ALBERT

Description: The question whether the chokka squid Loligo vulgaris reynaudii resource can be managed effectively is examined in the light of developments in the fishery and knowledge of the resource gathered in recent years. The history of the fishery since its inception in 1985, management controls and the current state of knowledge of stock identity, distribution, seasonality and abundance, life cycle and population dynamics are reviewed as a background to a discussion of management alternatives. Long-term measures, such as fleet limitation, seasonal closures and de facto closed areas and size limits, all appropriate in the early stages of a fishery when knowledge is limited, should be replaced by more-flexible alternatives as knowledge improves. Methods of stock assessment, stock-recruitment studies and further basic biological analyses are recognized as being crucial to improving management methods. An explanation embracing physical oceanographic features and plankton productivity in the vicinity of the spawning grounds is advanced for the mechanisms underlying hatchling survival. The possible contribution of trophic studies to squid management is recognized. Effective management of the chokka squid resource is concluded to be possible provided that the specific areas needing attention be addressed by means of goal-orientated research. Rational, but not necessarily optimal, management decisions can, however, be made even in the absence of stock-recruitment data, by the employment of common-sense measures which generally include some form of effort control.

Description: Squid on their spawning grounds feed mainly at night when they are more dispersed. In all, 28,5 per cent of squid sampled at night had food in their stomachs, whereas only 6,7 per cent of those collected by day had food. Most stomachs contained only a single prey species (90,8% of those analysed). Teleosts dominated the prey of squid collected at night (58%M), followed by crustaceans (25%), polychaetes (9%) and cephalopods (3%). By day the prey was dominated by cephalopods (61%), followed by teleosts (20%), crustaceans (14%) and polychaetes (2%). Bregmaceros sp. was the most frequently identified teleost, Loligo vulgaris reynaudii (cannibalism) the dominant cephalopod, ?Betaeus sp. (Alpheidae; pieces of coral were also found) the commonest crustacean and Nereis sp. the commonest polychaete. There were seasonal differences in the diet too: squid caught during summer seemed to have similar proportions of the four main prey components. Also, the incidence of feeding was higher than in winter. There were, however, no significant differences in stomach mass expressed as a percentage of body mass between day and night nor between season nor between sexes. The average stomach mass of all samples was 0,6 per cent of body mass, less than on the feeding grounds, where it is generally about 2 per cent.

Description: The location of spawning grounds of the squid Loligo vulgaris reynaudii (D'Orbigny) was investigated in the years 1988–1990. At least 39 spawning sites were found during this period along the inshore areas of the Eastern Cape coastline between Algoa Bay and Plettenberg Bay. The substrate chosen for egg laying was mostly fine sand or flat reef, frequently in large and relatively shettered bays. Spawning was found to occur sporadically throughout the year, and some spawning sites were used repeatedly within a particular year and in subsequent years. Squid migrate in discrete schools separated by sex in the vicinity of the spawning sites; these schools mix during spawning. Mating and egg deposition behaviour is described from observations made on the spawning grounds. Cannibalism was seen on a number of occasions, but no post-spawning mortality was recorded. Egg beds consisted mostly of large concentrations of egg strands (〉3 m in diameter), with smaller aggregations of one to ten egg strands surrounding these, with single strands in the immediate vicinity. Three basic patterns of echotraces were identified and interpreted according to diving observations. These patterns were classified as loose patches, dense patches, and complex patterns. The first two represent non-spawning schooling patterns and the third, mating and egg laying behaviour. This observation led to the general classification of squid aggregations: schools (non-spawning mode) and concentrations (spawning mode). Concentrations as far as Loligo vulgaris reynaudii was concerned were further divided into two patterns: suprabenthic and benthic (spawning) squid.

Description: Available knowledge is reviewed and new data incorporated in a synthesis of the life history and ecology of the chokka squid Loligo vulgaris reynaudii. We attempt to show that these aspects are essential to rational management of the resource. The life cycle is descriptionbed in detail from the egg to adult stage, mainly in biological terms, including a comprehensive descriptionption of maturation, migration and reproduction. Possible ecological interactions, particularly those of paralarvae and copepods, are discussed. Predator-prey relationships and the current state of knowledge on the effect of the physical environment on squid availability and abundance are summarized.

Description: Potential fecundity in Loligo vulgaris reynaudii was estimated to be about 17 000 eggs, calculated as the total number of discernible oocytes in the ovary and oviduct. Squid were observed to spawn up to 8140 eggs over a 36 h period in captivity. First estimations of actual fecundity are therefore between 8000 and 17 000 eggs. Factors complicating a more accurate estimation of actual fecundity in this species include difficulties with aquarium maintenance, their behaviour of spawning over a protracted period and in multiple sites, and atretic oocytes observed in both developing and mature ovaries. Detailed morphological and histological analysis of gonads collected at regular intervals over a complete spawning season will allow a more precise calculation of actual fecundity.

Description: Opportunistically collected information on sea temperature and wind was used in a preliminary investigation of physical factors affecting jigged catches of chokka squid Loligo vulgaris reynaudii. Results revealed sea temperature and wind to be correlated with catches during part of the summer upwelling season (October and December) in 1988. Multiple linear regression analysis confirmed that sea temperature was a highly significant explanatory variable (p = 0,0000) for catches from three boats, as well as for the overall catch. Wind direction also played a significant role (p = 0,0085) in the overall catch. A statistical linear multiple regression model is proposed for each boat and for the total catch. Upwelling events are suggested to play a major role in the availability of squid on the inshore spawning grounds (〈50 m) during summer. With further study, other independent physical variables, such as currents, swell height and turbidity, are likely to be introduced into the proposed model.

Description: Squids are capable of a high degree of visual signaling, most of which is expressed through the neurally controlled chromatophore organs in the skin. An accurate catalog (or ethogram) of these signals is an essential prerequisite to quantified behavioral analyses and experimentation. Body patterns such as those described here may also be useful for distinguishing between morphologically identical species or subspecies of commercial importance. The natural behavior of Loligo vulgaris reynaudii on spawning grounds was filmed by divers, and the body patterning repertoire was described in detail; 23 chromatic components, 4 postural components, and 9 locomotor components of body patterning were observed and correlated with different types of behaviors. Most of the chromatic components were expressed during intraspecific behaviors (e.g., agonistic behavior among males, courtship, mating) and, to a lesser extent, during interspecific interactions with fishes. Several of the most basic types of body patterns are described, the most distinctive of which are Lateral Display and White Flashing used between males in agonistic contests. This species is comparable to other Loligo spp. in its complexity of body patterning behavior.

Description: 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 behaviors that lead these animals to aggregate for sexual selection. Each dawn, the squid navigatefor several kilometers, toward the shore, to small, well-defined zones near egg beds on the substrate. After several hours of circling above these 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.