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

Abstract

Floating objects play a pivotal role in pelagic ecosystems by serving as shelters, meeting points, cleaning stations, nurseries, and feeding grounds. The abundance of these objects is increasing globally in the form of flotsam, plastics, discarded or lost fishing gear, and fish aggregating devices (FADs) deployed by commercial fisheries. However, it is difficult to measure how often and in what ways fish interact with floating objects in pelagic environments. Dolphinfish (Coryphaena hippurus) is prevalent among the fish species that associate with floating objects, but the extent to which dolphinfish utilize them is unclear. This study applies existing knowledge of FAD-associated dolphinfish diving behavior to identify periods of potential association with floating objects in a remote telemetry dataset of 23 fish with a total of 678 days at liberty spanning two distinct regions within the Eastern Pacific Ocean. Fish inhabiting waters off the western coast of Baja California Sur, Mexico spent significantly more time exhibiting behavior indicative of association with floating objects than those off the coast of Oaxaca, Mexico. When not exhibiting this behavior, dolphinfish in both regions occupied similar vertical habitats, with western Baja fish utilizing more of the water column than Oaxaca fish. Observed regional differences in behavior were coincident with regional differences in size (Oaxaca fish fork lengths ranged from 103 to 118 cm (mean = 110 cm), while Baja fish ranged from 85 to 106 cm (mean = 93 cm)). Although larger fish in the Baja region displayed behavior consistent with smaller Baja fish, future studies should investigate whether the observed regional differences are due to (i) size, (ii) sex, (iii) oceanography, or (iv) availability of floating objects. Dolphinfish are an important mid-trophic level predator and potentially sustainable fishery resource. Understanding their behavior and use of floating objects is of both ecological and economic importance–particularly in the context of expanding international FAD-based fisheries. Our study suggests dolphinfish spend a large amount of their time exhibiting potential floating object associated behavior, and this could influence their population structure and growth.

Movement and population dispersal of dolphinfish (Coryphaena hippurus) across the Eastern Tropical Pacific inferred from carbon and nitrogen stable isotope analyses

“…Niche metrics were lower for juvenile dolphinfish relative to adults. This difference is consistent with the expected reduced mobility of juveniles in relation to adults, as young dolphinfish tend to remain in areas for longer periods (up to 5 months) (Kraul, 1999) and spend more time associated with objects such as Sargassum or fish aggregating devices (FADs), whereas larger individuals are more commonly unassociated (Farrell et al, 2014;Ortega-Garcia et al, 2022).…”

“…Niche metrics were lower for juvenile dolphinfish relative to adults. This difference is consistent with the expected reduced mobility of juveniles in relation to adults, as young dolphinfish tend to remain in areas for longer periods (up to 5 months) (Kraul, 1999) and spend more time associated with objects such as Sargassum or fish aggregating devices (FADs), whereas larger individuals are more commonly unassociated (Farrell et al ., 2014; Ortega‐Garcia et al ., 2022). Juveniles, which grow more rapidly than adults (Moltó et al ., 2020), would likely have faster muscle stable isotope turnover rates and so reach isotopic steady state with local food webs sooner than adults (Thomas & Crowther, 2015).…”