Marine Mammal Stock Research Articles

State of stocks and harvesting of marine mammals in Russia in 2000–2020

Purpose: analysis of stocks and harvest of marine mammals in the coastal waters of Russia in 2000–2020.Method: collection and analysis of statistics data on the harvest of marine mammals provided by the territorial bodies of the Federal Agency for Fishery, as well as the results of a survey of the indigenous population about their harvest. The capture of marine mammals to ensure the traditional way of life of the indigenous population of the coastal regions of Russia continues to this day.Novelty: presents new data on the state of stocks and harvest of marine mammals in the coastal waters of Russia in 2000–2020.Results: By the beginning of the 21st century, commercial harvest for marine mammals had practically ceased for economic reasons. The trapping of marine mammals to ensure the traditional way of life of the indigenous population of the coastal regions of Russia continues to this day. The most intensive use of marine mammals is observed in Chukotka, where cetaceans, walruses and true seals are hunted. The meat and fat of marine mammals is used by the indigenous population for food purposes, as well as food for domestic dogs and fur-bearing animals when they are kept in cages. In Kamchatka, Sakhalin and along the entire mainland coast of the Sea of Okhotsk, the harvest of marine mammals by the indigenous population is significantly lower than in Chukotka. In these areas, seal fat is used for medical purposes. In remote villages of the Far North, hunted seals and beluga whales are also used for food, but collecting statistics on their production in these areas is difficult and is based on expert estimates. For a long time after the cessation of commercial fishing, the stocks of marine mammals were not assessed. Only thanks to federal funding of environmental projects of the Russian Academy of Sciences, thanks to Russian-A merican cooperation in the field of marine mammal research and the support of environmental organizations, new information has been obtained about marine mammal stocks in the last two decades of the 21st century. It is shown that despite the cessation of industrial harvesting of marine mammals, there is no significant increase in their stocks.

Vulnerability to climate change of United States marine mammal stocks in the western North Atlantic, Gulf of Mexico, and Caribbean.

Climate change and climate variability are affecting marine mammal species and these impacts are projected to continue in the coming decades. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species using currently available information. We conducted a trait-based climate vulnerability assessment using expert elicitation for 108 marine mammal stocks and stock groups in the western North Atlantic, Gulf of Mexico, and Caribbean Sea. Our approach combined the exposure (projected change in environmental conditions) and sensitivity (ability to tolerate and adapt to changing conditions) of marine mammal stocks to estimate vulnerability to climate change, and categorize stocks with a vulnerability index. The climate vulnerability score was very high for 44% (n = 47) of these stocks, high for 29% (n = 31), moderate for 20% (n = 22), and low for 7% (n = 8). The majority of stocks (n = 78; 72%) scored very high exposure, whereas 24% (n = 26) scored high, and 4% (n = 4) scored moderate. The sensitivity score was very high for 33% (n = 36) of these stocks, high for 18% (n = 19), moderate for 34% (n = 37), and low for 15% (n = 16). Vulnerability results were summarized for stocks in five taxonomic groups: pinnipeds (n = 4; 25% high, 75% moderate), mysticetes (n = 7; 29% very high, 57% high, 14% moderate), ziphiids (n = 8; 13% very high, 50% high, 38% moderate), delphinids (n = 84; 52% very high, 23% high, 15% moderate, 10% low), and other odontocetes (n = 5; 60% high, 40% moderate). Factors including temperature, ocean pH, and dissolved oxygen were the primary drivers of high climate exposure, with effects mediated through prey and habitat parameters. We quantified sources of uncertainty by bootstrapping vulnerability scores, conducting leave-one-out analyses of individual attributes and individual scorers, and through scoring data quality for each attribute. These results provide information for researchers, managers, and the public on marine mammal responses to climate change to enhance the development of more effective marine mammal management, restoration, and conservation activities that address current and future environmental variation and biological responses due to climate change.

