Student Connection

TC 00-08 Swordfish larvae

9-15 July 2000  We have just completed our second and final larval swordfish collection cruise for the year. As before, our collection efforts were conducted off the Kona coast of the Island of Hawaii. Our primary collecting gear for swordfish larvae was the Issacs-Kidd trawl which we towed at the surface along the starboard side of our ship (see picture from previous cruise TC 00-06). After towing this gear for an hour at the sea surface, the collected sample is removed from the back (cod end) of the net, it’s contents poured into a plastic tray, and the sample sorted and examined inside our ship’s wet lab. We were surprised by the results of this cruise since not one swordfish larvae was collected by the Issacs-Kidd trawl. This contrasts to just 6 weeks earlier, when we were able to capture 31 swordfish larvae. Several other surface dwelling animals that were common 6 weeks ago were caught in very low abundance during this cruise. This includes juvenile (1-4 cm in length) mahimahi, flying fish, sargassumfish, and the Portuguese man-of-war jellyfish. Also unexpected, were the large numbers of juvenile broomtail filefish which were captured during this cruise. These fish have apparently been reported to be unusually abundant around the Hawaiian Islands since spring of this year.

While daytime surface Issac-Kidd tows were being conducted from the Townsend Cromwell, an aluminum safeboat with two scientists aboard was launched each morning and spent the day investigating nearby surface slicks in greater detail. These operations included towing small surfacenets along each side of the safeboat, dip-netting any young swordfish or other billfish seen within these surface slicks, and if possible, to video record the behavior of young billfish found swimming within the slicks. As luck would have it, a small billfish (this term includes marlin, sailfish, spearfish, and swordfish) was dip-netted on the second day and returned to our ship still alive. We placed this billfish in our large baitwell and it remained alive for just under two days. Although we were disappointed that it did not survive longer, no one as yet has been successful at keeping these open ocean animals alive in captivity for more than a few days. We were surprised to discover that after retrieving it from the bottom of our baitwell, a closer examination of this billfish revealed that it was not a spearfish as we thought but instead a young swordfish. On the last day (July 14^th) of our cruise off Kona, another young swordfish of similar size was dip-netted at the surface while it swam along a surface slick that contained a fair amount of floating debris. This fish was quickly brought back to our ship and temporarily kept in a large barrel before being transferred to a shore side facility. Unfortunately, this animal appeared to be behaving erratically and will probably not likely survive captivity. From our experiences, we can now recognize the appearance of these animals in the water by rounded tips of the pectoral (side) fins, the pale coloration of the bill near its tip, and the eel-like swimming motion of these young swordfish as they move along the top of the water. We hope that from this initial work, we will learn how to be able to keep these young swordfish and perhaps other young billfish alive in captivity. Once we have this ability, a number of controlled laboratory studies can be conducted to learn more about the behavior, growth, and physiology of these little known but important game and food fishes.

Last modified July 21,  2000