Albert Tester Memorial Symposium 2012
37th Annual Albert L. Tester Memorial Symposium
University of Hawaii at Manoa
March 14 – 16, 2012
Abstracts ( only shark related )
Contributed talks and posters
Department of Zoology & Hawaii Institute of Marine Biology
(Advisors: Timothy C. Tricas and Kim N. Holland)
Putative magnetoreceptor innervation in two species of elasmobranch fish, Sphryna lewini and Carcharhinus plumbeus
Sharks and rays are important predators in marine environments and demonstrate movement and orientation patterns that are correlated with the earth’s magnetic field. One controversial topic is whether they use magnetic cues mediated by their well-studied electrosense or a separate magnetite-based sense organ as recently shown in the olfactory organ of the rainbow trout.
Putative magnetoreception modalities, receptor structures and their subsequent pathways of sensory transduction remain undefined for most species. One such modality is the magnetite or iron-mineral based hypothesis, which was described in several bird species, as well as two teleost fish. In all cases the trigeminal nerve was reported to act as the pathway of mediation, and a nasal organ homologue the receptor structure.
Here I describe contrasting distributions of the superficial opthalmic branch of the trigeminal nerve in the scalloped hammerhead shark, Sphryna lewini, and the sandbar shark, Carcharhinus plumbeus. In the sandbar shark the nerve pathway is comparable to that described for the rainbow trout. Candidate nerve pathways identified for the hammerhead shark are in great contrast. Work to determine their sensory projections is ongoing.
Definition of these putative magnetoreceptor pathways will provide important evidence to solve the long standing controversy of whether sharks indirectly perceive magnetic information through their electrosensory system (via electro-magnetic induction), or directly via a magnetosensory system homologous to that described for bony fish and birds.
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Leigh Ann BoswellDepartment of Zoology & Hawaii Institute of Marine Biology
(Advisor: Timothy C. Tricas)
Olfactory receptor neuron identification in the nasal epithelium of juvenile hammerhead sharks
Damage to the peripheral olfactory system of teleost fishes that are exposed to aquatic toxicants can cause deficits in fitness-related behaviors such as feeding, predator avoidance, and mate recognition. However, it is currently unknown how the shark olfactory system responds to exposure to toxicants, and for many species the composition and density of olfactory receptor neurons (ORNs) involved in odorant detection is still unclear. The histology of the olfactory rosette organ was examined in juvenile scalloped hammerhead, Sphyrna lewini, to identify and quantify the ORNs present in their chemosensory epithelium. Both microvillar ORNs (mORN) and crypt neurons (CN) were identified in the sensory epithelium of the lamellae throughout the olfactory rosette. The densities of mORNs ranged from 11.7 ± 6.8 to 19.8 ± 5.6 cells/100μm2 while the CN densities were much lower, ranging from 0.1 ± 0.3 to 0.6 ± 0.6 cells/100μm2. These preliminary data confirm the presence of two receptor neuron types in the olfactory epithelium of S. lewini and provide baseline densities of ORNs. These results provide the second example of a shark species containing two ORNs in the olfactory organ and give the first quantitative densities of each ORN type throughout the peripheral olfactory system.
