Review Status of Marine Mammals in the United States ANDREW J. READ* AND PAUL R. WADE† *Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, NC 28516, U.S.A., email aread@duke.edu †Office of Protected Resources, National Marine Fisheries Service, c/o National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, U.S.A., email paul.wade@noaa.gov Abstract: The 1994 amendments to the U.S. Marine Mammal Protection Act required, for the first time, an assessment of the status of every marine mammal stock in the United States. We draw conclusions about the status of marine mammals from assessments of 153 stocks conducted to meet the requirements of these amendments. We found important regional differences in the status of stocks. Most stocks in the Atlantic and Pacific experience human-induced mortality (takes), primarily from gill-net fisheries. The proportion of stocks with takes was lower in the Gulf of Mexico and Hawaii, areas with few gill-net fisheries. Estimated takes exceeded removal limits for 29% of stocks in the Atlantic, 14% in the Pacific, 8% in Alaska, 7% in the Gulf of Mexico, and 0% in Hawaii. Twenty-eight stocks are listed as threatened or endangered under the U.S. Endangered Species Act. Most, but not all, baleen whale stocks are recovering after cessation of commercial harvests. Many species of pelagic cetaceans, including beaked and sperm whales, are vulnerable to mortality in pelagic drift-net fisheries. Most pinniped stocks experience takes, but none of these takes exceeds removal limits, and all pinniped stocks on mainland coasts of the United States are increasing in abundance. Quantitative data on trends in abundance are available for few cetacean stocks, emphasizing the difficulty of monitoring trends in these species. These stock assessments have greatly advanced our understanding of the status of marine mammals in the United States, but information gaps remain, particularly regarding stock structure and possible mortality in unmonitored fisheries. Estado de los Mamíferos Marinos en los Estados Unidos Resumen: Las enmiendas al Acta de Protección de Mamíferos Marinos de EUA de 1994 exigieron, por pri– mera vez, una evaluación del estado de todas las poblaciones de mamíferos marinos en los Estados Unidos. Derivamos conclusiones sobre el estado de los mamíferos marinos a partir de evaluaciones de 153 poblaciones realizadas para cumplir con los requerimientos de estas enmiendas. Encontramos diferencias regionales importantes en el estado de los grupos. La mayoría de las poblaciones del Atlántico y del Pacífico experimentan mortalidad inducida por humanos (capturas), debido, principalmente, a pesquerías que usan redes agalleras. La proporción de poblaciones que sufren mortalidad por capturas fue menor en el Golfo de México y Hawai, donde hay pocas pesquerías que usan redes agalleras. Las capturas estimadas excedieron los límites de remoción en 29% de las poblaciones del Atlántico, 14% de los del Pacífico, 8% de los de Alaska, 7% de los del Golfo de México y 0% de los de Hawai. Veintiocho de estas poblaciones se consideran amenazados o en peligro según el Acta de Especies Amenazadas de los Estados Unidos. La mayoría de las poblaciones de ballenas Mysticeti se están recobrando después del cese de las capturas comerciales. Muchas especies de cetáceos pelágicos, incluyendo las ballenas picudas y los cachalotes, son vulnerables a la mortalidad en pesquerías que usan redes de arrastre. La mayoría de las poblaciones de pinípedos experimentan capturas, pero ninguna de estas capturas exceden los límites de remoción y todas las poblaciones de pinípedos en las costas continentales de los Estados Unidos están incrementando su abundancia. Se dispone de datos cuantitativos de tendencias en la abundancia para pocas poblaciones de cetáceos, señalando la dificultad de monitorear tendencias en estas especies. Estas evaluaciones de poblaciones pueden mejorar en gran medida el entendimiento del estado de los mamíferos marinos en los Estados Unidos, pero aún persisten lagunas en la información, especialmente en lo referente a la estructura de poblaciones y la posible mortalidad en pesquerías no monitoreadas. Paper submitted February 22, 1999; revised manuscript accepted November 24, 1999. 929 Conservation Biology, Pages 929–940 Volume 14, No. 4, August 2000 930 Status of Marine Mammals in the United States Introduction The territorial waters of the United States harbor a diverse assemblage of marine mammals, including pinnipeds, manatees, sea otters, polar bears, mysticetes, and odontocetes. More than 60 species—approximately half the world’s marine mammal species diversity—occur in these waters (Barlow et al. 1997; Hill et al. 1997; Waring et al. 1997). Marine mammals have been protected under U.S. law since passage of the Marine Mammal Protection Act (MMPA) in 1972. Until recently, however, most applied research focused on a relatively small number of species also listed under the U.S. Endangered Species Act (ESA). Thus, although marine mammals have been protected for more than 25 years, it has not been possible to conduct a comprehensive assessment of their status and the effects of this legal protection. The goal of the MMPA is that marine mammals “. . . should not be permitted to diminish beyond the point at which they cease to be a significant functioning element in the ecosystem of which they are a part, and, consistent with this major objective, they should not be permitted to diminish below their optimum sustainable population” (16 U.S.C. 1361 Sec. 2.). The National Marine Fisheries Service has interpreted “optimum sustainable population” as “a population size which falls within a range from the population