PHISICAL AND TROPHIC CONDITIONS IN NORTHERN PATAGONIA GULFS

DANS, SILVANA LAURA; GARAFFO, GRISELDA VALERIA; DEGRATI, MARIANA; SVENDSEN, GUILLERMO MARTIN; GAGLIARDINI, DOMINGO ANTONIO; CRESPO, ENRIQUE ALBERTO

Puerto Madryn

Taller; IWC Southern Right Whale Die-Off Workshop; 2010

IWC

The Golfo San José is a small semi-enclosed bay of 814 km2, connected with the Golfo San Matías by a narrow mouth of 9 km located in the northwestern side of the Gulf . It is approximately elliptical (minor and major axis of ca. 38 and 56 km long). The mean and maximum depths are 30 m and 120 m, the later in a narrow depression at the middle of the Gulf´s mouth. The coastline is irregular, presenting several prominent points. The tidal regimen is semidiurnal with average amplitude that varies between 8.7 and 2.96 meters. Winds blow predominantly from the SW quadrant with a mean speed of 15 km h-1. No permanent watercourses flow into the Gulf. Oceanographic information, suggested the existence of two distinct broad areas (the West and East portions of the Gulf) based on the analysis of chemical and physical variables. At the flood tide, a water jet funnels out through the western side of the Gulf mouth to the San Matías Gulf, while water flows in from the eastern side. Turbulence and eddies are only present in the western side of the San José Gulf. A thermal front extends from South to North. the East/West zone is warmer/colder in summer but colder/warmer in winter. The Golfo Nuevo is 2,500 km2, and its maximum depth is 184 m (Mouzo et al.1978). It is a semienclosed basin approximately 70 km long and 60 km wide. It is connected to the Atlantic Ocean by shallow waters of an average depth of 44 m and length of 16 km (Mouzo et al. 1978). Golfo Nuevo is homogenous in its superficial layer with respect to temperature from May to November (cold season) when lower temperatures occur. However, it is spatially variable between December and April (warm season), with lower temperatures along the southern coast. Low temperatures also can occur along the northern coast. The highest temperatures occur in the central area of the gulf. In the summer a cyclonal movement of the water can be observed in satellite images. Some acoustic surveys were carried out in May and November-December 2007 within this gulf. Macrozooplancton, possibly Munida gregaria, and anchovy Engraulis anchoita schools were detected. Anchovy schools were located between 20 and 55 mts of depth, where the bottom depth was between 66 and 88 mts, being deeper and located at deeper areas during winter conditions than during summer conditions. Macrozooplancton were located at depth between 75 and 85mts and didn’t show differences between seasons, and the bottom depth where it was found was 90mts or more. Both Anchovy and macrozooplancton were mainly located in the southwestern portion of Golfo Nuevo, but also in the northern area. The Golfo San Matías also shows a NE-SW front mainly during summer, with two distinctive water masses, being the northern area warmer and with higher salinity than the southern one. Adults as well as mother-calf pairs were recorded in the northern area of this gulf. Recently, several sightings of right whales were recorded in front of Peninsula Valdes, far from the coast and near the break, in an apparently feeding behavior.