Ommastrephid Squid Research Articles

Seasonal variability in the feeding ecology of an oceanic predator

Complementary approaches (stomach contents, DNA barcoding, and stable isotopes) were used to examine seasonal shifts in the feeding ecology of an oceanic predator, yellowfin tuna (Thunnus albacares, n = 577), in the northern Gulf of Mexico. DNA barcoding greatly enhanced dietary resolution and seasonally distinct prey assemblages were observed for both sub-adults and adults. In general, diet was characterized by ommastrephid squids and exocoetids in spring, juvenile fishes (i.e., carangids and scombrids) in summer, migratory coastal fishes during fall, and an increased consumption of planktonic prey (e.g., amphipods) in winter. Seasonal variability in bulk stable isotope values (δ13C, δ15N, and δ34S) was also observed, with low δ15N values and high δ34S values during late summer/early fall and high δ15N values (low δ34S) during late winter/early spring. Bayesian stable isotope mixing models corroborated seasonal diet shifts, highlighting the importance of oceanic nekton in spring/summer, coastal nekton during fall, and oceanic plankton during winter. Seasonal shifts in diet appeared to be influenced by prey reproductive cycles, habitat associations, and environmental conditions. Findings highlight the complex food web dynamics supporting an opportunistic oceanic predator and the importance of seasonal cycles in prey availability to predator resource utilization in open-ocean ecosystems.

Environmental fluctuation influences the ontogenetic dispersal and distribution of two ommastrephid squids in the Pacific Ocean

Environmental fluctuation influences the ontogenetic dispersal and distribution of two ommastrephid squids in the Pacific Ocean

Feeding ecology of the shortfin mako shark, Isurus oxyrinchus, in the Ecuadorian Pacific Ocean

Abstract Shortfin mako shark, Isurus oxyrinchus, is listed as an endangered species with declining global population. Thus, studies regarding its biology and ecology are important to recommend fishery management and conservation measures. This study aimed to determine the diet composition and feeding habits of I. oxyrinchus in Ecuadorian waters. Samples were obtained from Santa Rosa fishing port (Ecuador). The total length (LT), sex and sexual characteristics were recorded, and stomach contents were collected. A total of 142 individuals were recorded, comprising 81 females (104–295 cm LT) and 61 males (127–245 cm LT). A total of 24 prey species were identified, including crustaceans, cephalopods, teleosts and cetaceans. According to the Prey-Specific Index of Relative Importance (PSIRI), the main prey taxa were the ommastrephid squid, Dosidicus gigas (42.57%) and Sthenoteuthis oualaniensis (21.04%), followed by fish from the family Hemiramphidae (11.85%). Isurus oxyrinchus is a specialist predator that preferred a low number of prey (Bi = 0.25), both by sex (Bi; females = 0.29 and males = 0.34) and life stages (Bi; juveniles = 0.27 and adults = 0.37). The trophic overlap was medium for sexes (J = 0.54) and biological cycle phases (J = 0.42). Trophic level (TLk) was 4.47, indicating that I. oxyrinchus is a tertiary predator. This information will help in fisheries management based on an ecosystem approach, where this species fulfils an ecological role, and its interactions with other species allow us to understand how the flow of nutrients and energy occurs within an ecosystem.

Biogeographic role of the Indonesian Seaway implicated by colonization history of purpleback flying squid, Sthenoteuthis oualaniensis (Lesson, 1830), in the Indo-Pacific Ocean