Detecting population trends for US marine mammals

AbstractTrend analysis can provide valuable information about marine mammal population dynamics, potentially revealing the influence of environmental factors and inform conservation and management decisions. We reviewed the marine mammal stock assessment reports (SARs) published by the US National Marine Fisheries Service and found that 80% of the selected 244 marine mammal stocks with SARs lack assessment for trends in population abundance. We compared trend analysis with another common management tool, potential biological removal (PBR), a measure of the maximum human‐caused mortality that can still result in positive population growth. We found that, generally, estimates of PBR were lower for declining stocks than for increasing or stable stocks and varied by life history characteristics. As a case study, we used a resampling approach on three well‐studied stocks, killer whale (Orcinus orca—Northern Resident), beluga (Delphinapterus leucas—Cook Inlet), and humpback whale (Megaptera novaeangliae—CA/OR/WA), to test the minimal amount of time and sampling necessary to detect population trends with high statistical power. We found seven sampling events over more than 10 years were needed for a high statistical power level for all three stocks. Altogether, these findings suggest that well‐studied stocks can provide crucial information on the statistical requirements for detecting trends. Furthermore, our proposed resampling approach might enable more frequent trend analysis, even with limited time series available for many stocks.

Estimation of In‐Water Density and Abundance of Harbor Seals

ABSTRACTEcologists and managers require accurate population estimates of marine mammals to assess potential anthropogenic threats to these animals. We present estimates of in‐water density and abundance of a distinct stock of harbor seals (Phoca vitulina richardii) in Hood Canal, Washington, USA. We used aerial line‐transect survey data collected from 2013 to 2016 to directly estimate harbor seal density and abundance in the waters of Hood Canal, a deep‐water fjord in the Salish Sea. We estimated a correction factor for trackline detection probability from dive and surface time data gathered from regional seal tagging studies, and applied this factor to correct for seals missed on the trackline during surveys. We applied conventional and multiple covariate line‐transect approaches in the analysis. The resulting best estimate of in‐water density of harbor seals in the Hood Canal study region was 5.80 seals/km2, with an estimated abundance of 2,009 seals. We did not derive a correction factor to account for the number of seals on land (i.e., hauled out). Therefore, these estimates do not reflect total stock size but provide a starting point to evaluate potential influences of anthropogenic activities, particularly those involving underwater noise, on this marine mammal stock. © 2021 The Wildlife Society.

Model-based unsupervised clustering for distinguishing Cuvier's and Gervais' beaked whales in acoustic data

Passive acoustic monitoring (PAM), particularly autonomous platforms, offers many advantages in monitoring phonating deep-diving marine mammals in oceanic environment. Relevant data can be obtained day and night continuously over long durations and in any weather conditions. It provides a cost-efficient solution with greater detection ranges when compared to traditional large research vessel and aerial visual surveys requiring keeping expert observers on station for long periods of time and relying on good visibility and calm seas. Therefore, PAM is becoming a preferred tool to assess population dynamics trends and health of deep-water marine mammal stocks. However the large volumes of collected data require robust automatic detection and classification algorithms to identify marine mammals in recordings. As for beaked whales, one of the challenging automatic processing goals is the identification of different species to advance our understanding of their role in the marine ecosystem. At present, traditional detection and classification methods employ searches for acoustic events above a user-defined signal-to-noise ratio threshold in the frequency band of interest and further rely on an experienced operator's manual inspection for species classification and removal of false positives. Current passive monitoring data collection systems yield large volumes of acoustic data, therefore a manual classification approach becomes very time-consuming and impractical. This paper focuses on developing a multi-stage automatic classifier for beaked whale species. The proposed method utilizes unsupervised machine clustering of signal attributes extracted from potential detection events flagged by an energy-band detector. The proposed algorithm was benchmarked against a manually annotated workshop dataset and applied to acoustic data collected in the northern Gulf of Mexico. The algorithm classifies beaked whale species in automatic mode with minimal operator involvement only at the validation stage. When compared with the manually annotated classification dataset, the proposed method achieved a recall rate of 82.8% for Cuvier's and 77.9% for Gervais' species in automatic mode. New insights on habitat use by different species of beaked whales in the Gulf of Mexico were gained when using the species-specific classifier. The high spatial resolution acoustic monitoring results showed that the habitat preferences of two dominating beaked whale species in the Gulf of Mexico support the habitat division (ecological niche) hypothesis.

