Sharkpedia Meghan Holst and Amani Webber-Schultz

This week we are joined by Dr. Ana Martins, a postdoctoral researcher at Dalhousie University studying the shark meat trade. The shark fin and meat trade is a common media topic but angler knowledge and opinions seem to be rarely incorporated into these discussions. In her home country of Brazil, Dr. Martins utilized angler knowledge to uncover trends in the shark meat trade. Listen through the episode until the end for a rather fishy field story which will have you laughing in your seat. 

The article which is the base of our discussion this week is, "Analysis of the supply chain and conservations status of sharks (Elasmobranchii: Superorder Selachimopha) based on fisher knowledge"



Article Summary:

Increasing fishing effort has caused declines in shark populations worldwide. Understanding biological and ecological characteristics of sharks is essential to effectively implement management measures, but to fully understand drivers of fishing pressure social factors must be considered through multidisciplinary and integrated approaches. Martins et al. aimed to use fisher and trader knowledge to describe the shark catch and product supply chain in Northeastern Brazil, and evaluate perceptions regarding the regional conservation status of shark species. They had 3 main objectives: identify the presence of a supply chain of two shark products (meat and fins), (2) describe the supply chain for each product, and (3) qualitatively evaluate fisher and trader perceptions regarding the regional conservation status of shark species. Several threatened shark species were reportedly often captured off shore and traded at local markets. This reported and observed harvest breaches current Brazilian environmental laws. Fishing communities are aware of population declines of several shark species, but rarely take action to avoid capture of sharks. The continuing capture of sharks is mainly due to a lack of knowledge of environmental laws, lack of enforcement by responsible authorities, and difficulties encountered by fishers in finding alternative income streams. National and regional conservation measures are immediately required to reduce overfishing on shark populations in Northeastern Brazil. Social and economic improvements for poor fishing communities must also be implemented to achieve sustainable fisheries.



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This week we join Kate McKinnon as Miss Frizzle on the Magic School Bus to explore shark noses up close!

Just kidding. But we do have shark-nose-specialist Dr. Lauren Simonitis! We break down her article Microstructure of the BonnetHead Shark (Sphyrna tiburo) Olfactory Rosette. (Simonitis & Marshall 2022). Learn all you could need to know about shark noses and more! 

Summary: The weird shape of hammerhead sharks means that their naris or noses are also weirdly shaped. Previous research has shown that the flow of water in hammerhead noses has a complex structure that changes the pressure and therefore changes the velocity of water in the nose itself. Simonitis et al., aim to describe the microstructure of the olfactory rosette of the bonnethead shark , sphyrna tiburo, and investigate differences in the individual lamellae themselves within the rosette. Specifically they looked at the degree of secondary folding, percent sensory area, and the relative surface area of the lamellae. This is the first time the olfactory nerve layer has been visually tracked through a shark lamella. They found that olfactory lamellae in areas of the olfactory organ that experience faster water flow, have a larger percentage of sensory area and more secondary folds compared to those exposed to lower water velocities. Their findings imply that there may be less sensitive portions along the rosette. Future work should look at flow and sensitivity inside a shark's nose with this information in mind.

Follow Dr. Simonitis on Twitter and Instagram @OceanExplauren

Follow some of Dr. Simonitis' work on Twitter and Instagram @MISS_Elasmo

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Just in time for Shark Week, we're going down under to investigate what warming waters will do to the distribution of tiger sharks on the east coast of Australia with tiger shark expert, Dr. Yuri Niella! 

This week we break down Dr. Yuri Niella et al. (2021) article, "Forecasting intraspecific changes in distribution of a wide-ranging marine predator under climate change."

Article Summary: (modified abstract)

Climate change is causing animal distributions to shift in response to changing temperatures. Typically shifts in these behaviors are evaluated at the species level, but in this study, Nuriella et al. studied behavioral shifts at the individual level. They investigated 115 tiger sharks, Galeocerdo cuvier, from 2002 to 2020, and evaluated how behavior and distribution differed between sex and maturation class (meaning, juveniles or adults). With this long-term data set, Nuriella et al. modeled how behavior and distribution may continue to change in tiger sharks to 2030, and included environmental factoers and predicted occurence of potential prey. Generalised Linear and Additive Models revealed that water temperature change, particularly at higher latitudes, was the factor most associated with shark movements. Females dispersed southwards during periods of warming temperatures, and while juvenile females preferred a narrow thermal range between 22 and 23 °C, adult female and juvenile male presence was correlated with either lower (23 °C) temperatures. During La Niña, sharks moved towards higher latitudes and used shallower isobaths. Inclusion of predicted distribution of their putative prey signifcantly improved projections of suitable habitats for all shark classes, compared to simpler models using temperature alone. Tiger shark range of the east coast of Australia is predicted to extend~3.5° south towards the east coast of Tasmania, particularly for juvenile males. This study will assist in evaluating the consequences of climate change to species distribution.

