Fine‐scale movements of the swordfish Xiphias gladius in the Southern California Bight

Abstract

This study reports on the fine-scale movements of swordfish (Xiphias gladius) outfitted with pop-off satellite archival transmitters (PSATs) in the Southern California Bight (SCB). PSATs were deployed on basking swordfish using traditional harpoon methods from 2004 to 2006. Transmitters were programmed for short-term deployment (2-90 days) and re-acquired using a signal direction finder. High-resolution (min )1 ) depth and temperature data from nine swordfish (approximately 45-120 kg) were collected (>193 days). All swordfish displayed diurnal vertical movements similar to those reported for other geographic locations. The dominant diurnal movement pattern entailed swordfish remaining below the thermocline (>68 ± 15 m) during the day and near the surface, within the upper-mixed layer, at night. Collectively, the average daytime depth (±SE) was 273 ± 11 m and the average night depth 31 ± 5 m. Three distinct vertical behaviors were recorded: 35% of the records following a strict diurnal pattern, with the entire day below the thermocline and the entire night near the surface; 52% of the records revealed routine surface-basking events during the day, with an otherwise similar distribution at night; and 13% of the records exhibited surface-oriented activity during the day and night. Surface basking (<3 m during the day) was recorded for eight individuals and occurred on 131 of the 193 days (68% of the dataset). Collectively, surface basking accounted for 8% of the total daytime records. The relevance of these vertical behaviors to SCB fisheries is discussed.

Modeling swordfish daytime vertical habitat in the North Pacific Ocean from pop-up archival tags

“…Holts et al (1994) acoustically tracked one swordfish in the Southern California Bight for 24 h. Takahashi et al (2003) recovered an archival tag deployed on a swordfish off the coast of Japan and examined vertical movement patterns and inferred possible tracks for the 11 mo deployment. Sepulveda et al (2010) presented observations from 9 pop-up satellite archival tags (PSATs) that were deployed and recovered in the Southern California Bight, with deployments ranging be tween 1 and 89 d. Dewar et al (2011) compiled observations from 9 and 15 swordfish tagged in the central and eastern North Pacific, respectively (8 of which, dataset CA1, are also part of this study), with fish being at liberty for 5 to 287 d. Common results across all studies are diel vertical movement patterns with occasional basking events, more frequently observed nearshore. The influence of light, temperature, and oxygen on daytime and night-time depths were also investigated (Dewar et al 2011).…”

A Principal Component Analysis of Vertical Temperature Profiles for Tracking Movements of Large Pelagic Fishes

“…The data retrieved has been critical to understanding the physical and physiological variables that relate fish behavior to its surrounding environment (Arnold and Dewar, 2001). Using electronic pop-up satellite tag (PSAT) technology, prior studies have shown swordfish moving against light so that during daylight hours they are found predominantly below the thermocline (300-1000 m), while night hours are spent above the thermocline in near-surface waters (Sepulveda et al, 2010;Lerner et al, 2013). These tagging studies also show that swordfish usually descend to depth one hour before sunrise and ascend after sunset.…”

“…Swordfish Xiphias gladius Linneaus, 1758 is a monogeneric species found circumglobally in tropical, subtropical, and temperate pelagic waters, where it supports numerous commercial fisheries (Sepulveda et al, 2010). The movement of swordfish is one of the most complex among pelagic fishes (Dewar et al, 2011).…”

“…The movement of swordfish is one of the most complex among pelagic fishes (Dewar et al, 2011). Previous swordfish tagging studies in the Atlantic, Pacific, and Mediterranean Sea have revealed large horizontal and vertical distribution patterns that vary considerably with season, gender, and ocean basin (Sedberry and Loefer, 2001;Neilson and Smith, 2010;Sepulveda et al, 2010;Dewar et al, 2011). Pop-up satellite archival tags (PSAT) are integrated with the combined technology of satellite telemetry and archival data storage tags.…”

“…These tagging studies also show that swordfish usually descend to depth one hour before sunrise and ascend after sunset. This is referred to as crepuscular diving behavior, and is a typical foraging strategy strongly associated with movement of the deep sound scattering layer (Sepulveda et al, 2010;Dewar et al, 2011). PSATs archive ambient light-level data, which are often used to estimate geolocation.…”