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The alteration of form and function through the life of a fish can have profound impacts on the ability to move through water. Although several studies have examined morphology and function in relation to body size, there is a paucity of data for chondrichthyans, an ancient group of fishes. Ratfishes are interesting in that they utilize flapping pe...
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... This term was originated by Huxley and Tessier (1936) to avoid confusion in the nomenclature of relative growth, and was derived from the Greek 'alloios', which means different (Gayon, 2000;Schmidt-Nielsen, 1975). Ever since Galileo Galilei (1637) revealed disproportionate growth relative to increasing mass in the skeleton of large mammals such as the elephant, scaling has become an informative field of study for biologists, providing insight into both intraspecific and interspecific relationships including the impacts of size on metabolism, feeding and locomotion in terrestrial and aquatic organisms (Birn-Jeffery and Higham, 2014;Cook, 1996;Cullen and Marshall, 2019;Dial et al., 2008;Domenici, 2001;Enquist et al., 2003;Gould, 1966;Higham et al., 2018;Killen et al., 2007;Norin and Gamperl, 2018;Vogel, 2005). Of relevance to the present research, scaling studies can have utility for advancing our understanding of the relationships between form, function, behaviour and ecology in species that can be difficult to study in their natural habitat, such as large sharks that swim in oceanic (i.e. ...
Disproportional changes (i.e. allometry) in shark morphology have been attributed to shifts in function associated with niche shifts in life history, such as in habitat and diet. Photographs of blue sharks ( Prionace glauca , 26-145 kg) were used to analyze changes in parameters of body and fin morphology with increasing mass that are fundamental to swimming and feeding. We hypothesized that blue sharks would demonstrate proportional changes (i.e. isometry) in morphology with increasing mass because they do not undergo profound changes in prey and habitat type, but as a result, we predicted that blue sharks would grow into bodies with greater turning inertias and smaller frontal and surface areas, in addition to smaller spans and areas of the fins relative to mass. Many aspects of morphology increased with isometry. However, blue sharks demonstrated negative allometry in body density, whereas surface area, volume and roll inertia of the body, area, span and aspect ratio of both dorsal fins, span and aspect ratio of the ventral caudal fin, and span, length and area of the mouth increased with positive allometry. The dataset was divided in half based on mass to form two groups: smaller and larger sharks. Besides area of both dorsal fins, relative to mass, larger sharks had bodies with significantly greater turning inertia and smaller frontal and surface areas, in addition to fins with smaller spans and areas, compared to smaller sharks. Hence, isometric scaling does not necessarily imply functional similarity, and allometric scaling may sometimes be critical in maintaining, rather than shifting, function relative to mass. Both allometric and isometric changes in blue sharks are predicted to promote reduced costs of transport in migration, but conversely, decreased unsteady performance, such as in escape responses. These changes are likely beneficial for larger sharks that probably experience reductions in predation pressure.
... To answer these questions, we measured 50 museum specimens of S. lewini (over a range of body sizes from 32 to 130 cm TL), gathering 13 morphometric linear measurements and five area measurements for each specimen. We followed the methods of Irschick & Hammerschlag (2014) and Higham et al. (2018), because these measurements specifically address lengths and areas of the head, pectoral, dorsal and caudal fins, and overall 'girth' of the shark body. From these data, we aimed to address whether there are any morphological differences present in S. lewini and discuss the implications of these results in relation to the life history of this shark. ...
Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.
... To answer these questions, we measured 50 museum specimens of S. lewini (over a range of body sizes from 32 to 130 cm TL), gathering 13 morphometric linear measurements and five area measurements for each specimen. We followed the methods of Irschick & Hammerschlag (2014) and Higham et al. (2018), because these measurements specifically address lengths and areas of the head, pectoral, dorsal and caudal fins, and overall 'girth' of the shark body. From these data, we aimed to address whether there are any morphological differences present in S. lewini and discuss the implications of these results in relation to the life history of this shark. ...
Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.
