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Home , False killer whale, Killer whale, Scars (The Walking Dead)

False Killer Dorsal Disfigurements as Possible Indicator of Long-Line Fishery Interactions in Hawaiian Waters1

Robin W. Baird 2 and Antoinette M. Gorgone3

Abstract: Scarring resulting from entanglement in fishing gear can be used to examine cetacean fishery interactions. False killer ( crassidens) are known to interact with the Hawai‘i-based and swordfish long-line fish- ery in offshore Hawaiian waters. We examined the rate of major dorsal fin dis- figurements of false killer whales from nearshore waters around the main Hawaiian Islands to assess the likelihood that individuals around the main is- lands are part of the same population that interacts with the fishery. False killer whales were encountered on 11 occasions between 2000 and 2004, and 80 dis- tinctive individuals were photographically documented. Three of these (3.75%) had major dorsal fin disfigurements (two with the fins completely bent over and one missing the fin). Information from other research suggests that the rate of such disfigurements for our study population may be more than four times greater than for other odontocete populations. We suggest that the most likely cause of such disfigurements is interactions with longlines and that false killer whales found in nearshore waters around the main Hawaiian Islands are part of the same population that interacts with the fishery. Two of the docu- mented with disfigurements had infants in close attendance and were thought to be adult females. This implies that even with such injuries, at least some fe- males may be able to produce offspring, despite the importance of the dorsal fin in reproductive thermoregulation.

Incidental mortality in fisheries is gear on beach-cast animals (e.g., Friedlaender probably the greatest conservation concern et al. 2001); (3) observations of animals in the for cetaceans worldwide (Read et al. 2003). wild with entangled fishing gear (e.g., Knowl- Identifying fishery interactions can be done ton and Kraus 2001); or (4) questionnaire sur- in a variety of ways: (1) using observers on veys of fishermen (e.g., Baird et al. 2002). fishing vessels (e.g., Jefferson et al. 1994); (2) Each of these methods has advantages and examination of wounds, scars, or entangled disadvantages: (1) observer programs provide the most comprehensive and quantitative data 1 Field efforts were funded by the National Marine but are expensive, particularly when fishing Fisheries Service, Southwest Fisheries Science Center, fleets are large; (2) only a small proportion of the Hawaiian Islands National Marine dead animals ever wash up on a beach, and Sanctuary, the M.R. & Evelyn Hudson Foundation, the U.S. Navy (through the SWFSC), and by a donation beach-cast animals are easily damaged by from Tom and Chris Brayton. Research was undertaken scavengers, obscuring marks; (3) observations under NMFS Scientific Research Permits No. 731-1509 of animals in the wild with entangled fishing and 774-1437. Manuscript accepted 12 November 2004. gear are opportunistic and likely reflect only 2 Corresponding author: Cascadia Research Collec- 1 a small proportion of animals entangled, even tive, 218 2 West 4th Avenue, Olympia, 98501 (e-mail: [email protected] or for large and easily observed ; and 4) [email protected]). questionnaire surveys often suffer from a stra- 3 National Marine Fisheries Service, 101 Pivers Island tegic response bias, with fishermen unlikely Road, Beaufort, North Carolina 28516. to provide information that could result in negative management actions. Rates and pat- Pacific Science (2005), vol. 59, no. 4:593–601 terns of entanglement-related scarring visible : 2005 by University of Hawai‘i Press in photographs of animals in the wild have All rights reserved also been used to assess the frequency of non-