As a bio]diversity hotspot, the East Indies (Coral) Triangle possesses the highest biodiversity on the earth. However, evolutionary hypotheses around this area remain controversial; e.g., center of origin, center of accumulation, and center of overlap have been supported by different species. This study aims to answer the evolutionary influence of the Indonesian Seaway on the biodiversity of the Coral Triangle by recovering the evolutionary origins of a wide-ranging ommastrephid squid (Sthenoteuthis oualaniensis) based on integrated molecular and oceanographic clues from the Indo-Pacific. Three new clades were revealed; viz., clade I from the South China Sea, clade II from the northern East Indian Ocean, and clade III from the southern East Indian Ocean. These two Indian Ocean clades formed a monophyly closely related to clade IV from the Central-Southeast Pacific. Clade VI from the central Equatorial Pacific and clade V from the northern Eastern Pacific sit in basal positions of phylogenetic trees. Ancestral Sthenoteuthis was inferred to have originated from the Atlantic Ocean and sequentially dispersed to the northern East Pacific, central Equatorial Pacific, and West Pacific through the open Panama Seaway and being transported by westward North Equatorial Current. The East Indian Ocean was likely colonized by an ancestral population of clade IV from the Southeast Pacific. Westward South Equatorial Circulation could have promoted transoceanic migration of S. oualaniensis through the wide paleo-Indonesian Seaway. Sea level regression since the Miocene and the closure of the Indonesian Seaway at 4–3 Ma were responsible for the population genetic differentiation of S. oualaniensis in the Indo-Pacific. Therefore, the Indonesian Gateway played an important role in influencing marine organisms’ migration and population differentiation through controlling and reorganizing circulations in the Indo-Pacific.

Genetic evidence for multiple mating and mixing of sperm from multiple males in the seminal receptacles of female Japanese flying squid (Todarodes pacificus)

ABSTRACT The genetic diversity of sperm and spermatangia stored by mated Japanese flying squid (Todarodes pacificus) was examined to better understand how this ommastrephid squid mates and stores sperm. Analyses were conducted using spermatangia implanted in the lips of immature squid collected in Tsugaru Strait, northern Japan, in July–August 2019, spermatangia implanted in the lips of mature squid collected in the East China Sea in April 2019, and sperm stored in the seminal receptacles of squid collected off Tosashimizu, Kochi Prefecture, Japan, in February 2019. DNA was extracted, microsatellite loci were amplified using five PCR primers, and allele peaks were analysed. Analysis of the spermatangia confirmed that females in the field mate with multiple males, suggesting that males transfer from 1 to at least 14 spermatangia in each mating. Analysis of the seminal receptacles showed that sperm from multiple males are mixed within individual sperm chambers. Spermatangia were also found implanted in the lips of males, providing evidence of same-sex sexual behaviour. To date, studies of cephalopod mating systems have focused on coastal species, and the results of this study add to our growing knowledge of more oceanic species.

Ommastrephid squid paralarvae potential nursery habitat in the tropical-subtropical convergence off Mexico

The Gulf of California and adjacent Pacific have passed through a prolonged warming period that affects the Humboldt squid D. gigas life cycle, which was the third largest fishery in Mexico until its total collapse after 2010. The aims of the present study were (i) to characterize the nursery habitat of paralarvae of the complex Sthenoteuthis oualaniensis–Dosidicus gigas (SD complex) on the basis of 1112 paralarvae collected from zooplankton trawls carried out during ten oceanographic cruises off northwestern Mexico between 2010 and 2017; and (ii) to model the seasonal and interannual variability of the nursery habitat, applying a generalized additive model (GAM) using a regional long-term (1922–2017) hydrographic database. The GAM showed significant relationships of paralarvae abundance with the seasonal average of thermocline depth, absolute salinity, and conservative temperature. The potential nursery habitat of the SD complex paralarvae showed its maximum expected abundance in the entrance of the Gulf of California during spring, when the thermocline depth was shallowest (<30 m). During summer the nursery habitat moved northward along the Pacific west coast of the peninsula. Autumn and winter were less suitable seasons for paralarvae nursery because the thermocline was deep throughout the area of study. Potential nursery habitat did not change interannually in location during La Niña conditions, but did increase the expected abundance in its southern extension. El Niño events contracted the nursery habitat near Cabo San Lucas, and caused the habitat to move northwards over both coasts of the Baja California peninsula. Despite seasonal and interannual climatic variability, two regions remained suitable habitats almost throughout the year. One was associated with coastal upwelling regions (Cabo Corrientes) and the second comprised the oceanic region of high mesoscale kinetic energy located south of Cabo San Lucas. We conclude that the potential nursery habitat of the SD complex is more coastal than oceanic, and is associated with a shallow thermocline in the tropical-subtropical convergence off Mexico. The recent anomalous warming period in this region could drive the changes in the morphology of D. gigas in the Gulf of California, given the effects of environmental variability over early stages of development throughout the adult ontogenesis.

