The Animal Welfare Implications of Cetacean Deaths in Fisheries

the incidence of broken beaks for harbour porpoises (χ 2 1=1.68, P=0.20) or common
dolphins (χ 2 1=1.45, P=0.23).
Whilst bycaught cetaceans can suffer a range of internal injuries, we did not
consider aspects of lung pathology as these have been well-documented elsewhere
(Tables 1 and 2). In general, a large proportion of bycaught cetaceans had
generalized organ congestion (liver, kidneys, spleen and adrenal glands) caused by
reduced blood flow. Internal injuries can be inflicted by the fishing equipment and
also by the cetacean struggling to free itself. Muscle tears and haemorrhaging are
frequently found in the longissimus dorsi muscle, peri- and sub-scapular areas,
thoracic and intercostal areas, and sub-cranial and mandibular regions; the thoracic
rete mirabile frequently also shows haemorrhaging (Figure 2). Since entrapped
cetaceans typically make powerful dorso-ventral and lateral movements, these
probably cause the haemorrhaging and tears in the longissimus dorsi muscle, which
is the primary swimming muscle. Similarly, because the pectoral fins frequently
become entangled, such movements will cause muscle tears and haemorrhaging in
the peri- and subscapular areas, and torsion of the body leads to internal
haemorrhaging of the thoracic rete mirabile. Whilst fractured skulls can occur when
cetaceans are dropped on the deck of the fishing boat (Kirkwood et al. 1997), or go
through the winches, such trauma was uncommon in this dataset, with only 1.6%
having a fractured skull, although 8.8% had bruising and haemorrhaging on the
dorsal aspect of the cranium.
There were significant differences in the levels of organ congestion between
juveniles and adults (harbour porpoises 52.3% versus 73.5%, χ 2 1=4.11, P=0.04;
common dolphins 60.6% versus 80.9%, χ 2 1=3.99, P=0.05). However, there were no
differences between juvenile harbour porpoises and common dolphins (χ 2 1=0.59,
P=0.44) or adults of the two species (χ 2 1= 0.61, P=0.43). There was a significant
relationship between the incidence of haemorrhaging and tears in the longissimus
muscle and both age and species (χ 2 3=26.70, P