436
26.2.7 Habitat and Environmental Degradation
Other major chronic impacts to both marine mammals and turtles include hypoxia
in the Mississippi River outflow region, which affects prey quality and density in a
previously rich foraging ground for GOM megafauna, as well as harmful algal
blooms (Magaña et al. 2003). Direct impacts to turtle habitats including loss of nesting beaches, seagrass beds, and coral reefs, are primarily associated with coastal
and continental shelf zones. The same suite of chronic impacts that affect GOM
marine mammal and sea turtle health may also have some effect on the health and
quality of their prey.
26.3 Quantifying Impacts on Pelagic Species/Stages
and Habitats
Although occasional reports of various direct impacts to marine mammals and sea
turtles including entanglements and ship strikes are reported, they are likely highly
underreported (Williams et al. 2011; Epperly et al. 1996) because they occur offshore and may go undetected. Carcasses are unlikely to strand following pelagic
deaths, particularly in regions or seasons where higher water temperatures accelerate decomposition (Nero et al. 2013). Equally difficult to quantify are the cumulative effects of chronic impacts such as pollution, noise, and prey depletion, since
these effects likely accumulate gradually at sublethal levels over many years.
One possible indicator of chronic stress is the occurrence, intensity, and length of
unusual mortality events (UMEs). A UME is an unexpected stranding event that
represents a significant die-off in a marine mammal population. From 1990 to 2104,
there were 12 UMEs in the GOM (Litz et al. 2014) with recovered carcass counts
ranging from 31 to 1141 animals and lasting from 1 to 52 months (Resources NOoP
2018). Coastal bottlenose dolphins are the predominant species in the stranding
record, likely because the bodies of this nearshore species are far more likely to
reach beaches. The proximate cause of the majority of these UMEs is typically
determined to be morbillivirus, biotoxins, and/or cold weather. However, the causes
of some events remain unknown, as in the case of the largest, longest-lasting event
that occurred from 2012 to 2014 with 1141 recovered carcasses. The occurrence of
these events suggests population-level immunodeficiencies (Di Guardo and
Mazzariol 2013) or other susceptibility in populations which are already experiencing chronic stress.
Turtle populations also experience mass stranding events such as cold stunning
events (Milton and Lutz 2003). In January 2010, unusually cold temperatures
resulted in a cold stunning event of unprecedented magnitude involving over 4500
sea turtles (primarily green turtles) in Florida (Avens et al. 2012). As in the case of
marine mammals, chronic stress associated with anthropogenic activity may be acting to decrease overall resilience of turtle populations (Lamont et al. 2012).
K. E. Frasier et al.
26.2.7 Habitat and Environmental Degradation
Other major chronic impacts to both marine mammals and turtles include hypoxia
in the Mississippi River outflow region, which affects prey quality and density in a
previously rich foraging ground for GOM megafauna, as well as harmful algal
blooms (Magaña et al. 2003). Direct impacts to turtle habitats including loss of nesting beaches, seagrass beds, and coral reefs, are primarily associated with coastal
and continental shelf zones. The same suite of chronic impacts that affect GOM
marine mammal and sea turtle health may also have some effect on the health and
quality of their prey.
26.3 Quantifying Impacts on Pelagic Species/Stages
and Habitats
Although occasional reports of various direct impacts to marine mammals and sea
turtles including entanglements and ship strikes are reported, they are likely highly
underreported (Williams et al. 2011; Epperly et al. 1996) because they occur offshore and may go undetected. Carcasses are unlikely to strand following pelagic
deaths, particularly in regions or seasons where higher water temperatures accelerate decomposition (Nero et al. 2013). Equally difficult to quantify are the cumulative effects of chronic impacts such as pollution, noise, and prey depletion, since
these effects likely accumulate gradually at sublethal levels over many years.
One possible indicator of chronic stress is the occurrence, intensity, and length of
unusual mortality events (UMEs). A UME is an unexpected stranding event that
represents a significant die-off in a marine mammal population. From 1990 to 2104,
there were 12 UMEs in the GOM (Litz et al. 2014) with recovered carcass counts
ranging from 31 to 1141 animals and lasting from 1 to 52 months (Resources NOoP
2018). Coastal bottlenose dolphins are the predominant species in the stranding
record, likely because the bodies of this nearshore species are far more likely to
reach beaches. The proximate cause of the majority of these UMEs is typically
determined to be morbillivirus, biotoxins, and/or cold weather. However, the causes
of some events remain unknown, as in the case of the largest, longest-lasting event
that occurred from 2012 to 2014 with 1141 recovered carcasses. The occurrence of
these events suggests population-level immunodeficiencies (Di Guardo and
Mazzariol 2013) or other susceptibility in populations which are already experiencing chronic stress.
Turtle populations also experience mass stranding events such as cold stunning
events (Milton and Lutz 2003). In January 2010, unusually cold temperatures
resulted in a cold stunning event of unprecedented magnitude involving over 4500
sea turtles (primarily green turtles) in Florida (Avens et al. 2012). As in the case of
marine mammals, chronic stress associated with anthropogenic activity may be acting to decrease overall resilience of turtle populations (Lamont et al. 2012).
K. E. Frasier et al.