Size Related Differences in Organic and Mineral Components of Molluscan Shell

A unique and rare event of consumption of a seabird (aviphagy) was recorded for a Southern Ocean squid in Australian waters. Petrel remains were identified in the stomach contents of a large (518 mm Mantle Length, 3.4 kg) female ommastrephid squid, Todarodes filippovae (Adam 1975) captured off the southern coast of Tasmania, Australia. The remains were identified as to being from either a fairy prion Pachyptila turtur or white-faced storm petrel Pelagodroma marina. This unique observation expands the evidence for aviphagy recorded in other cephalopods to now include squid.

Assessing Cephalopods Fisheries in the Strait of Sicily by Using Poor Data Modeling

Cephalopods, including octopuses, squids, and cuttlefishes, are exploited by both bottom trawl and small-scale fisheries (SSF) in most of the Mediterranean areas. Bottom trawl fisheries regard cephalopods as a valuable bycatch, whereas for SSF, they are among the main target species. Cephalopods account for a relatively small proportion of the total landings in the Mediterranean. However, from an economic point of view, four cephalopods, Eledone cirrhosa, Eledone moschata, Octopus vulgaris, and Sepia officinalis, account for approximately 15% of the total landing value. Despite their economic importance, there are very few stock assessments of cephalopods in the Mediterranean because it is difficult to assess them by classical age-based methods, given their short life-cycles, and highly variable growth and recruitment. The production of E. cirrhosa, E. moschata, Illex coindettii, Loligo vulgaris, O. vulgaris, S. officinalis, and Todaropsis eblanae in the waters off the south of Sicily accounts for approximately 8% of the total Mediterranean yield of cephalopods. This study presents the first attempt to assess the state of these cephalopods in the Strait of Sicily by using surplus production models. Since species-wise landing statistics may be unreliable because of their morphological similarity, some octopuses (E. cirrhosa and E. moschata) and ommastrephid squids (I. coindetii and T. eblanae) were assessed combined. Landing data and abundance indices from trawl surveys were used to describe cephalopod stock dynamics through the Bayesian State Space Schaefer model (BSM) and Surplus Production model in Continuous Time (SPiCT) models. As survey data were not considered reliable indicators of their abundance, O. vulgaris, S. officinalis, and L. vulgaris stocks were assessed using the Catch-Maximum Sustainable Yield (CMSY) model. Overall, squid and cuttlefish stocks were observed to be in healthy conditions. However, assessments of octopus stocks indicated that their condition was critical or recovering. Here, we discuss the different stock statuses in the light of evolving fisheries and environmental factors in the area over time. Although cephalopods are not a priority in the current management system of Mediterranean fisheries, the importance of these species in the food web and their relevance for SSF underline their importance and their exploitation status should be periodically evaluated.

Ommastrephid squid spawning in the North Sea: oceanography, climate change and species range expansion

The lesser flying squid (Todaropsis eblanae) and the shortfin squid (Illex coindetii) are two abundant ommastrephids of the northeast Atlantic. Spawning ground existence was inferred from the captures of mature, mated females in summer 2016–2019 and their occurrences were compared with respective oceanographic data from international surveys to gain insight into environmental predictors of their presence throughout the North Sea. Spawning T. eblanae were found in relatively cooler and more saline waters (6–8°C, 34.2–35.1 psu) in the northern North Sea linked to the Fair Isle Current and East Shetland Atlantic Inflow, whilst spawning I. coindetii occurred across the entire North Sea (mostly at 9–10.5°C, 34.1–34.8 psu). We hypothesize that a combination of water salinity and water temperature are key factors in the spatiotemporal distribution of spawning ommastrephid squids as they define water density that is crucial for pelagic egg mass to attain neutral buoyancy.

