van der Hoop Julie

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  • Article
    Response to ‘On the importance of understanding physiology when estimating energetics in cetaceans’
    (Company of Biologists, 2017-02-15) Fahlman, Andreas ; van der Hoop, Julie ; Moore, Michael J. ; Levine, Gregg ; Rocho-Levine, Julie ; Brodsky, Micah
    We are grateful for the interest in our paper by two eminent physiologists and hope this response to their comments will clarify the objectives of our paper. The analysis in Fahlman et al. (2016) was not intended to provide an accurate method to estimate field metabolic rate (FMR) in large mysticetes; the objective was to measure the dynamic changes in physiology associated with recovery from exercise and show that they are important to consider when estimating FMR. While static averages can provide useful estimates of FMR for a variety of situations, these need to be appropriately selected. For example, we illustrate that it is not possible to use selected average values chosen from excised tissues or resting animals (as in Blix and Folkow, 1995) to provide meaningful estimates of FMR for animals at different activities (i.e. the dolphins in our study). Our study highlights the importance of temporal variation in physiological models: the Blix and Folkow (1995) estimates rely on the assumption that only breathing frequency (fR) changes with activity, while we argue that both the tidal volume (VT) and mixed lung O2 content also vary with activity and recovery from a dive (Ridgway et al., 1969). Including this variation in all three parameters reduces temporal uncertainty in the same conceptual model (see Eqn. 1 in Fahlman et al., 2016).
  • Article
    Entanglement is a costly life-history stage in large whales
    (John Wiley & Sons, 2016-12-11) van der Hoop, Julie ; Corkeron, Peter ; Moore, Michael J.
    Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life-history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of individual whales. Differences in measured blubber thicknesses and estimated blubber volumes between normal and entangled, emaciated whales indicate between 7.4 × 1010 J and 1.2 × 1011 J of energy are consumed during the course to death of a lethal entanglement. Increased thrust power requirements to overcome drag forces suggest that when entangled, whales require 3.95 × 109 to 4.08 × 1010 J more energy to swim. Individuals who died from their entanglements performed significantly more work (energy expenditure × time) than those that survived; entanglement duration is therefore critical in determining whales’ survival. Significant sublethal energetic impacts also occur, especially in reproductive females. Drag from fishing gear contributes up to 8% of the 4-year female reproductive energy budget, delaying time of energetic equilibrium (to restore energy lost by a particular entanglement) for reproduction by months to years. In certain populations, chronic entanglement in fishing gear can be viewed as a costly unnatural life-history stage, rather than a rare or short-term incident.
  • Presentation
    Don’t assume it’s ghost gear : accurate gear characterization is critical for entanglement mitigation [poster]
    (Woods Hole Oceanographic Institution, 2017-10-25) Henry, Allison G. ; Barco, Susan G. ; Cole, Tim ; Johnson, Amanda ; Knowlton, Amy R. ; Landry, Scott ; Mattila, David K. ; Moore, Michael J. ; Robbins, Jooke ; van der Hoop, Julie ; Asmutis-Silvia, Regina
    Entanglement is a significant conservation and welfare issue which is limiting the recovery of a number of marine species, including marine mammals. It is therefore important to reliably identify the causes of these events, including the nature of the entangling gear in order to reduce or prevent them in the future. A recently published review of marine debris assessed 76 publications and attributed a total of 1805 cases of cetacean entanglements in “ghost gear”, of which 78% (n=1413) were extracted from 13 peer reviewed publications. We examined the 13 publications cited in the review and found that the specific gear type or status of gear involved in the reported events was rarely mentioned beyond the fact that it was fishing related. This is likely due to the fact that determinations of debris as the entangling material are very difficult. In fact, in reviewing 10 years of large whale entanglement records for the U.S., the authors of another study reported that Hawaii was the only region in which any entangling gear was positively identified as ghost gear. The assumption that entangling gear is marine debris unless otherwise stated is dangerous because it could impact efforts to modify or restrict risk-prone fishing in key marine mammal habitats. Entanglement in actively fished gear poses a very real threat, and claims that only lost or abandoned fishing gear is responsible for entanglements can undermine conservation efforts.
