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We work hard to provide our participants and the public with the necessary information to stay informed about sustainable shipping practices along the West Coast.

Vessel Speed Reduction Research

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Ship strikes are one of the primary threats to large whales along the U.S. west coast and around the world.

  • Panigada et al. (2006) analyzed fin whale stranding records in the Mediterranean and determined that 46/287 (16%) of recorded fatalities were attributed to ship strikes.

  • Douglas et al. (2008) examined 130 records from 1980-2006 of large whale strandings in Washington state. They found that 19/130 records had evidence of ship strikes and that fin whales had the highest incidence of recorded ship strikes. They noted that there are dramatic differences in occurrences of observed ship strikes by species, which they attribute to differences in overall vulnerability and carcass recovery rates.

  • In California, Berman-Kowalewski et al. (2010) summarized data on blue whale strandings from 1988 to 2007 along the coast of California and identified regions of strandings associated with ship strikes. They found that 8 out of 21 stranded whales recorded during the 20 year study period were confirmed to have died as a result of a ship strike and suggested that ship strikes are an important cause of blue whale mortality along the California coast - particularly in years when the food sources overlap with the shipping lanes - and that the issue will need to be addressed in order to protect and maintain the critically endangered Eastern Pacific population of blue whales. For blue whales specifically, research suggests that their delayed and relatively slow response to avoid ships could put them at increased risk from ship strikes.

  • Peltier et al. (2019) examined stranding data collected between 1972 and 2017 to provide a comprehensive review of confirmed collision records of large whales in France. During the study time period, the authors found that the frequency of recorded strikes increased over the decades examined and that a total of 51 ship strike incidents were recorded in total, pointing to ship strikes as the  number one cause of large whale mortality in French waters. The researchers also noted that the issue appears particularly critical in the Mediterranean Sea, where one in five stranded whales on record showed evidence of ship strike.

  • For the state of California, the NOAA National Marine Fisheries Service (2019) Strandings Database from 1986-2019 includes 107 observed and recorded incidents of fatal vessel collisions on large whales and 61 incidents of fatal vessel collisions on endangered large whales in the same time period.

Observed ship strike incidents are presumed to represent a small fraction of the total number of ship strikes occurring due to most incidents and whale carcasses not being observed or recorded.

  • Kraus et al. (2005) examined population estimates and stranding records for North Atlantic right whales and estimated a carcass recovery rate of 17%, reflecting an average of 2.4 dead whales seen each year in U.S. east coast waters out of a total estimated mortality of 14 whales per year. The authors also noted that right whales are the most buoyant whale species and thus provide a conservative limit scenario for extrapolation to other species.

  • Redfern et al. (2013) noted that the number of observed ship strike deaths of blue whales in the U.S. West Coast EEZ regularly exceeds annual Potential Biological Removal limits for the species, and estimated that actual totals of ship strike fatalities are much higher than observed incidents.

  • Rockwood et al. (2017) estimated ship strike mortality for blue humpback and fin whales in U.S. West Coast waters using a naval encounter model and found that mortality estimates from the model were far higher than current minimum estimates of ship strikes derived from stranding records. Their most conservative model estimated mortality to be 7.8x, 2.0x, and 2.7x the annual limit for blue, humpback, and fin whales, respectively, suggesting that whale mortality from vessel collisions may be a significant impediment to population growth and recovery. They estimate that 80 endangered blue, fin, and humpback whales are killed by ship strikes each year off of the U.S. west coast.

Reducing speeds of large vessels have been shown to reduce the risk of fatal ship strikes on large whales.

  • Laist et al. (2001) examined historical records of ship strikes going back to the 1800s and found that fatal ship strikes began occurring when ship speeds began increasing to 13-15 knots and increased in frequency as the number and size and speeds of ships increased in the mid-1900s. Their study finds that the most lethal or severe recorded events involve ships travelling at 14 knots or greater and the researchers conclude that reducing ship speeds below 14 knots may be beneficial to the long term sustainability of large whales.

  • Vanderlaan et al. (2007) analyzed historical records of ship strikes on large whales - mainly focusing on North Atlantic right whales - and evaluated the effect of vessel speed on lethal and nonlethal injuries. They found that the probability of lethal injury drops below 50% at 11.8 knots and increases to nearly 100% at speeds over 15 knots.

  • Using a Bayesian change-point model, Gende et al. (2011) examined humpback whale sightings made by observers aboard cruise ships in Alaska to determine the relationship between whale distance and ship speed. They found that the relationship between whale distance and ship speed changed at 11.8 knots with whales encountering ships, on average, 114 meters closer when ship speeds were above 11.8 knots. The authors note that their results demonstrate that ship speed influences encounter distance between large ships and large whales and suggest that reduced ship speed may be an effective management action in reducing the probability of a ship strike taking place.

