Distribution and abundance of western gray whales off northeastern Sakhalin Island, Russia, 2001’003

In 2001–2003, >60,000 km of aerial surveys and 7,700 km of vessel surveys were conducted during June to November when critically endangered Korean–Okhotsk or western gray whales (Eschrichtius robustus) were present off the northeast coast of Sakhalin Island, Russia. Results of surveys in all years indicated gray whales occurred in predominantly two areas, (1) adjacent to Piltun Bay, and (2) offshore from Chayvo Bay, hereafter referred to as the Piltun and offshore feeding areas. In the Piltun feeding area, the majority of whales were observed in waters shallower than 20 m and were distributed from several hundred meters to ∼ 5 km from the shoreline. In the offshore feeding area during all years, the distribution of gray whales extended from southwest to northeast in waters 30–65 m in depth. During all years, the distribution and abundance of whales changed in both the Piltun and offshore feeding areas, and both north–south and inshore–offshore movements were documented within and between feeding seasons. The discovery of a significant number of whales feeding in the offshore area each year was a substantial finding of this study and raises questions regarding western gray whale abundance and population levels, feeding behavior and ecology, and individual site-fidelity. Fluctuations in the number of whales observed within the Piltun and offshore feeding areas and few sightings outside of these two areas indicate that gray whales move between the Piltun and offshore feeding areas during their summer–fall feeding season. Seasonal shifts in the distribution and abundance of gray whales between and within both the Piltun and offshore feeding areas are thought, in part, to be a response to seasonal changes in the distribution and abundance of prey. However, the mechanism driving the movements of whales along the northeast coast of Sakhalin Island is likely very complex and influenced by a multitude of factors. *Deceased     

Effects of fishing rope strength on the severity of large whale entanglements

Entanglement in fixed fishing gear affects whales worldwide. In the United States, deaths of North Atlantic right (Eubalaena glacialis) and humpback whales (Megaptera novaeangliae) have exceeded management limits for decades. We examined live and dead whales entangled in fishing gear along the U.S. East Coast and the Canadian Maritimes from 1994 to 2010. We recorded whale species, age, and injury severity and determined rope polymer type, breaking strength, and diameter of the fishing gear. For the 132 retrieved ropes from 70 cases, tested breaking strength range was 0.80–39.63 kN (kiloNewtons) and the mean was 11.64 kN (SD 8.29), which is 26% lower than strength at manufacture (range 2.89–53.38 kN, mean = 15.70 kN [9.89]). Median rope diameter was 9.5 mm. Right and humpback whales were found in ropes with significantly stronger breaking strengths at time of manufacture than minke whales (Balaenoptera acuturostrata) (19.30, 17.13, and 10.47 mean kN, respectively). Adult right whales were found in stronger ropes (mean 34.09 kN) than juvenile right whales (mean 15.33 kN) and than all humpback whale age classes (mean 17.37 kN). For right whales, severity of injuries increased since the mid 1980s, possibly due to changes in rope manufacturing in the mid 1990s that resulted in production of stronger ropes at the same diameter. Our results suggest that broad adoption of ropes with breaking strengths of ≤7.56 kN (≤1700 lbsf) could reduce the number of life‐threatening entanglements for large whales by at least 72%, and yet could provide sufficient strength to withstand the routine forces involved in many fishing operations. A reduction of this magnitude would achieve nearly all the mitigation legally required for U.S. stocks of North Atlantic right and humpback whales. Ropes with reduced breaking strength should be developed and tested to determine the feasibility of their use in a variety of fisheries.     

Modeling Effectiveness of Gradual Increases in Source Level to Mitigate Effects of Sonar on Marine Mammals

Ramp‐up or soft‐start procedures (i.e., gradual increase in the source level) are used to mitigate the effect of sonar sound on marine mammals, although no one to date has tested whether ramp‐up procedures are effective at reducing the effect of sound on marine mammals. We investigated the effectiveness of ramp‐up procedures in reducing the area within which changes in hearing thresholds can occur. We modeled the level of sound killer whales (Orcinus orca) were exposed to from a generic sonar operation preceded by different ramp‐up schemes. In our model, ramp‐up procedures reduced the risk of killer whales receiving sounds of sufficient intensity to affect their hearing. The effectiveness of the ramp‐up procedure depended strongly on the assumed response threshold and differed with ramp‐up duration, although extending the duration of the ramp up beyond 5 min did not add much to its predicted mitigating effect. The main factors that limited effectiveness of ramp up in a typical antisubmarine warfare scenario were high source level, rapid moving sonar source, and long silences between consecutive sonar transmissions. Our exposure modeling approach can be used to evaluate and optimize mitigation procedures. Modelado de la Efectividad de los Incrementos Graduales en el Nivel de la Fuente para Mitigar Efectos de Sonar sobre Mamíferos Marinos     

Effects of Multiple Levels of Social Organization on Survival and Abundance

Abstract: Identifying how social organization shapes individual behavior, survival, and fecundity of animals that live in groups can inform conservation efforts and improve forecasts of population abundance, even when the mechanism responsible for group‐level differences is unknown. We constructed a hierarchical Bayesian model to quantify the relative variability in survival rates among different levels of social organization (matrilines and pods) of an endangered population of killer whales (Orcinus orca). Individual killer whales often participate in group activities such as prey sharing and cooperative hunting. The estimated age‐specific survival probabilities and survivorship curves differed considerably among pods and to a lesser extent among matrilines (within pods). Across all pods, males had lower life expectancy than females. Differences in survival between pods may be caused by a combination of factors that vary across the population's range, including reduced prey availability, contaminants in prey, and human activity. Our modeling approach could be applied to demographic rates for other species and for parameters other than survival, including reproduction, prey selection, movement, and detection probabilities.     

Efficacy of a Voluntary Area to Be Avoided to Reduce Risk of Lethal Vessel Strikes to Endangered Whales

Abstract: Ocean‐going vessels pose a threat to large whales worldwide and are responsible for the majority of reported deaths diagnosed among endangered North Atlantic right whales (Eubalaena glacialis). Various conservation policies have been implemented to reduce vessel‐strike mortality in this species. The International Maritime Organization adopted the Roseway Basin Area to be avoided on the Scotian Shelf as a voluntary conservation initiative to reduce the risk of lethal vessel strikes to right whales. We initiated the Vessel Avoidance & Conservation Area Transit Experiment to evaluate the efficacy of this initiative because the effectiveness of the avoidance scheme in reducing risk without the imposition of vessel‐speed restrictions depends entirely on vessel‐operator compliance. Using a network of automatic identification system receivers, we collected static, dynamic, and voyage‐related vessel data in near real time from the Roseway Basin region for 12 months before and 6 months after the implementation of the area to be avoided. Using pre‐ and post‐implementation vessel navigation and speed data, along with right whale sightings per unit effort data, all resolved at 3′N latitude by 3′W longitude, we estimated the post‐implementation change in risk of lethal vessel strikes. Estimates of vessel‐operator voluntary compliance ranged from 57% to 87% and stabilized at 71% within the first 5 months of implementation. Our estimates showed an 82% reduction in the risk of lethal vessel strikes to right whales due to vessel‐operator compliance. We conclude that the high level of compliance achieved with this voluntary conservation initiative occurred because the area to be avoided was adopted by the International Maritime Organization. Our results demonstrate that international shipping interests are able and willing to voluntarily alter course to protect endangered whales.