Search

Understanding the habitat use and behavior of commercially exploited species throughout ontogeny is useful for devising effective management and conservation strategies. Differences in habitat use can often be exploited to separate target and non-target species, and determinations of home range size can inform the proper scale of conservation actions. In tropical tuna purse seine fisheries in the Pacific Ocean, juvenile silky sharks, Carcharhinus falciformis, comprise a large proportion of the total elasmobranch bycatch. There is now growing recognition of declines in silky shark populations and the need for international collaboration in conservation efforts. Yet, very little is known about the movement behavior or habitat use for this species. In this study, movement behavior of juvenile silky sharks was investigated using pop-up satellite archival tags placed on sharks that were captured during chartered research cruises on a commercial tuna purse seine fishing vessel using drifting Fish Aggregating Devices (FADs) in the western and central Pacific Ocean and on sharks captured using pelagic longlines in the eastern tropical Pacific. Analysis of horizontal and vertical movement behavior revealed silky sharks spend nearly 100% of their time in the shallow, warm waters of the mixed layer. Juvenile silky shark depth and thermal preferences overlapped with the preferred habitat of the primary target tuna species, indicating vulnerability to capture in purse seine and shallow-set longline fisheries throughout the tropical and subtropical regions of the Pacific Ocean where temperatures range between 24 and 29 °C. Reconstruction of horizontal movements showed dispersal between adjacent national jurisdictions and international waters, highlighting the need for international collaborations in the implementation of conservation measures.

The ocean is a dynamic environment inhabited by a diverse array of highly migratory species, many of which are under direct exploitation in targeted fisheries. The timescales of variability in the marine realm coupled with the extreme mobility of ocean-wandering species such as tuna and billfish complicates fisheries management. Developing ecoinformatics solutions that allow for near real-time prediction of the distributions of highly mobile marine species is an important step towards the maturation of dynamic ocean management and ecological forecasting. Using 25 years (1990-2014) of NOAA fisheries’ observer data from the California drift gillnet fishery, we model relative probability of occurrence (presence-absence) and catchability (total catch) of broadbill swordfish Xiphias gladius in the California Current System (CCS). Using freely-available environmental datasets and open source software, we explore the physical drivers of regional swordfish distribution. Comparing models built upon remotely-sensed datasets with those built upon a data-assimilative configuration of the Regional Ocean Modelling System (ROMS), we explore trade-offs in model construction and address how physical data can affect predictive performance and operational capacity. Swordfish catchability was found to be highest in deeper waters (>1500m) with surface temperatures in the 14-20°C range, isothermal layer depth (ILD) of 20-40m, positive sea surface height anomalies and during the new moon (

Fronts—i.e., the boundaries between water masses—are ubiquitous in the world oceans and have been shown to significantly influence pelagic ecosystems with enhanced local productivity and increased abundances of forage fish and top predators. Here we use data from archival tags to document how four juvenile albacore tunas foraged at and exploited a thermal front. Of the 3098 observed trips, the albacore mainly swam across the front between the warm side above the thermocline and the cold side below the thermocline with an average of 78 ± 20.4 cross‐frontal trips per fish per day. The warm frontal surface waters provided a thermal resource, allowing the tuna to maintain higher body temperatures and thus forage more efficiently in the food‐rich waters of the cold side of the front. Foraging success of the tunas decreased as the cross‐front thermal gradient weakened. This first look into small‐scale use of fronts by a top predator demonstrates that ephemeral, submesoscale oceanic features can play a significant role in pelagic ecology.

We have developed a set of tools that operate within an aquatic geographic information system to improve the accessibility, and usability of remote-sensed satellite and computer-modeled oceanographic data for marine science and ecosystem-based management. The tools form the Pelagic Habitat Analysis Module (PHAM), which can be applied as a modeling platform, an investigative aid in scientific research, or utilized as a decision support system for marine ecological management. Applications include fisheries, marine biology, physical and biological oceanography, and marine spatial management. The GIS provides a home for diverse data types and automated tools for downloading remote sensed and global circulation model data. Within the GIS environment, PHAM provides a framework for seamless interactive four-dimensional visualization, for matching between disparate data types, for flexible statistic or mechanistic model development, and for dynamic application of user developed models for habitat, density, and probability predictions. Here we describe PHAM in the context of ecosystem-based fisheries management, and present results from case study projects which guided development. In the first, an analysis of the purse seine fishery for tropical tuna in the eastern Pacific Ocean revealed oceanographic drivers of the catch distribution and the influence of climate-driven circulation patterns on the location of fishing grounds. To support management of the Common Thresher Shark (Alopias vulpinus) in the California Current Ecosystem, a simple empirical habitat utilization model was developed and used to dynamically predict the seasonal range expansion of common thresher shark based on oceanographic conditions.

A fishery-independent abundance survey was initiated by the National Marine Fisheries Service (NMFS) and the California Department of Fish and Game (CDFG) in 1994 to track the relative abundance and size of juvenile shortfin mako (Isurus oxyrinchus) and blue (Prionace glauca) sharks in the Southern California Bight (SCB). The survey was designed based on data from an experimental commercial shark longline fishery that operated in the SCB during 1988–1991. Survey sets were conducted annually during the summer months within seven 10 × 10 min spatial blocks in the SCB close to the California Channel Islands. Between 1994 and 2013, survey effort totaled 460 sets. The standardized catch-per-unit-effort (CPUE) of shortfin mako showed a generally declining trend from 1994 through 2010 with increases during the final years to a level similar to those of the mid-1990s. For blue sharks, the standardized CPUE showed a generally declining trend throughout the time series with the lowest values in 2012 and 2013, and an anomalously high CPUE in 2000. Catch rates varied across the survey area with fewer, larger sharks caught in the more northern blocks of the survey. Sharks of age classes 0–2 represented the majority of those caught in the survey (approximately 81% of blue sharks and 58% of makos), yet there was variability in the sizes of blue and mako sharks caught by year. The sex ratio of age-0 sharks caught was not different from 1:1 for shortfin makos, but skewed toward females for blue sharks. Although the survey area is relatively small and results show interannual and spatial variability in CPUE that is not fully understood, these data represent the first and only fishery-independent survey that has targeted these shark species in the SCB. The results of the survey and associated data provide useful information regarding regional relative abundance, size- and sex-compositions, and spatial distributions of shortfin mako and blue sharks, all of which are essential for stock assessments and fisheries management.

