Cetaceans are the principal marine mammals affected by tuna fisheries. They may be incidentally captured in purse seines or become entangled or hooked on longlines (e.g., false killer whales in the Hawaii-based deep-set longline fishery). Entanglement is a significant problem in medium-scale, semi-industrial and artisanal tuna drift gillnet fisheries. In the tropical tuna purse-seine fishery, species such as baleen whales or dolphins (as well the whale shark Rhincodon typus), may serve as sighting cues by purse-seine fishers for the presence of tuna schools at the surface of the sea and/or may be caught accidentally when fishing for the targeted species [1].
Successful techniques to release cetaceans from purse seine nets have been employed for some time, e.g., the backdown procedure and Medina panel, and there have been advances in techniques for safe handling and release of megafauna from purse seines, longlines and gillnets [2,3,4]. Dynamic spatio-temporal fishery management strategies can help fishers to avoid interactions in the first place. For example, a recent study identified the principal environmental variables influencing the co-occurrence between baleen whales, whale sharks and tuna purse-seine fisheries [1]. 'Weak' circle hooks can reduce bycatch (but not depredation), though post-interaction mortality is unknown. Sub-surface gillnets have been shown to reduce cetacean bycatch in Indian Ocean fisheries, though not for deep-diving cetaceans. Pingers (acoustic alarms) have been shown to mitigate bycatch of some cetacean species, predominantly in gillnet fisheries, albeit with strong caveats [5].
SeaLlifeBase is a source of biological and distribution data for marine mammal species. FAO's guide to the Marine Mammals of the World provides species identification and distribution information. Locate handy Species ID guides here. NOAA's 'Find a Species - Dolphins & Porpoises' and 'Whales' has information on protection status, biology and population status, distribution, threats, conservation measures and research.
Cetacean mortality can be reduced by following techniques outlined in Guidelines for the safe and humane handling and release of bycaught small cetaceans from fishing gear. See also FAO's Marine Mammal Bycatch Mitigation factsheets.
References
- Escalle, L., Pennino, M.G., Gaertner, D., Chavance, P., Delgado de Molina, A., Demarcq, H., Romanov, E., and Merigot, B. 2016. Environmental factors and megafauna spatio-temporal co-occurrence with purse-seine fisheries. Fisheries Oceanography 25(4): 433–447. doi:10.1111/fog.12163.
- Escalle, L., Murua, H., Amande, J.M., Arregui, I., Chavance, P., Delgado de Molina, A., Gaertner, D., Fraile, I., Filmalter, J.D., Santiago, J., Forget, F., Arrizabalaga, H., Dagorn, L., and Merigot, B. 2016. Post-capture survival of whale sharks encircled in tuna purse-seine nets: tagging and safe release methods. Aquatic Conservation: Marine and Freshwater Ecosystems 26(4): 782–789. doi:10.1002/aqc.2662.
- Poisson, F., Vernet, A.L., Seret, B., and Dagorn, L. 2012. Good practices to reduce the mortality of sharks and rays caught incidentally by the tropical tuna purse seiners. EU FP7, EBFMtuna-2012 Montpellier, France.
- Hamer, D., Minton, G. 2020. Guidelines for the safe and humane handling and release of bycaught small cetaceans from fishing gear. CMS Technical Series No. 43. UNEP/CMS Secretariat, Bonn, Germany.
- FAO. 2021. Fishing operations. Guidelines to prevent and reduce bycatch of marine mammals in capture fisheries. FAO, Rome, Italy.
