Development and validation of 107 SNP markers in Todarodes pacificus (Ommastrephidae)

Todarodes pacificus is a commercially important squid species; however, there is little information available regarding the population genetics of this species and effective molecular markers are still unavailable. In the present study, 107 novel single nucleotide polymorphism (SNP) markers were developed using Genotyping-by-Sequencing (GBS). The observed and expected heterozygosities ranged from 0.0345 to 0.5862 and 0.0339 to 0.4994, respectively. The polymorphism information content ranged from 0.0333 to 0.3747. Among these SNPs, all loci have been confirmed to fit the Hardy-Weinberg equilibrium (p > 0.05). The novel SNPs developed in this study will be helpful for the genetic conservation and scientific management of Todarodes pacificus.

Quality Index Method for Freshness Assessment of Chilled Japanese Flying Squid (Todarodes pacificus)

Aims: To develop and apply a quality index method (QIM) scheme for evaluating the freshness and estimating the shelf life of raw whole Japanese flying squid (Todarodes pacificus) stored at low temperatures. Study design: A QIM scheme was developed through pre-observation and formation of a preliminary scheme, finalization of the protocol and training of judges. The scheme was then applied to evaluate the freshness of squid in comparison with control methods, which were quantitative descriptive analysis (QDA), Torry scoring, and total viable count (TVC) determination. Place and duration of study: Nha Trang University, Vietnam, between February and June 2012; and from November 2019 to January 2020. Methodology: A total of 399 Japanese flying squids (Todarodes pacificus) of 50-70 g stored at 0-2°C were used in the study. Seven judges engaged in the QIM establishment and application. Control methods were QDA, Torry and TVC check. Principle component analysis (PCA) was used for studying the dataset main variance. Partial least square regression (PLS-R) was carried out to evaluate the possibility to predict storage time of the developed QIM scheme. Results: The formulated QIM scheme for Japanese flying squid stored at low temperatures composed of 8 parameters, which are odour, eyes, skin pigment, skin elasticity, body shape, body texture, ink sac integrity, and head-body connection, forming a quality index (QI) range of 0-15. The PLS-R showed that the developed QIM protocol could give a shelf life estimation accuracy of ± 1.0 day if 7 squids from each batch were evaluated. The PCA showed that QDA parameters clustered into good and bad attribute groups, which characterised flesh and old/spoilt squid, respectively. QDA, Torry and TVC results revealed a maximal squid shelf life of 12 days at 0-2 °C. Conclusion: The QIM scheme for chilled Japanese flying squid (Todarodes pacificus) could be used to estimate the remaining shelf life of the product with the precision of ± 1.0 day, using at least 7 squids of the same storage time for assessment. Squid exhibited a shelf life of 12 days at 0-2 °C.

Influence of Spawning Ground Dynamics on the Long-Term Abundance of Japanese Flying Squid (Todarodes pacificus) Winter Cohort

Japanese flying squid (Todarodes pacificus) is one of the most commercially important resources in the Pacific Ocean and its abundance is largely affected by environmental conditions. We examined the influence of environmental factors in potential spawning grounds of the winter cohort, approximated from Japanese and South Korean catch and catch per unit effort (CPUE) data of Japanese flying squid. Annual spawning ground dynamics were constructed using sea surface temperature (SST), submarine elevation and mean Kuroshio axis data from 1979 to 2018. Based on these information, we generated a suite of spawning ground indices including suitability SST-weighted area of potential spawning ground (SSWA), mean values (January–April) of suitable SST (MVSS), and the meridional position (MP) of SST isolines (18–24°C). Comparable interannual-decadal variability patterns were detected between the squid abundance and spawning ground indices, with abrupt shifts around 1990/1991 and in recent decades. In particular, the Pacific Decadal Oscillation is negatively correlated with spawning ground indices, suggesting its role in regulating the environmental dynamics in the area. Further, the gradient forest model underpinned the importance of SSWA, SSWA_Lag1 and MVSS_Lag1 on squid abundance. The CPUE is also shown to be a better abundance index than the annual catch in modeling the species’ response to environmental variability in its spawning grounds. Our findings suggest that it is imperative to pay more and timely attention to the relationship between the abundance of Japanese flying squid and environmental changes, especially under adverse environmental conditions.

Current state of resources for japanese flying squid Todarodes pacificus in the northwestern Tatar Strait (Japan Sea)

Data on commercial catches of japanese flying squid Todarodes pacificus in the northwestern Tatar Strait in 2003–2019 are analyzed. To assess the resours status in the study area, the relative number (individuals per jigger winch per hour) and biomass (kilograms per vessel per day) marks recognized to be the most applicable winch per hour or the catch in kg per vessel per day. The average CPUE value was 35.6 ± 3.6 ind./winch/hour; increasing trend of CPUE is observed (α = 1.5 ± 0.6, r2 = 0.3, p < 0.03). The squid abundance decreased slightly in the last 2 years, with CPUE decreasing to 28 ind./winch/hour in 2019, though the squid biomass was relatively stable (average CPUE 582.0 ± 45.8 kg/vessel/day) — decreased number of caught individuals was compensated by individual body weight increasing. Long-term tendency to the body weight increasing was noted: the average body weight was 205.0 ± 4.0 g in 2004, 256.0 ± 3.5 g in 2012, and 297.0 ± 6.3 g in 2019. Possible climate change influence on the squid population was discussed. Because of warming in the reproductive area of T. pacificus in the southern Japan Sea, SST in the spawning period reached 20–25 оC and exceeded the value optimal for reproduction and larvae development (15–23 оC), so the squid abundance decreased. On the contrary, in the northern Japan Sea (in the Tatar Strait) the warming caused better conditions for the squid feeding: the higher zooplankton biomass in this area was observed under SST 13–18 оC that is reached every year recently. On the other hand, the Tsushima Current intensifying promoted active migrations of T. pacificus to the northwestern Tatar Strait. These factors of climate warming ensure favorable environments for northward migrations of T. pacificus and forming of dense feeding aggregations in the northwestern Tatar Strait that allows to expect good conditions for the squid fishery in this area in the nearest future.