Squalidae

Abstract: The Bluntnose spiny dogfish Squalus acutipinnis Regan, 1908 is redescribed based on the re-examination of its type specimens and non-type material from Southern Africa. The taxonomic confusion concerning its validity is mainly related to its heterogeneous type series. Its taxonomic status is clarified as a valid species endemic to the Southwestern Indian Ocean when compared to congeners from the region and other valid species with which it has been placed in synonymy. Squalus acutipinnis can be distinguished from all species of the “megalops-cubensis group” by fewer total, precaudal, and monospondylous vertebrae (except from Squalus megalops, Squalus brevirostris, and Squalus crassispinus). Squalus acutipinnis is clearly distinct from Squalus megalops from Southern Australia and the Japanese S. brevirostris through characters of pectoral fin and external measurements. The South African species differs from S. crassispinus by having more slender first and second dorsal-fin spines. Squalus acutipinnis is al...

Abstract: Bomb radiocarbon has previously been used to validate the age of large pelagic sharks based on incorporation into vertebrae. However, not all sharks produce interpretable vertebral growth bands. Here we report the first application of bomb radiocarbon as an age validation method based on date-specific incorporation into spine enamel. Our results indicate that the dorsal spines of spiny dogfish, Squalus acanthias, recorded and preserved a bomb radiocarbon pulse in growth bands formed during the 1960s with a timing which was very similar to that of marine carbonates. Using radiocarbon assays of spine growth bands known to have formed in the 1960s and 1970s as a dated marker, we confirm the validity of spine enamel growth band counts as accurate annual age indicators to an age of at least 45 year. Radiocarbon incorporation into northeast Atlantic dogfish spines occurred in similar years as those in the northwest Atlantic and northeast Pacific, although the amount of radiocarbon differed in keeping with the radiocarbon content of the different water masses. Published reports suggesting that Pacific dogfish are longer lived and slower growing than their Atlantic counterparts appear to be correct, and are not due to errors in interpreting the spine growth bands. Radiocarbon assays of fin spine enamel appears to be well suited to the age validation of sharks with fin spines which inhabit the upper 200 m of the ocean.

Abstract: In sharks bioluminescence is only known from the family Squalidae. It evolved independently in two out of six squalid subfamilies, Dalatiinae and Etmopterinae. The distribution of photophores was mapped in several species. It is suggested that in the Dalatiinae, which do not school, but migrate vertically, luminescence serves as ventral countershading. The Etmopterinae school and feed close to the bottom. Their luminescence is an aid in schooling. Four different placoid scale patterns are found in luminescent sharks and they allow to accommodation the photophores in the skin.