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Behavior and Movements of Tuna in Hawaiian Waters
P.I. Kim Holland, Co-PIs David Itano & Laurent Dagorn
 
Background

Investigation of the behavior, physiology and movement patterns of tuna and other pelagic (“blue water’) species such as marlin and mahimahi has a been a long-standing emphasis for HIMB researchers. This research is particularly pertinent for Hawaii where these species have great importance both commercially and culturally. Also, Hawaii researchers enjoy the great advantage that these species are available year-round and occur not far from shore.

Whose Fish Are They? We are specifically interested in the range of movements and ‘residency’ of tuna and marlin caught in Hawaiian waters – are Hawaiian fish “locals” or do they range over large areas of the Pacific? If they are “locals” how far do they roam away from our shores? That is, what is the ‘catchment area’ that supports Hawaii’s near shore pelagic fisheries? This kind of information will help design science-based management options for Hawaii’s open ocean ecosystem.

Fish Aggregation Devices (FADs). Within the general theme of investigating the movement of fishes around Hawaii, one topic of particular emphasis is the impact of Fish Aggregating Devices (FADs) on the behavior and dispersal of pelagic fishes – especially tuna. The first modern FADs designed for deep, high energy environments were first deployed in Hawaii in the late 1970s. These FADs proved to be very effective in enhancing fishing success and since then, FADs have become essential components of commercial and artisanal fisheries throughout all of the world’s oceans and Hawaii has established itself as a leader in FAD-related research. One of Hawaii’s anchored FADs is shown in Figure 1. Details about the Hawaii FAD array can be found at http://www.hawaii.edu/HIMB/FADS/

Marlin Tagging Cradle

 

Figure 1. Hawaii has a network of over 50 FADs anchored at a range of depths and distances from shore. They consist of a single sphere anchored with chain and polyester rope. Details of the array can be found on the Hawaii FAD web page.

FADs can be very effective. In Hawaii, at certain locations and at certain times of year, large aggregations of tuna can be found around FADs and sometimes these aggregations persist for weeks. In the commercial fisheries of the world, well over 50% of the world’s tuna catch is now caught using either anchored or drifting FADs.

It is still unclear exactly why FADs work but there are two leading hypotheses as to why this aggregation behavior evolved. The first hypothesis is the “indicator log” hypothesis. That is, drifting logs washed out to sea from river mouths drift along within the nutrient rich waters emanating from the river and after a few weeks, these nutrients cause a plankton bloom. These plankton then support higher trophic level organisms that become food for tunas. Thus, associating with a log may enhance a tuna’s chances of finding food. Similarly, a log that becomes entrained where two ocean currents meet might also indicate where nutrients and forage are concentrated which, again, is a good place for a tuna to be.

The ”meeting point” hypothesis suggests that drifting objects such as logs serve as meeting points where individual tuna can find and join a school of conspecifics. For instance, after a night of foraging alone, individual fish can reform into schools more easily if they rendezvous at a log or other structure. Small schools can join to form larger ones. It is generally believed that, within some limits, larger schools are more effective at hunting for prey and in confusing would-be predators.

Obviously, regardless of which of these (or other) hypotheses is correct, tunas did not evolve this behavior in the presence of anchored man-made buoys. Apparently, the association of tuna with these man-made structures is a phenomenon that has been transferred from some other, natural, behavior.

To try and address these questions and to get a better feeling for how fishers exploit the FAD phenomenon, we have been conducting a series of tagging experiments that involve both traditional tag-and-recapture studies using “spaghetti” tags and tracking experiments that use archival tags and acoustic and satellite transmitters.  For the acoustic tagging studies, all of the FADs around the island of Oahu are equipped with acoustic receivers that can detect fishes carrying acoustic transmitters.  In this way, we can monitor the residence times of tuna and detect any movements as they move among the FADs in the array.

Tuna live in a 3D World. While it is true that all fishes – even flat fishes like halibut – live in a three dimensional world, tuna are truly three dimensional in their movements.  Our tracking research has demonstrated that tropical tunas are constantly and rapidly changing depth in the ocean.  In fact, tropical tunas are more like a flock of pigeons wheeling and swooping as they change altitude by hundreds of meters.  The only difference is that these “pigeons” can weigh over 100 kilos!   The thermal vertical structure of the ocean plays an important role in determining the swimming depths of the various tuna species.

 
Methods
Most of what we know about the behavior and movements of fish comes from the results of tagging experiments. These are of three basic types: 1. Tag-and-recapture experiments in which “spaghetti” tags are used to reveal the basic dispersal patterns of individual fish, 2. Acoustic tracking in which acoustic transmitters are placed in the fish. These transmitters can either be actively followed by a tracking boat or detected by receivers deployed in key locations within the animal’s range and, 3. Archival tags that record the movements of the fish. These tags have to be recovered (i.e., the fish caught a second time) in order for the data to be downloaded or, in some cases, the tags transmit the data to satellites. Figures 2 and 3 show the tagging process.
 

Marlin Tagging Cradle

 

Figure 2. Releasing a tagged yellowfin tuna. This fish is equipped with two “spaghetti” tags and acoustic and archival tags that are implanted in its gut cavity.

Marlin Tagging Cradle

 

Figure 3. Satellite tag attached to yellowfin tuna just prior to release.

The investigation of the behavior of fish around FADs uses two basic systems, both of which use acoustic transmitters.  When fish are released carrying acoustic tags, their movements can be followed using a tracking boat or the residence and inter-FAD movements of these fish can be monitored using acoustic receivers attached to the mooring gear of the each FAD (Figure 4).
 

Marlin Tagging Cradle

 

Figure 4. Acoustic receiver attached to the mooring chain of a FAD.

 
Progress so Far

Horizontal Movements of Hawaii Tuna.  Results of tag-and-recapture experiments and from electronic tracking suggest that yellowfin and bigeye tuna found in coastal Hawaiian waters typically do not make large scale trans-Pacific movements.  Although we have had some long distance recoveries from Mexico and Japan, the preponderance of evidence is that Hawaii yellowfin stay within a few hundred miles of the islands.   Two illustrations support this interpretation.  Figure 5 shows the recovery points of yellowfin and bigeye tuna released in Hawaii (principally at Cross Seamount and near Midway atoll).  Most yellowfin were recaptured fairly close to the islands whereas bigeye tuna appeared to have a somewhat larger dispersal pattern.   Data from the electronic tag (Wildlife Computers Mk9)carried by a yellowfin tuna tagged and subsequently recaptured at CO FAD after 265 days at liberty also show that this fish made a loop that took it a few hundred mile north and south of the islands before it was recaptured at the same FAD as where it was originally tagged (Figure 6).

 

Ulua active tracks

 

Figure 5.  Recapture locations of Yellowfin (red) and bigeye (blue) tuna tagged in the Hawaii Archipelago.  The dense red field around the main Hawaiian Islands indicates that, although there were some long distance movements, most yellowfin were recaptured fairly close to the islands.

 
 
Marlin Tagging Cradle

Figure 6. Movements of a yellowfin tuna caught and recaptured at CO FAD off Kaena Point, Oahu. The points were derived using light-based geolocation modeling using light levels recorded by the tag on the fish.

Vertical Movements of Hawaii Tuna.  Sonic tracking experiments and data acquired from implanted tags recovered when fish are recaptured show that, even though yellowfin tuna and bigeye tuna can often be caught “side by side” in the same school, their vertical distribution in Hawaii is usually very different.  Yellowfin are predominantly found in the Surface Mixed Layer which, in Hawaii, typically extends from the surface down to about 75 meters (40 fathoms) in depth.  By contrast, bigeye spend most of the daytime around 200 meters down where the temperature is between 14 and 17 C.   At night, both species are found predominantly within the SML.  Figure 7 shows a 45 minute segment of a bigeye depth track.  Figure 8 shows 265 days of a yellowfin track.  Most of the movements of this fish were within the Surface Mixed Layer but there was also a lot of deeper diving – such as the 900 meter dive towards the end of the track.

 

Ulua active tracks

Figure 7. Diving behavior of 57 cm bigeye tuna. In Hawaii, bigeye tuna spend daytime hours around 200 meters below the surface. This 45 minute trace shows a rapid dive to 380 meters where water temperature was 9.0C. At nighttime, tracking experiments show that bigeye move closer to the surface. A similar shallowing of their depth behavior occurs when bigeye associate with FADs.
 

Ulua active tracks

 

Figure 8.  Data record from an implanted tag recovered from a yellowfin tuna after 265 days at liberty.  The top panel shows the water temperatures experienced by the tuna carrying the tag. The unevenness of the upper surface of the red trace reflects the changing surface temperatures experienced by the fish during its movements.  The middle panel shows the dive depths of the fish.  The trace is displayed in two colors with the green representing the time that the fish was in the surface mixed layer.  Notice how the thickness of this layer changes with the seasons.  Similarly, in the bottom trace which records light levels, the trace gets narrower as day length decreases in winter.  The bumps in the lower part of the light curve indicate full moon periods.

 

The Impact of FADs. Active tracking of acoustically tagged yellowfin reveals that tuna associate with FADs in the daytime and often depart at night – presumably to feed – before returning the next day. The “catchment” area of a FAD is about 5 miles. That is, this is the distance that tuna will roam before going back to the FAD (Figure 9). The data from acoustic receivers on the FAD moorings indicate that most tuna do not “hopscotch” between FADs but, rather, visit only one FAD and then depart for long periods of time – or permanently. These results indicate that FAD networks do not seem to permanently “trap” tuna but rather seem to focus their local movements rather than radically alter them. Our data indicate that FADs tend to bring bigeye tuna closer to the surface than they are when they are not associated with a FAD. By contrast, FADs do not seem to significantly alter the vertical behavior of yellowfin tuna.