  • Article
    Criteria and case definitions for serious injury and death of pinnipeds and cetaceans caused by anthropogenic trauma
    (Inter-Research, 2013-04-11) Moore, Michael J. ; van der Hoop, Julie ; Barco, Susan G. ; Costidis, Alexander M. ; Gulland, Frances M. ; Jepson, Paul D. ; Moore, Kathleen M. T. ; Raverty, Stephen A. ; McLellan, William A.
    Post-mortem examination of dead and live stranded beach-cast pinnipeds and cetaceans for determination of a cause of death provides valuable information for the management, mitigation and prosecution of unintentional and sometimes malicious human impacts, such as vessel collision, fishing gear entanglement and gunshot. Delayed discovery, inaccessibility, logistics, human safety concerns, and weather make these events challenging. Over the past 3 decades, in response to public concern and federal and state or provincial regulations mandating such investigations to inform mitigation efforts, there has been an increasing effort to objectively and systematically investigate these strandings from a diagnostic and forensic perspective. This Theme Section provides basic investigative methods, and case definitions for each of the more commonly recognized case presentations of human interactions in pinnipeds and cetaceans. Wild animals are often adversely affected by factors such as parasitism, anthropogenic contaminants, biotoxins, subclinical microbial infections and competing habitat uses, such as prey depletion and elevated background and episodic noise. Understanding the potential contribution of these subclinical factors in predisposing or contributing to a particular case of trauma of human origin is hampered, especially where putrefaction is significant and resources as well as expertise are limited. These case criteria descriptions attempt to acknowledge those confounding factors to enable an appreciation of the significance of the observed human-derived trauma in that broader context where possible.
  • Article
    Absolute probability estimates of lethal vessel strikes to North Atlantic right whales in Roseway Basin, Scotian Shelf
    (Ecological Society of America, 2012-10) van der Hoop, Julie ; Vanderlaan, Angelia S. M. ; Taggart, Christopher T.
    Vessel strikes are the primary source of known mortality for the endangered North Atlantic right whale (Eubalaena glacialis). Multi-institutional efforts to reduce mortality associated with vessel strikes include vessel-routing amendments such as the International Maritime Organization voluntary “area to be avoided” (ATBA) in the Roseway Basin right whale feeding habitat on the southwestern Scotian Shelf. Though relative probabilities of lethal vessel strikes have been estimated and published, absolute probabilities remain unknown. We used a modeling approach to determine the regional effect of the ATBA, by estimating reductions in the expected number of lethal vessel strikes. This analysis differs from others in that it explicitly includes a spatiotemporal analysis of real-time transits of vessels through a population of simulated, swimming right whales. Combining automatic identification system (AIS) vessel navigation data and an observationally based whale movement model allowed us to determine the spatial and temporal intersection of vessels and whales, from which various probability estimates of lethal vessel strikes are derived. We estimate one lethal vessel strike every 0.775–2.07 years prior to ATBA implementation, consistent with and more constrained than previous estimates of every 2–16 years. Following implementation, a lethal vessel strike is expected every 41 years. When whale abundance is held constant across years, we estimate that voluntary vessel compliance with the ATBA results in an 82% reduction in the per capita rate of lethal strikes; very similar to a previously published estimate of 82% reduction in the relative risk of a lethal vessel strike. The models we developed can inform decision-making and policy design, based on their ability to provide absolute, population-corrected, time-varying estimates of lethal vessel strikes, and they are easily transported to other regions and situations.
  • Article
    Spectral reflectance of whale skin above the sea surface: a proposed measurement protocol
    (Wiley Open Access, 2020-03-10) Cubaynes, Hannah C. ; Rees, W. Gareth ; Jackson, Jennifer A. ; Moore, Michael J. ; Sformo, Todd L. ; McLellan, William A. ; Niemeyer, Misty E. ; George, John C. ; van der Hoop, Julie ; Forcada, Jaume ; Trathan, Phil N. ; Fretwell, Peter T.
