Elsevier

Journal of Marine Systems

Volume 179, March 2018, Pages 31-37
Journal of Marine Systems

Opportunistic acoustic recordings of (potential) orangeback flying squid Sthenoteuthis pteropus in the Central Eastern Atlantic

https://doi.org/10.1016/j.jmarsys.2017.11.003Get rights and content

Highlights

  • Opportunistic visual detection of orangeback squid in the Central Eastern Atlantic.

  • Previously unobserved acoustic echotraces in the echograms likely from squid.

  • Frequency response, swimming speed and behaviour agreesagree with squid literature.

  • Mesopelagic fish layers are also described and acoustically analyzed.

  • This study provides more insight into the migrating behaviour of oceanic squids.

Abstract

Squids are fast swimmers that are difficult to catch by nets and to record with echosounders in the open ocean. A rare detection of orangeback flying squid Sthenoteuthis pteropus in the Central Eastern Atlantic Ocean off the coast of Senegal was accomplished during the MAFIA oceanographic survey carried out between Brazil and the Canary Islands in April 2015. Although net sampling did not yield any subadult or adult individuals, dozens were visually detected from the vessel jumping out of the water at night and displaying their characteristic dorsal photophore patch. A few squids were caught with fishing lines and identified at the species level. The acoustic echograms revealed distinctive previously unobserved acoustic echotraces that seemed to be caused by those squids, which were the only new species detected at that station (over a bottom depth ranging from 4010 to 5215 m, between 10° 45 N 22° 41 W and 10° 53 N 22° 40 W). The acoustic response and swimming behaviour shown by those echotraces reinforced this hypothesis. The (potentially) squid recordings dove rapidly (0.19 m/s to 0.48 m/s) from around 10 m below the mesopelagic fish layer, which had migrated to the subsurface at night (35 m depth), to depths of 70–95 m, and swam upward, apparently attacking fish from below. The morning squid migration to deeper waters (250–300 m) was also recorded acoustically. Downward movements of squid swimming at speeds of 0.22 m/s were calculated from the echogram, while the mesopelagic migrating fish swam at 0.27 m/s reaching 250 m depth. Sv120  Sv38 averaged 2.7 ± 3.2 dB for the squid echotraces while the mesopelagic layer showed values of  −8.8 ± 0.9 dB. These ranges agreed with values in the literature and from theoretical models. This study provides more insight into the migrating behaviour of oceanic squids, a species group that is poorly represented in the acoustic literature due to challenges in studying them.

Introduction

Oceanic squids have wide geographical ranges, from polar regions to the tropics Jereb and Roper, 2010, Arkhipkin et al., 2015. Squids are ecologically important as major predators, but are also vital as the prey of valuable commercial fish species and many endangered marine animals like whales, seals, and sharks (Boyle and Rodhouse, 2005). They serve as an important trophic link between small mesopelagic organisms and top vertebrate predators Gilly et al., 2006, Coll et al., 2013 Despite their importance in marine food webs, there is a lack of knowledge regarding their behaviour and daily rhythms (Watanabe et al., 2006). Squids are difficult to catch with nets (Clarke, 2006), which may be related to the considerable differences between the composition of trawl catches and what is found in the stomach contents of predators (Hoving et al., 2014). They are rarely detected acoustically, except for large individuals or aggregations in shallow waters or enclosed bays Benoit-Bird and Gilly, 2012, Benoit-Bird et al., 2008, Jefferts et al., 1987, Vaughan and Recksiek, 1979. In addition, several studies have been carried out in the Pacific Ocean to estimate their scattering properties Chen et al., 2013, Jefferts et al., 1987, Jones et al., 2009, Kang et al., 2005, Lee, 2013, Lee et al., 2012, Zhang et al., 2015.

The orangeback flying squid Sthenoteuthis pteropus (Fig. 1) is an opportunistic short-lived carnivore, among the fastest growing squids (Merten et al., 2016) that inhabits the Central Eastern Atlantic Ocean between 42°N ° N and 36°S ° S and surface water temperatures ranging from 16 to 32°C  ° C, usually above 20 to 22°C  ° C (Jereb and Roper, 2010). In the current study, we present an analysis of opportunistic field data of a rare and difficult-to-observe event. Visual detections of flying squids coincided with new acoustic echotraces detected on echograms carried out during a survey crossing the Central Eastern Atlantic. Several indications suggested that squids were producing those acoustic echotraces. This work tests this hypothesis based on acoustic properties and swimming behaviour. To our knowledge, this is the first recording of acoustic data showing the natural behaviour of flying squid aggregations in the open ocean.

Section snippets

Material and methods

Acoustic data were recorded in April 2015 during the “Migrants and Active Flux In the Atlantic Ocean” (MAFIA) survey from the Brazilian coast to the Canary Islands on board the RV Hesperides, along the track shown in Fig. 2, alternating 24-hour 24-h navigation with 24-h stations. Mesopelagic fishes were caught by means a midwater trawl, the “Mesopelagos” net, with a mean mouth opening of 5 ×7 5 × 7  m and a total length of 58 m (more information in Olivar et al., 2017). Fishing lines were deployed

Results

Hundreds of individual orangeback squid were observed at station 8 from the vessel deck at night, jumping and flying above the water’s surface, and four individuals of 24, 25, 26 and 30 cm mantle length (ML) were caught with fishing lines and identified at the species level. The station at which squids were detected showed a clear oceanographic front, with surface temperatures descending from 26° C  ° C at station 7 to 22° C  ° C at station 9 (Fig. 2), and a maximum surface salinity (38.8 psu), 3.1