593 594 PACIFIC SCIENCE . October 2005 lethal entanglements (Robbins and Mattila EEZ, in international waters, and in other 2001). At least for some species, use of this central Pacific U.S. EEZs may involve false technique may result in more accurate (and killer whales from the Hawaiian population, likely much higher) estimates of fisheries in- but data are lacking to examine potential teractions than are available from examina- links. We have been photo-identifying false tion of beach-cast animals or opportunistic killer whales as part of a population assess- observations of animals carrying fishing gear. ment of this species in nearshore waters of Such studies may work well on large animals the main Hawaiian Islands. This species is where a high proportion of individuals that easy to approach and photograph, though interact with fishing gear break free, though scarring is difficult to document because applicability is questionable to smaller spe- scars heal the same color as the background cies, or those more difficult to approach and body pigmentation (R.W.B., pers. obs.). In photograph, or those where fishing gear en- this study we use photographs of false killer tanglement usually results in death. whales to assess whether animals around the False killer whales (Pseudorca crassidens) main islands exhibit potential signs of in- have been documented interacting with the teractions with long-line fisheries, and we Hawai‘i-based tuna and swordfish long-line compared injury rates with those of other fishery (Nitta and Henderson 1993, Carretta populations of odontocetes. et al. 2004). The estimated size of the Hawai‘i ‘‘stock’’ of false killer whales, from a line tran- materials and methods sect survey covering the entire Hawaiian Exclusive Economic Zone (EEZ), is only 268 Fieldwork occurred around all the main individuals, with a coefficient of variation Hawaiian Islands from 2000 to 2004, though (CV) of 1.08 (Barlow 2003). Mobley et al. effort varied among islands. We used a variety (2000) derived an estimate of 121 individuals of research vessels ranging in size from 6 to 18 (CV ¼ 0.47) based on aerial surveys within m long. During 2002 and 2003 we often used approximately 45 km of the main Hawaiian two research vessels simultaneously but main- Islands. This stock is listed as ‘‘strategic’’ by tained a distance of at least several kilometers the U.S. National Marine Fisheries Service between the vessels to cover different por- (NMFS), because the estimated level of seri- tions of the study area. Survey speeds were ous injury and mortality from this fishery generally between 16 and 30 km/hr, and two (less than four animals per year) is greater to five observers scanned 360 degrees around than the Potential Biological Removal (PBR) the boat. Search effort was concentrated in level (approximately one per year) set sea conditions less than Beaufort 4, off the by NMFS (Carretta et al. 2004). Most false leeward coasts of all islands. We searched killer whales caught in the long-line fishery nonsystematically both near shore and out to are released alive but usually trailing gear approximately 42 km from shore, in waters up and/or with apparent injuries or hooks to 4,000 m deep, attempting to cover as much embedded. This fishery does not occur within of the study area as possible given sea condi- approximately 80 km of the Hawaiian Islands tions. All encounters with all species of odon- but extends offshore and into international tocetes were recorded, and in the case of false waters outside the Hawai‘i EEZ, as well as killer whales, we made efforts to obtain multi- into other U.S. territorial waters in the cen- ple photographs of every individual in each tral Pacific. False killer whales in the near- group encountered, using Canon SLR film shore waters of the main Hawaiian Islands (2000–2002) or digital (2003–2004) cameras are genetically distinct from animals in the with 100- to 300-mm zoom lenses. All photo- eastern tropical Pacific Ocean (Chivers et al. graphs were examined and individuals identi- 2003); however, the offshore range of the fied based on the size and location of notches Hawaiian population has not yet been deter- on the dorsal fin. The program Finscan (Hill- mined. Some or all of the fishery interactions man et al. 2003) was used to assist in match- that occur throughout the Hawaiian Islands ing individuals. Individuals were considered False Fishery Interactions . Baird and Gorgone 595 distinctive (or ‘‘marked’’) if the notches on (estimated at less than a year of age) the first the dorsal fins were large enough to be recog- time they were seen. Individual HIPc177 was nizable in any good-quality photograph. We seen with the infant surfacing in infant posi- classified individuals as having major dorsal tion, further suggesting a mother-offspring fin disfigurements if they were missing the relationship ( J. Mann, pers. comm.). Photo- dorsal fin or if it was completely bent over at graphs were obtained of both the left and the base. right side of individual HIPc177, and from examination of photographs only a small results amount of unpigmented scar tissue (estimated at @1cm2) was visible at the site of the miss- Between 2000 and 2004 we spent 1,684 hr ing dorsal fin, suggesting that the wound had searching for cetaceans, covering 23,558 km healed completely. The area of the missing of trackline on 234 different vessel days (a fin was raised @1 cm above the dorsal surface day with two boats searching simultaneously of the whale. was counted as two vessel days). Search effort was spread over 10 months of the year (all discussion except July and August), though the total number of search days per month for all 5 yr Collapsed or missing dorsal fins have not pre- varied from 6 to 49. During this time we viously been reported for false killer whales encountered 417 groups of odontocetes, and have only rarely been reported for any representing 16 species. False killer whales cetaceans. Natural sources of cetacean dorsal were encountered on 11 occasions (2.6% fin injuries include both intra- (e.g., Chu and of encounters), tied for the seventh most Nieukirk 1988, Visser 1998) and interspecific frequently encountered species. False killer interactions, as from predatory (e.g., whales were documented during each of the 5 Corkeron et al. 1987) or killer whales ( yr, in a total of eight different months of the orca). Anthropogenic sources of such injuries year (with no obvious seasonality), off O‘ahu, include entanglements with fishing gear (e.g., Maui, La¯na‘i, and Hawai‘i. Group size ranged Green et al. 1991, Mann et al. 1995), gunshot from 3 to 41 individuals (mean ¼ 19.4, wounds (e.g., Bigg et al. 1987), boat strikes SD ¼ 