true

ISRA FACTSHEETS

SOUTH AMERICAN ATLANTIC REGION

ISRA FACTSHEETS

SOUTH AMERICAN ATLANTIC REGION

Mar del Plata Shelf Break ISRA

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Mar del Plata Shelf Break ISRA

Mar del Plata Shelf Break

Summary

Mar del Plata Shelf Break is located off the coast of the Buenos Aires Province in Argentina. It includes part of the continental shelf and its transition to the slope. The habitat is characterised by sediment-covered substrates. The area is highly productive, influenced by the permanent Argentine Shelf-break Front. Within this area there are: reproductive areas (e.g., Shortfin Sandskate Psammobatis normani).

Mar del Plata Shelf Break

Mar del Plata Shelf Break

DESCRIPTION OF HABITAT

Mar del Plata Shelf Break is located off the coast of the Buenos Aires Province in Argentina. It includes part of the continental shelf and its transition to the slope. The habitat is characterised by sediment-covered substrates, shaped by the annual transport of over 80 million tons of suspended sediment from large river systems, such as the Río de la Plata (Preu et al. 2012). It also features large-scale contourite channels, morphological terraces, and plastered drift sequences, all controlled by the circulation of Antarctic Bottom Water (Hernández-Molina et al. 2009). This area is highly productive and influenced by the permanent Argentine Shelf-break Front (Vazquez et al. 2016). This front marks the boundary where subantarctic shelf waters meet the cooler, more saline waters of the Malvinas Current, creating a significant thermohaline front (Lutz & Carreto 1991).

This Important Shark and Ray Area is benthic and subsurface and is delineated from 50–250 m based on the bathymetry in the area.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Mar del Plata Shelf Break is an important reproductive area for three ray species.

High densities of egg cases were found in the area for Broadnose Skate, Patagonian Skate, and Shortfin Sandskate (Vazquez et al. 2016).

Between 2009–2014, eight research cruises conducted bottom trawls on the northern Argentine continental shelf (36°S–41°S) at depths of 50–200 m, with additional sampling on the continental slope down to the Mar del Plata Canyon (200–3,447 m depth) (Vazquez et al. 2016). Sampling employed two types of bottom trawl nets and two dredges, with trawling durations of 20–30 minutes at speeds of 1.5–3 knots, resulting in a total of 122 fishing hauls, capturing a total of 515 egg cases of 10 species of sharks, rays, or chimaeras. Catch-per-unit-effort (CPUE; egg cases/km2) for each species was calculated based on the area swept by survey trawls (Alverson & Pereyra 1969) expressed as egg cases per km2 (egg cases/km2). After taxonomic identification, the number of egg cases per haul for each species was recorded (Vazquez et al. 2016).

Between 2009–2014, 49 Broadnose Skate egg cases were collected during 18 hauls in the area and adjacent areas limited to the shelf waters ranging from 94–251 m (Vazquez et al. 2016). The Broadnose Skate was the fourth most abundant species in the hauls across the broader region, with egg cases densities ranging from 62–540 egg cases/km2 (Vazquez et al. 2016). Of the five hauls with the highest densities, three were within the area in depths up to 145 m (Vazquez et al. 2016).

Between 2009–2014, 94 Patagonian Skate egg cases were collected during 30 hauls in the area and adjacent areas limited to the shelf waters ranging from 84–201 m (Vazquez et al. 2016). The Patagonian Skate was the second most abundant species in the hauls across the broader region, with egg cases densities ranging from 169–1,619 egg cases/km2 (Vazquez et al. 2016). The highest densities were observed within the area including all five hauls with similarly high densities between 1,001–1,619 egg cases/km2, five hauls (of the six) with 301–1,000 egg cases/km2 and one haul (of the three) with 1–300 egg cases /km2 (Vazquez et al. 2016).

Between 2009–2014, 238 Shortfin Sandskate egg cases were collected during 19 hauls in the area and adjacent areas from 73.7–112 m depth, finding full egg cases in hauls at 75 and 95.7 m depth (Vazquez et al. 2016). The Shortfin Sandskate was the most abundant species in hauls, with egg cases densities between 72–12,326 egg cases/km2. The major concentrations were observed within the area, including three hauls (of the five with similar densities) with densities estimated between 3,001–12,326 egg cases/km2, two hauls (of the two) with 1,001–3,000 egg cases/km2, and one haul (of the three) with 301–1,000 egg cases/km2 (Vazquez et al. 2016).

Mar del Plata Shelf Break

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