level of a given species or stock which is the largest supportable within the ecosystem to the population level which results in maximum net productivity” (50 C.F.R. 216.3). Therefore, a population is designated as “depleted” under the MMPA if it is estimated to be below its maximum net productivity level—the population size that provides “the greatest net annual increment in population numbers or biomass resulting from additions to the population due to reproduction and/or growth less losses due to natural mortality” (50 C.F.R. 216.3). Estimating maximum net productivity levels for populations of marine mammals has proven extremely difficult, even when extensive demographic data are available (e.g., Ragen 1995). It is generally accepted that the maximum net productivity level of most marine mammals falls between 50% and 80% of carrying capacity and is more likely to occur in a range of 50-70% (Taylor & DeMaster 1993). It is often difficult to assess the status of a population relative to maximum net productivity level, however, because of problems estimating carrying capacity and historical levels of exploitation. Prior to 1994, for example, maximum net productivity level was estimated for only a handful of marine mammal populations, and only four stocks were designated as depleted without also being listed as endangered or threatened under the ESA. The 1994 amendments to the MMPA require an assessment of the status of every marine mammal stock in U.S. waters. The Act defines a stock as “a group of marine Conservation Biology Volume 14, No. 4, August 2000 Read & Wade mammals of the same species or smaller taxa in a common spatial arrangement, that interbreed when mature” (16 U.S.C. 1361 Sec. 3). Stock assessment reports must include information on stock structure, abundance, trends, the sources and magnitude of anthropogenic mortality and serious injury (for brevity, referred to here as takes), and an evaluation of whether the level of takes is greater than the potential biological removal level, a limit specified under the MMPA. The reports are drafted by the National Marine Fisheries Service and the U.S. Fish and Wildlife Service and are reviewed by three regional scientific review groups (Atlantic, Pacific, and Alaska), also established under the 1994 amendments. After this peer review and a public comment period, the reports are revised and published as a formal assessment of the status of marine mammal stocks under the MMPA (Barlow et al. 1997; Hill et al. 1997; Waring et al. 1997). The stock assessments are then revised and updated on a regular schedule. Under the 1994 amendments, the maximum allowable annual removal limit for each stock of marine mammals is referred to as the potential biological removal level, or PBR. The PBR is defined as the product of a conservative estimate of abundance (Nmin), one-half the maximum rate of per capita net production, and a recovery factor, ranging from 0.1 to 1.0. Wade (1998) described an objective method for estimating Nmin and setting the recovery factor. By this method, Nmin is calculated as the twentieth percentile estimate of abundance from a lognormal distribution, and the recovery factor is determined by the status of the stock (endangered, threatened, depleted, unknown, etc.). Marine mammal stocks for which takes exceed PBR are designated as strategic. Once a stock is declared strategic, management actions must be formulated to reduce levels of mortality and serious injury to below PBR. Stocks listed as endangered or threatened under the ESA, or depleted under the MMPA, are automatically considered strategic. In anticipation of the 1994 amendments, and subsequent to their being signed into law, the National Marine Fisheries Service and U.S. Fish and Wildlife Service conducted a significant amount of research to estimate the abundance, stock structure, and level of human-caused mortality of marine mammals. Much of this information is summarized in the published stock assessment reports. This research provided an opportunity, for the first time, to summarize the status of all stocks of marine mammals in U.S. waters. Drawing from recent stock assessment reports, we provide a review of the current status of marine mammals in the United States. We describe levels of takes, trends in abundance, and status of marine mammals, and we compare these variables among taxa and regions. To better interpret differences, we also examined regional and taxonomic patterns in the level of takes in commercial fisheries. Read & Wade Status of Marine Mammals in the United States 931 Methods Results We obtained information from published marine mammal stock assessment reports (Barlow et al. 1997; Hill et al. 1997; U.S. Fish and Wildlife Service 1997; Waring et al. 1997). For each stock, the information included whether takes were documented, whether the takes exceeded the estimated PBR, and whether the stock was designated as strategic or not. The stock assessment reports include trends in abundance, but the reports have not followed consistent criteria in reporting trends because no management action is tied to their existence. Therefore, we needed to interpret the reports to determine whether or not a trend in abundance had been documented. Our criteria for evidence of a conclusive trend (increasing, stable, or decreasing) was either a quantitative estimate provided in the report or citation of a published reference documenting a quantitative trend. We did not include qualitative conclusions made in the reports. We used the existence of takes, their magnitude, and trends in abundance to define the status of each stock. We tested whether significant differences existed in the status of