  • Conn et al. (2013) analyzed the NOAA vessel speed restrictions along the U.S. east coast, which focus on reducing the negative impacts of ship strikes on the critically endangered North Atlantic right whale population. By examining the estimation of the probability of lethal injury given a ship strike at different vessel speeds and the estimation of the effect of transit speed on the rate of ship strikes, the study found that vessel speed is positively correlated to both components and that limiting vessel speed could be an effective measure to mitigate whale mortality caused by ship strikes.

  • Laist et al. (2014) examined interactions between ship traffic and North Atlantic right whales along the U.S. east coast before and after implementation of mandatory seasonal management areas and VSR requests in critical habitat for right whales. The researchers found that in the 18 year time period before NOAA mandatory VSR was implemented, 13 of 15 (87%) right whales and 12 of 26 (46%) humpback whales killed by ships were found inside or near the later-established seasonal management areas. During the first 5 years after the NOAA mandatory VSR was implemented, no recorded right whale deaths attributed to large vessel strikes found inside or near active seasonal management areas, suggesting that the mandatory VSR in seasonal management areas off of the east coast has been effective at reducing North Atlantic right whale ship strike fatalities.

  • Wiley et al. (2016) examined two independent collisions between non-commercial vessels and North Atlantic right whales and highlighted that in both cases there were numerous experienced crew and excellent weather conditions, but the ship strikes still occurred, signalling that speed is the likely main factor in avoiding fatal ship strikes to large whales.

  • Crum et al. (2019) applied a modeling framework based on encounter theory to quantify the risk of lethal collisions between endangered North Atlantic right whales and vessels. Using AIS data and spatially explicit estimates of right whale abundance, they modeled risk at fine spatiotemporal scales before and after the implementation of the NOAA mandatory VSR in the southeastern U.S. They found that expected seasonal mortality rates of right whales decreased 22% on average after the speed rule was implemented, indicating that the rule is effective at reducing lethal collisions.

Reducing large vessel speeds reduces underwater noise.

  • Gassman, Wiggins, and Hildebrand (2017) opportunistically measured underwater radiated noise from container ships in the Santa Barbara Channel and compared it with AIS data to estimate signature source levels and directionality and estimate noise emissions at different speed levels. They found that source levels were significantly lower (up to tens of dB) for transits at 13.4 knots and 9.5 knots than at 20.4 knots.

  • McKenna et al. (2009) recorded and analyzed noise data from a high-frequency acoustic recording package to understand the contribution of noise from commercial ship traffic to the acoustic environment of the Channel Islands National Marine Sanctuary and its surrounding waters. They found that the level of noise generated by ships is related to the size, speed, and power of the vessel, along with a number of other factors including type, propeller, engine, age, and any damage to the vessel. They also found that larger, faster ships generate more noise because they produce more propulsion power which is converted into acoustic power via bubble cavitation.

  • Joy et al. (2019) examined AIS data and noise data from a hydrophone in the Salish Sea during a voluntary, incentivized commercial vessel slowdown trial in 2017 and found that slower vessel speeds during the trial reduced underwater noise in the area by 1.2dB, despite longer passage times.

Reducing the speeds of large vessels decreases fuel consumption, leading to a decrease in harmful air emissions and greenhouse gases.

  • Lindstad et al. (2011) analyzed global historical data and created a model to calculate costs and emissions associated with large ships traveling at different speeds. The authors’ results show that there is a substantial potential for reducing CO2 emissions in shipping by slowing large vessels down. The authors also note that since these emissions reductions calculations are based solely on decreases in speeds of these vessels, they can be implemented and start achieving benefits in the short-term.

  • SBCAPCD (2023) analyzed AIS data to quantify air emissions reductions associated with the 2022 Protecting Blue Whales and Blue Skies Vessel Speed Reduction Program, which encourages container and car carrier lines to enroll and slow their vessels to 10 knots or less in VSR zones off of San Francisco Bay and southern California. They found that the combined efforts of all enrolled companies in 2019 across over 266,148 nautical miles helped to reduce approximately 921 tons of smog-forming nitrogen oxides (NOx) and more than 32,600 metric tons of regional greenhouse gases.

Reducing vessel speeds to 10 knots has minimal to no economic impact on the shipping industry.