Evidence for Feeding on Seabirds by the Southern Ocean Ommastrephid Squid Todarodes filippovae

All previously known localities of Pyrgophorus parvulus (Guilding, 1828) on the Caribbean island of Montserrat were destroyed by volcanic eruptions starting in 1995. Here we document a population in a freshwater stream only indirectly affected by that eruption. Specimens collected on Montserrat are morphologically consistent with P. parvulus and 16S DNA sequences indicate genetic consistency.

What is on the menu? Feeding, consumption and cannibalism in exploited stocks of the jumbo squid Dosidicus gigas in south-central Chile

Only few studies on the feeding and cannibalism behavior of the jumbo squid have been conducted in the Humboldt Current System despite this species is currently considered an important economic resource. It is possible that the diet of this ommastrephid squid varies throughout the year, among areas and body size. Therefore, we herein collected jumbo squids from commercial catches during January to December 2014 using purse-seine nets. The stomach contents were analyzed in terms of frequency of occurrence, number, and weight of prey items. The diet composition was analyzed using Detrended Correspondence Analysis. The variation of jumbo squid diet composition was evaluated from different biological and temporal predictors (sex, maturity, body size and months), considering and analyzing cannibalism. Daily ration was estimated using three methods to calculate consumption and consumption/biomass ratio. Our results suggest that there are significant differences in diet throughout the year, among sizes, and between sexes, however, no differences were found according to the interactions of these factors, except for the interaction between sex and month. In addition, significant differences were detected for each factor (sex, month and body size) when evaluating cannibalism, although these differences were only significant when factors were evaluated independently. Body size was the best predictor of diet composition, richness and cannibalism variation. Stomach content weight was highly biased due to the advanced level of digestion, which in turn biased the diet based on weight, daily ration and consumption analyses. In this sense, the bioenergetic model based on water temperature fitted better than models based on stomach content weight and body mass. These results showed that D. gigas mostly predates on crustaceans and cephalopods, which contrasts with most ecosystem models that suggest that this species highly predates on commercially-exploited fish species.

Habitat suitability response to sea-level height changes: Implications for Ommastrephid squid conservation and management

Sea level rise, amplified by anthropogenic climate change, causes visible impacts on wildlife habitats in low-lying coastal areas. However, the potential consequences of sea level height (SLH) changes for pelagic fish habitats in the open oceans are poorly understood, especially for climate-sensitive Ommastrephid squid. In this study, the impacts of SLH changes were estimated under three different SLH change scenarios (5 cm, 20 cm, and 35 cm) for the western stock of winter-spring neon flying squid Ommastrephes bartramii, an ecologically- and commercially-important species in the northwest Pacific Ocean (NWPO). A habitat suitability index (HSI) modeling approach was applied to predict the habitat suitability of O. bartramii, using data from 2006 to 2014 for model construction and data from 2015 for model validation. Results showed that the decreasing catch-per-unit-effort (CPUE) of O. bartramii from 2006 to 2015 was highly correlated with the increases in sea level height (SLH). Significant positive relationships were found between the HSI values for latitudinal centers of gravity (LATGHSI) and SLH. The monthly-averaged HSI of O. bartramii was negatively correlated with the SLH, except in July and November. SLH scenarios revealed that the predicted suitable habitat (areas with HSI≥0.6) exhibited a decreasing trend with increasing SLH from August to October. In July and November, the suitable habitat initially increased in the +5 cm and +20 cm scenarios, but largely declined under the +35 cm scenario. The poor habitat (areas with HSI≤0.2) significantly increased under all SLH scenarios. A poleward shift of LATGHSI was observed under all scenarios. These findings suggest that the O. bartramii habitats in the NWPO are at risk to SLH changes and have important implications for better conservation and fishery management regarding pelagic short-lived Ommastrephid squid in global oceans.

