and sublethal toxicity to other organisms in these environments. In the case of sea
lice, the pyrethroids from fish bath treatments are typically released into the surrounding area after the prescribed therapeutic duration [179]. Several reviews have
considered the potential impacts of sea lice pesticide treatments on nontarget aquatic
biota [37, 180]. One study estimated that the concentration of deltamethrin at
approximately 100–350 m from the treatment area was sufficient to immobilize
the benthic marine amphipod Eohaustorius estuarius in as little as 1 h. Given its
tendency to sorb to particles instead of remaining in the water column, deltamethrin
release from sea lice treatments is likely to impact sediment dwelling organisms
more strongly than those in the water column [181]. A previous study using a similar
approach to track cypermethrin during a simulated bath treatment found
cypermethrin in the surrounding water between 2 and 5.5 h after tarp release, at
distances ranging from 900 to 3,000 m away from the pen at low ng L
À1
concentrations – the same range of concentrations causing irreversible immobilization in the E. estuarius population after 48 h of exposure [69]. Burridge et al. [179]
tested the acute, short-term toxicity of Alphamax® (active ingredient deltamethrin)
on several nontarget marine organisms including American lobsters (Homarus
americanus) at a variety of different life stages and shrimp (Crangon septemspinosa
and Mysid spp.) to determine toxicity over short- term exposures (1, 24 h) that may
realistically follow bath treatment chemical release. Deltamethrin concentrations
ranging from 3.4 to 18.8 ng L
À1 caused lethality in 50% of animals after only 1 h,
with lobsters being the most sensitive. Concentrations ranging from 0.8 to 27 ng L
À1
were sufficient to cause the same effects after only 24 h of exposure, with the earliest
life stages of lobsters being the most sensitive [179]. These findings are important
because they demonstrate that nontarget animals near fish pens being treated for sea
lice come in contact with pyrethroids at concentrations that cause acute toxicity on
ecologically relevant timescales. Further, they highlight that other important fisheries such as the American lobster, sometimes located near salmon fisheries [179], are
likely to be impacted by sea lice treatments. It is likely that invertebrate assemblages
near sea lice treatment pens are experiencing toxicity from pyrethroids released after
treatment. Given the evidence of acute toxicity in some marine organisms at low
pyrethroid concentrations, it follows that these same assemblages may be experiencing strong selective pressures from these nontarget pyrethroid exposures, potentially
contributing to mortality or the development of resistance in some populations.
These effects could also extend to other fisheries, such as shrimp farming in Central
Asia, which sometimes use pyrethroids to treat pests [38], but for which treatment
regimes and other exposure data are severely lacking. As the doses of pyrethroids in
sea lice treatments are increased to compensate for the development of resistance in
sea lice populations [121], effects on nontarget animals near salmon fisheries are
only likely to become more severe.
The arthropod taxa and life stages for which nontarget, adaptive resistance to
pyrethroids has been documented are among the most sensitive to pyrethroids in
comparison to other members of the aquatic community. The selection for and rise in
frequency of resistance mutations of large effect (Vgsc L1014F/S, M918L, L925I/V)
in these sensitive groups are consistent with exposure to acutely toxic concentrations
134
K. M. Major and S. M. Brander
lice, the pyrethroids from fish bath treatments are typically released into the surrounding area after the prescribed therapeutic duration [179]. Several reviews have
considered the potential impacts of sea lice pesticide treatments on nontarget aquatic
biota [37, 180]. One study estimated that the concentration of deltamethrin at
approximately 100–350 m from the treatment area was sufficient to immobilize
the benthic marine amphipod Eohaustorius estuarius in as little as 1 h. Given its
tendency to sorb to particles instead of remaining in the water column, deltamethrin
release from sea lice treatments is likely to impact sediment dwelling organisms
more strongly than those in the water column [181]. A previous study using a similar
approach to track cypermethrin during a simulated bath treatment found
cypermethrin in the surrounding water between 2 and 5.5 h after tarp release, at
distances ranging from 900 to 3,000 m away from the pen at low ng L
À1
concentrations – the same range of concentrations causing irreversible immobilization in the E. estuarius population after 48 h of exposure [69]. Burridge et al. [179]
tested the acute, short-term toxicity of Alphamax® (active ingredient deltamethrin)
on several nontarget marine organisms including American lobsters (Homarus
americanus) at a variety of different life stages and shrimp (Crangon septemspinosa
and Mysid spp.) to determine toxicity over short- term exposures (1, 24 h) that may
realistically follow bath treatment chemical release. Deltamethrin concentrations
ranging from 3.4 to 18.8 ng L
À1 caused lethality in 50% of animals after only 1 h,
with lobsters being the most sensitive. Concentrations ranging from 0.8 to 27 ng L
À1
were sufficient to cause the same effects after only 24 h of exposure, with the earliest
life stages of lobsters being the most sensitive [179]. These findings are important
because they demonstrate that nontarget animals near fish pens being treated for sea
lice come in contact with pyrethroids at concentrations that cause acute toxicity on
ecologically relevant timescales. Further, they highlight that other important fisheries such as the American lobster, sometimes located near salmon fisheries [179], are
likely to be impacted by sea lice treatments. It is likely that invertebrate assemblages
near sea lice treatment pens are experiencing toxicity from pyrethroids released after
treatment. Given the evidence of acute toxicity in some marine organisms at low
pyrethroid concentrations, it follows that these same assemblages may be experiencing strong selective pressures from these nontarget pyrethroid exposures, potentially
contributing to mortality or the development of resistance in some populations.
These effects could also extend to other fisheries, such as shrimp farming in Central
Asia, which sometimes use pyrethroids to treat pests [38], but for which treatment
regimes and other exposure data are severely lacking. As the doses of pyrethroids in
sea lice treatments are increased to compensate for the development of resistance in
sea lice populations [121], effects on nontarget animals near salmon fisheries are
only likely to become more severe.
The arthropod taxa and life stages for which nontarget, adaptive resistance to
pyrethroids has been documented are among the most sensitive to pyrethroids in
comparison to other members of the aquatic community. The selection for and rise in
frequency of resistance mutations of large effect (Vgsc L1014F/S, M918L, L925I/V)
in these sensitive groups are consistent with exposure to acutely toxic concentrations
134
K. M. Major and S. M. Brander