Conservation of the vaquita Phocoena sinus

• 1 The vaquita Phocoena sinus is a small porpoise that is endemic to the northern Gulf of California, Mexico. It is the most critically endangered marine small cetacean in the world. The most precise estimate of global abundance based on a 1997 survey is 567 (95% CI 177–1073).
• 2 Vaquitas mainly live north of 30°45′N and west of 114°20′W. Their ‘core area’ consists of about 2235 km² centred around Rocas Consag, 40 km east of San Felipe, Baja California. Genetic analyses and population simulations suggest that the vaquita has always been rare, and that its extreme loss of genomic variability occurred over evolutionary time rather than being caused by human activities.
• 3 Gill nets for fish and shrimp cause very high rates of by‐catch (entanglement) of vaquitas. Estimates of bycatch rates are from 1993–94 and refer to one of three main fishing ports: 84 per year (95% CI 14–155) using only data collected by observers and 39 per year (95% CI 14–93) using combined data from observers and interviews with fishermen. Boats from other ports may experience similar rates, and the total is probably well above what would be sustainable.
• 4 Other less well‐characterized and longer‐term risk factors include the potential for disturbance by trawling to affect vaquita behaviour, and the uncertain effects of dam construction on the Colorado River and the resultant loss of freshwater input to the upper Gulf. However, entanglement is the clearest and most immediate concern.
• 5 Progress towards reducing entanglement has been slow in spite of efforts to phase out gill nets in the vaquita’s core range, and the development of schemes involving compensation for fishermen. The Biosphere Reserve in the northern Gulf has fallen far short of its potential for vaquita conservation. On 29 December 2005, the Mexican Ministry of Environment declared a Vaquita Refuge that contains within its borders the positions of approximately 80% of verified vaquita sightings. In the same decree, the state governments of Sonora and Baja California were offered $1 million to compensate affected fishermen. The effectiveness of this major initiative remains to be seen.
• 6 The vaquita’s survival does not depend on more or better science but on improved management. As a funding priority, implementation of conservation measures and evaluation of their effectiveness should come ahead of more surveys or improved estimation of by‐catch.

     

Estimating the success of protected areas for the vaquita,Phocoena sinus

Bycatch in artisanal gill nets threatens the vaquita, Phocoena sinus, with extinction. In 2008 the Mexican government announced a conservation action plan for this porpoise, with three options for a protected area closed to gill net fishing. The probability of success of each of the three options was estimated with a Bayesian population model, where success was defined as an increase in vaquita abundance after 10 yr. The model was fitted to data on abundance, bycatch, and fishing effort, although data were sparse and imprecise. Under the first protected area option, the existing Refuge Area for the Protection of the Vaquita, bycatch was about 7% of population size, and probability of success was 0.08. Under the second option with a larger protected area, the probability of success was 0.35. The third option was large enough to eliminate vaquita bycatch and had a probability of success >0.99. Probability of success was reduced if elimination of vaquita bycatch was delayed or incomplete. Despite considerable efforts by the Mexican government to support vaquita conservation, abundance will probably continue to decline unless additional measures to reduce vaquita bycatch are taken, such as banning gill nets within the vaquita's range and developing effective alternative fishing gear.     

Phylogenetic Relationships among the True Porpoises (Cetacea: Phocoenidae)

Portions of the cytochrome b gene and control region of the mitochondrial DNA molecule were sequenced to investigate systematic relationships among the six extant species of true porpoises, (Cetacea: Phocoenidae). Phylogenetic analyses of mitochondrial cytochrome b sequences support a close relationship between Burmeister′s porpoise, Phocoena spinipinnis, and the vaquita, Phocoena sinus, and the association of these two species with the spectacled porpoise, Australophocaena dioptrica. The latter result is not in concordance with a recent morphological reclassification which groups A. dioptrica with Dall′s porpoise, Phocoenoides dalli, in the subfamily Phocoenoidinae. The molecular analysis found no support for this grouping. A dioptrica was originally described as a member of the genus Phocoena, and our results support returning it to that genus at this time. Finally, the data suggest that the tropical species Neophocaena phocaenoides, the finless porpoise, may represent the most basal member of the family. The control region sequences corroborated the relationships among the closely related taxa P. sinus, P. spinipinnis, and A. dioptrica, but were unable to resolve the deeper branches of the tree, probably as a result of a high level of saturation of these sequences.     

