The Animal Welfare Implications of Cetacean Deaths in Fisheries

some comparative measures which can be interpreted in terms of animal welfare
(Iossa et al. 2007).
Table 5. The time limits to unconsciousness used to assess performance in killing
traps for terrestrial and semi-aquatic mammals (Anon. 1998b)
Time to
Species
unconsciousness
45 seconds Stoat
120 seconds American marten, pine marten, sable
300 seconds American badger, bobcat, Canadian beaver, Canadian otter,
coyote, Eurasian badger, Eurasian beaver, Eurasian lynx,
Eurasian otter, grey wolf, muskrat, raccoon, raccoon dog
The performance of each trap is assessed using a set of criteria. For killing traps,
one criterion is the time elapsed between triggering the device and the onset of
unconsciousness, which varies with body weight up to a maximum time of 300
seconds for the largest species (Table 5). For restraining traps the criteria are the
number, type and nature of injuries. The ISO standards were agreed in 1999;
subsequent technological advancements have reduced time to unconsciousness
below these thresholds for many species (Iossa et al. 2007). However, even the
times to unconsciousness stipulated in the ISO guidelines (Table 5) are significantly
shorter than the predicted times to death in most bycaught cetaceans (Table 3).
A specific type of killing trap used for semi-aquatic mammals is the drowning
trap, for which the method of death has significant similarities with cetaceans
entrapped in fishing gear. Many of the species commonly caught in drowning traps
have dive times that far exceed the 300 second threshold (Iossa et al. 2007), and
experimental studies have shown that, even if an animal struggles and consumes
more oxygen, electroencephalogram (EEG) activity occurs beyond the 300 second
threshold (Gilbert & Gofton 1982). Drowning traps have been criticised because
drowning-induced hypoxia is not considered an acceptable method of euthanasia by
veterinary and laboratory researchers and does not meet accepted standards for
killing traps (Close et al. 1996; Ludders et al. 1999; Beaver et al. 2001).
Restraining traps are designed to hold the animal unharmed with the minimum
stress until the trap is checked. There are two principle considerations when
assessing welfare: the mortality of target and non-target species and the injuries
suffered by restrained individuals. Trapping standards are one of the few sectorial
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