Conserving and recovering vulnerable marine species: a comprehensive evaluation of the US approach for marine mammals

AbstractHuman-caused mortality due primarily to bycatch in fisheries is considered a major threat to some long-lived, slow-growing, and otherwise vulnerable marine species. Under many jurisdictions these species are designated as “protected”, and fisheries are subject to a management system that includes monitoring and assessment of bycatch impacts relative to management objectives. The US management system for marine mammals is one of the most sophisticated in the world, with a limit on human-caused mortality computed using the potential biological removal (PBR), formula. Fisheries are categorized according to their impact relative to PBR, and take reduction teams established to develop take reduction plans (TRPs) when bycatch exceeds PBR. The default values of the parameters of the PBR formula were selected in the late 1990s using management strategy evaluation (MSE), but the system, in particular the classification of fisheries, has yet to be evaluated in its entirety. A MSE framework is developed that includes the PBR formula, as well as the processes for evaluating whether a stock is “strategic”, assigning fisheries to categories, and implementing TRPs. The level of error associated with fisheries classification was found not to impact the ability to achieve the conservation objective established for a stock under the US Marine Mammal Protection Act (i.e. maintain or recover the stock to/at optimum sustainable population). However, this ability is highly dependent on the life history and absolute abundance of the species being managed, as well as on the premise that bycatch is reduced if bycatch is estimated to exceed the PBR. The probability of correctly classifying fisheries depends on both the coefficient of variations (CVs) of the estimates of bycatch and the marine mammal stock’s abundance because classification depends on the ratio of the estimate of bycatch by fishery-type to the stock’s PBR, and the precision of the former depends on the bycatch CV and the latter on the abundance estimate CV. Moreover, the probability of correctly classifying a fishery decreases for smaller populations, particularly when a fishery has low to moderate impact.

Evaluating the efficacy of environmental legislation: A case study from the US marine mammal Take Reduction Planning process

There have been limited efforts to evaluate the efficacy of environmental management programs, in part because environmental legislation often lacks objective, quantifiable criteria to use in such assessments. Here we evaluate the ecological outcomes of an important element of one well-known environmental statute, the US Marine Mammal Protection Act (MMPA), using take reduction planning as a case study. Take reduction planning is mandated by the MMPA as a means to reduce mortality of marine mammals in US fisheries to below statutory thresholds. We used data from formal Stock Assessment Reports to assess and rank the success of five Take Reduction Plans (Harbor Porpoise, Bottlenose Dolphin, Atlantic Large Whale, Pelagic Longline, and Pacific Offshore Cetacean) in mitigating the bycatch of 15 marine mammal stocks. In general, Take Reduction Plans have had an uneven record of meeting their statutory requirements. Successful plans were characterized by straightforward regulations and high rates of compliance. Unsuccessful plans covered marine mammal–fisheries interactions in the northeastern US, had low compliance with complex regulations and sometimes focused on very small stocks. This study emphasizes the importance of requiring legally mandated, quantitative metrics and long-term monitoring programs to evaluate the efficacy of a well-known element of an established environmental management program.

A review of the battle for food in the Barents Sea: cod vs. marine mammals

Cod, harp seal and minke whale are the main top predators in the Barents Sea ecosystem. In the last decade, the abundance of cod has increased considerably, and is at a record high level. In spite of this, the growth and condition of cod has remained rather stable, although some decrease is seen in size at age of large, mature cod. During the same period, the abundance of harp seals has declined whereas the minke whale stock has been at a stable level. The body condition (blubber thickness) of these two mammal stocks has, however, decreased, with the strongest decrease observed for harp seals. A possible hypothesis for explaining this is that cod outperform the marine mammal stocks in the competition for food. The main advantages for cod are most likely larger availability of food (mainly capelin) during winter-spring than for marine mammals, as well as a wider range of prey species being available to cod than to marine mammals. Harp seals are more dependent on prey items found close to the ice edge than the other two predator stocks are, which could partly explain why the performance of harp seals is worse than that of the two other main top predators in the area.

