Marine Pollution Bulletin 60 (2010) 1939–1945

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Marine Pollution Bulletin

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Extent and frequency of vessel oil spills in US marine protected areas

Tracey Dalton a,*, Di Jin b

a Marine Affairs Department, University of Rhode Island, Kingston, RI 02881, USAb Marine Policy Center, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

a r t i c l e i n f o a b s t r a c t

Keywords:Marine protected areasOil spillsMaritime safetyUnited States

0025-326X/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.marpolbul.2010.07.036

* Corresponding author. Tel.: +1 401 874 2434.E-mail address: dalton@uri.edu (T. Dalton).

Little is known about how marine protected areas (MPAs) may be vulnerable to vessel oil spills in theUnited States. This study investigated individual size, frequency, and total amount of vessel oil spilledin US MPAs, and how characteristics of MPAs and individual spill events influenced spills. Vessel oil spillsin US waters (2002–06) and MPA boundaries were mapped. Total number and volume of oil spills insideand outside MPAs were computed. Results show that the presence of a MPA does not seem to preventvessel oil spills or reduce the amount of oil spilled, and that a variety of MPA attributes (e.g., scale of pro-tection, fishing restrictions, and others) and spill event characteristics (e.g., vessel type, year of spill, andothers) affect oil spills inside and outside MPAs. These results can be used to develop MPA rules and mar-ine transportation policies that reduce the vulnerability of sensitive resources to oil spills.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Marine protected areas are a popular tool for managing humaninteractions with designated areas in the marine environment.MPAs can have a variety of objectives, and one primary goal com-mon to many MPAs is to maintain or enhance ecosystem health, abroad term that can include physical, biological, and chemical fea-tures (Rapport et al., 1998). Typical studies of the ecosystem healthof MPAs focus on the stress of extractive activities, such as fishing,on biological features (e.g., Halpern, 2003; Lester et al., 2009).Although water quality is an important component of ecosystemhealth and MPAs are vulnerable to water quality threats from landdevelopment and sedimentation, excessive nutrients, and vessel oilspills, few studies have focused on water quality in MPAs. Sedi-mentation and excessive nutrients result from landside activitiesthat are typically outside the boundaries of the MPA, making it dif-ficult to manage these threats using MPA policies. In contrast, oilspills from vessels result from activities on the water and can beaddressed by MPA policies, such as designated shipping lanes,restrictions on hazardous uses, or zones that separate conflictingor dangerous vessel activities.

If MPAs are to achieve goals of maintaining and enhancing eco-system health, then it is important to understand and mitigatethreats to ecosystem health from all sources, including oil spills.Little is known about how MPAs may be vulnerable to vessel oilspills in the United States. This study investigates the amountand frequency of spills in MPAs, and how management character-istics of MPAs influence these spills. First we present background

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on vessel oil spills in US waters, potential impacts of oil spills,and the system of MPAs in the US. We then present our methodsand results. Finally, we discuss how management can be improvedto reduce vulnerability of resources in marine protected areas to oilspills.

2. Background

2.1. Vessel oil spills in the United States

The United States imports over 60% of its total oil consumption.In 2009, of the 6.8 billion barrels of crude oil and petroleum prod-ucts supplied to the US market, 4.3 billion barrels were imported(US EIA, 2010). Most of the imports were carried in tankers. Inaddition, 1.6 billion barrels of exports and domestic coastal tradeof petroleum products were also shipped in tankers and bargesin 2008 (US Army Corps of Engineers, 2009).

Environmental damages due to a single large spill of crude oil orpetroleum products in a biologically sensitive marine area canamount to billions of dollars. For the Exxon Valdez spill off of Alas-ka in 1989, Exxon paid $2.2 billion for clean-up, $1 billion to settlestate and federal lawsuits, and $300 million for lost wages to11,000 fishermen and business firms. The cost to the fisheries ofsouth-central Alaska was estimated to be $108.1 million, the larg-est component being a $65.4 million reduction in the pink salmonfishery in the first year following the accident (Cohen, 1995). In1994, an Alaska jury awarded an additional $5.3 billion in punitiveand compensatory damages to those harmed by the spill. TheExxon Valdez accident was the impetus for the US Congress to passthe Oil Pollution Act of 1990, which strengthened accountabilityfor vessel oil spills in US waters.

