Distribution and Habitat Associations of Billfish and Swordfish Larvae across Mesoscale Features in the Gulf of Mexico

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.

鱼卵仔鱼调查（Ichthyoplankton surveys）于2006至2008年的三年周期内，在墨西哥湾北部（northern Gulf of Mexico, NGoM）的表层水域开展，旨在明确该区域作为旗鱼（Istiophorus platypterus）、蓝枪鱼（Makaira nigricans）、白枪鱼（Kajikia albida）及剑鱼（Xiphias gladius）早期生活栖息地的相对价值。
夏季调查中，旗鱼为采集到的优势旗鱼科鱼类，37.5%的采样站位检出旗鱼仔鱼。蓝枪鱼与白枪鱼仔鱼的检出站位占比分别为25.0%与4.6%，剑鱼的检出站位占比为17.2%。研究发现了高产区域，旗鱼的最大密度估计值（22.09尾/1000 m²）显著高于其余三个物种：蓝枪鱼（9.62尾/1000 m²）、白枪鱼（5.44尾/1000 m²）及剑鱼（4.67尾/1000 m²）。
旗鱼科鱼类与剑鱼仔鱼的分布及丰度存在时空差异，通过广义可加模型（Generalized Additive Models, GAMs）分析显示，多项环境变量——海面温度、盐度、海面高度、与环流（Loop Current）的距离、流速、水深及马尾藻（Sargassum）生物量——均为具有显著影响的变量。
墨西哥湾北部的中尺度特征会影响旗鱼科与剑鱼仔鱼的分布和丰度，锋面区域或邻近环流的区域通常具有更高的仔鱼密度。四种物种的栖息地适宜性均与其所处水团的物理化学属性密切相关，在水温较低、盐度较高的陆坡水域中，仔鱼的观测丰度更高。
本研究结果凸显了墨西哥湾北部作为旗鱼科鱼类与剑鱼早期栖息地的重要价值，同时可为评估人为活动（即深水地平线漏油事件（Deepwater Horizon oil spill））对大西洋旗鱼科及剑鱼种群的影响提供宝贵的基准数据。