Aaron N. Rice

Predicting trophic position in sharks of the north-west Atlantic Ocean using stable isotope analysis

Trophic positions (TP) were estimated for the blue shark (Prionace glauca), short¢n mako (Isurus oxyrinchus), thresher shark (Alopias vulpinus), and basking shark (Cetorhinus maximus) using stable isotope ratios of carbon (d 13 C) and nitrogen (d 15 N). The basking shark had the lowest TP (3.1) and d 15 Nv alue (10.4%), whereas the thresher shark had the highest values (4.5, 15.2%). Mako sharks showed considerable variation in TP and isotopic values, possibly due to foraging from both inshore and oishore waters. Thresher sharks were signi¢cantly more enriched in d 15 N than blue sharks and mako sharks, suggesting a diierent prey base. The d 13 C values of thresher sharks and mako sharks varied signi¢cantly, but neither was signi¢cantly diierent from that of blue sharks. No statistical diierences were found between our TP estimations and those derived from published stomach contents analyses, indicating that stable isotope data may be used to estimate the trophic status of sharks.

USE OF ISOTOPIC ANALYSIS OF VERTEBRAE IN RECONSTRUCTING ONTOGENETIC FEEDING ECOLOGY IN WHITE SHARKS

We conducted stable 13C and 15N analysis on white shark vertebrae and demonstrated that incremental analysis of isotopes along the radius of a vertebral centrum produces a chronological record of dietary information, allowing for reconstruction of an individuals trophic history. Isotopic data showed significant enrichments in 15N with increasing sampling distance from the centrum center, indicating a correlation between body size and trophic level. Additionally, isotopic values verified two distinct ontogenetic trophic shifts in the white shark: one following parturition, marking a dietary switch from yolk to fish; and one at a total length of >341 cm, representing a known diet shift from fish to marine mammals. Retrospective trophic-level reconstruction using vertebral tissue will have broad applications in future studies on the ecology of threatened, endangered, or extinct species to determine life-long feeding patterns, which would be impossible through other methods.

Coordination of feeding, locomotor and visual systems in parrotfishes (Teleostei: Labridae).

SUMMARY Fishes require complex coordinated motions of the jaws, body and fins during feeding in order to successfully execute the strike or bite and then move away from the predation site. In conjunction with locomotor systems, sensory modalities guide coordinated feeding behavior, with vision playing an important role in many fishes. Although often studied separately, the locomotor, feeding and visual systems have not previously been examined together during fish feeding. To explore feeding coordination, we examined the kinematics of feeding behavior in two species of herbivorous parrotfish, Sparisoma radians and Scarus quoyi, which exhibit different single bite and repetitive bite strategies. Kinematic data on pectoral fin movements and body position show distinctive differences in strategies for the approach and post-strike motion between these species. Sparisoma and Scarus exhibited significant differences in the magnitude of jaw protrusion, time to maximum jaw protrusion, cranial elevation, and order of events in the feeding sequence. Oculomotor data show that both species orient the pupil forward and downward directed at the site of jaw contact until 100 ms before the bite, at which point the visual field is rotated laterally. Combinations of kinematic variables show repeated patterns of synchrony (onset and duration) for the approach to the food (distance, velocity, eye movement), prey capture (eye movement, jaw movement, fin movement) and post-capture maneuvering (fin movement, distance). Kinematic analyses of multiple functional systems reveal coordination mechanisms for detecting and approaching prey and executing the rapid opening and closing of the jaws during acquisition of food. Comparison of the coordination of feeding, swimming and sensory systems among fish species can elucidate alternative coordination strategies involved in herbivory in coral reef fishes.

Soundscapes from a Tropical Eastern Pacific reef and a Caribbean Sea reef

Underwater soundscapes vary due to the abiotic and biological components of the habitat. We quantitatively characterized the acoustic environments of two coral reef habitats, one in the Tropical Eastern Pacific (Panama) and one in the Caribbean (Florida Keys), over 2-day recording durations in July 2011. We examined the frequency distribution, temporal variability, and biological patterns of sound production and found clear differences. The Pacific reef exhibited clear biological patterns and high temporal variability, such as the onset of snapping shrimp noise at night, as well as a 400-Hz daytime band likely produced by damselfish. In contrast, the Caribbean reef had high sound levels in the lowest frequencies, but lacked clear temporal patterns. We suggest that acoustic measures are an important element to include in reef monitoring programs, as the acoustic environment plays an important role in the ecology of reef organisms at multiple life-history stages.

