Horn Sharks Research Articles

Little Sharks in a Big World: Mitochondrial DNA Reveals Small-scale Population Structure in the California Horn Shark (Heterodontus francisci).

The California horn shark (Heterodontus francisci) is a small demersal species distributed from southern California and the Channel Islands to Baja California and the Gulf of California. These nocturnal reef predators maintain small home-ranges as adults and lay auger-shaped egg cases that become wedged into the substrate. While population trends are not well documented, this species is subject to fishing pressure through portions of its range and has been identified as vulnerable to overexploitation. Here, we present a survey of 318 specimens from across the range, using mtDNA control region sequences to provide the first genetic assessment of H. francisci. Overall population structure (ΦST = 0.266, P < 0.001) is consistent with limited dispersal as indicated by life history, with two distinct features. Population structure along the continuous coastline is low, with no discernable breaks from Santa Barbara, CA to Bahia Tortugas (Baja California Sur, Mexico); however, there is a notable partition at Punta Eugenia (BCS), a well-known biogeographic break between tropical and subtropical marine faunas. In contrast, population structure is much higher (max ΦST = 0.601, P < 0.05) between the coast and adjacent Channel Islands, a minimum distance of 19 km, indicating that horn sharks rarely disperse across deep habitat and open water. Population structure in most elasmobranchs is measured on a scale of hundreds to thousands of kilometers, but the California Horn Shark has population partitions on an unprecedented small scale, indicating a need for localized management strategies which ensure adequate protection of distinct stocks.

Feature Extraction, Selection, and K-Nearest Neighbors Algorithm for Shark Behavior Classification Based on Imbalanced Dataset

This paper presents the feature extraction, selection and K-Nearest Neighbors (K-NN) algorithm to classify behaviors of sharks based on the data collected by tri-axial acceleration data loggers (ADLs). Because these behaviors are hard to observe in the wild and do not occur frequently, being able to adequately classify them is extremely challenging. In the proposed scheme, we first employ several transformations to enrich the static and dynamic acceleration data. Then, the enhanced data is converted from time to the frequency domain through the fast Fourier transform (FFT) for noise removal. A modified K-NN approach integrated with feature selection is developed and conducted on the frequency domain data to improve the F1-score for minority classes. The acceleration data of California horn sharks ( Heterodontus francisci ) gathered through ADLs mounted on the first dorsal fin is used to demonstrate our algorithm. A comparison study shows that the features extracted and selected by our proposed scheme can significantly improve the performance of classification on the imbalanced dataset.

A rapid PCR-RFLP method for species identification of the eastern Pacific horn sharks (genus Heterodontus)

Accurate species identification is essential for the successful implementation of species conservation strategies and research. East Pacific horn sharks (genus Heterodontus) may be subject to overfishing and depletion in some areas, mandating an assessment of risk and vulnerability to exploitation. Unfortunately, morphological identification of the three eastern Pacific species can be challenging, creating uncertainty about species identifications and the true extent of their respective ranges. To address this problem, we developed a PCR-RFLP method to quickly and accurately identify the three species of Heterodontus occupying the coastlines and islands of the eastern Pacific (H. francisci, H. mexicanus, and H. quoyi). The PCR-RFLP assay requires only a single amplification of the mitochondrial NADH2 locus (1216 bp) and a single digestion step with restriction enzyme AluI. The assay was tested on 67 individuals representing all three species and resulted in unambiguous species identification for 100% of individuals tested.

Environmental effects on daytime sheltering behaviors of California horn sharks (Heterodontus francisci)

California horn sharks (Heterodontus francisci) are relatively small (122 cm maximum total length; TL), nocturnally active sharks that have been observed refuging in shelters during the day; however, little is known about how they select their daytime resting shelters, and what factors may drive their degree of shelter fidelity. Depending on body size, thermal tolerance, and ability to avoid predators, horn sharks may need to balance tradeoffs when selecting a quality shelter. This study quantified vertical daytime distributions via dive surveys and shelter fidelity via acoustic telemetry during June – August 2016 and June – November 2017 in a temperate rocky reef (33˚26’ N, -118˚29’ W). Immature individuals ( 58 cm TL) were found in deeper (> 10 m), cooler habitats sheltering in larger caves and rock ledges. The sizes and relative abundances of sharks varied between land-associated and offshore-isolated reefs, indicating habitat type may be a likely driver of ontogenetic shifts in shelter behavior. No sharks returned to their shelters in 2016 coinciding with the period of El Nino conditions (increased temperature, shifts in community assemblage), yet shelter fidelity was 47% in 2017 under non-El Nino conditions. By quantifying sheltering behavior in a residential mesopredator, this study provides a framework for understanding how environmental conditions influence horn shark behaviors and their potential impacts on their community.