... Chimaeras, comprising the group Holocephali, rely solely on their pectoral fins to produce movement (Combes and Daniel 2001). Unlike sharks, the caudal fin remains rigid during swimming and it is not thought to contribute to forward movement (Higham et al. 2018). Moreover, the locomotion of Chimaeras is unique in the fact that both oscillatory and undulatory motions are observed in the pectoral fin movement of these animals (Combes and Daniel 2001). ...
... Especially the anterior (feeding, respiration) and posterior (locomotion) parts of the body of many fish species show distinct ontogenetic allometry (Gisbert 1999;Irschick and Hammerschlag 2015). Contrary to isometric growth, these changes drive the shape of morphological structures related to, e.g., feeding and locomotion and thus ensuring the survival of early ontogenetic stages occupying a distinct ecological niche (Reiss and Bonnan 2010;Richardson et al. 2011;Higham et al. 2018). More specifically, the differences in the shape of the caudal fins in the tiger and in the white shark are believed to relate to a shift in swimming mode in search for prey seemingly require a change in locomotor ability (Irschick and Hammerschlag 2015). ...
... Contrary to isometry, allometric change influences the relative shape of morphological structures this way ensuring that a fish is able to cope with the relevant environmental constraints during growth. Therefore, allometric growth not only closely matches specific ecological requirements but also allows shift in resource use, e.g., in feeding (e.g., Gisbert 1999;Karachle and Stergiou 2011;and Richardson et al. 2011) and in locomotion (e.g., Morrow 1950;Irschick and Hammerschlag 2015;and Higham et al. 2018). ...
Many pelagic shark species change body and fin shape isometrically or by positive allometry during ontogeny. But some large apex predators such as the white shark Carcharodon carcharias or the tiger shark Galeocerdo cuvier show distinct negative allometry, especially in traits related to feeding (head) or propulsion (caudal fin). In particular, changes in propulsion are attributed to a shift in swimming mode. The more heterocercal caudal fin of younger individuals with its large caudal fin span seemingly aids in hunting small, agile prey. In contrast, the less heterocercal caudal fin with a larger fin area in larger individuals aids a long-distance slow swimming mode. We were interested if negative allometric effects can be observed in a planktivorous shark, the basking shark Cetorhinus maximus, a large species adapted to long-distance slow swimming. To address this question, we compared three size classes, specifically < 260 cm (juveniles), 299–490 cm (subadults), and from adults > 541 cm total length. Comparing literature data, we found negative allometric growth of the head and of the caudal fin, but a more rapid decrease of relative caudal fin size than of relative head length. Hereby, we provide the first evidence for early negative allometric growth of the caudal fin in a large pelagic filter-feeding shark. Our study further demonstrates that ecomorphological approaches may add valuable insight into the life history of animals that are challenging to study in their natural habitat, including large roving sharks such as the basking shark.
Several elasmobranch species undergo shifts in body proportions during their ontogenetic growth. Such morphological changes could reflect variation in diet, locomotion, or, more broadly, in the species’ interactions with their environment. However, to date, only a few studies have been conducted on this topic, and most of them focused on particular body regions. In the present study, the ontogenetic growth of five different demersal shark species was investigated by using both traditional linear morphometry of the entire body and shape analysis of the caudal fin. A total of 449 sharks were analysed: 95 little gulper sharks, 80 longnose spurdogs, 103 kitefin sharks, 124 velvet belly lanternsharks, and 47 angular roughsharks. From each specimen, 36 linear morphometric measurements were taken. While a first canonical analysis of principal coordinates ruled out the possibility of different growth patterns between males and females, the same analysis statistically discriminated between small and large individuals in every species based on their morphology. A Similarity Percentage analysis revealed that the most important measurements in distinguishing these two groups were those related to body lengths, indicating that large individuals are more elongated than small individuals. The shape analysis of caudal fins revealed allometric growth during ontogenetic development, with adult individuals having a wider fin (discriminant analysis, p < 0.05). These findings could be related to changes in predatory skills, supporting the hypothesis of a shift in the ecological role that these sharks play in their environment, thus providing new essential information for their conservation.
