Online Resource 2. Overview of stressors in the Gulf of Mexico (GOM)

We classify stressors in a drivers, pressures, and states framework (Table OR2.1) (Kelble

et al. 2013; Cook et al. 2014). Drivers are overarching stressors, such as human population

growth, that cause ecosystem change and lead to a cascade of other stressors. Pressures are

stressors caused or intensified by drivers that afflict the ecosystem and change its state, such as

coastal development. Finally, states describe the status of the ecosystem and/or communities

resulting from pressures created or intensified by drivers (Kelble et al. 2013; Cook et al. 2014).

Most of the drivers, pressures, and states in the GOM are related, and one often contributes to

another (Fig. OR2.1).

Climate change/sea-level rise/subsidence/changes in water quantity/storms

Global climate change is the result of increasing levels of carbon dioxide and other

greenhouse gases in the atmosphere trapping and containing heat (Twilley et al. 2001; Pachauri

et al. 2014). Population growth, land alteration, burning of fossil fuels, and industrial activities

are some of the many factors that contribute to high greenhouse gas levels in the atmosphere.

Human activities can interact with global climate change to alter marine ecosystems and the

natural resources that reside in these ecosystems (Twilley et al. 2001; Pachauri et al. 2014). As

air temperature rises, changes in rainfall and in the frequency of storms and hurricanes, fewer

freezing events, increased water temperatures, and more frequent harmful algal blooms (HABs)

may be expected (Moore et al. 2008). These changes may encourage a shift in the distribution

range of plant and animal species, resulting in an alteration of biological communities (Doyle et

al. 2010; Pachauri et al. 2014; Karnauskas et al. 2015), significant changes in biodiversity

patterns, and an increased opportunity for species invasion (Twilley et al. 2001).

1

Models used by the Intergovernmental Panel on Climate Change (IPCC) predict a slight

increase in average precipitation in the Mississippi watershed and a slight decrease in the eastern

region of the GOM (Pachauri et al. 2014). This may have serious implications for environmental

and human health. Coastal ecosystems of the GOM rely on water flow from areas beyond the

GOM coast. This flow has already been altered by engineering projects (dredging, levees, canals,

dams) (Cowan et al. 2008), and the growing water demand, resulting in a change in water

quantity reaching the GOM ecosystems (Sklar and Browder 1998). Anthropogenic alterations to

water flow along with climate driven changes to precipitation will interact and exacerbate each

other (Twilley et al. 2001). A wetter climate could cause increased flooding (Wang et al. 2013),

leading to an increase in the number of engineering projects to protect human populations.

However, this would result in further altered water flow (Twilley et al. 2001), and the flooding

events would increase sediment and nutrient loadings (Wang et al. 2013). A drier climate could

lead to decreased runoff and decreased freshwater input into the GOM (Twilley et al. 2001).

Warmer temperatures are predicted to increase global sea levels and the rate of sea-level

increase. The GOM shoreline is extensive and particularly vulnerable to sea-level rise due to its

extensive development, flat topography, and high subsidence rate. Models have projected that

the relative sea-level (considering sea level rise and subsidence rates) along the GOM coast

could rise anywhere from 15 to 44 inches over the next 100 years (Twilley et al. 2001). Such sea

level rises would result in submerged coastal wetlands (habitat loss), loss of coastline, loss and

damage of infrastructure, an increase in the occurrence of storm surges, and reduced storm

protection (Twilley et al. 2001; Reed 2002; Cowan et al. 2008; Donoghue 2011). Damage would

be worst in areas with high human disturbance (Twilley et al. 2001), and along the Louisiana

coast where subsidence and land loss are particularly prevalent (Cowan et al. 2008; Rose and

2

Sable 2013). In addition, intruding salt water could threaten aquifers and ultimately reduce

freshwater supply, worsened by the growing needs of the expanding human population adjacent

to the GOM (Twilley et al. 2001). The IPCC predicts that climate change will cause an increase

in extreme weather events, including storms, flooding, and intense precipitations, which would

worsen the aforementioned consequences (Pachauri et al. 2014).

