Do western Atlantic bluefin tuna spawn outside of the Gulf of Mexico? Results from a larval survey in the Atlantic Ocean in 2013

In 2013, a larval survey was conducted north and east of the Bahamas aboard the NOAA Ship NANCY FOSTER. Sampling areas were selected based on larval habitat model predictions, and daily satellite analysis of surface temperature and ocean color. Samples were collected at 97 stations, and 18 larval BFT (Thunnus thynnus) were found at 9 stations. Six of these stations came from oceanographically complex regions characterized by cyclonic and anticyclonic gyres. Larvae ranged in size from 3.22mm to 7.58 mm, corresponding to approximately 5-12 days in age. Analysis of satellite derived surface currents and CTD data suggest that these larvae were spawned and retained in this area. Larval habitat models show areas of high predicted abundance extending east to 650 W, but the actual extent of spawning in this area remains unknown.En prens

Trophic Ecology of Atlantic Bluefin Tuna (Thunnus thynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

The present study uses stable isotopes of nitrogen and carbon (δ15Nandδ13C) as trophic indicators for Atlantic bluefin tuna larvae (BFT) (6–10mm standard length) in the highly contrasting environmental conditions of the Gulf of Mexico (GOM) and the Balearic Sea (MED). These regions are differentiated by their temperature regime and relative productivity, with the GOM being significantly warmer and more productive. MED BFT larvae showed the highest δ15N signatures, implying an elevated trophic position above the underlyingmicrozooplankton baseline. Ontogenetic dietary shifts were observed in the BFT larvae from the GOM and MED which indicates early life trophodynamics differences between these spawning habitats. Significant trophic differences between the GOM and MED larvae were observed in relation to δ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages. These low δ15N levels in the zooplankton from the GOM may be an indication of a shifting isotopic baseline in pelagic food webs due to diatrophic inputs by cyanobacteria. Lack of enrichment for δ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton— zooplankton—larval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvaeVersión del editor4,411

Larval parrotfish abundance and distribution in the U.S. Virgin Islands: a baseline for management assessments

Individual biological groups within dynamic coral reef systems are vital to overall ecosystem resilience. Herbivorous parrotfishes are no exception, as their grazing behavior assists in the success of coral recruits and reduces the impact of competitive algal growths. Despite their importance, parrotfish are also vulnerable to local overfishing in the U.S. Virgin Islands (USVI). In recent years, managers have implemented many regulations, along with specific gear and fishing bans in recent years. To assess the impact of these regulations, larval parrotfish were collected in the USVI in 2007, 2008, and 2009, as part of a comprehensive larval distribution and supply study in the area. Larvae were collected using plankton net tows, and were visually identified to the genus level. Total abundance and distribution over time and by region showed significant differences due to year, water column depth, and region. These results provide insights about likely locations of local spawning grounds, and may be used as a baseline of larval parrotfish status prior to recent regulations. During a crucial time period of overfishing of the stock, this project offers a unique fishery-independent look at the valuable parrotfish populations of the Virgin Islands.</p

Biplot of mean nitrogen and carbon stable isotopes in bluefin tuna larvae.

<p>Mean (±SE) δ¹³C versus δ¹⁵N (‰) values mesozooplankton (MESO-triangles) and bluefin tuna larvae (BFTL-circles) in Eastern Gulf of Mexico (E-GOM) (●), Western Gulf of Mexico (W-GOM) (●) and Balearic Sea (MED) (○) regions. Microzooplankton as primary consumers has been used as baseline. The ellipses represent the isotopic variance for each region, encircling the isotopic signature for the different plankton size fractions (MICRO, MESO and BFTL).</p