Background Most information on shortfin makos (Isurus oxyrinchus) in the eastern North Pacific (ENP) currently comes from fisheries data and short-term tracking studies. Although range has been inferred from catch and conventional tag data, little is known about the migration patterns and behavior in the ENP. This long-term electronic tagging study was designed to examine in detail the movement patterns and behavior of mako sharks in the ENP. Results In this study, a total of 105 mako sharks (104–280 cm fork length) were successfully tagged in the California Current between 2002 and 2014 with Argos satellite tags, including 93 satellite-linked radio-transmitting (SLRT) tags and 71 pop-up satellite archival tags (PSATs). This included 29 males that are in the size range of maturity, but only one mature female. Mean track durations from SLRT data were 337 days (max 1025), and PSAT tags were 136 days (max 272). Estimated minimum distance traveled in 1 year ranged from 6945 to 18,800 km/year. Habitats utilized included the entire California Current, the Sea of Cortez and offshore in the areas of the North Pacific Subtropical Gyre, North Pacific Transition Zone and North Equatorial Current. Seasonal movements within the California Current coincided with periods of higher primary productivity and chlorophyll a, and sea surface temperatures (SSTs) between 15 and 25 °C. SST ranged from 11 to 31 °C throughout the range, indicating a broad thermal tolerance. Conclusions Some of the key findings include the discovery of a high degree of variability between individuals in their vertical and horizontal movements, a strong influence of body size and season on mako shark movements, and the repetitive use of certain areas by individuals. These results expand our understanding of the distribution of mako sharks in the ENP. Although mako sharks are thought to comprise a single stock throughout the North Pacific, horizontal distribution of tagged mako sharks in this study was limited to the ENP demonstrating some spatial substructure. This study provides important data that can be used to identify fishery and gear vulnerabilities and inform management.

Factors influencing organic contaminant accumulation in sharks, especially across ontogeny, are not well-known. Contaminant concentrations were measured in three species of sharks (Blue, Shortfin Mako, and Common Thresher) across a range of size classes (neonatal to adult) that vary in their ecological and physiological characteristics. Empirical data was compared to a theoretical framework that predicted the shape of lifetime accumulation curves. We found that a one-size-fits-all accumulation model was not appropriate as species-specific characteristics had a significant effect on contaminant accumulation trajectories. Maternal offloading likely has an important effect on determining neonatal shark contaminant starting points, and trophic ecology and physiology may interact to affect the shape of species' contaminant accumulation curves. Makos were found to have the highest accumulation potential and Blues the lowest, with Threshers being intermediate in accumulation potential. Changes in species' ecology and/or physiology were also reflected in contaminant signature changes over ontogeny. If contaminant concentrations are to be used as a proxy for risk, species-specific characteristics need to be taken into account when estimating contaminant exposure and its potential negative effects on shark health and human consumption safety.

This study presents findings on an oxytetracycline injected adult male shortfin mako Isurus oxyrinchus recaptured in waters off of southern California after 6 years at liberty. During the period at liberty, the vertebral band-pair deposition rate was validated at one per year. This result indicates that from a time at or near sexual maturity, male I. oxyrinchus in the north-east Pacific Ocean exhibit a band-pair deposition rate of one band pair per year, while deposition rates for juveniles in the area have been validated at two band pairs per year.

Natal origin of subadult (age-1) Pacific bluefin tuna (PBT, Thunnus orientalis ) from the California Current Large Marine Ecosystem (CCLME) was determined using natural tracers in ear stones (otoliths). Age-0 PBT collected from the two known spawning areas in the western Pacific Ocean (East China Sea, Sea of Japan) were used to establish baseline signatures from otolith cores over 4 years (2014–2017) based on a suite of trace elements (Li, Mg, Mn, Sr, Zn and Ba). Distinct chemical signatures existed in the otolith cores of age-0 PBT collected from the two spawning areas, with overall classification accuracy ranging 73–93% by year. Subadult PBT collected in the CCLME over the following 4 years (2015–2018) were then age-class matched to baselines using mixed-stock analysis. Natal origin of trans-Pacific migrants in the CCLME ranged 43–78% from the East China Sea and 22–57% from the Sea of Japan, highlighting the importance of both spawning areas for PBT in the CCLME. This study provides the first estimates on the natal origin of subadult PBT in this ecosystem using otolith chemistry and expands upon the application of these natural tracers for population connectivity studies for this species.

To fill data gaps on movements, behaviors and habitat use, both near- and offshore, two programs were initiated to deploy satellite tags on basking sharks off the coast of California. Basking sharks are large filter-feeding sharks that are second in size only to whale sharks. Similar to many megafauna populations, available data suggest that populations are below historic levels. In the eastern North Pacific (ENP) Ocean, the limited information on basking sharks comes from nearshore habitats where they forage. From 2010 to 2011, four sharks were tagged with pop-off satellite archival tags with deployments ranging from 9 to 240 days. The tags provided both transmitted and archived data on habitat use and geographic movement patterns. Nearshore, sharks tended to move north in the summer and prefer shelf and slope habitat around San Diego, Point Conception and Monterey Bay. The two sharks with 180 and 240 days deployments left the coast in the summer and fall. Offshore their paths diverged and by January one shark had moved to near the tip of the Baja Peninsula, Mexico and the other to the waters near Hawaii, USA. Vertical habitat use was variable both within and among individuals and changed as sharks moved offshore. Nearshore, most time was spent in the mixed layer but sharks did spend hours in cold waters below the mixed layer. Offshore vertical movements depended on location. The shark that went to Hawaii had a distinct diel pattern, with days spent at ~450–470 m and nights at ~250–300 m and almost no time in surface waters, corresponding with the diel migration of a specific portion of the deep scattering layer. The shark that moved south along the Baja Peninsula spent progressively more time in deep water but came to the surface daily. Movement patterns and shifts in vertical habitat and use are likely linked to shifts in prey availability and oceanography. Data collected indicate the potential for large-scale movements and the need for international dialogue in any recovery efforts.

