Novel deep-water spawning patterns of bonefish (Albula vulpes), a shallow water fish

Abstract

Coastal marine fishes that form spawning aggregations most commonly exhibit a two-point movement pattern, with locations separated by migration: home range to spawning aggregation site and return to home range. However, the bonefish, Albula vulpes, partakes in a unique three-point spawning migration. Bonefish migrate up to 80 km from shallow water home flats to form nearshore pre-spawning aggregations (PSA) before moving offshore to spawn. Although these broad patterns have previously been documented, details of the offshore spawning-associated diving behavior have yet to be rigorously examined. Using active acoustic telemetry and sonar data in 2019 in Abaco, The Bahamas, we provide a complete account of bonefish offshore spawning movements and novel deep diving behavior to 137.9 m. Bonefish were continuously observed at depths ≥ 100 m for 2 h; a time period that included multiple depth changes and culminated in a spawning ascent to 67.3 m at 0.57 m s−1. These new data on bonefish offshore movements and deep dives, coupled with CTD data, suggest that bonefish actively spawn at pycnoclines and thermoclines. Two previous tracking attempts (2013, 2018) at this location reflect spatiotemporal plasticity in spawning, a behavior counter to other aggregation forming fishes. This is the first detailed documentation of such deep spawning for a shallow water coastal fish species. The ecological motivation for diving to the deepest depths remains speculative. Future work must examine the dynamic relationship between bonefish diving behavior, spawning site selection, and oceanographic features.