Background information and definitions
Introducing vessel speed limits may reduce disturbance and the risk of lethal collisions and severe injury to marine and freshwater mammals (Vanderlaan & Taggart 2007, Currie et al. 2017, Chion et al. 2018). Speed limits may be permanent, seasonal (e.g. during migration, breeding, or nursing periods) or temporary (e.g. in response to mammal sightings within an area) and may apply to all vessels or to certain vessel types or sizes. Speed limits may also be mandatory or voluntary, although greater compliance has been reported with mandatory speed limits (Lagueux et al. 2011). Enforcement may be required if compliance is low (Silber et al. 2014).
This intervention is often combined with changes to shipping routes, see Divert shipping routes.
Chion C., Turgeon S., Cantin G., Michaud R., Ménard N., Lesage V., Parrott L., Beaufils P., Clermont Y. & Gravel C. (2018) A voluntary conservation agreement reduces the risks of lethal collisions between ships and whales in the St. Lawrence Estuary (Québec, Canada): From co-construction to monitoring compliance and assessing effectiveness. PLOS ONE, 13, e0202560.
Currie J., Stack S. & Kaufman G. (2017) Modeling whale-vessel encounters: the role of speed in mitigating collisions with humpback whales (Megaptera novaeangliae). Journal of Cetacean Research and Management, 17, 57–64.
Lagueux K.M., Zani M.A., Knowlton A.R. & Kraus S.D. (2011) Response by vessel operators to protection measures for right whales Eubalaena glacialis in the southeast US calving ground. Endangered Species Research, 14, 69–77.
Silber G.K., Adams J.D. & Fonnesbeck C.J. (2014) Compliance with vessel speed restrictions to protect North Atlantic right whales. PeerJ, 2, e399.
Vanderlaan A.S.M. & Taggart C.T. (2007) Vessel collisions with whales: the probability of lethal injury based on vessel speed. Marine Mammal Science, 23, 144–156.
Supporting evidence from individual studies
A before-and-after study in 1986–2005 at a creek and canal in the Indian River estuarine system, USA (Laist & Shaw 2006) reported that after setting vessel speed limits in ‘zones’, a similar number of Florida manatee Trichechus manatus latirostris deaths were recorded to before the speed limits, but setting and enforcing speed limits throughout all areas resulted in fewer manatee deaths. Results are not based on assessments of statistical significance. Average numbers of manatees killed by vessels were similar before (1.8 manatees/year) and after (1.8–2.1 manatees/year) vessel speed limits were introduced to specific zones. Fewer manatees were killed by vessels (average 0.3 manatees/year) after speed limits were introduced and enforced by patrols in all areas. Year-round speed limits (8–11 km/h) were set within specific zones in 1990 and 1994, although low compliance was reported (see original paper for details). In 2002, the creek and canal were designated as manatee refuges and year-round speed limits (8–11 km/h) were set throughout. Patrolling enforcement officers issued warnings and speeding tickets in 2002–2005. Manatees killed by vessels were recorded within the creek, canal and adjacent waters during five years before speed limits were set (1986–1990), 13 years after speed limits were set in zones (1990–2002) and four years after speed limits were set and enforced in all areas (2002–2005).Study and other actions tested
A before-and-after study in 1990–2013 of 10 coastal areas in the North Atlantic Ocean, USA (Laist et al. 2014) found that after setting vessel speed limits, fewer North Atlantic right whale Eubalaena glacialis deaths caused by vessel collisions were recorded than before speed limits were set. The total number of right whale deaths in the 10 areas caused by vessel collisions was lower during five years after speed limits were put in place (0 deaths) than during 18 years before (total 13 deaths). In December 2008, mandatory speed limits (≤18.5 km/h for vessels ≥19.8 m long) were put in place in 10 areas with key habitats for North Atlantic right whales (migration routes, feeding areas, calving grounds) during periods of peak whale occurrence. Numbers of whale deaths caused by vessel collisions inside (or within 83 km from) the 10 areas during 18 years before (1990–2008) and five years after (2009–2013) speed limits were set were extracted from national databases.