Active acoustic telemetry tracking and tri-axial accelerometers reveal fine-scale movement strategies of a non-obligate ram ventilator

BackgroundCalifornia horn sharks (Heterodontus francisci) are nocturnally active, non-obligate ram ventilating sharks in rocky reef habitats that play an important ecological role in regulating invertebrate communities. We predicted horn sharks would use an area restricted search (ARS) movement strategy to locate dense resource patches while minimizing energetic costs of travel and nighttime activity. As ectotherms, we predicted environmental temperature would play a significant role in driving movement and activity patterns.MethodsContinuous active acoustic tracking methods and acceleration data loggers were used to quantify the diel fine-scale spatial movements and activity patterns of horn sharks. First passage time was used to identify the scale and locations of patches indicative of ARS. Activity was assessed using overall dynamic body acceleration (ODBA) as a proxy for energy expenditure. Behavior within a patch was characterized into three activity patterns: resting, episodic burst activity, and moderate, consistent activity.ResultsAfter resting in daytime shelters, individuals travelled to multiple reefs throughout the night, traversing through depths of 2–112 m and temperatures of 10.0–23.8 °C. All sharks exhibited area restricted search patch use and arrived at their first patch approximately 3.4 ± 2.2 h (mean ± SD) after sunset. Sharks exhibited moderate, consistent activity in 54% of the patches used, episodic burst activity in 33%, and few (13%) were identified as resting at night. ODBA peaked while sharks were swimming through relatively deeper (~ 30 m), colder channels when traversing from one patch to the next. There was no consistent pattern between ODBA and temperature.ConclusionsWe provide one of the largest fine-scale, high-resolution paired data sets for an elasmobranch movement ecology study. Horn sharks exhibited ARS movement patterns for various activity patterns. Individuals likely travel to reefs known to have profitable and predictable patches, potentially tolerating less suitable environmental temperatures. We demonstrate how gathering high-resolution information on the movement decisions of a community resident enhances knowledge of community structure and overall ecosystem function.

Neogene ‘Horn Sharks’ Heterodontus (Chondrichthyes: Elasmobranchii) from the Southeastern Pacific and Their Paleoenvironmental Significance

Horn sharks (Elasmobranchii: Heterodontus Blainville) correspond to a genus of chondrichthyan fishes, mostly distributed in warmtemperate to tropical regions of the Pacific and Indian Oceans. The fossil record shows that, in contrast to its current distribution, horn sharks were widely distributed both in the eastern Pacific and western Atlantic during the Neogene, being subsequently extirpated from some of these areas. In this contribution, we describe new Heterodontus teeth from three Pliocene localities in the Coquimbo Region, in north-central Chile, and make an extensive revision of the fossil record of the genus in the Americas, in order to specify the timing of their extirpation in the southeastern Pacific and discuss the possible causes of this event. The new specimens described herein belong to a species with a Heterodontusfrancisci type dentition. Our analysis suggest that the removal of horn sharks occurred in the context of a general faunal turnover in the transition from Pliocene to Pleistocene, and that it was probably controlled by an interplay between the oceanographic, tectono-eustatic and ecological changes occurred in the region at that time.

Two new species of Acanthobothrium Beneden, 1849 (Tetraphyllidea: Onchobothriidae) from horn sharks in the Gulf of California, Mexico.

