The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described. This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal. Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes. Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ. Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction. A possible association with the unique thoracic development of the species is suggested. The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed.
Photo-identification surveys over three years along 390 km of coastline north of Cape Town, revealed that Heaviside's dolphin distribution was consistent between years and higher in areas more exposed to swells and with greater long-term availability of small hake Merluccius capensis (their principal prey). Dusky dolphin sighting rates varied considerably between years, but were generally higher in areas with lower hake availability and sandier shores (mostly straighter coastline). Large groups of 50-200 dusky dolphins were only seen in St Helena Bay, the site of a wind-driven upwelling zone. Heaviside's dolphins were found in shallower, cooler water than dusky dolphins and were more likely to be seen during brighter phases of the moon (when nocturnal light conditions may influence the vertical migration patterns of prey) and in areas of high hake abundance. Near-shore fishing activity was higher in the northern half of the study area and clustered around harbours. Set netting occurred only at Yzerfontein and St Helena Bay, but due to changes in the industry is currently thought to be a low threat to the population. Interactions between Heaviside's and dusky dolphins were usually neutral and sympatry appears to be mediated by differences in overall range and the type and size of prey species taken.
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