Detection of zooplankton prey in squid paralarvae with immunoassay.

Sustainable management of economically important squid requires monitoring of changes in their abundance, which are related inter alia, to their success in the food chain. The highest mortality is expected in the paralarval stages, which are prone to starvation. Causes of starvation may be linked to the lack of suitable prey. A multiple detection system was developed for the simultaneous identification of five putative zooplankton prey in the guts of paralarval Chokka squid, Loligo vulgaris reynaudii, by employing polyclonal rabbit antisera in conjunction with solid phase immunoassays. Specificities of antisera were validated by ELISA screening against different zooplankton taxa. Cross-reactions observed with ELISA were minimized through manipulation of antibody and antigen concentrations resulting in more specific detection of target prey antigens when used in an immunodot assay. Application of this optimised immunoassay detected multiple predation in paralarval squid samples collected from diverse areas in the Agulhas Bank ecosystem on the south coast of South Africa.

Choreography of the squid's "nuptial dance".

A mass spawning of squid resembles, at first glance, a chaotic "nuptial dance" (1). But for the first time, we have applied 3-D, radio-linked acoustic positioning (RAP) to this confusing process, and our early results now reveal a choreography that is, in fact, well organized in time and space. Remote tracking with RAP of individual Loligo vulgaris reynaudii off South Africa has provided insights into the daily sequence of behaviours that lead these animals to aggregate for sexual selection. Each dawn, the squid navigate for several kilometers, towards the shore, to small, well-defined zones near egg beds on the substrate. After several hours of circling above the egg beds, a pelagic, 3-D lek-like aggregation of large males forms: females are drawn in, and the aggregation condenses as the females and males pair, mate, and lay eggs. Smaller "sneaker males" remain on the periphery of the mating arena and, from this station, attempt extra-pair copulations (EPCs). The mating system of squids is thus unexpectedly complex, rivaling those of mammals and birds (2, 3). Commercial squid-jigging fishermen in South Africa have recently been attracted to the spawning grounds, and they have been successful. Moreover, their activities may be selective for large males. Thus, attention should be devoted to ensuring that such targeted fishing does not alter the characteristics of squid population genetics. Remote tracking and video observations, in combination with genetic analyses, may offer a new opportunity to monitor mating effort and reproductive success, and thus to manage the fishery.

Nuclear Microprobe Mapping of Statoliths of Chokka Squid Loligo vulgaris reynaudii d'Orbigny, 1845.

Loliginid squid statoliths were broken in half and their elemental composition was assessed using the nuclear microprobe technique. Proton induced X-ray emission and proton backscattering were used simultaneously. True, quantitative maps of calcium and strontium distribution in the frontal plane were obtained using a rapid-matrix-transform method called Dynamic Analysis. These measurements were complemented by observations with scanning electron microscopy and light microscopy. In juvenile and adult statoliths, Sr was concentrated in the wing and adjacent areas, whereas the Ca concentration was highest on the edge of the lateral dome. In contrast, Sr and Ca were uniformly distributed in the statoliths of paralarval squid. Increments showed best definition in the areas anterior and adjacent to the wing, corresponding to areas of high Sr content. Although temperature, sex, maturity, and the administration of oxytetracycline may influence the quantitative distribution of Ca and Sr in the statoliths of adult squid, they do not appear to affect the general pattern described above. The finding that Sr is concentrated in regions adjacent to the macula where the clearest increments are found in loliginid statoliths supports the hypothesis linking strontium with the regulation of statolith deposition and the definition of daily increments.