Episodic cold snaps can have significant environmental implications. El Niño events are

characterized by a significant decrease in winter and spring temperatures in the GOM region

(Twilley et al. 2001). In 2010, an unprecedented cold front affected the entire GOM (Carmichael

et al. 2012; Pirhalla et al. 2015). Following the event, an unusually large snowmelt caused

abnormally high inflow of cold freshwater into the GOM lowering water temperatures

(Carmichael et al. 2012). Cold snap events can cause metabolic stress and mortality in resident

marine organisms (Carmichael et al. 2012; Matich and Heithaus 2012; Pirhalla et al. 2015).

Nutrient loading/eutrophication/hypoxia/red tides

The Mississippi and Atchafalaya rivers drain about 40% of the contiguous U.S into the

GOM (Mitsch et al. 2001; Rabalais et al. 2002). This freshwater discharge is diverted by currents

onto the Louisiana and Texas continental shelves and carries with it nutrients from the

watershed, a process known as nutrient loading. The GOM coastal waters are naturally nitrogen

limited, therefore controlling the possible primary productivity (Mitsch et al. 2001). However,

since the introduction of nitrogen fertilizers in the early 1950s, the concentration of nutrients

carried by the Mississippi and Atchafalaya rivers and discharged into the GOM has increased

significantly (Mitsch et al. 2001; Rabalais et al. 2002; Scavia et al. 2004). Increased nutrient

loading causes eutrophication, in which primary production increases without control. The algal

3

blooms resulting from nutrient loading increase water turbidity and decrease the overall water

quality (Rabalais et al. 2002; Rabotyagov et al. 2014). Eutrophication can lead to hypoxic

conditions. The phytoplankton that is not consumed sinks to the bottom and decomposes.

Decomposition of that material consumes high amounts of oxygen, which can overcome the rate

of oxygen diffusion at the surface. Stratification of the water column further impedes the

diffusion of oxygen to the bottom of the ocean, resulting in bottom waters with oxygen

concentrations below those required by most organisms (Rabalais et al. 2002).

Red tide events caused by the dinoflagellate Karenia brevis have plagued the GOM large

marine ecosystem (LME) for centuries (Magana et al. 2003; Steidinger 2009). Although

documented throughout the GOM LME, such harmful algal blooms frequently occur on the West

Florida Shelf (WFS), a region of the GOM of critical ecological and economic importance

(Cannizzaro et al. 2008; Vargo 2009). Red tide blooms generally start offshore at depth

(Steidinger and Vargo 1988), and are then transported inshore by winds and tidal currents

(Steidinger and Haddad 1981). The release of brevetoxin, a neurotoxin produced by K. brevis,

can inhibit breathing in marine mammals and poison shellfish (Tester et al. 2002; Landsberg et

al. 2009). The detrimental ecosystem impacts of red tide events include mass mortalities of

marine mammals, increased sea turtle strandings (Landsberg et al. 2009), and extensive fish kills

(Flaherty and Landsberg 2011; Driggers et al. 2016). During 2005, the WFS experienced an

extensive red tide that covered more than 500 square miles and lasted about 13 months (FWRI

2005). This extensive red tide caused an increase in the mortality of many economically

important resources such as gag grouper (Mycteroperca microlepis) and red grouper

(Epinephelus morio), possibly through suffocation or ingestion of affected prey (e.g., Naar et al.

2007; Landsberg et al. 2009; Flaherty and Landsberg 2011). Decomposition of HABs can

4

exacerbate oxygen depletion and further the process leading to hypoxia and reduced water

quality (Rabalais et al. 2002).

The GOM houses the largest zone of oxygen-depleted waters in the Western Atlantic, and

the second largest in the world in area, with a long-term average area of 13,751 km² (estimate for

the period 1985-2014) and a five-year average area of 14,353 km² (estimate for the period 2010-

2014) (Hypoxia Task Force 2015). This hypoxic zone has been recurring seasonally since the

1950s, usually occurring from June to August off the coast of Louisiana, and became large scale

in the 1970s (Scavia et al. 2004; Rabotyagov et al. 2014). However, official mapping of the

hypoxic region of the GOM did not begin until 1985 (Rabalais et al. 2002; Rabotyagov et al.

