Dolphinfish movements in the Eastern Pacific Ocean of Mexico using conventional and electronic tags

Abstract

Background: The dolphinfish, Coryphaena hippurus, is a fast-swimming, predatory fish exhibiting relatively fast growth and early maturation among marine teleosts. It is an important, potentially renewable resource throughout its global subtropical-to-tropical range. Understanding the ecology of this wide-ranging fish is critical to proper fisheries management, but studies have historically depended heavily upon aggregated catch data reported by fisheries. This study uses tagging data to explore finer scale dolphinfish movements in two subregions of the Eastern Pacific Ocean (EPO)-the west coasts of Baja California Peninsula (WBC) and Oaxaca (OAX), Mexico. Results: Adult dolphinfish (fork length 66-129 cm) were tagged with conventional (n = 132 tags) and electronic tags (n = 30 tags, miniPAT) between 2010 and 2014. Recapture rate of conventional tags was 4.5% with a maximum days of liberty of 141 days (mean = 56 d); 20 electronic tags reported but all did so prior to programmed release dates, with days at liberty ranging from 4 to 62 (mean = 24 d). Fish remained within the region they were tagged except for six fish tagged in WBC and one in OAX. Latitudinal (WBC) and longitudinal (OAX) extensions of observed fish movements (determined via a novel analytical approach) increased with days at liberty. Despite occasional deep dives (max 262 m), fish remained surface oriented with short excursions below the isothermal layer but larger OAX fish (fork length [103 cm, 120 cm]) inhabiting warmer waters (sea surface temperatures (SST) > ~ 26 °C) spent more time below the isothermal layer than smaller fish (fork length [90 cm, 112 cm]) inhabiting colder WBC surface waters (SST > ~ 22 °C). Conclusions: This study reveals movements of dolphinfish that infer regional differences in thermal habitat utilization and displacement over time. This inference evokes questions important to fisheries management regarding the three-dimensional extent of the dolphinfish's realized thermal niche, its population structure, and the spatiotemporal connectivity of its habitats within the multinational EPO. With improved tag retention, longer deployments should capture increasing displacements along observed axes (N/S vs. E/W); the orientation of seasonal displacement axes suggest longer-distance movements would provide opportunities for reproductive mixing via trans-national migrations.

Vertical distributions of dolphinfish (Coryphaena hippurus) in the Eastern Pacific Ocean suggest variability in potential associations with floating objects

“…Tags were deployed on dolphinfish in two distant and distinct Mexican regions of the Eastern Pacific Ocean (EPO, as delineated by Harley 2015 [ 29 ]). A full description of tag deployment and geolocation processing methodology can be found in Perle et al [ 13 ]. Briefly, “Northern” tagging locations within Mexican waters were west of the Baja California Peninsula (WBC), while “southern” tagging locations occurred in the coastal waters west of Oaxaca, Mexico (OAX, Table 1 ).…”

“…Although close in proximity and connected by regional currents, the two regions present dolphinfish significantly different physical environments. The sea surface temperatures of the WBC region vary seasonally (average temperatures ranging from approximately 18°C in the months of Feb-Apr to 24°C in Aug-Sep) and are cooler than those of the OAX region (average sea surface temperatures remain approximately 26–28°C throughout the year) [ 13 ]. Vertical characteristics of the water column also differ.…”

“…Vertical characteristics of the water column also differ. The isothermal depth (i.e., the maximum depth at which the temperature remains within 0.8°C of the average temperature of the upper 5 m) is significantly deeper in the WBC than in the OAX [ 13 ]. The oxygen minimum zone (OMZ) is also deeper in the WBC than in the OAX [ 32 ].…”

“…With its circumtropical distribution (limited to sea surface temperatures between 19°C–31°C; [ 13 ]), early maturation (within the first year; [ 14 , 15 ]), fast growth rates [ 15 ] and high food value [ 16 ], dolphinfish have the potential to serve as a sustainable source of protein for a growing human population [ 17 ]. Dolphinfish comprise a large component of bycatch in the worldwide purse seine fisheries [ 1 , 4 , 5 , 8 , 18 , 19 ].…”

“…Tracking studies have provided insights into the behavior of dolphinfish at known FADs [ 25 , 26 ], but little is known about the frequency, distribution, and ontogenetic patterns of its association with floating objects in general. Diving behavior of dolphinfish has been shown to be highly surface oriented [ 13 , 27 , 28 ]; however, dolphinfish are known to shift diving behavior according to whether or not they are associated with a FAD [ 26 ]. Over tracking intervals of hours to several days, Whitney et al [ 26 ] found dolphinfish occupied unique depth distributions when associated with observed FADs versus when not.…”