1940 T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945

A number of studies have analyzed vessel accident oil spillsfrom oil-cargo vessels. Oil spillage from a tanker accident is greaterwhen the tanker is adrift and when the accident occurs on a coastalwaterway, but less for larger vessels and for US-flag tankers. Fortank barge accidents, oil spillage is greater for collision and mate-rial/equipment failure accidents (Anderson and Talley, 1995).Grounding accidents incur the smallest vessel damage costs, butthe largest oil-cargo spillage (Talley, 1999). For tank barges, spillsare greater for accidents occurring on a river, at nighttime, andwith older barges (Talley, 2000). Although the total spill volumesare greater when tankers, tank barges, and tugboats are involved,adjusted for vessel tonnage, other types of vessels are also signifi-cant contributors of oil spills. Collision, equipment failure, andgrounding are three main accident types associated with largespills. Spill size is greater during bad weather and at nighttime.When a vessel is underway or adrift, the expected spill size is lar-ger at both the absolute and unit levels. US-flag vessels are associ-ated with smaller spills (Jin et al., 2008).

2.2. Impacts of oil spills

Oil pollution can affect coastal and marine resources in numer-ous ways. For instance, exposure to oil and other hydrocarbons canaffect feeding, growth, development, and reproduction of livingorganisms (Capuzzo, 1987). Oil can directly affect the survival of

Fig. 1. Study area showing marine protected areas and vessel oil spills (2002–06) in US wHawaii; and (e) Puerto Rico and the US Virgin Islands.

fish, sea birds, and marine mammals, and indirectly affect theseorganisms by reducing availability of prey (Oil in the Sea III,2003). Oil can also penetrate the plumage of sea birds or fur ofmarine mammals, affecting heat insulation and buoyancy (Islamand Tanaka, 2004).

2.3. US system of marine protected areas

MPAs protect natural and cultural resources in US waters by lim-iting or restricting human activities that can have undesirable im-pacts on the marine environment. To date, over 1000 MPAs havebeen designated in US waters. Although goals vary among MPAs,they can include protecting biodiversity, increasing fish biomasswithin MPA boundaries, enhancing fish stocks outside MPA bound-aries, improving social conditions in affected communities, andothers (Boersma and Parrish, 1999; Palumbi, 2002; Mascia, 2004).Currently, US MPAs are managed at a variety of government levelsto achieve varying resource protection goals. For instance, fisheryclosures designated in federal waters and managed by the NationalMarine Fisheries Service are established to rebuild declining fishstocks. National Marine Sanctuaries, managed by NOAA’s NationalMarine Sanctuary Program, are established to protect areas ofspecial national significance. Massachusetts (MA) Ocean Sanctuar-ies, designated in MA state waters and overseen by the state ofMassachusetts, prevent alteration of the seafloor or seabed. Many

aters of the (a) East coast and Gulf coast states; (b) West coast states; (c) Alaska; (d)

T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945 1941

other MPAs are managed through partnerships and collaborationsof government agencies and non-governmental organizations.

In 2000, an Executive Order (EO) was issued that directs US fed-eral government agencies with responsibility for MPA manage-ment to develop a National System of MPAs that represents thediverse marine ecosystems of the US. The National System is ‘‘envi-sioned as a ‘system of sites and systems’ that will be developed toachieve conservation and management objectives that could not beaccomplished by individual MPAs”. (Framework, 2008, p.7) The EOrecognizes that water quality is an important component of theNational System of MPAs, and directs the EPA to develop new reg-ulations to protect coastal and marine waters from pollution.

As mandated by the EO, the National MPA Center was estab-lished to provide technical assistance to agencies with responsibil-ity for MPA management. The MPA Center compiled data, such asobjectives, activities allowed, constancy of protection, and othercharacteristics, on existing marine protected areas in the US to in-form the development of the National System of MPAs.

3. Methods

To investigate the volume and frequency of oil spills inside andoutside of US MPAs, we mapped all oil spills occurring in US watersduring 2002–06 and the boundaries of local, state/territorial,

Table 1Variables, measurement, and descriptive statistics: MPA attributes.