13.0). (e.g., Wells and Scott 1997, Visser and Fertl We took approximately 2,500 photograph 2000), scarring from tags (e.g., Scott et al. frames and documented 80 marked individual 1990), and deliberate notches placed in the false killer whales. Of these, one is missing fin for identification purposes (e.g., Bigg the dorsal fin entirely (catalog no. HIPc177 1982). In extreme cases individuals of some [Figure 1, top]), two have their dorsal fins species have been documented with bent- bent over completely at the base (catalog over or missing dorsal fins. Bent-over dorsal nos. HIPc166 and HIPc186 [Figure 1, middle, fins have been reported most frequently in bottom]), and a fourth has the dorsal fin par- killer whales (Bigg et al. 1987, Baird and tially bent over (catalog no. HIPc127). All Stacey 1989, Visser 1998). Killer whales are three of these latter individuals have notches/ highly sexually dimorphic, and the dorsal fin injuries at the base of the leading edge of the of an adult male is approximately twice the fin, and no other individuals in the catalog height of the dorsal fin of an adult female. have notches at the base of the leading edge All cases of collapsed fins in killer whales of the fin. For the purpose of comparisons have been adult males, and presumably the with other populations of odontocetes, we high frequency of such disfigurements for consider only the first three individuals to this species is related to the unusually large have ‘‘major’’ dorsal fin disfigurements, thus fin. In Prince William Sound, , col- giving a rate of major disfigurements of lapsed dorsal fins have been documented for 3.75% of the ‘‘marked’’ population. The first three adult males (Matkin et al. 1999), two of two individuals were thought to be adult fe- which had their fins collapse shortly ex- males, based on the close proximity of infants posure to oil from the Exxon Valdez spill, sug- Figure 1. (Top) (catalog no. HIPc177) with missing dorsal fin. (Middle) False killer whale (catalog no. HIPc166) with dorsal fin bent over to right with injury at base of leading edge of fin. (Bottom) False killer whale (cat- alog no. HIPc186) with dorsal fin bent over to left with injury at base of leading edge of fin. False Killer Whale Fishery Interactions . Baird and Gorgone 597 gesting that dorsal fin collapse may be related cause the fin is thickest at the anterior end) in some cases to poor health or stress (Matkin or through heating of the fin during healing, et al. 1999). Visser (1998) reported one adult resulting in softening of the and sub- male killer whale with a collapsed fin and with sequent bending of the fin ( J. McBain, pers. an indentation around the thorax, suggesting comm.). For the animal missing the fin, a that the individual may have been entangled line wrapped at the base of the dorsal fin at some time. could work its way through the fin slowly, For Hawaiian false killer whales, the as was documented for a spinner in most likely causes of the disfigurements we Hawaiian waters (Green et al. 1991; see also have documented include sharks, boat strikes, Norris 1992). It is possible that the missing or fishing gear entanglements. bite dorsal fin is simply a congenital defect; how- wounds are typically jagged, and dorsal fin ever the presence of scar material at the site injuries from sharks appear to be relatively of the missing fin suggests that this is un- uncommon, compared with injuries on other likely. Such disfigurements suggest that false parts of the body (Heithaus 2001). Depend- killer whales seen around the main Hawaiian ing on propeller size, boat strike wounds can Islands are part of the same population that be somewhat linear (e.g., Wells and Scott interacts with long-line fisheries in areas at 1997, Visser and Fertl 2000), though exam- least 80 km from shore. It is also possible ples of odontocetes with recognized boat that such disfigurements may have come strike wounds involving the dorsal fin consist from interactions with other Hawaiian fish- of a series of vertical cuts through the fin and/ eries, such as the nearshore commercial or or along the body adjacent to the fin, unlike sports troll fishery, although there is no infor- the injuries we observed. It thus seems un- mation available to assess the likelihood of likely that the disfigurements we have docu- this possibility. mented resulted from shark bites or boat Few published data are available on rates strikes. of such major dorsal fin disfigurements from Observer reports from the Hawai‘i other populations of odontocetes, though we long-line fishery have noted that false killer were able to compile unpublished data from a whales struggle vigorously when hooked (E. number of researchers (Table 1). The rate of Forney, pers. comm.), and a photograph of major dorsal fin disfigurements in our study one hooked false killer whale from this fish- is more than four times higher than for any ery shows a linear mark extending posteriorly other population of odontocete that we were from the mouth along the side of body (Fig- able to find data on. Of the 14 studies (in- ure 2), presumably an abrasion from strug- cluding ours), our total number of marked gling against the longline. All three of the individuals ranks 13th, yet our number of in- animals we documented with completely or dividuals with major disfigurements is tied for partially bent-over fins had injuries at the first rank. Although survey methods may vary leading edge base of the fin. Such injuries between studies, individuals with missing or are consistent with line or fishing gear inju- bent-over fins are quite unusual and are likely ries documented from other cetaceans (see, to have been noted if seen (personal commu- e.g., Norris 1992, Wells et al. 1998, Robbins nications from sources in Table 1). Some of and Mattila 2001). We suggest that the major the populations in Table 1 are known to in- dorsal fin disfigurements we have docu- teract with fisheries (e.g., North Carolina mented from Hawai‘i false killer whales are Tursiops [Friedlaender et al. 2001]; New Zea- most likely a result of long-line interactions land Orcinus [Visser 2000]), though it is pos- such as this, with an animal struggling against sible that lower rates of dorsal fin injuries may a longline rolling against the gear and injur- be due to higher rates of mortality per inter- ing or severing the dorsal fin in such strug- action, differences in gear type used (e.g., gill gles. Injuries at the base of the leading edge nets versus longlines), or species differences of the fin could result in dorsal fin collapse ei- in how animals respond to hooking or entan- ther through loss of structural support (be- glement. 598 PACIFIC SCIENCE . October 2005

