This study investigated the relationship between olfactory morphology, habitat occupancy, and lifestyle in 21 elasmobranch species in a phylogenetic context. Four measures of olfactory capability, that is, the number of olfactory lamellae, the surface area of the olfactory epithelium, the mass of the olfactory bulb, and the mass of the olfactory rosette were compared between individual species and groups, comprised of species with similar habitat and/or lifestyle. Statistical analyses using generalized least squares phylogenetic regression revealed that bentho-pelagic sharks and rays possess significantly more olfactory lamellae and larger sensory epithelial surface areas than benthic species. There was no significant correlation between either olfactory bulb or rosette mass and habitat type. There was also no significant difference between the number of lamellae or the size of the sensory surface area in groups comprised of species with similar diets, that is, groups preying predominantly on crustaceans, cephalopods, echinoderms, polychaetes, molluscs, or teleosts. However, some groups had significantly larger olfactory bulb or rosette masses than others. There was little evidence to support a correlation between phylogeny and morphology, indicating that differences in olfactory capabilities are the result of functional rather than phylogenetic adaptations. All olfactory epithelia exhibited microvilli and cilia, with microvilli in both nonsensory and sensory areas, and cilia only in sensory areas. Cilia over the sensory epithelia originated from supporting cells. In contrast to teleosts, which possess ciliated and microvillous olfactory receptor types, no ciliated olfactory receptor cells were observed. This is the first comprehensive study comparing olfactory morphology to several aspects of elasmobranch ecology in a phylogenetic context.

ABSTRACT1. Over the past two decades the number of fisheries targeting shark resources has increased dramatically. A combination of factors, including relatively slow growth rate, low fecundity and late age of maturity, result in low recovery rates from exploitation for most shark species. This, in turn, is reflected in the poor record of sustainability of shark fisheries.2. One of the greatest challenges is to find a way to deal with the substantial levels of shark bycatch taken in many non-target fisheries. Poor general recording of shark landings and paucity of shark landing data at the species level also undermine the development of effective shark management strategies.3. This paper reviews the problems that must be faced worldwide if shark resources are to be managed sustainably and lays out a comprehensive set of prioritized management strategies to facilitate the sustainable management of global shark fisheries. It is acknowledged that the majority of sharks are harvested in developing countries and that the management of shark resources in developing and developed countries will need to incorporate different management strategies relevant to local socio-economic agendas. The management recommendations deal with methods to improve the global regulation of fisheries, ways to improve global conservation ethics and encourage active participation in management, as well as means by which specific management strategies may be implemented.

Bamboo sharks (Chiloscyllium griseum) were tested for their ability to perceive subjective and illusionary contours as well as line length illusions. Individuals were first trained to differentiate between squares, triangles, and rhomboids in a series of two alternative forced-choice experiments. Transfer tests then elucidated whether Kanizsa squares and triangles, grating gaps and phase shifted abutting gratings were also perceived and distinguished. The visual systems of most vertebrates and even invertebrates perceive illusionary contours despite the absence of physical luminance, color or textural differences. Sharks are no exception to the rule; all tasks were successfully mastered within 3–24 training sessions, with sharks discriminating between various sets of Kanizsa figures and alternative stimuli, as well as between subjective contours in >75% of all tests. However, in contrast to Kanizsa figures and subjective contours, sharks were not deceived by Müller-Lyer (ML) illusions. Here, two center lines of equal length are comparatively set between two arrowheads or –tails, in which case the line featuring the two arrow tails appears to be longer to most humans, primates and birds. In preparation for this experiment, lines of varying length, and lines of unequal length randomly featuring either two arrowheads or -tails on their ends, were presented first. Both sets of lines were successfully distinguished by most sharks. However, during presentation of the ML illusions sharks failed to succeed and succumbed either to side preferences or chose according to chance.

Object categorization is an important function of the visual system, quickly providing an animal with relevant information about its surrounding and current situation, as for example during predator detection. While the ability to categorize objects has already been observed in several vertebrate and even invertebrate species, no attempt has previously been made to evaluate this function in fish, the most species-rich vertebrate group. This study assessed form discrimination abilities and object categorization skills in the African cichlid Pseudotropheus sp. Fish could discriminate between a variety of two-dimensional geometrical shapes, forms and sizes and learned to distinguish between two categories, "fish" versus "snail". Performance remained undisturbed by extensive modifications to the stimuli, as long as key features were maintained. Results indicate that fish not only memorized the features of the positive stimulus (categorized the positive stimulus), but also categorized the negative stimulus. During transfer trials involving a previously unknown object, fish were able to discriminate between both the negative and the positive stimulus and the unknown stimulus and responded accordingly.