Marine Mammals
3-Alpha Code | Name | Scientific Name |
---|---|---|
WLE | WHALE (UNIDENTIFIED) | Cetacea |
TGW | GINKGO-TOOTHED BEAKED WHALE | Mesoplodon ginkgodens |
SXX | SEALS NEI | Otariidae, phocidae |
SSL | STELLER SEA LION | Eumetopias jubatus |
SSF | SUBANTARCTIC FUR SEAL | Arctocephalus tropicalis |
SPW | SPERM WHALE | Physeter macrocephalus |
SPP | SPECTACLED PORPOISE | Australophocaena dioptrica |
SNP | NORTHERN ELEPHANT SEAL | Mirounga angustirostris |
SMH | HAWAIIAN MONK SEAL | Monachus schauinslandi |
SIW | SEI WHALE | Balaenoptera borealis |
SHW | SHORT-FINNED PILOT WHALE | Globicephala macrorhynchus |
SGF | GUADALUPE FUR SEAL | Arctocephalus townsendi |
SEN | NORTHERN FUR SEAL | Callorhinus ursinus |
SEK | SOUTH AFRICAN FUR SEAL | Arctocephalus pusillus |
SEC | HARBOUR SEAL | Phoca vitulina |
SEA | ANTARCTIC FUR SEAL | Arctocephalus forsteri |
RTD | ROUGH-TOOTHED DOLPHIN | Steno bredanensis |
RNW | NORTHERN RIGHT WHALE DOLPHIN | Lissodelphis borealis |
PYW | PYGMY SPERM WHALE | Kogia breviceps |
PIW | LONG-FINNED PILOT WHALE | Globicephala melas |
PHR | HARBOUR PORPOISE | Phocoena phocoena |
PDA | DALL'S PORPOISE | Phocoenoides dalli |
ODN | TOOTHED WHALES NEI | Odontoceti |
MYS | BALEEN WHALES NEI | Mysticeti |
MIW | MINKE WHALE | Balaenoptera acutorostrata |
MEW | MELON-HEADED WHALE | Peponocephala electra |
MEP | BEAKED WHALES NEI | Mesoplodon spp |
MAM | AQUATIC MAMMALS NEI | Mammalia |
KPW | PYGMY KILLER WHALE | Feresa attenuata |
KIW | KILLER WHALE | Orcinus orca |
HUW | HUMPBACK WHALE | Megaptera novaeangliae |
GRW | GRAY WHALE | Eschrichtius robustus |
GLO | PILOT WHALES NEI | Globicephala spp |
FRD | FRASER'S DOLPHIN | Lagenodelphis hosei |
FIW | FIN WHALE | Balaenoptera physalus |
FAW | FALSE KILLER WHALE | Pseudorca crassidens |
DWW | DWARF SPERM WHALE | Kogia simus |
DWP | PACIFIC WHITE-SIDED DOLPHIN | Lagenorhynchus obliquidens |
DST | STRIPED DOLPHIN | Stenella coeruleoalba |
DSP | SPOTTED DOLPHINS NEI | Stenella spp. |
DSI | SPINNER DOLPHIN | Stenella longirostris |
DRR | RISSO'S DOLPHIN | Grampus griseus |
DPN | PANTROPICAL SPOTTED DOLPHIN | Stenella attenuata |
DLP | DOLPHINS NEI | Delphinidae |
DDU | DUSKY DOLPHIN | Lagenorhynchus obscurus |
DCZ | LONG-BEAKED COMMON DOLPHIN | Delphinus capensis |
DCO | COMMON DOLPHIN | Delphinus delphis |
DBZ | INDO-PACIFIC BOTTLENOSE DOLPHIN | Tursiops aduncus |
DBO | BOTTLENOSE DOLPHIN | Tursiops truncatus |
CSL | CALIFORNIA SEA LION | Zalophus californianus |
BRW | BRYDE'S WHALE | Balaenoptera edeni |
BLW | BLUE WHALE | Balaenoptera musculus |
BEW | BAIRD'S BEAKED WHALE | Berardius bairdii |
BCW | CUVIER'S BEAKED WHALE | Ziphius cavirostris |
BBW | BLAINVILLE'S BEAKED WHALE | Mesoplodon densirostris |
ASL | AUSTRALIAN SEA LION | Neophoca cinerea |