Variable Measurement

Total oil spill volume in a MPA Thousands of gallonsMax. volume/spill in a MPA Thousands of gallonsNumber of oil spills in a MPA NumberEcosystem scale 1 if MPA is managed at an ecosystem scale, 0Seasonal 1 if MPA is seasonal, 0 otherwiseAll fishing restricted 1 if MPA restricts fishing, 0 otherwiseAll fishing prohibited 1 if MPA prohibits all fishing, 0 otherwiseState MPA 1 if state MPA, 0 otherwiseNatural heritage 1 if primary conservation focus is natural herArea (1000 km2) Area of MPA in thousands of km2

West Coast 1 if MPA on west coast, 0 otherwiseAlaska 1 if MPA in Alaska, 0 otherwise

Note: Variables that are not statistically significant in regression models are not shown

Table 2Variables, measurement, and descriptive statistics: characteristics of individual oil spills.

Variable Measurement

Oil spill size Thousands of gallonsIn MPA 1 if spill is inside an MPA, 0 otherwiseFishing vessel 1 if a fishing vessel, 0 otherwiseFreight ship 1 if a freight ship, 0 otherwiseFreight barge 1 if a freight barge, 0 otherwiseTanker 1 if a tanker, 0 otherwiseTank barge 1 if a tank barge, 0 otherwiseOffshore supply vessel 1 if a offshore supply vessel, 0 otherwiseTugboat 1 if a tugboat, 0 otherwiseUS flag 1 if US flag, 0 otherwiseVessel total loss 1 if vessel total loss in accident, 0 otherwiseVessel damage 1 if vessel damaged in accident, 0 otherwiseYear 2002 1 if year 2002, 0 otherwiseYear 2003 1 if year 2003, 0 otherwiseYear 2004 1 if year 2004, 0 otherwiseFebruary 1 if February, 0 otherwiseApril 1 if April, 0 otherwiseMay 1 if May, 0 otherwiseOctober 1 if October, 0 otherwiseNovember 1 if November, 0 otherwise

Note: Variables that are not statistically significant in regression models are not shown

regional, and federal MPAs in the US (Fig. 1). Our study area in-cludes (1) US waters surrounding the continental states, Alaska,Hawaii, and the Caribbean; and (2) inland waters that extendabout 50 miles in from the coast. Oil spill data came from the USCoast Guard Marine Information for Safety and Law Enforcement(MISLE) information system, which includes information on vesseltype, date of the oil spill, location of the spill (geographic coordi-nates), and other related information (e.g., country where vesselis registered, or vessel flag). US MPA data came from the MPA Cen-ter Inventory, which includes information on MPA boundaries,conservation objective of the MPA (natural heritage, cultural heri-tage, or sustainable production), level of protection depending onthe level and types of activities allowed (e.g., fishing prohibitedwithin an entire MPA), permanence of protection (permanent, con-ditional, or temporary), constancy of protection (year-round, sea-sonal, or rotating), ecological scale of protection (ecosystem orfocal resource), and other management characteristics (e.g., ageof MPA, size of MPA, level of government responsible for MPA, etc.).

We computed total volume and number of oil spills inside andoutside MPA boundaries. A set of descriptive statistics was devel-oped to examine the characteristics of vessel oil spills (2002–06)and MPAs in US waters (Tables 1 and 2). Stepwise regressions wereused to analyze the effects of MPA management attributes on thevolume and frequency of vessel oil spills in MPAs and the effectsof individual spill characteristics on oil spill size. The result of a

Mean Std. dev. Min. Max.

11.98 65.79 0.0002 684.728.67 45.93 0.0002 321.05

23.57 64.30 1 760otherwise 0.56 0.50 0 1

0.11 0.32 0 10.23 0.42 0 10.02 0.15 0 10.64 0.48 0 1

itage, 0 otherwise 0.76 0.43 0 122.16 94.67 0.0009 956.96

0.13 0.34 0 10.16 0.36 0 1

in table.

Mean Std. dev. Min. Max.

0.23 5.74 0.0001 321.050.30 0.48 0 10.22 0.41 0 10.04 0.20 0 10.02 0.15 0 10.02 0.15 0 10.06 0.24 0 10.05 0.22 0 10.12 0.33 0 10.88 0.32 0 10.09 0.28 0 10.16 0.37 0 10.21 0.41 0 10.19 0.39 0 10.19 0.39 0 10.07 0.26 0 10.08 0.27 0 10.08 0.28 0 10.08 0.28 0 10.06 0.25 0 1

in the table.

Table 6Quantity and number of vessel oil spills inside and outside MPAs by vessel flag (2002–06).