    Great whales have been detected using very‐high‐resolution satellite imagery, suggesting this technology could be used to monitor whales in remote areas. However, the application of this method to whale studies is at an early developmental stage and several technical factors need to be addressed, including capacity for species differentiation and the maximum depth of detection in the water column. Both require knowledge of the spectral reflectance of the various whale species just above the sea surface, as when whales bodies break the surface of the water to breath, log or breach, there is, at times, no sea water between the whale's skin and the satellite sensor. Here we tested whether such reflectance could be measured on dead whale tissue. We measured the spectral reflectance of fresh integument collected during the bowhead subsistence harvest, and of thawed integument samples from various species obtained following strandings and stored at −20°C. We show that fresh and thawed samples of whale integument have different spectral properties. The reflectance of fresh samples was higher than the reflectance of thawed samples, as integument appears to darken after death and with time, even under frozen conditions. In this study, we present the first whale reflectance estimates (without the influence of sea water and for dead tissue). These provide a baseline for additional work, needed to advance the use of satellite imagery to monitor whales and facilitate their conservation.
  • Dataset
    Entanglement is a costly life history stage in large whales
    ( 2016-06-28) van der Hoop, Julie
    Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of each individual whale.
  • Article
    Estimating energetics in cetaceans from respiratory frequency : why we need to understand physiology
    (The Company of Biologists, 2016-04-15) Fahlman, Andreas ; van der Hoop, Julie ; Moore, Michael J. ; Levine, Gregg ; Rocho-Levine, Julie ; Brodsky, Micah
    The accurate estimation of field metabolic rates (FMR) in wild animals is a key component of bioenergetic models, and is important for understanding the routine limitations for survival as well as individual responses to disturbances or environmental changes. Several methods have been used to estimate FMR, including accelerometer-derived activity budgets, isotope dilution techniques, and proxies from heart rate. Counting the number of breaths is another method used to assess FMR in cetaceans, which is attractive in its simplicity and the ability to measure respiration frequency from visual cues or data loggers. This method hinges on the assumption that over time a constant tidal volume (VT) and O2 exchange fraction (ΔO2) can be used to predict FMR. To test whether this method of estimating FMR is valid, we measured breath-by-breath tidal volumes and expired O2 levels of bottlenose dolphins, and computed the O2 consumption rate (V̇O2) before and after a pre-determined duration of exercise. The measured V̇O2 was compared with three methods to estimate FMR. Each method to estimate V̇O2 included variable VT and/or ΔO2. Two assumption-based methods overestimated V̇O2 by 216-501%. Once the temporal changes in cardio-respiratory physiology, such as variation in VT and ΔO2, were taken into account, pre-exercise resting V̇O2 was predicted to within 2%, and post-exercise V̇O2 was overestimated by 12%. Our data show that a better understanding of cardiorespiratory physiology significantly improves the ability to estimate metabolic rate from respiratory frequency, and further emphasizes the importance of eco-physiology for conservation management efforts.
  • Thesis
    Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-02) van der Hoop, Julie
    Animal movement is motivated in part by energetic constraints, where fitness is maximized by minimizing energy consumption. The energetic cost of movement depends on the resistive forces acting on an animal; changes in this force balance can occur naturally or unnaturally. Fishing gear that entangles large whales adds drag, often altering energy balance to the point of terminal emaciation. An analog to this is drag from tags attached to cetaceans for research and monitoring. This thesis quantifies the effects of drag loading from these two scenarios on fine-scale movements, behaviors and energy consumption. I measured drag forces on fishing gear that entangled endangered North Atlantic right whales and combined these measurements with theoretical estimates of drag on whales’ bodies. Entanglement in fishing gear increased drag forces by up to 3 fold. Bio-logging tags deployed on two entangled right whales recorded changes in the diving and fine-scale movement patterns of these whales in response to relative changes in drag and buoyancy from fishing gear and through disentanglement: some swimming patterns were consistently modulated in response. Disentanglement significantly altered dive behavior, and can affect thrust production. Changes in the force balance and swimming behaviors have implications for the survival of chronically entangled whales. I developed two bioenergetics approaches to estimate that chronic, lethal entanglements cost approximately the same amount as the cost of pregnancy and supporting a calf to near-weaning. I then developed a method to estimate drag, energy burden and survival of an entangled whale at detection. This application is essential for disentanglement response and protected species management. Experiments with tagged bottlenose dolphins suggest similar responses to added drag: I determined that instrumented animals slow down to avoid additional energetic costs associated with drag from small bio-logging tags, and incrementally decrease swim speed as drag increases. Metabolic impacts are measurable when speed is constrained. I measured the drag forces on these tags and developed guidelines depending on the relative size of instruments to study-species. Together, these studies quantify the magnitude of added drag in complementary systems, and demonstrate how animals alter their movement to navigate changes in their energy landscape associated with increased drag.
