Dharmamony Vijai

World squid fisheries

Abstract Some 290 species of squids comprise the order Teuthida that belongs to the molluscan Class Cephalopoda. Of these, about 30–40 squid species have substantial commercial importance around the world. Squid fisheries make a rather small contribution to world landings from capture fisheries relative to that of fish, but the proportion has increased steadily over the last decade, with some signs of recent leveling off. The present overview describes all substantial squid fisheries around the globe. The main ecological and biological features of exploited stocks, and key aspects of fisheries management are presented for each commercial species of squid worldwide. The history and fishing methods used in squid fisheries are also described. Special attention has been paid to interactions between squid fisheries and marine ecosystems including the effects of fishing gear, the role of squid in ecosystem change induced by overfishing on groundfish, and ecosystem-based fishery management.

Observations on the spawning behavior, egg masses and paralarval development of the ommastrephid squid Todarodes pacificus in a laboratory mesocosm.

ABSTRACT The spawning behavior of ommastrephid squids has never been observed under natural conditions. Previous laboratory observations of Japanese flying squid (Todarodes pacificus) suggest that pre-spawning females might rest on the continental shelf or slope before they ascend above the pycnocline to spawn, and that the egg masses might settle in the pycnocline. Here, two mesocosm experiments were conducted in a 300 m3 tank that was 6 m deep to investigate this hypothesis. In the first experiment, a thermocline (2.5–3.5 m) was established in the tank by creating a thermally stratified (17–22°C) water column. In the second experiment, the temperature was uniform (22°C) at all depths. Prior to spawning, females did not rest on the tank floor. In the stratified water column, egg masses remained suspended in the thermocline, but in an unstratified water column, they settled on the tank bottom, collapsed and were infested by microbes, resulting in abnormal or nonviable embryos. Eleven females spawned a total of 18 egg masses (17–80 cm in diameter), indicating that females can spawn more than once when under stress. Paralarvae hatched at stage 30/31 and survived for up to 10 days, allowing us to observe the most advanced stage of paralarvae in captivity. Paralarvae survived after consumption of the inner yolk, suggesting they might have fed in the tank. Highlighted Article: Mesocosm observations on the reproduction of the squid Todarodes pacificus reveal the animals spawning behavior, egg mass properties and paralarval development in a simulated natural environment.

Embryonic and paralarval development following artificial fertilization in the neon flying squid Ommastrephes bartramii

Ommastrephidae are the most important commercial fishery group among cephalopods. However, little is known about their embryonic development. This article provides details of embryonic development observed in three ommastrephids: Ommastrephes bartramii, Sthenoteuthis oualaniensis, and Eucleoteuthis luminosa. All embryos were obtained through artificial fertilization conducted onboard the research vessel Kaiyo Maru during a cruise around the Hawaiian Islands in December 2013. The embryonic and paralarval stages of O. bartramii are explained in detail. The hatchling stages were compared between all three species, as well as with information on Illex argentinus hatchlings from the literature. The species-specific effects of the oviducal gland powder on chorion expansion were analyzed. The results indicated that the overall chemical nature of the oviducal gland was species specific, although the inducer of chorion expansion was the same across species. In addition, treatment with oviducal gland jelly induced partial parthenogenesis in the early stages of embryonic development through the expansion of the perivitelline space and blastodisc formation.

Intraspecific kleptoparasitism in squid school and schooling behavior of its prey

Schooling is postulated to have significant effects on predator–prey relationships (Neill and Cullen 1974). The observations reported here are the results of experiments conducted to test the feeding behavior of schools of Japanese flying squid (Todarodes pacificus) on schools of the Japanese anchovy (Engraulis japonicus). In the wild, T. pacificus is a generalist predator feeding opportunistically and taking whatever is available, including E. japonicus. The experiments were conducted during the period July–August 2014 in a large (300-m) tank. Live squid were collected from set nets from the inshore waters of southern Hokkaido, and anchovies were collected by angling. Healthy squids (n = 400, 9.5–16.6 cm mantle length, ML) and anchovies (n = 250, 7.5–13.6 cm, body length) were then gently released into the tank with a 1-day interval. Video footage from the tank was annotated, reviewed, and analyzed. In addition to the systematic description of the hunting behavior of squid given by Neill and Cullen (1974) and Foyle and O’Dor (1988), we recorded two new observations. Fi rs t , we observed (s ix ins tances) in t raspeci f ic kleptoparasitism (sharing of food by individuals of the same school) by the squid. After one squid (the host) successfully captured an anchovy (∼12 cm), many other squids (up to five, ∼10–14 cm ML, Fig. 1a, b) shared the prey. On most occasions, the host showed minimum resistance and the feasting was peaceful, lasting for about 30 s to 5 min. The peak of hunting was during the introduction of prey (anchovies); as time passed (hours and days), the frequency of attacks also decreased. Kleptoparasitism could benefit the Bparasitic^ squid in the natural environment considering the escape competency of anchovies (Iyengar 2008), but at considerable cost to the host. Such social foraging would be advantageous if the eventual gain as a Bparasite^ outweighs the loss incurred as a host. Second, the schooling behavior of anchovies varied based on the hunting behavior of the squid. Sometimes, when the squids actively foraged, the anchovy schools remained far away from the squid and descended near the bottom of the tank to avoid predation (Fig. 1c). Other times, when the squid are not hunting, the anchovies swam freely among the squid (Fig. 1d). Schooling of prey can reduce the risk of being eaten due to a Brelay-race effect^, in which the predator switches from one prey to another instead of concentrating on a single victim (Neill and Cullen 1974). While our observations are suggestive, to fully understand how anchovies regulate their schooling behavior in response to squid foraging activity, further investigation is needed. Communicated by M. Vecchione

