Cartilaginous fishes

Cartilaginous fishes (chondrichthyes) are an ancient group of animals, having changed little in 100 million years. However ancient does not mean obsolete, but rather that they hit on a very successful body plan early on. The two modern groups of cartilaginous fishes are chimaerans (holocephali) and elasmobranchs (elasmobranchii). The later group is further split into sharks and dogfishes (selachimorpha), and rays (rajiformes).

Cimaerans

In general the chimaerans are deep sea fishes living on benthic animals. They are also named rat tails because they do not have a normal caudal fin but a long whip-like tail. The only other group of fishes around Iceland that have a tail like that are the totally unrelated grenadiers (macrouridae). However, both groups are most common in deep waters. The common rat-tail or rabbit fish (Chimaera monstrosa) is the only Icelandic chimera that is not confined to deep waters and consequently the only rat tail that has sustained some (but very low) catches recently. It might be because they were discarded in the past but are retained more now.

Rays and sharks

Rays (or skates) are benthic fishes that feed on a variety of benthic animals over a wide depth range. On the other hand the sharks are usually pelagic top predators also found over a wide depth range. Exceptions occur, as some shark species are strictly benthic and some skate species are pelagic. Sharks and rays can be found all over the world, but are most common in warm waters. The number of species declines considerably as the waters get colder and in Icelandic waters they are not common by any standards. Only four species have sustained commercial catches on regular basis: Greenland shark, spiny dogfish, grey skate and starry ray.

Other species that occur over the Icelandic continental shelf and have at one time or another been harvested in low amounts, these are the porpeagle (Lamna nasus) of which small amounts were targeted between 1959 and 1962, and nowadays they sometimes occur as bycatch in other fisheries. The basking shark (Cetorhinus maximus), the second largest fish on earth is frequently seen in Icelandic waters and occasionally gets entangled in nets or trawls for other species. Blue sharks (Prionace glauca) were previously considered very rare vagrants in Icelandic waters, but because they were a common bycatch in recent Japanese blue-fin tuna fisheries, it is now known that they occur regularly in the open ocean in the southern extreme of the EEZ.

Several other cartilaginous fish species are rather common in deep waters W, SW an S of Iceland and some have been reported in minute quantities as bycatch in recent deep-water fisheries. These are the black dogfish (Centroscyllium fabricii), Portuguese shark (Centroscymnus coelolepis), shagreen ray (Raja fullonica), knifenose chimaera (Rhinochimaera atlantica) and large eyed rabbitfish (Hydrolagus mirabilis).

Jawless fishes

The third main group of fish-like animals, besides the bony fishes and the cartilaginous fishes are the jawless fishes (agnatha or cyclostomata). These are the most primitive of all true vertebrates and have in fact recently been declassified as fishes, so that now they make up their own group. More than 400 million years ago the jawless fishes ruled the ocean, now there are only 2 groups left, hagfishes (myxini) and lampreys (cephalaspidomorphi) with about 100 species in total. A single species of each group has been found in Icelandic waters; The white-headed hagfish (Myxine ios) and the sea lamprey (Petromyzoan marinus). Both are rare.

Editor