Estimating effectiveness of speed reduction measures for decreasing whale-strike mortality in a high-risk region

Rockwood, R. Cotton; Adams, Jeff; Silber, Greg; Jahncke, Jaime

doi:10.3354/esr01056

Cited by 23 publications

(21 citation statements)

References 57 publications

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“…For this study, we used the mean of predicted whale density for all months and years when cruises were conducted. While monthly density estimates for the years we are analyzing [as in Rockwood et al (2020a)] would allow us to estimate temporal variability, such whale model predictions are not available for this region. Only 90% confidence intervals for the mean density estimates were available, and the majority of the uncertainty captured by those was derived from interannual variation in environmental drivers of whale distributions (Becker et al, 2016).…”

Section: Whale Datamentioning

confidence: 99%

“…To estimate mortality, we utilized an encounter probability model developed by Martin et al (2016) and adapted in Rockwood et al (2017Rockwood et al ( , 2020a. More detailed model descriptions including all equations can be found in those publications.…”

Section: Model Frameworkmentioning

confidence: 99%

“…We integrate the effect of three-dimensional habitat use by whales on the risk of being in the vertical strike zone by use multi-sensor tag data to quantify whale time-at-depth. Here, as in Rockwood et al (2017Rockwood et al ( , 2020a, the strike zone is conservatively defined as the draft of the vessel though scale models suggest whales may be at risk up to twice the vessel draft (Silber et al, 2010). Finally, we convert encounter rates to estimates of whale mortality by multiplying with the probability of collision avoidance, the probability of mortality given a collision and the numbers of whales.…”

Section: Model Frameworkmentioning

confidence: 99%

“…As in Rockwood et al (2020a), we made several changes to improve performance and accuracy compared to the original formulation in Rockwood et al (2017). First, since using a linear relationship between avoidance response with increasing vessel speed resulted in very similar mortality results as a logistic relationship (Rockwood et al, 2017), we chose to limit our analysis to only the logistic formulation of avoidance.…”

Section: Model Frameworkmentioning

confidence: 99%

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Modeling Whale Deaths From Vessel Strikes to Reduce the Risk of Fatality to Endangered Whales

et al. 2021

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Vessel strikes have been documented around the world and frequently figure as a top human cause of large whale mortality. The shipping lanes in the Santa Barbara Channel, California and nearby waters have some of the highest predicted whale mortality from vessel strikes in the United States waters of the eastern Pacific. Beginning in 2007, National Oceanographic and Atmospheric Administration requested voluntary vessel speed reductions (VSRs) for vessels greater than 300 GT traveling in the Santa Barbara Channel shipping routes to decrease whale mortality from ship strikes. We employed a ship strike model using whale density data and automatic identification system (AIS) vessel data to estimate mortality under several management scenarios. To assess the effect of the VSR on strike mortality, we bootstrapped speeds from vessels greater than 19 m long that transited when no VSR was in place. Finally, we calculated the predicted mortality for hypothetical cooperation scenarios by artificially adding speed caps post-hoc to real vessel transits. For 2012–2018, we estimated that in our study area on average during summer/fall (June–November) 8.9 blue, 4.6 humpback, and 9.7 fin whales were killed from ship strikes each year (13–26% greater than previously estimated). We evaluated winter/spring (January–April) humpback mortality for the first time, resulting in an estimate of 5.7 deaths on average per year. Poor cooperation with the VSR led to low (5% maximum) to no reductions in the estimated number of strike mortalities. Evaluating potential scenarios showed that if 95% cooperation occurred in the lanes, whale deaths there would decrease by 22–26%. Adding VSRs with similar cooperation levels at the northern end of the Santa Barbara Channel and south of Channel Islands National Marine Sanctuary could decrease estimated strike mortalities in those areas by 30%. If VSRs were added and cooperation reached 95% there and in the lanes, we estimate a 21–29% decrease in vessel strike mortalities could be attained relative to estimated mortality in the entire study area. To decrease the vessel strike related whale mortalities in this region, we recommend expanding the VSR areas and increasing cooperation voluntarily, or considering mandatory speed limits if desired cooperation levels cannot otherwise be met.