Aetobatus narinari, a circumglobal batoid, is subjected to increasing fishing pressures, especially throughout South-east Asia. However, its management and protection is complicated by the lack of relevant life history information. It appears to be a late-maturing, long-lived stingray with a size-at-maturity of ∼130 and >150 cm in ventral disc width for males and females respectively. Like other myliobatids, A. narinari is a matrotrophic viviparous species exhibiting lipid histotrophy as indicated by trophonemata. Only the left ovary and uterus are functional. The presence of mature sperm in the testes, collecting ducts, epididymis and ductus deferens coincided with the estimated time of parturition and mating. Catches indicated an unbiased sex ratio. Aetobatus narinari is a hard-prey specialist that feeds mainly on gastropods, molluscs and hermit crabs (Diogenidae). Molluscs comprised numerically and gravimetrically the most important prey group (Index of Relative Importance (IRI): 85.9% in Australia, 99.9% in Taiwan) and were observed in 83.3% and 100% of stomachs containing food from Australia and Taiwan respectively. Minor dietary shifts from a gastropod–crustacean to a more gastropod–bivalve based diet occurred as body size increased. This study provides vital biological data for the effective management and conservation of A. narinari.

The ability to recognize and distinguish between visual stimuli is fundamental for everyday survival of many species. While diverse aspects of cognition, including complex visual discrimination tasks were previously successfully assessed in fish, it remains unknown if fish can learn a matching-to-sample concept using geometrical shapes and discriminate between images and their mirror-image counterparts. For this purpose a total of nine Malawi cichlids (Pseudotropheus sp.) were trained in two matching-to-sample (MTS) and three two-choice discrimination tasks using geometrical, two-dimensional visual stimuli. Two out of the three discrimination experiments focused on the ability to discriminate between images and their mirror-images, the last was a general discrimination test. All fish showed quick associative learning but were unable to perform successfully in a simultaneous MTS procedure within a period of 40 sessions. Three out of eight fish learned to distinguish between an image and its mirror-image when reflected vertically; however none of the fish mastered the task when the stimulus was reflected horizontally. These results suggest a better discrimination ability of vertical compared to horizontal mirror-images, an observation that is widespread in literature on mirror-image discrimination in animals. All fish performed well in the general visual discrimination task, thereby supporting previous results obtained for this species.

Fish move in a three-dimensional environment in which it is important to discriminate between stimuli varying in colour, size, and shape. It is also advantageous to be able to recognize the same structures or individuals when presented from different angles, such as back to front or front to side. This study assessed visual discrimination abilities of rotated three-dimensional objects in eight individuals of Pseudotropheus sp. using various plastic animal models. All models were displayed in two choice experiments. After successful training, fish were presented in a range of transfer tests with objects rotated in the same plane and in space by 45° and 90° to the side or to the front. In one experiment, models were additionally rotated by 180°, i.e., shown back to front. Fish showed quick associative learning and with only one exception successfully solved and finished all experimental tasks. These results provide first evidence for form constancy in this species and in fish in general. Furthermore, Pseudotropheus seemed to be able to categorize stimuli; a range of turtle and frog models were recognized independently of colour and minor shape variations. Form constancy and categorization abilities may be important for behaviours such as foraging, recognition of predators, and conspecifics as well as for orienting within habitats or territories.

Adaptation of brain structures, function and higher cognitive abilities most likely have contributed significantly to the evolutionary success of elasmobranchs, but these traits remain poorly studied when compared to other vertebrates, specifically mammals. While the pallium of non-mammalian vertebrates lacks the mammalian neocortical organization responsible for all cognitive abilities of mammals, several behavioural and neuroanatomical studies in recent years have clearly demonstrated that elasmobranchs, just like teleosts and other non-mammalian vertebrates, can nonetheless solve a multitude of cognitive tasks. Sharks and rays can learn and habituate, possess spatial memory; can orient according to different orientation strategies, remember spatial and discrimination tasks for extended periods of time, use tools; can imitate and learn from others, distinguish between conspecifics and heterospecifics, discriminate between either visual objects or electrical fields; can categorize visual objects and perceive illusory contours as well as bilateral symmetry. At least some neural correlates seem to be located in the telencephalon, with some pallial regions matching potentially homologous areas in other vertebrates where similar functions are being processed. Results of these studies indicate that the assessed cognitive abilities in elasmobranchs are as well developed as in teleosts or other vertebrates, aiding them in fundamental activities such as food retrieval, predator avoidance, mate choice and habitat selection.