During their migrations, marine predators experience varying levels of protection and face many threats as they travel through multiple countries’ jurisdictions and across ocean basins. Some populations are declining rapidly. Contributing to such declines is a failure of some international agreements to ensure effective cooperation by the stakeholders responsible for managing species throughout their ranges, including in the high seas, a global commons. Here we use biologging data from marine predators to provide quantitative measures with great potential to inform local, national and international management efforts in the Pacific Ocean. We synthesized a large tracking data set to show how the movements and migratory phenology of 1,648 individuals representing 14 species—from leatherback turtles to white sharks—relate to the geopolitical boundaries of the Pacific Ocean throughout species’ annual cycles. Cumulatively, these species visited 86% of Pacific Ocean countries and some spent three-quarters of their annual cycles in the high seas. With our results, we offer answers to questions posed when designing international strategies for managing migratory species.

Horizontal behavior of highly migratory marine species is difficult to decipher because animals are wide-ranging, spend minimal time at the ocean surface, and utilize remote habitats. Satellite telemetry enables researchers to track individual movements, but population level inferences are rare due to data limitations that result from difficulty of capture and sporadic tag reporting. We introduce a Bayesian modeling framework to address population level questions with satellite telemetry data when data are sparse. We also outline an approach for identifying informative variables for use within the model. We tested our modeling approach using a large telemetry dataset for Shortfin Makos (Isurus oxyrinchus), which allowed us to assess the effects of various degrees of data paucity. First, a permuted Random Forest analysis is implemented to determine which variables are most informative. Next, a generalized additive mixed model is used to help define the relationship of each remaining variable with the response variable. Using jags and rjags for the analysis of Bayesian hierarchical models using Markov Chain Monte Carlo simulation, we then developed a movement model to generate parameter estimates for each of the variables of interest. By randomly reducing the tagging dataset by 25, 50, 75, and 90 percent and recalculating the parameter estimates, we demonstrate that the proposed Bayesian approach can be applied in data-limited situations. We also demonstrate how two commonly used linear mixed models with maximum likelihood estimation (MLE) can be similarly applied. Additionally, we simulate data from known parameter values to test each model's ability to recapture those values. Despite performing similarly, we advocate using the Bayesian over the MLE approach due to the ability for later studies to easily utilize results of past study to inform working models, and the ability to use prior knowledge via informed priors in systems where such information is available.

Most spatial marine management techniques (e.g., marine protected areas) draw stationary boundaries around often mobile marine features, animals, or resource users. While these approaches can work for relatively stationary marine resources, to be most effective marine management must be as fluid in space and time as the resources and users we aim to manage. Instead, a shift towards dynamic ocean management is suggested, defined as management that rapidly changes in space and time in response to changes in the ocean and its users through the integration of near real-time biological, oceanographic, social and/or economic data. Dynamic management can refine the temporal and spatial scale of managed areas, thereby better balancing ecological and economic objectives. Temperature dependent habitat of a hypothetical mobile marine species was simulated to show the efficiency of dynamic management, finding that 82.0 to 34.2 percent less area needed to be managed using a dynamic approach. Dynamic management further complements existing management by increasing the speed at which decisions are implemented using predefined protocols. With advances in data collection and sharing, particularly in remote sensing, animal tracking, and mobile technology, managers are poised to apply dynamic management across numerous marine sectors. Existing examples demonstrate that dynamic management can successfully allow managers to respond rapidly to changes on-the-water, however to implement dynamic ocean management widely, several gaps must be filled. These include enhancing legal instruments, incorporating ecological and socioeconomic considerations simultaneously, developing ‘out-of-the-box’ platforms to serve dynamic management data to users, and developing applications broadly across additional marine resource sectors.

In June 2013, a record-breaking female Isurus oxyrinchus (total length 373 cm, mass 600 kg) was captured by rod and reel off Huntington Beach, California, where it was subsequently donated to research and provided a rare opportunity to collect the first data for a female I. oxyrinchus of this size. Counts of vertebral band pairs estimate the shark to have been c. 22 years old, depending upon assumptions of band-pair deposition rates, and the distended uteri and spent ovaries indicated that this shark had recently given birth. The stomach contained a c. 4 year-old female California sea lion Zalophus californianus that confirmed the high trophic position of this large I. oxyrinchus, which was corroborated with the high levels of measured contaminants and tissue isotope analyses.

Chemical signatures in otoliths and muscle tissue of albacore (Thunnus alalunga) from two regions of the North Pacific were characterized to examine population structure. Regions included northern (offshore northwest United States and Canada, >40°N) and southern (offshore southwest United States and Mexico

The common thresher shark ( Alopias vulpinus ) is the focus of a popular southern California recreational fishery that targets individuals using multiple fishing gears and techniques. Despite increasing trends in the use of catch and release techniques in the recreational fishery for thresher sharks, a comprehensive estimate of post-release survival is not available for all modes of capture. This study focused on assessing post-release survival in two modes of capture routinely observed in the southern California recreational fishery: (1) sharks that are caught using caudal-based angling techniques and unintentionally released with trailing gear left embedded and (2) sharks that are caught and released using mouth-based angling techniques. Post-release survivorship was assessed using pop-up satellite archival tags programed for 10- and 90-day deployments, with the former used for mouth-caught sharks and the latter for individuals with trailing gear. Post-release survivorship estimates for the trailing gear studies were based on data from nine common thresher sharks (111-175 cm FL) while the mouth-based experiments utilized data from an additional seven sharks (125-187 cm fork length, FL). For the trailing gear studies, six sharks died within 5 days after release, one died after 81 days, and two sharks survived the deployment period for an overall survivorship rate of 22%. All seven mouth-hooked common thresher sharks survived the acute (∼10 days) effects of capture (100% survivorship). These results suggest that in the southern California recreational thresher shark fishery, caudal-based angling techniques, which often result in trailing gear left embedded in the shark, can negatively affect post-release survivorship. This work also reveals that mouth-based angling techniques can, when performed properly, result in high survivorship of released sharks.