Figure 2. Hooked false killer whale from the Hawai‘i long-line fishery, showing linear mark along side of body ap- parently as a result of long-line abrasion. Examination of a high-resolution scan of the original photo shows that the mark is not equally dark along the irregular surface of the body, and it clearly extends into the shadowed area of the back, indicating that the mark is not a shadow from the longline. Photo by Eric Forney, courtesy NOAA Fisheries, Pacific Islands Region.

Our results also have implications re- lation, providing cooled blood to the female garding the ability of seriously injured ani- reproductive system (Rommel et al. 1993). mals to survive and reproduce. The dorsal fin Two of the individuals with disfigurements is known to be of importance in thermoregu- were thought to be adult females and both TABLE 1 Summary of Rates of Major Disfigurements (Completely Missing or Bent Over at Base) for Odontocete Populations

No. of Marked Individuals % with Major (No. with Major Dorsal Dorsal Fin Species Location Fin Disfigurements) Disfigurements Sourcea

Tursiops truncatus Charleston, SC, USA 398 (3) 0.7 E. Zolman Tursiops truncatus Hilton Head, SC, USA @500 (1) @0.2 C. Gubbins Tursiops truncatus Moray Firth, Scotland @120 (0) 0 B. Wilson Tursiops truncatus North Carolina, USA 778 (2) 0.26 K. Urian Tursiops truncatus Hawai‘i, USA 220 (1) 0.45 R.W.B. and A.M.G. Tursiops aduncus Monkey Mia, Australia @600 (0) 0 J. Mann longirostirs Hawai‘i, USA 213 (0) 0 S. Rickards Steno bredanensis Hawai‘i, USA 120 (0) 0 R.W.B. and D. L. Webster Globicephala macrorhynchus Bahamas 86 (0) 0 D. Claridge Peponocephala electra Bahamas 109 (0) 0 D. Claridge Orcinus orca 117 (1) 0.85 I. Visser Orcinus orca , Canada/ 331 (2) 0.6 Bigg et al. (1987) Washington, USA Pseudorca crassidens Costa Rica 50 (0) 0 A. Acevedo Pseudorca crassidens Hawai‘i, USA 80 (3) 3.75 This study