stocks among regions and taxa. In each case, we conducted a contingency-table analysis using a chisquare test statistic. For the taxonomic comparison, we contrasted the status of cetaceans to that of pinnipeds, with null hypotheses of no differences in the proportion of stocks having (1) takes, (2) takes greater than PBR, and (3) trends in abundance. We did not compare the status of other marine mammals (manatees, polar bears, and sea otters) because of the limited number of these stocks. We examined regional patterns by grouping stocks into five geographic areas: Atlantic, Gulf of Mexico, Pacific, Hawaii, and Alaska. In cases where the distribution of a stock spanned more than one region, we followed the convention of the published stock assessment reports, which assign each stock to one area. To determine whether take levels exceed PBR, a quantitative estimate of anthropogenic mortality and serious injury is required for each stock. As noted below, most takes occur as incidental mortality in commercial fishing operations, except in Alaska. The MMPA requires that each commercial fishery operating in the United States be placed in one of three categories, reflecting the magnitude of incidental mortality in that fishery. Under this scheme, a fishery has (I) frequent, (II) occasional, or (III) a remote likelihood of or no known incidental mortality and serious injury of marine mammals during the course of its operations. We obtained information from the 1997 List of Fisheries on the number of category I, II, and III fisheries in each region (50 C.F.R. 229) and on whether or not independent observers had been placed on vessels to collect data on the frequency of marine mammal takes. A total of 153 stocks of marine mammals has been defined in the United States (Appendix). Multiple stocks have been identified for species such as harbor seals, harbor porpoises, and bottlenose dolphins. In contrast, several species of beaked whales are lumped into single stocks in both the Atlantic and Pacific due to the difficulty of differentiating these species at sea. Most stocks of marine mammals experienced some level of anthropogenic mortality and serious injury. With the exception of aboriginal harvests in Alaska, these takes occurred primarily in commercial fishing operations. Only 19 stocks, however, experienced takes that exceeded their estimated PBR level (Table 1). Takes of these 19 stocks occurred primarily in gill net fisheries and, to a lesser extent, from collisions with vessels. The subsistence harvest of three Alaskan stocks also exceeded their estimated PBR level. In addition, 28 stocks were listed as threatened or endangered under the ESA. A few stocks were considered strategic because the exact magnitude of takes was unknown, but likely exceeded PBR. A greater proportion of pinniped stocks experienced takes than cetacean stocks ( p , 0.01; Table 2). All but one pinniped stock experienced some level of anthropogenic mortality and serious injury, but only 58% of cetacean stocks were subjected to takes. Only two pinniped stocks, but 15 cetacean stocks, experienced takes greater than PBR. Most baleen whales are also listed as endangered or threatened under the ESA, but few odontocete or pinniped stocks are listed. Most coastal marine mammals experienced takes in commercial fishing operations. Surprisingly, however, many pelagic cetaceans, including sperm whales and beaked whales, were taken in pelagic drift net fisheries. Large takes of marine mammals occurred in pelagic drift net fisheries off both the Atlantic and Pacific coasts. Quantitative trends in abundance were available more frequently for pinnipeds than for cetaceans ( p , 0.01; Table 2). All 11 pinniped stocks along the mainland United States coast are increasing. Only three pinniped stocks (western Steller sea lions, Gulf of Alaska harbor seals, and Hawaiian monk seals) were described as decreasing. Trend data were available for seven mysticetes, all of which are increasing. Little information was available on trends in abundance for odontocetes: of 100 stocks, 4 are known to be increasing in abundance, 2 are decreasing, and 4 are stable. Trend data were also available for 5 other stocks (1 manatee, 3 sea otter, and 1 polar bear), all known to be increasing. Of the 37 marine mammal stocks for which clear quantitative trend data existed, 27 are increasing, 5 are decreasing, and 5 are stable. In two other pinniped stocks (eastern Steller sea lions and southeast Alaska harbor seals), the trend data were unclear because some rookeries were increasing, whereas others were stable or decreasing. Conservation Biology Volume 14, No. 4, August 2000 932 Status of Marine Mammals in the United States Read & Wade Table 1. Marine mammal stocks from the United States for which anthropogenic mortality and serious injury (takes) exceed potential biological removal (PBR), a removal limit set under the U.S. Marine Mammal Protection Act.a PBR b Stock Right whale, western North Atlantic Average annual take b 0 2 Cuvier’s beaked whales, western North Atlantic Mesoplodon beaked whales, western North Atlantic Short-finned pilot whale, western North Atlantic Common dolphin, western North Atlantic Atlantic spotted dolphin, western North Atlantic Pantropical spotted dolphin, western North Atlantic Bottlenose dolphin, Coastal Migratory Harbor porpoise, Gulf of Maine Manatee, Floridac 9 9 4 155 16 16 25 483 n.e. 10 10 42 234 22 22 29 1,834 n.e. Manatee, Antilleanc n.e. n.e. Humpback whale, California/Oregon/Washington/Mexico Minke whale, California/Oregon/Washington Sperm whale, California/Oregon/Washington Mesoplodon beaked whales, California/Oregon/Washington Short-finned pilot