The South Patagonian stock (SSP) is the most abundant and is the main support of the Argentine fishery

Science to take care of fishing resources: the Illex argentinus squid

ARGENTINA
Friday, October 30, 2020, 08:00 (GMT + 9)

Researchers from CONICET published a paper in Fisheries Oceanography with a fundamental contribution to advise on the management of Argentine squid.

The squid –Illex argentinus- is one of the most important organisms for the fishing industry of our country due to its abundance in the Argentine Sea and the ecological role it fulfills, being a predator and prey. Understanding the mechanisms of its population dynamics makes it possible to improve the management measures of this fishing resource that is commercially exploited by several countries in addition to Argentina. For this reason, CONICET researchers recently published a study in the academic journal Fisheries Oceanography that evaluates what factors generate recruitment fluctuations, that is, the annual incorporation of new individuals into the fishery for the main squid stock.

INIDEP Illex squid infographic (click on the image to enlarge)

The research was carried out in a multidisciplinary way by the doctoral fellow María Luz Torres Alberto and the researcher Eduardo Marcelo Acha, both members of the Institute for Marine and Coastal Research (IIMyC-CONICET, UNMdP) and the National Institute for Fisheries Research and Development ( INIDEP), together with Marcela Ivanovic, Head of the Cephalopod Fisheries program of the National Institute for Fisheries Research and Development (INIDEP), Nicolás Bodnariuk and Martín Saraceno researchers from the Center for Sea and Atmosphere Research (CIMA-CONICET, UBA), of the Franco-Argentine Institute for the Study of Climate and its Impacts (UMI IFAECI, CNRS, CONICET-UBA-IRD) and of the Department of Atmospheric and Ocean Sciences, (FCEN, UBA).

The work includes fishing aspects, models that explain the movement of squid eggs from the laying area to the hatching area, processing of satellite products and interpretation of oceanographic aspects. María Luz Torres Alberto explains that the research focused on analyzing the relationship between the variability of the environmental conditions to which the early stages - eggs and paralarvae - were exposed and their recruitment. For this, they used a time series that goes from 1993 to 2017 of fishery data and a model based on satellite products.

Dynamics of the Confluence of Malvinas and Brazil currents, and a southern Patagonia (Source: Wiley Online Library)

It should be noted that the Argentine squid is one of the most important commercial species for our country. Their catches fluctuate enormously from one year to another (between 50 thousand and 600 thousand tons per year), possibly due to the effect of environmental causes during the initial stages of their development. It is important to know what these factors are, since the squid's life cycle lasts approximately one year and it is a semi-parasite species, that is, it has a single reproductive episode and dies after this event. In addition, these organisms have a highly energetic life cycle, they are voracious, which is why ecologically they are considered opportunistic, that is, they feed on any organism that has the size to be their food and this translates into the variability of their diet that adapts quickly to changes during its short life cycle. They also make extensive migrations and have accelerated growth, reaching maturity in one year.

“Knowing the commercially exploited species is of great importance for the conservation of the ecosystem and the proper management of the fishing resource. In this sense, this work allows us to learn a little more about these organizations of great economic interest for the Argentine fishing sector and the international community ”, adds Torres Alberto.

In this way, the time series that covered 24 years of catch per unit of effort (CPUE) of the squid fleet and a shorter series of evaluation of the fishing stock, in recruitment indices, based on research campaigns, was analyzed. To know the environmental conditions to which the squid specimens were exposed during their first stages, satellite products of surface temperature (SST) and sea level height were used. With all this information, they modeled the drift of the egg masses along the external platform and slope –considering the two possible spawning areas: Patagonia and South of Brazil-, to estimate the annual recruitment according to the conditions for each year throughout. throughout the time series.

Nuevo Gulf (Fig. 1) is a semi-enclosed basin 2.44x109 m2 in surface area and 2,54x1011 m3 in volume, with mean and maximum depths of 90 and 170 m respectively (Rivas & Ripa, 1989; Rivas, 1990). Its narrow mouth, 16 km in width and 7,13x105 m2 in transverse section, opens to the inner shelf off northern Patagonia. Estimations of mean monthly chlorophyll-a concentration at its western sector range within 0.20- 4.20 mg m-3 (Gil, 2001).Source: Lat. Am. J. Aquat. Res., 38(2): 297-301, 2010

Several stocks have been identified - as the group of organisms is commonly called - of this species according to the season and spawning area, but the South Patagonian stock (SSP) is the most abundant and is the main support of the Argentine fishery, representing approximately the 80 percent of the annual catches. Reproduction of the SSP takes place in autumn-winter, however there are controversies regarding the location of the spawning area. Once spawned, the newly hatched masses of eggs and paralarvae depend on the currents to achieve favorable temperature and feeding conditions for their development.

For this reason, the specialists considered that the variability of the currents of the region –from the Malvinas or Brazil- could control the survival of the paralarvae. This is important given that if in the paralarvae stage, between being hatchling and adult, they run the risk of being taken to the oceanic environment, beyond the continental slope, where there are no oceanographic mechanisms that allow their return to the continental shelf, they are considered losses to the squid population.

The research results support the hypothesis of the existence of a Patagonian spawning area and indicate that SSP recruitment is associated with three processes linked to the dynamics of currents in the region: transport, temperature and retention on the Continental platform. "We hope that the knowledge generated will contribute to improve the advice given to the authorities in charge of legislating on the fisheries management of this species," concludes Torres Alberto.

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