Saint Helena, CA, United States
Saint Helena, CA, United States

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Wegner N.C.,University of California at San Diego | Sepulveda C.A.,Pfleger Institute of Environmental Research | Olson K.R.,University of Notre Dame | Hyndman K.A.,Georgia Regents University | Graham J.B.,University of California at San Diego
Journal of Morphology | Year: 2010

This study examines the functional gill morphology of the shortfin mako, Isurus oxyrinchus, to determine the extent to which its gill structure is convergent with that of tunas for specializations required to increase gas exchange and withstand the forceful branchial flow induced by ram ventilation. Mako gill structure is also compared to that of the blue shark, Prionace glauca, an epipelagic species with lower metabolic requirements and a reduced dependence on fast, continuous swimming to ventilate the gills. The gill surface area of the mako is about one-half that of a comparably sized tuna, but more than twice that of the blue shark and other nonlamnid shark species. Mako gills are also distinguished from those of other sharks by shorter diffusion distances and a more fully developed diagonal blood-flow pattern through the gill lamellae, which is similar to that found in tunas. Although the mako lacks the filament and lamellar fusions of tunas and other ram-ventilating teleosts, its gill filaments are stiffened by the elasmobranch interbranchial septum, and the lamellae appear to be stabilized by one to two vascular sacs that protrude from the lamellar surface and abut sacs of adjacent lamellae. Vasoactive agents and changes in vascular pressure potentially influence sac size, consequently effecting lamellar rigidity and both the volume and speed of water through the interlamellar channels. However, vascular sacs also occur in the blue shark, and no other structural elements of the mako gill appear specialized for ram ventilation. Rather, the basic elasmobranch gill design and pattern of branchial circulation are both conserved. Despite specializations that increase mako gill area and efficacy relative to other sharks, the basic features of the elasmobranch gill design appear to have limited selection for a larger gill surface area, and this may ultimately constrain mako aerobic performance in comparison to tunas. © 2010Wiley-Liss, Inc.


Sepulveda C.A.,Pfleger Institute of Environmental Research | Aalbers S.A.,Pfleger Institute of Environmental Research | Ortega-Garcia S.,Centro Interdisciplinario Of Ciencias Marinas Ipn Av Ipn S N Col Playa Palo Of Santa Rita | Wegner N.C.,University of California at San Diego | Bernal D.,University of Massachusetts Dartmouth
Marine Biology | Year: 2011

The depth distribution and temperature preferences of wahoo (Acanthocybium solandri) were quantified in the eastern North Pacific using archival tags. One hundred and eight data-loggers were deployed on wahoo (105-165-cm fork length) from 2005 to 2008 at three locations off of the coast of Baja California Sur, Mexico (Alijos Rocks, 25°00′N/115°45′W; Magdalena Bay Ridge, 25°55′N/113°21′W; Hurricane Bank, 16°51′N/117°29′W). Twenty-five tagged individuals (23%) were recaptured within close proximity (< 20 km) of their release sites. Collectively, depth and temperature data from 499 days revealed a predominant distribution within the upper mixed layer, with an average (±SD) depth of 18 ± 4 m during the day and 17 ± 6 m at night. Wahoo spent 99.2% of the daytime and 97.9% of night above the thermocline, and the greatest depth achieved by any fish was 253 m. Mean dive duration (3.8 ± 2.9 vs. 2.3 ± 0.8 min) and the vertical rate of movement (3.8 ± 1.3 vs. 3.0 ± 0.5 m min-1) were greater at night when compared to day. Ambient temperatures obtained from tag records ranged from 11.1 to 27.9°C, with an average of 25.0 ± 1.1°C. These data identify the importance of the warm, upper mixed layer for the wahoo. High recapture rates proximal to the deployment sites suggest seasonal site fidelity and reveal the economic importance of this resource to both commercial and recreational fisheries of the region. © 2011 Springer-Verlag.


