Target Strength and swimbladder morphology of Mueller’s pearlside (Maurolicus muelleri)

Abstract

In the last few years, there has been increasing interest in the commercial exploitation of mesopelagic fish and a trawl-acoustic methodology has been recommended to make estimates of abundance of these resources. This study provides relevant information on the scattering properties of a key mesopelagic fish species in the Bay of Biscay, Mueller’s pearlside (Maurolicus muelleri), necessary to convert the acoustic density into numerical abundance. The target strength (TS) of pearlside was estimated for the first time at five frequencies commonly used in acoustic surveys. A high-density filter was applied to reduce the bias derived from overlapping echoes erroneously assigned to single targets. Its relationship with fish length (b20) was also determined (−65.9 ± 2, −69.2 ± 3, −69.2 ± 2, −69.5 ± 2.5 and −71.5 ± 2.5 dB at 18, 38, 70, 120 and 200 kHz, respectively). Biomass estimates of pearlside in the Bay of Biscay during the four years of study (2014–2017) are given using the 38 kHz frequency. Morphological measurements of the swimbladder were obtained from soft X-ray images and used in the backscattering simulation of a gas-filled ellipsoid. Pearlside is a physoclist species, which means that they can compensate the swimbadder volume against pressure changes. However, the best fit between the model and the experimental data showed that they lose that capacity during the trawling process, when the swimbladder volume is affected by Boyle’s law.

Vertical stratification of environmental DNA in the open ocean captures ecological patterns and behavior of deep-sea fishes

“…Also, it has been demonstrated that eDNA shedding rates are influenced by diet, feeding activity -being up to 10-fold times higher in fed fishes than in starving ones-and lifecycle stage of the individuals (Klymus et al 2015;Hansen et al 2018). Thus, the noticeable high relative abundance of M. muelleri DNA at epipelagic depths during night may not only indicate a higher biomass but also elevated feeding activity, in line with the existing ecological knowledge on this species; M. muelleri is a very abundant myctophid in the Bay of Biscay, well-known to perform DVM in big, compact schools to feed close to the surface after the sunset (Sobradillo et al 2019).…”

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“…Orestias demersal behavior challenges the acoustic assessments, as Orestias can hide among submerged macrophytes [22] so our acoustics assessment may have been underestimated. However, the choice of the threshold (-68 dB) to observe small fish was based on Love's equation [46], which is successfully used in freshwater ecosystems [39,[43][44][45]54].…”

First Insight of Meso- and Bentho-Pelagic Fish Dynamics Around Remote Seamounts in the South Atlantic Ocean

“…Previous studies suggested the mesopelagic community in the area was dominated by pearlside (Maurolicus inventionis) a small swimbladdered fish of the Sternoptychidae family (Kalinowski and Linkowski, 1983). Therefore, biomass of pearlside was estimated based on a Target Strength/Length relationship for a similar species of the same genus, Maurolicus muelleri (Sobradillo et al, 2019). Bluenose warehou (Hyperoglyphe antarctica), was selected as the likely species dominating a bentho-pelagic aggregation observed.…”