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Have you ever wondered how sharks perpetually regenerate their teeth? Why can't humans do the same thing, or can they?! This week expert Dr. Gareth Fraser joins us to tell us all about this special shark superpower.

We jump into Dr. Fraser's article, "The Dental Lamina: An Essential Structure for Perpetual Tooth Regeneration in Sharks" (Fraser et al. 2020)

Article Summary:
Methods of studying evolutionary, development, and regenerative biology have been improving over the past few years. This paper utilizes the embryonic small-spotted catshark (Scyliorhinus canicula) using new techniques that allow them to research key developmental and regenerative processes that classical models can not. The development of shark teeth and their subsequent regeneration is a lesser studied area of research. Fraser et al. explore the role of the dental lamina, the tissue that is the first evidence of teeth in an embryo, in the development of highly regenerative dentition in sharks. Sharks regenerate whole teeth at a time as opposed to other systems such as the murine model where incisors exhibit continuous renewal and growth of the same tooth. Studying shark teeth on a genetic level can provide important context into the evolution of vertebrate tooth regeneration.

Learn more about Dr. Fraser's work at: www.fraser-lab.net

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Manta ray research using drones?! This week guest expert Vicky Fong joins us to tell us all about the swimming behavior of manta rays, and why understanding these behaviors can be important for their conservation!

We jump into Vicky's article, "Using Drones to Assess Volitional Swimming Kinematics of Manta Ray Behaviors in the Wild" (Fong, Hoffmann, and Pate; 2022)

Article Summary: (abstract)
Drones have become increasingly popular tools to study marine megafauna but are underutilized in batoid research. They used drones to collect video data of manta ray (Mobula cf. birostris) swimming and assessed behavior-specific kinematics in Kinovea, a semi-automated point-tracking software. They describe a ‘resting’ behavior of mantas making use of strong currents in man-made inlets in addition to known ‘traveling’ and ‘feeding’ behaviors. No significant differences were found between the swimming speed of traveling and feeding behaviors, although feeding mantas had a significantly higher wingbeat frequency than traveling mantas. Resting mantas swam at a significantly slower speed and wingbeat frequency, suggesting that they were continuously swimming with the minimum effort required to maintain position and buoyancy. Swimming speed and wingbeat frequency of traveling and feeding behaviors overlapped, which could point to other factors such as prey availability and a transitional behavior, influencing how manta rays swim. These baseline swimming kinematic data have valuable applications to other emerging technologies in manta ray research.

Follow Vicky on Instagram @vicky.fong

Follow the Florida Manta Project on Instagram @MarineMegaFauna and Jessica Pate @FloridaMantaGirl 

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Everything you need to know about Tiger Shark teeth! This week PhD student Julia Türtscher joins ut to tell us amazing things about shark teeth, like, did you know males and females can have differently shaped teeth? Or that teeth can change SEASONALLY?! Learn everything you need to know about shark teeth and what Julia and her team learned about tiger sharks from preserved jaws!

This week we dive into Julia's article, "Heterodonty and ontogenetic shift dynamics in the dentition of the tiger shark Galeocerdo cuvier (Chondrichthyes, Galeocerdidae)" Türtscher et al. (2022)

Article Summary:
The lifelong tooth replacement in elasmobranch fishes (sharks, rays, and skates) has led to the assemblage of a great number of teeth from fossil and extant species. Evaluating tooth morphology is important for taxonomic descriptions, and understanding how elasmobranchs have evolved when comparing extant teeth to fossil teeth. Heterodonty (various tooth morphologies) occurs in most elasmobranch species and has proven to be one of the main challenges for comparing extant and fossil teeth. Although numerous shark species are discovered and described every year, detailed descriptions of tooth morphologies and heterodonty patterns are lacking or are only insufficiently known for most species. In this study, Türtscher and colleagues generate 2D models of tiger shark teeth Galeocerdo cuvier to describe how teeth develop and change from embryo to adult. Türtscher and colleagues' results reveal rather gradual and subtle shape changes from embryos to adults, mostly characterized by the increasing size and complexity of the teeth. They furthermore provide the first comprehensive description of embryonic dental morphologies in tiger sharks. Finally, multiple cases of tooth file reversal are described. This study contributes to our knowledge of dental traits across age stages in the extant tiger shark G. cuvier and provides a baseline for further studies on the dental variation in sharks. Therefore, it has the potential to assist in elucidating the underlying developmental and evolutionary processes behind the vast dental diversity observed in elasmobranch fishes today and in deep time.

Follow Julia Türtscher on Twitter @JuTuertscher and Instagram @julia_tuertscher

Learn about shark sightings in the Mediterranean @haisichtungen_mittelmeer

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