Quantity (Gallons) Number

1942 T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945

stepwise regression is an ordinary least-squares estimation of alinear multivariate model including only variables significant ator above the 15% level. Separate stepwise regressions were devel-oped for the total volume and frequency of spills in a MPA and for

Table 3Vessel oil spills inside and outside US MPAs per year (2002–06).

Quantity (Gallons) Number

Year Inside Outside Inside Outside

2002 41,163 87,557 472 11772003 71,906 76,987 411 10642004 956,556 274,770 425 10562005 80,527 87,142 533 10512006 27,050 115,300 467 1121Total 1177,203 641,756 2308 5469

Table 4Major oil spills (2002–06).

Date Vessel type Vessel flag Quantity(Gallons)

Inside MPA

December 2004 Freight ship Malaysia 321,052 YesNovember 2004 Tanker Cyprus 263,371 YesFebruary 2004 Tanker Singapore 219,555 YesMarch 2004 Tank barge US 151,200 No

Table 5Quantity and number of vessel oil spills inside and outside MPAs by vessel type(2002–06).

Vessel type Quantity (Gallons) Number

Inside Outside Inside Outside

Commercial fishing 71,510 66,152 667 990Freight barge 1425 7391 56 121Freight ship 354,413 46,315 87 248Offshore supply 8380 7720 73 316Passenger 5079 8303 134 348Tank barge 93,337 357,628 93 416Tanker 600,417 31,685 57 124Tugboat 26,110 74,185 215 762Recreational 10,772 17,355 640 1372Other 5761 25,024 287 773Total 1177,203 641,756 2309 5470

Note: Total number of spills inside and outside MPAs are slightly different fromthose in Table 3 due to different types of vessels involved in the same spill event.

Flag Inside Outside Inside Outside

US 222,169 554,004 2088 4768Non-US 955,034 87,752 220 703

1

10

100

1000

10000

0 - 10 10-100 100-1,000

Size of O

Lo

g (

Nu

mb

er o

f O

il S

pill

s)

Fig. 2. Number of oil spills (logarithmic sc

the size of spill of an individual oil spill event over the study period(2002–06). In each case, the model results identify key factorsaffecting a specific aspect of vessel oil spills.

4. Results

Despite fewer spills occurring inside MPAs than outside duringour study period, the total volume was greater inside MPAs thanoutside (Table 3). It should be noted that three of the four biggestoil spills in US waters (all greater than 150,000 gals) occurred in-side MPAs in 2004 (Table 4). If oil spills in 2004 are excluded fromanalysis, the average yearly volume of oil spilled is less inside ofMPAs (55,000 gals/year) than outside (92,000 gals/year).

Although the amount of oil spilled by oil-cargo vessels (tankersand tank barges) is considerably greater than that spilled by othervessels, freight ships, fishing vessels, and tugboats also contributesignificant shares to the total amount of oil spilled (Table 5). Spillsfrom tankers and freight ships account for 51% and 30% of the totalspill volume inside MPAs, respectively. In contrast, tank barges aremajor contributors (56%) of oil spilled outside MPAs. Commercialfishing vessels and recreational vessels contribute only 6% and1%, respectively, of total volume spilled in MPAs, yet they accountfor 29% and 28% of the total number of spills in MPAs. Although thespill frequency inside MPAs is greater for US-flag vessels, the cor-responding amount of oil spilled (19%) is considerably smaller thanthat from foreign-flag vessels (81%) (Table 6).

Log-normal frequency distribution of oil spill size inside andoutside MPAs shows that the number of spills is lower inside MPAsthan outside for spill sizes smaller than 100 thousand gallons.However, for large spills greater than 100 thousand gallons, thenumber of oil spills is higher inside MPAs (Fig. 2).

Federal fisheries closures had 71% of the total volume of oilspilled within their boundaries, while state and territorial MPAshad 28% of the total volume of oil spilled within their boundaries

1,000-10,000 10,000-100,000 100,000+

il Spill (Gallons)

INSIDE MPA

OUTSIDE MPA

ale) by individual spill size (2002–06).

Table 9Determinants of vessel oil spill size.

Features of spill incidents Volume ln(Volume)

T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945 1943

(Table 7). All other types of MPAs (National Estuarine Research Re-serves, Marine Sanctuaries, National Parks, Minerals ManagementService, Wildlife Refuges) had less than 1% of the total volume ofoil spills within their boundaries. On average, spills in fisheries clo-sures tended to be larger than those in other types of MPAs.

