Common Thresher Shark Alopias Vulpinus Research Articles

Note on a Juvenile Common Thresher Shark Alopias vulpinus (Bonnaterre 1788) in the waters of Slovenia (Northern Adriatic Sea)

Abstract A specimen of common thresher shark Alopias vulpinus (Bonnaterre 1788) was caught in a fishing net in the waters off Piran (Gulf of Trieste, northern Adriatic Sea). It was a juvenile male with a total length of 2841 mm. In recent decades, other cases of juvenile specimens of common thresher shark have been recorded in Slovenian coastal waters. Despite the drastic decline in the population of this species, thresher shark continues to be caught in local Adriatic fisheries.

Insights into vertebral band pair deposition rate in the juvenile common thresher shark (Alopias vulpinus) in the northeastern Pacific Ocean.

Validation of band pair deposition rates in elasmobranch vertebrae is essential for accurate age estimation using band pair counting techniques. We present a validation study of the vertebral band pair deposition rate for juvenile common thresher sharks Alopias vulpinus in the northeastern Pacific Ocean (NEPO) using tag and recapture with oxytetracycline (OTC) injection. A total of 14 juvenile A. vulpinus marked with OTC from 1998 through 2013 were recaptured with times at liberty ranging from 1.08 to 3.81 years with an average of 2.14 years (±0.97 years standard deviation, SD). Shark size ranged from 80 to 128 cm fork length (LF) at the time of OTC injection and from 112 to 168 cm LF for those measured at recapture. The slopes of the relationships between band pairs post OTC and years at liberty for each reader ranged from 0.84 to 0.95, slightly lower than the 1.0 slope expected from annual band pair formation. These findings preliminarily support previous age and growth assumptions based on a one band pair per year deposition rate. However, high variation in band pair deposition rates between samples, coupled with regression slopes falling just under one band pair per year, indicates that further investigation is needed to refine band pair deposition rate estimates.

Spiral valve parasites of blue and common thresher sharks as indicators of shark feeding behaviour and ecology.

This study documented the parasite faunas of the spiral valves of blue sharks Prionace glauca (L. 1758) and common thresher sharks Alopias vulpinus (Bonnaterre, 1788) caught in the California Current Large Marine Ecosystem (CCLME) north of the Mexican border. The spiral valves of 18 blue and 19 thresher sharks caught in the CCLME from 2009 to 2013 were examined for parasites. Seven parasite taxa were found in blue sharks and nine in threshers. The tetraphyllidean cestode Anthobothrium sp. (78% prevalence) was the most common parasite in blue sharks, and the phyllobothriid cestode Paraorygmatobothrium sp. (90% prevalence) was the most common in threshers. An adult nematode of the genus Piscicapillaria was found in threshers for the first time and may be a new species. Adult individuals of Hysterothylacium sp. were found in both shark species. The adult acanthocephalan Rhadinorhynchus cololabis and remains of the parasitic copepod Pennella sp. - both parasites of Pacific saury, Cololabis saira - were found in the intestines of threshers, indicating recent feeding on saury. This study paves the way for a more comprehensive examination, including more samples and a wider variety of shark species, to provide a greater understanding of shark feeding behaviour and possibly provide information on shark population biology.

Common thresher shark Alopias vulpinus movement: Bayesian inference on a data-limited species

Within the fields of biology and ecology, animal movement is arguably one of the most basic, and yet, often one of the most difficult areas of study. Where and why animals migrate, and what patterns can be derived from individual movements in order to make population-level inferences are key areas when attempting to define basic population dynamics. These questions are of equal interest to biologists and managers, with many species assessments identifying improvements in the understanding of population-level movement as a key research need. We aimed to improve our understanding of population level movement for common thresher sharks Alopias vulpinus by leveraging the largest satellite tagging dataset available for this species. Using a Bayesian approach specifically designed to address population-level questions with sparse telemetry data, we identified that A. vulpinus off the west coast of North America are partial migrators which conditionally migrate, based on a combination of fixed intrinsic states (size, sex) and variable extrinsic states (e.g. season, environment). Waters of the Southern California Bight were identified as an area where, seasonally, a large variety of sizes of A. vulpinus can be found. While smaller juveniles can be found throughout the year, larger sub-adults and adults often move out of the Bight during certain seasons (spring and winter). Knowledge of how A. vulpinus distribute along the coast, and that season, size, and to some extent sex, play important roles in where and what type of animals are likely to be found, are key pieces of information when attempting to accurately characterize basic biological parameters like age, growth, and reproduction, as well as understanding the effects of variable fishing pressures across the species’ range.