2014; Hypoxia Task Force 2015). The establishment and size of the hypoxic zone has been

linked to nitrogen loading from fertilizer use in agriculture (Rabalais et al. 2002; Karnauskas et

al. 2013). The hypoxic conditions are considered a symptom of degraded water quality

(O’Connor and Whitall 2007). Hypoxia can encourage some mobile organisms to move out of

the impacted area and can cause benthic organisms to die (Karnauskas et al. 2013). Hypoxic

conditions have been found to enhance the survival and growth of jellyfish due to the reduction

of the natural sessile community (Miller and Graham 2012), contributing to decreased marine

diversity as resident organisms leave the area (Rabalais et al. 2002). In addition, O’Connor and

Whitall (2007) linked hypoxia to a decrease in brown shrimp (Farfantepenaeus aztecus) landings

in Texas. Unfortunately, efforts to study the economic effects of the GOM hypoxic zone have

been extremely limited to date, and the short and long-term effects of hypoxia on the marine

ecosystem and living marine resources are currently uncertain (Rabotyagov et al. 2014).

Population growth/urban sprawl/habitat loss

5

According to the National Oceanic and Atmospheric Administration (NOAA)’s State of

the Coast Report (National Ocean Service 2011), the population of GOM states, which amounted

to 56.2 million people in 2010, will be 15% larger by 2020. This figure greatly surpasses the

expected national average of 11% in the same time frame (National Ocean Service 2011).

Because the GOM area is prone to flooding (National Ocean Service 2011), its population

growth will be accompanied by enhanced alterations to coastal lands and estuary water flow

(Twilley et al. 2001). Increases in urbanization and development will alter the quantity of water

flows, and aggravate subsidence and erosion. This will decrease water availability and water

quality in the GOM estuaries and coastal areas (Twilley et al. 2001; National Ocean Service

2011). Population growth will also increase carbon dioxide emissions, thereby further driving

climate change (Pachauri et al. 2014).

Increases in urbanization and development will also further habitat loss and ultimately

effect ecosystem services (Sklar and Browder 1998; Mendoza-González et al. 2012). Fish

production in the GOM is dependent on the nursery habitats provided by estuaries and coastal

wetlands and marshes (Cowan et al. 2008; Minello et al. 2012). The human-created configuration

of the Mississippi River has resulted in discharge moved offshore, which is believed to be linked

to wetland and vegetative losses (Cowan et al. 2008; Pirhalla et al. 2015). The water flow

alterations can flood areas where inflow is increased and cause increased salinity in areas where

inflow is decreased, thereby putting stress on vegetation that requires specific environmental

conditions (Pirhalla et al. 2015). Wetland loss is a particular concern in Louisiana (Couvillion et

al. 2011) where the United States Geological Survey (USGS) found that, from 1985 to 2010,

wetland loss has occurred at a rate of 16.57 square miles per year due to the combined effects of

coastal development, subsidence, hurricanes, and sea-level rise (Couvillion et al. 2011).

6

Overfishing/unsustainable fishing practices

Because of the long history of commercial and recreational fishing in the GOM, some

species have experienced overfishing (meaning that the fishing mortality rate is higher than the

management target) or been overfished (meaning that the spawning stock biomass is below the

management target). Since the 1950s, commercial fish landings in the GOM have been

dominated by menhaden (Brevoortia spp.; mainly Gulf menhaden, Brevoortia patronus), which

peaked in the mid-1980s (Karnauskas et al. 2013). Landings of invertebrates (primarily shrimp,

Farfantepenaeus aztecus, F. duorarum, Pleoticus robustus, and Litopenaeus setiferus; followed

by blue crab, Callinectes sapidus, and Eastern oyster, Crassostrea virginica) have been relatively

stable since the 1950s. Menhaden and the dominant shrimp species are neither overfished nor

experiencing overfishing (SEDAR 2013b; NOAA Fisheries 2016). Commercial landings of fish

(excluding menhaden) peaked in the early 1990s and have since declined. Recreational landings

of fish amount to about 25% of the total catch of fish (excluding menhaden) and have remained

fairly consistent since recreational data began to be collected in 1980 (Karnauskas et al. 2013), in

part because the increased recreational fishing effort has coincided with an increase in catch-and-

release fishing. Nevertheless, there have been changes in the species composition of both

recreational and commercial catches, as some stocks have been overfished to the point that they

become rare in the catch. Defining a “stock collapse” as either a formal declaration of overfished

status by a stock assessment, or reduction in catch by at least 90% that continued for more than