Characteristics of MPAs influence the volume and frequency ofoil spills within the boundaries of US MPAs (Table 8). If a MPA isseasonal, it would be likely to have 22,750 more gallons of oilspilled in it and have 25.95 more spills occurring within its bound-aries than other MPAs. The maximum volume of an oil spill in aMPA found in waters off of Alaska is likely to be 21,690 gallonsgreater than in other MPAs. For each additional 1000 km2 of areain a MPA, there is likely to be 0.09 more oil spills within its bound-aries. If the primary conservation focus of a MPA is natural heri-tage, then the maximum volume of an oil spill within itsboundaries is likely to be 16,120 gallons greater. If a MPA is fo-cused on managing at an ecosystem-scale level, it is likely to have21,540 fewer gallons of oil spilled in it and have 21.66 fewer oilspills occurring within its boundaries. The maximum volume ofan oil spill in a MPA focused on managing at an ecosystem-scale le-vel would be 20,430 gallons smaller than in other types of MPAs. A

Table 7Total amount of oil spilled and average size of oil spill by MPA type (2002–06).

MPA type Total oil spilled Avg. size of spill/MPA

Gallons % Gallons %

Federal fisheries closure 1987,577 71.4 40,563 85.7State/territorial MPA 778,074 28.0 5052 10.7Other MPA 17,883 0.6 1720 3.6

Table 8Determinants of vessel oil spill volume and frequency in MPAs.

MPA features Totalvolume

ln(Totalvolume)

Max.volume

ln(Maxvolume)

Number

Coefficient (t-value)Ecosystem scale �21.54** �1.26*** �20.43*** �1.19*** �21.66**

(�2.39) (�3.06) (�2.94) (�2.99) (�2.45)Seasonal 22.75 1.53*** – 1.44*** 25.95*

(1.61) (2.52) (2.43) (1.93)All fishing

restricted– �0.58 - �0.67* –

(�1.39) (�1.65)All fishing

prohibited– �3.00** – �3.34** –

(�2.44) (�2.80)State MPA – �1.53*** – �1.61*** �16.57*

(�4.12) (�4.44) (�1.88)Natural heritage

(primary FC)– – 16.12* – –

(1.85)Area (1000 km2) – – – – 0.09**

(2.03)West Coast – – – – �17.30

(�1.44)Alaska – 1.88*** 21.69** 1.57*** –

(3.55) (2.32) (3.05)Intercept 21.61*** �0.98** 4.53 �1.34** 43.70***

(3.01) (�2.18) (0.60) (�3.06) (4.80)

R-Square 0.05 0.28 0.07 0.28 0.14Number of

observations232 232 232 232 232

F Value 6.01 14.61 5.52 14.23 7.20p > F 0.003 <0.0001 0.001 <0.0001 <0.0001

Note: 1. Results of stepwise regressions (ordinary least-squares estimates). Allvariables left in the models are significant at 15% level.2. Volumes are in 1000 gallons.3. A dash in a column indicates that the explanatory variable is not statisticallysignificant and thus excluded from the model.

* Against the reported coefficient denotes significance at 10% significance level** Against the reported coefficient denotes significance at 5% significance level.

*** Against the reported coefficient denotes significance at 1% significance level.

MPA that is managed at a state or territorial level is likely to have16.57 fewer spills in it, while a MPA found off the US West Coast islikely to have 17.3 fewer oil spills in it than other MPAs.

Given that spill volume is log-normally distributed, we also pro-duced estimations for log-transformed total volume and maximumvolume. According to these models, MPAs that are seasonal andthose that are found in waters off of Alaska are likely to have moreoil spilled in them than other MPAs and the maximum volume ofan oil spill event is likely to be greater in these types of MPAs.MPAs that focus on managing at an ecosystem-scale, those that re-strict and prohibit all fishing, and those managed at the state orterritorial level are likely to have less oil spilled in them than otherMPAs and the maximum volume of an oil spill event in these typesof MPAs is likely to be smaller. All the models are significant atp < 0.01, but explanatory powers of the models (R2) are generallylow because there are additional factors affecting volume and fre-quency of oil spills that are not included in the models.