Concerns about bycatch of protected species have become a dominant factor shaping fisheries management. However, efforts to mitigate bycatch are often hindered by a lack of data on the distributions of fishing effort and protected species. One approach to overcoming this problem has been to overlay the distribution of past fishing effort with known locations of protected species, often obtained through satellite telemetry and occurrence data, to identify potential bycatch hotspots. This approach, however, generates static bycatch risk maps, calling into question their ability to forecast into the future, particularly when dealing with spatiotemporally dynamic fisheries and highly migratory bycatch species. In this study, we use boosted regression trees to model the spatiotemporal distribution of fishing effort for two distinct fisheries in the North Pacific Ocean, the albacore (Thunnus alalunga) troll fishery and the California drift gillnet fishery that targets swordfish (Xiphias gladius). Our results suggest that it is possible to accurately predict fishing effort using < 10 readily available predictor variables (cross-validated correlations between model predictions and observed data -0.6). Although the two fisheries are quite different in their gears and fishing areas, their respective models had high predictive ability, even when input data sets were restricted to a fraction of the full time series. The implications for conservation and management are encouraging: Across a range of target species, fishing methods, and spatial scales, even a relatively short time series of fisheries data may suffice to accurately predict the location of fishing effort into the future. In combination with species distribution modeling of bycatch species, this approach holds promise as a mitigation tool when observer data are limited. Even in data-rich regions, modeling fishing effort and bycatch may provide more accurate estimates of bycatch risk than partial observer coverage for fisheries and bycatch species that are heavily influenced by dynamic oceanographic conditions.

As upper-level predators, sharks are important for maintaining marine food web structure, but populations are threatened by fishery exploitation. Sustainable management of shark populations requires improved understanding of migration patterns and population demographics, which has traditionally been sought through physical and/or electronic tagging studies. The application of natural tags such as elemental variations in mineralized band pairs of elasmobranch vertebrae cartilage could also reveal endogenous and exogenous processes experienced by sharks throughout their life histories. Here, elemental profiles were characterized in vertebrae encompassing complete life histories (birth-to-death) of shortfin mako ( Isurus oxyrinchus ), common thresher ( Alopias vulpinus ) and blue shark ( Prionace glauca ) of known tag and recapture locations in the eastern North Pacific Ocean. All sharks were injected with oxytetracycline at initial capture, released and subsequently recaptured, with individual liberty times ranging from 215 days to 6 years. Vertebral band pairs forming over the liberty intervals were verified by counting the number of band pairs deposited since the oxytetracycline band. Regular oscillations in vertebrae manganese (Mn) content corresponded well with the number of validated band pairs, suggesting that Mn variation could be used to age sharks. Increases in vertebrae barium concentration were correlated with times when individuals occupied areas with high coastal upwelling indices, the timing and spatial intensity of which varied from year to year. Interspecific relationships were probably influenced by behavioural differences in horizontal and vertical habitat use, feeding habits and thermoregulatory physiology. These results indicate that vertebral sclerochronology has the potential to advance our knowledge of elasmobranch life history including age and growth estimation and environmental reconstruction.

a b s t r a c t Accurate estimates of age and growth parameters are important for fisheries management because these values affect stock assessment models. Age and growth of North Pacific albacore (Thunnus alalunga) was assessed by examining annual growth increments in sagittal otoliths from 486 fish collected in different regions of the North Pacific Ocean. A wide size range of albacore (52-128 cm fork length, FL) was collected in an attempt to incorporate size-at-age information over juvenile, sub-adult, and adult life history stages. Overall, ages ranged from 1 to 15 years, with the majority of fish between 2 and 4 years of age. Growth models fit otolith-based size-at-age well, and Akaike's Information Criterion corrected for small sample size indicated that the specialized von Bertalanffy (VB) model provided the best fit. The estimated bio- logical parameters of the specialized VB model were L∞ = 124.1 cm FL, K = 0.164 year−1, and t0 = −2.239. Daily ages were also determined and verified correct age-1 assignments for fish 55-61 cm FL, with daily ages ranging from 378 to 505 days. In addition, dorsal fin spines and length frequency (LF) analysis were used to obtain estimates of size-at-age and corroborated results from otolith-based techniques. Model- ing exercises resulted in nearly an order of magnitude difference in spawning stock biomass (SSB) when comparing growth parameters obtained from this study relative to previous stock assessment models of North Pacific albacore. Results suggest North Pacific albacore is a relatively long lived tuna species and provide updated biological parameters useful for future stock assessment models.

Bycatch of sharks in longline fisheries has contributed to declines in shark populations and prompted the need for exploring novel technologies to reduce the incidental capture of sharks. One potential strategy is to exploit the unique electrosensory system of sharks, used to detect weak electric fields. Metals from the lanthanide series, made up of neodymium (Nd) and praseodymium (Pr), produce strong electric fields in water. In this study, we tested the effects of an Nd/Pr alloy on shark catch rates. Using longline fishing gear, we compared the catch rates of baited hooks affixed with either a block of the metal alloy (experimental) or a lead weight (control). Four experiments were conducted in different regions of the Pacific Ocean. Two bottom longline experiments were conducted inside and offshore of Kaneohe Bay, Hawaii. One of these experiments targeted young of the year scalloped hammerhead sharks (Sphyrna lewini), while the other targeted sandbar (Carcharhinus plumbeus) and tiger sharks (Galeocerdo cuvier). In the Southern California Bight (SCB), pelagic longlines were deployed to target mako (Isurus oxyrinchus) and blue sharks (Prionace glauca) and longlines targeting pelagic sharks were set in the Eastern Tropical Pacific (ETP) off Ecuador. There was a significant reduction in juvenile hammerhead sharks caught on hooks with the lanthanide metal compared to the controls. In contrast, there was no difference in the catch rates for experiments targeting sandbar sharks in Hawaii or those conducted in the SCB and Ecuador. These results suggest that there are inter-specific differences regarding the effects of lanthanide metals on catch rates. This may reflect the diverse feeding strategies and sensory modalities used by shark species for detecting and attacking prey.

