The Influence of an Electric Light on the Capture of Oceanic Cephalopods by a Midwater Trawl

Abstract

A total of 57 comparative hauls using a rectangular midwater trawl with a fishing mouth area of 50 m 2 (RMT 50) were carried out along the sides of an imaginary triangle south of Madeira in 1986. A total of 1258 cephalopods were caught, giving a mean of 22 per haul with a range from 0 to 67. The nets were used with a diver's light on the top bar which was either switched off or was operated with a 20, 70 or 150 W bulb, powered by a car battery. A significantly greater number of individuals per haul was caught with lights on than without lights, increasing from a mean of 13-5-251, a factor of 1-8. Similarly, the number of species caught was increased from a mean of 7 to 10-4, a factor of 1-5 and the volume of cephalopods was increased from a mean of 411-162-3ml, a factor of 3-9. Similar comparisons made for catches during day or night separately and on the three courses separately also showed marked increases with the lights. Samples show that increase in power of the lights increased the total number of cephalopod individuals caught. In the 12 species with more than ten individuals, in 33 of the 36 comparisons (of number of individuals, species and volumes) there is an increase with the light. The most influenced species was Taonius pavo which increased in numbers by a mean factor of 3-9 times with 20W, 40 times with 70W and 6-1 times with 150W when compared with the numbers caught with no light. Increases by Helicocmnchia pfefferi, Pyroteuthis margaritifera and Pterygioteuthis gemmata are significant for some lights. Abraliopsis pfefferi and Liocranchia reinhardti increased in lengths of individuals with increasing wattage of the lights. The results show conclusively that midwater trawling could be made much more cost-and time-effective by using inexpensive lights on the nets and biological studies of so-called rare species could be greatly facilitated.

The influence of artificial light on the capture of deep-water demersal fish by bottom trawling

“…In a separate analysis of the ¢sh catches Swinney et al (1986) found that signi¢cantly more ¢sh were caught when lights were attached and 12 species were attracted by light. Clarke & Pascoe (1998) carried out a detailed analysis of the cephalopod catches and found a signi¢cant increase in numbers caught when lights were attached to the trawl. In a separate series of experiments Hargreaves & Herring (1992) investigated the e¡ect of light on the crustacean catch of opening/closing midwater trawls at 800 m and concluded that turning on a light had no signi¢cant e¡ect on the numbers or sizes of numerically dominant species.…”

The history of theJournal of the Marine Biological Association of the United Kingdomand the influence of the publication on marine research

“…A comparison of catches, made using nets of different mesh sizes, with those using a plankton pump were reported (Pyefinch, 1949), with the pump being considered best for quantitative sampling. Other net designs described included a neuston net (David, 1965) and mid-water trawls with lights to attract fish and cephalopods (Clarke & Pascoe, 1985, 1998). Mobile deep-sea benthic carnivores can also be effectively observed using baited camera landers, with baited traps used to recover fauna in depths of >9000 m (Jamieson et al ., 2012).…”

Uncommon pelagic and deep-sea cephalopods in the Mediterranean: new data and literature review

“…Kear (1994) included A. morisii in a study on the morphology and function of the mandibular muscles of 23 cephalopods. In the experiments dealing with light attraction on pelagic cephalopods undertaken around Madeira, Clarke & Pascoe (1998) found that sizes of A. morisii increased with an increase in the wattage of the lights. In the Atlantic Ocean, A. morisii has been reported in the northwest (Lu & Roper, 1979), the northeast (Clarke & Lu, 1975) and the subtropical waters of the Brazil Current (Rodhouse et al, 1992).…”