Electrosensory pore distribution and feeding in the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae)

Abstract

The megamouth shark Megachasma pelagios is a rare, large filter-feeding shark. Little to nothing is known of its sensory biology, particularly in relation to its feeding behaviour. We describe the abundance and distribution of ampullary pores over the head and propose that both the spacing and orientation of electrosensory pores enables M. pelagios to use passive electroreception to maximise feeding efficiency. KEY WORDS: Ampullae of Lorenzini · Electroreception · Filter feeding · Megamouth sharkResale or republication not permitted without written consent of the publisher Aquat Biol 11: 225-228, 2011 whereby water and prey would be pushed aside, due to its densely packed papillose gill rakers and relatively small internal gill rakers (Compagno 1990).M. pelagios tracked off the coast of California performed vertical migrations with the onset of sunrise and sunset (Nelson et al. 1997). This crepuscular migration allowed M. pelagios to consistently sample the water column at a specific level of illumination, with the shark staying at shallow depth at night (12 to 25 m) and in the deep during the day (120 to 166 m), but still well above the sea bed, which is at 700 to 850 m (Nelson et al. 1997). M. pelagios was thought to be following an isolume of 0.4 lux, the same light cue used by its vertically migrating prey (Nelson et al. 1997). As a result, a correlation was found between the diel depth distribution of M. pelagios and the vertically migrating krill Euphausia pacifica, which is common in southern California waters (Nelson et al. 1997). The highest night-time concentration of adults and juveniles of E. pacifica was reported to be between the surface and 40 m, with a deeper adult daytime peak located at 200 m (Brinton 1962, Nelson et al. 1997. MATERIALS AND METHODSA specimen of Megachasma pelagios (referred to as Megamouth 3) 5 m in length was stranded in Mandurah, Western Australia, in 1988 (Berra & Hutchins 1990. Access to the shark was given during its relocation from the Museum of Western Australia to the Western Australian Maritime Museum in Fremantle. The specimen had been fixed in 70% ethanol for 22 yr and, although it was apparent that some degree of tissue shrinkage had occurred, the ampullary pores were easily distinguishable from the lateral line pores, given the obvious size difference. Due to limited access to the specimen during this time, the lateral line pores could not be counted and/or their distribution mapped. No dissection of the ampullary pores was allowed, negating any chance of histological analysis. Pores were counted in situ, and photographs were used to produce the pore map presented here, with the aid of a Corel-DRAW graphics suite (Fig. 1). RESULTSA total of 225 ampullary pores were present on the head of Megachasma pelagios (Fig. 1), with significantly more pores (75%) located on the dorsal (D) surface of the head than the ventral (V, 4%) and lateral (L, 21%) surfaces combined (25%; see Table 1). Ampullary pores were found in the most dense assem- (Table 1). Pore fi...

Is the Megamouth Shark susceptible to mega-distortion? Investigating the effects of twenty-two years of fixation and preservation on a large specimen of Megachasma pelagios (Chondrichthyes: Megachasmidae)

“…A few measurements could not be collected (mostly of the head) because of the way the specimen was lying on the stretcher. A number of other measurements/samples were taken at this time by other researchers, including skin chromametric readings, denticle and tooth samples, and lateral line and electrosensory pore mapping (Kempster 2011;MacLeod unpublished data). The data collection and documentation took approximately one hour.…”

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

“…Fortunately, sharks have an advantage over most other marine predators, as they possess the ability to orient towards the bioelectric fields of their prey (Kalmijn 1974). Passive electroreception has been identified as a possible mechanism for M. pelagios to orientate towards and follow zooplankton populations through their DVM (Kempster & Collin 2011), negating the need to follow ambient light cues, as previously suggested (Nelson et al 1997). In the present paper we describe the abundance and distribution of ampullary pores on a C. maximus specimen and discuss how this may enable the shark to track the DVM of zooplankton.…”

“…Sharks have been shown to detect electric fields as weak as 1 nV cm -1 (Kalmijn 1978, 1982, Kajiura & Holland 2002. It is therefore possible that Cetorhinus maximus may use passive electroreception to determine the presence, and to some degree the abundance, of planktonic prey around its head, as we earlier proposed for Megachasma pelagios (Kempster & Collin 2011). However, unlike M. pelagios, the snout of C. maximus protrudes anteriorly in front of the mouth, and is covered in electrosensory pores (Fig.…”

Electroreceptive and Mechanoreceptive Anatomical Specialisations in the Epaulette Shark (Hemiscyllium ocellatum)

“…Previously, it has been widely assumed that ampullary pores are restricted to the head of sharks [19], [32], [45]–[46]. In H. ocellatum , some pores of pore field a are located close to the pelvic fins and have canals which extend posteriorly over 29% of the total body length.…”