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ISRA FACTSHEETS

SOUTH AMERICAN ATLANTIC REGION

ISRA FACTSHEETS

SOUTH AMERICAN ATLANTIC REGION

San Jorge Gulf ISRA

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San Jorge Gulf ISRA

San Jorge Gulf

Summary

San Jorge Gulf is located in the north part of San Jorge Gulf, in Argentina. It is situated on the Patagonian continental shelf. The area is characterised by sand, mud, and gravel substrates with patches of rocky areas. The area is influenced by mesoscale currents, associated with the tidal front North Patagonian Frontal System. This area overlaps with the Norte del Golfo San Jorge Key Biodiversity Area. Within the area there are: threatened species (Shorttail Yellownose Skate Zearaja brevicaudata) and reproductive areas (e.g., Smallthorn Sandskate Psammobatis rudis).

San Jorge Gulf

San Jorge Gulf

DESCRIPTION OF HABITAT

San Jorge Gulf is located in the northern part of the San Jorge Gulf in Argentina. It is situated on the Patagonian continental shelf. The area is characterised by sand, mud, and gravel substrates with patches of rocky areas (Van der Molen & Caille 2001). It is influenced by mesoscale currents, associated with the tidal front North Patagonian Frontal System, which begins to form in early austral spring, coinciding with the increase in solar heating (Sabatini & Martos 2002). The dynamics of this frontal system leads to high nutrient availability in the region, primarily due to upwelling and concentration processes, which enhance primary and secondary productivity (Chidichimo et al. 2022).

This area overlaps with the Norte del Golfo San Jorge Key Biodiversity Area (KBA 2025).

This Important Shark and Ray Area is benthic and pelagic and is delineated from inshore and surface waters (0 m) to 100 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Vulnerable Shorttail Yellownose Skate (Pollom et al. 2021).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

San Jorge Gulf is an important reproductive area for one shark and two ray species.

Narrowmouth Catshark, Shorttail Yellownose Skate, and Smallthorn Sandskate egg cases, neonates, and young-of-the-year (YOY) were regularly captured in the area.

Between 2010–2018, an official monitoring program was carried out in Chubut province by scientific observers onboard commercial trawl fishing vessels targeting Argentine Red Shrimp Pleoticus muelleri and Argentine Hake Merluccius hubbsi (Ruibal Nuñez 2020). During fishing operations covering an area of >181,500 km2, incidental captures and egg capsules were randomly sampled. Data on the date, depth, coordinates, and species identification were recorded (Ruibal Nuñez 2020). Neonates were identified based on their size and the presence of open umbilical scars (Ruibal Nuñez 2020). Additionally, between 2016–2017, information from research cruises carried out in the area and adjacent waters was also used to estimate the relative abundance of egg cases per km2 in research sets (Ruibal Nuñez 2020).

Between 2016–2017, this area had the highest density of egg cases for the Narrowmouth Catshark (1,439 egg cases/km2) compared to adjacent waters where density estimates were as low as 289 egg cases/km2 (Ruibal Nuñez 2020). Additionally, between 2010–2018, a total of 64 Narrowmouth Catshark neonates (5% of all captured individuals, n = 1,291) were recorded in commercial fisheries, along with 777 YOY and juveniles (60.2%). While neonates and YOY/juveniles were captured throughout the San Jorge Gulf and offshore waters (outside the area), ~35% of the records were recorded in the area (Ruibal Nuñez 2020). Neonates and juveniles were found from 60 m depth in the area and adjacent waters. Narrowmouth Catsharks sizes ranged from 8–79 cm total length (TL) (Ruibal Nuñez 2020). The size-at-birth for the species is 14–20 cm TL, while maturity is reached between 40–53 cm TL (Ebert et al. 2021). Two distinct size modes were identified for both sexes, one for YOY/juveniles (females at 30–35 cm TL and males between 25–30 cm TL), and another for adults (females at 45–50 cm TL and males between 60–65 cm TL) (Ruibal Nuñez 2020). Neonates were present in the area and adjacent waters from March–November, while egg cases with near-term embryos were collected in November. Females carrying egg capsules were recorded from March–October in the same areas where neonates and egg cases were collected. Therefore, an egg laying season was established between Apil–October for the area and adjacent waters (Ruibal Nuñez 2020).

Between 2016-2017, this area had the highest density of egg cases for the Shorttail Yellownose Skate (3,037 egg cases/km2) compared to adjacent waters where density estimates were as low as 163 egg cases/km2 (Ruibal Nuñez 2020). Higher densities were found between 80–96 m depth. Additionally, between 2010–2018, a total of 84 Shorttail Yellownose Skate neonates (19.7% of all captured individuals, n = 425) were recorded in commercial fisheries, along with 298 YOY and juveniles (70.1%). While neonates and YOY/juveniles were captured throughout the San Jorge Gulf and offshore waters (outside the area), ~25% of the records were recorded in the area (Ruibal Nuñez 2020). Shorttail Yellownose Skates sizes ranged from 14–121 cm TL (Ruibal Nuñez 2020). The size-at-birth is unknown for the species; however, neonates were found in the area and adjacent waters from 15 cm TL and near-term embryos measured between 15–16 cm TL (Ruibal Nuñez 2020), and maturity is reached between 79–94 cm TL (Pollom et al. 2021). Two distinct size modes were identified for both sexes, one for neonates/YOY at 15–25 cm TL, and another for adults, measuring 80–90 cm TL in females and 60–70 cm TL in males (Ruibal Nuñez 2020). Neonates and juveniles were found from 50 m depth but the highest percentage of neonates, and egg cases with embryos was observed between 60–110 m in the area and adjacent waters. Egg cases with early-term embryos were collected from February–November and females carrying egg capsules were recorded from March–April in the same areas were neonates and egg cases were collected. Therefore, an egg laying season was established between autumn and spring for the area and adjacent waters (Ruibal Nuñez 2020).

Between 2016–2017, this area had the highest density of egg cases for the Smallthorn Sandskate (1,557 egg cases/km2, encompassing one of the three sets with maximum densities), compared to adjacent waters where density estimates were as low as 207 egg cases/km2 (Ruibal Nuñez 2020). Higher densities were found between 80–95 m depth. Egg cases with initial-stages embryos were found between September–March and near-term embryos were collected in winter months in the area and adjacent waters (Ruibal Nuñez 2020). Females carrying egg capsules were also found during this period, establishing an egg laying season between spring and summer. Neonates from 7.1 cm TL were found with open umbilical wounds in the area. However, these individuals could not be identified to the species level within Psammobatis spp. due to the subtle differences present during the early life stages (Ruibal Nuñez 2020).

San Jorge Gulf

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