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28. June


A peculiar squid photographed in the trawl aquarium


A gallery of lanternfishes


Todays Highlights

Date:June 28, 2004
Author:  Richard Young, University of Hawaii, USA, and Odd Aksel Bergstad, Institute of Marine Research, Norway

It has been nearly a week since we passed south of the Subpolar Frontal Zone into progressively warmer and more saline surface waters. During this period we have seen evidence of a gradual changeover in the species composition of the fauna with newly encountered species becoming a more important component of the fauna and formerly common species becoming rare or absent. We had anticipated these changes and were expecting increasing species diversity in the fauna as we moved further south. However we were not prepared for the dramatic changes we saw in our large midwater trawl taken last night. For example within the cephalopods (squid and octopods), a group that some of us consider the most spectacular and most beautiful members of the fauna, we caught total of 54 individuals distributed among 22 species and 16 families. To give indication of the diversity this represents, all of our previous trawls combined had captured a total of 28 species in 17 families. The diversity in this one tow was breathtaking. Six of the 22 species (27%) were new records for the cruise and five of these represented the first records for five families.

The high diversity of this catch was also seen with the more numerous midwater fishes. A total of 1108 individual fish were taken representing 76 species in 27 families. Twenty percent of these species were new records for the cruise. All previous tows combined had yielded 95 species of fishes. We are anxious for the next large trawl to see if the catch was just unusual or the harbinger of a consistent change in the fauna.

Another feature of southern areas is the diversity of fish species inhabiting the mesopelagic zone. This is the twilight zone of the ocean where some daylight still penetrates and a diurnal light cycle is detectable. Mesopelagic fishes are visual feeders usually with big eyes adapted to low light levels. Often they feed near the surface at night (see previous report), and spend the day in deeper layers, down to about 1000 m. The lanternfishes of the family Myctophidae are typical small mesopelagic fishes, usually 10 cm or less (Photo: T. Sutton and F. Porteiro). They have impressive light organs (photophores) spread around the body in species-specific patterns. Many of the Myctophids may look similar, but fish taxonomist can tell the species apart based on characters such as photophore number, and pattern, eye size, mouth morphology and body dimensions.

 

Weather Conditions

It was overcast all day. No wind in the morning, quite breezy in the afternoon. It gets gradually warmer, however, and the surface temperature of the nice blue water here is around 18.5 C.

 

Tomorrows expected highlights

Leg 1 of the cruise is rapidly coming to an end (3 July) and everybody is anxious to finish the remaining stations in time. Discovery of new patterns in the distribution or species composition data keeps us excited about the next few trawls, and the acousticians also monitor interesting changes in distribution patterns of scattering layers.

 

Cruise journal

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