Discussion

An opportunistic visual detection of the squid Sthenoteuthis pteropus took place at an oceanic station in the Central Eastern Atlantic close to Senegal and Cape Verde. The visual detection and identification of squid in subsurface waters concurred with previously unobserved echotraces detected on the echograms recorded at 38 and 120 kHz. A few individual squid were caught with a fishing line, having lengths between 24 and 30 cm, sizes that fall into the lower size range of mature female

Conclusion

An opportunistic visual detection of orangeback squid flying out of the water at night in the Central Eastern Atlantic coincided with previously unobserved acoustic echotraces detected on echograms. Acoustic properties, behaviour, swimming speeds and hydrography in the area are consistent with these echotraces being produced by these squid species. This manuscript provides more insight into the acoustic properties (which allow their identification on echograms) and natural behaviour of oceanic

Acknowledgments

The authors are grateful to the crew and technicians on board the R/V Hesperides for their help during the survey, and to all colleagues who participated in the survey. This research was funded by Spanish Ministerio de Economía y Competitividad (MINECO) through project CTM2012-39587-C04-03. RV was financed by the MINECO project AGL2012-39077.

References (50)

  • M. Peña

    Incrementing data quality of multi-frequency echograms using the adaptive wiener filter (AWF) denoising algorithm

    Deep-Sea Res. I Oceanogr. Res. Pap.

    (2016)
  • J. Zhang et al.

    Hydroacoustic studies on the commercially important squid Sthenoteuthis oualaniensis in the South China Sea

    Fish. Res.

    (2015)
  • H. Arakawa et al.

    Relationship Between Underwater Irradiance and Distribution of Japanese Common Squid Under Fishing Lights of a Squid Jigging Boat 64

    (1998)
  • A. Arkhipkin et al.

    World squid fisheries

    Rev. Fish. Sci. Aquac.

    (2015)
  • I. Arnaya et al.

    Studies of Acoustic Target Strength of Squid, 5: Effect of Swimming on Target Strength of Squid

    (1990)
  • I.N. Arnaya et al.

    Studies on acoustic target strength of squid: effect of behavior on averaged dorsal aspect target strength

    Bull. Fac. Fish. Hokkaido Univ.

    (1989)
  • K.J. Benoit-Bird

    The effects of scattering-layer composition, animal size, and numerical density on the frequency response of volume backscatter, sv, ts

    ICES J. Mar. Sci.

    (2009)
  • K.J. Benoit-Bird et al.

    Coordinated nocturnal behavior of foraging jumbo squid Dosidicus gigas

    Mar. Ecol. Prog. Ser.

    (2012)
  • K.J. Benoit-Bird et al.

    Controlled and in situ target strengths of the jumbo squid Dosidicus gigas and identification of potential acoustic scattering sources

    J. Acoust. Soc. Am.

    (2008)
  • P. Boyle et al.

    Cephalopods: Ecology and Fisheries

    (2005)
  • G.B. Chen et al.

    Hydroacoustic scattering characteristics and biomass assessment of the purpleback flying squid Sthenoteuthis oualaniensis (Lesson, 1830) from the deepwater area of the South China Sea

    J. Appl. Ichthyol.

    (2013)
  • M. Clarke

    Oceanic cephalopod distribution and species diversity in the eastern north Atlantic. Arquiplago

    Life Mar. Sci.

    (2006)
  • D. Demer et al.

    Calibration of acoustic instruments

  • Echoview Software, Version 7.1

    (2016)
  • W.F. Gilly et al.

    Vertical and horizontal migrations by the jumbo squid Dosidicus gigas revealed by electronic tagging

    Mar. Ecol. Prog. Ser.

    (2006)
  • Cited by (9)

    • Unveiling the bathypelagic zone with an acoustic vertical profiler

      2023, Deep-Sea Research Part I: Oceanographic Research Papers
    • Carbon remineralization by small mesopelagic and bathypelagic Stomiiforms in the Northeast Atlantic Ocean

      2022, Progress in Oceanography
      Citation Excerpt :

      In the study area (Northeast Atlantic) two vertically separated DSLs have been detected: the migrant DSL (300–400 m depth) and the non-migrant DSL (400–600 m depth) (Peña et al., 2020). The migrant DSL is mainly composed of zooplankton and fishes (Dragesund and Olsen, 1965; Clarke, 1970; Sutton et al., 2010; Sutton, 2013; Olivar et al., 2012; Peña et al., 2018) while the scattering of the non-migrant DSL was found to correlate with the abundance of non-migrant Cyclothone braueri (Peña et al., 2014), even masking the echo of migrant layers at 38 kHz (Peña et al., 2020). Although estimating the abundance of mesopelagic fishes from net sampling is difficult due to the catch efficiency of midwater trawls (Meillat, 2012; Pakhomov et al., 2019), the abundance of non-migrant species sampled using large zooplankton nets (e.g. MOCNESS) or midwater trawls (Olivar et al., 2017, 2018) provide evidence of their relative contribution in these scattering layers.

    • Diel vertical migration and individual behavior of nekton beyond the ocean's twilight zone

      2020, Deep-Sea Research Part I: Oceanographic Research Papers
      Citation Excerpt :

      Sthenoteuthis (uncertain species complex; Jereb and Roper, 2010) are reported to aggregate in shoals at mesopelagic and upper bathypelagic depths during day (Shchetinnikov, 1992; Shulman et al., 2002; Jereb and Roper, 2010), being rather inactive while in their daytime shoals (Jereb and Roper, 2010). They ascend for foraging (primarily on myctophids) in upper layers at night (Shchetinnikov, 1992; Shulman et al., 2002; Jereb and Roper, 2010; Peña et al., 2018). The migrations to upper layers were nocturnal.

    View all citing articles on Scopus
    View full text