Satellite telemetry reveals physical processes driving billfish behavior

Maxwell B Kaplan,Andrij Z Horodysky,Joel K Llopiz,Camrin D Braun

doi:10.1186/s40317-014-0020-9

Maxwell B Kaplan, Andrij Z Horodysky

Open Access

https://doi.org/10.1186/s40317-014-0020-9

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Abstract

Pop-up satellite archival transmitting (PSAT) tags are capable of storing high-resolution behavioral and environmental information for extended periods of time (approximately 1 year), rendering them especially valuable for studying highly mobile species. In this review, we synthesize published PSAT data to understand the biophysical drivers that influence movements of billfishes (families Xiphiidae and Istiophoridae). To date, over 1,080 PSATs have been deployed on billfishes, with individuals demonstrating both trans-equatorial and trans-basin movements. Using this dataset, we identify four main physical variables that drive billfish behavior: temperature, light, oxygen, and complex water mixing (e.g. fronts and eddies). Of the seven species that have been studied with PSAT technology, all exhibited a strong thermal preference for water >22°C, though vertically migrating swordfish additionally occupied waters <10°C while at depth. Ambient light levels influence vertical movements, especially those associated with foraging, as billfish possess large eyes and thermoregulatory abilities that facilitate feeding behaviors below warm surface layers. Mounting evidence suggests that some billfishes actively avoid regions with low dissolved oxygen (<3.5 mL L−1). Human-induced climate change is expected to increase the horizontal and vertical extent of hypoxic water and may further compress habitat and concentrate fishing pressure on pelagic fishes. Finally, complex submeso- and mesoscale processes provide critical habitat for spawning, larval feeding, and retention, but our understanding of these and other behavioral aspects of billfish biology remains limited. Future research efforts should leverage technical advancements while integrating existing and future tag data with chemical and physical oceanographic datasets to gain a better understanding of the relevant biophysical interactions for billfishes, thereby enhancing management capabilities for this ecologically and economically important group of fishes.

Highlights

Tag technologies Historically, insights into the behavior and ecology of large pelagic fishes in their natural environment were limited to those obtained visually and at the ocean’s surface
Swordfish, and blue marlin dominate the focus of this body of work, (Figure 1) while there were no published reports of Pop-up satellite archival transmitting (PSAT) studies on roundscale, Mediterranean, or shortbill spearfish
Four of 29 tagged fish stayed in the vicinity of the Bump for extended periods of time where numerous thermal fronts are generated by Gulf Stream deflection and upwelling. Those fish that moved away occupied regions above submarine canyons and seamounts, which exhibit complex oceanographic processes. Supporting these results, catches of swordfish are high along frontal regions in the Mid-Atlantic Bight off southern New England where Labrador Current waters interact with the Gulf Stream [133], and PSAT data indicate swordfish frequently occupy and traverse this region (Figure 2c)

Summary

Introduction

Tag technologies Historically, insights into the behavior and ecology of large pelagic fishes in their natural environment were limited to those obtained visually and at the ocean’s surface. Swordfish, and blue marlin dominate the focus of this body of work (cumulatively make up 70% of tag deployments), (Figure 1) while there were no published reports of PSAT studies on roundscale, Mediterranean, or shortbill spearfish.

Results

Conclusion