This study describes the feeding ecology of three pelagic shark species in the California Current: shortfin mako (Isurus oxyrinchus); blue (Prionace glauca); and thresher (Alopias vulpinus) sharks. Stom- ach contents of sharks collected from 2002 to 2008 were identified to the lowest taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks sampled (53 to 248 cm fork length (FL)), 238 stomachs contained 42 prey taxa, with jumbo squid (Dosidicus gigas) and Pacific saury (Cololabis saira) representing the most important prey based on the geometric index of importance (GII). In addition, 158 blue sharks were sampled (76 to 248 cm FL) and 114 stomachs contained 38 prey taxa, with jumbo and Gonatus spp. squids representing the most important prey. Lastly, 225 thresher sharks were sam- pled (108 to 228 cm FL) and 157 stomachs contained 18 prey taxa with northern anchovy (Engraulis mor- dax) and Pacific sardine (Sardinops sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet based upon Simpson's diversity index (1/D) (8.43±1.16), feeding on many species of teleosts and cephalopods, followed by blue sharks (6.20±2.11) which consumed a wide range of prey (primarily cephalopods), while thresher sharks were most specialized (2.62±0.34), feeding primarily on coastal pelagic teleosts. Dietary overlap was lowest between blue and thresher sharks (Sorensen similarity index00.321 and Simplified Morisita Horn index0 0.006), and seasonal variability in diet was greatest for blue sharks (Simplified Morisita Horn index0 0.260, Analysis of Similarity (ANOSIM) p

Archival tags were used to study the seasonal movements, migration patterns and vertical distribution of juvenile North Pacific albacore (Thunnus alalunga). Between 2001 and 2006, archival tags were deployed in North Pacific albacore in two regions of the Northeast Pacific: (i) off Northern Baja California, Mexico and Southern California, and (ii) off Washington and Oregon. Twenty archival tagged fish were recovered with times at liberty ranging from 63 to 697 days. Tagged albacore exhibited five distinct, seasonal migratory patterns. Depth and temperature data also showed a broad range of vertical behaviors. In certain regions such as off Baja California, Mexico, juvenile albacore make frequent dives to depths exceeding 200 m during the day and remain in the surface mixed layer at night, whereas off Oregon and Washington they remain near the surface both day and night. Water temperatures encountered ranged from 3.3 to 22.7� C. Peritoneal temperatures were significantly higher by an average of approximately 4� C, as expected in these warm-bodied fish. This study provides a comprehensive examination of horizontal and vertical movements of juvenile albacore in the Northeast Pacific. The results reveal diverse behavior that varies regionally and seasonally as albacore move among different habitats throughout the entire North Pacific.

The common thresher shark ( Alopias vulpinus ) is the focus of a popular southern California recreational fishery that typically captures individuals by hooking them in the caudal fin. This technique reduces the ability for forward locomotion and the capacity for ram ventilation. This study assessed the post-capture survivorship of tail-hooked adult and sub-adult common thresher sharks using pop-up satellite archival tags (PSATs) and quantified physiological indicators of capture stress in the blood. Survival of the acute effects of capture was determined from the depth and temperature records of 10-day PSAT deployments. Survivorship estimates were based on 19 common thresher sharks [160–221 cm fork length (FL); ∼67–151 kg] captured in southern California from 2007 to 2009 using recreational stand-up tackle (36 kg). Five mortalities were observed over the course of the study resulting in an overall post-release mortality estimate of 26%. All mortalities occurred in large individuals (≥180 cm FL) with fight times ≥85 min. The archived depth and temperature data from surviving sharks resembled those of previous common thresher movement studies with a diel depth distribution predominantly within the uniformed temperature surface layer. Capture induced stress parameters measured from the blood of eight additional common thresher sharks that were not tagged revealed plasma lactate and hematocrit levels that were significantly elevated with increased fight time. Similarly, all thresher sharks showed heightened heat shock protein 70 ( hsp 70 ) values relative to those obtained from blood that was allowed to recover in vitro for 24 h. Collectively, our findings indicate that large tail-hooked common thresher sharks with prolonged fight times (≥85 min) exhibit a heightened stress response which may contribute to an increased mortality rate. These results suggest that for larger individuals the current caudal-based capture methods used in the California recreational fishery may not be suitable for an effective catch-and-release based conservation strategy.

We investigated the potential use of open coastal habitat over the continental shelf as a nursery area for the common thresher shark Alopias vulpinus. Seven juvenile threshers were tracked using acoustic telemetry to determine their movement patterns and nursery habitat in the Southern California Bight (SCB). Tracked sharks occupied waters over the continental shelf 87% of the time. These waters had an average (± SD) sea surface temperature of 18.8 ± 1.6°C and chlorophyll concen- trations that were an order of magnitude higher than in adjacent waters offshore of the continental shelf. Tracked sharks had a mean rate of movement of 1.63 ± 0.56 km h -1 , and some sharks exhibited high site fidelity. The vertical distribution of juvenile threshers was generally limited to the upper 20 m of the water, and most sharks showed diel depth distribution patterns, with daytime depths significantly greater than nighttime depths. An analysis of SCB commercial fishery observer data confirms that juvenile common threshers are most frequently captured over the continental shelf. This region appears to provide juvenile threshers with ample food resources and reduced predation risk relative to adult habitat, and partially satisfies more quantitative nursery area criteria recently established in the literature.

The lumped parameter describing skeletal muscle diffusional conductance for O(2), DM(O(2)), reflects all of the resistances for O(2) in moving from red cell to muscle fiber mitochondria. The purpose of our study was to determine if the carotenoid compound, trans sodium crocetinate (TSC), which has been reported to increase the diffusivity of O(2) in plasma, improves DM(O(2)) and thus, V(O(2),max) in maximally contracting in situ skeletal muscle. V(O(2),max) was measured in the isolated perfused canine gastrocnemius (n=5) during 3 min of isometric tetanic contractions at 1 Hz, while the animal was breathing 12% O(2) (PA(O(2))=32+/-2 Torr, mean+/-S.E.) under two experimental conditions. The first was a control contraction period and the second (following 60 min recovery) was performed within 5 min after infusion of a 0.1 mg x ml(-1) solution of TSC (total dose 100 microg kg(-1)). There were no significant differences in convective O(2) delivery (11.9+/-2.3 vs. 12.1+/-2.2 ml x min(-1) x 100 g(-1)), V(O(2),max) (9.5+/-1.5 vs. 9.6+/-1.5 ml x min(-1) x 100 g(-1)) or calculated DM(O(2)) (0.37+/-0.03 vs. 0.37+/-0.04 ml x min(-1) x 100 g(-1) x Torr(-1)) between contraction periods. As such, our results show that TSC does not improve performance in maximally contracting canine gastrocnemius muscle in situ under moderately hypoxic conditions, suggesting either that TSC in this situation does not increase plasma O(2) diffusivity or that this step in O(2) diffusion from red cell to myocyte does not constrain DM(O(2)).

