Electrosensory pore distribution and feeding in the basking shark Cetorhinus maximus (Lamniformes: Cetorhinidae)

We compiled historical reports of megamouth sharks Megachasma pelagios (mostly fishery by‐catch and strandings) from 1976 to 2018 (n = 117) and found that they are distributed globally (highest latitude, 36°) with three hotspots: Japan, Taiwan and the Philippines. Despite possible biases due to variability in fishing effort, more individuals were reported at higher latitudes in the summer, suggesting seasonal, latitudinal migrations. Sex ratios were female‐biased in Japan, but more even in Taiwan and the Philippines, suggesting some sexual segregation. Females (total length, LT = 3.41–7.10 m) were larger than males (LT = 1.77–5.39 m) and matured at a larger LT (5.17 m) than males (4.26 m). Also, we reviewed the systematics, feeding ecology and swimming behaviour of Megachasma pelagios based on the literature. Our review shows that, compared with their morphology, anatomy and genetics, behavioural ecology of this species remains largely unknown and electronic tagging studies are warranted.

Section: Discussionmentioning

confidence: 99%

Distribution, body size and biology of the megamouth shark Megachasma pelagios

Watanabe

Papastamatiou

2019

“…Megachasma pelagios and the basking shark Cetorhinus maximus (Gunnerus 1765) are exceptions amongst the Lamniformes, as they are two of the largest, non‐predatory Selachimorpha known that feed exclusively by filtering water to consume zooplankton. Megachasma pelagios and C. maximus show the lowest pore abundances of any Lamniformes (225 and 301 pores, respectively); however, the percentage of ventral pores differs greatly between the two species (Table I; 3·56 and 64·78%, respectively; Kempster & Collin, 2011 a , b ). Both inhabit similar environments with global distributions and utilize similar filter feeding mechanisms; however, M. pelagios has a terminal mouth as opposed to C. maximus which has a sub‐terminal mouth placement (Compagno, 1984).…”

Section: Phylogenetic Adaptations In Number and Distribution Of Electmentioning

confidence: 97%

“…The number of electrosensory pores expressed by a species is likely to have important implications for the function of the individual's electrosensory system (Kajiura, 2001; Jordan, 2008; Kempster & Collin 2011 a , b ; Wueringer et al , 2011). It is therefore important to determine if pore abundance varies ontogenetically and sexually or whether it is conserved from birth.…”

Section: Intraspecific Variation In Electrosensory Pore Numbermentioning

confidence: 99%

“…Electrosensory pore abundance differs greatly between species of this order (Table I), ranging from 225 pores for the megamouth shark Megachasma pelagios Taylor, Compagno & Struhsaker 1983 to 1483 pores for the pelagic thresher Alopias pelagicus Nakamura 1935 (Raschi et al , 2001; Cornett, 2006; Kajiura et al, 2010; Kempster & Collin, 2011 a , b ). Similarly, the relative abundance of ventral pores varies greatly between species ranging from just 3·56% for M. pelagios to 68·69% for the salmon shark Lamna ditropis Hubbs & Follett 1947 (Fig.…”

Section: Phylogenetic Adaptations In Number and Distribution Of Electmentioning

confidence: 99%

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Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs

Kempster

McCarthy

Collin

2012

Electroreception is found throughout the animal kingdom from invertebrates to mammals and has been shown to play an important role in prey detection, facilitating social behaviours, the detection of predators and orientation to the earth's magnetic field for navigation. Electroreceptors in elasmobranchs, the ampullae of Lorenzini, detect minute electric fields and independently process these stimuli, thereby providing spatial information to the central nervous system on the location of a source, often potential prey. The ampullae of Lorenzini are individually connected to a single somatic pore on the surface of the skin, with the spatial separation of each pore directly influencing how electrical stimuli are detected and processed. Pore abundance varies across taxonomic groups resulting in unique species-specific differences. The intricate distribution patterns created by the specific positioning of somatic pores on the head are, however, consistent within families, resulting in patterns that are identifiable at higher taxonomic levels. As elasmobranchs evolved, the electrosensory system became more complex and highly specialized, which is evident by a general trend of increasing pore abundance over time. The elasmobranch electrosensory system has evolved to operate efficiently under the environmental conditions of the particular habitat in which a species lives. For example, reduced pore abundance is evident in oceanic pelagic elasmobranchs, for whom visual cues are thought to be of great importance. Pore abundance and spatial distribution may be influenced by multiple factors including head morphology, phylogeny, feeding behaviour and habitat.

“…Relatively few pores and low electrosensory resolution are seen in species that feed with an indiscriminate suction or ram‐feeding method of prey capture. For example, the basking shark Cetorhinus maximus (Gunnerus 1765) and megamouth shark Megachasma pelagios (Taylor, Compagno & Struhsaker 1983) are pelagic planktivores (301 and 225 pores, respectively) that have most of their pores distributed dorsally (Figure ) around the anterior margin of the mouth (Kempster & Collin, , ). These fishes live in the clear water of the open ocean and approach large groups of their small prey directly from the side or below.…”

Section: Anatomymentioning

confidence: 99%

Electroreception in marine fishes: chondrichthyans

Newton

Gill

Kajiura

2019

Electroreception in marine fishes occurs across a variety of taxa and is best understood in the chondrichthyans (sharks, skates, rays, and chimaeras). Here, we present an up‐to‐date review of what is known about the biology of passive electroreception and we consider how electroreceptive fishes might respond to electric and magnetic stimuli in a changing marine environment. We briefly describe the history and discovery of electroreception in marine Chondrichthyes, the current understanding of the passive mode, the morphological adaptations of receptors across phylogeny and habitat, the physiological function of the peripheral and central nervous system components, and the behaviours mediated by electroreception. Additionally, whole genome sequencing, genetic screening and molecular studies promise to yield new insights into the evolution, distribution, and function of electroreceptors across different environments. This review complements that of electroreception in freshwater fishes in this special issue, which provides a comprehensive state of knowledge regarding the evolution of electroreception. We conclude that despite our improved understanding of passive electroreception, several outstanding gaps remain which limits our full comprehension of this sensory modality. Of particular concern is how electroreceptive fishes will respond and adapt to a marine environment that is being increasingly altered by anthropogenic electric and magnetic fields.