  • Article
    Assessment of management to mitigate anthropogenic effects on large whales
    (John Wiley & Sons, 2012-10-01) van der Hoop, Julie ; Moore, Michael J. ; Barco, Susan G. ; Cole, Timothy V. N. ; Daoust, Pierre-Yves ; Henry, Allison G. ; McAlpine, Donald F. ; McLellan, William A. ; Wimmer, Tonya ; Solow, Andrew R.
    United States and Canadian governments have responded to legal requirements to reduce human-induced whale mortality via vessel strikes and entanglement in fishing gear by implementing a suite of regulatory actions. We analyzed the spatial and temporal patterns of mortality of large whales in the Northwest Atlantic (23.5°N to 48.0°N), 1970 through 2009, in the context of management changes. We used a multinomial logistic model fitted by maximum likelihood to detect trends in cause-specific mortalities with time. We compared the number of human-caused mortalities with U.S. federally established levels of potential biological removal (i.e., species-specific sustainable human-caused mortality). From 1970 through 2009, 1762 mortalities (all known) and serious injuries (likely fatal) involved 8 species of large whales. We determined cause of death for 43% of all mortalities; of those, 67% (502) resulted from human interactions. Entanglement in fishing gear was the primary cause of death across all species (n= 323), followed by natural causes (n= 248) and vessel strikes (n= 171). Established sustainable levels of mortality were consistently exceeded in 2 species by up to 650%. Probabilities of entanglement and vessel-strike mortality increased significantly from 1990 through 2009. There was no significant change in the local intensity of all or vessel-strike mortalities before and after 2003, the year after which numerous mitigation efforts were enacted. So far, regulatory efforts have not reduced the lethal effects of human activities to large whales on a population-range basis, although we do not exclude the possibility of success of targeted measures for specific local habitats that were not within the resolution of our analyses. It is unclear how shortfalls in management design or compliance relate to our findings. Analyses such as the one we conducted are crucial in critically evaluating wildlife-management decisions. The results of these analyses can provide managers with direction for modifying regulated measures and can be applied globally to mortality-driven conservation issues.
  • Article
    Erratum to “Vessel strikes to large whales before and after the 2008 Ship Strike Rule”
    (John WIley & Sons, 2016-06-15) van der Hoop, Julie ; Vanderlaan, Angelia S. M. ; Cole, Timothy V. N. ; Henry, Allison G. ; Hall, Lanni ; Mase-Guthrie, Blair ; Wimmer, Tonya ; Moore, Michael J.
  • Preprint
    Behavioral impacts of disentanglement of a right whale under sedation and the energetic cost of entanglement
    ( 2013-03) van der Hoop, Julie ; Moore, Michael J. ; Fahlman, Andreas ; Bocconcelli, Alessandro ; George, Clay ; Jackson, Katharine ; Miller, Carolyn A. ; Morin, David ; Pitchford, Thomas ; Rowles, Teresa K. ; Smith, Jamison ; Zoodsma, Barb
    Protracted entanglement in fishing gear often leads to emaciation through reduced mobility and foraging ability, and energy budget depletion from the added drag of towing gear for months or years. We examined changes in kinematics of a tagged entangled North Atlantic right whale (Eg 3911), before, during and after disentanglement on 15 Jan 2011. To calculate the additional drag forces and energetic demand associated with various gear configurations, we towed three sets of gear attached to a load-cell tensiometer at multiple speeds. Tag analyses revealed significant increases in dive depth and duration; ascent, descent and fluke stroke rates; and decreases in root mean square fluke amplitude (a proxy for thrust) following disentanglement. Conservative drag coefficients while entangled in all gear configurations (mean ± SD Cd,e,go = 3.4x10-3 ± 0.0003, Cd,e,gb = 3.7x10-3 ± 0.0003, Cd,e,sl = 3.8x10-3 ± 0.0004) were significantly greater than in the nonentangled case (Cd,n = 3.2x10-3±0.0003; P = 0.0156, 0.0312, 0.0078 respectively). Increases in total power input (including standard metabolism) over the nonentangled condition ranged 1.6%-120.9% for all gear configurations tested; locomotory power requirements increased 60.0%-164.6%. These results highlight significant alteration to swimming patterns, and the magnitude of energy depletion in a chronically entangled whale.