Coefficient (t-value)In MPA 0.37*** 0.16***

(2.68) (3.37)Fishing vessel – 0.53***

(9.36)Freight ship 0.96*** 0.62***

(2.69) (5.59)Freight barge – 0.51***

(3.46)Tanker 3.18***

(7.10)0.83***

(5.70)Tank barge 1.01***

(3.83)0.83***

(8.98)Offshore supply vessel – 0.81***

(7.82)Tugboat – 0.77***

(11.09)US flag �0.52**

(�2.24)–

Vessel total loss 1.31** 2.05***

(5.72) (25.99)Vessel damage 0.66*** 1.01***

(3.72) (16.80)Year 2002 – 0.14***

(2.58)Year 2003 – 0.22***

(3.81)Year 2004 0.72***

(4.41)–

February 0.40*

(1.63)0.38*

(1.64)April – �0.12

(�1.44)May – �0.15**

(�1.93)October – �0.12

(�1.52)November 0.39

(1.50)–

Intercept �0.01 �6.38***

(0.06) (�148.63)R-Square 0.02 0.12Number of observations 7935 7935F value 16.17 78.41p > F <0.0001 <0.0001

Note: 1. Results of stepwise regressions (ordinary least-squares estimates). Allvariables left in the models are significant at 15% level.2. Volumes are in 1000 gallons.3. A dash in a column indicates that the explanatory variable is not statisticallysignificant and thus excluded from the model.

* Against the reported coefficient denotes significance at 10% significance level.** Against the reported coefficient denotes significance at 5% significance level.

*** Against the reported coefficient denotes significance at 1% significance level.

1944 T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945

Certain features of spill incidents affect the size of individual oilspills in US waters (Table 9). The volume of individual vessel spillswas greater for those spills that occurred inside the boundaries of aMPA, involved a tanker, tank barge, offshore supply vessel, tugboat,freight ship, freight barge, fishing vessel, resulted in total loss ordamage to the vessel, occurred in 2002, 2003 and 2004, and oc-curred in February and November. The volume of individual spillswas smaller for those spills that occurred in April, May andOctober.

5. Discussion

5.1. Oil spills and MPAs

Over 1000 MPAs have been established in the US to protect nat-ural and cultural resources and to ensure sustainable resource pro-duction. While these MPAs may be mitigating undesirable impactsfrom some threats such as fish harvesting or seabed gravel mining,our findings suggest that they are not protecting resources withintheir boundaries from oil spills. This snapshot of the extent and fre-quency of vessel oil spills in US waters shows that, while therewere consistently fewer spills inside MPAs than outside, therewas no dramatic difference in the amount of oil spilled by vesselsinside and outside MPA boundaries in 2002–06. This is not surpris-ing, given that most MPAs in the US do not regulate vessel naviga-tion to minimize pollution, leaving resources targeted forprotection inside MPAs vulnerable to oil spills. Although thereare complex factors influencing the extent to which oil will affectbiological resources, like the type of oil spilled, water temperature,and susceptibility of organisms to certain effects (Oil in the Sea III,2003), our findings suggest that resources inside MPAs are no moreprotected from oil spills than those outside their boundaries.

There are certain features that seem to make some MPAs lessvulnerable to oil spills than others. MPA sites that are designatedto protect ecosystems, rather than individual species, tend to havea smaller amount of oil spilled and fewer oil spills. This is not sur-prising, given that sites designated to protect an individual speciesmost likely focus regulations on one or two activities that affectthat species, while sites designated to protect ecosystems are prob-ably more comprehensive in nature regulating a variety of activi-ties that could result in oil spills. For example, a fisheries closureintended to protect a specific species of fish, like cod or haddock,might have rules in place to limit bottom trawling that targetsthese particular fish; whereas, a marine sanctuary established toprotect ecological integrity might have rules limiting a variety ofactivities like cargo shipping, passenger ferries, and even fishing.

We also found that sites where fishing is restricted or prohib-ited tend to have fewer oil spills than sites where fishing is al-lowed. Perhaps MPA sites that regulate fishing have fewer fishingvessels transiting the area, reducing the likelihood that they wouldbe involved in oil spill incidents. State MPAs are likely to have lessoil spilled in them, which could be related to the fact that stateMPAs tend to be smaller on average than federally-managed MPAs,like National Marine Sanctuaries or Federal fisheries closures.There could also be certain management features of state MPAsthat we did not examine here that reduce oil spill vulnerability. Fu-ture studies should investigate why state MPAs have less oil spilledin them than other MPA sites. West coast MPAs also seem to havefewer spills, perhaps because many oil spills off the west coast,particularly in California, occur close to shore and many MPAboundaries are offshore (see Fig. 1).