Sexual dimorphism and developmental patterns in the external morphology of the vaquita,Phocoena sinus

A total of 56 vaquitas (Phocoena sinus) were examined to evaluate their sexual dimorphism and isometric and/or allometric growth in 35 external characteristics. Absolute and relative (to total length) measurements and growth rates were compared between sexually immature and mature females and males. T‐tests and analysis of variance (ANOVA) and covariance (ANCOVA) were used to evaluate sexual dimorphism. Sexual dimorphism in the vaquita was detected in the total length, head region (from blowhole to tip of upper jaw), anterior section of the body (from dorsal fin to tip of upper jaw), dorsal fin and the genital and anal regions. Fluke width is relatively larger in mature males than immature males, but in females this relative metric does not change during their development. In addition, males present a higher dorsal fin. These somatic changes are probably related to the swimming capacity (speed, agility, maneuvering) during the breeding season and/or foraging activities. A linear model of growth was used to determine possible proportional changes with respect to total body length through the development of 33 external characteristics. The anterior region of the body and the flippers were relatively larger in immature individuals than in mature ones.     

Comparative anatomy of the bony labyrinth of extant and extinct porpoises (Cetacea: Phocoenidae)

The inner ear anatomy of cetaceans, now more readily accessible by means of nondestructive high‐resolution X‐ray computed tomographic (CT) scanning, provides a window into their acoustic abilities and ecological preferences. Inner ear labyrinths also may be a source for additional morphological characters for phylogenetic analyses. In this study, we explore digital endocasts of the inner ear labyrinths of representative species of extinct and extant porpoises (Mammalia: Cetacea: Phocoenidae), a clade of some of the smallest odontocete cetaceans, which produce some of the highest‐frequency clicks for biosonar and communication. Metrics used to infer hearing ranges based on cochlear morphology indicate that all taxa considered could hear high‐frequency sounds, thus the group had already acquired high‐frequency hearing capabilities by the Miocene (9–11 Mya) at the latest. Vestibular morphology indicates that extant species with pelagic preferences have similarly low semicircular canal deviations from 90°, values indicating more sensitivity to head rotations. Species with near‐shore preferences have higher canal deviation values, indicating less sensitivity to head rotations. Extending these analyses to the extinct species, we demonstrate a good match between those predicted to have coastal (such as Semirostrum cerutti) preferences and high canal deviation values. We establish new body length relationships based on correlations with inner ear labyrinth volume, which can be further explored among other aquatic mammals to infer body size of specimens consisting of fragmentary material.     

Life history of harbor porpoises (Phocoena phocoena) in Scottish (UK) waters

Life history parameters were determined for stranded and bycaught harbor porpoises (Phocoena phocoena) from Scottish (UK) waters (1992–2005). Fetal growth rate was 84.4 mm/mo and mean size at birth was 76.4 cm (range 65–88 cm). Males and females had a similar range of body lengths (65–170 cm and 66–173 cm, respectively), although asymptotic lengths were higher in females than males (approximately 158 cm and 147 cm, respectively). Nonpregnant females were significantly lighter, in relation to their length than males. Maximum estimated age was 20 yr for both sexes. Age at sexual maturity (ASM) was estimated as 4.35 yr in females and 5.00 yr in males. Conception occurred mainly in July and August although reproductively active males were recorded during April to July. Gestation lasted 10–11 mo, with calving mainly between May and July. Lactating females were recorded during June to November, while small calves with solid food in their stomachs were found mainly during February to May. Estimated pregnancy rate (0.34–0.40) is lower than recorded elsewhere, but is likely underestimated due to the prevalence of mature females of poor health status in the sample. Nevertheless, cetacean strandings can be an essential source of data on demographic parameters.     