  • Preprint
    Rebuttal to published article “A review of ghost gear entanglement amongst marine mammals, reptiles and elasmobranchs” by M. Stelfox, J. Hudgins, and M. Sweet
    ( 2016-11) Asmutis-Silvia, Regina ; Barco, Susan G. ; Cole, Tim ; Henry, Allison G. ; Johnson, Amanda ; Knowlton, Amy R. ; Landry, Scott ; Mattila, David K. ; Moore, Michael J. ; Robbins, Jooke ; van der Hoop, Julie
    We reviewed the findings of the recently published article by Stelfox et al. (2016): “A review of ghost gear entanglement amongst marine mammals, reptiles and elasmobranchs” published in this journal (Volume 111, pp 6–17) and found that they are both flawed and misleading as they do not accurately reflect the prevalence of “ghost gear” cases reported in the literature. While we commend the authors for recognizing the importance of attempting to quantify the threat and for recommending more comprehensive databases, the methods, results and conclusions of this review have not advanced the understanding of the issue. As authors of the papers on whale entanglements in the North Atlantic that were reviewed by Stelfox et al. (2016) and others who are knowledgeable about the topic, we provide specific comments regarding misrepresentations of both the source of entanglement (e.g., actively fished gear versus “ghost gear”) and the number of reported entanglements for whale species included in the North Atlantic.
  • Preprint
    Bottlenose dolphins modify behavior to reduce metabolic effect of tag attachment
    ( 2014-10) van der Hoop, Julie ; Fahlman, Andreas ; Hurst, Thomas P. ; Rocho-Levine, Julie ; Shorter, K. Alex ; Petrov, Victor ; Moore, Michael J.
    Attaching bio-telemetry or -logging devices (‘tags’) to marine animals for research and monitoring adds drag to streamlined bodies, thus affecting posture, swimming gaits and energy balance. These costs have never been measured in free-swimming cetaceans. To examine the effect of drag from a tag on metabolic rate, cost of transport and swimming behavior, four captive male dolphins (Tursiops truncatus) were trained to swim a set course, either non-tagged (n=7) or fitted with a tag (DTAG2; n=12), and surface exclusively in a flow-through respirometer in which oxygen consumption (Graphic) and carbon dioxide production (Graphic; ml kg−1 min−1) rates were measured and respiratory exchange ratio (Graphic/Graphic) was calculated. Tags did not significantly affect individual mass-specific oxygen consumption, physical activity ratios (exercise Graphic/resting Graphic), total or net cost of transport (COT; J m−1 kg−1) or locomotor costs during swimming or two-minute recovery phases. However, individuals swam significantly slower when tagged (by ~11%; mean ± s.d., 3.31±0.35 m s−1) than when non-tagged (3.73±0.41 m s−1). A combined theoretical and computational fluid dynamics model estimating drag forces and power exertion during swimming suggests that drag loading and energy consumption are reduced at lower swimming speeds. Bottlenose dolphins in the specific swimming task in this experiment slowed to the point where the tag yielded no increases in drag or power, while showing no difference in metabolic parameters when instrumented with a DTAG2. These results, and our observations, suggest that animals modify their behavior to maintain metabolic output and energy expenditure when faced with tag-induced drag.
  • Article
    Swimming kinematics and efficiency of entangled North Atlantic right whales
    (Inter-Research, 2017-01-12) van der Hoop, Julie ; Nowacek, Douglas P. ; Moore, Michael J. ; Triantafyllou, Michael S.
