Gulf of Mexico
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LME 5: Gulf of Mexico

Bordering countries:

Mexico, United States of America

LME total area:

1,530,387 km²

LME overall risk:

This LME falls in the cluster of LMEs that exhibit medium numbers of collapsed and overexploited fish stocks, as well as very high proportions of catch from bottom impacting gear.
Based on a combined measure of the Human Development Index and the averaged indicators for fish & fisheries and pollution & ecosystem health modules, the overall risk factor is medium.

Productivity

Chlorophyll-A:

The annual Chlorophyll a concentration (CHL) cycle has a maximum peak (0.297 mg.m^-3) in January and a minimum (0.159 mg.m^-3) during June. The average CHL is 0.208 mg.m^-3. Maximum primary productivity (317 g.C.m^-2.y^-1) occurred during 1998 and minimum primary productivity (227 g.C.m^-2.y^-1) during 2012. There is a statistically insignificant decreasing trend in Chlorophyll of -0.221 % from 2003 through 2013. The average primary productivity is 270 g.C.m^-2.y^-1, which places this LME in Group 3 of 5 categories (with 1 = lowest and 5= highest).

Primary productivity:

Sea Surface Temperature:

Between 1957 and 2012, the Gulf of Mexico LME #5 has warmed by 0.16, thus belonging to Category 4 (slow warming LME). The Gulf of Mexico’s thermal history is quite peculiar. The global cooling of the 1960s transpired as an SST drop of <1°C, followed by a slow warming until present. The relatively slow warming of the last 50 years was modulated by strong interannual variability with a typical magnitude of 0.5°C. The all-time high of >26.4°C in 1972 was a major event as SST increased by 0.8°C in just two years. This event was localized within the Gulf of Mexico LME. The relative stability of the Gulf of Mexico’s thermal regime can be explained by the Gulf Stream (Loop Current) flowing through the Gulf of Mexico.

Fish and Fisheries

The Gulf of Mexico LME fisheries are multispecies, multigear and multifleet in character and include artisanal, commercial and recreational fishing. Species of economic importance include brown shrimp (Penaeus aztecus), white shrimp (Penaeus setiferus), pink shrimp (Penaeus duorarum), Gulf menhaden (Brevoortia patronus), king mackerel (Scomberomorus cavalla), Spanish mackerel (S. maculatus), red grouper (Epinephelus morio), red snapper (Lutjanus campechanus), seatrout, tuna and billfish.

Annual catch:

Total reported landings showed an increase to over 1.6 million t in 1984, followed by a decline to 750,000 t in recent years.

Catch value:

In 1981, the annual value of the reported landings was over 2.4 billion US$ (in 2005 value).

Marine Trophic Index and Fishing-in-Balance index:

The MTI has increased slightly from the early 1950s to 2010. The very low value of the MTI (2.4-2.5) is due to the high proportion of small, low trophic-level fishes, especially Gulf menhaden and shrimps in the landings, and the exclusion of the shrimp trawler bycatch in estimating mean trophic levels. The decline of the FiB index from the mid-1980s is likely a result of the declining reported landings.

Stock status:

The Stock-Catch Status Plots indicate that collapsed and overexploited stocks now account for about 60% of all commercially exploited stocks in the LME, with overexploited stocks contributing almost 70% of the reported landings.

Catch from bottom impacting gear:

The percentage of catch from the bottom gear type to the total catch reaches its first maximum at 72% in 1953 and then this percentage declined steadily to around 19% in the 1970s. This percentage then further declined to around 10% in the recent decade.

Fishing effort:

The total effective effort increased from around 2 million kW in the 1950s to its peak at 200 million kW in the mid- 2000s.

Primary Production Required:

The primary production required (PPR) to sustain the reported landings in the LME reached 8% of the observed primary production in 1994, but this is probably an underestimate due to the high level of shrimp bycatch absent from the underlying statistics.

Catch potential projections (under global warming):

Pollution and Ecosystem Health

Pollution

Nutrient ratio, Nitrogen load and Merged Indicator:

Human activities in watersheds are affecting nutrients transported by rivers into LMEs. Large amounts of nutrients (in particular nitrogen load) entering coastal waters of LMEs can result in high biomass algal blooms, leading to hypoxic or anoxic conditions, increased turbidity and changes in community composition, among other effects. In addition, changes in the ratio of nutrients entering LMEs can result in dominance by algal species that have deleterious effects (toxic, clog gills of shellfish, etc.) on ecosystems and humans. An overall nutrient indicator (Merged Nutrient Indicator) based on 2 sub-indicators: Nitrogen Load and Nutrient Ratio (ratio of dissolved Silica to Nitrogen or Phosphorus - the Index of Coastal Eutrophication Potential or ICEP) was calculated.