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Christina ComfortDepartment of Oceanography & Pelagic Fisheries Research Program
(Advisor: Kevin Weng)
Movements and behavior of bluntnose sixgill sharks (Hexanchus griseus)
Bluntnose sixgill sharks, Hexanchus griseus, are large apex predators and scavengers with a wide global range, but little is known of their behavior and ecology, particularly in deeper habitats. Most published work has been in temperate latitudes where the sharks inhabit shallower water, and so this study aims to describe the behavior of H. griseus in the deep oligotrophic habitat of Hawaii. We investigated the movements of two bluntnose sixgill sharks using pop-up satellite archival tags. Both animals exhibited regular diel vertical migrations, with median day/night depths of 613m/267m and 618m/334m for each shark, respectively. The sharks spent 78.3% and 77.6% of their time, respectively, in hypoxic waters (<60μmol/kg oxygen) at their daytime residence depths. It was found that the animals exhibited higher rates of vertical movement in shallow, warm water than they did in deep, cool water. These results suggest that bluntnose sixgill sharks may be more active foragers in the warmer, more productive waters at night and rest in cooler water during the day, an energy efficiency strategy utilized by the dogfish Scyliorhinus canicula, another bentho-pelagic elasmobranch. One animal likely remained on the Oahu slope for its time at liberty, as the temperature record is consistent with the physical oceanography of the Oahu slope, and the tag popped up off Kaena Point, Oahu. The second tag surfaced near Johnston atoll (18°N, 167°W), and the observed water temperature increase is consistent with travel to that location. Previously undocumented, bluntnose sixgill sharks swimming in the pelagic over long distances could allow large-scale population connectivity of the species and have implications for management and conservation.
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Melanie HutchinsonCo-authors: James Anderson, John O‟Sullivan, Kim Holland
Department of Zoology & Hawaii Institute of Marine Biology
(Advisor: Kim Holland)
Dive behavior of scalloped hammerhead sharks (Sphyrna lewini) in Hawaii
The seasonal habitat use and ecology of the globally endangered scalloped hammerhead shark, Sphyrna lewini in Kaneohe Bay, Oahu, Hawaii has been well studied. Yet their offshore migration patterns after leaving the area have remained a mystery. To elucidate their behavior and monitor their vertical and horizontal movements outside of Kaneohe Bay, we fitted seven adult (248 cm Total Length ± 11) male hammerhead sharks with either pop-up archival tags (PAT) (n = 4), or satellite-linked transmitters (smart position only tags SPOT) (n = 4), where one shark was double tagged with both a PAT and a SPOT, and acoustically coded transmitters. Results from the PATs show vertical range expansions exceeding depths of at least 1250 m, which are previously un-documented for this species. Vertical profiles showed very clear diel dive activity. Some of the tagged hammerheads also exhibited previously unrecorded thermal tolerances to at least 3°C, spending an average 34.7% of their time in temperature ranges from 3° – 6° C. Suggesting this species may have some physiological adaptations to life at such temperatures. Horizontal movement and range data from the SPOT and acoustic transmitters are indicative of local (main Hawaiian Islands) residence with seasonal returns into and out of Kaneohe Bay. These results reveal that S. lewini exploit an expanded niche in the offshore waters of Hawaii, with scales of movement suggesting they may be pursuing deep water prey.
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Kehau ManoiCo-authors: James Anderson, Stuart Donachie, Kim N Holland
Department of Biology
(Advisors: Stuart Donachie, Kim N. Holland)
Investigating ecological connectivity between distinct elasmobranch populations using oral bacteria: A proof of concept study
Ecological connectivity is a term used in reference to the movement of organisms from one place or habitat to another. In a marine context, understanding ecological connectivity has important applications in conservation, and in fisheries management and planning.
A synthesis of knowledge from satellite tag derived movement data, as well as biophysical modeling largely focusing on larval dispersal and reproductive phenology demonstrates a level of inter and intra-specific connectivity in marine environments at differing scales. These approaches have some significant drawbacks including equipment costs, difficulty of data recovery, and life-history specificity.
This project begins to address connectivity among elasmobranch species through the analysis of oral bacteria cultivated from the teeth of live, line-caught sharks. Analysis of oral micro-flora will determine the utility of this concept for elucidating connectivity. Here we aim to describe bacteria, yeasts and fungi cultivated from the teeth of prevalent shark species caught in waters around the Main Hawaiian Islands. We aim to isolate specific marker species to provide real-time evidence of connectivity between elasmobranchs at both species and population levels. These data can be compared with satellite derived movement and habitat-use data to elucidate possible connectivity.
Source: Program – 2012 A. Tester Memorial Symposium