Measuring the Economic Value of Increased Precision in Scientific Estimates of Marine Mammal Abundance and Bycatch: Harbor Porpoise Phocoena phocoena in the Northeast U.S. Gill‐Net Fishery

AbstractMarine mammal stock assessments provide information that is valuable to public sector management and the private fishing sector; however, data are costly to collect. The precautionary approach, which is widely used in fishery and marine mammal management, advocates a conservative management decision with priority to the resource when there is uncertainty regarding the impact on the resource from human activity. The potential biological removal (PBR) control rule of the U.S. Marine Mammal Protection Act explicitly incorporates uncertainty in input variables into the determination of allowable levels of human‐induced mortality for a stock. Less uncertainty results in higher PBR values for a given stock level. Variations in government funding levels can disrupt the scientific data collection that is necessary for PBR calculation. We present an economic net benefit framework that examines the indirect value of information from marine mammal stock assessments to the commercial fishing industry. Using the harbor porpoise Phocoena phocoena and the U.S. Atlantic sink gill‐net fishery as a case study, we estimated the difference between total public sector data collection costs and total private sector benefits from increased profits. Net benefits represent a measure of the value of information to society, while the difference in profits measures the value of the information to the private sector. Several results are forthcoming. First, the optimal allocation of funding showed that abundance surveys are a more cost‐effective means to reduce uncertainty in PBR input variables than increasing observer coverage of the fishing industry. Second, for all levels of PBR in this empirical example, total benefits to the private sector for a higher PBR exceeded the costs of collecting additional scientific data to increase the precision of input variables and thus increase PBR. Since net benefits are positive, the private sector may consider funding of scientific data collection for marine mammals as a way to reduce uncertainty, thereby allowing a higher PBR value.Received March 19, 2013; accepted November 14, 2013

An index of optimum sustainable population for the Pacific Walrus

The United States Marine Mammal Protection Act of 1972 (MMPA) specified that marine mammal stocks be maintained at an optimum sustainable population level (OSP). However, the information needed to directly estimate OSP for most stocks was not available and indices to OSP were soon proposed but to our knowledge none were fully developed. In 1994, a new management regime was adopted under the MMPA, potential biological removal (PBR), which was specifically developed to assess marine mammal mortalities associated with commercial fisheries. Pacific walruses (Odobenus rosmarus divergens) are rarely killed in commercial fisheries, the greatest source of human caused mortality is the subsistence harvest by Alaskan and Russian natives, and PBR estimates have been erroneously used to make inference about the sustainability of the subsistence harvest. It is clear that an index to OSP is needed for the Pacific walrus because PBR as calculated for fisheries is not appropriate. In this study, we explored calf:cow ratios (CCR), estimated from spring harvest data, as an index to population abundance and OSP as a function of habitat carrying capacity (K). Eight of the 10 characteristics of an effective index are applicable to CCRs. Based on abundance estimates when the Pacific walrus population was at or near K and a simulated estimate of maximum net productivity, CCRs of 0.41–0.47 reflect a Pacific walrus population at OSP. The best use of the CCR index will be to inform subsistence hunters of the status of the population and to promote self-regulation of the harvest by hunters. However, because other factors which may be weakly density-dependent such as disease and physical trauma could effect CCRs and the same CCR can be expressed by a declining or increasing population, the index will need to be combined with other information (e.g., habitat change and use patterns, population trend, physical condition of individuals, survival rates, etc.) in a weight of evidence approach in order to have stronger inference. Furthermore, our analyses are based on a data set that included periods when climatic conditions differed from those of recent decades, requiring evaluation of the index into the future.