whale, California/Oregon/Washington Beluga whale, Cook Inlet Steller sea lion, Western United States 1 1 2 11 6 15 383 2 1 4 13 13 40 447 Harbor seal, Gulf of Alaska 673 886 Primary source of mortality collision with large vessels/ entanglements pelagic drift nets pelagic drift nets pelagic drift nets pelagic drift nets pelagic drift nets pelagic drift nets gill nets gill nets collisions with small watercraft collisions with small watercraft pelagic drift nets pelagic drift nets pelagic drift nets pelagic drift nets pelagic drift nets subsistence harvest subsistence harvest/ fisheries subsistence harvest/ fisheries a Information is taken from Barlow et al. (1997), Hill et al. (1997), U.S. Fish and Wildlife Service (1997), and Waring et al. (1997). Values are rounded to the nearest integer. c PBR and average annual take levels were not estimated (n.e.) for the two manatee stocks, but in both cases takes exceed removal limits recommended by the U.S. Fish and Wildlife Service. b There were significant differences among regions in the proportion of stocks with takes ( p , 0.01; Table 2). The Atlantic, Pacific, and Alaska regions had a high proportion of stocks with takes, but few stocks in the Gulf of Mexico and Hawaii experienced takes. There was also a significant regional difference in the proportion of stocks with takes greater than PBR ( p , 0.05). Takes exceeded PBR for nine stocks in the Atlantic, five in the PaTable 2. cific, three in Alaska, two in the Gulf of Mexico, and zero in Hawaii. Most estimates of trends in abundance were from stocks in the Pacific and Alaska regions. There was a significant difference in the occurrence of category I and II fisheries among regions ( p , 0.05; Table 3). These fisheries occurred most frequently in the Atlantic, Pacific, and Alaska regions and seldom or not at all in the Gulf of Mexico or Hawaii. Four of the six cate- Taxonomic and regional analysis of the status of marine mammal stocks in the United States.a Taxon Stocks Stocks with takes Stocks with takes greater than PBR b Stocks with trend data Strategic stocksc Stocks listed under ESA 23 100 23 7 31 28 37 20 37 153 12 (0.52) 60 (0.60) 22 (0.96) 7 (1.00) 26 (0.84) 12 (0.43) 30 (0.81) 3 (0.15) 30 (0.81) 101 (0.66) 3 (0.13) 12 (0.12) 2 (0.09) 2 (0.29) 9 (0.29) 2 (0.07) 5 (0.14) 0 (0.00) 3 (0.08) 19 (0.12) 7 (0.30) 10 (0.10) 17 (0.74) 5 (0.71) 6 (0.19) 1 (0.04) 18 (0.49) 1 (0.05) 13 (0.35) 39 (0.26) 17 (0.74) 22 (0.22) 5 (0.22) 3 (0.43) 16 (0.52) 7 (0.25) 10 (0.27) 4 (0.20) 10 (0.27) 47 (0.31) 16 (0.70) 5 (0.05) 4 (0.17) 3 (0.43) 6 (0.19) 3 (0.11) 7 (0.19) 4 (0.20) 8 (0.22) 28 (0.18) Mysticetes Odontocetes Pinnipeds Other d Atlantic Gulf of Mexico Pacific Coast Hawaii Alaska Total a The proportion of stocks in each category is presented in parentheses. Potential biological removal (PBR) is a take limit specified under the U.S. Marine Mammal Protection Act. c Strategic stocks include, but are not limited to, those for which takes exceed PBR or are listed as endangered or threatened under the Endangered Species Act or as depleted under the Marine Mammal Protection Act. d Other taxa include two stocks of manatees, three stocks of sea otters, and two stocks of polar bears. b Conservation Biology Volume 14, No. 4, August 2000 Read & Wade Status of Marine Mammals in the United States Table 3. Regional incidence of fisheries in the United States that take marine mammals during the course of their operations. Category Region d Atlantic Gulf of Mexicod Pacific Coast Hawaii Alaska Total Ia II b II c 4 1 2 0 0 6 6 0 5 0 13 24 40 16 40 21 38 155 a Fisheries that frequently take marine mammals during the course of their operations. b Fisheries that occasionally take marine mammals during the course of their operations. c Fisheries that have a remote likelihood of taking marine mammals during the course of their operations. d The large pelagics longline fishery operates in both the Atlantic and Gulf of Mexico regions and so is counted twice. gory I fisheries employ gill or drift nets. The proportion of fisheries monitored with observer programs also differed significantly among regions ( p , 0.05). In particular, only 1 of the 13 category II fisheries in Alaska was monitored. Discussion Our analysis suggests that, in general, the Marine Mammal Protection Act and Endangered Species Act have been successful in protecting and enhancing the recovery of populations of marine mammals in the United States. After 25 years of protection, most pinnipeds are recovering from past unregulated takes in commercial fisheries or historical harvests. Likewise, most baleen whales are increasing now that they have been protected from harvest. The continued population growth of the eastern North Pacific gray whale stock and its removal from the List of Threatened and Endangered Wildlife in 1994 is a good example of the success of this protection (Hill et al. 1997). Only 12% of marine mammal stocks experience anthropogenic mortality and serious injury that exceed PBR. This generally positive assessment does not mean that problems do not exist. Serious conservation problems remain with several stocks of marine mammals, and many others are of uncertain status. Future research should address those stocks for which serious management issues remain. A particular advantage of the current stock assessment process is that management efforts are directed toward those stocks in need of attention, either from field research required to elucidate information on status or from direct management intervention when anthropogenic mortality exceeds PBR. We found important regional differences in the status of marine mammal stocks. Marine mammal stocks in the 933 Atlantic, Pacific, and