Egg Masses of Flying Squids (Cephalopoda: Ommastrephidae)

ABSTRACT Ommastrephid squids have a pelagic lifestyle, with reproductive behavior that is characterized by the extrusion of fragile, neutrally buoyant egg masses, the release of paralarvae into the surface plankton, and the use of large-scale current patterns for larval transport, leading to the assisted migration of populations. Although the exact process of egg mass formation is unknown, the most accepted hypothesis suggests that, at spawning, eggs are first coated with oviducal gland secretion and released with nidamental gland secretions. Subsequently, the eggs mix with broken spermatophores or spermatangia for fertilization. The fertilized eggs are then extruded into the seawater to form a globular mass. These neutrally buoyant gelatinous egg masses are thought to maintain their location in the water column by floating at the interface between water layers of slightly different densities (above the pycnocline). The embryos develop within a favorable temperature range. Once hatched, the paralarvae leave the egg mass and swim to the surface. This review assimilates and assesses all available literature on the egg masses of ommastrephid squids. The data presented here clearly show how fragmentary our knowledge is about this important reproductive stage. Thus, increased efforts are required to develop observation and sampling techniques in the wild to obtain more direct evidence about reproduction in squids.

Orientation Patterns of Japanese Flying Squid Todarodes pacificus Embryos within Egg Masses and Responses of Paralarvae to Light

Squid embryos develop in the perivitelline fluid inside the chorion, which is an envelope secreted by the ovarian follicle. The onset of hatching initiates local dissolution of the chorion when the hatching gland enzyme facilitates the release of the developed paralarvae. In the present study, we investigated the pre-hatching behavioral patterns of Todarodes pacificus embryos and their responses to light after hatching. Observations of orientation were conducted using embryos developing inside chorions embedded within intact egg masses, while phototactic experiments were conducted on paralarvae that hatched from these egg masses. Within the restricted chorion and along the animal–vegetal axis, the embryos demonstrated a variety of orientation patterns that were categorized as swirls, glides, and somersaults. The contributions of these orientations to enhance oxygen diffusion and stimulate paralarval swimming immediately after hatching are discussed. Paralarvae exhibited normal diel vertical migration and responded positively to light sources. Vertical migration and phototaxis in T. pacificus paralarvae could have great adaptive significance because they hatch in neritic environments and are transported by ocean currents during their planktonic life.

Structure and properties of the egg mass of the ommastrephid squid Todarodes pacificus

The Japanese flying squid, Todarodes pacificus, is thought to spawn neutrally buoyant egg masses that retain a specific location in the water column by floating at the interface between water layers of slightly different densities. It is important to understand the physical process that determines the vertical distribution of the egg masses to predict their horizontal drift in relation to embryo survival and subsequent recruitment. Here, mesocosm experiments were conducted in a 300 m3 tank by creating a thermally stratified (17–22°C) water column to obtain egg masses. A cage net methodology was developed to sustain egg masses for detailed observation. We measured the density of the egg masses of T. pacificus, and used this information to infer the vertical distribution patterns of the egg masses at the spawning grounds (Tsushima Strait, Japan). When measured separately, the density of the outer jelly of each egg mass was 2.7 σ units higher than that of the surrounding water. The outer jelly and the specific gravity of embedded individual eggs (~1.10) cause the egg masses to have very slight negative buoyancy relative to the water in which they are formed. Analysis of the vertical profile of the spawning ground showed that water density (σθ) increased sharply at ~30 m depth; thus, egg masses might settle above the pycnocline layer. In conclusion, we suggest that T. pacificus egg masses might retain their location in the water column by floating at the interface between water layers of slightly different densities, which happen to be above the pycnocline layer (actual depth varies seasonally/annually) in the Tsushima Strait between Korea and Japan.