The blue shark (Prionace glauca) is subjected to high levels of fishery catch and by-catch worldwide; thus, knowledge of their productivity and population status is vital, yet basic assumptions of band-pair deposition rates in vertebrae used for age and growth models are being made without direct validation studies in the Pacific Ocean. As such, the purpose of the present study was to validate vertebral band-deposition rates of blue sharks tagged and recaptured in the eastern Pacific Ocean. Vertebrae of 26 blue sharks marked with oxytetracycline (OTC) were obtained from tag–recapture activities to determine timing of centrum growth-band deposition. Results from band counts distal to the OTC mark on each vertebra indicated that a single band pair (1 translucent and 1 opaque) is formed per year for blue sharks ranging from 1 to 8 years of age. Length–frequency modal analysis was also used to obtain growth estimates from a dataset spanning 26 years of research and commercial catch data. Results provide support for annual band-pair deposition in blue shark vertebrae and will aid in future blue shark age and growth studies in the Pacific Ocean.

We tested the hypothesis that contracting skeletal muscle can rapidly restore force development during reperfusion after brief total ischemia and that this rapid recovery depends on O2 availability and not an alternate factor related to blood flow. Isolated canine gastrocnemius muscle ( n = 5) was stimulated to contract tetanically (isometric contraction elicited by 8 V, 0.2-ms duration, 200-ms trains, at 50-Hz stimulation) every 2 s until steady-state conditions of muscle blood flow (controlled by pump perfusion) and developed force were attained (3 min). While maintaining the same stimulation pattern, muscle blood flow was then reduced to zero (complete ischemia) for 2 min. Normal blood flow was then restored to the contracting muscle; however, two distinct conditions of oxygenation (at the same blood flow) were sequentially imposed: deoxygenated blood (30 s), blood with normal arterial O2content (30 s), a return to deoxygenated blood (30 s), and finally a return to normal arterial O2 content (90 s). During the ischemic period, force development fell to 39 ± 6 (SE)% of normal (from 460 ± 40 to 170 ± 20 N/100 g). When muscle blood flow was restored to normal by perfusion with deoxygenated blood, developed force continued to decline to 140 ± 20 N/100 g. Muscle force rapidly recovered to 310 ± 30 N/100 g ( P < 0.05) during the 30 s in which the contracting muscle was perfused with oxygenated blood and then fell again to 180 ± 30 N/100 g when perfused with blood with low[Formula: see text]. These findings demonstrate that contracting skeletal muscle has the capacity for rapid recovery of force development during reperfusion after a short period of complete ischemia and that this recovery depends on O2availability and not an alternate factor related to blood flow restoration.

An hypoxia-induced metabolic down-regulation has been implicated as an important protective mechanism against tissue deoxygenation in mammals. Whether the same response to hypoxia occurs in northern elephant seals was studied. The effects of hypercapnia were also examined to determine whether the reduced ventilatory response of seals to CO 2 is associated with an analogous protective metabolic down-regulation. Thirty three seals (7–300-days-old) were studied using open-flow respirometry with simultaneous monitoring of apnea frequencies and heart rates. Hypoxia (11% O 2 ) and hypercapnia (7% CO 2 ) caused increases in metabolism of up to 38% with corresponding decreases in the percent time spent apneic (%AP) and increases in heart rate. The metabolic, breathing and heart rate responses to altered inspired gases were independent of age. Metabolism was strongly negatively correlated with %AP suggesting that elevated metabolism during hypoxia and hypercapnia exposure is attributable to decreases in %AP. In young elephant seals metabolic down-regulation is not an automatic protective response to experimentally-imposed hypoxia or hypercapnia.

The purpose of this study was to validate aging results of juvenile Shortfin Mako (Isurus oxyrinchus) by vertebral band counts. Vertebrae of 29 juvenile Shortfin Mako marked with oxytetracycline (OTC) were obtained from tag-recapture activities to determine centrum growth-band deposition. Tagging occurred off southern California from 1996 to 2010, and time at liberty of the 29 sharks ranged from 4 months to 4.4 years (mean=1.3 years). Growth information also was obtained from length-frequency modal analyses (MULTIFAN and MIXDIST) by using a 29-year data set of commercial and research catch data, in addition to a tag-recapture growth model (e.g, the GROTAG model). For vertebrae samples used for age validation, shark size at time of release ranged from 79 to 142 cm fork length (FL) and from 98 to 200 cm FL at recapture. Results from band counts of vertebrae distal to OTC marks indicate 2 band pairs (2 translucent and 2 opaque) are formed each year for Shortfin Mako of the size range examined. Length-frequency analyses identified 3 age class modes. Growth rate estimates from 26.5 to 35.5 cm/year were calculated for the first age-class mode (85 cm FL) and from 22.4 to 28.6 cm/year for the second age-class mode (130 cm FL). Results from the tag-recapture growth model revealed fast growth during time at liberty for tagged fish of the 2 youngest age classes. Collectively, these methods suggest rapid growth of juvenile Shortfin Mako in the southern California study area and indicate biannual deposition of growth bands in vertebrae for the first 5 years.

Acoustic telemetry was used to track vertical and horizontal movement patterns and to monitor the stomach temperatures of seven juvenile shortfin mako sharks (Isurus oxyrinchus Rafinesque) in the Southern California Bight from July to November 2002. Makos (80–145 cm fork length, FL) were attracted to the tracking vessel, where they were fed a mackerel containing an acoustic transmitter that reported temperature and pressure. Tracks ranged from 6.8–45.4 h. Collectively, the mako sharks spent 80% of the track record at 0–12 m, 15% at 12–24 m, and 5% at depths >24 m. The average horizontal swimming speed was 2.3 km h−1 or 0.55 FLs s−1, and the greatest distance traveled was 145 km in 45.4 h. For the six tracks >21 h, there was a positive correlation between body size and maximum depth. Makos used more of the water column during daylight hours. Mean stomach temperature was 3.8±1.5°C above ambient, and body size was positively correlated with both maximum and average stomach temperature. Stomach content analyses of four makos captured at the end of tracking verified the occurrence of feeding events as indicated by changes in stomach temperature.

