Chokka Research Articles

Early post-cleavage stages and abnormalities identified in the embryonic development of chokka squid eggs Loligo vulgaris reynaudii

Six early, post-cleavage embryonic stages for chokka squid Loligo vulgaris reynaudii eggs that were developed in an aquarium are identified and described, expanding the embryonic stages for this species from 14 to 20. The influence of water temperature on embryonic development is described. At temperatures 15°C, high percentages of morphological abnormalities were observed in embryonic development. Gross forms are described and illustrated.

Behavioural interactions of predators and spawning chokka squid off South Africa: towards quantification

The interaction of a suite of predators with mating and spawning chokka squid (Loligo vulgaris reynaudii) was studied at inshore (<50 m) spawning grounds off South Africa. This study provides the first detailed records of predator–prey interactions of squids on their spawning grounds and is the first attempt to time disruptions caused by predators to the egg-laying behaviour of squids, thereby quantifying the perceived threat to the prey. The squids are focused on mate choice and reproduction while they aggregate over egg beds and they may be more vulnerable to predation than at other times. Their vulnerability to different predators in the field is examined and the tactics used against different predatory species are illustrated using recordings made with underwater video cameras. Predators recorded included two cephalopods (Octopus vulgaris and L. v. reynaudii), five teleosts (Pagellus bellotii natalensis, Spondyliosoma emarginatum, Pachymetopon aeneum, Cheimerius nufar and Pomatomus saltatrix), seven chondrichthyians (Squalus megalops, Mustelus mustelus, Carcharias taurus, Dasyatis brevicaudata, Gymnura natalensis, Poroderma africanum and P. pantherinum) and three marine mammals (Arctocephalus puscillus, Tursiops aduncus and Delphinus delphis). Analysis of behavioural interactions between predators and prey showed that predator disruption of egg laying may be quantified in terms of time. Marine mammals caused the most acute disruption, whereas other taxa had more chronic disruption effects because they spent more time on the spawning grounds. During November 1995, the suite of predators changed during the course of a 2-day period of underwater video recording, possibly because of an increase in water temperature. The hypothesis that predators would be concentrated around a spawning aggregation was tested by surveying the spawning ground using an underwater camera towed by a boat navigating with differential GPS. The results supported the hypothesis because predators were located only around the spawning sites. The serial spawning of chokka squids in recently upwelled water may reduce predation pressure. Furthermore, it may be difficult for predators to predict the specific spawning site on a particular day because squids disperse away from egg beds at night and use numerous spawning sites along the coast.

Assessment of the South African chokka squid Loligo vulgaris reynaudii: Is disturbance of aggregations by the recent jig fishery having a negative impact on recruitment?

An assessment of the South African chokka squid Loligo vulgaris reynaudii fishery is undertaken. Two fisheries catch chokka: the directed jig and the trawl fishery. Chokka is a by-catch in the latter fishery, which targets primarily Cape hake ( Merluccius spp.) and Agulhas sole ( Austroglossus pectoralis). A population dynamics model is fitted to the jig and trawl CPUE indices, and two biomass indices from scientific surveys, by means of an observation-error estimator. The dynamics are modelled for two periods: January–March and April–December. Parameters estimated are the annual recruitment R and the catchability coefficients corresponding to each biomass index; a composite somatic growth and mortality parameter, g, is fixed externally. Within this approach, two models for annual recruitment are considered: (A) recruitment is constant above a biomass threshold, below which it starts to decline; (B) recruitment depends on jig-induced fishing mortality, larger values of which have an increasing negative impact on reproductive success. The parameters estimated for model A have wide confidence intervals and the model is unable to fit the decline in the early years of the trawl CPUE time-series. A better fit is achieved for the approach taken in model B. The linkage in this model of declines in recruitment to disturbance caused by the jig fishery is, however, somewhat ad hoc, and a basis for an independent test of this link is suggested. Model B estimates the current biomass to be heavily depleted. Stochastic projections under the assumption that the current effort level is maintained, show that the risk of the spawning biomass falling below 20% of its pristine level over the next 10 years is close to 90%. Effort needs to be cut to 2/3 of that at present to achieve a substantial reduction in this level of risk. Some alternative scenarios that are investigated, such as that of a non-linear relationship between jig CPUE and biomass, give more pessimistic results.