Between 1993 and 1996, 26 individuals of two species of horn sharks were collected from the upper Gulf of California and their spiral intestines examined for onchobothriid tapeworms. Heterodontus francisci was found to host Acanthobothrium puertecitense n. sp. Based on the criteria of Ghoshroy & Caira (2001), this is a Category 4 species (with >15 mm total length, >50 proglottids, >80 testes and a symmetrical ovary). It differs from the four Category 4 species previously reported from either the western Atlantic or eastern Pacific Oceans, including A. bajaense (emend.) which was described from H. francisci, in hook-shape, total length, number of proglottids, number of testes and number of columns of vitelline follicles. H. mexicanus was found to host Acanthobothrium santarosaliense n. sp., which, based on the criteria of Ghoshroy & Caira (2001) is a Category 3 species (with >15 mm total length, >50 proglottids, >80 testes and an asymmetrical ovary). A. santarosaliense differs from the five Category 3 species previously reported from either the western Atlantic or eastern Pacific Oceans in its size, euapolytic nature, lack of dark matrix from the bases of the hooks, hook-shape, and distribution and number of testes. In addition to the difference in ovarian symmetry, A. puertecitense possesses fewer testes, fewer proglottids, is a shorter worm, possesses a more anterior genital pore and vitelline follicles which extend further forward anteriorly than in A. santarosaliense. This represents the first report of onchobothriids from H. mexicanus and the first report of onchobothriids from H. francisci in the Gulf of California. The apparent host-specificity of both new species should be viewed with caution until a greater sample of host individuals of both species can be examined. The fact that both new tapeworm species are known only from the Gulf is also considered to be a preliminary result, given the small sample of host individuals examined from these regions to date. This brings the total number of species of Heterodontus known to host Acanthobothrium to four and the total number of Acanthobothrium species described from heterodontiform sharks to five.

The effectiveness of sodium lauryl sulphate as a shark repellent in a laboratory test situation

Swim‐through chemical repellency tests, using sodium lauryl sulphate (SLS), cupric acetate, and rotenone, were conducted in a specially‐designed roundabout tank on horn sharks, Heterodontus francisci, swell sharks, Cephaloscylliun ventriosum, and leopard sharks, Triakis semifasciata. Effective concentration thresholds (EC50s) were calculated for two levels of response: (1) minimum noticeable and (2) strong. The SLS EC50s were: horn shark 43.6 and 174.5 ppm; swell shark 95.1 and 160.0 ppm; and leopard shark inconclusive and 113.1 ppm. No response was discernible from cupric acetate. Rotenone evoked a weak response with an EC50 of 5.7 ppm, but no strong response.The ratio of the minimum noticeable EC50: 24‐hour lethal concentration (LC50) indicated the relative repellency (compared to toxicity) of the chemicals. The ratio for SLS was 19:1 and for rotenone 57:1. SLS did not provoke a repellency response at a low enough concentration to function effectively as a classical, surrounding‐cloud type, repellent. The range of potency of SLS, however, does allow it to be used as a directional repellent.

Elasmobranch pericardial function 2. The influence of pericardial pressure on cardiac stroke volume in horn sharks and blue sharks

The importance of negative pericardial pressure to heart function in clasmobranchs has been questioned due to the discovery of positive pericardial pressures in healthy horn sharks (Heterodontus francisci). We therefore implanted electromagnetic flow probes on the ventral aorta of horn sharks and blue sharks (Prionace glauca) and assessed stroke volume and pericardial pressure as pericardial fluid volume (PFV) was varied to test the hypothesis that elasmobranchs are capable of maintaining a relatively large stroke volume at pericardial pressures near and above ambient. Stroke volume was maximum between zero and 25% maximum PFV (maximum PFV: the volume of pericardial fluid required to open the pericardioperitoneal canal), where pericardial pressure was most negative. At 50% maximum PFV (pericardial pressure near or slightly above ambient) stroke volume was 70% and 98% of its maximum in horn sharks and blue sharks, respectively. At a larger PFV, stroke volume declined drastically, reaching zero where both PFV and pericardial pressure were maximum. Thus, at a pericardial pressure apparently associated with resting or mild activity, stroke volume is a relatively large proportion of the apparent maximum. Increased circulatory demands associated with strenuous activity may induce ejection of pericardial fluid through the perieardioperitoneal canal, which then lowers pericardial pressure. The lowered pericardial pressure causes an increase in stroke volume, indicating that control is in part effected by changing pericardial pressure.

