Patagonian Squid Loligo Gahi Research Articles

The role of the Falkland Current in the dispersal of the squid Loligo gahi along the Patagonian Shelf

Interannual and seasonal variations of the Falkland Current were studied using oceanographic data from a transect crossing the Current to the east of the Falkland Islands between 1999 and 2004. It was revealed that in austral autumn–winter of 2000 and 2002 the Falkland Current shifted from its normal offshore position westwards and entered the feeding grounds of the spring-spawning cohort of the Patagonian squid Loligo gahi located in the north-eastern part of the Falkland Shelf (at 50–51°S). A good correspondence was observed between the inshore movement of the Current in May–July with the squid abundance (in terms of CPUE) in the following September–October much further north ‘downstream’ on the Patagonian Shelf (46°S). Both age structure and earlier genetic studies revealed that squid occurred in both regions (51° and 46°S) belonged to the same cohort. Analysis of the dynamics of the Falkland Current with catches of L. gahi in both regions suggested that in years when the Current was intensified and shifted westwards (2000 and 2002), a part of squid population was likely to be displaced from their common feeding grounds much further north and aggregated on the shelf at 46°S. Reduction of fishing effort and its re-allocation to other areas is recommended in years of such displacements.

The effects of environmental factors on the embryonic survival of the Patagonian squid Loligo gahi

Seawater temperature and salinity are environmental variables that impose physiological limits for the embryonic development of marine invertebrates. For cephalopod species, these limits have rarely been established. This work presents experimental results on the embryonic survival of the Patagonian squid Loligo gahi, which is the last decades' most important loliginid species in terms of volume of commercial catches worldwide, as a function of seawater temperature and salinity. Reference magnitudes of surface seawater temperature and salinity within the area of distribution of the species were explored by analysis of satellite databases and published information. Embryos were incubated under eight constant regimes of temperature within 4–22 °C and four constant salinity regimes within 20–34.33‰ (12 °C). Also, to determine the effects of sudden temperature changes on embryonic survival, embryos were incubated at four variable regimes of temperature, with thermal shifts (6-day long 2-°C magnitude alterations of the incubation temperature) applied both at early and late stages of embryonic development. Embryonic survival was zero in incubations at constant temperature regimes ≤5° and at 22 °C, low at 6 °C, and high within 8–20 °C. A function was fitted by nonlinear regression to relate embryonic survival and mean incubation temperature. Thermal shifts applied in incubations at 20–22–20 °C variable regime of temperature provoked low embryonic survival compared to that observed in incubation at 20 °C constant regime. Embryonic survival was zero in incubations conducted at 20.0‰ and 34.3‰ salinity, and high at 26.4‰ and 32.8‰ salinities.

Variation in the diet of Genypterus blacodes(Ophidiidae) around the Falkland Islands

The diet change with size, season and area was investigated using the stomachs of 496 kingclip Genypterus blacodes collected around the Falkland Islands (south‐west Atlantic) between August 2001 and September 2002. The key prey species were rockcod Patagonotothen spp., benthic isopods and Patagonian grenadier Macruronus magellanicus. Kingclip <50 cm total length (LT) fed mainly on crustaceans and small fishes. With size the diet shifted away from crustaceans towards Patagonotothen spp. in kingclip 50–100 cm LT, and finally towards larger fishes such as M. magellanicus and Micromesistius australis australis in kingclip >100 cm LT. The niche breadth was highest in fish >100 cm LT and the lowest in fish <50 cm LT. The larger kingclip generally selected larger individuals of the same prey species, with the exception of the Patagonian squid Loligo gahi, where all ingested squid were of similar size, regardless of the predator length. The importance of the main prey species varied substantially between five consequent seasons studied, and appeared to follow the seasonal abundance and availability of prey. The spatial variability in the diet was found in kingclip caught in regions occupied by transformed temperate and sub‐Antarctic waters. The rockcod, which is available throughout the year around the Falkland Islands, was the most important prey in the kingclip diet. Kingclip takes advantage of other seasonally abundant prey species during their seasonal migrations (e.g. L. gahi) and also scavenge on discards from fishing vessels when available.