Alaska experience takes that are more frequent and of greater magnitude than stocks in the Gulf of Mexico or Hawaii. In general, this pattern is correlated with regional variation in the prevalence of set-gill-net and drift-net fisheries. In areas where these fisheries are absent or rare, levels of anthropogenic mortality and serious injury are generally low. An obvious exception to this pattern is Alaska, where all pinniped stocks and several cetacean stocks are harvested for subsistence purposes by native Alaskans. Many coastal stocks of pinnipeds and cetaceans in Alaska are also subjected to takes in commercial fisheries. Because so few fisheries have been monitored in Alaska, however, we do not know the magnitude of these takes. Therefore, although only a few stocks in Alaska had takes greater than PBR, this result should be considered uncertain pending observations of the many category II gill-net fisheries in that area. We also found taxonomic differences in the status of marine mammals in the United States. In general, a higher proportion of pinniped stocks experience takes than do stocks of cetaceans. This is due partly to the coastal habitat of most pinniped species, at least during some portion of their life cycle. Perhaps more important, many pinniped stocks occur in areas where gill-net fisheries occur. For example, there are 11 stocks of pinnipeds on the Atlantic and Pacific coasts, where gill-net fisheries are common; 10 of these stocks experience takes. In contrast, there are 19 stocks of cetaceans in Hawaii, where gill-net fisheries are rare, and only 2 of these stocks experience takes. Despite the frequent takes of pinnipeds in gill-net fisheries, most pinniped stocks are increasing in abundance, at least along the coasts of contiguous United States. Data on trends in abundance were available for only one-quarter of marine mammal stocks. This finding underscores previous arguments that it is unwise to link the need for management action to the documentation of a negative trend in abundance. It is difficult to document such trends because of the time required to obtain a series of reliable abundance estimates and the limited statistical power of trend analyses ( Taylor & Gerrodette 1993). In particular, little information was available on trends of odontocetes, because it is difficult to obtain precise estimates of abundance for these animals. In contrast, trend indices were available for most stocks of pinnipeds, usually in the form of annual pup counts made when adult females and their young are on shore. Despite these limitations, over 80% of stocks for which trend data were available are either increasing or stable, which reinforces the conclusion that the MMPA and ESA have been effective in promoting the recovery and protection of marine mammals in the United States. The adoption of explicit removal limits (PBRs) has greatly facilitated assessment of status. The current stock assessment process is much more tractable than the pre- Conservation Biology Volume 14, No. 4, August 2000 934 Status of Marine Mammals in the United States vious scheme, which required determination of maximum net productivity levels. The amendments also require that each stock assessment be updated on a regular basis, so new information on the status of marine mammals will be incorporated as it becomes available. Assessments of strategic stocks are reviewed annually, and those of other stocks are reviewed every 3 years (Wade & Angliss 1997). This requirement ensures that the stock assessment reports continue to provide current information on the status of marine mammals and at the same time provide a growing time series of data for each stock. Several methodological problems remain unresolved in the stock assessment process and many stock assessments are incomplete or based on fragmentary data (Wade & Angliss 1997). For example, some species, such as beaked whales, are difficult to distinguish during abundance surveys and are lumped together in the assessments. Abundance estimates for most deep-diving species, such as sperm whales, are negatively biased because adequate correction factors have not been developed to account for their diving behavior. Stock definition is problematic in species that have large geographical ranges. Bottlenose dolphins, for example, are distributed continuously along the coastline from the Mexican border to North Carolina. Improved resolution of stock structure in this and other widely distributed species is required for adequate management. In addition, the geographic range of many pelagic species extends into the territorial waters of Canada or Mexico, complicating assessment of their status. Finally, it is difficult and often prohibitively expensive to monitor all commercial fisheries with the potential to take marine mammals during the course of their operations. In some cases, the cost of such programs approaches or exceeds the value of the fisheries themselves. The large number of unmonitored category II fisheries in Alaska, for example, is a reminder of the large amount of work yet to be performed. Several marine mammal stocks continue to face critical conservation issues. These issues fall into the two general categories of conservation problems defined by Caughley (1994): the paradigms of small and of declining populations. Under the first paradigm are several endangered marine mammals—Hawaiian monk seal, northern right whale, and Florida manatee—that exist only as small populations. These populations are not recovering, despite 25 years of legal protection and intensive conservation efforts that continue today (Marine Mammal Commission 1998). In the case of monk seals and right