No abstract

A total of 1280 (670 females and 610 males) Squatina guggenheim, an angel shark endemic to the south‐west Atlantic, was caught during five research cruises (1995, 1997 and 1998) carried out in the Argentine‐Uruguayan Common Fishing Zone (AUCFZ) at depths of 3·5–266 m. All angel sharks captured were sexed and measured. Of the 947 examined for stomach contents, 556 (58·7%) contained food and 391 (41·3%) were empty. Numerically, bony fishes were the principal dietary component (89·7%), followed by crustaceans (4·8%) and molluscs (4·4%). The most important prey species were Engraulis anchoita (58·3%), shrimps (4·4%) and Ilex argentinus (2·3%). Male and female diets were not found to differ significantly (P > 0·01), however, the diets of different size classes showed significant differences (P ≤ 0·01) (group 1, 23–44, group 2, 45–74 and group 3, 75–91 cm LT). Low rates of cannibalism were observed. The spatial and seasonal variability in the trophodynamics of S. guggenheim is discussed.

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The occurrence of changes in the trophic level (TL) of sharks with growth has not been quantified until now. Here length-related changes on Squatina guggenheim Marini trophic level were determined, and shifts in type, size and trophic level of its prey were analysed. Sampling took place during five bottom trawl surveys conducted in the ArgentineUruguayan Common Fishing Zone during spring (), using an Engel bottom-trawl net to capture the sharks. Three length groups were defined based on diet composition and using a cluster analysis (group I, 23-60 cm; group II, 61-80 cm; group III, 81-91 cm L T ). An ANOSIM procedure detected significant differences (P<0.05) in the diet spectrum between the three length groups. The smallest sharks (group I) ingested fish prey ranging from 5 to 21 cm L T , medium sharks (group II) fed on fish prey between 11 and 35 cm L T , and largest sharks (group III) preyed on fish between 13 and 40 cm L T . Diet structure of length groups were discriminated by almost the same prey taxa that characterized them. The increase of S. guggenheim body length promoted a decrease in the relative importance of small pelagic fishes. Contrarily, prey as medium benthopelagic fishes, medium pelagic squid and medium benthopelagic fishes showed an inverse tendency, indicating a broad diet spectrum of adults. Predator-length and prey-length relationship indicated a trend where 44.8% of S. guggenheim diet was integrated by prey <20% of their own body length and 32.8% of their diet was composed by prey >30% of their own length. The increase of mean prey weight was associated with the increase of predator weight and length. Smallest sharks (group I) were identified as secondary consumers (TL<4) whereas medium sharks (group II) and largest sharks (group III) were placed as tertiary consumers (TL>4). The study revealed an increase in S. guggenheim TL with shark growth as a consequence of changes on type, size and TL of prey ingested.

Vooren & Da Silva (1991) a través de la utilización de los siguientes caracteres morfológicos externos: presencia o ausencia de una fila medio-dorsal de espinas; forma y tamaño de la aleta pectoral, y patrón de coloración dorsal]]>