Ontogenetic variation of δ13C and δ15N recorded in the gladius of the jumbo squid Dosidicus gigas: geographic differences

Predatory role of the commander squid Berryteuthis magister in the eastern Bering Sea: insights from stable isotopes and food habits

“…As a result, O. bartramii are likely to encounter greater latitudinal shifts in isotope signatures over their lifetime and assimilate a wider range of δ 15 N in their tissues (Parry 2003). The work of Ruiz-Cooley et al (2010) further corroborates our findings of Berryteuthis magister trophic records. These authors reconstructed the feeding chronologies of individual Humboldt squid Doscidicus gigas using the δ 15 N signatures of proostracum sec-tions sub-sampled from squid gladii.…”

“…It is plausible that squid also shift their foraging strategy in response to changes in seasonal and/or annual prey availability. This notion is supported by the findings Ruiz-Cooley et al (2010), which suggest that the variable but increasing δ 15 N and δ 13 C along the proostracum of Doscidicus gigas gladii is an effect of prey availability and optimal foraging strategy. Feeding chronologies of squid captured in multiple seasons and years are needed to evaluate if the B. magister trophic records reflect seasonal environmental conditions or are instead an effect of sampling year (e.g.…”

“…Feeding chronologies from squid hard parts, such as eye lenses (Parry 2003) and gladii (Ruiz-Cooley et al 2010) are a valuable tool because they offer several measures of individual feeding events that are integrated over time scales intermediate to stomach content and stable isotope analysis of muscle tissue. For instance, fish lens cells are nearly ametabolic because most of the cells (all but those in the youngest, differentiating layer) lack the cellular functions of protein synthesis and catabolism (Wistow & Piatigorsky 1988, Nicol 1989, Horwitz 1992, Dove 1999).…”

Range Expansion of the Jumbo Squid in the NE Pacific: δ15N Decrypts Multiple Origins, Migration and Habitat Use

“…In British Columbia, for example, regional declines in hake abundance have been attributed to D. gigas predation [14]. However, a major puzzle regarding D. gigas range expansions is that studies to date have not been able to detect long-distance migration using bulk stable isotope ratios or electronic tagging, implying that medium to large squid move only within modest latitudinal distances (∼4° of latitude) [9], [15]. The fundamental mechanism for D. gigas expansions is therefore unclear: it is unknown whether D. gigas expanded its range into the NCCS through migration, or through passive dispersal of egg masses and paralarvae.…”

“…Natural stable isotope abundances can provide time-integrated information about the trophic position of species in a given habitat [16], [17]. In D. gigas , bulk isotope ratios from consecutive sections along gladii (internal shell) can also track ontogenetic shifts [15]. Isotope ratios from muscle indicate recent assimilated diet (<2 months), while consecutive sections along gladii represent a continuous dietary record throughout the period of time in which the gladius was formed [18], [19].…”