Swordfish Xiphias gladius diet in the Florida Straits

Swordfish Xiphias gladius inhabit the Florida Straits year-round and provide a significant role in the food web as top-level predators. However, little is known about the diet composition and thus ecological role of swordfish in Florida. This study investigated swordfish diet by analyzing stomach contents of 131 swordfish in the Florida Straits from April 2007 to December 2008. Identifiable species included 13 teleost species, 3 cephalopod species, and 1 crustacean species. Cephalopods dominated the swordfish diet by weight (72.4%) and number (69.9%), and ranked highest in importance in the diet by the index of relative importance (IRI; 81.5%). Teleosts occurred the most (99.1%) but represented the second highest importance in diet by weight (25.2%), number (26.3%), and IRI (17.6%). Illex sp. was the prey with the greatest dietary importance, followed by unidentifiable ommastrephid squids. Stomach fullness index values ranged from 0 (empty) to 8.98 (mean = 0.37). A positive significant correlation between swordfish length and prey length was found (r2 = 0.104, P = 0.037), and no significant correlations were found between swordfish weight and prey weight (r2 = –0.075, P = 0.065). This is the first study to report a comprehensive diet of swordfish inhabiting waters in the Florida Straits region and suggests swordfish may be opportunistic feeders, altering their diet when abundance or presence of prey changes.

Tied hands: synchronism between beak development and feeding-related morphological changes in ommastrephid squid paralarvae

Ommastrephid squid produce some of the smallest cephalopod hatchlings, whose feeding behavior has not been observed. The present study aimed at indirectly filling this knowledge gap by describing ontogenetic changes in beak morphology and morphometry and integrating these results with published datasets on Illex argentinus arm crown morphology and gut contents. Individuals [0.7–15 mm mantle length (ML)] were measured, weighed, and had their buccal mass extracted. Jaw measurements were correlated with ML to determine whether jaw development occurred linearly with ML. For a 10 mm increment in ML, weight increased 430-fold. The jaws of hatchlings were rudimentary, but in larger paralarvae the rostrum protrudes and the jaw features (teeth, slit, groove) disappear. Increases in ML were predicted by beak robustness indices and rostrum protrusion, with growth discontinuities pointing to faster growth in individuals ≤ 2 mm ML. Morphological changes in the beak and arm crown are in synchrony with a transitional event in the feeding ecology of paralarvae: the onset of active predation on crustaceans and masticating their exoskeletons for ingestion. Integration of the results with published data has led to the proposal of a hypothesis of four size-differentiated developmental stages in the feeding ecology of I. argentinus rhynchoteuthions.

Ommastrephid squid paralarvae distribution and transport under contrasting interannual conditions in the tropical-subtropical convergence off Mexico

The distribution and transport of paralarvae of the complex Sthenoteuthis oualaniensis - Dosidicus gigas (SD complex, Cephalopoda: Ommastrephidae) in the tropical-subtropical convergence off Mexico were analyzed under contrasting interannual environmental conditions. Two El Niño years were sampled (2010 and 2016), in which the SST were up to 3 °C above the average throughout the study area, while during La Niña year (2012) the SST anomalies were up to 2 °C below the average. During El Niño years, a relative shallow thermocline (<60 m depth) was detected around Cabo Corrientes, where the paralarvae were found with mean abundance of 2 org 1000 m−3. During La Niña condition, a shallower thermocline was detected in the entrance of the Gulf of California (~20 m depth) and the paralarvae abundance rose to 84 org 1000 m−3 with high frequency of occurrence. In both El Niño and La Niña conditions the paralarvae were mainly found in the strongly stratified waters (>80 cycles h−1). In addition, a simple dispersion Lagrangian model based on observed satellite geostrophic currents, suggested association of the SD complex paralarvae with mesoscale structures, in which the eggs and hatched paralarvae had an appropriate habitat for a nursery, retaining the paralarvae until their recruitment in a ~100 km radius. But during warm extreme events, with less mesoscale activity, the paralarvae could be transported as far as 500 km southeast of the spawning zone. Even though the interannual ENSO conditions modulate the magnitude of the paralarvae abundance, the shallow and well developed thermocline could help paralarvae to increase their survival chances, while mesoscale activity retains them near the productive coastal waters.

