Protected Species and Marine Aquaculture Interactions

attributed from 1970 to 2009, about 57% involved entanglement with fishing gear
(van der Hoop et al. 2013).
Waring et al. (2015) also provide entanglement data available for fin (9 entanglements),
sei (2), minke (40), and sperm (3) whales resulting in serious injury or death
in the Atlantic and Gulf of Mexico from 2008– 2012. The U. S. Atlantic and Gulf of
Mexico Marine Mammal Stock Assessments (Waring et al. 2012, 2015) additionally
include data about dolphin and porpoise species, and pilot whales which are often
caught in pelagic longline fisheries, gillnets and trawls. Similarly, hundreds of gray,
harbor and harp seals perish in fisheries each year (Waring et al. 2012, 2015).
Entanglement undoubtedly poses a threat to protected species. It is known that
animals frequently survive entanglement because scarring patterns can readily be assessed
during necropsies, photo identification, and field observation.
For instance, Knowlten et al. (2005) found that 75.6%
of whales had scars indicating they had been entangled at least
once. In Canada, Vanderlaan et al. (2011) examined the risk of
lethal entanglement for right whales in fishery gear. The analysis
used spatial overlap between fishing season, area of gear deployment,
and whale critical habitat to identify fisheries of
greatest threat to whales. They determined that groundfish
hook and line gear (i.e., bottom longline gear) is the greatest threat during the summer
residency period of right whales, while the lobster trap lines are the greatest
threat during migratory periods in spring and fall. This spatial and temporal risk assessment
approach could be adapted to analyze the areas where aquaculture gear
could be deployed to reduce risk of harmful interactions with right whales or other
protected species.
Knowlton et al. (2012) examined photographs of 626 north Atlantic right whales
taken from 1980–2009 finding that 83% had been entangled. Juveniles were entangled
at higher rates than adults. Over half the whales had been entangled more than
once, and a quarter of the whales acquired new scars each year. The authors calculated
an annual entanglement rate of 25.9% for animals with adequate photographic data
collected in consecutive years, thus allowing definite evidence that entanglement scarring
had occurred between the dates of sequential pictures. During this time, there
were 86 known serious entanglement incidents, the frequency of which has increased
since the mid-1990s.
An early study of humpback whale entanglement in the main Hawaiian islands
from 1972– 1996 reported 7 entangled whales (at least two entangled in fishery gear)
of 26 total whales injured or dead (Mazzuca et al. 1998). The authors noted an increasing
trend over the 25-year period in annual frequency of entanglement in lines.
Two of the entangled whales had shark injuries and a third was noted to have large
tiger sharks swimming near it during attempts to disentangle the animal. The authors
note that if entanglement stresses and weakens whales they may be at higher
risk for shark predation. Studies of Gulf of Maine humpback whales used scar-based
entanglement evidence to estimate an annual entanglement mortality rate of 3%,
Entanglement
undoubtedly poses
a threat to
protected species.
44 | ProtEctEd SPEciES and MarinE aquaculturE intEractionS