A 50-kHz transmitter was placed in the stomach of a 44-cm (estimated) skipjack tuna, Katsuwonus pelamis, at Kaula Bank, Hawaii. With a few interruptions the fish was tracked from August 30 to September 6, 1969. The fish made nightly journeys of 25–106 km away from the bank and, with one exception, returned to the bank every morning to remain there for the day. Another skipjack tuna, about 40 cm long, was tracked for 12 hr at Penguin Bank, Hawaii. It also stayed at the bank during the day and left at night. Both fish swam close to the surface at night but swam at various depths during the day. The repeated morning returns of the skipjack tuna to Kaula Bank imply that skipjack tuna can navigate and that they have a sense of time.

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Five hundred ten measurements of swimming speeds of skipjack tuna (Euthynnus pelamis) from four schools and 33 of yellowfin tuna (Thunnus albacares) from one school were made from underwater motion‐picture records obtained at sea. The relation of swimming speed to rate of tail beats is described for yellowfin averaging 51.9 cm long and for skipjack averaging 57.2 cm long. At similar rates of tail beats, yellowfin swam faster than skipjack when speed was measured in body lengths per second. Variations in the mean swimming speed of the schools of feeding skipjack were unrelated to body length. The difference between the swimming speeds of tunas observed during this study, which ranged from 0.5 to 14.4 body lengths per second (0.3 to 6.9 m per second), and higher speeds previously reported for tunas is discussed.

ObjectivesTo determine: (1) the incidence of incidental ‘mastoiditis’ reported on magnetic resonance imaging scans performed in patients with asymmetrical sensorineural hearing loss and/or unilateral tinnitus; (2) how many of those patients have actual otological pathology and/or require treatment; and (3) the financial implications of such a reporting practice.MethodRetrospective case series.ResultsBetween October 2015 and November 2016, 500 patients underwent magnetic resonance imaging of the internal auditory meatus to rule out cerebellopontine angle lesions. There was an incidental finding of increased mastoid signalling in 5.8 per cent (n= 29), of which 20.7 per cent (6 of 29) were reported as bilateral cases. The diagnosis of ‘mastoiditis’ was found in 39.7 per cent (29 of 73). None of these patients had any pathology identified clinically. Other significant pathology was identified in a further 8.8 per cent (n= 44).ConclusionThe diagnosis of mastoiditis is primarily clinical. An incidental finding of high signalling in the mastoid region on magnetic resonance imaging is highly unlikely to represent actual clinical disease. In patients who are scanned for other reasons and who do not complain of otological symptoms, such findings are unlikely to require otolaryngology input.

Dolphins riding bow waves were observed through underwater viewing ports. The postures assumed by the dolphins show that they present their bodies rather than the ventral surfaces of their flukes to the propellant forces of the bow wave.