Azores Islands using pop-up satellite archival tags and found that vertical movements revealed a shallower distribution of bigeye in comparison with previous studies in the tropical Pacific and tropical Atlantic.
Abstract: Movement patterns of 17 bigeye tuna (Thunnus obesus) near the Azores Islands were analyzed between April and May 2001 and 2002 using pop-up satellite archival tags. Despite short attachment durations (1 to 21 days, 8.2 days on average), their vertical movements revealed much shallower distribution of bigeye tuna in comparison with previous studies in the tropical Pacific and tropical Atlantic. Depth and temperature histograms were unimodal, although overall depth distribution during the day was deeper than during the night due to daily incursions in deeper waters. Although generalized additive models showed significant nonlinear relationships with weight of the fish and sea level anomaly (as a proxy for variability of thermocline depth), the effect of these variables on bigeye depth appeared minor, suggesting that vertical movements of bigeye in the Azores during the spring migration may be influenced by food availability in upper water layers.
42 citations
TL;DR: In this paper, a smoothed satellite SST field is used to compensate for the missing areas due to cloud cover, which may not correspond well with the local average of SST measured by the tags.
Abstract: Pop-up satellite archival tags (PSATs) and data loggers (archival tags) have become key tools for tracking movements of marine animals, but uncertainties in location estimates can range from tens to hundreds of kilometers. Sea surface temperature (SST) may be used in models to improve light-based geolocation by comparing SSTs measured in tags to those measured by satellites (e.g. with a Kalman filter). Daily SST measurements are retrieved from the data recorded in the tag by averaging the near surface temperatures. Raw satellite SST data are represented as points in a grid, but measurement noise and areas missing due to cloud cover can produce an uneven SST field that may not correspond well with the local average of SST measured by the tags. A smoothed satellite SST field is used to compensate for these problems. We used 2 crossvalidation schemes to analyze what degree of smoothing produces the optimal match with the SST from the tag. Simulations based on data returned by PSATs deployed on Atlantic bluefin tuna Thunnus thynnus are used as a test case. We demonstrate that the optimal scale of smoothing, which affects overall variance in any type of geolocation estimation, is influenced by the scale of diffusive animal movement and that treatment of satellite SST in a geolocation framework should be carefully considered. The developed crossvalidation scheme provides an objective method for choosing the optimal smoothing scale and allows for better control of the overall geolocation process.
7 citations