Nitrogen load:

The Nitrogen Load risk level for contemporary (2000) conditions was very high. (level 5 of the five risk categories, where 1 = lowest risk; 5 = highest risk). Based on a “current trends” scenario (Global Orchestration), this remained the same in 2030 and 2050.

Nutrient ratio:

The Nutrient Ratio (ICEP) risk level for contemporary (2000) conditions was high (4). According to the Global Orchestration scenario, this remained the same in 2030 and 2050.

Merged nutrient indicator:

The risk level for the Merged Nutrient Indicator for contemporary (2000) conditions was very high (5). According to the Global Orchestration scenario, this remained the same in 2030 and 2050.

POPs:

Data are available for only one sample at a rural location in Mississippi State (USA). The location shows a concentration (ng.g^-1 of pellets) of 28 for PCBs, 13 for DDTs, and 0.1 for HCHs. These correspond to risk category 2 for PCBs, 2 for DDTs, and 1 for HCHs, of the five risk categories (1 = lowest risk; 5 = highest risk). This is probably due to minimal anthropogenic activities involving the use of POPs (PCBs in industries and DDT and HCH pesticides in agriculture). More samples and locations are necessary to properly evaluate this LME.

Plastic debris:

Modelled estimates of floating plastic abundance (items km^-2), for both micro-plastic (<4.75 mm) and macro-plastic (>4.75 mm), indicate that this LME is in the group with relatively high levels of plastic concentration. Estimates are based on three proxy sources of litter: shipping density, coastal population density and the level of urbanisation within major watersheds, with enhanced run-off. The high values are due to the relative importance of these sources in this LME. The abundance of floating plastic in this category is estimated to be on average over 100 times higher that those LMEs with lowest values. There is limited evidence from sea-based direct observations and towed nets to support this conclusion.

Ecosystem Health

Mangrove and coral cover:

0.36% of this LME is covered by mangroves (US Geological Survey, 2011) and 0.09% by coral reefs ().

Reefs at risk:

This LME has a present (2011) integrated threat index (combining threat from overfishing and destructive fishing, watershed-based and marine-based pollution and damage) of 174. 2% of coral reefs cover is under very high threat, and 6% under high threat (of the 5 possible threat categories, from low to critical). When combined with past thermal stress (between 1998 and 2007), these values increase to 8% and 19% for very high and high threat categories respectively. By year 2030, 7% of coral cover in this LME is predicted to be under very high to critical level of threat from warming and acidification; this proportion increases to 9% by 2050.

Marine Protected Area change:

The Gulf of Mexico LME experienced an increase in MPA coverage from 6,671 km² prior to 1983 to 290,795 km² by 2014. This represents an increase of 4,259%, within the medium category of MPA change.

Cumulative Human Impact:

The Gulf of Mexico LME experiences an above average overall cumulative human impact (score 3.81; maximum LME score 5.22), which is well above the LME with the least cumulative impact. It falls in risk category 3 of the five risk categories (1 = lowest risk; 5 = highest risk). This LME is most vulnerable to climate change. Of the 19 individual stressors, three connected to climate change have the highest average impact on the LME: ocean acidification (0.92; maximum in other LMEs was 1.20), UV radiation (0.53; maximum in other LMEs was 0.76), and sea surface temperature (1.41; maximum in other LMEs was 2.16). Other key stressors include commercial shipping, sea level rise, ocean based pollution, and demersal destructive commercial fishing.

Ocean Health Index:

The Gulf of Mexico LME scores above average on the Ocean Health Index compared to other LMEs (score 71 out of 100; range for other LMEs was 57 to 82) but still relatively low. This score indicates that the LME is well below its optimal level of ocean health, although there are some aspects that are doing well. Its score in 2013 increased 5 points compared to the previous year, due in large part to changes in the scores for clean waters and natural products. This LME scores lowest on food provision, coastal protection, coastal livelihoods, and iconic species goals and highest on artisanal fishing opportunities, coastal economies, lasting special places and species diversity goals. It falls in risk category 3 of the five risk categories, which is an average level of risk (1 = lowest risk; 5 = highest risk).

Socio-economics

Indicators of demographic trends, economic dependence on ecosystem services, human wellbeing and vulnerability to present-day extreme climate events and projected sea level rise, are assessed for the Gulf of Mexico LME. To compare and rank LMEs, they were classified into five categories of risk (from 1 to 5, corresponding to lowest, low, medium, high and highest risk, respectively) based on the values of the individual indicators. In the case of economic revenues, the LMEs were grouped to 5 classes of revenues from lowest, low, medium, high and highest, as revenues did not translate to risk.

