Settlement of concave scallop Euvola vogdesi on artificial collectors in the NE coast of the Gulf of California: Seasonal changes and potential origin

GASPAR SORIA; MIGUEL LAVIN; GUIDO MARINONE

Florianopolis

Workshop; International Pectinid Workshop; 2013

In NW Mexico there are three commercially important scallop species: Argopecten ventricosus, Nodipecten subnodosus, and Euvola vogdesi. The production of both fisheries and aquaculture activities of these species fluctuated markedly over the last decades. A. ventricosus landings accounted for the majority of total captures followed by N. subnodosus and E. vogdesi. The objective of this research was to assess the natural availability of E. vogdesi larvae (optimum site locations, timing, depth variances, and intensity of settlement), needed for the development of sustainable aquaculture and conservation initiatives in the area of Puerto Peñasco. We evaluated bimonthly settlement of E. vogdesi larvae on netlon® collectors (200 x 40 cm; mesh opening = 7x12 mm) in 6 sites from June 2007 to August 2008. At each site, we deployed three vertical lines, and tied collectors at 1, 3, 5, and 7 m starting from the anchor. We characterized sea surface temperature (SST, oC) and surface chlorophyll-a concentration (SSChl, mg m-3) using monthly Aqua/MODIS satellite data for the period July 2002-September 2011. Also, we recorded bottom temperature at each site every 4 hours, and measured sea surface salinity, temperature, and dissolved oxygen every two months. We used repeated measures ANOVA to evaluate differences in the number of settled larvae between main factors, and performed one-way ANOVAs to compare larvae settlement at different depths for each site and month separately. We used an Eulerian 3-D baroclinic numerical model (mesh size of ~1.31 x 1.54 km) to estimate the velocity field of the Gulf of California based on the circulation pattern for the winter which is anti-cyclonic overall. To assess the potential origin of larvae settling in the study area we modeled the release of 4,000 passive particles (i.e. virtual larvae) from 9 localities (total 108,000) and tracked particles for up to 30 days for 3 release dates (December 2007, and January and February 2008). The maximum SST was recorded in August-September (~31 oC) and the minimum in January-February (~15 oC), while the minimum SSChl was observed in June-September (mean SSChl range = 1.5-2 mg m-3) and the maximum in January-March (mean SSChl range = 2-5 mg m-3). In winter, San Jorge Island showed the highest monthly-mean of bottom temperature (15.3 oC) compared to other sites (range 14.4-14.9 oC). At 30 days, the model predicted particles from NW localities such as Rocas Consag and El Borrascoso settling within the study area. A total of 7,014 E. vogdesi larvae settled in artificial collectors throughout the study period. Larvae settlement showed highly variable patterns between periods (repeated measures 3-way ANOVA; p < 0.001). Over all larvae settlement showed a single peak in January-February, the season with the highest SSChl concentration and the lowest temperature. During this bimonthly period, mean larvae settlement was consistently higher in San Jorge Island than in any other site. Larvae settlement decayed abruptly from April to June, and was absent in most of the collection sites in autumn. With the exemption of San Jorge Island, larvae settlement during January-February showed similar abundances at each sampling depth for each site. In San Jorge Island larvae settlement was higher at 1, 3, and 5 m than the upper level. Settlement of the concave scallop E. vogdesi larvae on artificial collectors along the area of Puerto Peñasco occurred over a short period (January-February and March-April), mainly in San Jorge Island. The collection season of E. vogdesi is constrained and the abundance of larvae collected is one order of magnitude lower than the corresponding values described for A. ventricosus for the same study area. Overall, larvae settlement showed higher recruitment abundances in winter, when primary productivity is comparatively higher than in summer. The presence of diverse settlement patterns suggest that large scale processes (seasonal reversing currents, proximity to parental stock, etc.) and local site conditions (e.g. sea water parameters and primary production) could be playing a significant role as drivers of the observed settlement patterns. The clockwise current circulation of the Northern Gulf of California during winter suggest that E. vogdesi larvae recruiting throughout January-February might be originating NW of the study area, including locations from the Baja California Peninsula, as suggested by the model.