    Marine mammals are streamlined for efficient movement in their relatively viscous fluid environment and are able to alter their kinematics (i.e. fluke stroke frequency, amplitude, or both) in response to changes in force balance. Entanglement in fishing gear adds significant drag and buoyant forces that can impact swimming behaviors across a range of timescales. We deployed biologging tags during the disentanglement of 2 North Atlantic right whales Eubalaena glacialis to (1) examine how their kinematics changed in response to drag and buoyancy from entanglement in fishing gear, and (2) calculate resultant changes in swimming efficiency for one individual. We observed variable responses in dive behavior, but neither whale appeared to exploit added buoyancy to reduce energy expenditure. While some of the observed changes in behavior were individually specific, some swimming kinematics were consistently modulated in response to high drag and buoyancy associated with entangling gear, affecting thrust production. In high drag and buoyancy conditions, fluke strokes were significantly shorter and more variable in shape, and gliding was less frequent. Thrust and efficiency significantly differed among dive phases. Disentanglement reduced thrust coefficients ~4-fold, leading to 1.2 to 1.8-fold lower power (W). Ideal propulsive efficiency was significantly lower when entangled, though we detected no difference in observed propulsive efficiency between the conditions. Similar to carrying heavy objects or changing shoes, we present another condition where animals perceive unique movement constraints over seconds to minutes and develop compensatory strategies, altering their movement accordingly.
  • Article
    Vessel strikes to large whales before and after the 2008 Ship Strike Rule
    (John WIley & Sons, 2014-05-01) van der Hoop, Julie ; Vanderlaan, Angelia S. M. ; Cole, Timothy V. N. ; Henry, Allison G. ; Hall, Lanni ; Mase-Guthrie, Blair ; Wimmer, Tonya ; Moore, Michael J.
    To determine effectiveness of Seasonal Management Areas (SMAs), introduced in 2008 on the U.S. East Coast to reduce lethal vessel strikes to North Atlantic right whales, we analyzed observed large whale mortality events from 1990–2012 in the geographic region of the “Ship Strike Rule” to identify changes in frequency, spatial distribution, and spatiotemporal interaction since implementation. Though not directly coincident with SMA implementation, right whale vessel-strike mortalities significantly declined from 2.0 (2000–2006) to 0.33 per year (2007–2012). Large whale vessel-strike mortalities have decreased inside active SMAs, and increased outside inactive SMAs. We detected no significant spatiotemporal interaction in the 4-year pre- or post-Rule periods, although a longer time series is needed to detect these changes. As designed, SMAs encompass only 36% of historical right whale vessel-strike mortalities, and 32% are outside managed space but within managed timeframes. We suggest increasing spatial coverage to improve the Rule's effectiveness.
  • Article
    Swimming energy economy in bottlenose dolphins under variable drag loading
    (Frontiers Media, 2018-12-11) van der Hoop, Julie ; Fahlman, Andreas ; Shorter, K. Alex ; Gabaldon, Joaquin ; Rocho-Levine, Julie ; Petrov, Victor ; Moore, Michael J.
    Instrumenting animals with tags contributes additional resistive forces (weight, buoyancy, lift, and drag) that may result in increased energetic costs; however, additional metabolic expense can be moderated by adjusting behavior to maintain power output. We sought to increase hydrodynamic drag for near-surface swimming bottlenose dolphins, to investigate the metabolic effect of instrumentation. In this experiment, we investigate whether (1) metabolic rate increases systematically with hydrodynamic drag loading from tags of different sizes or (2) whether tagged individuals modulate speed, swimming distance, and/or fluking motions under increased drag loading. We detected no significant difference in oxygen consumption rates when four male dolphins performed a repeated swimming task, but measured swimming speeds that were 34% (>1 m s-1) slower in the highest drag condition. To further investigate this observed response, we incrementally decreased and then increased drag in six loading conditions. When drag was reduced, dolphins increased swimming speed (+1.4 m s-1; +45%) and fluking frequency (+0.28 Hz; +16%). As drag was increased, swimming speed (-0.96 m s-1; -23%) and fluking frequency (-14 Hz; 7%) decreased again. Results from computational fluid dynamics simulations indicate that the experimentally observed changes in swimming speed would have maintained the level of external drag forces experienced by the animals. Together, these results indicate that dolphins may adjust swimming speed to modulate the drag force opposing their motion during swimming, adapting their behavior to maintain a level of energy economy during locomotion.