A combined visual and acoustic estimate of 2008 abundance,and change in abundance since 1997, for the vaquita,Phocoena sinus

A line‐transect survey for the critically endangered vaquita, Phocoena sinus, was carried out in October–November 2008, in the northern Gulf of California, Mexico. Areas with deeper water were sampled visually from a large research vessel, while shallow water areas were covered by a sailboat towing an acoustic array. Total vaquita abundance in 2008 was estimated to be 245 animals (CV = 73%, 95% CI 68–884). The 2008 estimate was 57% lower than the 1997 estimate, an average rate of decline of 7.6%/yr. Bayesian analyses found an 89% probability of decline in total population size during the 11 yr period, and a 100% probability of decline in the central part of the range. Acoustic detections were assumed to represent porpoises with an average group size of 1.9, the same as visual sightings. Based on simultaneous visual and acoustic data in a calibration area, the probability of detecting vaquitas acoustically on the trackline was estimated to be 0.41 (CV = 108%). The Refuge Area for the Protection of the Vaquita, where gill net fishing is currently banned, contained approximately 50% of the population. While animals move in and out of the Refuge Area, on average half of the population remains exposed to bycatch in artisanal gill nets.     

Comparative morphology of porpoise (Cetacea: Phocoenidae) pterygoid sinuses: Phylogenetic and functional implications

High‐resolution X‐ray computed tomographic scans were used to examine pterygoid sinus morphology within extant porpoise species and one delphinid (Tursiops truncatus), in order to consider: 1) intraspecific and interspecific variation among the studied species; 2) the most parsimonious sequence of character acquisition; and 3) the potential functional roles of the preorbital lobes of the sinuses in sound reflection. Scans revealed that the pterygoid/palatine regions are mediolaterally broader in the earliest diverging phocoenid (Neophocaena phocaenoides) and Tursiops truncatus than the dorsoventrally elongated sinuses observed in other species. Rostrocaudal lengths of the sphenoidal regions of the sinuses in all individuals studied are proportionally similar, indicating conservatism in this region across species. The neonate Phocoena phocoena has shorter preorbital lobes than adults, but they are still proportionally longer than Neophocaena phocaenoides and Phocoena spinipinnis. The preorbital lobes broaden mediolaterally to varying degrees across species; in particular, Phocoenoides dalli has the largest dorsal and lateral expansion of this region. Assuming the highest pulse frequency produced by porpoises is 150 kHz, all regions of the preorbital lobes are thick enough to reflect the wavelengths produced. In addition, the neonate preorbital lobes are not as elongated as they are in adults, and the dorsal third of this region may not reflect sound to the same extent. This study reinforces the importance of using nondestructive methods to quantify variation in endocranial anatomy and the value of CT data for recovering phylogenetically useful information, as well as functional roles sinuses play in concert with the soft tissue head anatomy for biosonar. J. Morphol. 2013. © 2012 Wiley Periodicals, Inc.     

Development and rudimentation of the peripheral olfactory system in the harbor porpoise Phocoena phocoena (Mammalia: Cetacea)

Serial sections of 13 embryos and fetuses of the harbor porpoise from 10 mm crown-rump length up to 167 mm total length were studied. Unlike the adult animals, ontogenetic stages of 18–27 mm crown-rump length still show a typical mammalian olfactory bulb. The olfactory bulb primordium is penetrated by olfactory nerve fibers, the latter passing through the cribriform plate. However, the olfactory bulb anlage is gradually reduced in later stages, its placodal component being largely uncoupled from the telencephalon. As a ganglionlike structure, the remains of the placodal component stay in contact with the nasal septum and mucosa via thin bundles of nerve fibers. The ganglion and plexus can be traced within the meninges until the adult stage of the porpoise. There is strong evidence that they represent the material of the terminalis system, which cannot be distinguished from the olfactory system in earlier stages. A vomeronasal organ could not be detected in the embryonal and fetal material investigated.     

Identifying critical habitat of the endangered vaquita (Phocoena sinus) with regional δ13C and δ15N isoscapes of the Upper Gulf of California,Mexico

The vaquita (Phocoena sinus) is the world's most endangered cetacean and has experienced a 60% reduction in the size of its population in the past decade. Knowledge of its basic ecology is essential for developing successful management plans to protect and conserve this species. In this study, we identified vaquita foraging areas by creating an isoscape of the Upper Gulf of California (UGC) based on sediment and zooplankton carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values. Our results confirm that this species is confined to the western region of the UGC, which is characterized by relatively high δ¹⁵N values (sediments: 10.2‰ ± 2.0‰, zooplankton: 15.8‰ ± 1.3‰), higher sea surface temperatures (～16°C–25°C), higher concentrations of silt in sediments, and the highest turbidity. In contrast, the eastern region of the UGC had relatively low sediment (7.7‰ ± 2.4‰) and zooplankton (14.6‰ ± 1.0‰) δ¹⁵N values, and the highest concentrations of sand in sediments. Our approach is an effective use of marine isoscapes over a small spatial scale (<200 km) to identify the environmental characteristics that define the critical habitat for an extremely endangered marine mammal.     

