Undersea Penetration by Ambient Light, and Visibility

Busby, Roswell F.

doi:10.1126/science.158.3805.1178

Cited by 4 publications

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“…Madsen and Herman (1980) note that human scotopic vision is possible down to depths of 800 m in the clearest tropical waters. Busby (1967) measured the horizontal limit of viewing as 5-6 m during daylight at a depth of 300 m in waters east of Miami. He also noted that the silhouette of DSV Alvin's sail was visible down to 650-700 m in the same waters.…”

Section: Hypothesis 1: Sperm Whales Use Vision To Locate and Capture mentioning

confidence: 99%

How Do Sperm Whales Catch Squids?

Fristrup¹,

Harbison

2002

Marine Mammal Science

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Vision may play a central role in sperm whale predation. Two complementary hypotheses regarding the detection and capture of prey items are presented, based on a review of mesopelagic ecology. The first hypothesis postulates that sperm whales locate their prey visually, either silhouetted against the midwater "sky," or by searching for bioluminescence produced by the movements of their prey. The second hypothesis postulates that sperm whales create a zone of stimulated bioluminescence around the mouth, which attracts squids and other visual predators. Studies of midwater fishes and invertebrates document the importance of vision in mesopelagic communities. If sperm whales search for silhouetted prey, they should be oriented upside-down to improve visual coverage and to facilitate the transition from search to prey capture. Prey capture events should be marked by excursions toward the surface. If they lure their prey, they should swim at a steady pace, with little rapid acceleration, and spend most of their time foraging at depths with the greatest potential for stimulated bioluminescence.Key words: Pbyseter macrorepbalm, foraging, vision, bioluminescence.The sperm whale, Pbyseter macrocepbalus, regularly dives to depths between 200 m and 1,000 m (Lockyer 1977, Watkins et al. 1993, where it feeds on a variety of squids and fishes (Clarke and MacLeod 1980, Martin and Clarke 1986, Rice 1989. In most parts of the world, squids constitute the major part of their diet (Clarke 1980, Kawakami 1980, Clarke et al. 1988). Clarke et al. (1993 examined specimens in the Azores, and estimated that only 23% of the diet consists of fast-swimming, larger cephalopods; the bulk of the diet consists of smaller, neutrally buoyant, luminescent species. They estimated that about 1,000 prey items are consumed per day. This implies that sperm whales locate and capture their prey efficiently. 42 FRISTRUP AND HARBISON: FORAGING BY PHYSETER 43In the 19th century it was hypothesized that sperm whales might passively lure their prey. Beale (1835) suggested that,". . . when the whale is inclined to feed, he descends a certain depth below the surface of the ocean, and there remains in as quiet a state as possible, opening his enormous mouth, until the lower jaw hangs down perpendicularly, or at right angles, with the body. The roof of his mouth, the tongue, and especially the teeth, being of a bright glistening white colour, must of course present a remarkable appearance, and which seems to be the incitement by which his prey are attracted; and when a sufficient number, I suppose, are within the mouth, he rapidly closes the jaw and swallows the contents." Gaskin (1967), believing that the white lining of the mouth could not attract squids at the great depths to which they dived, proposed that the luminous mucus from previous prey items might coat the mouth and serve to lure more prey. The problem with Gaskin's hypothesis is that living squids are not covered with luminous slime, and that the generalized bioluminescence he reported was d...

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Section: Hypothesis 1: Sperm Whales Use Vision To Locate and Capture mentioning

confidence: 99%