Biology and distribution patterns of some deep-sea fishes

The often odd looking deep-sea fishes reflect their special adaptation to the deep-sea environment. For all these species we know little or nothing about where they occur, how fast they grow, and how old they get. Such information gives us important knowledge regarding both the system they are living in and the vulnerability of the different species.

Inge Fossen

Student of the month
Inge Fossen
PhD -student at University of Bergen, Norway (second year)

Describing biology and distribution patterns of some demersal deep-sea fish species. The study is based on analyses of catch rates, sampling of biological data, and indications from age analysis.

- Cand. scient. Aquaculture from The Norwegian College of Fishery Science (NFH), University of Tromsø, 1996. Thesis: Otoliths and growth of long rough dab in the Barents Sea
- Three years for the Institute of Marine Research, Bergen, as a replacement scientist at NatMIRC, Swakopmund, Namibia
- Four years as a scientist at Møre Research, Ålesund

Long line catch rates
Longline catch rates (relative to symbol size) at depths (m) for different fish species

Onboard the scientific vessels detailed information describing the fish catches were continuously recorded. In his work Inge use this catch information (catch rates of different species and the depths caught) to show at which depths the different species are found. This is used to describe which species lives at the different depths and areas.

Detailed information regarding the individual specimens were also recorded. Information such as size composition, the portion of females and males, and how many are mature at different stations and depths are used to give more detailed information on how individual species are distributed. From this we can learn more about how they are adapted to the deep-sea conditions and how they utilise the available resources.

Othotliths from Macrourus berglax, Antimora rostrata and Coryphaenoides armatus.
On the longliner MS Loran also the ear stones from the bony fishes were collected. These ear stones form the bases of an initial attempt to age some of these deep-sea species. Back in the laboratory the ear stones (size of a pea) were mounted in black plastic and thin slices (0.4mm) was sawed through their centre and than photographed (see images). The hope is that these ear stones has similar zonation pattern as trees with zones that reflects their age.

Form with otholits
A form with otholits
Knowledge of age opens for a description of how big fishes are at a certain age and thereby an indication of growth. The speed of growth and the age when the fishes reach puberty are important knowledge to scientist when they are giving advices to managers regarding the amount of fishing which should be allowed. Deep-sea species are thought to be slow growing and late maturing compared to shallower living species in general. This makes them more vulnerable to exploitation.

A lot of work still remains before we fully understand the fish communities in the deep-sea, but this study might hopefully bring us one step closer. Stay tuned for more results of the work on deep-sea fishes! A number of studies are being carried out at this very moment from the scientists involved in the MAR-ECO project.