Life history of Japanese Stypocaulon durum (Sphacelariales, Phaeophyceae)

Phenology, morphology, life history and responses to different temperature and photoperiod conditions were studied in Japanese Stypocaulon durum (Ruprecht) Okamura. Erect thalli of the species were collected year-round, but the mature thalli forming either uniloc-ular sporangia or two different types of plurilocular structures (evidently gametangia) on separate thalli were found only in winter. ln culture, an isomorphic life history is suggested for the species, alternating between a sporophyte forming unilocular sporangia and gam-etophytes forming plurilocular macro- (female) and micro- (male) gametangia. Contents of unilocular sporangia were not released, but germinated in situ, developing into erect thalli forming plurilocular gametangia. Macrogametangia released aplanogametes (oospores), but male gametangia appeared to be non-functional, although flagellated cells were once formed in the loc-uli. This is the first report of plurilocular gametangia in the species. Although the species grew well and matured under considerably lower temperature conditions than European Stypocaulon scoparium (L.) Sauvageau, its temperature requirements showed similarity to northwestern Atlantic Stypocaulon species. This supports the notion that northwestern Atlantic Stypocaulon is conspecific with S. durum.     

Exploring Trade-Offs between Fisheries and Conservation of the Vaquita Porpoise (Phocoena sinus) Using an Atlantis Ecosystem Model

Background

Minimizing fishery bycatch threats might involve trade-offs between maintaining viable populations and economic benefits. Understanding these trade-offs can help managers reconcile conflicting goals. An example is a set of bycatch reduction measures for the Critically Endangered vaquita porpoise (Phocoena sinus), in the Northern Gulf of California, Mexico. The vaquita is an endemic species threatened with extinction by artisanal net bycatch within its limited range; in this area fisheries are the chief source of economic productivity.

Methodology/Principal Findings

We analyze trade-offs between conservation of the vaquita and fisheries, using an end-to-end Atlantis ecosystem model for the Northern Gulf of California. Atlantis is a spatially-explicit model intended as a strategic tool to test alternative management strategies. We simulated increasingly restrictive fisheries regulations contained in the vaquita conservation plan: implementing progressively larger spatial management areas that exclude gillnets, shrimp driftnets and introduce a fishing gear that has no vaquita bycatch. We found that only the most extensive spatial management scenarios recovered the vaquita population above the threshold necessary to downlist the species from Critically Endangered. The scenario that excludes existing net gear from the 2008 area of vaquita distribution led to moderate decrease in net present value (US$ 42 million) relative to the best-performing scenario and a two-fold increase in the abundance of adult vaquita over the course of 30 years.

Conclusions/Significance

Extended spatial management resulted in the highest recovery of the vaquita population. The economic cost of proposed management actions was unequally divided between fishing fleets; the loss of value from finfish gillnet fisheries was never recovered. Our analysis shows that managers will have to confront difficult trade-offs between management scenarios for vaquita conservation.     

Life history strategy of Leptinaria unilamellata (d'Orbigny, 1835) (Mollusca,Pulmonata, Subulinidae)