Status of marine mammals in Korea

Although marine mammals, particularly cetaceans, have been protected in Korea for more than 24 years after a commercial whaling moratorium in 1986, relatively little effort has been focused on assessing their current status of marine mammals in this area after this protection and the efficacy of this protection. Thus, for the first time, the status of marine mammals in Korea was investigated using potential biological removal (PBR) and mortality data. A total of 5 stocks of marine mammals were investigated and 4 stocks experienced anthropogenic mortalities that exceeded their estimated PBR level. Therefore, these 4 stocks were considered strategic. These mortalities were mainly associated with commercial fishing activities. To conserve and manage marine mammals in this area effectively, it urgently needs to investigate the efficiency of various bycatch mitigation measures and to apply these measures in field actually for reducing bycatch. This study has advanced our understanding of the current status of marine mammals in Korea, but quantitative data on abundance are not available for most small cetaceans such as common dolphin, harbor porpoise. Thus, further study needs to examine abundance of small cetaceans for investigating of the current status of these stocks in Korea.

Integrating multiple techniques to identify stock boundaries of common bottlenose dolphins (Tursiops truncatus)

ABSTRACT Under US policy, a stock is a group of animals shown to be demographically independent from other such groups. Evidence of demographic delineations for marine mammal stocks is gained primarily through genetic analysis. However, additional techniques play an important role in determining fine‐scale ranging patterns that can be used to define a stock's geographic boundaries. In cases where genetic studies have not yet been performed, movement and ranging pattern data are essential in identifying a targeted geographic region for tissue sampling and genetic studies. Photo‐identification surveys, vessel‐based radio telemetry, automated radio telemetry systems (ARTS), and satellite‐linked telemetry are sampling techniques that have been used to determine common bottlenose dolphin ranging patterns and provide detailed insight into stock boundaries. The results of near simultaneous use of these sampling techniques are compared using data from a case study of bottlenose dolphins within the estuaries of southern Georgia. Satellite‐linked and radio telemetry were determined to be useful sampling techniques for identification of short‐term ranging patterns. Satellite‐linked telemetry had the second lowest cost per location ($122) and identified dolphin ranging patterns within and outside of the study area boundaries. Vessel‐based radio telemetry was more costly ($195 per location) and had relatively limited tracking coverage. However, this sampling technique permitted visual observations of animal and tag condition. The combination of vessel‐based radio telemetry and ARTS, which had the lowest cost per location ($34), was an effective method for determining ranging patterns of tagged individuals within and outside of the study area. Photo‐identification surveys, relative to satellite‐linked and radio telemetry, were not as efficient for determination of targeted individuals’ short‐term ranging patterns and had the highest cost per location of the four sampling techniques ($292). However, photo‐identification is more effective than any other technique for compiling data on large numbers of individuals within a designated study area. Photo‐identification surveys are essential for long‐term monitoring and provide additional insight into dolphin stock structure that cannot be determined through telemetry alone. Copyright © 2013 John Wiley & Sons, Ltd.

The Marine Mammal Protection Act at 40: status, recovery, and future of U.S. marine mammals

Passed in 1972, the Marine Mammal Protection Act has two fundamental objectives: to maintain U.S. marine mammal stocks at their optimum sustainable populations and to uphold their ecological role in the ocean. The current status of many marine mammal populations is considerably better than in 1972. Take reduction plans have been largely successful in reducing direct fisheries bycatch, although they have not been prepared for all at-risk stocks, and fisheries continue to place marine mammals as risk. Information on population trends is unknown for most (71%) stocks; more stocks with known trends are improving than declining: 19% increasing, 5% stable, and 5% decreasing. Challenges remain, however, and the act has generally been ineffective in treating indirect impacts, such as noise, disease, and prey depletion. Existing conservation measures have not protected large whales from fisheries interactions or ship strikes in the northwestern Atlantic. Despite these limitations, marine mammals within the U.S. Exclusive Economic Zone appear to be faring better than those outside, with fewer species in at-risk categories and more of least concern.