1.5 generations, de Mutsert et al. (2008) identified 15 fish and shellfish stocks in the GOM that

had experienced at least one stock collapse since the 1960s. In the GOM, as in the rest of the

U.S., fisheries management has improved since 2007, when the reauthorized Magnuson-Stevens

7

Fishery Conservation and Management Act (MSFCMA) strengthened requirements to end

overfishing for federally managed fisheries. In 2007, four species under the management of the

Gulf of Mexico Fishery Management Council (GMFMC) were experiencing overfishing (NOAA

Fisheries 2008). Currently, of the 29 assessed stocks in GMFMC management plans, none are

experiencing overfishing. Of the 18 stocks with known overfished status in 2007, three remain

overfished at present: gray triggerfish (Balistes capriscus), greater amberjack (Seriola dumerili),

and red snapper (Lutjanus campechanus) (NOAA Fisheries 2016). Attempts to reduce

overfishing have been less successful for highly migratory species (HMS), which are assessed

and managed by NOAA-Fisheries Highly Migratory Species Division. Of the 26 Atlantic HMS

stocks whose distribution ranges include the GOM, 19 have known status, and of these, six are

experiencing overfishing: dusky shark (Carcharhinus obscurus), scalloped hammerhead

(Sphyrna lewini), bigeye tuna (Thunnus obesus), blue marlin (Makaira nigricans), white marlin

(Kajikia albidus), and Atlantic sailfish (Istiophorus albicans). Six HMS stocks, dusky shark,

sandbar shark (C. plumbeus), scalloped hammerhead, blue marlin, white marlin, and bluefin tuna

(T. thynnus), are overfished, while three HMS stocks, bigeye tuna, albacore (T. alalunga) and

Atlantic sailfish, have been overfished but are now rebuilding (NOAA Fisheries 2016). In

addition to the federally managed stocks, there are also more than 27 coastal populations that are

managed by the GOM states, in some cases coordinated by the Gulf States Marine Fisheries

Commission (Fish and Wildlife Research Institute ; Oyster Technical Task Force 2012; GDAR

2013; SEDAR 2013b; Flounder Technical Task Force 2015; GSMFC 2015). Of the 10 stocks for

which status is known, none are overfished, but stone crab (Menippe mercenaria) is thought to

be experiencing overfishing on the west coast of Florida (FWC 2011). Many of the stocks that

are managed entirely by the GOM states are mainly caught in recreational fisheries, so that it is

8

difficult to collect enough data on total effort, total catch, species composition, and survival of

live releases to conduct accurate assessments.

Although relatively few of the assessed stocks in the GOM are experiencing overfishing,

there is cause for concern because the vast majority of the target stocks have not yet been

assessed (Karnauskas et al. 2013). For example, only 12 of the 31 species listed in the GMFMC

Reef Fish Fishery Management Plan have been assessed since 2005 (GMFMC 2016), so it is

possible that any number of stocks could be overfished or experiencing overfishing. Karnauskas

et al. (2013) evaluated trends in abundance for the assessed species in the GOM and noted that

species that were important to commercial and recreational fisheries were more likely to be

increasing in abundance and the less important species were more likely to be decreasing.

In addition to removing biomass of target species, fisheries impact the GOM ecosystem

through bycatch, habitat damage, and indirect effects. Under the Marine Mammal Protection Act,

fisheries are classified by how often they interact with marine mammals, from I (often) to III

(seldom) (Moore et al. 2009). Four fisheries in the GOM interact with marine mammals: the

pelagic longline fishery (I), gillnet fisheries (II), the shrimp trawl fishery (III), and the demersal

shark longline fishery (III). Sea turtles are caught in the pelagic longline, demersal longline, and

shrimp trawl fisheries, and seabirds are caught in the pelagic longline fishery (Moore et al.

