Water column structure influences long-distance latitudinal migration patterns and habitat use of bumphead sunfish Mola alexandrini in the Pacific Ocean

Ching-Tsun Chang,June-Ru Chen,Brian N Popp,Michael K Musyl,Yuan-Hsing Ho,Yuuki Y Watanabe,Wei-Chuan Chiang,Shian-Jhong Lin,Chi Hin Lam

doi:10.1038/s41598-021-01110-y

Abstract

Satellite-tracking of adult bumphead sunfish, Mola alexandrini, revealed long-distance latitudinal migration patterns covering thousands of kilometers. Horizontal and vertical movements of four bumphead sunfish off Taiwan were recorded with pop-up satellite archival tags in 2019–2020. Two individuals moved northward and traveled to Okinawa Island and Kyushu, Japan and two moved southwards; crossing the equator, to Papua New Guinea and New Caledonia. During daytime, bumphead sunfish descended below the thermocline and ascended to mixed layer depths (MLD) during nighttime. The N–S migrants, however, demonstrated different habitat utilization patterns. Instead of using prevailing currents, the northward movements of sunfish cohorts exhibited extensive use of mesoscale eddies. Fish in anticyclonic eddies usually occupied deeper habitats whereas those in cyclonic eddies used near-surface habitats. On northward excursions, fish spent most of their time in regions with high dissolved oxygen concentrations. Southward movement patterns were associated with major currents and thermal stratification of the water column. In highly stratified regions, fish stayed below the thermocline and frequently ascended to MLD during daytime either to warm muscles or repay oxygen debts. These results for bumphead sunfish present important insights into different habitat use patterns and the ability to undergo long-distance migrations over varying spatial-temporal scales and features.

Highlights

Bumphead sunfish Mola alexandrini are widely distributed throughout tropical and temperate regions
From 2019 to 2020, four pop-up satellite archival tags (PSATs) were deployed on bumphead sunfish ranging from 160 to 220 cm total length (Table 1) and PSATs stayed attached for 78–240 days at-liberty
The maximum depths visited were significantly influenced by thermocline, mixed layer depths (MLD), dissolved oxygen concentration (DO), and sea surface temperatures (SST)

Summary

Introduction

Bumphead sunfish Mola alexandrini are widely distributed throughout tropical and temperate regions. Studies have shown that bumphead sunfish apparently prefer warmer waters compared to their congener (ocean sunfish, M. mola)[7,8] but movement studies are limited[7,9,10] (Table 1), and movement corridors and behaviors in the Pacific Ocean are not well characterized. Prior satellite tagging data indicated that bumphead sunfish traveled thousands of kilometers near the equatorial front and dove into mesopelagic depths (1112 m) in the Galapagos Islands[10]. A clear diel vertical movement pattern was described where tagged fish descended to the mesopelagic zone during daytime and ascended to the epipelagic zone during n ighttime[9,10]. Tracking studies of ocean sunfish indicated seasonal migration patterns to high latitudes in summer to locate preferred water temperatures and/ or areas with high prey p roductivity[3,5]. The thermocline segregates warm water near the surface from deeper and cooler water, Scientific Reports | (2021) 11:21934

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Conclusion