  • Using AIS data from 2015 for the Santa Barbara Channel region, Gonyo et al. (2019) estimated the economic impact of a variety of ship strike risk reduction strategies, including a 10 knot and 12 knot VSR request, on the shipping industry and estimated that shipping travel costs would increase minimally by 1.3-2.0% (+$880,765-$1,360,034 to a 2015 travel cost estimate of $66,658,476) across the study area as a result of changes in vessel speed impacting vessel transportation costs and inventory carrying costs across industry.

Targeted analyses have shown that cooperation with the NOAA voluntary Vessel Speed Reduction (VSR) in southern California - and other, similar voluntary VSR requests - has been low.

  • Wiley et al. (2008) determined the levels of compliance in 2003 and 2004 with a voluntary VSR program in the northeast U.S. focused on reducing speeds of whale watch vessels to reduce the risk of ship strikes on endangered whales. The authors found that the level of noncompliance was high and that the voluntary conservation program did not achieve the goal of substantially limiting vessel speed near whales. Their findings suggest the importance of establishing quantifiable metrics and frequent evaluations of compliance to ensure efficacy of voluntary conservation efforts like VSR.

  • McKenna et al. (2012) analyzed Automatic Identification System (AIS) data for a total of 405 large commercial vessels to monitor changes in their speeds before and after voluntary VSR requests in the Santa Barbara Channel across 2007-2009. The study found that there was no change in average daily vessel speed related to the VSR requests, that few ships reduced their speeds significantly on an individual basis, and none fully cooperated with the voluntary VSR request in any of the three years studied. The authors recommended that future VSR efforts pursue mandatory regulations or incentives to motivate higher levels of compliance and lower speeds of large vessels in these areas.

  • Freedman et al. (2016) examined AIS data across 2015 to quantify cooperation levels with the 2015 NOAA voluntary VSR requests in the Santa Barbara Channel region and compare it with cooperation levels of vessels participating in the 2014 incentive-based VSR program. They found that cooperation levels with the NOAA voluntary VSR requests were low - with only 13% of daily average ship speeds traveling at the requested 10 knots or less - and were significantly lower than vessels enrolled in the incentive-based program in 2014.


An increase in cooperation with NOAA voluntary VSR requests is estimated to significantly reduce ship strike risk to endangered whales in southern California

  • Rockwood et al. (2017) estimated ship strike mortality risk to blue, fin, and humpback whales off of the U.S. west coast using a naval encounter model to quantify risk as the likelihood of co occurrence. They found that the majority of mortalities were occurring within 10% of the EEZ in areas where whale distribution and density data overlaps at a high frequency with shipping data and that significant mortality risk reductions can be achieved by implementing VSR requests in these areas. 

  • Redfern et al. 2019 found that a large decrease in ship strike risk can be achieved by higher cooperation levels with speed reduction requests in the southern California Bight. Using AIS data and whale habitat and tagging data, the authors created a model to estimate ship strike risk and fatal ship strike risk for blue, fin, and humpback whales within the study area associated with three proposed mitigation strategies. They found that reducing 100% of ship speeds to 10 knots or less in the Santa Barbara Channel would result in a 22-24% decrease in fatal ship strike risk to endangered whales.

  • Using a naval encounter model, Rockwood and Jahncke (2019) found that increasing cooperation with NOAA voluntary VSR requests in the Santa Barbara Channel to 80% or above would decrease blue, fin, and humpback whale mortality in the region by 20-30% - which would be roughly a ten-fold improvement compared to the current VSR cooperation levels and effectiveness. 


Mandatory east coast NOAA VSR requests see higher levels of compliance than west coast voluntary VSR requests.

  • Using AIS data, Silber, Adams, and Fonnesbeck (2014) quantified vessel operator compliance with a December 2008 regulation aimed at reducing collisions with the endangered North Atlantic right whale that requires vessels 65 feet or greater in length to travel at speeds of 10 knots or less at prescribed times and locations along the U.S. eastern seaboard. The researchers found that compliance with these mandatory VSR requests increased over the 5 year study period - particularly for companies that receive notices of violations and accompanying fines - from 40-45% of all vessel mileage in these areas traveled at speeds of 10 knots or less in 2008 to 70-75% in 2013. 


Regulatory changes - particularly related to emissions rules and standards - have been proven to have a significant impact on vessel behavior.

  • Moore et al. (2018) examined AIS data from 2008-2015 in waters off of southern California to evaluate the role of vessel emission regulations and economic events on vessel routes and speeds within the study time period and area. They found that the establishment of emissions-related regulations had a profound influence on behavior and resulted in significant changes in vessel routes and speeds. They also found that ship speeds became progressively slower in the Southern California Bight from 2008-2015.