2009). Table OR2.2 summarizes the annual total bycatch of fish, shellfish and protected species,

and fisheries landings from the U.S. National Bycatch Report First Edition (Karp et al. 2011) as

well as Updates 1 (National Marine Fisheries Service 2013) and 2 (National Marine Fisheries

Service 2016) and for the menhaden purse seine fishery. Explanations of how bycatch estimates

are determined for each fishery are provided in the corresponding versions of the U.S. National

Bycatch Report (Karp et al. 2011; National Marine Fisheries Service 2013; National Marine

9

Fisheries Service 2016). Note that a few small-scale studies have investigated bycatch in the

menhaden fishery as described in Sagarese et al. (2016), yet this fishery is not subject to a federal

observer program to determine the magnitude of bycatch. Bycatch of juvenile red snapper in the

shrimp trawl fishery, which is up to 1.25 million individuals per year (NOAA Fisheries 2016),

has contributed to the failure of the red snapper rebuilding plan (SEDAR 2013a). Although

bycatch has been relatively well studied in the GOM, there is less data to evaluate other indirect

effects of fishing. Trawls have been shown to damage fragile benthic communities in other

regions (Rijnsdorp et al. 2016), but no data are available on the impact of fishing on benthic

fauna in the GOM. There is also a lack of empirical data on how the effects of fishing propagate

through the food web, although it is known that GOM commercial fisheries catches (excluding

menhaden) have been increasingly focused on higher trophic level species, which is the opposite

of what would be expected if fisheries were fishing down the food web (Munyandorero and

Guenther 2010; Karnauskas et al. 2013).

Oil and gas exploration

The GOM is an important region for offshore oil production, providing energy as well as

numerous employment opportunities; the sector of offshore oil production employed about

55,000 workers in 2014 (National Research Council 2014). Oil platforms are located off the

coast of all GOM states, with the exception of Florida, with the majority found off of Louisiana

and Texas (Fig. OR2.2). The net number of platforms in the GOM has been increasing since the

1940s, while the occurrence of oil spills in the region has been increasing since 1992

(Karnauskas et al. 2013). While the vast majority of oil spills in the GOM have been minor, the

2010 Deepwater Horizon (DWH) oil spill is a reminder of the hazardous potential. The DWH

10

well released about 172 million gallons of oil into the GOM over 87 days following the initial

explosion on April 20th, 2010. Furthermore, chemical dispersants were released to help degrade

harmful hydrocarbons as part of the response (Lubchenco et al. 2012). The event resulted in

severe environmental and economic hardships (Upton 2011; Lubchenco et al. 2012; National

Research Council 2014). The DWH oil spill caused mortality of planktonic organisms and fish

larvae and resulted in the coating of larger organisms, causing suffocation. Sub-lethal effects of

the DWH oil spill include a decrease in the growth and reproduction potentials of marine

organisms, thereby decreasing their future productivity and contaminating these organisms as a

food source to humans and marine life (Upton 2011). To ensure public safety, several fisheries

closures, covering up to 88,500 square miles, were implemented following the DWH oil spill

(Lubchenco et al. 2012), severely harming the recreational and commercial fishing industries

(Upton 2011). Fisheries were reopened through mid-November 2010 on a species-by-species

basis after sampling had ensured that the oil and dispersant chemicals were no longer

contaminants in GOM seafood (Upton 2011). The lack of seafood supply combined with public

uncertainty over the safety of GOM seafood drove consumers to purchase products from other

regions.

In the GOM, petroleum platforms function as artificial reefs (Sheehy and Vik 2010;

Karnauskas et al. 2013). This effect is considered to be beneficial to fishes and is even

encouraged in the rigs-to-reef program as a cost effective and environmentally favorable way to

decommission platforms. While petroleum platforms can serve as habitat and as a rich foraging

ground for commercially valuable fish species, they have also been found to increase the range

of non-indigenous species (NIS), which has a negative impact on fisheries (more on this issue of

NIS in the next section). The occurrence of many NIS populations is only episodic and their

11

impact is relatively benign. However, currents connect petroleum platforms, thereby allowing the

spread of planktonic larvae and, consequently, increasing the risk of the NIS becoming invasive

(Sheehy and Vik 2010).