Nonlinear acoustic complexity in a fish ‘two-voice’ system

Acoustic signals play essential roles in social communication and show a strong selection for novel morphologies leading to increased call complexity in many taxa. Among vertebrates, repeated innovations in the larynges of frogs and mammals and the syrinx of songbirds have enhanced the spectro-temporal content, and hence the diversity of vocalizations. This acoustic diversification includes nonlinear characteristics that expand frequency profiles beyond the traditional categorization of harmonic and broadband calls. Fishes have remained a notable exception to evidence for such acoustic innovations among vertebrates, despite their being the largest group of living vertebrates that also exhibit widespread evolution of sound production. Here, we combine rigorous acoustic and mathematical analyses with experimental silencing of the vocal motor system to show how a novel swim bladder mechanism in a toadfish enables it to generate calls exhibiting nonlinearities like those found among frogs, birds and mammals, including primates. By showing that fishes have evolved nonlinear acoustic signalling like all other major lineages of vocal vertebrates, these results suggest strong selection pressure favouring this mechanism to enrich the spectro-temporal content and complexity of vocal signals.

North Atlantic Right Whale acoustic signal processing: Part I. comparison of machine learning recognition algorithms

This paper compares three different approaches currently used in recognizing contact calls made from the North Atlantic Right Whale (NRW), Eubalaena glacialis. We present two new approaches consisting of machine learning algorithms based on artificial neural networks (NET) and the classification and regression tree classifiers (CART), and compare their performance with earlier work that employs multi-Stage feature vector testing (FVT) approach. A combined total of over 100,000 noise and NRW up-call events were used in the study. Calls were primarily recorded from two areas, Cape Cod Bay and Great South Channel. Of the three classifiers, the CART had the highest assignment rates, overall 86.45% with highest false positive rates (≪100 per hour). The FVT Method had exceptionally low false positive rates, with ≪50 per hour. However, it had an overall assignment rate less than the NET. The CART had statistically the same false positive rate as the NET with the highest assignment rates, 2.2% higher than the NET and 11.75% greater than the FVT Method. Details of the results are shown and extensions to the research are discussed.

Novel underwater soundscape: acoustic repertoire of plainfin midshipman fish

Toadfishes are among the best-known groups of sound-producing (vocal) fishes and include species commonly known as toadfish and midshipman. Although midshipman have been the subject of extensive investigation of the neural mechanisms of vocalization, this is the first comprehensive, quantitative analysis of the spectro-temporal characters of their acoustic signals and one of the few for fishes in general. Field recordings of territorial, nest-guarding male midshipman during the breeding season identified a diverse vocal repertoire composed of three basic sound types that varied widely in duration, harmonic structure and degree of amplitude modulation (AM): ‘hum’, ‘grunt’ and ‘growl’. Hum duration varied nearly 1000-fold, lasting for minutes at a time, with stable harmonic stacks and little envelope modulation throughout the sound. By contrast, grunts were brief, ~30–140 ms, broadband signals produced both in isolation and repetitively as a train of up to 200 at intervals of ~0.5–1.0 s. Growls were also produced alone or repetitively, but at variable intervals of the order of seconds with durations between those of grunts and hums, ranging 60-fold from ~200 ms to 12 s. Growls exhibited prominent harmonics with sudden shifts in pulse repetition rate and highly variable AM patterns, unlike the nearly constant AM of grunt trains and flat envelope of hums. Behavioral and neurophysiological studies support the hypothesis that each sound types unique acoustic signature contributes to signal recognition mechanisms. Nocturnal production of these sounds against a background chorus dominated constantly for hours by a single sound type, the multi-harmonic hum, reveals a novel underwater soundscape for fish.

Adenosine and nitric oxide regulate regional vascular resistance via interdependent and independent mechanisms during sepsis