Population:

The coastal area includes the southern coast of the United States of America and the eastern shoreline of Mexico. Covering about 140,753 km², current and projected population in 2100 are both in the large population size category (high risk) with a density of 81 persons per km² in 2010 and increasing to 129 per km² in 2100. About 24% of coastal population lives in rural areas, and is projected to decrease slightly to 23% in 2100.

Coastal poor:

The indigent population makes up 31% of the LME’s coastal dwellers. The Gulf of Mexico places in the highest-risk category based on percentage and absolute number of coastal poor (present day estimate).

Revenues and Spatial Wealth Distribution:

Fishing and tourism depend on ecosystem services provided by LMEs. The Gulf of Mexico LME ranks in the high revenue category in fishing revenues based on yearly average total ex-vessel price of US 2013 $1.7 billion (thousand million) for the period 2001-2010. Fish protein accounts for 8% of the total animal protein consumption of the coastal population. Its yearly average tourism revenue for 2004-2013 of US 2013 $252 billion places it in the highest revenue category. On average, LME-based tourism income contributes 9% to the national GDPs of the LME coastal states. Spatial distribution of economic activity (e.g. spatial wealth distribution) measured by night-light and population distribution as coarse proxies can range from 0.0000 (totally equal distribution and lowest risk) to 1.0000 (concentrated in 1 place and most inequitable and highest risk). The Night Light Development Index (NLDI) thus indicates the level of spatial economic development, and that for the Gulf of Mexico LME falls in the category with lowest risk.

Human Development Index:

Using the Human Development Index (HDI) that integrates measures of health, education and income, the present-day Gulf of Mexico LME HDI belongs to the highest HDI and lowest risk category. Based on an HDI of 0.856, this LME has an HDI Gap of 0.144, the difference between present and highest possible HDI (1.000). The HDI Gap measures an overall vulnerability to external events such as disease or extreme climate related events, due to less than perfect health, education, and income levels, and is independent of the harshness of and exposure to specific external shocks.
HDI values are projected to the year 2100 in the contexts of shared socioeconomic development pathways (SSPs). The Gulf of Mexico LME is projected to maintain its position in the lowest risk category (highest HDI) in 2100 under a sustainable development pathway or scenario. Under a fragmented world scenario, this LME is projected to slip to the high risk category (low HDI) because of reduced income level and bigger population size compared to estimated income and population values in a sustainable development pathway.

Climate-Related Threat Indices:

The Climate-Related Threat Indices utilize the HDI Gaps for present-day and projected 2100 scenarios. The contemporary climate index accounts for deaths and property losses due to storms, flooding and extreme temperatures incurred by coastal states during a 20-year period from 1994 to 2013 as hazard measures, the 2010 coastal population as proxy for exposure, and the present day HDI Gap as vulnerability measure.
The Contemporary Threat Index incorporates a Dependence Factor based on the fish protein contribution to dietary animal protein, and on the mean contribution of LME tourism to the national GDPs of LME coastal states. The HDI Gap and the degree of dependence on LME ecosystem services define the vulnerability of a coastal population. It also includes the average of risk related to extreme climate events, and the risk based on the degrading system states of an LME (e.g. overexploited fisheries, pollution levels, decrease in coastal ecosystem areas).
The 2100 sea level rise threat indices, each computed for the sustainable world and fragmented world development pathways, use the maximum projected sea level rise at the highest level of warming of 8.5 W/m² in 2100 as hazard measure, development pathway-specific 2100 populations in the 10 m × 10 km coast as exposure metrics, and development pathway-specific 2100 HDI Gaps as vulnerability estimates.
Present day climate threat index to the Gulf of Mexico LME is within the high-risk (high threat) category. The combined contemporaneous risk due to extreme climate events, degrading LME states and the level of vulnerability of the coastal population, is medium. In a sustainable development scenario, the risk index for sea level rise in 2100 is in the lowest risk category, and which increases to high-risk category under a fragmented world development pathway.

Governance

Governance architecture:

In this LME, none of the transboundary arrangements for fisheries (OLDESPECA, WECAFC and ICCAT) appear to be closely connected. However, the arrangements for pollution and biodiversity within the LME are closely integrated within the Cartagena Convention. The specific biodiversity arrangement for turtles does not appear to be linked to any of the arrangements within the LME. Overall, no integrating mechanisms, such as an overall policy coordinating organisation for the LME, could be found. However, this is not to suggest that there is not an abundance of collaboration and interactions amongst the fisheries arrangements through participation in each other’s meetings, complementing the integration found within the arrangements for pollution and biodiversity.
The overall scores for ranking of risk were: