Thresher Sharks

The thresher shark family contains three species that use their long caudal fin for feeding and stunning prey.  Off California, the bigeye and common thresher sharks are more prevalent, but in some years pelagic threshers may also occur here.  PIER has worked on this unique group of pelagic sharks for various projects that are further described in more detail below.

Survivorship in Commercial Fisheries

Recently, the PIER team has focused on the post-release survivorship of bigeye thresher sharks, a frequent catch in the recently-authorized deep-set fishery targeting swordfish.  Because bigeye threshers do not have the same market value as swordfish, it is not uncommon for them to be released in an attempt to save hold space for more valuable product.  PIER documented the survivorship of bigeye thresher sharks following release on both deep-set buoy gear and linked buoy gear through support from the NOAA Bycatch Reduction and Engineering Program.

Survivorship in Recreational Fisheries

Past work by the PIER team has focused on documenting post-release survivorship in the California recreational fishery for common thresher sharks.  The common thresher is a great game fish that provides anglers with a challenge during the spring and fall months.  This PIER-NOAA collaboration resulted in several outreach products including a short video segment on catch-and-release survivorship produced by the NOAA Ocean Media Center.

Additional studies at PIER include work on the Feeding Behavior and Ecology of the common thresher as well as NSF sponsored studies that focused on thresher shark muscle physiology.

As with most PIER research, thresher shark studies have been conducted through productive collaborations with other research organizations, including NOAA SWFSC, University of Massachusetts, Dartmouth, MiraCosta College and the University of Calgary, Canada.

Thresher Shark Feeding Behavior and Ecology

Collaborative Researchers: Diego Bernal, Ph.D. (University of Massachusetts)
Objectives: This study was performed to document the role of the common thresher shark caudal fin during feeding.

Baited lures were slow-trolled from the PIER research vessel Malolo within the field of view of an underwater video camera. All video clips containing thresher shark feeding events were selected for frame-by-frame analysis to evaluate the specific body posture and caudal fin orientation associated with each feeding behavior. Video footage was recorded for 33 thresher shark feeding attempts, 42% of which made active attempts to strike the baited lure with their caudal fin. This work showed that all of the recorded feeding events were initiated with the upper lobe of the caudal fin (Aalbers et al., 2010).

Two distinct caudal-based feeding behaviors were documented during this study. The most prevalent feeding strategy was initiated by a rapid forward undulation of the anterior body which resulted in a posterior-traveling sinusoidal wave that consequently advanced to the uppermost tip of the caudal fin (Video clip #1 link). The second predominant feeding behavior involved a lateral strike of the caudal fin while the shark was positioned directly adjacent to the baited lure (Video clip #2 link).

This study confirms that the common thresher shark uses its elongate caudal fin to immobilize prey prior to consumption and provides insight into the evolution of this unique feeding strategy among Alopiid sharks. Additional work is necessary to more precisely understand the kinematics of the disproportionately long caudal fin during swimming and feeding.  Watch additional underwater video footage of thresher shark feeding activity.

This material is based on work supported by the National Science Foundation under grants (IOS-0617384 & IOS-0617403) any opinions, findings or conclusions expressed in this material are those of the authors and do not necessarily reflect the views of NSF. Additional support was provided by the George T. Pfleger Foundation and the Bycatch Reduction and Engineering program through NOAA.

Catch-and-release survivorship in the southern California recreational fishery

Project support provided by the NOAA Bycatch Reduction Engineering Program

Collaborative Researchers:

Diego Bernal, Ph.D. (University of Massachusetts)
Craig Heberer, NOAA Southwest Region 
Suzy Kohin, Ph.D., NOAA SWFSC

Objectives and Background:

This project uses PSAT technology to estimate survivorship in three different components of the Southern California recreational fishery for thresher sharks.  Initial work started off with quantifying catch and release mortality in the caudal-based (tail-hook) fishery.  This Fishery usually targets larger thresher sharks by trolling lures with large J-hooks.  When thresher sharks intiate a strike with their tail, they are frequently foul hooked and brought to the boat tail first.  This work identified relatively high mortality rates for foul-hooked sharks that remained on the line for more than 85 minutes (Heberer et al., 2010).  At times, this foul-hooking strategy represents the largest component of the recreational fishery.  Recommendations from this work have been presented at over a dozen public venues and assisted in the production of a NOAA and PIER endorsed brochure on best fishing practices.

Scott Aalbers with a large female thresher shark tagged and ready for release.

The second and third phases of this work are currently underway and focus on additional modes of capture as well as issues that surround the recreational fishery.  Because several different techniques are used to catch threshers and not all threshers are hooked in the tail, the team of collaborators have focused on assessing catch and release mortality using mouth-hooking techniques as well as studying the effects of trailing gear (lures left embedded in the caudal fin of sharks that are lost during the fight).  These studies are currently in the data collection phase .

Swimming Muscle Physiology of Thresher Sharks

The Functional Significance of Divergent Locomotor Designs in Pelagic Fish (National Science Foundation IOB-0617384)

Collaborative Researchers:
Diego Bernal, Ph.D. (University of Massachusetts)
Jeanine Donley, Ph.D (Mira Costa College)
Douglas Syme, Ph.D. (University of Calgary, Canada)

This project  compared several aspects of locomotor muscle function and design within a single family of large pelagic sharks, the thresher sharks (Alopiidae). Within the thresher family there are three different species (common thresher, bigeye thresher and pelagic thresher) that all possess an extremely elongate upper caudal lobe, which is as long as their entire body.

Superficially, all three thresher species appear to be very similar, however, recent studies have shown that the internal anatomy of the common thresher is surprisingly distinct from the pelagic and bigeye threshers (Sepulveda et al. 2005).

In the common thresher, the red muscle (sometimes referred to as the blood-line) is condensed in to a solid, piston-like muscle mass that is predominantly distributed over the anterior body in a medial position (i.e. near the vertebral column). Anatomically, this layout is strikingly similar to that of tunas and lamnid sharks, two groups known for specialized swimming muscle physiology. Common threshers also differ from the other two species in having a blood supply to the RM through a set of lateral vessels that give rise to a countercurrent heat exchange system. This heat exchange system allows for RM temperature elevation, just as it does in tunas and lamnid sharks (Bernal et al., 2005).

Whole-body reconstructions of the three thresher shark species, showing the very different positions of the red, aerobic locomotor muscle (RM).

The threshers are the only group known to posses both regionally endothermic and ectothermic taxa, and represent the ideal system for testing hypotheses on the evolution of divergent locomotor mechanisms.

This study examined the swimming biomechanics and twitch kinetics of this group and compared these data to other high performnce species (i.e., mako sharks).