Long-term trends in albatross diets in relation to prey availability and breeding success

Diet analyses can reveal important changes in seabird foraging ecology and, by inference, resource availability and predator–prey dynamics within the wider marine ecosystem. Here, we analysed stomach contents of 1544 grey-headed albatross Thalassarche chrysostoma (GHA) and black-browed albatross T. melanophris (BBA) chicks from Bird Island, South Georgia. We describe dietary shifts (1996–2017), and link those to annual prey availability indices and breeding success. Annual variability in diet was high, and long-term trends in the main components were broadly similar in both albatrosses. Fish consumption (by mass) generally increased over time. Mackerel icefish Champsocephalus gunnari occurrence increased in GHA diets, but was unrelated to local densities derived from fisheries/research cruises. Cephalopod consumption declined until the early 2000s, then plateaued, and the occurrence of the ommastrephid squid Martialia hyadesi declined over time in both albatrosses. In BBAs, Antarctic krill Euphausia superba consumption decreased over time. Conversely, Antarctic krill consumption by GHAs increased until the early 2000s, decreased until the mid-2010s, and increased again in 2017. Antarctic krill consumption was unrelated to local densities based on acoustic surveys, and did not correlate with breeding success. Remotely sensed chlorophyll-a within core foraging areas showed a positive relationship with Antarctic krill in GHA diets, but a negative relationship with M. hyadesi occurrence in both albatross diets. Dietary shifts had consequences for GHA breeding success, which was negatively related to the importance of the cranchiid Galiteuthis glacialis and positively related to M. hyadesi importance. These results highlight the complex mechanisms linking prey availability, diet and breeding success in albatrosses.

First Evidence of Illex coindetii (Vérany, 1839) in the Baltic Sea and the Kattegat

I. coindetii (Verany 1839, Memorie della Reale Accademia delle Scienze di Torino, series 2, 1:91–98) is an oceanic, benthopelagic ommastrephid squid occurring in subtropical / temperate, offshore and coastal waters and continental slope areas. In the Eastern Atlantic, the species is widely distributed, but an evidence that the species occurs in the brackish Baltic Sea and Kattegat has never been published. Here we present the first observation of undetermined, immature and developing individuals of I. coindetii in the Baltic Sea and Kattegat. To our best knowledge, this is at the same time the first description of the occurrence of a squid of the genus Illex at low salinities. Individuals were fished in October 2018 during night in a depth range of 10 m to 52 m and in salinities between 20.5–33.8 psu. We assume that the species originated from the North Sea.

