Silva
Tammy L.
Silva
Tammy L.
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ArticleLarval transport pathways from three prominent sand lance habitats in the Gulf of Maine(Wiley, 2022-03-15) Suca, Justin J. ; Ji, Rubao ; Baumann, Hannes ; Pham, Kent ; Silva, Tammy L. ; Wiley, David N. ; Feng, Zhixuan ; Llopiz, Joel K.Northern sand lance (Ammodytes dubius) are among the most critically important forage fish throughout the Northeast US shelf. Despite their ecological importance, little is known about the larval transport of this species. Here, we use otolith microstructure analysis to estimate hatch and settlement dates of sand lance and then use these measurements to parametrize particle tracking experiments to assess the source–sink dynamics of three prominent sand lance habitats in the Gulf of Maine: Stellwagen Bank, the Great South Channel, and Georges Bank. Our results indicate the pelagic larval duration of northern sand lance lasts about 2 months (range: 50–84 days) and exhibit a broad range of hatch and settlement dates. Forward and backward particle tracking experiments show substantial interannual variability, yet suggest transport generally follows the north to south circulation in the Gulf of Maine region. We find that Stellwagen Bank is a major source of larvae for the Great South Channel, while the Great South Channel primarily serves as a sink for larvae from Stellwagen Bank and Georges Bank. Retention is likely the primary source of larvae on Georges Bank. Retention within both Georges Bank and Stellwagen Bank varies interannually in response to changes in local wind events, while the Great South Channel only exhibited notable retention in a single year. Collectively, these results provide a framework to assess population connectivity among these sand lance habitats, which informs the species' recruitment dynamics and impacts its vulnerability to exploitation.
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ArticleTemporal and spatial distributions of delphinid species in Massachusetts Bay (USA) using passive acoustics from ocean gliders(Inter Research, 2019-11-21) Silva, Tammy L. ; Mooney, T. Aran ; Sayigh, Laela S. ; Baumgartner, Mark F.Knowledge about marine mammal habitat use is necessary for informing ecosystem-based management and mitigating human impacts. Massachusetts Bay is an important marine mammal foraging area in the Gulf of Maine and an area of substantial human activity, but delphinid habitat use is poorly understood. The goals of this work were to (1) document temporal and spatial occurrence of delphinid species in Massachusetts Bay using passive acoustic monitoring from ocean gliders and (2) explore the potential influences of environmental conditions on delphinid distributions. Gliders were deployed in late fall and early winter of 2014 and 2015-2016 and were equipped with a digital acoustic recorder and conductivity-temperature-depth instrument. Gliders surveyed an area of approximately 1000 km2. Delphinid whistles were detected on 93 of 128 (73%) deployment days. Animals were detected more often at night. Presence was consistent over 2 years, although detection rates showed annual and monthly variability. Spatial distribution differed between years, but most detections occurred close to Stellwagen Bank. Visual assessment of spectrograms suggests the presence of 2 species, Atlantic white-sided dolphins and common dolphins. The reoccurrence of 2 probable signature whistles over several weeks and consecutive winter seasons suggests prolonged occupancy during winter and possible annual site fidelity. These data show a consistent and frequent presence of delphinids near a known marine mammal foraging area (Stellwagen Bank) during late fall and winter and are a first step towards understanding both how odontocetes influence the Massachusetts Bay/Gulf of Maine ecosystem and how they may be impacted by human activities.
