Hawaii Striped Marlin Research

Tracking Striped Marlin in Hawaiian Waters

P.I. Kim Holland, Co-PI David Itano

Project Overview

The Hawaii striped marlin tagging project has two complementary goals. The first is to develop appropriate methodologies for tagging very active open ocean fishes – especially marlin – and the second is to learn more about the movement patterns of striped marlin (Tetrapturus audax) when they are in the vicinity of the Hawaiian Islands. Of particular interest is whether or not there is a general pattern to their direction of movement when they leave the islands or whether their movements are typified by a more or less random dispersal.

Background

Ulua school

Figure 1. Striped Marlin at the stern of the vessel following release from the tagging cradle. Fish are sometimes towed by the bill for a few seconds to accelerate resuscitation.

The next major breakthrough in understanding the movements of open ocean fishes (such as tunas, marlin and mahimahi) will be when techniques are developed that will allow their movements to be tracked for longer periods – in the range of one or two years or more. This will allow us to discern if there are regular routes for their large scale movements and which environmental cues might influence these movements. Although there is good progress towards this goal in some species of sharks (which are thick-skinned and comparatively slow moving), long-term external attachment of electronic tags to large, active teleosts has proved elusive. Externally attached “pop-up” transmitters that uplink data to satellites are the tool of choice because it is not necessary for the fish to be caught a second time in order to obtain information regarding its horizontal and vertical behavior. To try and lengthen the attachment duration of external tags (and also allow surgical implantation of other types of tag), this project involved designing and testing new versions of two key components of tracking technology – an articulated, outboard cradle for restraining the animals during tagging and a new type of anchor for attaching external tags to the fish.

Hawaii has an annual “run” of juvenile striped marlin which appear in Hawaiian waters roughly between the months of December and April. Hawaii is unusual in that virtually all striped marlin in these waters are juveniles – large adults are very rare. The juveniles range from about 10 – 40 kilos and probably represent 1 and 2 year old fish. In other words, Hawaii appears to be part of a nursery area which sub-adult fish use for a few months every year before moving on to other parts of the ocean where they grow to be sexually mature. The question is – where do these small striped marlin go when they leave Hawaii and do they all go to more or less the same place via the same routes? These medium-sized, very active fish were chosen as an appropriate candidate for testing new methods of attaching electronic tags to open ocean fishes.

Progress so Far

An articulated cradle for small research boats was designed and tested and the results have been extremely positive. The core concept is that the trailing edge of the cradle can be lowered into the water alongside the boat so that captured fish can be guided into the cradle without being lifted out of the water as a dead weight or without the use of nets which can cause abrasions - and which often aren’t large enough! Once the animal has been guided into the padded cradle, the hinged outer door of the cradle can be snugged up and locked tight against the side of the fish to restrain it and prevent injury due to struggling.

Marlin Tagging Cradle

Figure 2. Cradle in deployed position with hinged outer wall open. The trailing edge of the cradle trails in the water allowing researchers to slide fish into the cradle with out applying excessive force to the hook or jaw.

The cradle is then lifted back up to a horizontal position where researchers can accurately and safely attach tags. Once in this position, a hose is placed into the animal’s mouth to provide water to the gills during the brief period that the fish remains restrained within the cradle. When the tag has been attached, the process is reversed – trailing edge of the cradle is lowered into the water, the hinged door is allowed to fall open and the fish slides out at the stern of the boat.

	Figure 3. Striped marlin in cradle with outer wall locked and cradle in retracted position. Green hose can be seen delivering seawater to the mouth of the fish.
	Figure 4. Striped marlin with pop-up tag attached just prior to release.

A new tag anchor system was developed to reduce the amount of vibration transmitted from the tag to the anchor and to promote healing around the attachment incision. By attaching the tag leader to a stiff post implanted in the dorsal musculature, vibration into the animal is reduced and the skin has a rigid structure around which to heal. Because the anchor is made from medical grade nylon, it can be cut to size to fit each individual fish and thereby minimize the profile of the attachment post. Tests with dead specimens showed that this anchor design has very good holding power and implantation on live marlin has proved to be straightforward and rapid.

Ulua active tracks

Figure 5. Striped marlin with Pop-up tag attached (Wildlife Computers mini-PAT). The tag is attached to the post of the anchor system. Also visible is a yellow “spaghetti” tag.

To date, the new cradle system has been successfully used to tag twelve striped marlin with pop-up satellite tags and to internally implant acoustic transmitters several others. We have also started using the cradle for tagging tuna and this cradle design has now been adopted by other groups around the world. Results of the tracks will be posted when all the satellite tags have transmitted their data.

This research was funded by the Large Pelagics Research Program (University of New Hampshire) and the Pelagic Fisheries Research Program (University of Hawaii).

Project Publications

Holland, K.N., D. Itano and M. Domeier. 2006. First successful surgical internal attachment of electronic tags in marlin. Proceedings of Fourth International Billfish Symposium. Bull. Mar. Sci. 79(3):871-874.

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