IN-SITU MONITORING OF THE DURATION OF EMBRYONIC DEVELOPMENT IN THE SQUID LOLIGO GAHI (CEPHALOPODA: LOLIGINIDAE) ON THE FALKLAND SHELF

Nineteen egg masses of the Patagonian squid Loligo gahi were monitored by divers at a near shore site (13‐18 m depth) located at the entrance to Port William, East Falkland, in the Southwest Atlantic over three summer and two winter periods in 1999‐2002. Six egg masses were monitored from early stages of embryogenesis until hatching. The duration of embryonic development varied from 51‐65 days in summer to 125 days in winter, while the daily-accumulated temperatures (DAT) required for complete embryogenesis varied rather less (521‐596° days). Hatching from one egg mass lasted at least 10 days in summer. The size and shape of the hatchling statolith matches the size and outline of the first stress mark in the juvenile statolith so confirming the ‘natal’ nature of the mark. The 4‐6-month difference in spawning time between the two main cohorts of L. gahi (May‐June in the autumn-spawning cohort and October‐November in the spring-spawning cohort) diminishes to just a 2‐3 month difference in hatching time (September‐October and December‐January, respectively). This allows the recruits of both cohorts to target the pronounced spring and early summer zooplankton bloom in the Southwest Atlantic.

Recent trends in diet composition and productivity of gentoo, magellanic and rockhopper penguins in the Falkland Islands

1. Over the past 14 years, data on diet composition and productivity of gentoo penguins (Pygoscelis papua), magellanic penguins (Spheniscus magellanicus) and rockhopper penguins (Eudyptes c.chrysocome) breeding in the Falkland Islands have been compiled as part of the Falkland Island Seabird Monitoring Programme. This paper comprises a summary of the data obtained so far, in particular concentrating on inter-annual and interspecific variation in productivity and general diet composition. 2. Productivity of all three penguin species has improved or remained stable over the last few years. The highest average productivity of 0.95 (ranging from 0.41 to 1.51) chicks fledged per breeding pair was observed in gentoo penguins. Productivity of rockhopper penguins during the same period was on average 0.80 (ranging from 0.63 to 0.91), and the lowest productivity of 0.78 (ranging from 0.19 to 1.49) was observed in magellanic penguins. 3. During the breeding season, all three penguin species preyed opportunistically on a mixture of fish, squid and crustaceans, with the general diet composition showing a high degree of spatial and temporal variation. The diet of all three penguin species overlapped with the commercial fishery for Patagonian squid Loligo gahi. There may also be some competition for Patagonian toothfish (Dissostichus eleginoides), hake (Merluccius sp.) and southern blue whiting (Micromesistius australis), because the juveniles of these commercially exploited species were regularly found in the penguin diet. Copyright © 2002 John Wiley & Sons, Ltd.

OOGENESIS AND GONAD DEVELOPMENT IN THE COLD WATER LOLIGINID SQUID LOLIGO GAHI (CEPHALOPODA: MYOPSIDA) ON THE FALKLAND SHELF

Oogenesis and gonad development were studied on histological sections of the ovaries of 12 females (98‐165 mm mantle length, ML, I‐V maturity stages) of the abundant Patagonian squid Loligo gahi sampled from the south-eastern part of the Falkland shelf. Additionally, reproductive systems of 136 females (80‐300 mm ML, I‐V maturity stages) were analysed microscopically to find atretic oocytes within the gonad. It was shown that the process of the oocyte development in the gonad and number of oogenetic stages in L. gahi are similar to those described before in a number of temperate loliginid species. However, development of both yolkless and vitellogenic oocytes in L. gahi is shifted to the earlier stages of the reproductive system maturation, giving probably more time for the yolk accumulation at low metabolic rates in cold water. Oocyte resorption was observed in the majority of mature females, but the proportion of atretic oocytes is always very low (about 1% of the total number of oocytes) showing a relative unimportance of this process in the L. gahi oogenesis.