Non-indigenous species

Human activities can cause the accidental or intentional introduction of NIS into the

marine environment. Vectors of introduction of NIS include ballast water, hull fouling, and

aquaria (Aguilar-Perera and Tuz-Sulub 2010). Ray (2005) reported that the GOM houses 74 non-

native species, ten of which are intentional introductions. Non-natives become invasive when

their presence is destructive to the native marine community and when the environment where

they are introduced lacks natural population controls (Ray 2005; Sheehy and Vik 2010). Invasive

species in the GOM include Asian tiger shrimp (Penaeus monodon; U.S. GOM), Australian

spotted jellyfish (Phylloriza punctate; Mississippi Sound), green-lipped mussel (Perna viridis;

Florida), brown mussel (Perna perna; Texas), Chinese mitten crab (Eriocheir sinensis;

Mississippi Sound), green porcelain crab (Petrolisthes armatus), Asian swamp eel (Monopterus

albus; Florida), and lionfish (Pterois volitans and P. miles) (Graham et al. 2003; Ray 2005;

Aguilar-Perera and Tuz-Sulub 2010; Sheehy and Vik 2010).

The lionfish invasion has received the most attention. Deliberately or accidently

introduced from aquaria (Aguilar-Perera and Tuz-Sulub 2010; Frazer et al. 2012) and first seen

in Florida waters in 1985, lionfish are now considered widespread throughout the western

Atlantic, including the GOM (Fig. OR2.3). It is likely that lionfish larval dispersal has been

aided by the Caribbean, Yucatan, and Loop currents (Aguilar-Perera and Tuz-Sulub 2010). The

first sighting of lionfish in the GOM linked to larval transport was of two individuals off of the

12

northern Yucatan Peninsula in 2009 (Aguilar-Perera and Tuz-Sulub 2010); sightings linked to

larval dispersal have since occurred in both the southern and northern GOM (Claydon et al.

2012; Frazer et al. 2012). Invaded areas have been found to have higher lionfish densities as well

as larger individuals when compared to native habitats in the Indo-Pacific, indicating a low

mortality, a lack of predation, and an overall absence of interspecific competition for lionfish in

the GOM (Frazer et al. 2012; Benkwitt 2015). Benkwitt (2015) found that increasing lionfish

density in the GOM can cause declines in the biomass of prey-sized native reef fishes.

The Australian spotted jellyfish invasion has received less attention, though is still

considered a significant problem in the GOM. Native to the tropical western Pacific, the

Australian spotted jellyfish was possibly introduced to the Atlantic through the Panama Canal in

the late 1950s and has been found in the northern GOM as early as 1993 (Sheehy and Vik 2010).

Substantial populations of Australian spotted jellyfish have recurred and episodically invaded

waters along the Louisiana and Florida coasts since 2000 (Graham et al. 2003; Sheehy and Vik

2010). Currently, Australian spotted jellyfish are found in swarms in densities up to 500,000

individuals per 150 km² in the GOM waters (Ray 2005; Sheehy and Vik 2010). Their swarms

can clog shrimp nets, resulting in substantial economic impacts to the shrimp fisheries (Graham

et al. 2003; Sheehy and Vik 2010). Furthermore, it has been suggested that Australian spotted

jellyfish indirectly affect local fisheries through the consumption of the eggs and larvae of native

species and competition with larvae of native species (Graham et al. 2003). Increased abundance

and range expansion of jellyfish in the GOM and worldwide has been attributed to eutrophication

and climate change (Sheehy and Vik 2010).

Pollution/marine debris/noise

13

The NOAA’s National Status and Trends Mussel Watch Program (MWP) monitors the

accumulation of organic and metal contaminants in bivalves to estimate the contamination levels

of coastal and estuarine waters of the GOM. Toxic mercury found in the GOM habitats has been

linked mainly to Mississippi River transport under strong precipitation events and to petroleum

operations (Karnauskas et al. 2013). High concentrations of cadmium, which are linked to urban

development, have been found in sediments of the northwestern and central GOM (Karnauskas

et al. 2013). While the concentration of cadmium in bivalves is currently below the U.S. Food

and Drug Administration’s (FDA) allowable level for human exposure through shellfish

consumption, it remains a concern due to its toxicity at high concentrations (Karnauskas et al.

