Age, maturation, and population structure of the Humboldt squid Dosidicus gigas off the Peruvian Exclusive Economic Zones

Age, maturation and population structure of the Humboldt squid Dosidicus gigas were studied based on random sampling of the Chinese jigging fishery off the Peruvian Exclusive Economic Zones （EEZ） during 2008-2010. Estimated ages ranged from 144 to 633 days, confirming that the squid is a short-lived species with longevity no longer than 2 years. Occurrence of mature females and hatching in each month indicated that Humboldt squid spawned year-round. Back-calculated hatching dates for the samples were from January 22^nd, 2008 to April 22nd, 2010 with a peak between January and March. Two size-based and two hatching date-based populations could be defined from mantle length （ML） at maturity and back-calculated hatching dates, respectively. Females matured at a larger size than males, and there was a significant difference in ML at maturity between the two hatching groups （P〈0.05）. The waters adjacent to 1 l^S off the Peruvian EEZ may be a potential spawning ground. This study shows the complexity of the population structure and large variability in key life history parameters in the Humboldt squid off the Peruvian EEZ, which should be considered in the assessment and management of this important resource.

The impact of spatial scale on local Moran's I clustering of annual fishing effort for Dosidicus gigas offshore Peru

The spatial scale(?shing grid) of ?sheries research af fects the observed spatial patterns of?sheries resources such as catch-per-unit-ef fort(CPUE) and ?shing ef fort. We examined the scale impact of high value(HH) clusters of the annual ?shing ef fort for Dosidicus gigas of fshore Peru from 2009 to 2012.For a multi-scale analysis, the original commercial ?shery data were tessellated to twelve spatial scales from 6′ to 72′ with an interval of 6′. Under these spatial scales, D. gigas clusters were identi?ed using the Anselin Local Moran's I. Statistics including the number of points, mean CPUE, standard deviation(SD),skewness, kurtosis, area and centroid were calculated for these HH clusters. We found that the z-score of global Moran's I and the number of points for HH clusters follow a power law scaling relationship from2009 to 2012. The mean ef fort and its SD also follow a power law scaling relationship from 2009 to 2012.The skewness follows a linear scaling relationship in 2010 and 2011 but ?uctuates with spatial scale in2009 and 2012; kurtosis follows a logarithmic scale relationship in 2009, 2011 and 2012 but a linear scale relationship in 2010. Cluster area follows a power law scaling relationship in 2010 and 2012, a linear scaling relationship in 2009, and a quadratic scaling relationship in 2011. Based on the peaks of Moran's I indices and the multi-scale analysis, we conclude that the optimum scales are 12′ in 2009 ? 2011 and 6′ in 2012, while the coarsest allowable scales are 48′ in 2009, 2010 and 2012, and 60′ in 2011. Our research provides the best spatial scales for conducting spatial analysis of this pelagic species, and provides a better understanding of scaling behavior for the ?shing ef fort of D. gigas in the of fshore Peruvian waters.

A Comparative Study of Spatially Clustered Distribution of Jumbo Flying Squid(Dosidicus gigas)Offshore Peru

We examined spatially clustered distribution of jumbo flying squid(Dosidicus gigas) in the offshore waters of Peru bounded by 78?–86?W and 8?–20?S under 0.5?×0.5? fishing grid. The study is based on the catch-per-unit-effort(CPUE) and fishing effort from Chinese mainland squid jigging fleet in 2003–2004 and 2006–2013. The data for all years as well as the eight years(excluding El Ni?o events) were studied to examine the effect of climate variation on the spatial distribution of D. gigas. Five spatial clusters reflecting the spatial distribution were computed using K-means and Getis-Ord Gi* for a detailed comparative study. Our results showed that clusters identified by the two methods were quite different in terms of their spatial patterns, and K-means was not as accurate as Getis-Ord Gi*, as inferred from the agreement degree and receiver operating characteristic. There were more areas of hot and cold spots in years without the impact of El Ni?o, suggesting that such large-scale climate variations could reduce the clustering level of D. gigas. The catches also showed that warm El Ni?o conditions and high water temperature were less favorable for D. gigas offshore Peru. The results suggested that the use of K-means is preferable if the aim is to discover the spatial distribution of each sub-region(cluster) of the study area, while Getis-Ord Gi* is preferable if the aim is to identify statistically significant hot spots that may indicate the central fishing ground.