whales, the anthropogenic threats are complex and difficult to resolve. In the case of the Florida manatee, the threat is well known, but the political will does not exist to implement effective conservation action (Marmontel et al. 1997). Several declining marine mammal stocks, such as the western Steller sea lion and harbor seal in the Gulf of Alaska, fall under the second Conservation Biology Volume 14, No. 4, August 2000 Read & Wade paradigm. Populations of these marine mammals are large but have declined for reasons that are not completely understood. The magnitude of known takes cannot explain the declines of these stocks. Investigations into possible contributing factors, such as oceanographic changes, entanglement in fishing debris, and ecological interactions with commercial fisheries have not yet provided a comprehensive explanation for these trends. Both categories of conservation problems will pose significant challenges to managers and conservation biologists in the next century. Another issue of widespread conservation significance is the entanglement of small cetaceans in set-gill-net and drift-net fisheries. In many areas, the mortality of dolphins, porpoises, and small whales exceeds PBR. To date, four take reduction teams have addressed this issue for a variety of small cetacean stocks. These teams, mandated under the 1994 amendments to the Marine Mammal Protection Act, are composed of stakeholders and charged with reducing take levels to below PBR. Unfortunately, the causes of entanglement are poorly understood, hampering efforts to develop effective solutions. To date, the approaches recommended by these take reduction teams and implemented by the National Marine Fisheries Service include acoustic alarms placed on nets (Kraus et al. 1997), time and area fisheries closures (62 FR 43302), modification of fishing gear and practices (62 FR 43302), and even the closure of fisheries with high by-catch rates of marine mammals (62 FR 63467). It is too early to assess the relative merits of these strategies, but it seems likely that managers and conservation biologists will have to deal with the problem of entanglement of small cetaceans in gill-net fisheries for the foreseeable future. Several other conservation and management issues merit attention. First, the recovery of many pinniped species has led to robust and growing stocks along the Pacific coast and in New England. The growth of pinniped populations, coinciding with declines in fish stocks due to over-harvest and habitat degradation, has prompted the commercial fishing industry to call for reductions in the size of several pinniped stocks (Kronman 1996). These issues are particularly vexing in cases where pinnipeds prey on fish stocks listed as threatened or endangered under the ESA, such as many salmonids in the Pacific Northwest (National Marine Fisheries Service 1997). In most cases, however, ecological interactions between marine mammals and commercially valuable fish stocks are poorly understood, and further study is required to allow an objective evaluation of their nature. An obvious exception to this generalization is the well-known case of sea otter predation on shellfish populations in California ( Estes & VanBlaricom 1985). Second, as traditional fish stocks collapse, new fisheries develop to absorb existing harvesting capacity. These new fisheries often take large numbers of marine mam- Read & Wade mals. For example, the collapse of groundfish stocks in New England has led to the displacement of gill-net fishing effort in the coastal waters of mid-Atlantic states in recent years. This displaced effort caused a large increase in the by-catch of harbor porpoises in the midAtlantic (Waring et al. 1997). Thus, as measures were being developed to conserve groundfish and harbor porpoises in New England, by-catches of porpoises increased in gill-net fisheries off the mid-Atlantic coast. This problem could be ameliorated if there was better coordination between managers working to regulate commercial fisheries and those concerned with marine mammals and other protected species. Finally, the development and increasing human use of many coastal habitats is also of concern. In the southeastern United States, for example, coastal development is encroaching rapidly on the habitat of bottlenose dolphins and manatees. It is difficult to evaluate the chronic effects of habitat loss and degradation, but the increasing number of collisions between recreational boats and manatees in these areas is a clear result of this coastal development (Marmontel et al. 1997). Our analysis indicates that the Marine Mammal Protection Act and Endangered Species Act have generally been successful in promoting the protection and recovery of marine mammals in the United States. In particular, the 1994 amendments to the MMPA have improved our understanding of the status of marine mammal stocks. Nevertheless, important gaps remain in our knowledge of the status of many stocks, and several endangered species continue to decline or show no signs of recovery despite protective legislation and intensive conservation efforts. Research efforts should continue to focus on these information needs and to address the critical status of small and declining populations. Acknowledgments This analysis would not have been possible without the hard work of many biologists from the National Marine Fisheries Service and U.S. Fish and Wildlife Service. We acknowledge the contribution these individuals have made to the conservation of marine mammals in the United States. 