Effects of hunting, fishing and climate change on the Hudson Bay marine ecosystem: II. Ecosystem model future projections

Simulations testing the future impacts of harvest and climate change to the Hudson Bay marine ecosystem were created utilizing an existing Ecopath with Ecosim model (Hoover et al., 2013). Building on past simulations depicting known changes to the region, a suite of future scenarios was constructed to include a variety of climate change and harvest levels. Previously identified ecosystem shifts favoring pelagic species (zooplankton, planktivorous fish) over benthic species (benthos, benthic feeding fish), are further exaggerated under future climate scenarios. Environmental forcing was incorporated to mimic the declines in sea ice, and increases in temperature causing shifts in the food web from an ice algae–benthos–benthic fish pathway to a spring bloom–zooplankton–planktivorous fish dominated ecosystem. Future simulations indicate some stocks are unable to sustain current harvest levels until the end of the future simulations (2069), and may be extirpated (narwhal, eastern Hudson Bay beluga, polar bears, and walrus). Larger populations of marine mammals (ringed seals and western Hudson Bay beluga) are identified to increase in biomass even under extreme harvest and climate scenarios (a high future climate scenario coupled with a doubling in harvest rates). Harvest mortality is highlighted as an important stressor for some marine mammal stocks and should be investigated further when setting future harvest or conservation targets.

Informing Species Conservation at Multiple Scales Using Data Collected for Marine Mammal Stock Assessments

BackgroundConservation planning and the design of marine protected areas (MPAs) requires spatially explicit information on the distribution of ecological features. Most species of marine mammals range over large areas and across multiple planning regions. The spatial distributions of marine mammals are difficult to predict using habitat modelling at ecological scales because of insufficient understanding of their habitat needs, however, relevant information may be available from surveys conducted to inform mandatory stock assessments.Methodology and ResultsWe use a 20-year time series of systematic aerial surveys of dugong (Dugong dugong) abundance to create spatially-explicit models of dugong distribution and relative density at the scale of the coastal waters of northeast Australia (∼136,000 km2). We interpolated the corrected data at the scale of 2 km * 2 km planning units using geostatistics. Planning units were classified as low, medium, high and very high dugong density on the basis of the relative density of dugongs estimated from the models and a frequency analysis. Torres Strait was identified as the most significant dugong habitat in northeast Australia and the most globally significant habitat known for any member of the Order Sirenia. The models are used by local, State and Federal agencies to inform management decisions related to the Indigenous harvest of dugongs, gill-net fisheries and Australia's National Representative System of Marine Protected Areas.Conclusion/SignificanceIn this paper we demonstrate that spatially-explicit population models add value to data collected for stock assessments, provide a robust alternative to predictive habitat distribution models, and inform species conservation at multiple scales.

Illegal, Unreported and Unregulated Fishing in the Circumpolar Arctic

Climate change has increased both marine access to much of the circumpolar Arctic and the migration of fish stocks into northern waters. As fish stocks become depleted in southern jurisdictions, Arctic fish stocks could become more attractive for illegal, unre ported, and unregulated (IUU) fishing. This situation has many parallels with the experiences of IUU fishing in the Southern Ocean around the Antarctic. However, unlike those in Antarctica, fish and marine mammal stocks in the circumpolar Arctic are subject to indigenous and local subsistence harvesting, which has priority over commercial harvesting. Arctic fish stocks are also characterized by lower growth rates, which increase their vulnerability to the impact of IUU fishing. In the Canadian Arctic, because of slow fish growth, limited seasonal fishing opportunities, and the high cost of shipping, extensive ecosystem and economic changes would be required to make commercial fisheries feasible. Fisheries have been very close to shore throughout the Canadian Arctic. Though attempts have been made to harvest Arctic char (Salvelinus alpinus) commercially, this species has been harvested primarily for subsistence and recreation. Arctic cisco (Coregonus autumnalis) or Pacific herring ( Clupea palasii) are potential commercial fishery targets in the Canadian Beaufort Sea, but these harvests would be subject to beluga whale feeding requirements. In this essay, I explore several northern fisheries to examine various IUU fishing scenarios for the Arctic: com mercial fishing in the Canadian and U.S. Beaufort Sea, the offshore halibut fishery adjacent to the Nunavut Territory of Canada, and the Irminger Sea redfish fishery in the Rey kjanes Ridge of the North Atlantic. I then consider current regulatory regimes for IUU fisheries in Antarctica and Europe, which provide potential models for Arctic fisheries.

