Biology of Hammerhead shark (original) (raw)
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The interactions between the evolutionary history of species and contemporary changes in their environment can result in both positive and negative outcomes for fitness and survival. Sharks are one the oldest groups of all extant vertebrates but, today, are among the most threatened globally, primarily because of destructive fishing practices. Hammerhead sharks (Sphyrnidae) exhibit extremely specialized traits and complex behaviors that have increased their vulnerability to human exploitation, which impedes conservation efforts. By bringing together published data on aspects of hammerhead shark phylogeny, morphology, biology, physiology, and ecology, we argue that the same novel adaptations that have historically contributed to evolutionary success have become maladaptive under current levels and modes of exploitation. Therefore, we suggest that future management be made in light of-rather than in spite of-the unique evolutionary and ecological traits possessed by hammerhead sharks, because similar patterns are threatening other taxa with high extinction risk.
The interactions between the evolutionary history of species and contemporary changes in their environment can result in both positive and negative outcomes for fitness and survival. Sharks are one the oldest groups of all extant vertebrates but, today, are among the most threatened globally, primarily because of destructive fishing practices. Hammerhead sharks (Sphyrnidae) exhibit extremely specialized traits and complex behaviors that have increased their vulnerability to human exploitation, which impedes conservation efforts. By bringing together published data on aspects of hammerhead shark phylogeny, morphology, biology, physiology, and ecology, we argue that the same novel adaptations that have historically contributed to evolutionary success have become maladaptive under current levels and modes of exploitation. Therefore, we suggest that future management be made in light of-rather than in spite of-the unique evolutionary and ecological traits possessed by hammerhead sharks, because similar patterns are threatening other taxa with high extinction risk.
The Effects of Electropositive Metals on Shark Catch Rates and Feeding Behavior
Bycatch of sharks in longline fisheries is one of several factors that have contributed to global declines of shark populations. Thus strategies to minimize the incidental capture of sharks are needed. One strategy is to exploit the unique electrosensory system of sharks. Sharks and other elasmobranchs use their electrosensory system to detect changes in electric fields. Metals from the lanthanide series, specifically Neodymium (Nd) and Praseodymium (Pr) generate strong electric fields in water. In this study we tested the effects of this E+ metal alloy on catch rates and feeding behaviors of several shark species impacted by longline fishing. We conducted several comparative assays using demersal longline fishing gear in Kaneohe Bay, Hawaii and pelagic longline fishing experiments in the Southern California Bight (SCB). In addition a laboratory behavior experiment using juvenile scalloped hammerhead sharks (Sphyrna lewini) was performed. Data from these experiments indicate that th...
The effects of a lanthanide metal alloy on shark catch rates
Fisheries Research, 2012
Bycatch of sharks in longline fisheries has contributed to declines in shark populations and prompted the need for exploring novel technologies to reduce the incidental capture of sharks. One potential strategy is to exploit the unique electrosensory system of sharks, used to detect weak electric fields. Metals from the lanthanide series, made up of neodymium (Nd) and praseodymium (Pr), produce strong electric fields in water. In this study, we tested the effects of an Nd/Pr alloy on shark catch rates. Using longline fishing gear, we compared the catch rates of baited hooks affixed with either a block of the metal alloy (experimental) or a lead weight (control). Four experiments were conducted in different regions of the Pacific Ocean. Two bottom longline experiments were conducted inside and offshore of Kaneohe Bay, Hawaii. One of these experiments targeted young of the year scalloped hammerhead sharks (Sphyrna lewini), while the other targeted sandbar (Carcharhinus plumbeus) and tiger sharks (Galeocerdo cuvier). In the Southern California Bight (SCB), pelagic longlines were deployed to target mako (Isurus oxyrinchus) and blue sharks (Prionace glauca) and longlines targeting pelagic sharks were set in the Eastern Tropical Pacific (ETP) off Ecuador. There was a significant reduction in juvenile hammerhead sharks caught on hooks with the lanthanide metal compared to the controls. In contrast, there was no difference in the catch rates for experiments targeting sandbar sharks in Hawaii or those conducted in the SCB and Ecuador. These results suggest that there are inter-specific differences regarding the effects of lanthanide metals on catch rates. This may reflect the diverse feeding strategies and sensory modalities used by shark species for detecting and attacking prey.