Incentive-based voluntary VSR programs have been proven to be effective in achieving vessel behavior change

  • Freedman et al. (2016) examined AIS data across 2015 to quantify cooperation levels with the 2015 NOAA voluntary VSR requests in the Santa Barbara Channel region and compare it with cooperation levels of vessels participating in the 2014 incentive-based VSR program.

  • The Port of Long Beach operates a year round Green Flag Incentive Program - and publishes annual results online - to reward vessel operators for slowing cargo ships down to 12 knots or less within 40 nautical miles of the harbor. Companies that cooperate at a 90% level or higher can earn up to a 25% reduction in port dockage rates. Port of Long Beach Green Flag Incentive Program (2020) shows a 92% cooperation level across all operators with these slow speed requests in 2019.


  • Panigada, Simone, Giovanna Pesante, Margherita Zanardelli, Frederic Capoulade, Alexandre Gannier, and Mason T. Weinrich. "Mediterranean Fin Whales at Risk from Fatal Ship Strikes." Marine Pollution Bulletin 52.10 (2006): 1287-298. ScienceDirect. Web.

  • Douglas, A. B., Calambokidis, J., Raverty, S., Jeffries, S. J., Lambourn, D. M., and Norman, S. A. (2008). Incidence of ship strikes of large whales in Washington State. J. Mar. Biol. Assoc. U. K. 88, 1121–1132. doi: 10.1017/s0025315408000295

  • Berman-Kowalewski, Michelle, Frances M. D. Gulland, Sarah Wilkin, John Calambokidis, Bruce Mate, Joe Cordaro, Dave Rotstein, Judy St. Leger, Paul Collins, Krista Fahy, and Samuel Dover. "Association Between Blue Whale (Balaenoptera Musculus) Mortality and Ship Strikes Along the California Coast." Aquatic Mammals 36.1 (2010): 59-66. Web.

  • Peltier H, Beaufils A, Cesarini C, Dabin W, Dars C, Demaret F, Dhermain F, Doremus G, Labach H, Van Canneyt O and Spitz J (2019) Monitoring of Marine Mammal Strandings Along French Coasts Reveals the Importance of Ship Strikes on Large Cetaceans: A Challenge for the European Marine Strategy Framework Directive. Front. Mar. Sci. 6:486. doi: 10.3389/fmars.2019.00486

  • NOAA National Marine Fisheries Service Strandings Database, 1986-2019

  • Kraus SD, Brown MW, Caswell H, Clark CW, Fujiwara M, et al. (2005) North Atlantic Right Whales iCrisis. Science (80-) 309: 561±562. PMID: 16040692

  • Redfern JV, McKenna MF, Moore TJ, et al. Assessing the risk of ships striking large whales in marine spatial planning. Conserv Biol. 2013;27(2):292‐302. doi:10.1111/cobi.12029

  • Rockwood RC, Calambokidis J, Jahncke J (2017) High mortality of blue, humpback and fin whales from modeling of vessel collisions on the U.S. West Coast suggests population impacts and insufficient protection. PLoS ONE 12(8): e0183052. 

  • Laist, David W., Amy R. Knowlton, James G. Mead, Anne S. Collet, and Michela Podesta. "Collisions Between Ships And Whales." Marine Mammal Science 17.1 (2001): 35-75. Web.

  • Vanderlaan, Angelia S. M., and Christopher T. Taggart. "Vessel Collisions With Whales: The Probability Of Lethal Injury Based On Vessel Speed." Marine Mammal Science 23.1 (2007): 1 

  • Gende, S. M., Hendrix, A. N., Harris, K. R., Eichenlaub, B., Nielson, J., and Pyare, S. (2011). A Bayesian approach for understanding the role of ship speed in whale-ship encounters. Ecol. Appl. 21, 232–240.

  • Conn, P. B., and G. K. Silber. "Vessel Speed Restrictions Reduce Risk of Collision-related Mortality for North Atlantic Right Whales.” Ecosphere 4.4 (2013): n. pag. Web.

  • Laist, Dw, Ar Knowlton, and D. Pendleton. "Effectiveness of Mandatory Vessel Speed Limits for Protecting North Atlantic Right Whales." Endangered Species Research 23.2 (2014): 133-47. Endangered Species Research. Web.

  • Wiley, David N., Charles A. Mayo, Eden Marie Maloney, and Michael J. Moore. "Vessel Strike Mitigation Lessons from Direct Observations Involving Two Collisions between Noncommercial Vessels and North Atlantic Right Whales (Eubalaena Glacialis)." Marine Mammal Science 32.4 (2016): 1501-509. Wiley Online Library. Web.