Fishery Biology of Jumbo Flying Squid Dosidicus gigas off Costa Rica Dome

The jumbo flying squid(Dosidicus gigas) population was surveyed with the help of Chinese squid jigging vessels off the Costa Rica Dome(4°–11°N, 90°–100°W) in 2009 and 2010. The daily catch of D. gigas in the two survey cruises ranged from 0 to 5.5 t and was mostly obtained from the areas bounded by 6°–9°N and 91°–94°W and by 6°30′–7°30′N and 96°–97°W. The sea surface temperature in the areas yielding the most catch ranged from 27.5 to 29℃. The sex ratio of the total catch was 3.75:1(female: male). The mantle length of the squid ranged from 211 to 355 mm(male) and from 204 to 429 mm(female) with an average of 297.9 and 306.7 mm, respectively. In the relationship of the mantle length(mm) and body weight(g) of the squid, there was no significant difference between sexes. The female and male were at a similar maturity, and most individuals are maturing or have matured with a few females being spent. The size(mantle length) and age at the first sexual maturity were 297 mm and 195 d in females, and less than 211 mm and 130 d in males, respectively. Most of the sampled stomachs(70.6%) had no food remains. The major preys of the squids were fish, cephalopods and crustaceans, with the most abundant Myctophum orientale and D. gigas. The preys in more than 65% of the non-empty sampled stomachs evidenced the cannibalism of D. gigas. The results improved current understanding of the fishery biology of D. gigas off the Costa Rica Dome, which may facilitate the assessment and management of relative fishery resources.

Examining spatiotemporal distribution and CPUE-environment relationships for the jumbo flying squid Dosidicus gigas offshore Peru based on spatial autoregressive model

The spatiotemporal distribution and relationship between nominal catch-per-unit-ef fort(CPUE) and environment for the jumbo flying squid( Dosidicus gigas) were examined in of fshore Peruvian waters during 2009–2013. Three typical oceanographic factors aff ecting the squid habitat were investigated in this research, including sea surface temperature(SST), sea surface salinity(SSS) and sea surface height(SSH). We studied the CPUE-environment relationships for D. gigas using a spatially-lagged version of spatial autoregressive(SAR) model and a generalized additive model(GAM), with the latter for auxiliary and comparative purposes. The annual fishery centroids were distributed broadly in an area bounded by 79.5°–82.7°W and 11.9°–17.1°S, while the monthly fishery centroids were spatially close and lay in a smaller area bounded by 81.0°–81.2°W and 14.3°–15.4°S. Our results show that the preferred environmental ranges for D. gigas offshore Peru were 20.9°–21.9°C for SST, 35.16–35.32 for SSS and 27.2–31.5 cm for SSH in the areas bounded by 78°–80°W/82–84°W and 15°–18°S. Monthly spatial distributions during October to December were predicted using the calibrated GAM and SAR models and general similarities were found between the observed and predicted patterns for the nominal CPUE of D. gigas. The overall accuracies for the hotspots generated by the SAR model were much higher than those produced by the GAM model for all three months. Our results contribute to a better understanding of the spatiotemporal distributions of D. gigas off shore Peru, and off er a new SAR modeling method for advancing fishery science.

Identifying Summer/Autumn Habitat Hotspots of Jumbo Flying Squid (Dosidicus gigas) off Chile

Abundance and distribution of jumbo flying squid(Dosidicus gigas)are evidently influenced by the changes of marine environment.In this study,the maximum entropy(MaxEnt)model was applied to examine the impacts of marine environmental variables on its potential distribution,and identified habitat hotspots of D.gigas in summer and autumn along the coast of Chile.The MaxEnt model was constructed by using the fisheries data of D.gigas from summer to autumn during 2011–2017 combined with critical environmental factors including mixed layer depth(MLD),sea surface salinity(SSS),sea surface height(SSH)and water temperature at depths of 0 m,25 m,50 m,100 m,150 m,200 m,300 m,400 m and 500 m.Results showed that the actual fishing efforts of D.gigas in summer and autumn were mostly distributed in the suitable habitat,indicating that the MaxEnt model can well predict the habitat hotspots of D.gigas off Chile.The key environmental factors and their suitable ranges for D.gigas showed significant intermonthly changes from December to May.The critical environmental factors of D.gigas off Chile were MLD,SSH,water temperature at different depths in summer(Temp_25 m in December,Temp_300 m in January and Temp_400 m in February)and SSH,SSS,Temp_400 m in autumn.Our findings suggest that selecting the key environmental factors is vital to study the potential distribution of D.gigas off Chile in each month to explore its habitat hotspots.