2013).

Marine debris is a pervasive pollution problem globally (Ribic et al. 2011).

Abandonment, improper disposal, and storm activity can result in traps, lines, rope, plastic, and

buoys left unattended in the ocean. While these objects can provide shelter and habitat,

organisms can also become trapped, resulting in ghost fishing (Leckemitchell and Mullin 1992;

Leckemitchell and Mullin 1997; Anderson and Alford 2014). Commercially important species,

such as red drum (Sciaenops ocellatus) and stone crab (Menippe adina), as well as river otters

(Lontra Canadensis), have been observed in abandoned crab traps off Louisiana (Anderson and

Alford 2014). Marine mammals, sea turtles, and seabirds can become entangled in drifting lines

resulting in injury or mortality (Mearns et al. 2015). Drifting debris is carried by the local

currents, resulting in its accumulation in the western GOM along the Texas coast where it can be

pushed up onto the beaches (Ribic et al. 2011).

Because the GOM is a hub for marine activities, anthropogenic ambient noises occur in

the region due to drilling, construction, shipping, and recreational boating (Azzara et al. 2013).

14

The port of New Orleans and port of Houston have a combined traffic flow of 14,000 ships

annually, leading to a chronic effect (Azzara et al. 2013). Cetaceans are known to use acoustics

to forage, communicate, and navigate (Horowitz and Jasny 2007; Stocker 2007); noise from

anthropogenic sources can result in behavioral changes and even mortality in cetaceans if

individuals occur very close to the noise source (Horowitz and Jasny 2007; Azzara et al. 2013).

However, it is not yet entirely clear how cetacean populations are being affected by noise

(Horowitz and Jasny 2007). While this issue falls under the Marine Mammal Protection Act and

Endangered Species Act (Horowitz and Jasny 2007; Stocker 2007), the number of noise sources,

the economic importance of those sources, and a lack of funding, have made it difficult to

manage and mitigate noise pollution (Horowitz and Jasny 2007).

15

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Anderson JA, Alford AB (2014) Ghost fishing activity in derelict blue crab traps in Louisiana. Mar Pollut Bull 79:261−267. doi: 10.1016/j.marpolbul.2013.12.002

Azzara AJ, von Zharen WM, Newcomb JJ (2013) Mixed-methods analytic approach for determining potential impacts of vessel noise on sperm whale click behavior. J Acoust Soc Am 134:4566−4574. doi: 10.1121/1.4828819

Benkwitt CE (2015) Non-linear effects of invasive lionfish density on native coral-reef fish communities. Biol Invasions 17:1383−1395. doi: 10.1007/s10530-014-0801-3

Cannizzaro JP, Carder KL, Chen FR, Heil CA, Vargo GA (2008) A novel technique for detection of the toxic dinoflagellate, Karenia brevis, in the Gulf of Mexico from remotely sensed ocean color data. Cont Shelf Res 28:137−158. doi: 10.1016/j.csr.2004.04.007

Carmichael RH, Graham WM, Aven A, Worthy G, Howden S (2012) Were multiple stressors a 'perfect storm' for Northern Gulf of Mexico bottlenose dolphins (Tursiops truncatus) in 2011? Plos One 7: e41155. doi: 10.1371/journal.pone.0041155

Claydon JAB, Calosso MC, Traiger SB (2012) Progression of invasive lionfish in seagrass, mangrove and reef habitats. Mar Ecol Prog Ser 448:119−129. doi: 10.3354/meps09534

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Couvillion BR, Barras JA, Steyer GD et al (2011) Land area change in coastal Louisiana (1932 to 2010). US Department of the Interior, US Geological Survey, U.S. Geological Survey Scientific Investigations Map 3164. https://pubs.usgs.gov/sim/3164/downloads/SIM3164_Pamphlet.pdf. Accessed 12 Dec 2016

Cowan JH, Grimes CB, Shaw RF (2008) Life history, history, hysteresis, and habitat changes in Louisiana's coastal ecosystem. B Mar Sci 83:197−215

de Mutsert K, Cowan JH, Essington TE, Hilborn R (2008) Reanalyses of Gulf of Mexico fisheries data: landings can be misleading in assessments of fisheries and fisheries ecosystems. P Natl Acad Sci USA 105:2740−2744. doi: 10.1073/pnas.0704354105

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Glossary of Online Resource 2El Niño Southern Oscillation (ENSO): El Niño is “a basin-wide warming of the tropical

Pacific Ocean east of the dateline. This oceanic event is associated with a fluctuation of a

global-scale tropical and subtropical surface pressure pattern called the Southern Oscillation.