Elasmobranch pericardial function. 1. Pericardial pressures are not always negative

Acute studies have led to the generalization that negative pericardial pressure is necessary for optimal cardiac function in elasmobranchs. We chronically instrumented horn sharks with pericardial catheters to test the hypothesis that ejection of pericardial fluid through the pericardioperitoneal canal (PPC) during routine handling could have accounted in part for previous measurements of exclusively negative pressures (-0.3 to -9.1 cm H2O) in elasmobranchs. Maximum and minimum pericardial pressures measured immediately following routine handling (acute pressures) were more negative than those measured in resting horn sharks at intervals from 1 to 27 days following handling (chronic pressures). Chronic pericardial pulse pressure was less than acute. Entirely positive pericardial pressures were observed on occasion. Handling of chronically catheterized horn sharks resulted in ejection of 21 per cent (range=10-26, n=5) of the initial pericardial fluid volume through the PPC and reduced pericardial pressure. Operating pericardial fluid volume of horn sharks averaged 2.0 ml.kg(-1) (range=1.6-2.6, n=9). The PPC opened after 4.3±0.2 ml.kg(-1) (x±S.E.) of elasmobranch saline had been slowly infused into the pericardium, corresponding to an average pressure of 1.3±0.2 cm H2O (n=10). The presence of the PPC plus a comparatively large pericardial fluid volume allows horn sharks to regulate pericardial pressure. Our analysis of pericardial pulse pressure, which can be an index of cardiac activity, suggests in contrast to previous studies that the elasmobranch heart can have relatively high stroke volumes at pericardial pressures near ambient. Thus, for venous return in resting or even moderately active elasmobranchs, it is more important that pericardial pressure be pulsatile than at a mean level which is negative.

Behavioral temperature regulation in the California horn shark, Heterodontus francisci.

Young horn sharks (<i>Heterodontus francisci) </i>were placed in an apparatus where they could choose between two chambers whose water temperatures differed by 10 °C. When the warmer chamber was at 26 °C, the sharks spent more time in the 26 °C water when the brain stem was cooled than when it was heated. With the brain stem kept constant at 12 °C, the sharks spent more time in the warmer chamber when it was at 26 °C than when it was at 31 °C. These findings demonstrate the importance of peripheral and rostral brain stem temperatures in the thermoregulatory behavior of a primitive member of the class Chondrichthyes.

Diel Activity Rhythms in the Nocturnal, Bottom-Dwelling Sharks, Heterodontus francisci and Cephaloscyllium ventriosum

The horn shark, Heterodontus francisci, and the swell shark, Cephaloscyllium ventriosum, exhibited distinct nocturnal activity patterns when observed underwater in the natural environment. Swimming activity began shortly after dusk and continued until dawn, after which very little activity was seen. Laboratory records for the horn shark under fixed and shifting LD 12:12 (12 hr light-12 hr dark) regimes indicated an exogenous rhythm, with an activity onset directly controlled by the onset of darkness. Horn sharks showed a high level of aperiodic activity in constant darkness and a low level of aperiodic activity in constant light. Activity in a swell shark appeared initiated by the onset of darkness during fixed LD 12:12 regimes, but slightly preceded darkness during a shifting (1 hr later/day) LD regime. This swell shark exhibited an endogenous (i.e., circadian) rhythm of shortened period (advancing phase drift) in constant darkness, and lengthened period (delaying phase drift) in constant light.

Aortic blood flow in free-swimming elasmobranchs

1. 1. Ventral aortic blood velocity and pressure in free-swimming elasmobranchs were recorded with the Doppler ultrasonic telemetry blood flowmeter. 2. 2. Ejection time from the heart varied with the heart rate. Peak injection velocities ranged from 12–14 cm/sec in Horn sharks, 12–20 cm/sec in skates and 8–15 cm/sec in dogfish. Acceleration of the blood lasted from 120 msec in the Horn shark (T = 24°C) to 450 msec in the skates (T = 9°C). Deceleration of flows was slow in all species. Oscillations from bulbus cordis contraction and respiratory movements were superimposed on the basic wavefrom. Participation of the bulbar contraction in the cardiac sequence varied widely. 3. 3. Heart rates increased during short-lasting exercise. Peak velocity and flow were largeley unchanged. Peak velocity and flow frequently increased in the post-exercise period. 4. 4. The hemodynamic effects of atropine, acetylcholine and adrenaline are discussed in relation to the fact that the fish heart receives parasympathetic but not, apparently, sympathetic innervation.