Ulua active tracks

Figure 9. Movements of Yellowfin Tuna associated with V FAD, Oahu. The fish moved away form the FAD at night and returned the next day. The influence of FADs extends to about 5 miles (red line).
 
Project Publications

Adam, S.M., J.R. Sibert, D. Itano and K.N. Holland. 2002.  Dynamics of bigeye and yellowfin tuna in Hawaii’s pelagic fisheries: analysis of tagging data using a bulk transfer model incorporating size specific attrition. Fish.Bull.101(2):215-228

Holland, K.N., A. Jaffe and W. Cortez. 2000.  The FAD system of Hawaii. In: Peche thoniere et dispositifs de concentration de poissons (Le Gall and Tacquet, Eds). Actes du Colloques d'IFREMER 28. 288p.

Itano D G. and K.N. Holland. 2000. Tags and FADs - movements and vulnerability of bigeye tunas in relation to FADs and natural aggregation points.  Aqua. Liv. Res. 13(4): 213-223.

Sibert, J.R., K.N. Holland and D. G. Itano. 2000.  Exchange rates of yellowfin and bigeye tunas and fishery interaction between Cross Seamount and nearshore FADs in Hawaii. Aqua. Liv. Res 13(4) 225-232.

Holland, K.N and R.D. Grubbs.  2007. Tunas and billfish at seamounts. In: Pitcher, T.J. et al. (Eds.) Seamounts: ecology, fisheries & conservation. Fish and Aquatic Resources Series, 12: pp. 189-201. Blackwell Press

Dagorn, L. C., K.N. Holland and D. G. Itano. 2007. Behavior of Yellowfin (Thunnus albacares) and Bigeye (Thunnus obesus) tuna in a network of fish aggregating devices (FADs). Marine Biology. 151(2): 595-606

Dagorn L, Holland K, Dalen J, Brault P, Vrignaud C, Josse E, Moreno G, Brehmer P, Nottestad L, Georgakarakos S, Trigonis V, Taquet M, Aumeeruddy R, Girard C, Itano D, Sancho G. 2007. New instruments to observe pelagic fish around FADs: satellite-linked acoustic receivers and buoys with sonar and cameras. In: Lyle J.M., Furlani D.M., Buxton C.D. (Eds), Cutting-edge technologies in fish and fisheries science. Australian Society for Fish Biology Workshop Proceedings, Hobart, Tasmania, August 2006, Australian Society for Fish Biology.

Graham, B., R.D. Grubbs, K.N. Holland and B. Popp. 2007.  A rapid ontogenic shift in the diet of juvenile yellowfin tuna from Hawaii.  Marine Biology.  150(4):647-658

Holland, K.N. 1996.  Biological Aspects of the Association of Tunas with Fish Aggregating Devices. FAD Newsltr. (2):1-8. South Pacific Commission, Noumea, New Caledonia

Holland, K.N and J.R. Sibert. 1994. Physiological thermoregulation in bigeye tuna (Thunnus obesus).  Environ. Biol. Fish. 40:319-327.

Holland, K.N., R.W. Brill and R.K.C. Chang. 1990.   Horizontal and vertical movements of yellowfin and bigeye tuna associated with fish aggregation devices.  Fish. Bull. 88:493-507.

Holland, K.N., Meyer C.G., Dagorn L.C. 2009. Inter-animal telemetry: results from first deployment of acoustic ‘business card’ tags. Endangered Species Res. doi: 10.3354/esr00226.

Technical Reports

Itano, D., K Holland, L. Dagorn, D.G. Grubbs and Y. Papastamatiou. 2004. Monitoring movement patterns, residence times and feeding ecology of tuna, billfish and oceanic sharks within a network of anchored FADs. Technical Report to the 17th meeting of the Secretariat of the Pacific Community (SPC) Standing Committee on Tuna and Billfish, Majuro, Marshal Islands.

Holland, K.N., R.D. Grubbs, B. Graham, D. Itano and L. Dagorn. 2003. FAD-associated tuna: Temporal dynamics of association and feeding ecology.  Technical Report to the 16th meeting of the SPC Standing Committee on Tuna and Billfish. Mooloolaba, Australia

Grubbs, R.D., K.N. Holland and D Itano. 2002. Comparative trophic ecology of yellowfin and bigeye tuna associated with natural and man-made aggregation sites in Hawaii.  Technical Report to the 15th meeting of the SPC Standing Committee on Tuna and Billfish. Honolulu.

Grubbs, R.D., K.N. Holland and D. Itano. 2001. Food Habits and trophic dynamics of structure-associated aggregations of yellowfin and bigeye tuna in the Hawaiian Islands: Project description, rationale and preliminary results. Technical Report to the 14th meeting of the Standing Committee on Tuna and Billfish. Noumea, New Caledonia  

 
 
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