Zygochlamys patagonica fishery: by-catch data from the “Observers On Board Program”

MARIANA ESCOLAR; MARIANO J. DIEZ; ANGEL MARECOS; SILVANA CAMPODÓNICO; EDUARDO VALLARINO; LAURA SCHEJTER; CLAUDIA BREMEC

Halifax, Nova Scotia, Canada

Workshop; 16th. International Pectinid Workshop; 2007

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} p.MsoBodyText, li.MsoBodyText, div.MsoBodyText {margin:0cm; margin-bottom:.0001pt; text-align:justify; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Since the beginning of the Patagonian scallop fishery in 1996 (Res. ex-SAGPyA N°150/96), an Observers On Board Program (INIDEP) was established. Observers are technically qualified to collect information about fishing practices. This information is a useful tool to evaluate the relationships between the non-target organisms and the resource, regarding to fishery fluctuations, together with the information from annual monitoring and evaluation cruises developed by the INIDEP (Schejter and Bremec, this workshop). Considering that bottom otter trawls scrape the seabed affecting the substrate as well as densities of the benthic species (Bergman et al., 1992; Orensanz et al.1991; Lasta and Bremec, 1998), the goals of this study were to build a database with information on catches, by-catches and fishing efforts (trawls shots number by area and year) provided by the observers and to determine the invertebrates by-catch composition between 1997 and 2002 in commercial fishing grounds of Patagonian scallops in the Argentine Sea.   Data of 640 samples were selected from ~1000 data registered from fishery trawls shots carried out by the commercial fleet at the Patagonian scallop grounds (discarded data correspond to incomplete information). The material collected was gained with non-selective bottom otter trawl by the F/V “Erin Bruce”, “Mister Big”, “Atlantic Surf I”, “Atlantic Surf II” and “Atlantic Surf III”, between 1997 and 2002. In all trips, daily samples (Vol.: 10 lt.) were taken from the total catch. Abundance (when possible) and wet weight of commercial ( ≥ 55 mm total shell height) and non-commercial Patagonian scallops, by-catch species, invertebrate remains and scallop shells were measured by observers onboard. The database was made considering fishery vessel, trip, date, initial and final trawl position, depth, trawling time and speed, trawl distance, swept area and species biomass. By-catch species were grouped into major taxa (Echinodermata, Brachiopoda, Porifera, Gastropoda, Ascidiacea, Anthozoa, Decapoda, Polychaeta) and biomass (wet weight (gr.)/100 m2) was estimated for the analysis.     Although these are preliminary results, they revealed that the scallop biomass was always higher than the by catch and the scallop shells. During the study period the scallop biomass varied between 98.7 and 3161.7 gr/100 m-2 (values corresponding to San Blas bed (39°48’ S, 56°10’W) 1999 and SWTango B bed (43°30’S, 59°36’W) 1999, respectively) and the by-catch biomass between 31.9 and 503.1 gr./100 m-2 (values corresponding to San Blas 1999 and 2002, respectively). The shells biomass ranged between 0.017 and 325.3 gr/100 m-2 (values corresponding to Valdes bed (42°24’S, 58°24’W) 2002 and SWTango B bed 1999, respectively). Regarding by-catch groups, Echinodermata dominated in almost all fishing grounds, reaching approximately 86% of the total biomass. On the other hand, in Tres Puntas bed (46°47’S, 65°24’W), Brachiopoda was the most abundant group, reaching approximately 94% of the total biomass during 2002. The relative % biomass of other taxonomic groups varied in the different grounds.      Summarizing, the composition of each analyzed catch by the observers onboard, was always dominated by the resource, the Patagonian scallop. The development of a historical database of the fishery will permit future analysis of long-term ecological effects and the relationship between the fishery disturbance and the benthic community structure, taking into account areas with different levels of commercial fishing effort. These data are useful, in coincidence with detailed sampling developed annually at laboratory, and the Observers Program should be enforced.