BBSR
Marine Invertebrates of Bermuda

Slender Inshore Squid (Loligo plei)

Kelly Pennoyer
and
James B. Wood (Ed)


Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 


Slender Inshore Squid <i>Loligo plei</i>
Taxonomy


Phylum:Mollusca
  Class: Cephalopoda
    Order:Teuthida
      Family:Loliginidae


Abstract


Loligo plei is a loliginid squid found in coastal waters typically in depths of 20 and 75 meters. L. plei is a warm water species typically found in the Gulf of Mexico, Caribbean and Venezuelan waters, near coral reefs.

Loligo plei is a very social creature and can often be found in schools. Many aspects of their behavior is based upon visual displays, both chromatophore displays and postural displays. These visual displays are used in signaling for reproduction, showing maturity, and as signs of aggression. Males are highly aggressive both in the lab and in the wild, and are known to show specific visual displays to show their dominance. Rarely they will physically attack others in order to show their dominance. Dominant males often have a larger supply of both females and food. Spawning is year round with a larger reproductive event in the summer. Individuals typically have a life span of one year and are semelparous.

All cephalopods are carnivores, the diet of Loligo plei changes as they age. Growth rate is directly proportional to the rate of feeding.

Recent research has focused on the shift between indirect fishing of Loligo plei to direct fishing and the effect it is having on their biomass. Another topic of recent research has been in the phylogeography of Loligo plei.

Introduction


A synonym for Loligo plei is Doryteuthis plei. The common name for Loligo plei is the slender inshore squid and the arrorw squid.

Loligo plei is a member of the Phylum Mollusca, which also includes clams, oysters, snails, nudibranchs, chitons, octopus and nautilus. The order Teuthida is comprised of nearly 30 families of squid (Hanlon & Messenger 1996). Teuthoids are powerful swimmers that can forage over great distances in both coastal and open waters (Hanlon et al. 1983). They utilize jet propulsion for quick bursts of movement where water is directed by the funnel to move the animal (Wilbur 1983). The Loliginidae are pelagic squids and can be found in surface waters to waters of considerable depths (Boycott 1965).

Loligo plei has a long slender body with maximum mantle lengths approaching 35 - 40cm (Sterrer 1986). This slender body is adapted for maneuverability in open waters (Boycott 1965). Males are typically 1.3 times larger than females (Perez et al. 2002). Fin length is 35-58% of the mantle length (Sterrer 1986).

Habitat


Present closer to shore typically in depths between 20 and 75 meters (Hanlon et al. 1983).At observations at the Bermuda biological station individuals were observed at depths of 5 to 10 meters (Boycott 1965). Loligo plei is a warm water species typically found east of Florida in the Gulf of Mexico, the Caribbean and in Venezuelan waters (Perez 2002). They are often found near coral reefs and it can be found to associate with the Caribbean reef squid, Sepioteuthis sepioidea (Hanlon & Messenger 1996).

Ecology


Loliginid squids are highly social, and can often be found in schools (Hanlon et al. 1983). Most aspects of squid behavior are done through body patterns which include body postures and movements and chromatophore displays (Hanlon et al. 1983). Loligo plei has 16 chromatic and 6 postural displays that have been described and associated with specific behaviors (Hanlon et al. 1983). Males in captivity have been found to establish and maintain a rank in a school based upon size and aggressive behavior, this aggressive behavior was a principle cause of death in laboratory experiments (Hanlon et al. 1983). In laboratory experiments it was found that females are very docile and will only engage in aggressive behavior occasionally while in the pursuit of prey (Hanlon et al. 1983).

The main predators of cephalopods are seabirds, whales and seals (Rathjen 1991).

All cephalopods are carnivores and capture food by their highly modified foot muscles, the arms and tentacles (Wilbur 1983). It has often been found that in laboratory experiments which involve squid a difficulty that arises is in feeding, both in finding what will be eaten and large enough quantities of it (LaRoe 1971). In the lab young individuals prefer mysid crustaceans (Mysidium columbiae) while the older individuals prefer Gambusia and Poecilia as well as penaeid shrimp and other fish that were 3-7 cm in length (LaRoe 1971). Both in captivity and in the wild it has been found that squid will eat prey of wide size ranges from plankton to fish (Hanlon et al 1983). In captivity some individuals consumed up to 180% of their body weight daily although individuals were sustained at a level of 45% body weight (LaRoe 1971).

In captivity the growth rate of Loligo plei has been found to be between 15 and 25 mm per month (LaRoe 1971). The growth rate is directly related to the feeding rate. The more food that is consumed the faster the growth rate (LaRoe 1971).

Visual displays are an important part in the signaling for reproduction of Loligo plei. It has been observed that mature males will leave the chromatophores over the testis unexpanded, making them appear more obvious, possibly to show that the individual is sexually mature (Boycott 1965). Along with accentuated testis adult males also show lateral flame components to other individuals (Hanlon & Messenger 1996). Females signal for courtship by distinctive body patterns with bands and downward curled arm positions (Hanlon & Messenger 1996). Another visual signal may be the red nidamental gland, which provides jelly to the eggs; this gland can be seen through their translucent skin (Hanlon & Messenger 1996).