Synchronous Variations in Abundance and Distribution of Ommastrephes bartramii and Dosidicus gigas in the Pacific Ocean

An analysis was performed in this study to investigate synchronous fluctuations in abundance and distribution of Om-mastrephes bartramii in the Northwest Pacific Ocean and Dosidicus gigas in the Southeast Pacific Ocean.The impacts of two Niño indices and regional water surface temperature on the two squids during 2006-2015 were evaluated,which possibly can explain the observed synchronicity.Catch per unit effort(CPUE)and the latitudinal gravity centers(LATG)of fishing effort were used to indi-cate squid abundance and distribution,respectively.The results indicated that both the CPUE and LATG showed highly interannual variations and synchronous fluctuation with significant negative associations between the two squid species from September to No-vember.Strong positive cross-correlations with 2-month lag was found between sea surface temperature(SST)anomaly in the Niño 3.4 and Niño 1+2 regions,which have significant linkage with the SST on the fishing ground of O.bartramii and D.gigas,respec-tively.Moreover,the proportion of favorable-SST area(PFSST)and the latitudinal location of the optimal SST for O.bartramii and D.gigas were positively correlated with the CPUE and LATG,respectively.Increased O.bartramii PFSST clearly corresponded to decreased D.gigas PFSST in phase as well as the latitudinal location of the optimal SST from September to November over 2006-2015.Our findings suggest that synchronous changes in abundance and distribution of the two squids were due to simultaneous variations in the PFSST and the latitudinal location of the optimal SST front which were affected by the SSTA changes in the Niño 3.4 and Niño 1+2 regions.

Gladius growth pattern and increment of jumbo squid(Dosidicus gigas)in the tropical Pacific Ocean

Gladius is an accepted hard tissue for determining the age,size-specific growth,and trophic dynamics of pelagic squid.However,little is known about the inter-and intra-stock variability of gladius growth pattern and increment deposition.In this study,the gladius growth patterns with somatic growth and gonad development were evaluated for two geographic stocks of the jumbo squid(Dosidicus gigas)in the tropical Pacific Ocean.The microstructure and periodicity of the gladius growth increments were also investigated.Results showed varied correlations between four gladius morphometric characteristics with dorsal mantle length,while growth in body weight almost followed a power model.Sexual gladius growth patterns occurred with gonad development,possibly due to different biological functions of these gladius parts and sex-specific energetic allocations.Gladius increments were observed formation in the stem and lateral plate and could be consistently enumerated.The daily periodicity of increment deposition,at least over 144 days old,was validated by comparing gladius increments with the ages obtained from the statoliths.The different oceanographic conditions between two areas likely influence the gladius growth and increment deposition and promote higher increment counts in squid from equatorial waters.Above all,these results provided new information on gladius microstructures and growth increment in different stocks of D.gigas and confirmed the use of this tissue for size-specific growth and age determination.

Inter-individual variation in trophic history of Dosidicus gigas,as indicated by stable isotopes in eye lenses

Isotopic signatures have been extensively used to reconstruct marine organism trophic habitat over their lifetime.In this study,sequential stable isotopic values ofδ13C andδ15N in eye lenses were measured to investigate the trophic history of Dosidicus gigas during ontogeny.A total of 281 segments from 33 lenses were examined withδ13C ranging from−20.17‰to−16.11‰andδ15N ranging from 5.15‰to 18.74‰.Sequential increasing but variableδ13C andδ15N values in eye lenses indicated that the prey used in the model had a wide range of values,it became able to consume prey from higher trophic levels,perhaps to maximize feeding success.High inter-individual differences in the range and considerable inter-individual variation in the trend of the isotopic values of the sequential segments from the nuclear to the periphery were considered to be the result of the effects of food and the best feeding strategy.These inter-individual isotopic differences in the life history of D.gigas confirmed the high degree of plasticity of feeding for this squid and its high potential to adapt to environmental change.Inter-individual differences ofδ15N values in the growth of D.gigas were more likely to be caused by differences in the baseline values of isotopes.According to the population discrimination model ofδ15N value changes during ontogeny,the D.gigas off Peru fit the model of“generalist population-generalist individuals”.

High Individual Variability in Beak Stable Isotopes of Jumbo Squid off Peruvian Exclusive Economic Zone(EEZ) Waters in the Analysis of Migratory and Foraging Ecology

Stable isotopes(δ^(13)C and δ^(15)N) have been widely used to track cephalopod habitat, migration and trophic structure. In this study, we analyzed the δ^(13)C and δ^(15)N values in 245 Dosidicus gigas beaks collected during 2009–2010 and in 2013 off Peruvian Exclusive Economic Zone(EEZ) waters. High individual variation in beak stable isotopes was shown with values ranging from-19.4‰ to-15.8‰ for δ^(13)C and from 5.0‰ to 15.1‰ for δ^(15)N. A generalized additive model(GAM) showed that latitude, mantle length and distance to shelf break significantly described the isotope variation with deviance ranging from 16.6% in δ^(13)C to 36.3% in δ^(15)N. Large variability in beak δ^(13)C values for a given size and sampling station indicated that D. gigas off the Peruvian EEZ waters migrate in different ways when they occupy a large range of habitats for their ontogeny. Low baseline δ^(15)N values suggested that spatial changes in diet trophic level may be the main determinative factor in beak δ^(15)N variation. We conclude that high variability in beak δ^(15)N values for a given set of explanatory variables indicated that D. gigas is an opportunistic predator with highly diverse dietary habitats. This study further develops our knowledge of the life history of D. gigas in such a highly dynamic region.