Sepulveda C.A.,Pfleger Institute of Environmental Research | Knight A.,Pfleger Institute of Environmental Research | Knight A.,California State University, Monterey Bay | Nasby-Lucas N.,Pfleger Institute of Environmental Research | And 3 more authors.
Fisheries Oceanography | Year: 2010

This study reports on the fine-scale movements of swordfish (Xiphias gladius) outfitted with pop-off satellite archival transmitters (PSATs) in the Southern California Bight (SCB). PSATs were deployed on basking swordfish using traditional harpoon methods from 2004 to 2006. Transmitters were programmed for short-term deployment (2-90 days) and re-acquired using a signal direction finder. High-resolution (min -1) depth and temperature data from nine swordfish (approximately 45-120 kg) were collected (>193 days). All swordfish displayed diurnal vertical movements similar to those reported for other geographic locations. The dominant diurnal movement pattern entailed swordfish remaining below the thermocline (>68 ± 15 m) during the day and near the surface, within the upper-mixed layer, at night. Collectively, the average daytime depth (±SE) was 273 ± 11 m and the average night depth 31 ± 5 m. Three distinct vertical behaviors were recorded: 35% of the records following a strict diurnal pattern, with the entire day below the thermocline and the entire night near the surface; 52% of the records revealed routine surface-basking events during the day, with an otherwise similar distribution at night; and 13% of the records exhibited surface-oriented activity during the day and night. Surface basking (<3 m during the day) was recorded for eight individuals and occurred on 131 of the 193 days (68% of the dataset). Collectively, surface basking accounted for 8% of the total daytime records. The relevance of these vertical behaviors to SCB fisheries is discussed. © 2010 Blackwell Publishing Ltd.


Marshall H.,University of Massachusetts Dartmouth | Field L.,University of Massachusetts Dartmouth | Afiadata A.,University of Massachusetts Dartmouth | Sepulveda C.,Pfleger Institute of Environmental Research | And 2 more authors.
Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology | Year: 2012

For many shark species, little information exists about the stress response to capture and release in commercial longline fisheries. Recent studies have used hematological profiling to assess the secondary stress response, but little is known about how, and to what degree, these indicators vary interspecifically. Moreover, there is little understanding of the extent to which the level of relative swimming activity (e.g., sluggish vs. active) or the general ecological classification (e.g., coastal vs. pelagic) correlates to the magnitude of the exercise-induced (capture-related) stress response. This study compared plasma electrolytes (Na +, Cl -, Mg 2+, Ca 2+, and K +), metabolites (glucose and lactate), blood hematocrit, and heat shock protein (Hsp70) levels between 11 species of longline-captured sharks (n=164). Statistical comparison of hematological parameters revealed species-specific differences in response to longline capture, as well as differences by ecological classification. Taken together, the blood properties of longline-captured sharks appear to be useful indicators of interspecific variation in the secondary stress response to capture, and may prove useful in the future for predicting survivorship of longline-captured sharks where new technologies (i.e., pop-up satellite tags) can verify post-release mortality. © 2012 Elsevier Inc.


Bernal D.,University of Massachusetts Dartmouth | Donley J.M.,Barnard College | McGillivray D.G.,University of Calgary | Aalbers S.A.,Pfleger Institute of Environmental Research | And 2 more authors.
Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology | Year: 2010

Through convergent evolution tunas and lamnid sharks share thunniform swimming and a medial position of the red, aerobic swimming musculature. During continuous cruise swimming these muscles move uniformly out of phase with local body curvature and the surrounding white muscle tissue. This design results in thrust production primarily from the caudal fin rather than causing whole-body undulations. The common thresher shark (Family Alopiidae) is the only other fish known to share the same medial red muscle anatomy as the thunniform swimmers. However, the overall body shape and extremely heterocercal caudal fin of the common thresher is not shared with the thunniform swimmers, which have both fusiform bodies and high aspect-ratio, lunate caudal fins. Our study used sonomicrometry to measure the dynamics of red and white muscle movement in common thresher sharks swimming in the ocean to test whether the medial position of red muscle is associated with uncoupling of muscle shortening and local body bending as characteristic of thunniform swimmers. Common threshers (∼ 60-100 kg) instrumented with sonomicrometric and electromyographic (EMG) leads swam alongside of the vessel with a tail-beat frequency of ∼ 0.5 Hz. EMG signals confirmed that only the red muscle was active during sustained swimming. Despite the more medial position of the red muscle relative to the white muscle, its strain was approximately 1.5-times greater than that of the overlying white muscle, and there was a notable phase shift between strain trajectories in the red muscle and adjacent white muscle. These results suggest an uncoupling (shearing) of the red muscle from the adjacent white muscle. Although the magnitude of the phase shift between red and white muscle strain was relatively constant within individuals, it varied among sharks, ranging from near zero (red and white in phase) to almost 180° out of phase. This extent in variability has not been documented previously for thunniform swimmers with a medial red muscle position and may be a characteristic of the thresher's unique body and caudal fin morphology. Nonetheless, the uncoupling of red and white muscle strain remains a consistent character associated with fishes having a medially positioned red muscle. © 2010 Elsevier Inc. All rights reserved.


