Chokka Squid Research Articles

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.

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.

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.

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 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.

Changes in the Eastern Cape demersal inshore trawl fishery between 1967 and 1995

Changes in the Eastern Cape demersal inshore trawl fishery operating out of Port Elizabeth over a 28-year period from 1967 to 1995 are described. The fishery is restricted to vessels operating between Slangbaai in the west to Port Alfred in the east. The principal target species are the shallow-water Cape hake and Cape horse mackerel. Eight of the more than 80 recorded species caught by the trawlers during the entire period contributed >98% to the total landed catch. These are hake, horse mackerel, panga, Agulhas sole, kingklip, Cape gurnard, silver kob and chokka squid. There was a notable decline in total catch and catch rate over the period reviewed, together with considerable change in the overall catch composition. For the two time-periods for which there are accurate catch data, hake, horse mackerel and panga consistently contributed in excess of 85% to the total annual landings. There were significant decreases in the size-at-(50%) recruitment for hake, horse mackerel and panga. Although at face value it would appear that the fishery is in decline, the causative factors are largely unknown and cannot be quantified properly owing to the paucity of comparable data. The need for further detailed investigation into the population dynamics of principal species in the Eastern Cape is discussed, particularly as it pertains to spawner biomass on the Agulhas Bank.

Investigation on the effects of different levels of effort and of the closed season in the jig fishery for chokka squid Lougo vulgaris reynaudii

After effort control, the closed season is the most important management tool used to regulate fishing mortality in the South African jig fishery for chokka squid Loligo vulgaris reynaudii. The dynamics of the stock biomass on the spawning grounds were modelled in order to assess the effects of current effort levels and the existing closed season on the resource. The model assumes that process error dominates over observation error. The model has three parameters: g, a parameter which combines natural mortality, emigration and somatic growth; q, the catchability; I, which represents immigration to the spawning grounds. Estimates of the parameters were obtained by fitting the model to catch per unit effort data, and were used to project the stock biomass forward in time to evaluate the impact of various effort levels both with and without a closed season. Results from the study indicate that the biological and economic gains provided by the current closed season are small and that there is little justification for urgent action to curtail current effort levels. However, in view of the apparently high risk associated with the current levels of effort and the great sensitivity of the results to basic model assumptions, both maintenance of the closed season and avoiding increases above the current level of effort are recommended. Further, the level of effort may need to be reduced, and the option of lengthening an existing closed season to effect this may well prove easier to implement than any attempt to reduce the present number of participants in the fishery.

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

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...

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.

Sexual maturation in squid: quantum or continuum?

A model is presented which tests the representation of the maturity process in terms of gonadosomatic indices (GSI) in chokka squid Loligo vulgaris reynaudii. It assumes that the true maturation process is reflected by the results of histological investigation, which cannot be used in large-scale ecological work in the field. However, the maturity scales used in ecological studies define some morphological categories which can be linked directly to microscopic development. Therefore, the overlap of GSI ranges for each morphological maturity category may be used to judge how well the GSIs represent the histological stages. Results have shown that the overlap is large and that GSI cannot be recommended as adequately reflecting the maturation process in squid. A morphological scale of maturity with possible broad applications in exploited families of squid is proposed as a better representation of the maturation process than GSI.

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.

Trends in pelagic fish populations of the Saldanha Bay region, southern Benguela upwelling system, 1980–1990: a predator's perspective

Changes in monthly and annual prey species composition of African penguins Spheniscus demersus are described from 1 454 stomach samples collected from two breeding islands in the Saldanha Bay region of the southern Benguela upwelling system between 1980 and 1990. The diet was dominated by anchovy, although pilchard, horse mackerel, round herring and chokka squid were also taken. The relative abundance of anchovy in penguin diet was highest between 1984 and 1989, coinciding with a period of favourable environmental conditions for recruitment of anchovy and a subsequent increase in fish biomass. The more recent decrease in dietary abundance of anchovy and its partial replacement by pilchard is consistent with independent (ship-borne acoustic) evidence of a recent increase in pilchard biomass. In contrast to these congruent trends, the size of anchovy taken by penguins between 1980 and 1990 has decreased dramatically, across years of good and poor recruitment. The reasons for this remain obscure but may reflect, in part, poor recruitment of anchovy in the latter part of the decade. Monthly changes in the size frequency distribution of anchovy consumed by penguins apparently reflect seasonal patterns of fish migration.

Can the Loligo squid fishery be managed effectively? A synthesis of research on Loligo vulgaris reynaudii

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.

A preliminary investigation of the effect of sea temperature fluctuations and wind direction on catches of chokka squidLoligo vulgaris reynaudiioff the Eastern Cape, South Africa

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.

The biomass and ecology of chokka squidLoligo vulgaris reynaudiioff the West Coast of South Africa

Migration, stock size and ecology of chokka squid Loligo vulgaris reynaudii off the West Coast of South Africa were studied and their relationship to other regions compared by analysis of distributional, biomass, and size composition, and biological data collected from biannual research cruises from 1983-1987. Biomass was lower than on the South Coast, higher in summer than in winter and declined over the duration of the study. The distribution of squid was generally continuous from the east up to between Cape Point and Cape Columbine. North of Cape Columbine it was more sporadic and occurred only occasionally in the far north (north of 31°S). Depth distribution, at up to 350 m, was much greater than on the S. Coast where an insignificant percentage of the biomass occurs over 200 m. The size composition was unimodal compared to a polymodal distribution on the S. Coast, and mean and modal sizes were smaller. Maturity rates and gonado-somatic indices were also much lower. The percentage of feeding squid was...