Spatial distribution of Loligo sanpaulensis paralarvae in San José Gulf (Patagonia, Argentina)

CRESPI ABRIL, AUGUSTO; VILLANUEVA GOMILA, LUJAN; BARÓN, PEDRO

Florianopolis

Simposio; Cephalopod International Advisory Council 2012 Brazil; 2012

Coastal regions off northern and central Patagonia are characterized by the presence of quasi-permanent productivity fronts that supports a large concentration of top predators and highly productive fisheries. San Jose Gulf is not an exception, this gulf presents two regions oceanographically different separated by a frontal area. One of these region (homogeneous region "HR") is thermally homogeneous with a high rate of water exchange through its mouth with San Matias Gulf, while the other (stratified region "SR") is thermally heterogeneous (vertically stratified) with low rate of water exchange. Based on the observation of egg masses attached to the bottom, it was suggested that waters San Jose Gulf are used as spawning grounds by Loligo sanpaulensis. However, the lack of records on the presence of paralarvae in the gulf is a limitation to ensure that the gulf is a suitable spawning ground for the species. In the present work, monthly surveys were conducted in five month from October 2011 to March 2012 in San José Gulf to capture paralarvae of L. sanpaulensis. Both SR and HR were sampled in each survey. The number of plankton hauls varied between surveys: 23 hauls (11 in SR and 12 in HG) in October 2011, 16 hauls (6 in SR and 10 in HG) in November 2011, 20 hauls (9 in SR and 11 in HG) in December 2011, 22 hauls (10 in SR and 12 in HG) in February 2012, and 18 hauls (10 in SR and 8 in HG) in March 2012. In all cases, plankton samples were obtained with a 300 µm-mesh size Hensen net, 70 cm mouth diameter equipped with a flowmeter. A total of 17 paralarvae of L. sanpaulensis was captured. Paralarvae were obtained in November 2011 and in March 2012. Paralarvae were present in 31% of the hauls conducted in November 2011 and 40% of the hauls conducted in March 2012. In November 2011, the proportion of hauls with presence of paralarvae was similar between both regions (~33%), while in March 2012 the proportion of hauls with paralarvae was higher in SR (50%) than in HR (25%). This is the first report of paralarvae of L. sanpaulensis in waters of San José Gulf. Evidently, the gulf is a suitable habitat for embryonic development during austral spring and summer. Paralarvae were found in two months of the five sampled, it suggests that individuals spawn in discrete pulses. However, this should be taken with caution since only one year was sampled. Paralarvae were present in SR and in HR showing no preferences for determined oceanographic condition.