Extraordinary numbers of giant squid, Architeuthis dux, encountered in Japanese coastal waters of the Sea of Japan from January 2014 to March 2015

Abstract

In total, 57 giant squid, Architeuthis dux, were found between January 2014 and March 2015 in Japanese coastal waters in the Sea of Japan. Occurrences were especially high around Sado Island and in Toyama Bay. All of the squid occurred individually, and 28 were found alive. The occurrences were categorized into three groups based on distance from the shore and the depth at which they were found: (1) washed ashore on a beach or found floating at the surface close to a beach (19 individuals); (2) caught in a fixed net set in coastal waters between 50 and 150 m depths (28 individuals); and (3) caught by bottom trawl or bottom gillnet fisheries several kilometers offshore between 200 and 300 m depths (ten individuals). Two size groups were recognized, one ranging between 80 and 160 cm dorsal mantle length (DML) with a mode at 110 cm and another larger than 160 cm DML. The sex ratio in the smaller group was nearly equal and the larger group was comprised of all females. The Sea of Japan was considered to be a large natural trap for giant squid migrating through southwestern Tsushima Strait.

How old are giant squids? First approach to aging Architeuthis beaks

“…Geographical variations may influence the life-span duration from different locations and therefore the maximum ages in the present study from the largest individual measured (see Table 4) should be taken with caution, as the specimen was caught off the coast of southern Australia (Norman and Lu 1997). Nonetheless, a maximum lifespan of around 3 yrs is plausible in the species, in accordance with previous studies suggesting a longevity of 2 yrs for males and 3 yrs for females based on modal size frequency distribution of mass findings (Kubodera et al 2018) and statolith ages (e.g., Jackson et al 1991, Fernández-Núñez and Hernández-González 1995, Lordan et al 1998) in both the Pacific Ocean and the Atlantic Ocean. Guerra et al (2006) summarized the age estimation of A. dux from different approaches and suggested lifespan durations between 1 and 3 yrs.…”

“…Förch (1998) recommended that Architeuthidae be reduced to a single genus and species, A. dux, consistent with the earliest adequate systematic description. Moreover, recent mitochondrial genome analyses suggest the presence of a single species with a worldwide distribution (Winkelmann et al 2013), supporting the hypothesis that only one global species, A. dux, is valid (Kubodera et al 2018).…”

“…Gauldie et al (1994) observed a rapid early growth and an apparent asymptotic growth in size-at-time data for the 24 specimens reported around New Zealand, in which large, faster-growing squid mature, spawn, and die in advance of slower growing members of their cohort. Results from size frequencies of mass findings within a relatively short period of time (Kubodera et al 2018) suggest a very rapid growth and an inclination towards an S-growth curve, with lower growth rates in earlier and later life stages. In the present study, the results from increment analysis indicate decreasing mean widths (see Fig.…”

“…Habitat preferences and specific migrations of giant squids are poorly known; A. dux has been associated with canyons and seamounts because (1) species from such topographical structures have been found in the stomach contents of giant squid (González et al 2002), and (2) there have been many specimens collected in areas with such structures Shea 2013, Escánez et al 2018). Despite numerous records from all major oceans (e.g., Kirk 1880, Aldrich 1968, Nigmatullin 1976, Roeleveld and Lipinski 1991, Ré et al 1998, González et al 2002, Martins and Perez 2009, Roper and Shea 2013, Kubodera et al 2018, the knowledge of their biology and ecology Shea 2013, Regueira et al 2014), and recent in situ observations (Kubodera and Mori 2005, Schrope 2013, Guerra et al 2018, the life history of the giant squid is still largely unknown.…”

“…Techniques that are used for age and longevity estimations of giant squids are based on hard structure analysis of statoliths (e.g., Jackson et al 1991, Gauldie et al 1994, Brunetti et al 1998, Lordan et al 1998, size frequency analysis of mass findings (Kubodera et al 2018), growth models for projections of the life span (Grist and Jackson 2007), and isotopic analysis of tissue (Landman et al 2004). However, growth and lifespan of giant squid still remain controversial and estimates of longevity range from 2 to 3 yrs (Gauldie et al 1994, Lipiński 1997, Lordan et al 1998, Grist and Jackson 2007 to >14 yrs (Landman et al 2004).…”