a All sources unpublished data except for Bigg et al. (1987). 600 PACIFIC SCIENCE . October 2005 were accompanied by infants estimated to be National Marine Fisheries Service South- less than a year of age. Our observations of an west Fisheries Science Center Administra- individual completely missing the dorsal fin tive Report LJ-03-13. accompanied by an infant implies that even Bigg, M. A. 1982. An assessment of killer with such major losses, adult females may be whale (Orcinus orca) stocks off Vancouver able to adequately thermoregulate and repro- Island, British Columbia. Rep. Int. Whal- duce, at least in some cases. ing Comm. 32:655–666. Bigg, M. A., G. M. Ellis, J. K. B. Ford, and acknowledgments K. C. Balcomb. 1987. Killer whales: A study of their identification, genealogy, Allan Ligon, Dan McSweeney, and Daniel and natural history in British Columbia Webster all provided substantial assistance in and Washington State. Phantom Press, the field efforts. Research vessels were pro- Nanaimo, British Columbia, Canada. vided by Island Marine Institute, Joe Mobley Carretta, J. V., K. A. Forney, M. M. Muto, J. (University of Hawai‘i), and the Wild Whale Barlow, J. Baker, and M. Lowry. 2004. Research Foundation. Bill Gilmartin and U.S. Pacific marine stock assess- Hannah Bernard from the Hawai‘i Wildlife ments: 2003. NOAA Tech. Memo. Fund administered much of the funding. We NMFS-SWFSC 358. thank Alejandro Acevedo, Diane Claridge, Chivers, S. J., R. G. LeDuc, and R. W. Baird. Cara Gubbins, Janet Mann, Susan Rickards, 2003. Hawaiian island populations of false Kim Urian, Ingrid Visser, Ben Wilson, and killer whales and short-finned pilot whales Eric Zolman for providing unpublished infor- revealed by genetic analyses. Page 32 in mation, and Kevin Busschler and Lesley Jantz Abstracts of the 15th Biennial Conference of the National Marine Fisheries Service, Pa- on the Biology of Marine , 14– cific Islands Region, for providing a photo- 19 December 2003, Greensboro, North graph from the observer program for the Carolina. Hawai‘i-based long-line fishery. Discussions Chu, K., and S. Nieukirk. 1988. Dorsal fin with Jim McBain regarding wound healing scars as indicators of age, sex, and social were very helpful. Bud Antonelis, Jason status in humpback whales (Megaptera no- Baker, Barbie Byrd, Karin Forney, Brad Han- vaeangliae). Can. J. Zool. 66:416–420. son, Bill McLellan, Joe Mobley, Ingrid Corkeron, P. J., R. J. Morris, and M. M. Bry- Visser, and an anonymous reviewer all pro- den. 1987. Interactions between bottlenose vided constructive comments on various ver- and sharks in , sions of the manuscript. Queensland. Aquat. Mamm. 13:109–113. Friedlaender, A. S., W. A. McLellan, and Literature Cited D. A. Pabst. 2001. Characterising an inter- action between coastal bottlenose dolphins Baird, R. W., and P. J. Stacey. 1989. Observa- (Tursiops truncatus) and the spot gillnet tions on the reactions of sea lions, Zalophus fishery in southeastern North Carolina, californianus and Eumetopias jubatus, to kill- USA. J. Cetacean Res. Manage. 3:293– er whales, Orcinus orca, evidence of ‘‘’’ 303. having a ‘‘search image’’ for predators. Green, H. C., J. Ostman, and A. D. Driscoll. Can. Field-Nat. 103:426–428. 1991. A case of dolphin entanglement Baird, R. W., P. J. Stacey, D. A. Duffus, and leading to a portion of the fin being cut K. M. Langelier. 2002. An evaluation of off—how ‘‘round nick’’ became ‘‘butch’’. (Eschrichtius robustus) mortality Page 29 in Abstracts of the Ninth Biennial incidental to fishing operations in British Conference on the Biology of Marine Columbia, Canada. J. Cetacean Res. Man- Mammals, 5–9 December 1991, Chicago, age. 4:289–296. Illinois. Barlow, J. 2003. Cetacean abundance in Ha- Heithaus, M. R. 2001. Shark attacks on waiian waters during summer/fall of 2002. bottlenose dolphins (Tursiops aduncus)in False Killer Whale Fishery Interactions . Baird and Gorgone 601

