The North Pacific right whale (Eubalaena japonica) was heavily exploited by both nineteenth century whaling and recent (1960s) illegal Soviet catches. Today, the species remains extremely rare especially in the eastern North Pacific. Here, we use photographic and genotype data to calculate the first mark-recapture estimates of abundance for right whales in the Bering Sea and Aleutian Islands. The estimates were very similar: photographic 5 31 (95% CL 23-54), genotyping 5 28 (95% CL 24 -42). We also estimated the population contains eight females (95% CL 7 -18) and 20 males (95% CL 17-37). Although these estimates may relate to a Bering Sea subpopulation, other data suggest that the total eastern North Pacific population is unlikely to be much larger. Its precarious status todaythe world's smallest whale population for which an abundance estimate exists-is a direct consequence of uncontrolled and illegal whaling, and highlights the past failure of international management to prevent such abuses.
The long-term effectiveness of acoustic pingers in reducing marine mammal bycatch was assessed for the swordfish and thresher shark drift gillnet fishery in California. Between 1990 and 2009, data on fishing gear, environmental variables, and bycatch were recorded for over 8,000 fishing sets by at-sea fishery observers, including over 4,000 sets outfitted with acoustic pingers between 1996 and 2009. Bycatch rates of cetaceans in sets with ≥30 pingers were nearly 50% lower compared to sets without pingers (p = 1.2 × 10−6), though this result is driven largely by common dolphin (Delphinus delphis) bycatch. Beaked whales have not been observed entangled in this fishery since 1995, the last full year of fishing without acoustic pingers. Pinger failure (≥1 nonfunctioning pingers in a net) was noted in 3.7% of observed sets. In sets where the number of failed pingers was recorded, approximately 18% of deployed pingers had failed. Cetacean bycatch rates were 10 times higher in sets where ≥1 pingers failed versus sets without pinger failure (p = 0.002), though sample sizes for sets with pinger failure were small. No evidence of habituation to pingers by cetaceans was apparent over a 14-year period of use. Bycatch rates of California sea lions in sets with ≥30 pingers were nearly double that of sets without pingers, which prompted us to examine the potential “dinner bell” effects of pingers. Depredation of swordfish catch by California sea lions was not linked to pinger use—the best predictors of depredation were total swordfish catch, month fished, area fished, and nighttime use of deck lights on vessels.
We describe a tandem aerial survey method for bottlenose dolphins (Tursiops truncatus) that uses two aircraft and independent observer teams to conduct consecutive surveys of the same coastal strip one hour apart. Alternatively, one aircraft with one observer team surveys the same coastal strip twice over several hours. Using mark‐recapture analysis, we corrected survey counts for visibility bias resulting from missing dolphin groups at the surface and submerged groups. Dolphin groups were considered “recaptured” when we determined that both observer teams had detected the same group. This tandem method is highly useful for estimating abundance (and visibility bias) for species where population closure may be assumed between flights. We assumed population closure between flights and matched groups using geographic location, group size, and expected travel rates. We derive a new variance estimator of population size which incorporates group‐size variability commonly encounteted in cetacean surveys. From six tandem surveys conducted from 1991 to 1994, we estimated the abundance of southern California coastal bottlenose dolphins to be between 78 (95% CI 60‐102) and 271 (240‐306) animals, with an average of 140 (128‐154). Variability in abundance estimates is likely due to seasonal and interannual movement of animals along the California and Baja California coast. Abundance estimates from tandem surveys averaged 53% higher than dolphin counts obtained from individual survey flights, demonstrating the importance of correcting for visibility bias.
The North Pacific right whale, Eubalaena japonica, is one of the most endangered species of whale in the world. On 10 August 2004, two right whales were located in the Bering Sea using headings to right whale calls provided by directional sonobuoys. A satellite-monitored radio tag attached to one of these whales functioned for 40 days. Over the 40-day period, this whale moved throughout a large part of the southeast Bering Sea shelf, including areas of the outer-shelf where right whales have not been seen in decades. In September, multiple right whales were acoustically located and subsequently sighted by another survey vessel approaching a near-real-time position from the tag. An analysis of photographs confirmed at least 17 individual whales (not including the tagged whales). Genetic analysis of biopsy samples identified 17 individuals: 10 males and 7 females. The discovery of seven females was significant, as only one female had been identified in the past. Genetics also confirmed the presence of at least two calves. Although the future of this population is highly uncertain, the discovery of additional females and calves gives some hope that this most critically endangered of all whale populations may still possess the capacity to recover.
The California sea lion (Zalophus californianus) population in the United States has increased steadily since the early 1970s. The Marine Mammal Protection Act of 1972 (MMPA) established criteria for management of marine mammals based on the concept of managing populations within the optimal sustainable population (OSP), defined as a range of abundance from the maximum net productivity level (MNPL) to carrying capacity (K). Recent declines in California sea lion pup production and survival suggest that the population may have stopped growing, but the status of the population relative to OSP and MNPL is unknown. We used a time series of pup counts from 1975 to 2014 and a time series of mark-release-resightrecovery data from 1987 to 2015 for survival estimates to numerically reconstruct the population and evaluate the current population status relative to OSP using a generalized logistic model. We demonstrated that the population size in 2014 was above MNPL and within its OSP range. However, we also showed that population growth can be dramatically decreased by increasing sea surface temperature associated with El Niño events or similar regional ocean temperature anomalies. In this analysis we developed a critical tool for management of California sea lions that provides a better understanding of the population dynamics and a scientific foundation upon which to base management decisions related to complex resource issues involving this species. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.
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