We tested the hypotheses that: (1) Ca 2 + handling and force production would be irreversibly altered in skeletal muscle during steady-state contractions when subjected to severe, prolonged hypoxia and subsequent reoxygenation; and (2) application of the cardio-protective drug trimetazidine would attenuate these alterations. Single, living skeletal muscle fibres from Xenopus laevis were injected with the Ca 2 + indicator fura 2, and incubated for 1 h prior to stimulation in 100 μM TMZ-Ringer solution (TMZ; n = 6) or standard Ringer solution (CON; n = 6). Force and relative free cytosolic Ca 2 + concentration ([Ca 2 + ] c ) were measured during continuous tetanic contractions produced every 5 s as fibres were sequentially perfused in the following manner: 3 min high extracellular P o 2 (159 mmHg), 15 min hypoxic perfusion (3-5 mmHg) then 3 min high P o 2 . Hypoxia caused a decrease in force and peak [Ca 2 + ] c in both the TMZ and CON fibres, with no significant (P < 0.05) difference between groups. However, basal [Ca 2 + ] c was significantly lower during hypoxia in the TMZ group vs. the CON group. While reoxygenation generated only modest recovery of relative force and peak [Ca 2 + ] c in both groups, basal [Ca 2 + ] c remained significantly less in the TMZ group. These results demonstrated that in contracting, single skeletal muscle fibres, TMZ prevented increases in basal [Ca 2 + ] c generated during a severe hypoxic insult and subsequent reoxygenation, yet failed to protect the cell from the deleterious effects of prolonged hypoxia followed by reoxygenation.

The lumped parameter describing skeletal muscle diffusional conductance for O(2), DM(O(2)), reflects all of the resistances for O(2) in moving from red cell to muscle fiber mitochondria. The purpose of our study was to determine if the carotenoid compound, trans sodium crocetinate (TSC), which has been reported to increase the diffusivity of O(2) in plasma, improves DM(O(2)) and thus, V(O(2),max) in maximally contracting in situ skeletal muscle. V(O(2),max) was measured in the isolated perfused canine gastrocnemius (n=5) during 3 min of isometric tetanic contractions at 1 Hz, while the animal was breathing 12% O(2) (PA(O(2))=32+/-2 Torr, mean+/-S.E.) under two experimental conditions. The first was a control contraction period and the second (following 60 min recovery) was performed within 5 min after infusion of a 0.1 mg x ml(-1) solution of TSC (total dose 100 microg kg(-1)). There were no significant differences in convective O(2) delivery (11.9+/-2.3 vs. 12.1+/-2.2 ml x min(-1) x 100 g(-1)), V(O(2),max) (9.5+/-1.5 vs. 9.6+/-1.5 ml x min(-1) x 100 g(-1)) or calculated DM(O(2)) (0.37+/-0.03 vs. 0.37+/-0.04 ml x min(-1) x 100 g(-1) x Torr(-1)) between contraction periods. As such, our results show that TSC does not improve performance in maximally contracting canine gastrocnemius muscle in situ under moderately hypoxic conditions, suggesting either that TSC in this situation does not increase plasma O(2) diffusivity or that this step in O(2) diffusion from red cell to myocyte does not constrain DM(O(2)).

Among terrestrial mammals, the morphology of the gastrointestinal tract reflects the metabolic demands of the animal and individual requirements for processing, distributing, and absorbing nutrients. To determine if gastrointestinal tract morphology is similarly correlated with metabolic requirements in marine mammals, we examined the relationship between basal metabolic rate (BMR) and small intestinal length in pinnipeds and cetaceans. Oxygen consumption was measured for resting bottlenose dolphins and Weddell seals, and the results combined with data for four additional species of carnivorous marine mammal. Data for small intestinal length were obtained from previously published reports. Similar analyses were conducted for five species of carnivorous terrestrial mammal, for which BMR and intestinal length were known. The results indicate that the BMRs of Weddell seals and dolphins resting on the water surface are 1.6 and 2.3 times the predicted levels for similarly sized domestic terrestrial mammals, respectively. Small intestinal lengths for carnivorous marine mammals depend on body size and are comparatively longer than those of terrestrial carnivores. The relationship between basal metabolic rate (kcal day(-1)) and small intestinal length (m) for both marine and terrestrial carnivores was, BMR=142.5 intestinal length(1.20) (r(2)=0.83). We suggest that elevated metabolic rates among marine mammal carnivores are associated with comparatively large alimentary tracts that are presumably required for supporting the energetic demands of an aquatic lifestyle and for feeding on vertebrate and invertebrate prey.

Reperfusion following prolonged ischemia induces cellular damage in whole skeletal muscle models. Ischemic preconditioning attenuates the deleterious effects. We tested whether individual skeletal muscle fibers would be similarly affected by severe hypoxia and reoxygenation (H/R) in the absence of extracellular factors and whether cellular damage could be alleviated by hypoxic preconditioning. Force and free cytosolic Ca2+([Ca2+]c) were monitored in Xenopus single muscle fibers ( n = 24) contracting tetanically at 0.2 Hz during 5 min of severe hypoxia and 5 min of reoxygenation. Twelve cells were preconditioned by a shorter bout of H/R 1 h before the experimental trial. In preconditioned cells, force relative to initial maximal values (P/Po) and relative peak [Ca2+]cfell ( P< 0.05) during 5 min of hypoxia and recovered during reoxygenation. In contrast, P/Poand relative peak [Ca2+]cfell more during hypoxia ( P < 0.05) and recovered less during reoxygenation ( P < 0.05) in control cells. The ratio of force to [Ca2+]cwas significantly higher in the preconditioned cells during severe hypoxia, suggesting that changes in [Ca2+]cwere not solely responsible for the loss in force. We conclude that 1) isolated skeletal muscle fibers contracting in the absence of extracellular factors are susceptible to H/R injury associated with changes in Ca2+handling; and 2) hypoxic preconditioning improves contractility, Ca2+handling, and cell recovery during subsequent hypoxic insult.

The hunting behavior of a marine mammal was studied beneath the Antarctic fast ice with an animal-borne video system and data recorder. Weddell seals stalked large Antarctic cod and the smaller subice fish Pagothenia borchgrevinki , often with the under-ice surface for backlighting, which implies that vision is important for hunting. They approached to within centimeters of cod without startling the fish. Seals flushed P. borchgrevinki by blowing air into subice crevices or pursued them into the platelet ice. These observations highlight the broad range of insights that are possible with simultaneous recordings of video, audio, three-dimensional dive paths, and locomotor effort.

