Time-series data collected over a four-year period were used to characterize patterns of abundance for pelagic fishes in the northern Gulf of Mexico (GoM) before (2007–2009) and after (2010) the Deepwater Horizon oil spill. Four numerically dominant pelagic species (blackfin tuna, blue marlin, dolphinfish, and sailfish) were included in our assessment, and larval density of each species was lower in 2010 than any of the three years prior to the oil spill, although larval abundance in 2010 was often statistically similar to other years surveyed. To assess potential overlap between suitable habitat of pelagic fish larvae and surface oil, generalized additive models (GAMs) were developed to evaluate the influence of ocean conditions on the abundance of larvae from 2007–2009. Explanatory variables from GAMs were then linked to environmental data from 2010 to predict the probability of occurrence for each species. The spatial extent of surface oil overlapped with early life habitat of each species, possibly indicating that the availability of high quality habitat was affected by the DH oil spill. Shifts in the distribution of spawning adults is another factor known to influence the abundance of larvae, and the spatial occurrence of a model pelagic predator (blue marlin) was characterized over the same four-year period using electronic tags. The spatial extent of oil coincided with areas used by adult blue marlin from 2007–2009, and the occurrence of blue marlin in areas impacted by the DH oil spill was lower in 2010 relative to pre-spill years.

The aim of this study was to investigate the role of the northern Gulf of Mexico (Gulf) as essential habitat of common dolphinfish (Coryphaena hippurus) and pompano dolphinfish (C. equiselis) during early life and to characterize conditions in which they were found. Eight ichthyoplankton surveys were conducted during the summer months from 2007 to 2010 in northern Gulf waters off Texas and Louisiana (26–28°N, 87–93°W), during which 1145 dolphinfish larvae were collected. C. hippurus, the dominant dolphinfish species, were collected in 57% of sampling sites with an overall mean density of 0.73 larvae 1000 m−3, whereas C. equiselis were only collected at 18% of sites with a mean density of 0.12 larvae 1000 m−3. Generalized additive models (GAMs) were used to examine the relationship between several environmental parameters and C. hippurus presence/absence and density. Both presence/absence and density GAMs indicated that catches of C. hippurus larvae increased near fronts and eddies and that increased abundances were most strongly associated with higher salinities and cooler temperatures. In addition, our models showed that C. hippurus larvae were positively associated with C. equiselis larvae, suggesting that C. hippurus and C. equiselis use similar habitats. Results of this study indicate that the Gulf may represent important spawning and/or nursery habitat of dolphinfishes and that mesoscale features and physicochemical conditions influence the distribution and abundance of C. hippurus larvae in this region.

Otolith chemistry of young-of-year (YOY) yellowfin tuna Thunnus albacares was examined to determine whether chemical signatures are distinct across major spawning areas in the Atlantic Ocean. YOY yellowfin tuna otoliths were collected from 4 locations in the Atlantic Ocean (Gulf of Mexico, Caribbean Sea, Cape Verde, and Gulf of Guinea) from 2013−2015, and trace element (Li, Mg, Mn, Sr, Zn, and Ba) and stable isotope (δ 13 C and δ 18 O) analyses were conducted to investigate regional variation in otolith chemical composition. Results indicated that significant regional differences in chemical signatures existed for each cohort of YOY yellowfin tuna investigated. Quadratic discriminant function analysis showed that nursery assignment accuracies based on otolith trace elements and stable isotopes were 64−85% for each cohort, justifying the use of these natural tracers as regional discriminators for yellowfin tuna. Significant interannual variability in regional signatures was also detected, highlighting the importance of age-class matching when using the baseline of nursery signatures to estimate the origin of sub-adult and adult yellowfin tuna. This study clearly demonstrates that baseline chemical signatures in the otoliths of YOY yellowfin tuna are distinct and can therefore serve as an effective tool for assigning older individuals to their nursery of origin, ultimately providing a way to improve our understanding of the population connectivity and mixing rates of this species in the Atlantic Ocean.