Mating in Loligo plei can occur in two basic positions the “head to head” and “male to parallel” (Hanlon & Messenger 1996). In the “head to head” position males place spermatophores in or near the seminal receptacle (Hanlon & Messenger 1996). It has been suggested that this position is used throughout the Loligo plei life cycle or before migration to spawning grounds (Hanlon & Messenger 1996). In the “male to parallel” position, spermatophores are deposited near the oviduct in the mantle (Hanlon & Messenger). Egg laying typically results very shortly after “male to parallel” mating (Hanlon & Messenger). Smaller non dominant males have been observed to sneak, where the smaller individual is able to deposit spermatophores while the larger dominant male is preoccupied in an agonistic contest with another male (Hanlon & Messenger 1996). Mate guarding has also been observed in Loligo plei where a male follow a female until she lays eggs (Hanlon & Messenger 1996).

Loliginids typically lay clusters of eggs in several gelatinous strands or fingers attached at the base forming mops (LaRoe 1971). These mops are laid on the bottom attached to hard substrates (Sterrer 1986). Breeding and spawning occurs year round, this is known because mature individuals are present throughout the year however there is a large reproductive event in the summer (Perez et al. 2002). Like many other loliginids, Loligo plei is semelparous, and typically has a life span of one year (Perez et al. 2002).

Recent Research


Recent research of Loligo plei has mostly concerned the effects of fishing. In recent decades there has been a shift to directed fishing from incidental by catch (Perez, 2002). Because of this shift in fishing it is being researched how fishing will effect squid populations. It has already been observed that this shift from indirect to direct fishing has lead to a decrease in biomass (Perez 2002).

Other recent studies have been on the phylogeography of Loligo plei and another related species, Loligo pealei in the Gulf of Mexico and the northwestern Atlantic Ocean. It was found that speciation was rejected on the basis of neucleotide sequencing was insufficient to support speciation (Herke & Foltz 2002). It was found that the Loligo plei individuals found in the northwest Gulf of Mexico and the north east Gulf Atlantic Ocean were comprised of separate populations, based on that the gene flow matched that of an isolation by distance model (Herke & Foltz 2002). This boundary was found at 88 and 89 degrees West longitude (Herke & Foltz 2002). The phylogeography could be due to oceanographic features; both the Florida peninsula and the strong easterly currents and the discharge of the Mississippi River which results in little Loligo plei population movement across these areas (Herke & Foltz 2002).

Commercial Importance


Increasingly as fish populations of commercial importance are being further exploited species once thought of as having little commercial importance are now being targeted, particularly cephalopods. Cephalopods are primarily caught using jigging, trawling, lift and seine net techniques (Rathjen 1991). In many areas trawling nets have been modified to increase the incidental capture of cephalopods , and this has allowed for for direct fishing practices (Perez, 2002). The reason that Loligo plei have become of more commercial importance over the past few decades is because of the fact that their populations can reach great numbers over short seasons and due to their increasing value as other fish stocks decline (Perez, 2002).

Bermuda Laws


There are now Bermudian laws pertaining to Loligo plei.

Personal Interest


I decided to do my web project on Loligo plei because of my increasing interest in animal behavior. I can easily be found to be staring at an organism big or small for extended periods of time, often to the dismay of awaiting friends. Cephalopods are highly intelligent and many species have very interesting dynamic group behavior. And my final research project will be focusing in on the schooling behavior of Sepioteuthis sepioidea.

References

Boycott, B.B. 1965. A comparison of living Sepioteuthis sepioidea and Doryteuthis plei with other squids, and with Sepia officinalis. Journal of Zoology. 147: 344-351.

Hanlon, R.T., R.F. Hixon, and W.H. Hulet. 1983. Survival, growth, and behavior of the loliginid squids Loligo plei, Loligo pealei, and Lolligunucual brevis (Mollusca: Cephalopoda) in closed sea water systems. Biological Bulletin. 165: 637-685.

Hanlon, R.T., and J.B. Messenger. 1996. Cephalopod Behavior. UK: Cambridge University Press, pages 103-4.

Herke, S.W., and D.W. Foltz. 2002. Phylogeography of two squid (Loligo pealei and L. plei) in the Gulf of Mexico and northwestern Atlanctic Ocean. Marine Biology. 140: 103-115.

LaRoe, E.T. 1971. The culture and maintenance of the loliginid squids Sepioteuthis sepioidea and Doryteuthis plei. Marine Biology. 9: 9-25.

Perez, J.A.A. 2002. Biomass dynamics of the squid Loligo plei and the development of a small-scale seasonal fishery off southern Brazil. Bulletin of Marine Science. 71(2): 633-651.

Perez, J.A.A, D.C. de Aguiar, and U.C. Oliveira. 2002. Biology and population dynamics of the long-finned squid Loligo plei (Cephalopoda: Loliginidae) in southern Brazilian waters. Fisheries Research. 58(3): 267 – 279.

Rathjen, W.F. 1991. Cephalopod capture methods: an overview. Bulletin of Marine Science. 49(1-2): 494-505.

Sterrer, W. 1986. Marine Fauna and Flora of Bermuda: A Systematic Guide to the Identification of Marine Organisms. Wiley-Interscience, U.S.A. page 496.

Wilbur, K.M. (ed). 1983. The Molluska. Vol. 6 Ecology. Academic Press, London, pages 269, 273.

Links

CephBase