Objective Adenosine receptor blockade increases regional resting vascular resistance during sepsis. In healthy subjects, part of adenosine’s actions are mediated via stimulation of nitric oxide synthase. Because nitric oxide synthase activity is thought to be a major contributor to altered vascular tone in sepsis, we tested the hypothesis that some of the nitric oxide–mediated resting regional resistance during sepsis is secondary to endogenous adenosine stimulation of nitric oxide synthase. Design Prospective, randomized, controlled experiment. Setting Shock-trauma and basic science laboratory. Subjects Male Sprague-Dawley rats. Interventions Twenty-four hours after sepsis or sham induction, rats were separated into two groups (n = 6 to 10 in each group). Group 1 received a 10-min infusion of the adenosine antagonist 8-sulfophenyltheophylline (0.9 mg/kg·min) followed by a 10-min infusion of l-nitro-arginine-methyl ester (0.5 mg/kg·min). Group 2 similarly received l-nitro-arginine-methyl ester followed by 8-sulfophenyltheophylline in the presence of l-nitro-arginine-methyl ester. Measurements and Main Results Hemodynamic and blood flow measurements (microspheres) were made before infusions, 10 mins after the administration of each single-agent infusion, and 10 mins after combined-agent infusions were administered. No significant resistance alterations were observed in nonseptic rats. In septic rats, adenosine receptor blockade alone increased hepatosplanchnic and skeletal muscle vascular resistance, but no further increases were seen when l-nitro-arginine-methyl ester was added. Nitric oxide synthase inhibition alone increased hepatosplanchnic and skeletal muscle vascular resistances. When 8-sulfophenyltheophylline was added to the infusion, skeletal muscle vascular resistance increased significantly more than with l-nitro-arginine-methyl ester alone, but there were no further increases in hepatosplanchnic resistance. Renal and adipose vascular resistances increased with l-nitro-arginine-methyl ester infusions, and 8-sulfophenyltheophylline produced no effect. Conclusions During sepsis, nitric oxide caused resting vasodilation independent of adenosine in the renal and adipose vasculature. In the hepatosplanchnic circulation, there is reciprocal adenosine-nitric oxide interaction in maintaining resting regional resistance. Skeletal muscle displayed a dual adenosine-mediated (nitric oxide–independent) and nitric oxide–mediated (adenosine receptors required) interaction to regulate resting resistance during sepsis. These data indicate that in the hepatosplanchnic and skeletal muscle vasculature, all of the resting nitric oxide–mediated vasodilation is secondary to endogenous adenosine action, but in adipose and renal vasculature, resting nitric oxide mediated vasodilation is independent of adenosine. Endogenous adenosine also appears to play a significant role in determining resting skeletal muscle resistance that is independent of nitric oxide synthase during sepsis.

North Atlantic right whale acoustic signal processing: Part II. improved decision architecture for auto-detection using multi-classifier combination methodology

Autonomous signal detection of the North Atlantic right whale (NRW), Eubalaena glacialis, is becoming an important factor in monitoring and conservation for this highly endangered species. Both online and offline systems exist to help study and protect animals within this population. In both cases auto-detection of species-specific calls plays a vital role in localizing individual animal by searching time-frequency passive acoustic data. This research presents an experimental system, referred to as the NRW-CRITIC, for automatic detection of the NRW contact call. In general, the CRITIC uses a combinatorial classifier approach to integrate a series of existing machine learning algorithms; each designed specifically for NRW contact call identification. The proposed configuration consists of several recognition methods running in parallel; these include linear discriminant analysis, artificial neural network (NET) and classification regression tree (CART). This paper presents the details for the NRW-CRITIC and discusses the approach used to combine multiple independent decisions into a single result. A side-by-side performance comparison, between the CRITIC and a well-known method, the feature vector testing (FVT), is summarized. Performance metrics are evaluated based on a large database of acoustic recordings consisting of over 58,000 NRW contact calls from various locations, including two critical habitats, Great South Channel and Cape Cod Bay. Results indicate the FVT algorithm yields a 74.7% detection probability with an error rate of 4.35%. In comparison the CRITIC, operating at similar information level yields a 78.02% detection probability with a 3.25% error rate, exceeding the performance of the FVT. Performance was also measured using data from a multi-channel acoustic array located in Massachusetts Bay. A side-by-side comparison of array presence is discussed for two separate days. Results show that with the FVT and CRITIC operating at 0% error for array presence, the FVT method had 18,769 and 24,469 false positives for the Massachusetts Bay datasets respectively. With the same 0% error condition the CRITIC provided successful detection with significantly lower number of false positive rates: 1,072 and 2,324 calls, respectively. Future extensions of this experimental work are also discussed.

Potential Bryde's whale (Balaenoptera edeni) calls recorded in the northern Gulf of Mexico

Several marine autonomous recording units (MARUs) were deployed in northeastern Gulf of Mexico from 2010–2012 to study the acoustic ecology of Brydes whales (Balaenoptera edeni) following the Deepwater Horizon oil spill. However, the acoustic repertoire of this sub-population is poorly documented, presently limiting the efficacy of acoustic monitoring applications. Numerous stereotyped, low-frequency signals from a putative biological sound source were found throughout the recordings. Sounds fell into three categories distinguished by spectral and temporal properties. Multiple calls overlapped temporally on individual MARUs, suggesting that multiple sources produced these sounds. The basic features are similar to those from other mysticetes, but they differ from any previously published sounds. Since Brydes whales are the most common mysticete in the Gulf and have previously been observed within the recording area on multiple occasions, it is likely that Brydes whales are the most probable source of these sounds. These results potentially identify a suite of previously undocumented calls from Brydes whales, which could facilitate future passive acoustic monitoring efforts to better understand the population dynamics and status of this sub-population.