Foraging ecology of large pelagic fishes in the US South Atlantic: structured piscivory shapes trophic niche variation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 631:181-199 (2019) - DOI: https://doi.org/10.3354/meps13126 Foraging ecology of large pelagic fishes in the US South Atlantic: structured piscivory shapes trophic niche variation Stephen J. Poland1,2, Frederick S. Scharf1,*, Michelle D. Staudinger1,3 1Department of Biology and Marine Biology, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403, USA 2North Carolina Division of Marine Fisheries, 3441 Arendell St., Morehead City, NC 28557, USA 3DOI Northeast Climate Adaptation Science Center, Morrill Science Center, 611 North Pleasant Street, University of Massachusetts, Amherst, MA 01003, USA *Corresponding author: scharff@uncw.edu ABSTRACT: Sustainable management of marine fishery resources requires an understanding of the ecological relationships that contribute to community structure and population dynamics. In offshore marine ecosystems, the functional roles played by many large pelagic predators are poorly understood, yet this knowledge is essential to ecosystem-based management approaches. Here we report on the results of a multiyear (2010-2013) study to evaluate the trophic relationships within a guild of apex predatory fishes in the western Atlantic Ocean. Quantitative diet analyses were completed for wahoo Acanthocybium solandri, dolphinfish Coryphaena hippurus, yellowfin tuna Thunnus albacares, and blackfin tuna T. atlanticus during multiple seasons. Fishes were the most important prey by mass for all predators during all seasons and occurred with high frequency; however, crustacean and molluscan prey were also important dietary components for most of the predators. The diversity of prey eaten was high, with nearly 50 unique families represented; yet, a few prey groups such as scombrid fishes (Auxis spp.), flying fish (exocoetids), and ommastrephid squids, occurred more universally and dominated the diets of some predators during certain seasons. Diet similarity was highest between dolphinfish and blackfin tuna and also between wahoo and yellowfin tuna, but was generally dependent on season and driven by overlap in fish prey. Importantly, the extent of piscivory and specialization on unique fish prey groups supported a structured piscivore guild within this pelagic ecosystem, leading to separation among trophic niches and reduced overlap in prey resources. Our findings provide a temporally (seasonal and inter-annual) extensive evaluation of the trophic relationships among large pelagic fish predators in the US South Atlantic, which should inform an ecosystem-based understanding of community dynamics and fishery impacts. KEY WORDS: Blackfin tuna · Yellowfin tuna · Wahoo · Dolphinfish · Trophic interactions · Predator-prey · Food habits · Trophic niche Full text in pdf format Supplementary material PreviousNextCite this article as: Poland SJ, Scharf FS, Staudinger MD (2019) Foraging ecology of large pelagic fishes in the US South Atlantic: structured piscivory shapes trophic niche variation. Mar Ecol Prog Ser 631:181-199. https://doi.org/10.3354/meps13126 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 631. Online publication date: November 21, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

First evidence of a new spawning stock of Illex coindetii in the North Sea (NE-Atlantic)

Global changes drive abundance and distribution of species worldwide. It seems that at least some cephalopod stocks profit from global changes as indicated by increases in biomass and/or expansion of their geographical distribution, as appears to be the case for the commercially important ommastrephid squid Illex coindetii, in the North Sea. Based on the recently increased abundance of this species seen in research trawl hauls, here we present the first evidence of a summer spawning stock of Illex coindetii in the North Sea and derive a description of its life cycle. Neither mated females nor spent males were reported from the area previously. In quarter 1 the majority of Illex coindetii were immature (maturity stage 0) and maturing (maturity stage 1–3) while in quarter 3 almost exclusively mature and spent individuals (maturity stage 4–6) were caught. We observed up to three spermatangia bundles attached to females in quarter 3, indicating that spawning and reproduction takes place in the North Sea and that the species is already established in this area. Estimated egg hatching dates suggest a prolonged hatching period and therefore likely a long spawning season, although cold temperature seems to limit year round reproduction. The intensity of individual migrations from adjacent waters into the North Sea is unknown and therefore the number of individuals staying permanently in the North Sea could not be estimated. It is consequently still unclear whether the North Sea individuals of I. coindetii constitute a new separate stock.

Defensive Ball Formation in Oceanic Squid Paralarvae

The head withdrawal reflex is a behavior that has been reported in young pelagic squids (paralarvae) and involves retraction of the head, arms, and proboscis (fused feeding tentacles) into the mantle cavity when the animals are disturbed. The present study investigated which artificial stimuli (mechanical, chemical, or light) trigger this behavior in three oceanic ommastrephid squid species: Sthenoteuthis oualaniensis, Eucleoteuthis luminosa, and Todarodes pacificus. All stimuli triggered ball formation and chromatophore expansion. During the early paralarval stage, the head was completely withdrawn into the mantle cavity, and the squid formed a ball posture with expanded orange chromatophores. This response might make it difficult for predators to recognize and consume the squid or it might facilitate feeding.