Investigation into the declining trend in chokka squid Loligo vulgaris reynaudii Catches made by South African trawlers

The trawl fishery, which targets Cape hake Merluccius spp. and Agulhas sole Austroglossus pectoralis, takes chokka squid Loligo vulgaris reynaudii as by-catch. Catch and effort data from the trawl fishery for the period 1978–1996 are used to obtain annual estimates of catch rate (catch per unit effort cpue) for that period. Examination of the cpue trend shows a sharp decline in the early 1980s and, in order to identify factors that could have influenced that decline, the distribution of fishing effort is investigated both temporally and spatially. There is a possible change in the incidence of squid-directed catches over time, but their overall scarcity could have had only a small impact on the annual cpue trend. Further, using distribution of fishing effort to evaluate the effects of possible changes in fishing patterns, rather than changes in resource abundance, on the trend in trawl cpue, it became clear that there had been a contraction of the trawling grounds and changes in fishing patterns in relati...

Tag recapture studies of the chokka squid Loligo vulgaris reynaudii d′Orbigny, 1845 on inshore spawning grounds on the south-east coast of South Africa

To study their migratory movements, Chokka squid ( Loligo vulgaris reynaudii) were tagged on their inshore spawning grounds in early summer: 1748 in November 1992 and 4335 in November 1993. Squids were captured by hand jigging in depths of 24–35 m. Diving observations revealed that the behaviour pattern of recently tagged individuals was similar to that of untagged squid on the spawning grounds. Recaptures from commercial jigging vessels subsequent to tagging were 33 (1.89%) in 1992 and 387 (9.04%) in 1993. The longest tag-recapture duration was 32 days. Loligo. v. reynaudii moved to other spawning sites within the general spawning area, up to 207 km within 18 days. In 1993, mean speed was calculated as 3.0 km/day and mean distance travelled 42.8 km in a mean time of 14 days. Squids dispersed predominantly eastward from those tagged on the westward limit of their inshore spawning grounds. Those tagged towards the centre appeared to move randomly between spawning sites, possibly influenced by environmental conditions and food availability. Loligo v. reynaudii may be considered an uniseasonal-iteroparous species, maximising their reproductive potential by depositing eggs over an extended period in a number of spawning sites.

Fecundity of the chokka squid Loligo vulgaris reynaudii on the southeastern coast of South Africa

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.

Confirmation of serial spawning in the chokka squid Loligo vulgaris reynaudii off the coast of South Africa

Ovary maturation and spawning in the chokka squid Loligo vulgaris reynaudii were investigated by collecting squid from across their distributional range on the southeastern coast of South Africa between 1992 and 1993. Based on histological examination of the ovarian tissue and the separation of multiple modes in oocyte size-frequency distribution, ovary development was characterised by eight distinct stages. Our study confirms serial spawning in L. v. reynaudii.

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.

The status and importance of cephalopod systematics in southern Africa

A checklist of southern African cephalopods published in 1974 listed 94 species for the region 20–45°S, 10–40°E. Just 23 years later the number of known species has doubled to an estimated 195, represented in the South African Museum collection by 4 252 accessioned lots (15 434 specimens, excluding many paralarvae). In 1995, cephalopods constituted the sixth most valuable fisheries resource worldwide (after shrimps and tunas). Only one subspecies, Loligo vulgaris reynaudii, is targeted in South Africa at present, but it is important commercially because of the high prices it commands internationally. A number of other species constitute alternate resources of potential commercial interest, including at least 12 sepiids, 7 loliginids, 6 ommastrephids and 9 octopods. Cephalopods are also important in the trophic relations of marine fish, birds and mammals. Knowledge of the southern African cephalopod fauna is important not only for regional biodiversity studies but also from a wider perspective. The region ...