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ArticleSensitivity of sand lance to shifting prey and hydrography indicates forthcoming change to the northeast US shelf forage fish complex(Oxford University Press, 2021-01-26) Suca, Justin J. ; Wiley, David N. ; Silva, Tammy L. ; Robuck, Anna R. ; Richardson, David E. ; Glancy, Sarah G. ; Clancey, Emily ; Giandonato, Teresa ; Solow, Andrew R. ; Thompson, Michael A. ; Hong, Peter ; Baumann, Hannes ; Kaufman, Les ; Llopiz, Joel K.Northern sand lance (Ammodytes dubius) and Atlantic herring (Clupea harengus) represent the dominant lipid-rich forage fish species throughout the Northeast US shelf and are critical prey for numerous top predators. However, unlike Atlantic herring, there is little research on sand lance or information about drivers of their abundance. We use intra-annual measurements of sand lance diet, growth, and condition to explain annual variability in sand lance abundance on the Northeast US Shelf. Our observations indicate that northern sand lance feed, grow, and accumulate lipids in the late winter through summer, predominantly consuming the copepod Calanus finmarchicus. Sand lance then cease feeding, utilize lipids, and begin gonad development in the fall. We show that the abundance of C. finmarchicus influences sand lance parental condition and recruitment. Atlantic herring can mute this effect through intra-guild predation. Hydrography further impacts sand lance abundance as increases in warm slope water decrease overwinter survival of reproductive adults. The predicted changes to these drivers indicate that sand lance will no longer be able to fill the role of lipid-rich forage during times of low Atlantic herring abundance—changing the Northeast US shelf forage fish complex by the end of the century.
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ArticleProbable signature whistle production in Atlantic white-sided (Lagenorhynchus acutus) and short-beaked common (Delphinus delphis) dolphins near Cape Cod, Massachusetts(Wiley, 2022-09-15) Cones, Seth ; Dent, Molly ; Walkes, Sam ; Bocconcelli, Alessandro ; DeWind, Christianna ; Arjasbi, Kayla ; Rose, Kathryn S. ; Silva, Tammy L. ; Sayigh, Laela S.Some delphinids produce a learned, individually specific tonal whistle that conveys identity information to conspecifics (Janik & Sayigh, 2013). These whistles, termed signature whistles, were first described by Caldwell and Caldwell (1965) and have been studied intensively over the past several decades (Janik & Sayigh, 2013). In common bottlenose dolphins (Tursiops truncatus) and potentially other species, signature whistles facilitate many ecologically-important behaviors, including individual recognition and maintenance of group cohesion (Janik & Slater, 1998). Additionally, signature whistle contours, or patterns of frequency change over time, can remain stable for several decades, aiding in long-term social bonds (Sayigh et al., 1990). Signature whistles account for approximately 38%–70% of all whistle production in free-swimming animals (Buckstaff, 2004; Cook et al., 2004; Watwood et al., 2005); this percentage can be up to 100% for isolated individuals in captivity (Caldwell et al., 1990). Most of our knowledge on the function and use of signature whistles stems from Tursiops spp., and their use and presence in other delphinid taxa is less understood. Nonetheless, seven additional delphinid species have been reported to produce signature whistles: Indo-Pacific bottlenose dolphins (Tursiops aduncus; Gridley et al., 2014), common dolphins (D. delphis; Caldwell & Caldwell 1968; Fearey et al., 2019), Atlantic spotted dolphins (Stenella plagiodon; Caldwell et al., 1970), Pacific white-sided dolphins (Lagenorhynchus obliquidens; Caldwell & Caldwell, 1973), Pacific humpback dolphins (Sousa chinensis; Van Parijs & Corkeron, 2001), and Guiana dolphins (Sotalia guianensis; Duarte de Figueiredo & Simão, 2009).
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ArticleHigh collocation of sand lance and protected top predators: implications for conservation and management(Wiley Open Access, 2020-10-06) Silva, Tammy L. ; Wiley, David N. ; Thompson, Michael A. ; Hong, Peter ; Kaufman, Les ; Suca, Justin J. ; Llopiz, Joel K. ; Baumann, Hannes ; Fay, GavinSpatial relationships between predators and prey provide critical information for understanding and predicting climate‐induced shifts in ecosystem dynamics and mitigating human impacts. We used Stellwagen Bank National Marine Sanctuary as a case study to investigate spatial overlap among sand lance (Ammodytes dubius), a key forage fish species, and two protected predators: humpback whales (Megaptera novaeangliae) and great shearwaters (Ardenna gravis). We conducted 6 years (2013–2018) of standardized surveys and quantified spatial overlap using the global index of collocation. Results showed strong, consistent collocation among species across seasons and years, suggesting that humpback whales and great shearwater distributions are tightly linked to sand lance. We propose that identifying sand lance habitats may indicate areas where humpbacks and shearwaters aggregate and are particularly vulnerable to human activities. Understanding how sand lance influence predator distributions can inform species protection and sanctuary management under present and future scenarios.