Integrating Dynamic Subsurface Habitat Metrics Into Species Distribution Models

Species distribution models (SDMs) have become key tools for describing and predicting species habitats. In the marine domain, environmental data used in modelling species distributions are often remotely sensed, and as such have limited capacity for interpreting the vertical structure of the water column, or are sampled in situ, offering minimal spatial and temporal coverage. Advances in ocean models have improved our capacity to explore subsurface ocean features, yet there has been limited integration of such features in SDMs. Using output from a data-assimilative configuration of the Regional Ocean Modeling System, we examine the effect of including dynamic subsurface variables in SDMs to describe the habitats of four pelagic predators in the California Current System (swordfish Xiphias gladius, blue sharks Prionace glauca, common thresher sharks Alopias vulpinus, and shortfin mako sharks Isurus oxyrinchus). Species data were obtained from the California Drift Gillnet observer program (1997-2017). We used boosted regression trees to explore the incremental improvement enabled by dynamic subsurface variables that quantify the structure and stability of the water column: isothermal layer depth and bulk buoyancy frequency. The inclusion of these dynamic subsurface variables significantly improved model explanatory power for most species. Model predictive performance also significantly improved, but only for species that had strong affiliations with dynamic variables (swordfish and shortfin mako sharks) rather than static variables (blue sharks and common thresher sharks). Geospatial predictions for all species showed the integration of isothermal layer depth and bulk buoyancy frequency contributed value at the mesoscale level (<100 km) and varied spatially throughout the study domain. These results highlight the utility of including dynamic subsurface variables in SDM development and support the continuing ecological use of biophysical output from ocean circulation models.

Movements and distribution of juvenile common thresher sharks Alopias vulpinus in Pacific coast waters of the USA and Mexico

Movements and distribution of juvenile common thresher sharks Alopias vulpinus in Pacific coast waters of the USA and Mexico

Age and Growth of the Common Thresher Shark in the Western North Atlantic Ocean

AbstractAge and growth estimates were generated for the Common Thresher Shark Alopias vulpinus in the western North Atlantic (WNA) using vertebral centra from 173 females and 135 males ranging in size from 56 to 264 cm FL. Assuming that vertebral band pairs were deposited annually, we estimated ages up to 22 years (228 cm FL) for males and 24 years (244 cm FL) for females. The growth of both sexes was similar until approximately age 8 (185 cm FL), after which male growth slowed. The growth of females slowed at a later age (∼age 12) than that of males. Relative goodness of fit for all candidate models supported the separate modeling of sexes. For males, von Bertalanffy growth parameters generated from the vertebral data using a set size at birth (81 cm FL) provided the best fit for the band counts (asymptotic length [L∞] = 225.4 cm FL; growth coefficient [k] = 0.17). For females, the standard three‐parameter von Bertalanffy growth model provided the best fit to the band counts (L∞ = 274.5 cm FL; k = 0.09; theoretical age at a length of zero [t0] = −4.82). These are the first growth parameters generated for Common Thresher Sharks in the WNA and can be used to make informed decisions for the management of this species.

The Reproductive Biology of the Common Thresher Shark in the Western North Atlantic Ocean

AbstractReproductive organs from 130 male and 256 female Common Thresher Sharks Alopias vulpinus were examined to describe the reproductive characteristics and determine size at maturity and reproductive seasonality for the species in the western North Atlantic Ocean. Males ranged in size from 78 to 237 cm FL and females ranged from 62 to 263 cm FL. The onset of maturity in males was best described by an inflection in the relationship of clasper length to FL in combination with the degree of clasper calcification. Males matured between 181 and 198 cm FL, and estimated median size at maturity was 188 cm FL. In females, changes in the relationship between ovary and uterus length and width with FL were used to estimate the size at maturity. Females matured between 208 and 224 cm FL; the estimated median size at maturity was 216 cm FL. Litter sizes averaged 3.7 young. The period of parturition is protracted, spanning late spring to late summer (May–August). As in other Lamniformes, young are nourished through oophagy. The proportion of mature females in the resting, pregnant, and postpartum stages provides evidence that indicates that the Common Thresher Shark does not reproduce annually.

The functional role of the caudal fin in the feeding ecology of the common thresher shark Alopias vulpinus

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.

Movement patterns and nursery habitat of juvenile thresher sharksAlopias vulpinusin the Southern California Bight

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.