The influence of the environment on chokka squid Loligo vulgaris reynaudii spawning aggregations: steps towards a quantified model

Published and anecdotal information was used to formulate a conceptual (logic) model which describes the biological components and dynamics of chokka squid spawning aggregations. Into this was integrated potential environmental influences. To determine quantitatively the impact of environmental factors on the spawning process (and ultimately catches), a theoretical methodology was developed based on the use of underwater video images to estimate the rate at which egg pods were deposited. Results from a pilot study undertaken off the Tsitsikamma coast of South Africa demonstrated the viability of this quantitative technique, and while not intended to be a definitive experiment, showed that: (i) an upwelling event was coincident with the formation of a spawning aggregation, supporting the hypothesis that changes in temperature trigger spawning; (ii) biological activities such as egg deposition, predator-induced interruptions in egg deposition, and absence of squid from the egg bed, occupied 19, 22, and 59% of the event time respectively, and (iii) spawning was completed in about 33 h in the absence of female immigration. An overall decline in the deposition rate, combined with the absence of adverse environmental conditions, indicated that spawning was terminated by the ovaries of female squid becoming partially or fully spent, rather than by environmental stimuli. Based on this experience, hardware was then designed and manufactured to realize the methodology, and it is currently being used in a new series of squid spawning experiments.

Ovarian atresia in cephalopods

Ovarian atresia is described for the first time in cephalopods. Detailed histological examination of ovaries of Loligo vulgaris reynaudii in various stages of maturity revealed atresia in primary, previtellogenic and vitellogenic oocytes. These were analysed separately. Previtellogenic and vitellogenic oocytes could be subdivided into five clear stages, whereas primary atretic oocytes are given a general description. Follicular atresia lowers the number of maturing and mature eggs in the ovary, so previous fecundity estimates for cephalopods may have been too high. To correct potential fecundity estimates for losses arising from atresia, it is necessary to estimate the duration of each atresia stage in relation to the total spawning period.

Field validation of age readings from the statoliths of chokka squid (Loligo vulgaris reynaudiid'Orbigny, 1845) and an assessment of associated errors

Lipinski, M. R., Durholtz, M. D., and Underhill, L. G. Field validation of age readings from the statoliths of chokka squid (Loligo vulgaris reynaudii d’Orbigny, 1845) and an assessment of associated errors. ‐ ICES Journal of Marine Science, 55: 240‐257. This paper describes the first successful field tag-recapture experiment, aimed at validating daily increments in the statoliths of chokka squid (Loligo vulgaris reynaudii). Seven hundred and forty-two squid were tagged and injected with oxytetracycline (OTC) and 63 were subsequently recovered after 4‐20 days spent free in the sea. Forty-seven statoliths were successfully prepared for increment reading, eight of which satisfied stringent requirements for validation: good visibility of increments, sharp definition of the OTC band and a clear, undamaged margin. These eight statoliths yielded results indicating that the increments in chokka males in the size range 290‐370 mm mantle length (ML) were deposited daily and that the same was true for a 173 mm ML female. The results of an analysis of the errors involved in the increment recognition stage (counting) do show, however, that proper statolith preparation, increment identification and subsequent reading are crucial for obtaining accurate age estimates. The error in counting increments in a poorly prepared statolith may be three times higher than the error for a well prepared statolith in the technique used, which is felt to be one of the best presently available. This technique relies on the grinding of both sides of the statolith in the frontal plane (contrary to the most frequently used transverse sections). Precise position of the grinding plane is determined and maintained during the procedure. ? 1998 International Council for the Exploration of the Sea

Daily net emigration from a spawning concentration of chokka squid (Loligo vulgaris reynaudiid'Orbigny, 1845) in Kromme Bay, South Africa

The net emigration from a spawning concentration of the loliginid squid, Loligo vulgaris reynaudii d’Orbigny, 1845, was investigated quantitatively using a combination of tagging and hydroacoustic techniques, midwater trawling, purse seining and SCUBA diving. Aquarium experiments were used to supply additional information on tag loss and mortality from tagging. The number of squid in a concentration containing T tagged individuals was assessed hydroacoustically and then c squid were caught by means of a midwater trawl or purse seine. It was assumed that the tn tagged squids in these catches were the result of natural mortality, tagging mortality and net stability of the concentration (the result of emigration and immigration) n days after tagging. The average net emigration was then calculated to be 0.2 per day for 7.5 days of observations. This result is a first attempt to solve the so-called ‘‘Hilborn’s problem’’, i.e. the problem of how to measure the aggregation dynamics of nektonic organisms in the sea (instead of modelling). ? 1998 International Council for the Exploration of the Sea

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.

