Night and Day: Diel Differences in Ship Strike Risk for Fin Whales (Balaenoptera physalus) in the California Current System

Abstract

Collisions with ships (ship strikes) are a pressing conservation concern for fin whales (Balaenoptera physalus) along western North America. Fin whales exhibit strong diel patterns in dive behavior, remaining near the surface for most of the night, but how this behavior affects ship-strike risk is unknown. We combined diel patterns of surface use, habitat suitability predictions, and ship traffic data to evaluate spatial and temporal trends in ship-strike risk to fin whales of the California Current System (CCS). We tested a range of surface-use scenarios and found that both increased use of the upper water column and increased ship traffic contribute to elevated ship-strike risk at night. Lengthening nights elevate risk during winter throughout the CCS, though the Southern California Bight experienced consistently high risk both day and night year-round. Within designated shipping lanes, total annual nighttime strike risk was twice daytime risk. Avoidance probability models based on ship speed were used to compare the potential efficacy of speed restrictions at various scales. Speed reductions within lanes may be an efficient remediation, but they would address only a small fraction (13%) of overall ship-strike risk. Additional speed restrictions in the approaches to lanes would more effectively reduce overall risk.

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

“…Thus, large increases in cooperation can safely be interpreted to result in meaningful conservation improvements while small increases in cooperation may not. Based on our model and other approaches to quantification of strike risk the most important factors include variation in whale distribution, vessel distribution, vessel speed, vessel sizes, and whale behavior through time (Calambokidis et al, 2019;Keen et al, 2019;Blondin et al, 2020;Rockwood et al, 2020a). Evaluation of speed distributions and using a full strike mortality model as done here will provide more robust VSR program evaluation.…”

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

“…Currently all relevant data relate to daylight hours, and it is crucial to understand the diel pattern of fin whale dives in the Mediterranean Sea to better estimate exposure not only during daylight hours but also during the night. In other parts of the world, Keen et al (2019) and Calambokidis et al (2019) from studies using suction cup tags have estimated that the risk to fin whales of a ship strike was higher at night than during the day. Following those tagged whales, it could be interesting to record how they react at a very close range to approaching vessels, as did McKenna et al (2015), and the results could also be useful for assessing the energy needs of a startle or avoidance reaction by the animal.…”

“…Bay of Ajaccio or Toulon, continental shelf in front of Civitaveccia), which are areas less suitable for fin whales and therefore this result should be taken with caution.For this study, the FLT dataset over 10 years recorded no ship strike with a fin whale. Because this study is only based on visual observation during the daylight hours, it is possible that the risk of strike might be at least the same or even higher during the night, depending on the whale's behaviour and dive pattern(Calambokidis et al, 2019;Keen et al, 2019). It will depend also on ship traffic patterns at night, and indeed, David & Di-Méglio (2010) stressed that ferries travelling at night are more numerous than during daylight, increasing the risk of whale exposure to vessels.…”

Western Gull Foraging Behavior as an Ecosystem State Indicator in Coastal California

“…For example, when the gull core foraging area overlaps with a shipping lane, vessel speed reductions could be implemented until that region is no longer highly utilized by gulls likened to a Seasonal Management Area with the designation of temporary "Areas to be Avoided." Keen et al (2019) found a 2-3 kt reduction significantly reduces ship strike risk by 20-50%. Core foraging areas could also indicate risky crab pot deployment locations, or signal fishers to retrieve deployed gear.…”

“…To reduce risks to whales, it is critical to identify where and when threats occur. While ship strikes often occur in the vicinity of large ports (especially off San Francisco for humpbacks) with peaks in high traffic summer months (Rockwood et al, 2017;Keen et al, 2019), the Dungeness crab fishery is usually open from mid-November to the end of June with the highest activity from mid-November to February (Carretta et al, 2015; Figure 6). Indicators that provide actionable high-resolution information are critical as more decision support tools are needed (Santora et al, 2020), especially given that earlier arrivals, longer residency and higher concentrations of whales in central California could lead to increased risks (Ingman et al, 2021).…”