Potential limits to anthropogenic mortality of small cetaceans in coastal waters of British Columbia

Small cetaceans are by-caught in salmon gillnet fisheries in British Columbia (BC) waters. In Canada, there is currently no generic calculation to identify when management action is necessary to reduce cetacean bycatch below sustainable limits. We estimated potential anthropogenic mortality limits for harbour ( Phocoena phocoena ) and Dall’s ( Phocoenoides dalli ) porpoises and Pacific white-sided dolphins ( Lagenorhynchus obliquidens ) using quantitative objectives from two well-established frameworks for conservation and management (the United States’ Marine Mammal Protection Act and the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), which are similar to some management objectives developed for marine mammal stocks elsewhere in Canada. Limits were calculated as functions of (i) a minimum abundance estimate (2004–2005); (ii) maximum rate of population increase; and (iii) uncertainty factors to account for bias in abundance estimates and uncertainty in mortality estimates. Best estimates of bycatch mortality in 2004 and 2005 exceeded only the most precautionary limits and only for porpoise species. Future research priority should be given to determining small cetacean stock structure in BC and refining species-specific entanglement rates in these and other fisheries. The approach offers a quantitative framework for Canada to meet its stated objectives to maintain favourable conservation status of cetacean populations.

Constructing a coherent joint prior while respecting biological realism: application to marine mammal stock assessments

AbstractBrandon, J. R., Breiwick, J. M., Punt, A. E., and Wade, P. R. 2007. Constructing a coherent joint prior while respecting biological realism: application to marine mammal stock assessments. – ICES Journal of Marine Science, 64: 1085–1100. Bayesian estimation methods, employing the Sampling–Importance–Resampling algorithm, are currently used to perform stock assessments for several stocks of marine mammals, including the Bering–Chukchi–Beaufort Seas stock of bowhead whales (Balaena mysticetus) and walrus (Odobenus rosmarus rosmarus) off Greenland. However, owing to the functional relationships among parameters in deterministic age-structured population dynamics models, placing explicit priors on each life history parameter in addition to the population growth rate parameter results in an incoherent joint prior distribution (i.e. two different priors on the estimated parameters). One solution to constructing a coherent joint prior is to solve for juvenile survival analytically, using values generated from the prior distributions for the remaining parameters. However, certain combinations of model parameter values result in values for juvenile survival that are larger than adult survival, which is biologically implausible. Therefore, to respect biological realism, certain parameter values must be rejected for some or all the remaining parameters. This study investigates several alternative resampling schemes for obtaining a realistic joint prior distribution, given the constraint on survival rates. The sensitivity of assessment results is investigated for data-rich (bowhead) and data-poor (walrus) scenarios. The results based on limited data are especially sensitive to the choice of alternative resampling scheme.

LESSONS FROM MONITORING TRENDS IN ABUNDANCE OF MARINE MAMMALS

AbstractWe assessed scientists' ability to detect declines of marine mammal stocks based on recent levels of survey effort, when the actual decline is precipitous. We defined a precipitous decline as a 50% decrease in abundance in 15 yr, at which point a stock could be legally classified as “depleted” under the U.S. Marine Mammal Protection Act. We assessed stocks for three categories of cetaceans: large whales (n= 23, most of which are listed as endangered), beaked whales (n= 11, potentially vulnerable to anthropogenic noise), and small whales/dolphins/porpoises (n= 69, bycatch in fisheries and important abundant predators), for two categories of pinnipeds with substantially different survey precision: counted on land (n= 13) and surveyed on ice (n= 5), and for a category containing polar bear and sea otter stocks (n= 6). The percentage of precipitous declines that wouldnotbe detected as declines was 72% for large whales, 90% for beaked whales, and 78% for dolphins/porpoises, 5% for pinnipeds on land, 100% for pinnipeds on ice, and 55% for polar bears/sea otters (based on a one‐tailedt‐test, α= 0.05), given the frequency and precision of recent monitoring effort. We recommend alternatives to improve performance.

Marine pelagic ecosystems: the West Antarctic Peninsula

The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2 degrees C increase in the annual mean temperature and a 6 degrees C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6 degrees C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along the WAP and the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response.