South Africa's Tsitsikamma National Park as a protected breeding area for the commercially exploited chokka squidLoligo vulgaris reynaudii

South Africa's Tsitsikamma National Park is within the general spawning area for Loligo valgaris reynaudii. Spawning squid use at least 10 areas within its boundaries, sporadically throughout the year, but mainly in early summer. Spawning occurred either on sand or low-profile rocky reef at depths between 22 and 35 m. Concentrations varied between a few hundred spawning pairs, with small and scattered egg mops, to thousands of spawning pairs with a large central egg bed surrounded by smaller egg mops. Squid paralarvae were captured within the boundaries of the Park, and squid tagged there moved to other spawning sites generally eastwards of it, where they were recaptured by commercial fishermen. The Park provides protection and undisturbed breeding sites for a portion of the spawning stock for part of the spawning period, and exports squid biomass through larval dispersal. It is unlikely that the Park markedly enhances the squid fishery, because spawning there is much less frequent than in open fishing areas.

The impact of fishing on chokka squidLoligo vulgaris reynaudiiconcentrations on inshore spawning grounds in the South-Eastern Cape, South Africa

A pilot study on the influence of fishing on spawning chokka squid Loligo vulgaris reynaudii was carried out between 1988 and 1991 along the coast of the South-Eastern Cape between Algoa Bay and Oyster Bay, in depths of 18–35 m. Behavioural patterns observed in the absence of fishing continued in the presence of large numbers of jigs in the water column, although the behaviour of individuals and paired squid occasionally altered in the immediate vicinity of the jigs. Squid reacted to the jigs in three ways, approaching them rapidly and grabbing them in their arms, approaching with caution and using the tentacles to touch them, or on occasion ignoring the jigs completely. Spawning at night continued in the presence of lights. At times lights attracted squid around the vessel, and on other occasions squid moved away from the area at dusk, returning at daybreak. Anchors and anchor chains did minimal damage to the egg beds during the study period, only 0.08% of the eggs located within 2 m of either side of th...

An Ethogram of Body Patterning Behavior in the Squid Loligo vulgaris reynaudii on Spawning Grounds in South Africa.

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.

Environment: the key to understanding the South African chokka squid (Loligo vulgaris reynaudii) life cycle and fishery?

This paper explores effects of environmental variability on the life cycle of the chokka squid, Loligo vulgaris reynaudii in South Africa, particularly the effect of physical and chemical influences on adult distribution, and the availability of spawning aggregations to the local jig fishery. The following hypotheses are presented: 1) temperature, dissolved oxygen and currents have a direct effect on the demersal distribution of adult chokka on the feeding grounds, but this is restricted to the west coast where environmental conditions are more extreme relative to the south coast, 2) chokka catches increase in proportion to the extent of coastal upwelling, 3) spawning behavior along the inshore regions (&lt;50m) is strongly influenced by turbidity near the seabed. High turbidity forces the spawning popuation to lay their eggs in deeper waters, and are thus not available to the jig fishery. 4) El Niño – Southern Oscillation (ENSO) events are linked with large fluctuations in the availability of spawning squid aggregations to the inshore jig fishery.

The location of spawning grounds, spawning and schooling behaviour of the squid Loligo vulgaris reynaudii (Cephalopoda: Myopsida) off the Eastern Cape Coast, South Africa

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.

The 1980s – a decade of change in the Benguela ecosystem

Changes that occurred in sea surface and some deeper temperatures, surface winds, currents, plankton and some dominant crustacean (rock lobster Jasus lalandii), molluscan (squid Loligo vulgaris reynaudii and abalone Haliotis midae), fish (anchovy Engraulis capensis, pilchard Sardinops ocellatus, Cape hakes Merluccius spp., sole Austroglossus pectoralis, kingklip Genypterus capensis and various species of linefish) and seabird (Cape gannet Morus capensis) resources in the Benguela ecosystem in the 1980s are documented. Although fishing had a clear influence on changes in some of the resources, a wide spectrum of organisms, from plankton to top predators, were influenced directly or indirectly by the abiotic environment. Concurrent changes in many of the resources suggest that the same environmental change may impact on more than one. Simultaneous change throughout the Benguela system indicates that environmental forcing sometimes takes place over wide geographic areas. At the northern and southern extremities of the Benguela system, responses to environmental change may be different because processes through which the change is mediated are different.