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Section: Whale Datamentioning

confidence: 99%

Section: Model Frameworkmentioning

confidence: 99%

Section: Model Frameworkmentioning

confidence: 99%

Section: Model Frameworkmentioning

confidence: 99%

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Modeling Whale Deaths From Vessel Strikes to Reduce the Risk of Fatality to Endangered Whales

et al. 2021

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“…Precautionary measures already in place in portions of the species' range (e.g. off Sakhalin Island where some oil and gas companies have established traffic corridors, imposed speed limits, and employed observers on their vessels to prevent ship strikes on gray whales, SEIC 2020; vessel routing and speed restrictions in waters off California, Freedman et al 2017, Moore et al 2018, Rockwood et al 2020 should be considered in other areas of apparently strong overlap between vessel and whale density. Moreover, these maps can help guide decisions about where to concentrate quantitative risk analyses for use in designing targeted, empirically based risk reduction and mitigation measures.…”

Section: Population-level Implicationsmentioning

confidence: 99%

Co-occurrence of gray whales and vessel traffic in the North Pacific Ocean

Silber¹,

Weller

Reeves³

et al. 2021

Endang. Species. Res.

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All species of large whales are susceptible to vessel strikes, but the true scale and geographical extent of such strikes is not known. This paper provides a qualitative assessment of the range-wide risks posed to gray whales Eschrichtius robustus by vessels, by comparing patterns of whale distribution with the density of vessel traffic seasonally throughout the North Pacific in 2019. Areas of very high vessel density were evident year-round near many coastlines, along inter-continental trade routes, and at hubs of commercial shipping near port entrances. Gray whales were exposed to vessel strikes throughout their range and in their feeding, southbound migration, wintering, and northbound migration periods. Areas of apparently high risk were in the Russian Far East (Kamchatka peninsula and Okhotsk Sea), Bering Sea (including the Aleutian Islands), Gulf of Alaska, and along the entire west coast of North America. Risk appeared greatest during south- and northbound migration when much of the gray whale population is moving through waters near shore. Tanker, container, and bulk-carrier ships represent considerable risk to whales in the North Pacific Ocean, but the large geographical extent of commercial fishing activities suggests that fisheries are also a substantial source of risk. Vessel-strike risk maps indicate the relative extent of exposure of gray (and other) whales to underwater vessel noise. The number of gray whales killed by ship strikes each year may be in the tens, or perhaps the low hundreds. Additional analyses, including quantitative assessments, are warranted to further clarify the risk of vessel strikes to gray whales.

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Computing ship strikes and near miss events of fin whales along the main ferry routes in the Pelagos Sanctuary and adjacent west area, in summer

David¹,

Arcangeli

Tepsich

et al. 2022

Aquatic Conservation

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The Mediterranean Sea is a high‐density maritime traffic area, particularly in the Pelagos Sanctuary. Ship strikes pose a substantial threat to fin whales (Balaenoptera physalus) according to reports from the IUCN, the IWC, the ACCOBAMS and the EU Habitats Directive. Near miss events (NMEs) were collected, as a proxy indicator of ship strikes for fin whales, along the main ferry routes crossing the Pelagos Sanctuary and adjacent western waters during ‘summertime’ (April to October). The ‘Fixed Line Transect Med Network’ carries out systematic surveys from ferries and collects data according to the ‘linear transect’ method. From 2008 to 2019, 13 different ferry routes were surveyed with 238,499 km monitored. Of the 2,775 fin whales encountered, 43 individuals were involved in NMEs (1.55% of the sightings). NMEs occur over the great majority of the routes monitored with enough effort and were correlated with the density index of fin whales. High‐risk areas for NMEs were identified in the central and deeper parts of the north‐western Mediterranean Sea and in some sections of the northern Tyrrhenian Sea. Of all NMEs, the majority of whales (63.4%) surfaced in front of the vessel (<50 m), leaving no time for the crew to manoeuvre the vessel. The others were travelling (26.8%) or resting (9.7%) without any noticeable reaction at the vessel. The speed of the ferries seems to play a role in the occurrence of the NME, as this parameter is significantly different (t‐test, P = 0.002) for NMEs compared to all fin whale sightings, whereas month and hour of day were not. Quantifying NMEs based on real‐time observation with observers on board, could be used as a feasible and efficient way to limit collisions, raising awareness by the crew, and testing or evaluating other potential tools that can help mitigate this threat.

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Estimating effectiveness of speed reduction measures for decreasing whale-strike mortality in a high-risk region

Cited by 23 publications

References 57 publications

Modeling Whale Deaths From Vessel Strikes to Reduce the Risk of Fatality to Endangered Whales

Modeling Whale Deaths From Vessel Strikes to Reduce the Risk of Fatality to Endangered Whales

Co-occurrence of gray whales and vessel traffic in the North Pacific Ocean

Computing ship strikes and near miss events of fin whales along the main ferry routes in the Pelagos Sanctuary and adjacent west area, in summer

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