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Conservation Biology Volume 14, No. 4, August 2000 936 Status of Marine Mammals in the United States Read & Wade Appendix List of marine mammal stocks used in our analysis of the status of marine mammals in the United States.a Stock Right whale, western North Atlantic Humpback whale, western North Atlantic Fin whale, western North Atlantic Sei whale, western North Atlantic Minke whale, western North Atlantic Blue whale, western North Atlantic Sperm whale, western North Atlantic Dwarf sperm whale, western North Atlantic Pygmy sperm whale, western North Atlantic N. bottlenose whale, western North Atlantic Cuvier’s beaked whales, western North Atlantic Mesoplodon beaked whales, western North Atlantic Killer whale, western North Atlantic Pygmy killer whale, western North Atlantic Risso’s dolphin, western North Atlantic Pilot whale, long-finned, western North Atlantic Pilot whale, short-finned, western North Atlantic White-sided dolphin, western North Atlantic White-beaked dolphin, western North Atlantic Common dolphin, western North Atlantic Atlantic spotted dolphin, western North Atlantic Pantropical spotted dolphin, western North Atlantic Striped dolphin, western North Atlantic Spinner dolphin Bottlenose dolphin, offshore Bottlenose dolphin, coastal migratory Harbor porpoise, Gulf of Maine Harbor seal, western North Atlantic Gray seal, northwestern North Atlantic Harp seal, northwestern North Atlantic Hooded Seal, northwest North Atlantic Bryde’s whale, northern Gulf of Mexico Sperm whale, northern Gulf of Mexico Dwarf sperm whale, northern Gulf of Mexico Region b Takes c Takes .PBR d Trend e ESA f MMPA g Eubalaena glacialis ATL Y Y + E S Megaptera novaeangliae Balaenoptera physalus Balaenoptera borealis Balaenoptera acutorostrata Balaenoptera musculus Physeter macrocephalus ATL ATL ATL ATL ATL ATL Y Y Y Y + E E E S S S E E S S Kogia simus ATL Y S Kogia breviceps ATL Y S Hyperoodon ampullatus ATL Ziphius cavirostris ATL Y Y S Mesoplodon spp. Orcinus orca ATL ATL Y Y S Feresa attenuata Grampus griseus ATL ATL Y Globicephala melaena ATL Y Globicephala macrorhynchus ATL Y Y S Lagenorhynchus acutus ATL Y Lagenorhynchus albirostris ATL Delphinus delphis ATL Y Y S Stenella frontalis ATL Y Y S Stenella attenuata ATL Y Y S Stenella coeruleoalba Stenella longirostris Tursiops truncatus Tursiops truncatus Phocoena phocoena Phoca vitulina ATL ATL ATL ATL ATL ATL Y Y Y Y Y Y Y Y D/S S Halichoerus grypus Phoca groenlandica Cystophora cristata ATL ATL ATL Y Y Y Balaenoptera edeni GOM Physeter macrocephalus GOM Kogia simus GOM Scientific name Y + + + + E S S continued Conservation Biology Volume 14, No. 4, August 2000 Read & Wade Status of Marine Mammals in the United States 937 Appendix (continued) Stock Pygmy sperm whale, northern Gulf of Mexico Cuvier’s beaked whale, northern Gulf of Mexico Blainville’s beaked whale, northern Gulf of Mexico Gervais’ beaked whale, northern Gulf of Mexico Bottlenose dolphin, outer Continental Shelf Bottlenose dolphin, continental shelf edge Bottlenose dolphin, western Gulf of Mexico coastal Bottlenose dolphin, northern Gulf of Mexico coastal Bottlenose dolphin, eastern Gulf of Mexico coastal Bottlenose dolphin, bay & sound coastal Atlantic spotted dolphin, northern Gulf of Mexico Pantropical spotted dolphin, northern Gulf of Mexico Striped dolphin, northern Gulf of Mexico Spinner dolphin, northern Gulf of Mexico Rough-toothed dolphin, northern Gulf of Mexico Clymene dolphin, northern Gulf of Mexico Fraser’s dolphin, northern Gulf of Mexico Killer whale, northern Gulf of Mexico False killer whale, northern Gulf of Mexico Pygmy killer whale, northern Gulf of Mexico Melon-headed whale, northern Gulf of Mexico Risso’s dolphin, northern Gulf of Mexico Short-finned Pilot Whale, northern Gulf of Mexico Manatee, Florida Manatee, Antillean Bryde’s whale, eastern Tropical Pacific Humpback whale, California/ Oregon/Mexico Fin whale, California/Oregon/ Washington Sei whale, eastern North Pacific Scientific name Region b Takes c Takes .PBR d Trend e ESA f MMPA g Kogia breviceps GOM S Ziphius cavirostris GOM Mesoplodon densirostris GOM Mesoplodon europaeus GOM Tursiops truncatus GOM Y Tursiops truncatus GOM Y Tursiops truncatus GOM Y Tursiops truncatus GOM Y Tursiops truncatus GOM Y Tursiops truncatus GOM Y Stenella frontalis GOM Y Stenella attenuata GOM Y Stenella coeruleoalba GOM Stenella longirostris GOM Steno bredanensis GOM Stenella clymene GOM Lagenodelphis hosei GOM Orcinus orca GOM Pseudorca crassidens GOM Feresa attenuata GOM Peponocephala electra GOM Grampus griseus GOM Y Globicephala macrorhynchus Trichechus manatus Trichechus manatus GOM GOM GOM Y Y Y Y Y + E E S S S Balaenoptera edeni PAC Megaptera novaeangliae PAC Y Y + E S Balaenoptera physalus Balaenoptera borealis PAC PAC Y + E E S S S continued Conservation Biology Volume 14, No. 4, August 2000 938 Status of Marine Mammals in the United States Read & Wade Appendix (continued) Stock Minke whale, California/Oregon/ Washington Blue whale, California/Mexico Sperm whale, California/Oregon/ Washington Dwarf sperm whale, California/ Oregon/Washington Pygmy sperm whale, California/ Oregon/Washington Mesoplodon beaked whale California/Oregon/Washington Baird’s beaked whale, California/ Oregon/Washington Cuvier’s beaked whale, California/ Oregon/Washington Killer whale, Eastern North Pacific southern resident Killer whale, California/Oregon/ Washington Pacific coast Risso’s dolphin, California/ Oregon/Washington Pilot whale, short-finned, California/Oregon/Washington Northern right whale dolphin, California/Oregon/Washington Pacific white-sided dolphin, California/Oregon/Washington Common dolphin, long-beaked, California Common dolphin, short-beaked, California/Oregon/Washington Striped dolphin, California/ Oregon/Washington