Objective assessment of maturity in the Patagonian squid Loligo gahi (Cephalopoda: Loliginidae) from Falkland Islands waters

An objective assessment of maturity in the loliginid squid Loligo gahi was tested using a method developed for L. pealeii utilizing principal component and discriminant analyses. Samples were taken from both seasons of the commercial fishery in the Falkland Islands (prosecuted south of 51°20′S) in 1994 and 1995. In addition, research samples were taken in January, June, and November, outside the fishing seasons, to provide individuals of a greater range of size and maturity. The method, using a combination of indices of somatic and gonad lengths and scoring abundance of eggs and spermatophores in females and males, respectively, proved to be successful both in a research context, when variables can be measured to a high degree of precision, and in a fisheries context where less precision is practicable. The method also detected anomalies in the maturity status of squid that might have been overlooked in a more subjective assessment, corroborating the accumulating evidence for batch-spawning in loliginid squid. Four stages of maturity were recognized for female squid and three for male squid.

Biochemical genetic studies on the Patagonian squid Loligo gahi d'Orbigny. II. Population structure in Falkland waters using isozymes, morphometrics and life history data

Genetic population structure of the commercially fished Patagonian squid Loligo gahi d'Orbigny was examined by collecting 19 samples (1189 individuals) from Falkland waters between March 1987 and April 1988 and subjecting individuals to electrophoretic and morphometric analysis. Morphological features (dorsal mantle length, fin length oblique, fin width, interorbital width, tentacle length, length of arms I and II, and mid-mantle circumference), sex and stage of reproductive maturity (Lipinski's universal scale) were recorded prior to electrophoresis. Analyses of allele frequencies at six polymorphic loci provided no evidence of stock separation, and the frequency distribution of genotypic classes almost exclusively fitted Hardy-Weinberg expectations for a randomly interbreeding population. Nei's mean genetic distances and identities between samples ranged from 0.000–0.002 and 0.997–1.00, respectively, supporting the contention of a genetically homogeneous breeding unit. Multivariate analyses revealed significant differences in the morphometrics among certain samples collected at approximately the same time, especially of interorbital width, first arm length and fin width. This morphological differentiation was not correlated with differences at the genetic level. The frequency distribution of dorsal mantle length and stages of reproductive maturity through the year were compatible with two alternative interpretations of population structure: (i) the existence of two temporally distinct separate spawning populations, one autumn- and the other spring-spawning, or, (ii) that slow-growing or late spawned individuals spawn at 18 months old while most squid spawn at 1 yr old in the austral spring and summer. Although it is not possible to discount either interpretation unequivocally, the latter hypothesis of population structure is more congruent with existing genetic evidence.

Biochemical genetic studies on the Patagonian squid Loligo gahi d'Orbigny. I. Electrophoretic survey of genetic variability

19 samples (1189 individuals) of the commercially fished Patagonian squid Loligo gahi d'Orbigny were collected from Falkland waters between March 1987 and April 1988 and subjected to starch gel electrophoresis. 41 enzyme-coding loci were screened for polymorphism. Clearly resolved enzyme phenotypes were obtained at 21 loci of which six exhibited polymorphism (glutamate oxaloacetate transaminase, GOT-II, E.C. 2.6.1.1.; α-glycerophosphate dehydrogenase, α- GPDH, E.G. 1.1.1.8; isocitrate dehydrogenase, ICD, E.C. 1.1.1.42; malate dehydrogenase, MDH-II, E.G. 1.1.1.37; phosphogluconate dehydrogenase, PGD, E.C. 1.1.1.44; and phosphoglucose mutase, PGM, E.G. 2.7.5.1). Routine scoring at the 21 loci revealed moderate levels of genetic variability, with the proportion of polymorphic loci, P = 0.273, mean heterozygosities per locus = 0.0693, and the effective number of alleles, N e , with values of 1.13–1.83.