421
red snapper on reefs off the Alabama coast, finding no evidence of the oil spill
affecting abundance of early life stages. They concluded that red snapper densities
at age 0 (settlement on the seabed) were similar to previous years and that juveniles
in 2011 were abundant on the reefs. In the eastern GoM substock, a sustained
recruitment decline may have an impact on the spawning stock biomass in the long
term. There is no conclusive evidence that this is due to the effect of the DWH oil
spill or alternatively to the influence of environmental factors (Deepwater Horizon
Natural Resource Damage Assessment Trustees 2016; Murawski et al. 2016). If
environmental variability is responsible, the spawning stock may recover once normal condition is re-established due to contribution of different year classes.
25.5 Tunas
Tunas are highly migratory species that are under the management of the
International Commission for the Conservation of Atlantic Tunas (ICCAT). In the
GoM, yellowfin tuna is the principal target (both in Mexico and the USA), although
incidental catches may include migratory species such as other tunas, including
marlins, billfish, sharks, sea turtles, and other species of fish. Among the most
important tunas is bluefin tuna because of its economic value and because it has
been intensively overexploited, leading to near-collapse of the Eastern and Western
Atlantic stocks (ICCAT 2007).
Tunas are long-lived species and have wide distribution in the pelagic environment of the GoM. Sexual maturity is reached between 2.5 and 3 years of age in
yellowfin tuna (González et al. 2002), whereas bluefin tunas reach reproductive
maturity at 8–12 years old. Yellowfin tunas spawn throughout the year, but intensity
varies by region, while bluefin spawns over a narrower time span. Spawning occurs
in the GoM in April to July for yellowfin tuna (Arocha et al. 2000) and April to June
for bluefin tuna (ICCAT 2007). Both species have high fecundity with pelagic larvae subjected to the current pattern for dispersion. The NGoM was designated as the
spawning area, and no fishing targeting on bluefin tuna is allowed in US waters of
the GoM.
During the Ixtoc 1 oil spill, there was not a Mexican fishery for tuna, which was
initiated after the oil spill in 1981. Atlantic landings of bluefin tuna show a decreasing trend since 2000 with an increasing trend in the last 10 years (Fig. 25.6).
The DWH oil spill overlapped the spawning area of bluefin tuna in the GoM, so
there was considerable concern that the spill could affect larval survival. The oil
spill could overlap the entire area, directly impacting the survival of young fish and,
in the medium term, spawning stock biomass and productivity. However, subsequent studies showed that the potentially affected spawning area was less than 10%
(Muhling et al. 2012). Hazen et al. (2016) suggested that although the oil overlapped with a small portion of predicted spawning area, the combined effect of
environmental variation and bycatch mortality may result in a significant impact on
25 Impacts of Deep Oil Spills on Fish and Fisheries
red snapper on reefs off the Alabama coast, finding no evidence of the oil spill
affecting abundance of early life stages. They concluded that red snapper densities
at age 0 (settlement on the seabed) were similar to previous years and that juveniles
in 2011 were abundant on the reefs. In the eastern GoM substock, a sustained
recruitment decline may have an impact on the spawning stock biomass in the long
term. There is no conclusive evidence that this is due to the effect of the DWH oil
spill or alternatively to the influence of environmental factors (Deepwater Horizon
Natural Resource Damage Assessment Trustees 2016; Murawski et al. 2016). If
environmental variability is responsible, the spawning stock may recover once normal condition is re-established due to contribution of different year classes.
25.5 Tunas
Tunas are highly migratory species that are under the management of the
International Commission for the Conservation of Atlantic Tunas (ICCAT). In the
GoM, yellowfin tuna is the principal target (both in Mexico and the USA), although
incidental catches may include migratory species such as other tunas, including
marlins, billfish, sharks, sea turtles, and other species of fish. Among the most
important tunas is bluefin tuna because of its economic value and because it has
been intensively overexploited, leading to near-collapse of the Eastern and Western
Atlantic stocks (ICCAT 2007).
Tunas are long-lived species and have wide distribution in the pelagic environment of the GoM. Sexual maturity is reached between 2.5 and 3 years of age in
yellowfin tuna (González et al. 2002), whereas bluefin tunas reach reproductive
maturity at 8–12 years old. Yellowfin tunas spawn throughout the year, but intensity
varies by region, while bluefin spawns over a narrower time span. Spawning occurs
in the GoM in April to July for yellowfin tuna (Arocha et al. 2000) and April to June
for bluefin tuna (ICCAT 2007). Both species have high fecundity with pelagic larvae subjected to the current pattern for dispersion. The NGoM was designated as the
spawning area, and no fishing targeting on bluefin tuna is allowed in US waters of
the GoM.
During the Ixtoc 1 oil spill, there was not a Mexican fishery for tuna, which was
initiated after the oil spill in 1981. Atlantic landings of bluefin tuna show a decreasing trend since 2000 with an increasing trend in the last 10 years (Fig. 25.6).
The DWH oil spill overlapped the spawning area of bluefin tuna in the GoM, so
there was considerable concern that the spill could affect larval survival. The oil
spill could overlap the entire area, directly impacting the survival of young fish and,
in the medium term, spawning stock biomass and productivity. However, subsequent studies showed that the potentially affected spawning area was less than 10%
(Muhling et al. 2012). Hazen et al. (2016) suggested that although the oil overlapped with a small portion of predicted spawning area, the combined effect of
environmental variation and bycatch mortality may result in a significant impact on
25 Impacts of Deep Oil Spills on Fish and Fisheries