Bottlenose dolphin, California coastal Bottlenose dolphin, California/ Oregon/Washington offshore Dall’s porpoise, California/ Oregon/Washington Harbor porpoise, inland Washington Harbor porpoise, Oregon/ Washington coast Harbor porpoise, Central California Harbor porpoise, Northern California Harbor seal, Oregon/Washington coast Harbor seal, inland Washington Harbor seal, California Northern elephant seal California sea lion Northern fur seal, San Miguel Island Guadalupe fur seal Sea otter, Washington Sea otter, California Fin whale, Hawaii Bryde’s whale, Hawaii Takes .PBR d Trend e ESA f MMPA g + E S S E S Region b Takes c Balaenoptera acutorostrata Balaenoptera musculus PAC PAC Y Y Y Physeter macrocephalus PAC Y Y Kogia simus PAC Kogia breviceps PAC Y Mesoplodon spp. PAC Y Berardius bairdii PAC Y Ziphius cavirostris PAC Y Orcinus orca PAC Orcinus orca PAC Y Grampus griseus PAC Y Globicephala macrorhynchus PAC Y Lissodelphis borealis PAC Y Lagenorhynchus obliquidens PAC Y Delphinus capensis PAC Y + Delphinus delphis PAC Y + Stenella coeruleoalba PAC Y Tursiops truncatus PAC Tursiops truncatus PAC Y Phocoenoides dalli PAC Y Phocoena phocoena PAC Y Phocoena phocoena PAC Y Phocoena phocoena PAC Y Phocoena phocoena PAC Phoca vitulina Phoca vitulina Phoca vitulina Mirounga angustirostris Zalophus californianus Callorhinus ursinus Arctocephalus townsendi Enhydra lutris Enhydra lutris Balaenoptera physalus Balaenoptera edeni PAC PAC PAC PAC PAC PAC PAC PAC PAC HAW HAW Scientific name Y S + Y S – – 0 Y Y Y Y Y Y Y Y + + + + + + + + + T S T E S S continued Conservation Biology Volume 14, No. 4, August 2000 Read & Wade Status of Marine Mammals in the United States 939 Appendix (continued) Stock Blue whale, Hawaii Sperm whale, Hawaii Dwarf sperm whale, Hawaii Pygmy sperm whale, Hawaii Cuvier’s beaked whale, Hawaii Blainville’s beaked whale, Hawaii Killer whale, Hawaii Pantropical spotted dolphin, Hawaii False killer whale, Hawaii Pygmy killer whale, Hawaii Pilot whale, short-finned, Hawaii Risso’s dolphin, Hawaii Melon-headed whale, Hawaii Rough-toothed dolphin, Hawaii Spinner dolphin, Hawaii Striped dolphin, Hawaii Bottlenose dolphin, Hawaii Hawaiian monk seal, Hawaii Humpback whale, western North Pacific Humpback whale, central North Pacific Northern right whale, North Pacific Gray whale, eastern Pacific Minke whale, Alaska Bowhead whale, western Arctic Fin whale, northeastern Pacific Sperm whale, North Pacific Baird’s beaked whale Stejneger’s beaked whale Cuvier’s beaked whale Killer whale, eastern North Pacific transient Killer whale, eastern North Pacific northern resident Pacific white-sided dolphin, North Pacific Beluga whale, Beaufort Sea Beluga whale, eastern Chukchi Sea Beluga whale, eastern Bering Sea Beluga whale, Bristol Bay Beluga whale, Cook Inlet Dall’s porpoise, Alaska Harbor porpoise, southeastern Alaska Harbor porpoise, Gulf of Alaska Harbor porpoise, Bering Sea Northern fur seal Ribbon seal Ringed seal Spotted seal Steller sea lion, eastern U.S. Steller sea lion, western U.S. Takes c Takes .PBR d Trend e Scientific name Region b Balaenoptera musculus Physeter macrocephalus Kogia simus Kogia breviceps Ziphius cavirostris Mesoplodon densirostris Orcinus orca Stenella attenuata Pseudorca crassidens Feresa attenuata Globicephala macrorhynchus Grampus griseus Peponocephala electra Steno bredanensis Stenella longirostris Stenella coeruleoalba Tursiops truncatus Monachus schauinslandi HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW HAW Megaptera novaeangliae ALA Megaptera novaeangliae Eubalaena glacialis Eschrichtius robustus Balaenoptera acutorostrata Balaena mysticetus Balaenoptera physalus Physeter macrocephalus Berardius bairdii Mesoplodon stejnegeri Ziphius cavirostris ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA Y Y Y + Y + Orcinus orca ALA Y Orcinus orca ALA Y Lagenorhynchus obliquidens Delphinapterus leucas Delphinapterus leucas Delphinapterus leucas Delphinapterus leucas Delphinapterus leucas Phocoenoides dalli Phocoena phocoena Phocoena phocoena Phocoena phocoena Callorhinus ursinus Phoca fasciata Phoca hispida Phoca largha Eumetopias jubatus Eumetopias jubatus ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA ALA Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y ESA f MMPA g E E S S E S E S E E S S E E E S S S Y Y Y – + 0 Y Y 0 0 S 0 D/S +/0/– – T E S S continued Conservation Biology Volume 14, No. 4, August 2000 940 Status of Marine Mammals in the United States Read & Wade Appendix (continued) Stock Bearded seal Harbor seal, southeastern Alaska Harbor seal, Gulf of Alaska Harbor seal, Bering Sea Walrus Sea otter, Alaska Polar Bear, Chukchi-Bering Sea Polar Bear, Beaufort Sea a Scientific name Erignathus barbatus Phoca vitulina Phoca vitulina Phoca vitulina Odobenus rosmarus Enhydra lutris Ursus maritimus Ursus maritimus Region b Takes c ALA ALA ALA ALA ALA ALA ALA ALA Y Y Y Y Y Y Y Y Takes .PBR d Trend e Y 0/+ – ESA f MMPA g + + Information is taken from Barlow et al. (1997), Hill et al. (1997), U.S. Fish and Wildlife Service (1997), and Waring et al. (1997). Region to which stock was assigned for analysis of geographical variation in status: ATL, Atlantic; GOM, Gulf of Mexico; PAC, Pacific; HAW, Hawaii; or ALA, Alaska. c Presence (Y) of documented anthropogenic mortality or serious injury. d Take levels in excess of potential biological removal (PBR) (Y). e Quantitative data indicating positive (1), negative (2), or stable (0) trend in abundance. f Listed as endangered (E) or threatened (T) under the U.S. Endangered Species Act. g Considered depleted (D) or strategic (S) under the U.S. Marine Mammal Protection Act. b Conservation Biology Volume 14, No. 4, August 2000