Using Different Standardized Methods for Species Identification:A Case Study Using Beaks from Three Ommastrephid Species

The cephalopod beak is a vital hard structure with a stable configuration and has been widely used for the identification of cephalopod species. This study was conducted to determine the best standardization method for identifying different species by measuring 12 morphological variables of the beaks of Illex argentinus, Ommastrephes bartramii, and Dosidicus gigas that were collected by Chinese jigging vessels. To remove the effects of size, these morphometric variables were standardized using three methods. The average ratios of the upper beak morphological variables and upper crest length of O. bartramii and D. gigas were found to be greater than those of I. argentinus. However, for lower beaks, only the average of LRL(lower rostrum length)/LCL(lower crest length), LRW(lower rostrum width)/LCL, and LLWL(lower lateral wall length)/LCL of O. bartramii and D. gigas were greater than those of I. argentinus. The ratios of beak morphological variables and crest length were found to be all significantly different among the three species(P < 0.001). Among the three standardization methods, the correct classification rate of stepwise discriminant analysis(SDA) was the highest using the ratios of beak morphological variables and crest length. Compared with hood length, the correct classification rate was slightly higher when using beak variables standardized by crest length using an allometric model. The correct classification rate of the lower beak was also found to be greater than that of the upper beak. This study indicates that the ratios of beak morphological variables to crest length could be used for interspecies and intraspecies identification. Meanwhile, the lower beak variables were found to be more effective than upper beak variables in classifying beaks found in the stomachs of predators.

Impacts of El Nino on the somatic condition of Humboldt squid based on the beak morphology

The Humboldt squid Dosidicus gigas has a short life span, and environmental variability plays a significant role in regulating its population dynamics and distribution. An analysis of 1 096 samples of D. gigas collected by the Chinese commercial fishing vessels during 2013, 2014, and 2016 off the Peruvian Exclusive Economic Zone, was conducted to evaluate the impacts of El Nino events on the somatic condition of D. gigas. This study indicates that the slopes of all beak variables in relation to mantle length (ML) for females were greater than those of males during 2013, 2014, and 2016, and slopes of the upper crest length and the lower rostrum length significantly differed between females and males in 2013 (P<0.05). Variation in the slopes for beak variables among years was studied;no significant difference was observed (ANCOVA, P>0.05). The Fulton's condition coefficients (K) of females and males in 2013 and 2014 were significantly greater than those in 2016 (P<0.01). The K values of females were greater than those of males in 2013, 2014, and 2016, and K values significantly differed between females and males in 2013. In normal years, the chlorophyll a (Chl a) concentration showed an N-shaped variability from January to December. However, in the El Nino period, it tended to weaken the upwelling coupled with warm and low Chl a concentration waters. We suggest that the poor somatic condition of D. gigas during the El Nino year was resulted from the low Chl a concentration in the waters, and the abundance of D. gigas would decrease due to the unfavourable environment and the lack of prey items in the El Nino year.

δ13C and δ15N in Humboldt squid beaks: understanding potential geographic population connectivity and movement

We quantified theδ^13C andδ^15N values in the lower beaks of Humboldt squid,Dosidicus gigas,collected from international waters off Costa Rica,Ecuador,Peru and Chile by Chinese squid jigging vessels during 2009,2010 and 2013.There was a significant difference in the isotopic values among regions with the lowest value off Ecuador and the highest off Chile,which were interpreted as a function of trophic effects as well as baseline values.However,constant trophic level of D.gigas across its geographic range showed that spatial variation in the baseline of primary production is the main driver responsible for the observed geographic isotope variability.Inter-regional difference and intra-regional convergence of isotope values indicated squid off Costa Rica,Ecuador and Chile belong to different geographically segregated populations,which were previously proved by integrated population identifying method.In contrast,the higher variations inδ^13C andδ^15N values in a given size group suggest the squid off Peru move and forage in different places.Moreover,potential population exchange could be responsible for the overlap of the isotope values between the squid off Peru and off Chile.On the whole,the spatial difference in isotopic values of Humboldt squid beaks improves our understanding of potential geographic population connectivity and movement.