Aalbers S.A.,Pfleger Institute of Environmental Research | Bernal D.,University of Massachusetts Dartmouth | Sepulveda C.A.,Pfleger Institute of Environmental Research
Journal of Fish Biology | Year: 2010

This study tests the hypothesis that the common thresher shark Alopias vulpinus uses its elongate caudal fin to both produce thrust and immobilize prey during feeding. Underwater video recorded in southern California from 2007 to 2009 revealed 34 feeding events, all of which were initiated with the upper lobe of the caudal fin. © 2010 The Authors. Journal compilation © 2010 The Fisheries Society of the British Isles.


Patterson J.C.,University of Massachusetts Dartmouth | Sepulveda C.A.,Pfleger Institute of Environmental Research | Bernal D.,University of Massachusetts Dartmouth
Journal of Morphology | Year: 2011

The thresher sharks comprise a single family (Alopiidae) of pelagic sharks most easily recognized by the elongate dorsal lobe of their caudal fin. Despite morphological similarities among the alopiids, the common thresher (Alopias vulpinus) is unique in that its red, aerobic myotomal muscle (RM) is medially positioned (i.e., closer to the vertebrae), its systemic blood is supplied through a lateral circulation which give rise to counter-current heat exchanging retia, and it is capable of regional RM endothermy. Despite this information, it remains unknown if the other two alopiid species (bigeye thresher, Alopias superciliosus and pelagic thresher, Alopias pelagicus) also possess some or all of the characteristics related to regional RM endothermy. Thus, this study aimed to 1) document the presence of vascular specializations necessary for heat retention and RM endothermy and 2) measure the in vivo muscle temperatures of all three alopiid species. Laboratory dissections of the thresher species showed that only A. vulpinus possesses the lateral branching of the dorsal aorta giving rise to a lateral subcutaneous circulation and retial system, and that RM temperatures are elevated relative to ambient temperature. By contrast, both A. pelagicus and A. superciliosus have a similar systemic blood circulation pathway, in which the dorsal aorta and postcardinal vein form the basis for the central circulation and in vivo RM temperature measurements closely matched those of the ambient temperature at which the sharks were captured. Collectively, the vascular anatomy and in vivo temperature data suggest that only one species of thresher shark (A. vulpinus) possesses the requisite vascular specializations (i.e., lateral subcutaneous vessels and retia mirabilia) that facilitate RM endothermy. © 2011 Wiley-Liss, Inc.


Cartamil D.P.,University of California at San Diego | Sepulveda C.A.,Pfleger Institute of Environmental Research | Wegner N.C.,University of California at San Diego | Aalbers S.A.,Pfleger Institute of Environmental Research | And 2 more authors.
Marine Biology | Year: 2011