This coupled atmosphere–ocean phenomenon has preferred time scales of two to about seven

years” (Pachauri et al. 2014).

Eutrophication: a phenomenon that occurs when a body of water is enriched with nutrients

to the point that nutrient concentrations surpass naturally occurring levels, which results in

increases in primary production and algae growth (Hypoxia Task Force 2015).

Hypoxia: situation where dissolved oxygen concentration is less than 2 mg per L (Rabalais et

al. 2002).

Non-indigenous species (NIS): species that are not normally native to a region (Sheehy and

Vik 2010).

Invasive species: an alien species whose introduction is likely to result in economic and/or

environmental harm (Ray 2005).

Marine debris: manufactured and solid anthropogenic waste that enters the marine

environment from any source (Ribic et al. 2011).

Ghost fishing: when dead organisms trapped within abandoned fishing traps attract more

individuals causing continual mortality (Anderson and Alford 2014).

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Table OR2.1. Classification of Gulf of Mexico (GOM) stressors into drivers, pressures

and states

Drivers Pressures StatesClimate changeNutrient loadingPopulation growth

Urban sprawl/coastal developmentOil/gas explorationOverfishing/unsustainable fishing practicesInvasive speciesStorms/hurricanesDredging, levees and canalsSubsidenceSea-level rise

HypoxiaEutrophicationHabitat and vegetation loss/degradationWater quality degradation/pollutionMarine debrisNoise pollutionChanges in water quantityReduced storm protectionCold snapsHarmful algal blooms

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Table OR2.2. Annual total bycatch average estimates and fisheries landings from the

United States (U.S.) National Bycatch Report and from the menhaden purse seine

fishery in the U.S. Gulf of Mexico (GOM) (Karp et al. 2011; National Marine Fisheries

Service 2013; National Marine Fisheries Service 2016). Methods of estimation can be found

in Karp et al. (2011), National Marine Fisheries Service (2013) and National Marine Fisheries

Service (2016) and reflect the average from the year(s) identified

Fishery 2013 total fish bycatch Sea turtle bycatch (year)

Marine mammal bycatch (year)

Seabird bycatch (year)

Annual total fishery landings (metric tons)

GOM coastal migratory pelagic troll

18,128.60 individuals 298.73

GOM coastal migratory pelagic gillnet

1,410.60 individuals 754.03

GOM reef fish bottom longline

948,273.80 individuals 11.90 individuals

5 individuals (2006-2010)

2325.46

GOM reef fish vertical line

2,072,390.40 individuals

32.90 individuals (2006-2008)

57 individuals (2010)

3918.29

GOM shrimp trawl

242,185,080.10 pounds 5,166.00 individuals (2002, 2009)

67995.19

Atlantic and GOM highly migratory species pelagic longline

1,373,378.00 pounds 742.70 individuals(2013)

145.40 individuals(2013)

34.00 individuals(1992-2013)

2794.08

Atlantic and GOM shark bottom longline

2,107.00 individuals 535.00 individuals (2004,2005)

100.25 individuals (2003)

291.79

GOM menhaden purse seine

Unknown 497500.00

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Fig. OR2.1 Illustration of the relationships between stressors in the Gulf of Mexico (GOM)

Many stressors in the GOM are related and one often causes or contributes to another

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Fig. OR2.2 Locations of oil platforms and pipelines in the Gulf of Mexico according to the

Bureau of Ocean Energy Management. This figure was inspired by:

https://www.data.boem.gov/homepg/data_center/mapping/geographic_mapping.asp

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Fig. OR2.3 Lionfish sightings in the Gulf of Mexico. This figure was produced from Reef

Environmental Education Foundation (REEF) survey data collected between 2011 and 2015

(REEF 2016)

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