Not surprisingly, cargo shipping makes up the bulk of spills in-side and outside MPAs, but these vessels are not the only ones con-tributing to oil pollution in US waters. Recreational boating andcommercial fishing are involved in numerous oil spill incidents in-

side and outside MPA boundaries. Since most MPAs do not limitrecreational boating, recreational vessels are probably as likely tobe inside an MPA as outside. More research is needed to under-stand how recreational boaters are using space in and aroundMPAs, and the risk they pose to ecosystem health from oil spills.

5.2. Management implications

To reduce the vulnerability of MPA resources to oil spills, MPApolicies can be designed to limit certain undesirable activitieswithin the boundaries of the protected area. Agencies with theresponsibility to manage US MPAs typically have authority to reg-ulate certain activities within their boundaries, such as fishing orvisitation, or at least they can cooperate with other US agenciesto restrict these certain activities. For instance, NOAA’s NationalMarine Fisheries Service can restrict fishing in parts of an MPA thathave sensitive biological resources, resulting in fewer fishing ves-sels that could be involved in oil spill incidents in that area.

To regulate shipping through an MPA, the InternationalMaritime Organization (IMO) would have to approve internation-ally-recognized instruments such as Areas to be Avoided, trafficseparation schemes, inshore traffic zones, precautionary areas, ordeep-water routes (Scovazzi, 2004; IMO, 2005; Detjen, 2006).Several MPAs in the US have coordinated with the IMO to establishsuch routing measures. The Florida Keys National Marine Sanctu-ary was designated as a particularly sensitive sea area (PSSA) in2002, and parts of the Sanctuary were designated as an Area tobe Avoided where tank vessels and vessels larger than 164 feet(50 m) are prohibited from entering (EPA rules). The Olympic CoastNational Marine Sanctuary off the coast of Oregon designated anArea to be Avoided in 1995 that advises operators of vessels carry-ing petroleum or hazardous materials to maintain a 25-mile(40.2 km) buffer from the coast (Galasso, 2000). Off the coast ofHawaii, the Papahanaumokuakea Marine National Monumentadopted ship reporting requirements for ships greater than 300gross tons (304.8 tonnes) that are transiting through the area. In2006, the IMO approved a shift in shipping lanes through the Stell-wagen Bank National Marine Sanctuary to reduce the risk of colli-sions between large ships and whales. Our results suggest thatthese types of routing measures should target certain types ofships, like tankers, freight ships, and foreign-flag vessels, to controloil spills in US MPAs.

Alternative technologies could also be used to prevent oil spillsassociated with shipping accidents. Double hull vessels, effective inpreventing oil spills or lessening their severity by reducing the vol-ume of oil spilled compared to single hull vessels, could be encour-aged in and around MPAs. The use of electronic charts andintegrated, computer-based navigation systems in MPAs could alsobe promoted to increase safety and efficiency of navigation byautomating traditional functions, such as plotting vessel positions(Jin et al., 1994; Kite-Powell et al., 1997).

6. Conclusions

Our investigation of the extent and frequency of oil spills in USMPAs from 2002–06 shows that the presence of a MPA does notseem to prevent vessel oil spills or reduce the amount of oil spilled,and that a variety of vessels, including industrial, commercial, andrecreational vessels, are contributing to oil spills inside and outsideMPAs.

It is important to note that MPAs are not necessarily protectedfrom oil spills that occur outside of their boundaries even if theyhave special measures in place, because the dynamic, fluid natureof the marine environment makes it difficult, if not impossible, toprevent pollution from crossing MPA boundaries (Boersma and

T. Dalton, D. Jin / Marine Pollution Bulletin 60 (2010) 1939–1945 1945

Parrish, 1999; Jameson et al., 2002). However, to reduce vulnera-bility to oil spills within MPA boundaries, our findings indicate thatplanners and managers should consider establishing ecosystem-based MPAs and limiting activities within MPAs that are likely toproduce oil spills such as industrial shipping, recreational boating,and commercial fishing. Planners and managers can consider coor-dinating with the IMO to implement navigational rules, like trafficseparation schemes or Areas to be Avoided, to manage oil spills inareas that are considered particularly sensitive.

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