Remote Predictions of Mahi-Mahi (Coryphaena hippurus) Spawning in the Open Ocean Using Summarized Accelerometry Data

Abstract

Identifying complex behaviors such as spawning and fine-scale activity is extremely challenging in highly migratory fish species and is becoming increasingly critical knowledge for fisheries management in a warming ocean. Habitat use and migratory pathways have been extensively studied in marine animals using pop-up satellite archival tags (PSATs), but high-frequency data collected on the reproductive and swimming behaviors of marine fishes has been limited by the inability to remotely transmit these large datasets. Here, we present the first application of remotely transmitted acceleration data to predict spawning and discover drivers of high activity in a wild and highly migratory pelagic fish, the mahi-mahi (Coryphaena hippurus). Spawning events were predicted to occur at nighttime, at a depth distinct from non-spawning periods, primarily between 27.5 and 30°C, and chiefly at the new moon phase in the lunar cycle. Moreover, throughout their large-scale migrations, mahi-mahi exhibited behavioral thermoregulation to remain largely between 27 and 28°C and reduced their relative activity at higher temperatures. These results show that unveiling fine-scale activity patterns are necessary to grasp the ecology of highly mobile species. Further, our study demonstrates that critical, and new, ecological information can be extracted from PSATs, greatly expanding their potential to study the reproductive behavior and population connectivity in highly migratory fishes.

The Effects of Temperature Acclimation on Swimming Performance in the Pelagic Mahi-Mahi (Coryphaena hippurus)

“…Results from this study generally agree with previous reported mahi distributions (see Introduction). Although fish in the present study were tested at an earlier age than wild-tagged adults, our results also tended to align with thermal ranges reported from PSAT data obtained from adult wild mahi (Schlenker et al, 2021). This, combined with the large habitat usage overlap across life stages of mahi (most time spent in surface waters), suggests that physiological performance observed in the present study may provide insight into thermal habitat utilization patterns of larger adults that are logistically difficult to test in laboratory settings.…”

“…Pharmacological blockade of the sarcoplasmic reticulum (SR) did not change contractile force between ∼21-26 • C, but was effective at temperatures below 20 • C, suggesting that mahi have the ability to recruit additional intracellular calcium needed for contraction at low temperatures, but are generally less reliant on the SR for contraction between ∼21-26 • C (Galli et al, 2009). Temperatures below 20 • C where SR recruitment would occur, would likely only be transient based on behavior of satellitetagged wild mahi (Merten et al, 2014b;Schlenker et al, 2021). Another recent study examining mitochondrial function in adult mahi reared close to 26 • C and assayed at 20, 26, and 30 • C, found that heart mitochondria were more sensitive when compared to those from the red muscle, and showed reduced phosphorylation efficiency as temperatures increased (Lau et al, 2020).…”

“…Mahi-mahi (Coryphaena hippurus) (referred to herein as "mahi") are an ecologically and economically important species that are circum-globally distributed (Palko et al, 1982). Mahi have large metabolic demands and are highly migratory, grow rapidly, and spawn frequently (Palko et al, 1982;Benetti et al, 1995a;Brill, 1996;Oxenford, 1999;Merten et al, 2014a;Stieglitz et al, 2017;Schlenker et al, 2021). Most life stages can be found in either open pelagic waters or associated with Sargassum brown algal mats floating in the surface (Casazza and Ross, 2008).…”

“…Larval mahi have been found year round in the Gulf of Mexico using ichthyoplankton surveys, but tend to be caught more frequently at temperatures above 24 • C but below 29 • C (Ditty et al, 1994;Kitchens and Rooker, 2014). Also, predicted spawning events for wild fish primarily occurred between 27.5 and 30 • C, which provides some insight in the habitat into which early development occurs (Schlenker et al, 2021).…”

“…Such changes could introduce a selective pressure, and/or lead to alterations in habitat use if swim performance and aerobic capacity decline at high temperatures. Limited laboratory data (Szyper and Lutnesky, 1991;Mager et al, 2018), and PSAT data showing that mahi spend little time beyond 31 • C despite access to warmer temperatures (Schlenker et al, 2021) suggests these changes may already be occurring. Given current knowledge from catch rates and PSATs, we hypothesized that mahi acclimated to the lowest (20 • C) and the highest (32 • C) temperatures would show declines in aerobic scope and swimming performance.…”