  • Crum, N., T. Gowan, A. Krzystan, and J. Martin. 2019. Quantifying risk of whale–vessel collisions across space, time, and management policies. Ecosphere 10(4):e02713. 10.1002/ecs2.2713

  • M. Gassmann, S.M. Wiggins, J.A. Hildebrand. Deep-water measurements of container ship radiated noise signatures and directionality. The Journal of the Acoustical Society of America. 142(3)(2017), pp.1563-1574.

  • McKenna MF, Soldevilla M, Oleson EM, Wiggins SM, Hildebrand JA (2009) Increased Underwater Noise Levels in the Santa Barbara Channel from Commercial Ship Traffic and its Potential Impact on Blue Whales (Balaenoptera musculus) In: Damiani CC, Garcelon DK (eds) Proceedings of the 7th California Islands Symposium. Institute for Wildlife Studies, Arcata, CA.

  • Joy R, Tollit D, Wood J, MacGillivray A, Li Z, Trounce K and Robinson O (2019) Potential Benefits of Vessel Slowdowns on Endangered Southern Resident Killer Whales. Front. Mar. Sci. 6:344. Doi: 10.3389/fmars.2019.00344

  • 2023 Results from the Protecting Blue Whales and Blue Skies Incentive-Based Vessel Speed Reduction Program.

  • Gonyo, Sarah & Goedeke, Theresa & Wolfe, K. & Jeffrey, Christopher & Gorstein, Matt & Poti, Matthew & Dorfman, Daniel. (2019). An economic analysis of shipping costs related to potential changes in vessel operating procedures to manage the co-occurrence of maritime vessel traffic and whales in the Channel Islands region. Ocean and Coastal Management. 177. 179-187. 10.1016/j.ocecoaman.2019.04.024.

  • Wiley, David & Moller, Just & Pace, Richard & Carlson, Carole. (2008). Effectiveness of Voluntary Conservation Agreements: Case Study of Endangered Whales and Commercial Whale Watching. Conservation biology : the journal of the Society for Conservation Biology. 22. 450-7. 10.1111/j.1523-1739.2008.00897.x. 

  • Mckenna, Megan F., Stephen L. Katz, Christopher Condit, and Shaun Walbridge. "Response of Commercial Ships to a Voluntary Speed Reduction Measure: Are Voluntary Strategies Adequate for Mitigating Ship-Strike Risk?" Coastal Management 40.6 (2012): 634-50. Web.

  • Freedman, Ryan & Herron, Sean & Byrd, Mary & Birney, Kristi & Morten, Jessica & Shafritz, Brian & Caldow, Chris & Hastings, Sean. (2017). The effectiveness of incentivized and non-incentivized vessel speed reduction programs: Case study in the Santa Barbara channel. Ocean & Coastal Management. 148. 31-39. 10.1016/j.ocecoaman.2017.07.013.

  • Rockwood RC, Calambokidis J, Jahncke J (2017) High mortality of blue, humpback and fin whales from modeling of vessel collisions on the U.S. West Coast suggests population impacts and insufficient protection. PLoS ONE 12(8): e0183052. 

  • Redfern JV, Moore TJ, Becker EA, et al. Evaluating stakeholder‐derived strategies to reduce the risk of ships striking whales. Divers Distrib. 2019;00:1–11. https ://

  • Rockwood, C and Jahncke J. 2019. Management recommendations to reduce deadly whale strikes off California. Unpublished report for the National Oceanic and Atmospheric Administration, the United States Coast Guard, and the Maritime Industry. 16 p.

  • Silber, G., Adams, J., & Fonnesbeck, C (2014) Compliance with Vessel Speed Restrictions to Protect North Atlantic Right Whales

  • Moore, T. J., Redfern, J. V., Carver, M., Hastings, S., Adams, J. D., and Silber, G. K. (2018). Exploring ship traffic variability off California. Ocean Coast. Manag. 163, 515–527. doi: 10.1016/j.ocecoaman.2018.03.010

  • Freedman R., Herron S., Byrd M., Birney K., Morten J., Shafritz B., Caldow C., & Hastings, S. (2017). The effectiveness of incentivized and non-incentivized vessel speed reduction programs: Case study in the Santa Barbara channel. Ocean & Coastal Management. 148. 31-39. 10.1016/j.ocecoaman.2017.07.013. 

  • 2019 Port of Long Beach Green Flag Incentive Program Operator Compliance Monthly Report.

Anchor 1
Ship Strikes
Speed Reduction
Underwater Noise
Fuel Consumption
Regulatory Measure
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