Ichthyoplankton surveys were conducted in surface waters of the northern Gulf of Mexico (NGoM) over a three-year period (2006–2008) to determine the relative value of this region as early life habitat of sailfish (Istiophorus platypterus), blue marlin (Makaira nigricans), white marlin (Kajikia albida), and swordfish (Xiphias gladius). Sailfish were the dominant billfish collected in summer surveys, and larvae were present at 37.5% of the stations sampled. Blue marlin and white marlin larvae were present at 25.0% and 4.6% of the stations sampled, respectively, while swordfish occurred at 17.2% of the stations. Areas of peak production were detected and maximum density estimates for sailfish (22.09 larvae 1000 m−2) were significantly higher than the three other species: blue marlin (9.62 larvae 1000 m−2), white marlin (5.44 larvae 1000 m−2), and swordfish (4.67 larvae 1000 m−2). The distribution and abundance of billfish and swordfish larvae varied spatially and temporally, and several environmental variables (sea surface temperature, salinity, sea surface height, distance to the Loop Current, current velocity, water depth, and Sargassum biomass) were deemed to be influential variables in generalized additive models (GAMs). Mesoscale features in the NGoM affected the distribution and abundance of billfish and swordfish larvae, with densities typically higher in frontal zones or areas proximal to the Loop Current. Habitat suitability of all four species was strongly linked to physicochemical attributes of the water masses they inhabited, and observed abundance was higher in slope waters with lower sea surface temperature and higher salinity. Our results highlight the value of the NGoM as early life habitat of billfishes and swordfish, and represent valuable baseline data for evaluating anthropogenic effects (i.e., Deepwater Horizon oil spill) on the Atlantic billfish and swordfish populations.

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Natural dietary markers (stable isotopes and fatty acids) were used to determine the trophic structure and characterize carbon source(s) of juvenile and adult fishes associated with floating Sargassum in mid-shelf waters of the Gulf of Mexico. Stable carbon isotope ratios (δ 13 C) of 4 autotrophs (Cladophora sp., phytoplankton [based on particulate organic matter, POM], S. fluitans, S. natans) were distinct (range -16.3 to -21.0 ‰), with S. fluitans and S. natans enriched by 2 to 5 ‰ relative to Cladophora sp. and POM. Stable nitrogen isotope ratios (δ 15 N) of both S. fluitans and S. natans were depleted by 5 to 7 ‰ compared to Cladophora sp. and POM. The majority of δ 13 C values of consumers were between -16 and -18 ‰, and δ 13 C values were most depleted for juvenile shrimps, juvenile crabs and certain juvenile fishes (e.g. Aluterus heudeloti, Monacanthus hispidus, Abudefduf saxatilis, Histrio histrio, Seriola dumerili). Stable carbon isotope ratios of adult fishes varied from -16.1 to -17.5 ‰. Enrichment of δ 15 N occurred with increasing trophic position, and the lowest values were observed for juvenile crustaceans, which ranged from 6.0 to 8.7 ‰. The majority of juvenile fishes were secondary heterotrophs (δ 15 N values ca. 8.0 to 11.0 ‰), while most adult fishes were tertiary consumers with δ 15 N values ranging from 11.9 to 14.3 ‰. Carbon source estimates from a 2-source mixing model indicated that the 78% of organic matter supplied to consumers (pooled across taxa) in the Sargassum complex was derived from POM. Fatty acid signatures of the primary producers were significantly different, and were used to further evaluate organic matter contribution to Sargassum-associated consumers. C 22 polyunsaturated fatty acids (PUFAs) (22:6n-3, 22:5n-3) were most abundant in POM, while high levels of C 18 and C 20 PUFAs were observed for Cladophora sp. and Sargassum spp. (18:2n-6 and 20:4n-6, respectively). Consumer signatures were dominated by 22:6n-3, and principal component analysis indicated that fatty acid signatures of each of the 6 juvenile and 6 adult fish species were highly similar to POM and distinct from the other producers within the Sargassum complex.

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Understanding large‐scale migratory behaviours, local movement patterns and population connectivity are critical to determining the natural processes and anthropogenic stressors that influence population dynamics and for developing effective conservation plans. Atlantic tarpon occur over a broad geographic range in the Atlantic Ocean where they support valuable subsistence, commercial and recreational fisheries. From 2001 through 2018, we deployed 292 satellite telemetry tags on Atlantic tarpon in coastal waters off three continents to document: (a) seasonal migrations and regional population connectivity; (b) freshwater and estuarine habitat utilization; (c) spawning locations; and (d) shark predation across the south‐eastern United States, Gulf of Mexico and northern Caribbean Sea. These results showed that some mature tarpon make long seasonal migrations over thousands of kilometres crossing state and national jurisdictional borders. Others showed more local movements and habitat use. The tag data also revealed potential spawning locations consistent with those inferred in other studies from observations of early life stage tarpon leptocephalus larvae. Our analyses indicated that shark predation mortality on released tarpon is higher than previously estimated, especially at ocean passes, river mouths and inlets to bays. To date, there has been no formal stock assessment of Atlantic tarpon, and regional fishery management plans do not exist. Our findings will provide critical input to these important efforts and assist the multinational community in the development of a stock‐wide management information system to support informed decision‐making for sustaining Atlantic tarpon fisheries.

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A preliminary assessment of some factors influencing the density and distribution of palearctic passerine migrants wintering in the Sahel zone of West Africa, Bird Study, 43:1, 73-84,