A large often greenish-appearing type of leptocephalus larva has been observed and photographed or filmed by divers at 4 different locations within the Indonesian Archipelago from 2008 to 2011, and this paper documents these sightings and evaluates what can be learned about this type of unusual eel larvae. These leptocephali (~300–400 mm long) appear to be exceptionally large metamorphosing larvae of some type of moray eel of the family Muraenidae. Because of the morphological similarities between these larvae and ribbon eels, Rhinomuraena quaesita, they are hypothesized to be their larvae, which have never been distinguished among leptocephali of the Muraenidae. These leptocephali were observed at Sangeang Island, in Lembeh Strait adjacent to north-eastern Sulawesi Island, in two different years at Ambon Island, and on two consecutive days at Bali, between December and June of 4 different years. All observations of the large leptocephali were at depths shallower than about 23 m in areas with mixed coral rubble or coarse sand and silt substrates during daylight hours. The larvae used various styles of anguilliform swimming and swam near the bottom or in the lower water column while being observed. One larva tried unsuccessfully several times to enter small crevices. They were all at the metamorphosing stage and may have been entering coastal habitats to find a hiding place where they could transform into juvenile eels. Further studies are needed to clearly identify these large leptocephali and to learn about their life history.

Swordfish in the Mediterranean Sea have been caught with harpoon since 1000 BC, when, from May to August, these animals come to the surface often in male–female pairs. At this time, swordfish exhibit a variety of swimming behaviours largely only known by fishermen targeting swordfish. Over four years from 2002 to 2005, we observed the behaviour of swordfish in surface waters from the sighting platform of a harpoon fishing boat. The behaviour of 207 swordfish pairs, 73 single females and 124 single males, were recorded. On the basis of behaviours identified by the fishing fleet, we classified a priori, the behaviour of single males, single females and pairs of swordfish across seven categories. After capture, the maturity stage of each fish was determined macrocospically and assigned to a gonadosomatic index (GSI). Both male and female of a higher GSI were more frequently observed in surface waters during June and July (analysis of variance (ANOVA) F(3,276) = 70.107; P = 0.001) and individual GSI was observed to be associated with differing behavioural grouping. The most frequent behaviours observed were: a female that swam rectilinear closely followed by the male, or two fish that swam near the surface and turn out going full circle. Both behaviours were associated with the maturity Stage IV. Our data suggest that reproductive behaviour of swordfish involve a long lasting surface courtship display with different phases influenced by gonad development.

The underwater sound of R/V "Johan Hjort" as a function of aspect angle has been mapped by cruising along parallel transects at various distances from the recording unit. At frequencies over 125 Hz there was a minimum in front of the vessel, and lobes of higher intensity on both sides. About 20% of the herring schools recorded during a survey in the North Sea seemed to react to the survey vessel. The distance at which the schools reacted varied from about 25 m and up to about 1000 m in front of the vessel. Within a sector of 20° on each side of the path of the vessel, the fraction of schools reacting increased to about 50%. Most of the schools that reacted seem to be herded in front of the vessel. This reaction pattern may indicate either that the schools reacted to the higher sound intensity to the side of the vessel or that the pattern occurred because of a "pursuit effect". Despite the apparent herding, more than 40% of the schools in front of the vessel were not recorded by the echo sounder. It is therefore argued that horizontal avoidance close to the vessel may have caused an underestimation of the biomass of herring of about 20%.