Shark Bay, Western Australia: Attack rate, in U.S. fisheries and a first attempt to bite scar frequencies and attack seasonality. estimate the magnitude of global marine Mar. Mamm. Sci. 17:526–539. mammal by-catch. Document SC/55/BC Hillman, G. R., B. Wu¨rsig, G. A. Gailey, presented to the International N. Kehtarnavaz, A. Drobyshevsky, B. N. Commission Scientific Committee. Araabi, H. D. Tagare, and D. W. Robbins, J., and D. K. Mattila. 2001. Moni- Weller. 2003. Computer-assisted photo- toring entanglements of humpback whale identification of individual marine verte- (Megaptera novaeangliae) in the Gulf of brates: A multi-species system. Aquat. Maine on the basis of caudal peduncle Mamm. 29:117–123. scarring. Document SC/53/NAH25 pre- Jefferson, T. A., B. C. Curry, and N. A. Black. sented to the International Whaling Com- 1994. Harbor mortality in the mission Scientific Committee. Monterey Bay gillnet fishery, Rommel, S. A., D. A. Pabst, and W. A. 1989. Rep. Int. Whaling Comm. Spec. Is- McLellan. 1993. Functional-morphology sue 15:445–448. of the vascular plexuses associated with Knowlton, A. R., and S. D. Kraus. 2001. the cetacean uterus. Anat. Rec. 237:538– Mortality and serious injury of northern 546. right whales (Eubalaena glacialis) in the Scott, M. D., R. S. Wells, A. B. Irvine, and western North Atlantic Ocean. J. Cetacean B. R. Mate. 1990. Tagging and marking Res. Manage. Spec. Issue 2:193–208. studies on small cetaceans. Pages 489–513 Mann, J., R. A. Smolker, and B. B. Smuts. in S. Leatherwood and R. R. Reeves, eds. 1995. Responses to calf entanglement in The . Academic Press, free-ranging bottlenose dolphins. Mar. New York. Mamm. Sci. 11:100–106. Visser, I. N. 1998. Prolific body scars and Matkin, C., G. Ellis, E. Saulitis, L. Barrett- collapsing dorsal fins on killer whales (Or- Lennard, and D. Matkin. 1999. Killer cinus orca) in New Zealand waters. Aquat. whales of southern Alaska. North Gulf Mamm. 24:71–78. Oceanic Society, Homer, Alaska. ———. 2000. Killer whale (Orcinus orca) in- Mobley, J. R., S. S. Spitz, K. A. Forney, R. A. teractions with longlines fisheries in New Grotefendt, and P. H. Forestell. 2000. Zealand waters. Aquat. Mamm. 26:241– Distribution and abundance of odontocete 252. species in Hawaiian waters: Preliminary Visser, I. N., and D. Fertl. 2000. Stranding, results of 1993–98 aerial surveys. National resighting, and boat strike of a killer whale Marine Fisheries Service Southwest Fish- (Orcinus orca) off New Zealand. Aquat. eries Science Center Administrative Re- Mamm. 26:232–240. port LJ-00-14C. Wells, R. S., and M. D. Scott. 1997. Seasonal Nitta, E. T., and J. R. Henderson. 1993. A incidence of boat strikes on bottlenose dol- review of interactions between Hawaii’s phins near Sarasota, Florida. Mar. Mamm. fisheries and protected species. Mar. Fish. Sci. 13:475–480. Rev. 55:83–92. Wells, R. S., S. Hofmann, and T. L. Moors. Norris, K. S. 1992. Dolphins in crisis. Natl. 1998. Entanglement and mortality of bot- Geogr. 182 (3): 2–35. tlenose dolphins, Tursiops truncatus, in rec- Read, A. J., P. Drinker, and S. Northridge. reational fishing gear in Florida. Fish. Bull. 2003. By-catches of marine mammals 96:647–650.