Abstract

Life history theory predicts that the patterns of resource allocation in animals are associated with different strategies, selected in the course of evolution. In the present study, the life history of Leptinaria unilamellata was characterized under laboratory conditions. We determined the growth, reproduction, and longevity patterns of this species and elucidated the strategy related to the development of embryos, through direct observations and examination of the morphology of the gravid uterus. Furthermore, we attempted to analyze the glycogen and galactogen contents of the albumen gland, digestive gland and cephalopedal mass in order to understand energy allocation to life history traits, for three life stages. Leptinaria unilamellata's life history is characterized by great longevity, a short juvenile phase, early sexual maturity, and repeated reproductive events, with little reproductive effort at each event and some mortality shortly after the first reproduction. In the terraria, we found juveniles but no eggs. However, the results of the anatomical study showed no morphological connection between the embryos and the parental organism. Thus, this species should be described as ovoviviparous rather than viviparous. Egg retention in the parent organism is the primary cause of the release of juveniles, instead of eggs, enabling the offspring to withstand environmental stress. The higher quantity of galactogen found in the adults' albumen gland, as compared to juveniles and senescent individuals, as well as the ratio of glycogen to galactogen, reveal the allocation of energy to reproduction rather than to growth. The remaining energy is directed to the maintenance of omeostasis. Such pattern was confirmed by the low levels of glycogen and galactogen observed in the senescent stage, compared to the juvenile and adult stages. In the life strategy of L. unilamellata, the distribution of the reproductive effort among many events associated with ovoviviparity indicates a long-term investment in reproductive success.     

Life history of Chnoospora implexa (Chnoosporaceae, Phaeophyceae) in culture

The life history of the brown alga Chnoospora implexa J. Agardh (Chnoosporaceae, Scytosiphonales) from Japan was studied in laboratory cultures. This species showed a heteromorphic and diphasic life history, alternating between erect gametophytes and discoid sporophytes. The gametophytes were dioecious and produced isogametes. The zygotes developed into sporophytes at 20°C under long‐day conditions, which formed plurilocular zoidangia. Zoids released from the plurilocular zoidangia developed again into sporophytes that always formed plurilocular zoidangia at 20°C and 25°C in long‐day conditions, and mainly unilocular zoidangia at 25°C in short‐day conditions. Zoids released from unilocular zoidangia developed into dioecious gametophytes. At 15°C zygotic erect thalli were formed and were revealed to be diploid by microspectrofluorometric measurements of nuclear DNA contents. The development and reproduction of unfused gametes were similar to those of zygotes. Some strains showed a direct‐type life history; gametophytic thalli were produced, but not via a sporophytic phase.     

Life history of the gulf darter,Etheostoma swaini (Pisces: Percidae)

Synopsis Etheostoma swaini, the gulf darter, was collected from the Black Creek drainage in southern Mississippi (February 1978 – April 1979). The gulf darter generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. Larval dipterans were the most important food items, both numerically and volumetrically. Chironomids were found in 71–100% of the stomachs in all except the unusual March 16 collection. The length frequency distribution and the scale annuli analysis indicated there were three year-classes present in the population at any one time. Fifty-one percent of the specimens taken were less than 12 months old. During the mid-February to late March spawning season gulf darters were most often collected over clean gravel or gravelsand substrates. Laboratory observations suggest that the female burrows into the gravel where the demersal, adhesive eggs are deposited. Female gulf darters significantly outnumbered males at a ratio of 59:41.     

The Ecological Role of the Vaquita, Phocoena sinus, in the Ecosystem of the Northern Gulf of California

From an ecosystem management perspective, analysis of the functional roles of species is a challenge. It is valuable to determine which species are irreplaceable within a given community based on their contribution to the system’s organization. This study relates the emergent functional and structural indices of biological groups estimated from a trophic model of the Northern Gulf of California to identify the roles of these groups in the ecosystem context, with a particular focus on the role of the vaquita, an endemic porpoise in critically endangered status. The simulation of removing each group allowed the analysis of the removal’s functional effect on the ecosystem’s global attributes and organization (based on Ulanowicz’s ascendency concept). Groups from lower trophic levels (TL) were more related to complexity indicators, suggesting their contribution to the organization and structure of energy flows in the food web. Groups from intermediate TL had higher values of structural indexes, indicating their function in the control of flows throughout the network. The vaquita along with other marine mammals, aquatic birds, and some species of fish with a high TL contribute in a similar way to the order (for example, ascendency/capacity-of-development ratio) of the system, showing a relatively high value of ascendency (contribution of the group to the organization inherent to the ecosystem) and the change in ecosystem ascendency when they were removed. The vaquita, like marine and coastal birds, plays a small role in the ecosystem. But like them, it does contribute substantially to ecosystem organization. This study thus provides information potentially useful for management in understanding the species’ role and in reducing uncertainty in decision-making.