Alterations in left atrial (LA) and left ventricular (LV) compliance and arterial and coronary sinus atrial natriuretic factor (ANF) concentrations at baseline and in response to both volume depletion and expansion were investigated in 15 conscious dogs with aortic banding-induced LV hypertrophy (LVH) (LV/body wt increased by 64%), which also induced LAH (LA/body wt increased by 61%). With volume expansion coronary sinus ANF increased more (P < 0.05) in dogs with LVH (+427 +/- 88 pg/ml) compared with control dogs (+146 +/- 45 pg/ml). Arterial ANF levels also rose more with volume expansion in LVH. In dogs with LVH, the LV end-diastolic pressure-diameter relationship was shifted to the left with a steeper slope with volume expansion, such that at any given diastolic dimension, diastolic pressure was higher. In contrast, the pressure-dimension relationship for the LA appendage was shifted in the opposite direction during both atrial systolic and diastolic phases, with a more shallow slope in hypertrophy compared with control dogs, resulting in an augmented pressure-dimension product during volume loading in LAH. In conclusion, in dogs with LVH and LAH, enhanced ANF was revealed in the coronary sinus and systemic circulation during volume expansion, which could be due, in part, to a more compliant, but hypertrophied, LA, which responded to equivalent volume loading with an augmented pressure-dimension product.

The effects of treadmill exercise on regional myocardial blood flow and function were examined in 10 adult, conscious dogs with left ventricular hypertrophy (LVH) induced by aortic banding in puppies, which resulted in a left ventricular (LV) weight/body weight ratio of 8.5 +/- 0.3. Data were compared with results from eight control dogs with an LV weight/body weight ratio of 4.9 +/- 0.2. At rest, LV systolic and end-diastolic pressures were significantly greater (p less than 0.01), and mean arterial pressure was significantly less (p less than 0.05) in LVH dogs. Mean myocardial blood flow (control dogs, 0.98 +/- 0.11 ml/min/g; LVH dogs, 1.16 +/- 0.06 ml/min/g) and the transmural blood flow distribution at baseline, as assessed by endocardial/epicardial blood flow ratio (control, 1.35 +/- 0.12; LVH, 1.21 +/- 0.09), were similar in the two groups. During exercise to a target heart rate (240 beats/min), LVH dogs demonstrated greater (p less than 0.01) increases in LV systolic and end-diastolic pressures. In control dogs, as expected, exercise augmented velocity of circumferential fiber shortening (16 +/- 9%) and shortening fraction (15 +/- 5%), but in LVH dogs, exercise reduced the velocity of circumferential fiber shortening (-14 +/- 6%) and shortening fraction (-17 +/- 5%). Exercise also increased full wall thickening (35 +/- 5%), subendocardial wall thickening (66 +/- 10%), and subepicardial wall thickening (44 +/- 9%) in control dogs. In LVH dogs, exercise increased subepicardial wall thickening (31 +/- 9%) and reduced subendocardial wall thickening (-40 +/- 7%); full wall thickening did not change (-11 +/- 9%). This was associated with a fall in endocardial/epicardial flow ratio to 0.72 +/- 0.05 (p less than 0.01) in LVH dogs. The subendocardial dysfunction persisted late into recovery, at a time when the transmural blood flow distribution had returned to baseline; this occurrence suggested myocardial stunning. Thus, in dogs with LVH, selective subendocardial hypoperfusion and profound selective depression in subendocardial wall thickening are observed during exercise. The subendocardial dysfunction persisted into recovery despite resolution of the perfusion abnormality.

The effects of isoproterenol were examined in 10 conscious, chronically instrumented adult dogs with left ventricular (LV) failure after pressure overload hypertrophy induced by aortic banding at 8-10 weeks of age (LV free wall plus septum-to-body weight ratio, 8.6 +/- 0.5 g/kg) and also in eight control dogs (LV free wall plus septum-to-body weight ratio, 5.1 +/- 0.3 g/kg). Baseline values of heart rate, LV end-diastolic pressure, LV end-diastolic stress, and LV systolic wall stress were greater in the LV failure dogs (p less than 0.01), whereas the ejection phase index, rate of change of LV short-axis diameter, LV dD/dt, was depressed compared with control animals. In the control animals, isoproterenol infusion increased Vcf and LV dD/dt significantly (p less than 0.05), whereas LV systolic wall stress did not change. In the LV failure dogs, the increases in Vcf and LV dD/dt were less (p less than 0.01), and LV systolic wall stress increased (p less than 0.01). In the control animals, LV end-diastolic pressure, LV end-diastolic stress, LV end-diastolic stress-dimension ratio, diastolic radial myocardial stiffness, and the time constant of isovolumic relaxation decreased (p less than 0.05), whereas in the LV failure dogs, LV end-diastolic pressure, LV end-diastolic stress, diastolic radial myocardial stiffness, and the LV end-diastolic stress-dimension ratio increased. In the LV failure group, the endocardial to epicardial blood flow ratio fell to 0.59 +/- 0.06 during isoproterenol infusion, that is, significantly lower than in control dogs (0.93 +/- 0.06). These data support the concept that potent sympathomimetic amines exert deleterious effects on systolic and diastolic function in the failing heart, potentially related to subendocardial hypoperfusion.

Determining light-based geolocations of electronically tagged marine animals by using irradiance measurements in an integrated random walk movement model is presented for improving the precision of the reconstructed geographical tracks. The model avoids making any irradiance threshold assumptions, or constraining the movement of the tag between dawn and dusk, which has limited the efficacy of previous models. Unlike previous models which relied on using previously calculated raw geolocations from outside sources, the new model uses irradiance data to produce the most probable track. The model generates two estimates of geographic positions per day (at dawn and dusk). Prior to this study, the model has been successfully evaluated for tags mounted on moorings, drifters, and in simulated cases. This paper documents the application of the model to wild caught swimming and diving mako sharks and blue marlin. The reconstructed tracks via the new model are compared to tracks adjusted using sea-surface temperature and to very accurate satellite-based tracks. The model performs well for the tested tags, which is surprising as these are pop-off satellite archival tags (PSATs), from which only a small fraction of the light record around approximately dusk and dawn is stored. The integrated model was vastly superior to classical purely light-based methods in all cases.