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ArticleWhistle characteristics and daytime dive behavior in pantropical spotted dolphins (Stenella attenuata) in Hawai‘i measured using digital acoustic recording tags (DTAGs)(Acoustical Society of America, 2016-07-19) Silva, Tammy L. ; Mooney, T. Aran ; Sayigh, Laela S. ; Tyack, Peter L. ; Baird, Robin W. ; Oswald, Julie N.This study characterizes daytime acoustic and dive behavior of pantropical spotted dolphins (Stenella attenuata) in Hawai‘i using 14.58 h of data collected from five deployments of digital acoustic recording tags (DTAG3) in 2013. For each tagged animal, the number of whistles, foraging buzzes, dive profiles, and dive statistics were calculated. Start, end, minimum, and maximum frequencies, number of inflection points and duration were measured from 746 whistles. Whistles ranged in frequency from 9.7 ± 2.8 to 19.8 ± 4.2 kHz, had a mean duration of 0.7 ± 0.5 s and a mean of 1.2 ± 1.2 inflection points. Thirteen foraging buzzes were recorded across all tags. Mean dive depth and duration were 16 ± 9 m and 1.9 ± 1.0 min, respectively. Tagged animals spent the majority of time in the upper 10 m (76.9% ± 16.1%) of the water column. Both whistle frequency characteristics and dive statistics measured here were similar to previously reported values for spotted dolphins in Hawai‘i. Shallow, short dive profiles combined with few foraging buzzes provide evidence that little spotted dolphin feeding behavior occurs during daytime hours. This work represents one of the first successful DTAG3 studies of small pelagic delphinids, providing rare insights into baseline bioacoustics and dive behavior.
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PreprintSuccessful suction-cup tagging of a small delphinid species, Stenella attenuata : insights into whistle characteristics( 2016-09) Silva, Tammy L. ; Mooney, T. Aran ; Sayigh, Laela S. ; Baird, Robin W. ; Tyack, Peter L.The Delphinidae is the most diverse family of cetaceans, with 38 species recognized. Small pelagic delphinids are also the most abundant cetaceans world-wide, yet their communication and behavior remain poorly understood. Many populations live in relatively remote habitats, which creates challenges in accessing study animals. Small odontocete species often face numerous anthropogenic stressors. For example, many pelagic delphinids incur significant interactions with fisheries (Gerrodette and Forcada 2005, Geijer and Read 2013). With a wide distribution, many delphinid populations utilize habitats that also are important for human seagoing activities that produce intense sound, such as seismic surveys or naval sonar exercises that may disturb or harm them. Many U.S. naval sonar exercises take place on naval training ranges such as those in in Hawai‘i (Baird et al. 2013), California (Carretta et al. 1995, Henderson et al. 2014), and the Bahamas (DeRuiter et al. 2013). At least one delphinid stranding event involving melon-headed whales (Peponocephala electra) was correlated with military activities (Southall et al. 2006); a mass stranding of melon-headed whales has also been associated with multi-beam echosounder operations as part of a seismic survey (Southall et al. 2013). Because many of these delphinid groups can number in the 100s to 1,000s, fisheries or sonar exposures can account for the highest estimates of marine mammal “takes” in related Environmental Impact Assessments (Department of the Navy 2013). Given the potential for anthropogenic interactions with large numbers of individual delphinids, improved methods of studying small delphinids are invaluable to understand, reduce, or mitigate potential human influences on these animals.