The common thresher shark (Alopias vulpinus) is a secondary target species of the California drift gillnet fishery (CA-DGN) and supports a growing recreational fishery in California waters. This study used archival tags to examine the movement patterns and habitat preferences of common threshers of the size range captured in the CA-DGN (<120 cm fork length). Depth and temperature-logging archival tags were deployed on 57 subadult and adult common threshers in the Southern California Bight. Tags from five individuals (8.8%) were recovered, and 154 days of data were successfully obtained from four of these. By night, shark movements were primarily limited to waters above the thermocline, which ranged in depth from 15 to 20 m. Sharks were significantly deeper by day, and daytime vertical distribution consisted of two distinct modes: a 'shallow mode' (wherein sharks occupied only the upper 20 m of the water column) and a 'deep mode' (characterized by frequent vertical excursions below the thermocline). This modal switch is interpreted as relating to regional differences in abundance of surface-oriented prey and prey in deeper water. Maximum dive depth was 320 m, greatest dive duration was 712 min, minimum temperature experienced during a dive was 9.1°C, and dive descent rate was significantly greater than ascent rate. Sharks inhabited waters corresponding to a sea surface temperature range of 16 to 21°C. The nocturnal depth distribution of common threshers has implications for management of drift gillnet deployment depths in the CA-DGN. © 2011 The Author(s).


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: Physiolg Mechansms&Biomechancs | Award Amount: 287.19K | Year: 2014

Temperature plays an important role in the biology of animals, particularly for those that sustain high levels of locomotor activity, as both muscle performance and blood-oxygen binding properties are directly affected. For most vertebrates, in which body temperature is similar to that of the surrounding environment, a change in ambient temperature will have profound effects on physiology. Marine pelagic fishes live in a thermally-stable environment marked by significant variation in temperature only with depth and latitude. While many fish remain within a narrow temperature range some are known to migrate across wide latitudinal ranges or dive into deeper, colder water. Of those species that routinely dive, few are capable of sustaining long periods of time within the cold, deep ocean. The swordfish is one of relatively few active fish species capable of diving for extended periods of time in the deep, cold, and oxygen depleted waters and then rapidly returning to the warm surface waters. The ability to withstand and routinely transition between disparate environmental regimes makes the swordfish an ideal candidate for studies of the effects of temperature and hypoxia on vertebrate muscle function and oxygen transport.

This study will assess the effects of temperature and hypoxia tolerance on muscle performance, cardiorespiratory function, and gene expression in fishes with different levels of tolerance for these extreme ambient conditions. This study builds upon previous NSF-funded research on muscle function and will increase our understanding of how selective pressures have lead to adaptations for life on the edge. This project will involve numerous students (high school, undergraduate, and graduate level) in hands-on field and laboratory research. The findings from this work will be communicated to the general public (including local fishermen and K-12) via seminars, presentations and internet portals. The results from this work will also be communicated in accessible formats to scientific, management, and public communities with the intent to foster greater awareness of scientific inquiry, discovery and progress.


Wegner N.C.,University of California at San Diego | Sepulveda C.A.,Pfleger Institute of Environmental Research | Bull K.B.,University of California at San Diego | Graham J.B.,University of California at San Diego
Journal of Morphology | Year: 2010

This comparative study of the gill morpho-metrics in scombrids (tunas, bonitos, and mackerels) and billfishes (marlins, swordfish) examines features of gill design related to high rates of gas transfer and the high-pressure branchial flow associated with fast, continuous swimming. Tunas have the largest relative gill surface areas of any fish group, and although the gill areas of non-tuna scombrids and billfishes are smaller than those of tunas, they are also disproportionally larger than those of most other teleosts. The morphometric features contributing to the large gill surface areas of these high-energy demand teleosts include: 1) a relative increase in the number and length of gill filaments that have, 2) a high lamellar frequency (i.e., the number of lamellae per length of filament), and 3) lamellae that are long and low in profile (height), which allows a greater number of filaments to be tightly packed into the branchial cavity. Augmentation of gill area through these morphometric changes represents a departure from the general mechanism of area enhancement utilized by most teleosts, which lengthen filaments and increase the size of the lamellae. The gill design of scombrids and billfishes reflects the combined requirements for ram ventilation and elevated energetic demands. The high lamellar frequencies and long lamellae increase branchial resistance to water flow which slows and streamlines the ram ventilatory stream. In general, scombrid and billfish gill surface areas correlate with metabolic requirements and this character may serve to predict the energetic demands of fish species for which direct measurement is not possible. The branching of the gill filaments documented for the swordfish in this study appears to increase its gill surface area above that of other billfishes and may allow it to penetrate oxygen-poor waters at depth. © 2009 Wiley-Liss, Inc.

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