Journal of Morphology, 2005
Many hypotheses have been advanced to explain the adaptive significance of the sphyrnid cephalofoil, including potential advantages of spacing the olfactory organs at the distal tips of the broad surface. We employed comparative morphology to test whether the sphyrnid cephalofoil provides better stereo-olfaction, increases olfactory acuity, and samples a greater volume of the medium compared to the situation in carcharhiniform sharks. The broadly spaced nares provide sphyrnid species with a significantly greater separation between the olfactory rosettes, which could lead to an enhanced ability to resolve odor gradients. In addition, most sphyrnid species possess prenarial grooves that greatly increase the volume of water sampled by the nares and thus increase the probability of odorant encounter. However, despite a much greater head width, and a significantly greater number of olfactory lamellae, scalloped hammerhead sharks do not possess a greater amount of olfactory epithelial surface area than the carcharhiniform sandbar sharks. Therefore, sphyrnid sharks might not possess any greater olfactory acuity than carcharhinids. Despite this, there are clear olfactory advantages to the cephalofoil head morphology that could have led to its evolution, persistence, and diversification.
Enhanced visual fields in hammerhead sharks
Several factors that influence the evolution of the unusual head morphology of hammerhead sharks (family Sphyrnidae) are proposed but few are empirically tested. In this study we tested the ‘enhanced binocular field’ hypothesis (that proposes enhanced frontal binocularity) by comparison of the visual fields of three hammerhead species: the bonnethead shark, Sphyrna tiburo, the scalloped hammerhead shark, Sphyrna lewini, and the winghead shark, Eusphyra blochii, with that of two carcharhinid species: the lemon shark, Negaprion brevirostris, and the blacknose shark, Carcharhinus acronotus. Additionally, eye rotation and head yaw were quantified to determine if species compensate for large blind areas anterior to the head. The winghead shark possessed the largest anterior binocular overlap (48deg.) and was nearly four times larger than that of the lemon (10deg.) and blacknose (11deg.) sharks. The binocular overlap in the scalloped hammerhead sharks (34deg.) was greater than the bonnethead sharks (13deg.) and carcharhinid species; however, the bonnethead shark did not differ from the carcharhinids. These results indicate that binocular overlap has increased with lateral head expansion in hammerhead sharks. The hammerhead species did not demonstrate greater eye rotation in the anterior or posterior direction. However, both the scalloped hammerhead and bonnethead sharks exhibited greater head yaw during swimming (16.9deg. and 15.6deg., respectively) than the lemon (15.1deg.) and blacknose (15.0deg.) sharks, indicating a behavioral compensation for the anterior blind area. This study illustrates the larger binocular overlap in hammerhead species relative to their carcharhinid sister taxa and is consistent with the ‘enhanced binocular field’ hypothesis.
Guidance on National Plan of Action for Sharks in India
This document entitled “Guidance on National Plan of Action for Sharks in India” is intended as a guidance to the NPOA-Sharks, and seeks to (1) present an overview of the current status of India’s shark fishery, (2) assess the current management measures and their effectiveness, (3) identify the knowledge gaps that need to be addressed in NPOA-Sharks and (4) suggest a theme-based action plan for NPOA-Sharks.
Fisheries Research, 2011
Hammerhead sharks have experienced a drastic global reduction in abundance, yet limited data exist on their general biology and population structure. We use generalised linear models (GLMs) to analyse historical mesh net and drumline catches (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) of Sphyrna lewini from the Queensland Shark Control Program (QSCP), which covers 10 locations on the north-east coast of Australia. Results show a significant decline in S. lewini female total length over the study period and a significant increase in annual CPUE on the Gold Coast. Sexual segregation was found in Cairns, where S. lewini males were most abundant. A positive linear relationship was found between maternal total length and litter size. Birthsize embryos were found in most months. However, normal birth size (0.50 m) embryos were found in pregnant females most often during spring and summer. Mesh nets were more selective for smaller S. lewini than drumlines. It is recognised that species selectivity of other, more potentially dangerous shark species varies between gear types, but replacement of mesh nets with drumlines would reduce the catch of smaller individuals of S. lewini and assist in their conservation.